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Achieving high performance and stability in cathodes for the oxygen reduction reaction is crucial for the advancement of proton ceramic fuel cells (PCFCs). The introduction of non-metal doping method presents an opportunity to simultaneously optimize the perovskite structure and augment the activity and stability of the oxygen reduction reaction. Herein, we develop a phosphorus-doped SrCo 0·8 Fe 0·15 P 0·05 O 3-δ (SCFP) cathode for PCFCs. The SCFP cathode shows a low area specific resistance of 0.24 Ω cm2 at 650 °C in wet air (5% H 2 O), which is smaller than that of the phosphorus-free SrCo 0·8 Fe 0·2 O 3-δ (SCF) electrode (0.34 Ω cm2). The Ni–BaZr 0.1 Ce 0·7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) anode-supported single cell with BZCYYb electrolyte and SCFP cathode exhibits a superior performance of 865 mW cm−2 at 650 °C under H 2 atmosphere. This underscores the effectiveness of the phosphorus-doping strategy as a promising approach for advancing cathode development in PCFCs. [Display omitted] [ABSTRACT FROM AUTHOR]

We develop a method for bifunctional regulation on the surface micro-morphology and nitrogen-doping configuration of graphene-based nanosheets by annealing chitin and graphene oxide. Systematic studies reveal that annealing temperature is a key to determine micro-morphology and type of nitrogen-doping of the graphene matrix, and 2D multi-wrinkled graphene (CS-rGO-600) with enriched active nitrogen species and moderate defects can be obtained successfully under an optimized annealing temperature. When used as a "green" electrocatalyst for oxygen reduction reaction (ORR), CS-rGO-600 exhibits superior performance, in terms of more outstanding electrode activity and durability, higher output power density in fuel cell system compared to that of Pt/C. These could be attributed to the fact that appropriate annealing treatment is not only conducive to exogenous nitrogen enrichment and oriented conversion but also beneficial to micro-structure construction. The synergistic effects between multi-wrinkled 2D structure and active sites endow CS-rGO-600 with superior ORR performance in the fuel cell. • CS-rGO-X was prepared via pyrolysis of biomass waste and GO. • Appropriate pyrolysis is conducive to N enrichment and structure construction. • Synergism between structure and active sites endow CS-rGO-600 with superior activity. • CS-rGO-600 with highest E onset (0.059 V) and P max (0.665 mWcm−2). [ABSTRACT FROM AUTHOR]

Low cathodic oxygen reduction reaction (ORR) efficiency is one of the important factors limiting the hydrogen fuel cells. Platinum can effectively reduce the ORR activation energy and improve the reaction rate; However, platinum's low reserves, versatility, and high price still limit its use in commercial, large-scale applications. It is very important to reduce the amount of Pt and improve the utilization rate and the stability of Pt-based catalyst. Here, an ultra-low Pt content catalyst Pt&Fe 2 O 3 /PM has been synthesized. The Pt content of the catalyst is only 4 wt%, and its nanoparticles are about 3 nm. Pt&Fe 2 O 3 /PM exhibit excellent ORR catalytic performance and longevity in acidic electrolyte. The ORR mechanism on Pt&Fe 2 O 3 /PM involves a direct four-electron path. The mass activity and specific activity of Pt&Fe 2 O 3 /PM is 4.8 and 10.3 times than that of commercial Pt/C, respectively. Furthermore, the catalyst's synthesis method is straightforward and amenable to scaling up, offering significant guidance for the creation of low-Pt catalysts. [Display omitted] • High dispersion low-Pt catalyst Pt&Fe 2 O 3 /PM was prepared by heat treatment. • The particle size of the Pt&Fe 2 O 3 /PM is ca. 3 nm, and the Pt content is ca. 4 wt%. • Pt&Fe 2 O 3 /PM has higher ORR activity and durability than commercial Pt/C. [ABSTRACT FROM AUTHOR]

Atomically dispersed active sites and hierarchical porosity in Fe–N–C catalyst materials are essential for efficient oxygen reduction reaction (ORR) electrocatalysis and effective mass transport, respectively. However, the majority of these catalysts fail to deliver outstanding electrocatalytic activity and stumble when used as cathode materials in fuel cells. Herein, we developed a catalyst with partially transformed metallic Fe into Fe-N x sites embedded in the carbonaceous matrix, and its excellent electrocatalytic performance is attributed to the hybrid nanoparticles and built-in Fe-N x site structures. The optimized Fe@Fe–N–C catalyst was tested for ORR performance both ex-situ using the rotating (ring)-disk electrode technique and in an anion exchange membrane fuel cell (AEMFC). The Fe@Fe–N–C electrocatalyst exhibited remarkably enhanced ORR activity in alkaline media with a half-wave potential of 0.822 V vs. reversible hydrogen electrode (RHE) and showed the maximum power density (P max) of 242 mW cm−2 in an AEMFC test, surpassing the peak power density obtained from the Pt/C cathode catalyst (P max = 220 mW cm−2) under H 2 –O 2 conditions. Therefore, the study provides a promising prospect for designing improved, cost-effective, and noble metal-free electrocatalysts for achieving high performance in AEMFCs. [Display omitted] • Hybrid Fe–N–C electrocatalysts with metallic Fe nanoparticles was developed. • A new strategy is proposed using melamine and N-hydroxysuccinimide to produce Fe–N–C. • The hybrid electrocatalyst with Fe and FeN x sites jointly promote the ORR activity. • The Fe@Fe–N–C cathode catalyst in AEMFC exhibits a peak power density of 242 mW cm−2. [ABSTRACT FROM AUTHOR]

Fuel cells have substantial development potential for commercial energy generation applications. Adding an ionic conducting electrolyte to a cathode to make a composite cathode lowers the Thermal Expansion Coefficient (TEC), raises the Triple Phase Boundary (TPB) area, and enhances the electrochemical performance of Solid Oxide Fuel Cells (SOFCs). In this review, the article presents the basic principles, criteria, and composite cathode development of SOFCs that operate SOFCs in the intermediate temperature ranges (600–800 °C). These composite cathodes improve the inter-component compatibility, Oxygen Reduction Reaction (ORR), and characteristics of mixed electronic-ionic conductors. In comparison with a single-phase cathode, composite material can reduce Polarization Resistance (R p) by about 30–40% and improve maximum power density (MPD) by about 30–50%. PBCO-40SDC and SBCN-20SDC composites exhibit enhanced stability and maintain their electrochemical performance with polarization resistances of 0.008 Ω cm2 and 0.079 Ω cm2 when operating at temperature of 700 °C. • Recent methods in IT-SOFC composite cathode development were explored. • Properties of nine materials studied, including conductivity and stability. • PBCO-40SDC outperforms with low polarization resistance at 700 °C. • Noteworthy development: exsolution of catalytically active nanoparticles. • Comprehensive study on thermal, electrical, and catalytic properties. [ABSTRACT FROM AUTHOR]

Nitrogen and sulphur co-doped nanocarbon composites based on silicon carbide-derived carbon (SiCDC), carbon nanotubes (CNT) and/or mesoporous carbon (MPC) are prepared for oxygen reduction reaction (ORR) and anion-exchange membrane fuel cell (AEMFC) studies. Thiosemicarbazide is used as nitrogen and sulphur doping agent. The rotating ring-disc electrode (RRDE) measurements exhibit good electrocatalytic activity towards the ORR for all the prepared catalysts in alkaline solution. Obtained materials are rich in pyridinic-N and consist of thiophene-S, which could improve the ORR performance due to the synergistic effect of N and S. Textural properties, including specific surface area (SSA) and porosity parameters are different amongst the three studied N,S-doped nanocomposite materials, which also affect the outcome of AEMFC test results. In AEMFC testing using Aemion+ (AF2-HLE8-10-X, 10 μm) anion-exchange membrane, N,S-SiCDC/MPC (with SSA dft = 952 m2 g−1) shows the highest performance with the peak power density (P max) of 379 mW cm–2. This result is comparable with the performance of Pt/C catalyst in AEMFC (P max = 347 mW cm–2), making N,S-doped nanocomposite materials promising cathode catalyst for AEMFCs. [Display omitted] • Thiosemicarbazide is used as nitrogen and sulphur doping agent of carbon materials. • Textural properties are different amongst the three studied N,S-doped nanocomposites. • The N,S-doped nanocomposite materials exhibit similar ORR activity in alkaline media. • The best-performing cathode catalyst in AEMFC is N,S-SiCDC/MPC, P max = 379 mW cm−2. [ABSTRACT FROM AUTHOR]

