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Coordination environment engineering is developed to synthesize Fe SA /NSC catalysts with the tailored N, S co-coordinated Fe atomic site. [Display omitted] • The Fe-N 3 S active site with the optimized electronic structure is constructed. • S doping promotes the OH* desorption, thus leading to enhanced kinetics process. • The catalyst displays impressive ORR activity in both alkaline and acidic mediums. • The catalyst exhibits excellent performance in Zn-air batteries and fuel cells. Atomically dispersed iron–nitrogen-carbon (FesbndNsbndC) materials have been considered ideal catalysts for the oxygen reduction. Unfortunately, designing and adjusting the electronic structure of single-atom Fe sites to boost the kinetics and activity still faces grand challenges. In this work, the coordination environment engineering is developed to synthesize the Fe SA /NSC catalyst with the tailored N, S co-coordinated Fe atomic site (Fe-N 3 S site). The structural characterizations and theoretical calculations demonstrate that the incorporation of sulfur can optimize the charge distribution of Fe atoms to weaken the adsorption of OH* and facilitate the desorption of OH*, thus leading to enhanced kinetics process and intrinsic activity. As a result, the S-modified Fe SA /NSC exhibits outstanding catalytic activity with the half-wave potentials (E 1/2) of 0.915 V and 0.797 V, as well as good stability, in alkaline and acidic electrolytes, respectively. Impressively, the excellent performance of Fe SA /NSC is further confirmed in Zn-air batteries (ZABs) and fuel cells, with high peak power densities (146 mW cm−2 and 0.259 W cm−2). [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D GnP/MoS 2 and 3D (GnP/MoS 2)/MWNT composites are prepared by a facile, robust and ecofriendly method. • Effects of N-doping of GnPs and mass fraction of MWNTs on ORR activity are explored and rationalized. • Best synergistic ORR activity is obtained for N-doped catalyst with 3:1 2D-to-1D ratio. • Catalysts exhibit excellent stability and methanol resistance in alkaline medium. • Promising route to develop bifunctional ORR/OER catalysts. Nanocomposites have garnered attention for their potential as catalysts in electrochemical reactions vital for technologies like fuel cells, water splitting, and metal-air batteries. This work focuses on developing three-dimensional (3D) nanocomposites through aqueous phase exfoliation, non-covalent functionalization of building blocks with surfactants and polymers, and electrostatic interactions in solution leading to the nanocomposites assembly and organization. By combining molybdenum disulfide (MoS 2) layers with graphene nanoplatelets (GnPs) to form a binary 2D composite (MoS 2 /GnP), and subsequently incorporating multiwalled carbon nanotubes (MWNTs) to create ternary 3D composites, we explore their potential as catalysts for the oxygen reduction reaction (ORR) critical in fuel cells. Characterization techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction elucidate material composition and structure. Our electrochemical studies reveal insights into the kinetics of the reactions and structure–activity relationships. Both the (MoS 2 /GnP)-to-MWNT mass ratio and nitrogen-doping of GnPs (N -GnPs) play a key role on the electrocatalytic ORR performance. Notably, the (MoS 2 / N -GnP)/MWNT material, with a 3:1 mass ratio, exhibits the most effective ORR activity. All catalysts demonstrate good long-term stability and methanol crossover tolerance. This facile fabrication method and observed trends offer avenues for optimizing composite electrocatalysts further. [ABSTRACT FROM AUTHOR]

[Display omitted] Lowering the operating temperatures of solid-oxide fuel cells (SOFCs) is critical, although achieving success in this endeavor has proven challenging. Herein, Bi 0.15 Sr 0.85 Co 0.8 Fe 0.2 O 3−δ (BiSCF) is systematically evaluated as a carbon dioxide (CO 2)-tolerant and highly active cathode for SOFCs. BiSCF, which features Bi3+ with an ionic radius similar to Ba2+, exhibits activity (e.g., 0.062 Ω cm2 at 700 °C) comparable to that of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ and PrBaCo 2 O 5+δ , while demonstrating a considerable advantage over Bi-doped cathodes. Moreover, BiSCF exhibits long-term stability over a period of 500 h, and an anode-supported cell with BiSCF achieves a power density of 912 mW cm−2 at 650 °C. The CO 2 -poisoned BiSCF exhibits quick reversibility or slight activation after returning to normal conditions. The exceptional CO 2 tolerance of BiSCF can be attributed to its reduced basicity and high electronegativity, which effectively restrict surface Sr diffusion and hinder subsequent carbonate formation. These findings highlight the substantial potential of BiSCF for SOFCs operating below 700 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • A two stage confinement strategy assisted facile synthesis of 5.3 nm highly ordered PtCoZn/NC. • PtCoZn/NC ordering and graphitization are promoted by regulating composition and calcination-time. • High intrinsic activity (2.8 mA cm-2 Pt) and slight E 1/2 loss (9 mV) in ADT were achieved by PtCoZn/NC. • It is evidenced weaker O binding and stronger Pt-Co/Zn bonding enhance activity and durability. • The ionomer-free and anti-sintering feature of carbon-walls also benefit the MEA performance. Intermetallic ordered PtCo is effective for high oxygen reduction reaction (ORR) activity and stability. However, preparing small-sized, highly ordered PtM alloys is still challenging. Herein, we report a controlled two-stage confinement strategy, in which highly ordered PtCoZn/NC nanoparticles of 5.3 nm size were prepared in a scalable process. The contradiction between the high ordering degree with the small particle size as well as the atomic migration with the space confinement was well resolved. An outstanding PEMFC performance was achieved for L1 0 -PtCoZn/NC with a high mass activity (MA) of 1.21 A/mg Pt at 0.9 V iR-free , 80.1 % MA retention after 30 k cycles in H 2 -O 2 operation, and a high mass-specific power density of 8.24 W mg-1 Pt in H 2 -Air operation with a slight loss of cell voltage@0.8 A cm−2 of 28 mV after 30 k cycles. The high performance can be ascribed to the high Pt area exposure, the enhanced Pt-Co coupling, and the prevented agglomeration in the mesoporous carbon wall. Overall, this strategy may contribute to the commercialization of fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] Palladium-based nanocatalysts play an important role in catalyzing the cathode oxygen reduction reaction (ORR) for fuel cells working under alkaline conditions, but the performance still needs to be improved to meet the requirements for large-scale applications. Herein, Au@Pd core–shell nanowires have been developed by coating Pd atomic layers on ultrafine gold nanowires and display outstanding electrocatalytic performance towards alkaline ORR. It is found that Pd overlayers with atomic thickness can be coated on 3 nm Au nanowires under CO atmosphere and completely cover the surfaces. The obtained ultrafine Au@Pd nanowires exhibit an electrochemical active area (ECSA) of 68.5 m2/g and a mass activity of 0.91 A/mg (at 0.9 V vs. RHE), which is around 3.1 and 15.2 times higher than that of commercial Pd/C. The activity loss of the ultrafine Au@Pd nanowire after 10,000 cycles of accelerated degradation tests is only ∼20 %, demonstrating its much better stability compared to commercial Pd/C. Further characterizations combined with density functional theory (DFT) calculations demonstrate that the electronic interactions between Pd atomic layers and underlying Au can increase the electronic density of Pd and promote the efficient activation of oxygen, thus leading to the improved ORR performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A plasma-assisted approach is developed to improve the SD and site utilization of Fe N C catalyst. • The plasma-assisted approach can give a 2.81-fold SD improvement and 1.98-fold higher site utilization, simultaneously. • The