Tailored nanostructures of manganese oxide (MO) were synthesized using a single-step sonochemical method with various morphology-directing agents. The tailored nanostructures of MO were utilized as the cathode material to catalyze the oxygen reduction reaction (ORR) occurring within fuel cells. The obtained MO with various structures were characterized via X-ray diffraction (XRD) analysis, and morphological characterizations were carried out via field emission scanning electron microscopy (FESEM). Raman studies were done to assess the various modes of Raman for MO nanostructures. All the nanostructures of MO were used to modify the surface of the glassy carbon electrode (GCE) to enhance its efficacy in catalyzing the ORR. Amongst five different nanostructures and the conventionally used Pt/C catalyst, MO@NH 3 OH has shown excellent performance with a higher current density of −0.854 mA/cm2 and a shifted overpotential of −0.44 V. Methanol solution with a higher concentration of 0.5 M was used for the tolerance study and it was observed that MO@NH 3 OH had shown adequate tolerance and remained unsusceptible to methanol passed towards the cathode side. The stability of the nanostructures was assessed over ∼3000 s using chronoamperometry (CA) and it was found that nanostructures exhibited an impressive 97 % retention of current, which is comparable to the Pt/C electrocatalyst. Therefore, the nanostructure of MO with nanowire morphology could be regarded as a promising Pt-free electrocatalyst obtained via a facile one-step process offering remarkable selectivity and stability while maintaining cost-effectiveness. [Display omitted] • The tailored nanostructures of manganese oxide were prepared. • The sonochemical method of synthesis was used as a single-step cost-effective method. • The synthesized material was used as the cathode material for oxygen reduction reaction (ORR). • The application aimed was proton exchange membrane fuel cells (PEMs). [ABSTRACT FROM AUTHOR]

Platinum-group-metal free catalysts have been widely studied in the last decade as an alternative to Pt, employed in fuel cells. Several carbon precursors have been investigated as carbon matrix for iron-nitrogen-carbon (Fe–N–C) catalysts, characterized by a large amount of micropores, fundamental to create Fe-N x -C active sites. Nonetheless, it is also acknowledged that wider pores are needed to facilitate mass transfer of oxygen/water (reagent/product of fuel cells) towards/from the active sites. Organic xerogels are known as easily tunable materials, that allow doping with a variety of heteroatoms. The present manuscript presents an investigation on the use of organic xerogels combined with iron and nitrogen in a single-step to obtain Fe–N-CXG electro-catalysts for the oxygen reduction reaction (ORR) of proton exchange membrane fuel cells. Several features of both organic xerogels and catalysts on the ORR activity are assessed: the textural properties of the organic xerogel, the iron loading of the Fe–N–C catalysts and the effect of acid-leaching of the catalysts. The present study proves the feasibility of using organic xerogels as carbon precursor to obtain PGM-free catalysts in an easy manner and scalable single-step synthesis. Catalysts obtained from organic xerogels synthesized at mildly acid pHs (5.8 and 6), with a nominal iron loading of 2 wt%, and subjected to two sets of acid leaching/thermal treatments, present enhanced catalytic activity towards the ORR. • Organic carbon xerogels are investigated as carbon matrix for Fe–N–C catalysts. • One-step and template-free synthesis of Fe–N–C catalysts is proposed. • Balanced iron doping creates enough active sites without impacting porosity. • Acid/thermal treatments enhance catalysts improving chemical properties. • High mesopore volume organic xerogels (pH 5.8) yield highly active ORR catalysts. [ABSTRACT FROM AUTHOR]

The transition-metals carbon catalysts belong to intensively studied alternatives to the Pt-based catalysts promoting the oxygen reduction reaction (ORR) in electrochemical fuel cells (FCs). Commonly studied Fe,Co–N–C composites are usually obtained through pyrolysis and used as such or after a chemical post-treatment with an oxidizing agent. This treatment is applied to remove inactive metal species, thus, promoting the electrochemical activity. The impact of an oxidizing agent is poorly addressed in the literature, while its nature may negatively affect the catalyst's performance. Herein we report the first comparative study on the effect of post-treatment with the most common oxidizing agents such as HCl, HNO 3 , H 2 SO 4 and H 2 O 2 , on the structural and electrochemical properties of the Fe,Co–N–C catalyst. The catalyst is made by pyrolysis of the Co,Zn-ZIF metal-organic framework enriched with iron and nitrogen. Its structure was observed withstanding the action of mineral acids but suffers from hydrogen peroxide. The treatment with either nitric or chloric acid may improve the electrochemical performance up to 4%, while other agents decrease that by 6% and slow down the ORR rate. These findings are useful for the careful design of post-treatment procedures for carbon catalysts. • The Fe,Co–N–C carbon-based catalyst was obtained from Fe,Co-ZIF-8 MOF via pyrolysis at 700 °C in an inert atmosphere. • The Fe,Co–N–C catalyst was treated with four oxidizing agents - chloric, nitric and sulfuric acids, and hydrogen peroxide. • Structural and compositional changes were assessed with multi-technique characterization of the catalysts. • The catalysts treated with nitric and chloric acids demonstrated improved performance for ORR in an acidic medium. [ABSTRACT FROM AUTHOR]

With the growing demand for fossil energy and the consequent environmental pollution problems, fuel cells (FCs) play a significant role in the affordable, secure and zero emission energy devices. The use of platinum (Pt) electrocatalysts for oxygen reduction reaction (ORR) has made outstanding contribution to the commercial realization of high activity FCs. Yet, the short lifetime of Pt catalyst remains a serious issue in real device evaluation system and lab-scale, demanding for the design of materials with higher stability. Thus, fundamental understanding of the connection between the elaborately designed materials and ORR stability is timely urgent in recent years. Here, the increased stability mechanisms of Pt-based nanocatalysts are summarized, focusing on the representative synthesis strategies of high stability Pt-based catalysts and the role of every design for performance enhancement. At last, several brief perspectives related to the future research of stability issues are provided in terms of catalysts' design limitations. [Display omitted] • Recent advances of Pt-based electrocatalysts for ORR in acid media are discussed. • The latest design strategies of stable Pt-based catalysts are summarized. • Speculation and discussion on the future researches of ORR catalysts are outlined. [ABSTRACT FROM AUTHOR]

Synthesis of a composite with high technical performance and low cost instead of Platinum-based electrocatalysts has become an investigation hotspot to develop fuel cells and storage technologies. So, in the current investigation, three new bifunctional electrocatalysts incorporating lanthanides into Zeolitic Imidazolate Framework (ZIF)-8 are fabricated and assessed. First, by using a facile protocol, three trimetallic composites consisting of Europium (Eu), Samarium (Sm), Copper (Cu), and ZIF-8 are prepared, and the fabricated samples are labeled as EuCu-ZIF, SmCu-ZIF, and SmEuCu-ZIF. Next, in order to eliminate the irreversible fusion and quick aggregation of metal nanoparticles through the high-temperature carbonization process, the mesoporous-silica-protected calcination technique is investigated. After the Hydrofluoric (HF) etching process, the Cu@Ln (Eu, Sm)-N-C electrocatalysts are formed. Based on the fabricated samples, the Cu@Eu-N-C electrocatalyst exhibited the best Oxygen Reduction Reaction (ORR) performance with an onset potential of −0.06 V vs Ag/AgCl. Additionally, the electron transfer number for this composite is found to be 3.68. The GCD experiments show that the Cu@Eu-N-C electrode has the greatest specific capacitance, measuring 431 F g−1 when tested at 1 A g−1. It is deduced that the introduction of Eu3+ and Sm3+ as metal ions in the ZIF-8 catalyst led to an improvement in defects in the carbon matrix and mass transfer, illustrating the fabricated catalysts have an acceptable efficiency for ORR and storage applications. Indeed, due to the use of metallic ions (Ln and Cu), highly effective active sites were formed, resulting in an outstanding improvement in ORR efficiency. Also, it was found that with the use of mesoporous-silica protection for the fabricated samples, there is a remarkable improvement in the onset potential and specific capacitance parameters. [Display omitted] • Incorporation of the lanthanides (Sm, Eu) and ZIF-8 has acceptable performance for ORR and supercapacitor. • In this investigation, three novel trimetallic electrocatalysts are synthesized and analyzed. • The impact of using the mSiO 2 coating technique on electrochemical aspects is investigated. • Based on the LSV curves, the onset potential of Cu@Eu-N-C was obtained as −0.06 V vs. Ag/AgCl. • The GCD measurements indicated that the specific capacitance of Cu@Eu-N-C at 1 A g−1 was 431 F g−1. [ABSTRACT FROM AUTHOR]