carbon defects near the Fe-N 4 sites can regulate the electronic structure and promoted the intrinsic activity of Fe-N 4 sites. • The hierarchical pore structure increased the abundance of edge sites and enhance the mass transport performance of Fe N C. Enhancing the density and utilization of FeN 4 sites can serve as a viable approach to enhance the catalytic efficacy of iron nitrogen carbon (Fe N C) catalysts for oxygen reduction reaction (ORR). Herein, we present a plasma-assisted method for enhancing the porosity of nitrogen-doped carbon. Our findings indicate that the ideal ratio of mesopore to micropore area is 0.463. This ratio not only promotes the diffusion of Fe3+ but also creates additional active sites for Fe3+ loading, leading to an increase in the number of available FeN 4 sites in Fe N C electrocatalysts during pyrolysis. The density (76.5 μmol g−1) and utilization (21.08 %) of d -FeNC-30 are significantly higher than those of FeNC without plasma treatment, with a 2.8-fold and 2-fold increase, respectively. Remarkably, it displays outstanding performance, evidenced by a half-wave potential of 0.835 V (vs. RHE) in a 0.1 M HClO 4 solution and a power density of 0.860 W cm−2 in proton exchange membrane fuel cells (PEMFCs). The developed plasma-assisted approach for improving the site density (SD) and utilization of FeN 4 provides a new perspective for high-performance ORR Fe N C catalysts. [ABSTRACT FROM AUTHOR]

Ternary PtZrNi NRs have excellent electrocatalytic activity in cathode and cathode reactions of fuel cells. [Display omitted] Pt-based alloys with precise structure and composition design have been considered to be effective and robust novel electrocatalysts for fuel cells. Whereas, the sluggish kinetics of oxygen reduction reaction (ORR) and low intrinsic activity of Pt limited their real application on a large scale. Herein, a novel ternary PtZrNi nanorods (PtZrNi NRs) was synthesized via a facile wet-chemical method to achieve high electrocatalytic performance for both ORR and alcohol oxidation reaction owing to the synergism of chosen three elements and prominent one-dimensional morphology. Specifically, the PtZrNi NRs show enhanced mass and specific activities of 0.755 A mg Pt -1 and of 0.97 mA/cm2 at 0.9 V RHE towards ORR in acidic media, which are 4.7 and 4.4 times of those of commercial Pt/C, respectively. Additionally, in alkaline media, the PtZrNi NRs also exhibit superior ORR mass and specific activities of 3.216 A mg Pt -1and 4.13 mA/cm2, enhanced by 34.6 and 31.3 times compared with those of commercial Pt/C, respectively. The PtZrNi NRs retain the nanorod shape well without agglomeration after an accelerated durability test (20000 cycles). This work may offer a new perspective for engineering high-performance Pt-based electrocatalysts for commercial fuel cells. [ABSTRACT FROM AUTHOR]

A novel methodology for promoting the topological carbon defects and B/N doping amounts of B/ N -enriched porous Co@BN-PCFs catalysts, which discloses a new direction for further boosting ORR catalytic efficiencies and stabilities of Co N C catalysts in both acids and bases. [Display omitted] • Carboxyl induced abundant mesopores and ultrahigh carbon topological defects in Co@BN-PCNFs. • Ultrahigh B and N doping amounts of 5.87 and 5.91 at.% with 8.70 at.% of B/N based electrocatalytic active centers. • The ORR E onset and E 1/2 values of Co@BN-PCNFs-900 are ∼ 64 and ∼ 63 mV more positive than 20 wt% Pt/C in 0.1 M KOH. • The ORR E onset and E 1/2 values of Co@BN-PCNFs-900 just ∼ 11 and ∼ 7 mV more negative than 20 wt% Pt/C in 0.1 M H 2 SO 4. • The comparatively stable topological edges, BC 3 and partial N C/Co N C induced excellent stability toward ORR. Transition metal-nitrogen-carbon (M N C) type catalysts have been considered a promising alternative to noble metals for oxygen reduction reaction (ORR) electrocatalysis. Nevertheless, poor stabilities of M N C catalysts in acidic solutions limit their commercialization. In this study, we design and synthesize novel three-dimensional (3D) cobalt (Co) nanoparticles encapsulated in ultrahigh content of boron (B) and nitrogen (N) -doped hierarchically porous carbon nanofibers (denoted as Co@BN-PCNFs) by carbonizing the 3D acetic acid/cobalt nitrate/4-hydroxybenzeneboronic acid/polyvinylpyrrolidone precursor networks woven using electrospinning method under a nitrogen atmosphere. The optimal Co@BN-PCNFs-900 catalyst has abundant micro/mesopores and numerous topological defects and exhibits the largest surface area. Under the synergistic effect of oxygen-containing acetic acid molecules and the electrospinning technology, 5.87 at.