The kinetic of the oxygen reduction reaction (ORR) at the cathodes of polymer-electrolyte-membrane fuel cells (PEMFCs) has been demonstrated to be slow, which is one of the pivotal issues in developing PEMFCs. Within the current piece of research, by performing first-principles calculations, we introduce a Co-doped vacancy BN nanosheet (Co-HBN) as an efficacious noble metal-free electro-catalyst for the ORR process (ORRP) in fuel cells. The results demonstrate a rise in the energies of adsorption (or adhesion) onto the Co–N active site of these electrocatalysts in the order of O < OH < OOH < O 2 < H 2 O 2 < H 2 O on this electrocatalyst and there is a consistent change in the adsorption energies (E ads)for all oxygen-containing intermediates (OCIs). Based on the small and large thermodynamic driving force for the generation of H 2 O 2 and for reducing OOH into O∗ (or to 2OH∗), respectively, the four-electron route was more favorable in comparison with the 2e− route. Furthermore, with the largest value of ΔG for Co-HBN electrocatalyst, the final reduction step (OH∗ + H+ + e− → H 2 O + ∗) has been regarded as the rate-limiting step. The d-band center of Co was considerably distant from the Fermi level. The greater gap between the frontier orbitals suggested that the electrocatalyst is not conducive to the adsorption of OCIs, which shows that the onset potential is larger and ORR is high. • The catalytic activity of a series of Co-doped v-BN has been theoretically explored in the ORR. • O 2 molecule can be directly dissociated on the Co-doped v-BN with 4e pathway. • It is reacting more favorable for the ER mechanism of OH∗ to convert into H 2 O. • The ORR reaction was found to be thermodynamically favorable in the Co-doped v-BN. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cell vehicles have attracted extensive attention for conversion equipment and new energy storage technologies. As an important component of hydrogen fuel cell vehicles, highly stable and active platinum-based (Pt-based) catalysts with 4-electron oxygen reduction reaction (ORR) selectivity are extremely important for promoting the application of this field. In this mini review, based on the ORR mechanism, the feasible strategies to enhance the catalytic stability and 4-electron selectivity of Pt-based catalysts were summarized. Furthermore, the effect mechanisms of each strategy in enhancing catalytic activity and 4-electron selectivity were emphatically discussed and their superiorities and limitations were evaluated. Finally, the research direction and current challenges of Pt-based catalysts were prospected from the perspective of their practical application in hydrogen fuel cell vehicles. • Research progress of Pt-based catalysts for 4-electron ORR is explored. • The strategies of enhancing 4-electron transfer in Pt-based catalysts are summarized. • The superiorities and limitations of each strategy are summarized. • The future researches of Pt-based catalysts applied in fuel cells is put forward. [ABSTRACT FROM AUTHOR]

Fe–N–C catalysts with excellent performance regarding the oxygen reduction reaction (ORR) have aroused enormous interest in direct-formate fuel cells (DFFCs). However, their limited mass transfer ability, insufficient ORR active sites, and complex fabrication processes remain significant obstacles to the widespread application of Fe–N–C catalysts. Herein, we propose a simple hydrothermal-annealing method with agarose powders to synthesize a uniform spherical Fe–N–C catalyst (∼3 μm) with well-developed mesopores (Fe/rG@C/H-Agar-900). The resultant Fe/rG@C/H-Agar-900 catalyst possesses rich oxygen-containing functional groups and enhanced interconnected pores, which can significantly boost the content of catalytic sites and facilitate mass transport, resulting in a high content of active sites. In the meantime, the mesopore content of Fe/rG@C/H-Agar-900, which can facilitate the formation of the three-phase gas/electrolyte/catalyst interfaces, was optimized by varying the annealing temperature. As a result, the Fe/rG@C/H-Agar-900 demonstrates a half-wave potential of 0.91 V vs. RHE, nearly four-electron pathway selectivity, excellent durability, and excellent formate tolerance for ORR. Furthermore, when used as the air cathode in membrane-less DFFCs, the Fe/rG@C/H-Agar-900-based device exhibits a remarkable peak power density of 24.5 mW cm−2, significantly outperforming the 20 wt% commercial Pt/C. This research facilitates the synthesis of an advanced Fe–N–C catalyst and promotes the practical development of membrane-less DFFCs. [Display omitted] • Spherical mesoporous carbon precursors were prepared by a hydrothermal-annealing method. • Fe–N–C catalyst prepared from agarose powder were used as the air-cathode catalyst for membrane-less DFFCs. • Annealing treatment expands the mesoporous structures of hydrocarbons. • Fe/rG@C/H-Agar-900 exhibits a highly positive E 1/2 (0.91 V vs. RHE) for ORR in alkaline solution. • A P max of 24.5 mW cm−2 is achieved by Fe/rG@C/H-Agar-900, which is 31% higher than that of Pt/C. [ABSTRACT FROM AUTHOR]

This paper proposes an environmentally friendly one-pot synthesis approach for the PtCu and PtNi nanoparticles with the gradient structure on the carbon support. This method offers exceptional advantages over other approaches. Among them there is a surfactant-free synthesis, being low-temperature, simple, fast, and one-pot. The bimetallic electrocatalysts with a reduced platinum content for proton-exchange membrane fuel cells have been obtained. The proposed method is promising in terms of scaling and transition to commercial production. In this study, we first attempted to apply the gradient synthesis strategy to the PtNi/C catalysts in order to make this method versatile. We obtained the high-performance PtNi/C and PtCu/C catalysts, exhibiting the specific ORR activity higher than that of the commercial Pt/C catalyst by 3 and 4.6 times, respectively. [Display omitted] • New Pt-based nanostructured ORR electrocatalysts were obtained by a simple, versatile, and scalable method. • The PtCu and PtNi nanoparticles with Pt overlayers supported on carbon were synthesized by a gradient strategy. • PtNi/C and PtCu/C showed enhanced activity in the ORR compared with the commercial Pt/C. • The surfactant-free one-pot synthesis was used to obtain the PtNi and PtCu nanoparticles. • The environmentally friendly method was used to prepare Pt-based electrocatalysts. [ABSTRACT FROM AUTHOR]

This article provides relevant information on the catalysts' morphological characteristics that allow for the optimal combination of activity and durability of the materials for proton-exchange membrane fuel cells. The home-made Pt/C and PtCu/C catalysts have been established to have at least by 20% higher values of the mass activity in the oxygen reduction reaction than the commercial Pt/C analogue (HiSPEC 3000, Johnson Matthey). The detailed analysis of the microstructure by transmission electron microscopy and the electrochemical parameters by electrochemical surface-sensitive methods after the stress testing has allowed estimating the contribution of various mechanisms to the degradation process. After the stress testing, the residual activity in the oxygen reduction reaction of the home-made materials has proved to be at least more than double that of the commercial Pt/C catalyst. A specific feature of this work is the presented correlation between the morphology and the electrochemical behavior of the catalysts, with this interconnection appearing to be a valuable resource for a wide range of scientists. [Display omitted] • The rapid and facile synthesis methods of the highly active catalysts are presented. • The PtCu/C catalyst is 2.5 times more active in the ORR than the commercial Pt/C. • The testing is conducted within the protocols with the long-term cycling and the potential hold. • The home-made materials are more robust against degradation than the commercial one. • The integrated approach to studying the catalysts' durability is presented. [ABSTRACT FROM AUTHOR]

Graphene has been proposed as support or as co-support for Proton Exchange Membrane Fuel cells (PEMFCs) electrocatalysts due to its high electronic conductivity, corrosion stability and high specific surface area compared to common carbon blacks, such as Vulcan. Despite such outstanding properties, comprehensive studies on long-term stability of graphene-supported Oxygen Reduction Reaction (ORR) catalysts are still unavailable or limited. The stability of graphene as support is now studied and compared with carbon black in terms of electrochemical performance and degradation mechanisms. Catalytic layers with Pt/G were prepared and subjected to a set of three different Accelerated Stress Tests (ASTs): cycling at high potentials, Open Circuit Potential (OCP) holding and cycling at low potentials. This study aims to assess if and why graphene is a better candidate as support. The Pt/G catalyst outperformed the reference catalyst in all ASTs, delivering both higher electrochemical active surface area (ECSA) and ORR mass-specific activity. Such electrochemical performance was correlated with morphological evidences associated to the support itself and with Pt nanoparticles. • Stability of Pt/G was studied via three different degradation protocols and compared to Pt/H. • Potential cycling below 1 V promotes higher ORR mass-specific activity loss, among all ASTs. • Pt/G maintained higher ECSA and ORR activity than Pt/H upon the different types of ASTs. • Pt/G is considerably more stable than Pt/H despite observing a higher particle growth. [ABSTRACT FROM AUTHOR]

Platinum (Pt) based catalysts have multiphase structure, such as two-dimensional (2D) nanosheets structure, with a large specific surface area and high atomic utilization ratio, and a large contact area with carbon support, which promotes the combination of catalyst and support, and improves the activity of catalyst. However, there are still many difficulties in the synthesis of 2D polymetallic alloy nanosheet catalysts. Herein, we synthesized palladium nanosheets (Pd NSs) catalyst with smooth surface structure via solvothermal method, smooth surface structure palladium platinum nanosheets (PdPt NSs) and palladium platinum nickel island particle nanosheets (PdPtNi IPNSs) catalyst. Compared with commercial TKK-Pt/C, the prepared PdPtNi IPNSs catalyst has better catalytic performance for oxygen reduction reaction (ORR), ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). This work provides a simple and feasible strategy for the synthesis of stable and efficient polymetallic 2D alloy nanostructured catalysts. • To achieve the smooth surface of Pd nanosheets (Pd NSs) via controllable preparation of catalysts. • The deposition method was used to get palladium platinum nickel island particle nanosheets (PdPtNi IPNSs) catalyst. • In oxygen reduction reaction, PdPtNi IPNSs achieved mass activity 7.59 times the Pt/C. • In ethanol oxidation reaction, the highest current density of PdPtNi IPNSs was 2.06 times that of Pt/C. • In methanol oxidation reaction, the highest current density of PdPtNi IPNSs was 3.47 times that of Pt/C. [ABSTRACT FROM AUTHOR]