% of B and 5.91 at.% of N atoms were doped into carbon nanofibers. Specifically, B/N electrocatalytic active centers (including BC 3 , pyridinic-N/Co N C, pyrrolic-N, and graphitic-N) of approximately 8.70 at.% were successfully introduced into the skeletons of Co@BN-PCNFs-900. In 0.1 M KOH, the ORR onset potential (E onset) and half-wave potential (E 1/2) of Co@BN-PCNFs-900 were ∼ 64 and ∼ 63 mV, respectively, more positive than those of 20 wt% Pt/C. Additionally, in 0.5 M H 2 SO 4 , the ORR E onset and E 1/2 values of Co@BN-PCNFs-900 were only ∼ 11 and ∼ 7 mV, respectively, more negative than those of 20 wt% Pt/C. As the 3D hierarchically porous architectures, topological carbon edges, BC 3 , and partial N C/Co N C are relatively stable, the Co@BN-PCNFs-900 exhibits excellent stability toward ORR catalysis in both acidic and basic media. These favorable properties of Co@BN-PCNFs-900 nanofibers make them the best non-noble metal-based carbonaceous electrocatalysts for ORR in acidic electrolytes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mass production of high activity and durability of Pt/C catalysts with microwave pipeline technology. • Retention rate of ORR catalytic activity of Pt 50 /CB acid -1200 catalyst reaches 82% after 30,000 cycles attenuation. • Power density of cell performance can reach 1.4 W-cm−2 and Pt content can reach 0.286 g Pt -kW−1. Traditional synthesis methodologies for fuel cell catalyst production involve long reactions and uncontrollable reaction processes. Synthesis methods for the production of catalysts typically have difficulties to achieve catalysts materials with consistency, high activity, and durability. In this study, a fast, simple, and suitable continuous pipeline microwave method for catalyst mass production was developed, with the carbon carrier being treated at different temperatures simultaneously. The method herein developed resulted in carbon-supported platinum (Pt) catalysts with high activity and high durability. In addition, the half-wave potential of the catalyst exceeded 0.9 V, the electrochemical active surface area reached 85.7 m2-g Pt −1, and the mass specific activity reached 171.1 mA-mg−1. Remarkably, after 30,000 cycles of Pt attenuation tests and 30,000 cycles of carbon carrier attenuation tests, the retention rate of the annealed carbon carrier catalyst reached 80 %. As a membrane electrode, the catalyst generated a single cell maximum power density of 1.4 W-cm−2, and the Pt content reached 0.286 g Pt -kW−1. The work provides an effective and practical method for the mass production of high-performance and high-durability catalysts, which guiding significance for mass production of catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mass production of high activity and durability of Pt/C catalysts with microwave pipeline technology. • Retention rate of ORR catalytic activity of Pt 50 /CB acid -1200 catalyst reaches 82% after 30,000 cycles attenuation. • Power density of cell performance can reach 1.4 W-cm−2 and Pt content can reach 0.286 g Pt -kW−1. Traditional synthesis methodologies for fuel cell catalyst production involve long reactions and uncontrollable reaction processes. Synthesis methods for the production of catalysts typically have difficulties to achieve catalysts materials with consistency, high activity, and durability. In this study, a fast, simple, and suitable continuous pipeline microwave method for catalyst