In this study, we design and prepare the cobalt-doped porous carbon nanofibers (Co@PCNFs) as efficient electrocatalysts based on the electro-blow spinning method and carbonization processes. The porous Co@PCNFs has the three-dimensional porous carbon network structures as the fast electron transport channels and endow the materials with high specific surface area. The central metal Co atoms will be converted into metal nanoparticles with high efficient catalysis in the PCNFs after the carbonization treatment. And the carbonized product still inherits the nanometer size of the ZIF-67 (40–50 nm) precursor, which is more beneficial to expose more active sites. These advantages enable the prepared electrocatalyst to exhibit excellent oxygen reduction reaction (ORR) performance (onset potential of 0.91 V vs. RHE, half-wave potential of 0.857 V vs. RHE), which is very close to commercial Pt/C. More importantly, the obtained Co@PCNFs catalyst exhibited superior electrochemical stability and methanol tolerance over commercial Pt/C under alkaline conditions. The work will open up novel options for various fields such as high performance Zn-air batteries and fuel cells in the future. [Display omitted] • Carbon nanofibers with 3D network structures are designed and prepared. • The porous structure can be used as a fast transport channel for electrons. • Layered pore structure absorbs more O 2 and fully contacts the active site. • Exhibited better stability than Pt/C catalyst. • The half-wave potential of Pt/C catalyst is close to that of the catalyst. [ABSTRACT FROM AUTHOR]

The microstructure of carbon supports for electrocatalysts plays a crucial role in dispersing active sites, establishing oxygen/ion transport channels, and thus determining the oxygen reduction reaction (ORR) activity. A facile and simple microstructure tuning strategy is adopted to synthesize hollow carbon nanoshells (CNSs) with tuneable microstructure in this study. The CNSs with expected macroporous (300–966 nm) and mesoporous (2–5 nm) structures were achieved by adjusting heating ramp rates during pyrolysis. The CNS prepared at 1 °C min−1 (CNS-1) possesses a well-developed mesoporous/macroporous structure, which is conducive to dispersing iron phthalocyanine during the synthesis and establishing triple-phase interfaces in the catalyst layer during the ORR. Therefore, the electrocatalyst (Fe–N/CNS-1), derived from the CNSs-1, exhibits a 44 mV higher half-wave potential (0.879 V vs. RHE) in a rotating disk electrode and a 14% higher maximum power density (16.1 mW cm−2) in a membrane-less direct formate fuel cell than that of Pt/C. This study delivers a promising microstructure tuning strategy for carbon supports to construct high-efficient ORR electrocatalysts. A microstructure tuning strategy for the carbon supports of the high-performance ORR catalysts to effectively establish triple-phase interfaces. [Display omitted] • A sample pyrolysis method was proposed to synthesize the macroporous CNSs. • The microstructure of the CNSs was tuned by adjusting the heating ramp rates. • Na 2 CO 3 templates played a vital role in the tuning process during pyrolysis. • The microstructure of CNS-1 was conducive to dispersing FePc and establishing TPIs. • Fe–N/CNS-1 exhibited an E 1/2 (0.879 V) in a RDE and a P max (16.1 mW cm−2) in a DFFC. [ABSTRACT FROM AUTHOR]

Silver nanocatalyst (40 wt%) is deposited on commercial mesoporous carbon support material (Ag/C) using two different wet chemical methods, to obtain high electrochemically active surface area. The catalyst materials are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis and are evaluated toward the oxygen reduction reaction (ORR) in alkaline media employing the rotating disk electrode method. It is worth noting that the Ag/C leads to oxygen reduction through a direct four-electron pathway in alkaline medium. The silver catalyst on mesoporous carbon exhibits relatively higher mass activity for ORR (38 A g−1) compared to that with Vulcan carbon (32 A g−1) at −0.2 V vs SCE at room temperature. Anion exchange membrane fuel cell shows maximum power density of 310 mW cm−2 with Ag/C cathode catalyst using H 2 and O 2 gases at 65% RH conditions at 65 °C. [Display omitted] • 40 wt% Ag/C catalysts were prepared onto novel mesoporous engineered carbon supports. • ORR on the synthesized Ag-based catalyst materials follows a four-electron pathway. • Mass activity for ORR on Ag/C catalysts surpassed that of Ag/VC. • Peak power density of 310 mW cm−2 with Ag/C cathode was obtained in AEMFC test. [ABSTRACT FROM AUTHOR]

We utilized quantum-chemical computations for computing the thermodynamic variations in the Gibbs free energy of the potential reaction steps in the oxygen reduction reaction (ORR) of the nickel- and nitrogen-doped graphene (NiN 3 -Gr) catalyst's active center. We observed the consistency of the energies of adsorption for all O-containing intermediates. The great thermodynamic driving forces (or motives) for reducing OOH into 2OH∗ or O∗ and the minor motives for generating H 2 O 2 show the advantageousness of following a 4-electron pathway compared to a 2-electron one. This reaction's rate-determining step has 0.94 eV energy barrier that is associated with the first H 2 O molecule formation. According to the thermodynamics results, at lower than 0.51 V electrode potential by the 4e− pathway, the elementary steps of ORR are downhill. The last step, which is the OH reduction into H 2 O with the largest value of ΔG, acts as the 4e− pathway's thermodynamic RDS. Experimental scientists can use the theoretical results achieved in the current study in order to synthesize and select appropriate combinations of NiN 3 -Gr for applications in fuel cells. • The catalytic activity of a series of N and Fe-doped GDY has been theoretically explored in the ORR at the DFT level. • O 2 molecule can be directly dissociated on the N 2 -doped Fe-GDY. • It is reacting more favorable for the ER mechanism of OH∗ to convert into H 2 O. • The ORR reaction was found to be thermodynamically favorable in the N 2 -doped Fe-GDY. [ABSTRACT FROM AUTHOR]

Modern Fe–N–C electrocatalysts are promising as alternatives to expensive Pt-based catalysts for oxygen reduction reactions (ORR). Although the activity of this type of electrocatalyst have been improved over the years, their durability and longevity need critical enhancements for practical applications in fuel cells. Typically, the incomplete oxygen reduction inevitably generates reactive oxygen species, including ·OH and HO 2 · radicals, which will fiercely attack the carbon support and directly damage active sites in Fe–N–C electrocatalysts. Herein, a durable and robust Fe–N–C@Ti 3 C 2 –TiO 2 electrocatalyst for high-efficiency ORR is synthesized, in which Ti 3 C 2 –TiO 2 could effectively scavenge ·OH radicals or decompose H 2 O 2 molecules, and synergistically work with Fe–N–C catalysts to improve the durability. Consequently, the Fe–N–C@Ti 3 C 2 –TiO 2 electrocatalyst shows prominent ORR performance in both alkaline and acidic electrolytes, low H 2 O 2 yield, and long-term stability. This work provides great prospects for the design of highly stable ORR electrocatalysts by introducing radical scavengers as an active defense to proactively eliminate H 2 O 2 and its radicals. • A durable and robust Fe–N–C@Ti 3 C 2 –TiO 2 catalyst for ORR was synthesized due to the synergy between Ti 3 C 2 –TiO 2 and Fe–N–C. • Ti 3 C 2 –TiO 2 could effectively scavenge ·OH radicals or decompose H 2 O 2 molecule to enhance the durability. • The as-prepared catalyst exhibits excellent ORR catalytic activity in both alkaline and acidic electrolytes. • This work provides great prospects for designing stable ORR catalysts by using radical scavengers as active defense. [ABSTRACT FROM AUTHOR]