mass production was developed, with the carbon carrier being treated at different temperatures simultaneously. The method herein developed resulted in carbon-supported platinum (Pt) catalysts with high activity and high durability. In addition, the half-wave potential of the catalyst exceeded 0.9 V, the electrochemical active surface area reached 85.7 m2-g Pt −1, and the mass specific activity reached 171.1 mA-mg−1. Remarkably, after 30,000 cycles of Pt attenuation tests and 30,000 cycles of carbon carrier attenuation tests, the retention rate of the annealed carbon carrier catalyst reached 80 %. As a membrane electrode, the catalyst generated a single cell maximum power density of 1.4 W-cm−2, and the Pt content reached 0.286 g Pt -kW−1. The work provides an effective and practical method for the mass production of high-performance and high-durability catalysts, which guiding significance for mass production of catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • We synthesized Au@PtNiAu concave octahedral core-shell nanocatalysts (Au@PtNiAu-COCS). • The mass activity of this catalyst is 11.22 times in ORR and 4.56 times in MOR than commercial Pt/C. • It exhibits a superior power density under fuel cell operation and better performance. • Its half-wave potential displacement after 30 k cycles is only 12 mV. • It retained the 78.8% of MA after 30 k cycles in ORR and lower CO oxidation overpotential in MOR. Despite the remarkable research efforts, the lack of ideal activity and state-of-the-art electrocatalysts remains a substantial challenge for the global application of fuel cell technology. Herein, is reported the synthesis of Au@PtNiAu concave octahedral core-shell nanocatalysts (Au@PtNiAu-COCS) via solvothermal synthesis modification and optimization approach. The special structure generating a large number of step atoms, enhancing the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activity and stability. The superior ORR mass activity of the Au@PtNiAu-COCS is 11.22 times than the exhibited of Pt/C initially by Pt loading, and 5.11 times by Pt + Au loading. After 30 k cycles the mass activity remains 78.8% (8.83 times the initial Pt/C activity) and the half-wave potential only shifts 12 mV. Au@PtNiAu-COCS has superior half-cell activity and gives ideal membrane electrode assemblies. Furthermore, for MOR the Au@PtNiAu-COCS show enhanced anti-toxic (tolerant) ability in CO. This work provides a new strategy to develop core-shell structure nanomaterials for electrocatalysis. [ABSTRACT FROM AUTHOR]

Co and Ni 3 C nanoparticles on nitrogen doped carbon layers supported on N -doped graphene (Co@NC-Ni 3 C/G) is designed and fabricated by a two simple steps procedure for bifunctional electrocatalytic of methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The prepared Co@NC-Ni 3 C/G-350 hybrids possess the excellent methanol oxidation current density of 44.8 mA cm−2 at potential of 1.47 V (vs. RHE), besides outstanding ORR catalytic efficiency in terms of half-wave potential (E 1/2 = 0.830 V vs RHE). [Display omitted] Designing highly efficient, long-lasting, and cost-effective cathodic and anodic functional materials as a bifunctional electrocatalyst is essential for overcoming the bottleneck in fuel cell development. Herein, a novel two-step synthesis strategy is developed to synthesize metal-organic framework (MOF) derived nitrogen-doped carbon (NC) with improved spatial isolation and a higher loading amount of cobalt (Co) and nickel carbide (Ni 3 C) nanocrystal decorated on graphene (denoted as Co@NC-Ni 3 C/G). Benefiting from multiple active sites of high N -doping level, uniform dispersion of Co and Ni 3 C nanocrystals, and a large active area of graphene, the Co@NC-Ni 3 C/G hybrids exhibit excellent methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) efficiency in an alkaline environment. For MOR, the optimized Co@NC-Ni 3 C/G-350 catalyst achieved a current density of 44.8 mA cm−2 at an applied potential of 1.47 V (V vs. RHE), which is significantly higher than Co@NC-Ni 3 C (42.07 mA cm−2) and Co@NC (24.1 mA cm−2) in 0.5 M methanol + 1.0 M KOH solutions. In addition, during the CO retention test, the Co@NC-Ni 3 C/G-350 catalyst exhibits excellent CO tolerance capacity. Excitingly, the as-prepared Co@NC-Ni 3 C/G-350 hybrid exhibits significantly improved ORR catalytic efficiency in terms of positive onset and half-wave potential (E onset = 0.90 V, E 1/2 = 0.830 V vs. RHE), small Tafel slope (34 mV dec−1) and excellent durability (only reduced 0.016 V after 5000 s test). This work provides new insights into MOF-derived functional nanomaterials for anode and cathode co-catalysts for methanol fuel cells. [ABSTRACT FROM AUTHOR]

This work proposes a cost-effective strategy to massively synthesize high-efficiency ORR electrocatalyst. [Display omitted] • A novel type of composite Co/N C was prepared. • A potential strategy was proposed to massively synthesize ORR catalysts. • High ORR activity of Co/N C triggered by Co-N heteroatomic interface. • The high stability of Co/N C in 0.1 M KOH. The development of high-efficiency and low-cost oxygen reduction electrocatalysts have become an urgent need to push fuel cells into practical application. Herein, an effective electrocatalyst Co/N C was successfully constructed, which was derived from abundant peanut shells, obtained by doping with cobalt ions and pyrolyzing in NH 3 atmosphere. Due to the abundant Co-N active sites triggered by Co-N heteroatomic interface, the prepared electrocatalysts present excellent oxygen reduction reaction (ORR) performance with more positive half-wave potential (E 1/2 = 0.83 V), incremental limiting current density (J L = 5.45 mA cm−2), higher durability and stronger resistance to methanol, which is superior to that of Pt/C (E 1/2 = 0.81 V and J L = 5.19 mA cm−2). This work proposes a potential strategy to synthesize efficient ORR electrocatalysts to instead of Pt-based catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • The nanoporous Ti 4 O 7 is synthesized while Pt is atomically dispersed on the Ti 4 O 7 surface by a one-step calcination method for the first time. • Carbon hollow spheres are added to the gel to synthesize nanoporous Ti 4 O 7 with high purity and specific surface area. • The as-prepared Pt/Ti 4 O 7 SAC exhibits a half-wave potential of 0.896 V and a mass activity of 4081.5 A/g Pt at 0.9 V with negligible degradation after 20,000 cycles. • Monatomic Pt electronically couples with the Tin+ to further reinforce electron delocalization. Although single atom catalyst (SAC) can maximize the atomic utilization, platinum (Pt)-based SAC is typically inactive to break the O = O bond in oxygen reduction. Herein, the nanoporous Ti 4 O 7 was synthesized while Pt was atomically dispersed on the Ti 4 O 7 surface by a one-step calcination method. The as-prepared Pt/Ti 4 O 7 SAC exhibits a half-wave potential of 0.896 V and a mass activity of 4081.5 A/g Pt at 0.9 V with negligible degradation after 20,000 cycles. Meanwhile, it exhibits a Pt utilization efficiency of 0.16 g Pt kW−1 in H 2 /O 2 fuel cell and a slight attenuation of the output current density (9.4%) after 120 h. The incorporated monatomic Pt electronically couples with the Tin+ (3 ≤ n < 4) to enhance bilateral electron transfer. The awakened Tin+ active sites synergize with monatomic Pt to moderate the adsorption intensity of O 2 and dissociate the O = O bond, opening up a four-electron pathway on the Pt-based SAC. [ABSTRACT FROM AUTHOR]