A porous nano-metal oxide composite consisting of zirconium oxide and vanadium oxide (ZrVNPs) was prepared using precipitation hydrothermal technique, followed by microwave sintering process in order to enhance the catalytic activity toward oxygen reduction reaction (ORR) which is a key reaction in the development of low-temperature fuel cell technology. Microwave sintering process conditions were optimized using response surface methodology models (RSM) and the optimized produced material was called ZrV-T. The physiochemical and electrochemical activities of the fabricated materials were investigated and the results elucidated that, the catalytic efficiency of prepared samples is influenced by morphology, lattice structure, and porosity, as well as metal–support interactions and interfacial structural changes that affect oxygen molecules adsorption and activation. The thermally treated composite (ZrV-T) exhibits higher oxygen reduction performance than the non-sintered material (ZrVNPs). Both materials have different half-wave potentials (E1/2 = −0.36 V) and (E1/2 = −0.29 V) for ZrVNPs and ZrV-T respectively. In addition, ZrV-T has a higher stability than the Pt/C catalyst in 0.1 M KOH solution by 4% after 120 min. Using ZrV-T is likely to reduce costs in FCs and promote the use of electrochemical energy devices and it may also be beneficial in other systems that promote catalytic activity. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a key step in many electrochemical devices such as fuel cells and metal-air batteries. However, the reaction proceeds at a significant overpotential requiring Pt-based catalysts. The scarcity and economical challenges associated with Pt is one of the major limitations for the commercialization of the devices. In this context, the electrochemical research community is constantly exploring other low-cost and earth-abundant materials as ORR catalysts. Carbon nanomaterials are identified as promising electrocatalysts due to their superb electronic conductivity together with high specific surface area. However, the low reactivity of carbon is the major limiting factor in the fabrication of ORR catalysts. Recent studies have proved that chemical modification of the carbon network (substitution of foreign atoms, Ex: N, S, B, F, P) could alter the reactivity of carbon nanomaterials for ORR. Many doping strategies have been proposed including single atom doping, co-doping and multi-atom doping. The heteroatom doped carbons have delivered promising results towards ORR in alkaline media. This review presents a rational approach of doping methods and the electrochemical properties of heteroatom doped carbons, and we believe that this review could be a guiding material to design advanced non-noble catalysts for ORR in the coming future. [Display omitted] • Overview of oxygen reduction reaction principle and mechanism. • Design and development of heteroatom doped carbon based electrocatalysts. • Half-cell studies of various heteroatom doped electrocatalysts. • AEMFC performance of heteroatom doped carbon catalysts. • Overview on the stability of heteroatom doped electrocatalysts. [ABSTRACT FROM AUTHOR]

FeN 4 single-atom catalysts are among the most promising electrocatalysts for oxygen reduction reaction (ORR), which has important roles in energy conversion systems, such as fuel cells and metal-air batteries. It has been investigated that the activity of FeN 4 single-atom catalysts is highly dependent on the density and distance of the FeN 4 active centers. However, controllable synthesis of FeN 4 single-atom catalysts with designed active center distance and density is still a remaining difficulty. In this work, a series of pyridyl conjugated microporous polymers with varying types of nitrogen are used as precursors to synthesize carbonaceous single-atom ORR catalysts with different amounts of FeN 4 active centers. The influence of the nature of the nitrogen groups in the precursors on the number of FeN 4 active sites and the ORR activity trend of the obtained FeN 4 –C catalysts was investigated. The catalyst with the highest density of FeN 4 sites showed a high efficiency for ORR, making its application in Zn-air batteries promising. FeN 4 –C catalysts with different active site densities are synthesized by a series of pyridyl conjugated microporous polymers with different amount and position of N as precursors. The FeN 4 –C single-atom catalysts carbonized from polymeric precursors show increasing ORR activity with the increasing of active site density. The optimized FeN 4 –C-4 catalysts with the highest density of FeN 4 active sites show superior ORR performance than Pt/C and having potential for applications in Zn-air battery. [Display omitted] [ABSTRACT FROM AUTHOR]

Exploring efficient non-precious metal cathode catalysts is attracting ever-increasing interest in the development of direct borohydride fuel cell (DBFC). Herein, a cobalt-based nitrogen-doped bamboo-like graphene tube (Co-NGT) is prepared as an efficient cathode catalyst. The Co-NGT consists of bamboo-like graphene tubes (40–130 nm in diameter and ∼10 μm in length), as well as cobalt nanoparticles (50–100 nm in diameter) confined in the graphene tubes. The Co-NGT shows an onset reduction potential of 0.964 V and an almost four-electron pathway towards oxygen reduction reaction, as well as a negative shift of 8 mV in half-wave potential after 10,000 CV cycles. The Tafel slope of the Co-NGT catalyst is 47 mV decade−1, which is by ca. 37.8 mV decade−1 smaller than for Pt/C. A DBFC using the Co-NGT cathode yields the biggest power density of 453 mW cm−2 at 60 °C and a life span of over 120 h. The excellent electrocatalytic properties and superior durability of Co-NGT catalyst arise from the highly graphitized NGT, providing strong interaction with Co nanoparticles and mitigating the agglomeration of Co nanoparticles. Our study guides for composition and structural design of high-efficient cathode catalysts of DBFC. [Display omitted] • The Tafel slope of Co-NGT towards ORR is 47 mV dec−1. • The half-wave potential is only 8 mV negative shift of Co-NGT after 10,000 CV cycles. • Maximum power density of 453 mWcm−2 is achieved by DBFC using Co-NGT cathode. [ABSTRACT FROM AUTHOR]

Rational design of efficient and durable non-noble transition metal doped carbon-based oxygen reduction electrocatalysts is the key to reduce catalyst cost and optimize fuel cell performance. Herein, hierarchically porous Fe/N co-doped porous carbon on N doped carbon nanotubes (Fe/N-C@NCNTs) are prepared via the pyrolysis of Fe-doped ZIF-8 embedded on polypyrrole nanotubes (PNTs). The as-prepared Fe/N-C@NCNTs electrocatalyst exhibits the limit current density of 5.7 mA cm−2 and the half-wave potential of 0.84 V (vs. RHE), indicating the excellent oxygen reduction performance. Furthermore, the electrocatalytic activity of Fe/N-C@NCNTs is only reduced by 7% after 650 min of the stability test. The remarkable oxygen reduction performance is attributed to the synergistic effects of abundant Fe-N x -C active sites, high graphitization degree and hierarchically porous structure of electrocatalyst. Schematic diagram of the synthesis process of Fe/N-C@NCNTs. [Display omitted] • The hierarchically pore size of the as-prepared catalysts were controlled by the amount of Fe doping. • One-dimensional Fe/N co-doped carbon nanotubes were constructed using polypyrrole nanotubes (PNTs) as substrate. • The as-prepared catalyst had a E 1/2 of 0.84 V and maintained 95% performance after 300 min of the stability test. [ABSTRACT FROM AUTHOR]

As proton-exchange membrane fuel cell technology has grown and developed, there has been increasing demand for the design of novel catalyst architectures to achieve high power density and realize wide commercialization. Herein, based on the two-dimensional biphenylene, we compare the oxygen reduction reaction (ORR) activity on the active sites with different biaxial lattice strains using first-principles calculations. The ORR free energy diagrams of biphenylene monolayers with varying lattice strains suggest that the biaxial tensile strains are unfavorable for catalytic activity. In contrast, the biaxial compressive strains could improve the catalytic performance. The biphenylene systems with the strain of −2% ∼ −6% (S -0.02∼-0.06) display overpotentials of 0.37–0.49 V. This performance is comparable to or better than the Pt (111) surface. The Bader charge transfer of adsorbed O species on various biaxial strain biphenylene catalysts could be a describer to examine the catalytic activity. The catalysts possessed the moderate transferred charge of O adsorbed species often promotes catalytic process and give the high catalysis efficiency. Overall, this work suggests that the lattice strain strategy can significantly enhance the catalytic activity of biphenylene materials and further provide guidance to design biphenylene-based catalysts in various chemical reactions. [Display omitted] • Lattice strains in 2D biphenylene could enhance ORR activity. • Compressive strains of −2% ∼ −6% endow their overpotentials of 0.37–0.49 V. • Charge transfer of adsorbed O species is a descriptor to examine ORR performance. • Moderate strains and moderate transferred charge lead to excellent efficiency. [ABSTRACT FROM AUTHOR]

The series of electrodes were fabricated by the scalable and manufacturable slot-die coating method for proton exchange membrane fuel cell (PEMFC) application. The inks with different amounts of solids were studied by rheological methods in order to establish a coating window with minimum manufacturing defects. The obtained electrodes were characterized by SEM, AFM, and optical microscopy, which showed that they were uniform and homogeneous with minimum defects. The electrochemical evaluation of the manufactured gas diffusion electrodes (GDE) showed that the main characteristics of the electrodes, like electrochemical surface area, proton resistivity, and double layer capacitance, were found to be close for all samples confirming the reproducibility of the slot-die process. Additionally, we studied the effects of membrane thickness on the performance of the GDE membrane electrode assemblies and determined that a decrease in membrane thickness favored the performance. The obtained results clearly demonstrated the applicability and feasibility of the approach for the Manufacturing of catalyst layers for the fuel cell application with potential for future mass production. [Display omitted] • Pt/C inks with high solid content were formulated. • Scalable Roll-2-Roll approach was used to coat 300 × 22cm electrode. • The electrodes possessed minimal inhomogeneities. • PEM fuel cell tests confirmed promising performance of scaled electrodes. [ABSTRACT FROM AUTHOR]