Cathodic oxygen reduction reaction is a decisive factor for fuel cell. In this work, for the first time, we demonstrated the synthesis of N -doped carbon hollow spheres derived from conjugated microporous polymers. The resulting sample remained the inherent porosity and N component with hollow spherical morphology, which exhibits excellent ORR performance with higher limiting current density and stability than that of commercial Pt/C catalyst in alkaline solution. [Display omitted] The exploitation non-precious or metal-free electrocatalysts of oxygen reduction reaction (ORR) is of significance for construction of next-generation fuel cells. In this work, hollow-spherical conjugated microporous polymers (CMPs) comprising porphyrin units were synthesized as precursors to prepare N -doping porous carbon spheres (CMP-NP-x) by a direct pyrolysis method. The as-resulted CMP-NP-x exhibited spherical morphology with hollow structure similar to that of CMPs precursors. The BET surface area of CMP-NP-x can be tailored by the pyrolysis temperature varying from 868 m2 g−1 to 1118 m2 g−1. According to XPS analysis, the pyrrolic N content in the sample decreased but the graphitic N and pyridinic N increased with increasing of the pyrolysis temperature from 800 °C to 1000 °C. Taking advantages of porous structure with large accessible surface areas and N species active sites, the resulting CMP-NP-x showed superior ORR activity and methanol tolerance to commercial Pt/C catalyst. In particular, CMP-NP-900 possesses the highest onset potential (0.930 V), half-wave potential (0.857 V) and limiting current density of 4.45 mA cm−2, compared with Pt/C catalyst and other samples, making it a promising metal-free catalyst superior to commercial Pt/C catalyst in alkalic condition. [ABSTRACT FROM AUTHOR]

The cathode's oxygen reduction reaction (ORR) plays a crucial role in a variety of fuel cells. Developing affordable and efficient non-precious electrocatalysts for the ORR poses a major hurdle in the realm of electrochemical energy technologies. This work presents a transition metal-based catalyst, Fe-ONC, in which Fe is loaded in an oxygen-enriched nitrogen-doped carbon (NC) material. Oxygen enrichment of the catalyst was achieved by a pre-oxidation strategy. The XPS analysis reveals that Fe-ONC exhibits a higher abundance of oxidized species. The Fe of Fe-ONC exists in the form of Fe 3 O 4 particles and Fe-N x , respectively, which are uniformly distributed in the NC. The even spread of iron sites and the plentiful presence of oxygen-rich species are key factors in the superior ORR efficiency of Fe-ONC. Fe-ONC's half-wave potential (E 1/2) in an alkaline environment (0.1 M KOH) stands at 0.891 V, markedly surpassing the standard commercial Pt/C value (0.840 V). Additionally, Fe-ONC demonstrated enhanced longevity and resistance to ethanol in comparison to commercially available Pt/C. Fe-ONC's outstanding efficacy highlights its potential as an alternative to precious metal catalysts. The document outlines a plan for creating ORR catalytic materials that are sustainable, economical, and efficient. We propose to oxygenate the initial catalyst Fe-NC by pre-oxidation treatment, which increases the content of oxides and iron species with high oxidation valence states in the catalyst Fe-ONC, thus improving the catalyst activity and ORR performance. [Display omitted] • Fe-ONC is oxygenated by pre-oxidation treatment. • Oxygen-enriched Fe-N x sites boost ORR efficiency significantly. • Fe-ONC achieves a notable E 1/2 of 0.891 V in alkaline conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen reduction reaction (ORR) has been extensively used in fuel cells and rechargeable metal-air batteries. • This review details the latest developments in ORR electrocatalyst development. • These electrocatalysts specifically include platinum group metals (PGM), transition metals and carbon-based catalysts. • The preparation and ORR performance of various electrocatalysts are discussed in detail. • Speculation and discussion on the development prospects and challenges of ORR electrocatalysts. Oxygen reduction reaction (ORR) has gradually been in the limelight in recent years because of its great application potential for fuel cells and rechargeable metal-air batteries. Therefore, significant issues are increasingly focused on developing effective and economical ORR electrocatalysts. This review begins with the reaction mechanisms and theoretical calculations of ORR in acidic and alkaline media. The latest reports and challenges in ORR electrocatalysis are traced. Most importantly, the latest advances in the development of ORR electrocatalysts are presented in detail, including platinum group metal (PGM), transition metal, and carbon-based electrocatalysts with various nanostructures. Furthermore, the development prospects and challenges of ORR electrocatalysts are speculated and discussed. These insights would help to formulate the design guidelines for highly-active ORR electrocatalysts and affect future research to obtain new knowledge for ORR mechanisms. [ABSTRACT FROM AUTHOR]