Graphene supported FeN5 active sites, exhibiting high activity and stability of oxygen reduction reaction, enable a H2-air fuel cell to decay little during the latter 20–100 h operation. [Display omitted] • Electrochemically-exfoliated graphene improves forming FeN 5 with NH 3. • Graphene benefits catalytic stability of oxygen reduction reaction. • Fuel cell keep stable with little decay in latter 80 h operation. • High half-wave potentials in alkaline medium (0.940 V). Metal-nitrogen-carbon catalytic material, generally thought as a promising low-cost electrocatalyst of oxygen reduction reaction (ORR), surfers from long-term catalytic durability for fuel cell and metal-air battery. Here, we describe an approach of synthesizing electrochemically exfoliated graphene supported penta-nitrogen coordinated iron exhibiting encouraging ORR catalytic activity and durability. The synthesized catalyst exhibits high half-wave potentials in alkaline medium (E 1/2 0.940 V) enabling high-performance zinc-air battery and in acidic condition for durable fuel cell with a high peak power density (630 mW cm−2). The current density of a proton exchange membrane fuel cell loading the catalyst as cathode tends to decay little after initial hours under H 2 -air measurement, remarkably inhibiting commonly decline tendency of iron–nitrogen-carbon catalysts. DFT calculation combined with extensive experimental investigations demonstrate that penta-nitrogen coordinated iron supported by graphene is thermodynamically stable, and thus benefits the catalytic stability of ORR. [ABSTRACT FROM AUTHOR]

The exploration of non-Pt catalysts with high electrocatalytic activity and durability is especially important for cathodic oxygen reduction reaction (ORR) in fuel cell. Here, cobalt and nitrogen doped hollow carbon sphere-bamboo like carbon nanotube (Co/NHCS-BCNT) is prepared by using SiO 2 sphere as sacrificial template. Co nanoparticles are confined in the cavity and top end of the in-situ formed BCNT, which can not only avoid the agglomeration of Co nanoparticles but also inhibit corrosion in caustic electrolyte. The synergistic effect between NHCS and well-dispersed Co particles makes Co/NHCS-BCNT have superior catalytic activity toward ORR. The electrochemical surface area (ECSA) of Co/NHCS-BCNT is 222 cm2, which is higher than those of NHCS (164 cm2) and HCS (135 cm2). The onset potential and half-wave potential of Co/NHCS-BCNT are 0.941 V and 0.814 V, respectively, which are close to commercial Pt/C (0.949 V, 0.807 V). The Tafel slope of Co/NHCS-BCNT (63.8 mV dec-1) is lower than that of Pt/C (71.7 mV dec-1). In addition, Co/NHCS-BCNT shows excellent durability and fuel selectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Electrocatalysts play a pivotal role in advancing proton-exchange membrane fuel cell (PEMFC) for hydrogen energy applications. In this study, we investigate a novel PtCu/C N electrocatalyst synthesized via a gram-scale synthesis approach, which demonstrates remarkable activity and stability in the oxygen reduction reaction (ORR). The catalyst's effectiveness stems from its unique structure, combining bimetallic nanoparticles (NPs) and an N-doped carbon support. Employing identical location transmission electron microscopy (IL-TEM) imaging, we observe significant NP structure reorganization upon activation influenced by the upper limiting potential. Notably, the PtCu/C N catalyst activated to 1.0 V surpasses the United States Department of Energy (DOE) target for ORR activity by 3.3-fold. These findings underscore the potential of this catalyst in enhancing the performance of PEMFCs, marking a significant advancement in hydrogen energy technology. [Display omitted] • Catalyst's effectiveness attributed to unique structure of bimetallic NPs and N-doped support. • Vital reorganization of NPs occurs under the upper limiting potential of activation. • PtCu/C N catalyst activated to 1.0 V surpasses DOE target for ORR activity by 3.3-fold. • IL-TEM method comes to the rescue in assessing NPs' reorganization. • Findings highlight potential of bimetallic catalyst in enhancing PEMFC performance. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) as the crucial reaction in fuel cells (FCs), requires high-performance electrocatalysts to achieve satisfied kinetics. Commercial electrocatalysts are generally based on Pt, but the high cost hinders the large-scale application of FCs. Many efforts have been made on non-noble metal electrocatalysts (NNMEs) as potential alternatives to Pt. Among them, transition metallomacrocycles (TMs) based electrocatalysts (TMEs) are one kind of the most efficient NNMEs. In this review, the catalytic characteristics of these TMEs based on two representatives: FeN 4 - and CoN 4 -centered TMs are summarized for ORR. The variation of ORR performances is reviewed based on the strategies to modify the active sites, conductivity, and morphology, including adjusting molecular structures, altering carbon supports and employing metal–organic-frameworks (MOFs) as precursors. Moreover, the prospects and challenges of such electrocatalysts and the corresponding solutions are also discussed in details. From this review, we will understand more clearly about the structure–activity relationship of TMEs based on FeN 4 - and CoN 4 -centered TMs in ORR, which will pave the way for the rational design of more TMEs based on MN 4 -centered TMs in the future. [ABSTRACT FROM AUTHOR]

Due to its exorbitant expense and scarcity on Earth, there is a need to anticipate a cost-effective and widely accessible catalyst that can effectively replace platinum, which is known for its efficiency in fuel cells. In this context, catalysts such as OH, H, and COOH group-functionalized cobalt-doped Graphyne-like boron nitride (referred to as BNyen) are being examined to enhance the mechanism of oxygen reduction reaction (ORR) via direct 4e− reduction. According to findings derived from DFT, it has been observed that reactions predominantly take place above Co metal center rather than edge site of BNyen. Additionally, the thermochemical characteristics point to the fact that these reactions release a significant amount of heat, suggesting their feasibility. By examining reversible potential of products and intermediates on phthalocyanines as well as adsorption energy (E ads), it has been determined that Co-BNyen(OH) serves as a superior catalyst for ORR process. In conclusion, this research affirms that BNyen materials hold significant promise as catalysts for ORR, a crucial process in fuel cell applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Platinum-based catalysts remain the top choice for oxygen reduction reaction (ORR) in fuel cells. However, their activity and durability in the acidic medium are still under improvement. In this work, the Pt nanoclusters anchored the nitrogen-doped carbon nanotubes (Pt-NCNTs) have been synthesized by using a series process of pyrrole coating on the CNTs and subsequent pyrolysis to the chemical immersion reduction of Pt ions. The inner CNTs of Pt-NCNTs function as the nanowires offering a high-speed pathway for electron transport, and the Pt nanoclusters increases the active sites. The theoretical calculation demonstrates that the local structural defects and the uneven charge distribution induced by nitrogen-containing functional groups and porous structure are favorable to capture Pt ions for the nucleation of Pt nanoclusters. Compared with the commercial 40 wt% Pt/C (0.94 and 0.80 V), the Pt-NCNTs-1000 with Pt loading amount of 33.0 wt% owns the more positive onset potential and half-wave potential of 0.97 and 0.81 V in the sulfuric acid medium. Meanwhile, the strong attachment of Pt nanoclusters on the nitrogen-doped porous carbon layer results in a stable interface to effectively prevent the metallic species from migration and agglomeration during the electrode reactions. Therefore, the ORR current of Pt-NCNTs-1000 retained 84.3% of the initial value after 50000 s operation superior to the commercial Pt/C (64.6%). [Display omitted] • N-doped porous carbon layer coated CNT was used as support to enhance Pt deposition. • Micropores and nitrogen groups strongly anchor Pt nanoclusters deposited on NCNTs. • CNTs act as nanowires to promote charges transport of electrode reactions. • Pt-NCNTs has a good ORR activity and durability compared with commercial 40 wt% Pt/C. [ABSTRACT FROM AUTHOR]

[Display omitted] • HME was applied as an oxygen electrode of the AEM-URFCs. • Introducing 3 D CNT framework provided high ECSA of catalysts, electron transport, mass transport. • The HME_URFC exhibited superior round-trip efficiency of 55% at 20 mA cm−2 with enhanced durability and cyclability. Developing three-dimensional porous oxygen electrodes (OE) is crucial for enhancing round-trip efficiency (RTE) of anion-exchange membrane-based unitized regenerative fuel cells (AEM_URFCs). Herein, a novel OE design of AEM_URFCs is presented based on a hierarchical mesh electrode (HME) with a porous carbon nanotube (CNT) framework. The HME, featuring square-shaped macropores achieved by dispersing catalyst nanoparticles on the CNT framework enhances surface area, mass transport, and electron transport. Half-cell test demonstrated superior oxygen reduction reaction and oxygen evolution reaction activity compared to conventional electrodes. Moreover, the HME maintained stable ORR and OER activity during the stability test. In single-cell tests, the AEM_URFCs with the HME exhibited higher RTE (55% at 20 mA cm−2), surpassing the conventional electrode (52%). Furthermore, RTE was maintained at a remarkable 41% under ultrahigh current density (250 mA cm−2), which is unprecedented in the literature. The AEM_URFCs featuring the HME displayed superior cyclability over 5 cycles and durable performances under both fuel cell and water electrolysis modes. [ABSTRACT FROM AUTHOR]

• Resonance structure as substrate molecules are introduced to form highly ordered PtCo alloys. • Synthesis of PtM (Co, Fe, Ni) ordered alloys use the same low temperature heat treatment conditions. • The ordered PtCo shows efficient electrocatalytic performance. Platinum-based ordered alloys have excellent catalytic performance for the cathodic oxygen reduction reaction (ORR) in fuel cells. However, these alloys exhibit a lower degree of ordering and larger crystal grains after heat treatment. Herein, a series of cyanamide group molecules (cyanamide, dicyandiamide, melamine) was employed as substrates to modify Pt-based alloys by promoting the binding between metal ions, leading to the preparation of ∼ 4 nm PtM (M = Co, Fe, Ni) ordered alloys after heat treatment. Among them, the PtCo ordered alloy prepared using hydrolyzed cyanamide with a unique resonance structure exhibits a high degree of order (93.1 %), and its mass activity of 0.915 A mg Pt -1 at 0.9 V is superior to that of Pt/C. The theoretically calculated adsorption energies of these alloys demonstrate that the resonance structure of the cyanamide substrate is beneficial for alloy formation, thereby facilitating ordered alloy synthesis. [ABSTRACT FROM AUTHOR]

High-efficiency catalysts are required for the oxygen reduction reaction (ORR) in fuel cell applications. Herein, we present a novel hybrid material that is based on uniformly deposited nanoscale molybdenum phosphide (Mo x P y) nanoparticles on the structure of graphene nanolayers doped with phosphorus atoms (PG). With a positive onset potential of only −0.046 V and a half-wave potential value of roughly −0.17 V (vs. Ag/AgCl), the obtained hybrid showed good catalytic activity for ORR in 0.1 M KOH electrolyte. It also demonstrated remarkable durability for oxygen reduction reaction in 0.1 M KOH electrolyte when compared to state-of-the-art Pt/C material. The excellent ORR performance can be correlated to the development of a highly conducting microporous structure with highly active sites, which in turn encourages optimal adsorption of intermediates during the ORR process and thus enhances the catalytic process. This work can open a new path for the growth of promising highly efficient catalysts for affordable fuel cell applications. [Display omitted] • Uniform Mo x P y nanoparticles dispersed P-doped G was prepared by a facile route. • The hybrid offered high catalytic performance for ORR, close to Pt/C. • The synergistic effect from Mo x P y and P-doped Gr produced enhanced ORR performance. • The hybrid showed much better durability and methanol tolerance than Pt/C. [ABSTRACT FROM AUTHOR]

This study presents the preparation of tridoped Fe, N, S carbon-based catalysts using ZIF-8 as the main carbon source and iron(II)acetate, 1,10-phenanthroline, ammonia gas and thiourea as precursors for Fe, N and S elements. Thiourea was mixed via planetary ball-milling with a Fe–N–C catalyst prepared by inert gas pyrolysis, and different pyrolysis conditions were applied thereafter. The main goal of the work is to synthesise active non-precious metal electrocatalysts for oxygen reduction reaction (ORR). High electrocatalytic ORR activity in alkaline media was observed for the two materials obtained after thiourea addition and subsequent pyrolysis. Physico-chemical characterisation revealed successful S- and N-doping for all three catalysts with enhanced porosity for the two materials that were subjected to additional pyrolysis after the thiourea addition. The sulphur doping was highest for the FeNSC3 material that was subjected to a second pyrolysis in N 2 and a third pyrolysis in NH 3 , compared to the FeNSC2 material that was subjected to a single pyrolysis in NH 3 flow after thiourea addition. The ORR activity of FeNSC2 with half-wave potential of 0.88 V was slightly higher than that of FeNSC3, and the former was selected for evaluation as a cathode catalyst in an anion-exchange membrane fuel cell. [Display omitted] [ABSTRACT FROM AUTHOR]

The slow reaction rates observed in the Oxygen Reduction Reaction (ORR) pose a significant obstacle in advancing fuel cell technology. Consequently, ORR plays a pivotal role in determining the operational efficiency of fuel cell and energy storage systems. Accordingly, the synthesis of a cathodic electrocatalyst with high efficiency has become an attractive topic for researchers. In this empirical study, three trimetallic electrocatalysts are synthesized and electrochemically appraised. By introducing three lanthanides, namely Gadolinium (Gd), Samarium (Sm), and Europium (Eu), into CuFeZIF-8, new composites successfully are synthesized as Cu@FeLn (Eu, Sm, and Gd)-N-C. These functional materials find application in the context of the ORR and supercapacitor technologies. In order to enhance stability, control surface area, and prevent agglomeration during high-temperature pyrolysis, the silicon cover protection technique is employed. The primary objective in this investigation is to assess the influence of mSiO 2 coating on the electrochemical parameters of these electrocatalysts. To characterize the fabricated samples, seven characterization tests are utilized. Electrochemical measurements are conducted employing a three-electrode cell configuration within an alkaline environment. The results illustrated that the Cu@FeGd-N-C sample, with an onset potential of −0.043 V vs. Ag/AgCl, exhibited the best ORR performance. Also, the electron transfer number of Cu@FeSm-N-C was computed as 3.56. The half-wave potentials of Cu@FeSm-N-C, Cu@FeEu-N-C, and Cu@FeGd-N-C were found to be −0.34, −0.23, and −0.18 V vs. Ag/AgCl, respectively. A less negative half-wave potential typically suggests superior performance, signifying a lower overpotential requirement for the ORR process. The specific capacitance for Cu@FeGd-N-C electrode at 1 A/g was determined as 144.4 F g−1. The inclusion of lanthanides, Fe, and Cu into ZIF-8 is observed to notably improve both catalytic activity and electron transfer. Also, the outcomes showed that mesoporous silica-protected pyrolysis could be a useful strategy for improving the efficiency of energy conversion and energy storage equipment. [Display omitted] • By introducing three lanthanides into CuFeZIF-8, new composites are synthesized and evaluated. • To prevent irreversible fusion, the strategy of applying an mSiO2 coating is implemented. • The synthesized catalysts were used for two applications: energy conversion and storage. • The best ORR performance is associated with the Cu@FeGd-N-C sample, with an onset potential of −0.043 V vs. Ag/AgCl. • The Cu@FeGd-N-C electrode exhibited a specific capacitance of 144.4 F g−1 at a current density of 1 A/g. [ABSTRACT FROM AUTHOR]

Fuel cell systems are environmentally friendly energy converters that directly transform the chemical energy of the fuel to electricity. The proton exchange membrane (PEM) fuel cells are one of the most common type of fuel cells since they deliver high power density and are lighter and smaller when compared to the other cells. However, commercialization of the PEM fuel cells is challenging due to the high cost of its components. In addition to high catalyst costs, the problem of poor water management is also a vital issue that needs to be overcome. While the gas diffusion layer of a fuel cell is essential for removing the by-product water, the Nafion solution contained in the catalyst layer has hydrophobic properties and is crucial for both preventing the water accumulation and increasing the effectiveness of the fuel cell. In this study, the effects of Carbon:Nafion ratio on the reduction potential was investigated. The cyclic voltammograms (CV) was produced for each ratio, and it was shown that the CVs exhibit characteristics of hydrogen adsorption/desorption peaks. All the linear sweep voltammogram (LSV) curves revealed well distinguished regions of kinetic, mixed and diffusion limited reaction rate. As a result, it was observed that the ratio of 1:5 resulted higher reduction potential compared to 1:3 and 1:7. Finally, a mathematical model was purposed, in which related the rotation rate and platinum coating with the current density, in order to gain insight about the responses of the fuel cell system. The constructed model is tested and validated experimentally for various parameters that are present in the system, and it may be utilized to determine oxygen reaction activities of the catalysts without performing any unnecessary electrochemical tests. • The catalyst layer of fuel cells, which has a vital role for water management, should be optimized. • Electrical conductivity of gas diffusion layer can be controlled by adjusting Catalyst:Nafion ratio. • The current density can be estimated directly from the rotation rate and Pt coating by using the proposed mathematical model. • Half-cell modeling makes performance values of the fuel cells more predictable. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR), one of the key reactions for fuel cells and zinc-air batteries, should be improved for higher performance. Herein, we fabricated hollow Fe, Co, and nitrogen co-doped carbon (H-FeCo-NC) catalyst, which was prepared by carbonization of core-shell particles made of polypyrrole (PPy)-coated polystyrene (PS) spheres as cores and (Zn, Co) bimetallic-zeolitic imidazolate frameworks (ZnCoBZIFs) as shells. PPy was used as a nitrogen and a carbon source. The H-FeCo-NC catalyst had a high surface area of 324.08 m2 g−1 with uniformly distributed Fe and Co species, and excellent ORR performance with the half-wave potential of 0.888 V vs. reversible hydrogen electrode in alkaline media. Furthermore, the H-FeCo-NC catalyst demonstrated exceptional stability, durability, and tolerance to methanol crossover. • Hollow Fe, Co, and N-doped carbon was prepared using polypyrrole and MOFs. • Polypyrrole served as the source of carbon and nitrogen. • Hollow FeCo-NC catalyst showed high surface area with high metal dispersion. • The ORR activity, stability, and durability of the H-FeCo-NC catalyst were excellent. [ABSTRACT FROM AUTHOR]

Synthesis of Pt-based catalysts with high activity and durability for oxygen reduction reaction (ORR) remains a very challenging task in the field of fuel cells. Here, Co-doped Pt nanoparticles (NP) with surface-defect ZrO 2 are supported on the multi-walled carbon nanotubes (MWCNTs) (denoted as Pt–Co + ZrO 2 /MWCNTs). The Pt–Co + ZrO 2 /MWCNTs displays an ORR mass activity of 0.98 A mg Pt −1 at 0.9 V, which is 4.1-fold higher than that of the commercial Pt/C (0.238 A mg Pt −1). Further durability test shows that the Pt–Co + ZrO 2 /MWCNTs remains nearly unchanged ORR mass activity after 50000 accelerated durability testings (ADTs). Based on the mass performance and surface performance, the fuel cell with Pt–Co + ZrO 2 /MWCNTs cathode has far better power performance than that with commercial Pt/C. Moreover, the fuel cell with Pt–Co + ZrO 2 /MWCNTs cathode undergo only a 6.1% maximum power loss after 50000 ADTs. However, that with commercial Pt/C cathode after 30000 ADTs has 39.6% maxinum power loss. More impressively, compared to the 220 mV loss of Pt/C after 30000 ADTs, the Pt–Co + ZrO 2 /MWCNTs cathode also displays only 20 mV loss at 0.8 A/cm2 after 50000 ADTs. The enhanced intrinsic activity of Pt–Co + ZrO 2 /MWCNTs may be attributed to the Co-doped Pt NPs and interface effect of Co-doped Pt NPs and surface defect-rich ZrO 2. Pt–Co alloy nanoparticles (NPs) on multi-walled carbon nanotubes (MWCNTs), nailed with oxygen vacancy-rich ZrO 2 NPs (denoted as Pt–Co + ZrO 2 /MWCNTs), were synthesized through syneresis crack, heat treatment and acid treatment. The Pt–Co + ZrO 2 /MWCNTs demonstrated superior ORR mass activity and catalytic durability in half-cell testing and single-cell testing. [Display omitted] • The Pt–Co alloy was anchored by oxygen vacancy-rich ZrO 2. • The Pt–Co + ZrO 2 /MWCNTs exhibited basically unchanged stability for ORR after 50000 ADTs. • The MEA with Pt–Co + ZrO 2 /MWCNTs showed 0.485 W/cm2 (cathode: 0.04 mg Pt /cm2). • The MEA with Pt–Co + ZrO 2 /MWCNTs has only 24.4% power loss after 50000 ADTs at 0.6 V. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) plays a crucial role in green-energy-related technologies including fuel cells and metal-air batteries. The rational design of cost-effective and high-efficiency electrocatalysts is of paramount importance to accelerate the sluggish kinetics of ORR. Recently, owing to the structural flexibility, high porosity, and large surface area, metal-organic frameworks (MOF)-derived carbon-based electrocatalysts have drawn significant attention as competent ORR catalysts. This review systematically summarizes recent progress toward advanced MOF-derived carbon-based electrocatalysts for ORR from the aspects of composition engineering, structural engineering, and the practical application in fuel cells and metal-air batteries, with the emphasis on the synthetic methods and the engineering mechanisms to achieve the enhanced ORR performance. Finally, some existing challenges and future perspectives for MOF-derived carbon-based electrocatalysts are proposed. • Recent advance on MOF-derived carbon-based ORR electrocatalysts is reviewed. • ORR mechanism and design principles of catalysts are discussed. • Composition engineering and structure engineering of MOF-derived carbon-based electrocatalysts are mainly scrutinized. • Facing challenges and future prospects of carbon-based electrocatalysts are addressed. [ABSTRACT FROM AUTHOR]

Developing economical electrocatalysts as alternatives to platinum for oxygen reduction reaction (ORR) to develop the applications of green energy devices like proton exchange membrane fuel cells (PEMFCs) is of paramount importance. In the current study, a different ratio of nitrogen-doped graphdiyne (GDY) with Fe single-site is reported to be more cost-effective and efficient for PEMFCs. The current study also demonstrates the design principle to improve the ORR activity associated with catalysts using Fe single-site with a greater Fe charge, which is controlled through the coordinated structure of the active center. Based on the simulation results, the formation of N 2 -doped GDY and N 2 -doepd Fe-GDY are more lucrative compared to the formation of Nx-doped GDY (x > 2) in terms of energy. O 2 molecules have a direct dissociation on the N 2 -doepd Fe-GDY via Eley-Rideal (ER) mechanism, which involves the formation of H 2 O by reacting with H+ from the electrolyte. Moreover, N 2 -doepd Fe-GDY exhibits better performance as an ORR catalyst in an acidic medium because of its low overpotential of 0.488 V. However, N 2 -doped GDY follows the OOH∗ formation pathway, showing a higher overpotential for ORR. Furthermore, in the structure under study, the thermodynamic favorability of ORR is observed since the reaction energies calculated at each reaction step are exothermic and the energy profile of all reaction steps are downhill. The results of the current work provide new insights into the construction of extremely efficient heterogeneous catalysts in electrochemical energy technologies. [Display omitted] • The catalytic activity of Fe-doped GDY has been theoretically explored in the ORR. • O 2 molecule can be directly dissociated on the N 2 -doped Fe-GDY. • It is reacting more favorable for the ER mechanism of OH∗ to convert into H 2 O. • The ORR reaction was found to be thermodynamically favorable in N 2 -doped Fe-GDY. [ABSTRACT FROM AUTHOR]

A non-precious metal electrocatalyst was obtained through the in-situ growth of iron phosphide (Fe 2 P) encapsulated by carbon nanotubes (CNTs) decorated with zeolitic imidazolate framework-8 (ZIF-8). Upon pyrolysis at a specific temperature, the ZIF-8/Fe 2 P@CNT catalyst exhibits high oxygen reduction reaction (ORR) ability and is close to the ideal electron transfer, which number is 3.99. The structure, high number of nitrogen-containing functional groups, and suitable surface properties of ZIF-8/Fe 2 P@CNT are critical for enhancing the ORR activity. ZIF-8/Fe 2 P@CNT exhibits a decay in electrocatalytic activity of 26 mV in the half-wave potential after 30 000 cycles, which is considerably superior to the decay of 123 mV for Pt/C after the same number of cycles. Therefore, ZIF-8/Fe 2 P@CNT exhibits excellent ORR activity and long-term stability and can be used as a fuel cell catalyst. [Display omitted] • ZIF-8 is grown in-situ on synthesized CNTs to form a ZIF-8/Fe 2 P@CNT catalyst. • Specific structure and unoccupied graphitic π∗ could catalyze the ORR activity. • ZIF-8/Fe 2 P@CNT exhibits excellent activity and long-term stability for fuel cell. [ABSTRACT FROM AUTHOR]

Naturally abundant well-decomposed peat was used as a precursor for synthesizing several non-platinum group metal-type oxygen electrocatalysts. The materials were studied in an alkaline environment, where it was discovered that the oxygen evolution (OER) and the oxygen reduction (ORR) activity of the catalysts can be severely influenced by changing the parameters of the peat carbonization procedure. High OER activity was achieved with a minimally treated catalyst which seemed to be because of a Co-rich FeCo alloy species. In both rotating disc electrode and anion exchange membrane fuel cell experiments, the catalyst based on ZnCl 2 -activated peat-derived carbon showed superior ORR performance with a peak power density of 51 mW cm−2. It was found that the peak power densities of the catalysts correlated with several physical parameters. Above all, we demonstrate the possibility of fabricating advanced functional carbon materials for oxygen electrocatalysis from peat. [Display omitted] • Bifunctional platinum-free oxygen catalysts prepared from abundant decomposed peat. • Physical and catalytical properties can be tuned by modifying synthesis conditions. • Correlations between particle size properties and AEMFC performance established. [ABSTRACT FROM AUTHOR]

Porous carbon materials are promising electrocatalysts for the oxygen reduction reaction (ORR). Their active sites, involving porosity and surface chemistry, are different from those of metal-doped carbons. The latter have been widely studied and are adapted to today's popular electrochemical devices, the rotating disk electrode being the most useful preliminary tool to evaluate their activity in ORR. However, porous carbon materials have been less explored, and experimental parameters need to be adjusted to achieve the best ORR performance. Therefore, in this study, the optimization of different key factors was investigated to evaluate their effect on the ORR performance of porous carbon electrocatalysts in alkaline medium. The parameters considered were: (i) the relevance of using RRDE or Koutecky-Levich equations for estimating the number of electrons transferred; (ii) the amount of ionomer (Nafion®); (iii) the carbon loading on the electrode; (iv) the carbon grinding method; and (v) the selection of the upper potential of ORR experiments. We conclude that an optimization of the experimental conditions should be done for each material studied, and we give important benchmarks for the appropriate evaluation of the catalytic activity in ORR of carbon-based catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]