[Display omitted] Committed to improving the utilization efficiency of Pt atoms and accurately controlling the morphology and composition of nanocatalysts to boost the Pt-based catalyst performance has become the focus of research. Herein, the PtRhNi truncated triangular nanoflakes (TA-NFs) catalyst with a unique PtRh-rich surface structure was successfully prepared by an effective one-pot synthetic method based on the galvanic replace reaction. The freestanding 2D nanostructure of PtRhNi TA-NFs, intrinsically possessing much high specific surface area and surface atomic, and the PtRh-rich characteristics of the surface is undoubtedly the most feasible model to simultaneously achieve high atom utilization. Benefiting from this novel structure, the as-obtained PtRhNi TA-NFs nanocatalyst exhibits excellent performance for ORR and MOR, delivering a mass activity of 0.92 A mg pt -1 for ORR, which is 2.03, 1.64, and 6.9-fold higher than that of PtRhNi nanoparticls (NPs), PtNi truncated triangle nanoflakes (TA-NFs) and commercial Pt/C, respectively. In addition, after 20 k cycles ADT test, PtRhNi TA-NFs show only 10 mV negative shift of half-wave potential and retain 70% of initial value of mass activity. Furthermore, a mass activity is 1.28 A mg pt −1 is achieved after applying this unique nanocatalyst for MOR, which is 1.28,1.5, and 2.6 times higher than that of PtRhNi NPs, PtNi TA-NFs and Pt/C, respectively. Impressively, the PtRhNi TA-NFs nanocatalyst shows an ultrahigh stability even after 2 k cycles ADT measurement in acid solution, and the mass activity is only drop 2% of initial value. This work provides a new strategy to synthesis high-performance of bifunction Pt-based electrocatalyst for ORR and MOR fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] Designing efficient electrocatalysts for the oxygen reduction reaction (ORR) is crucial to enhance the energy efficiencies of metal-air batteries and fuel cells. Palladium (Pd) catalysts show great potential due to their high intrinsic activity towards ORR but suffer from inferior durability. Here, we aim to employ tin oxide (SnO 2) supports to tailor the lattice strain and electron density of Pd catalysts to enhance their ORR performance. By using electrospinning and solvothermal techniques, a hierarchical Pd/SnO 2 hybrid catalyst was facilely synthesized with Pd nanoparticles anchored onto both the inside and outside walls of nanotube-like SnO 2 supports. Owing to the SnO 2 supports and the endowing metal-support interactions, tensile-strain and electron-rich features were both verified for the Pd nanoparticles in the Pd/SnO 2 catalyst. In comparison, no such features were found for the Pd nanoparticles in the Pd/C catalyst. As a consequence, the Pd/SnO 2 hybrid catalyst exhibits 2.5-times higher mass activity than the Pd/C catalyst and greatly improved durability with a current decay of 4% loss over 50 h compared with that (18%) of the Pd/C catalyst. [ABSTRACT FROM AUTHOR]

Fe N C catalyst containing abundant atomic Fe-N x sites is synthesized using a MgCl 2 -assisted synthesis approach. The catalyst delivered an excellent oxygen reduction activity in alkaline and acidic electrolytes with outstanding stability. [Display omitted] • Highly active Fe N C catalyst is synthesized by a simplified salt-assisted approach. • Only a single heat-treatment step is employed to produce a highly active catalyst. • The synthesized Fe N C catalyst consists of atomic Fe-N x sites exclusively. • Optimized catalyst delivers excellent ORR activity in acidic and alkaline media. Nitrogen-doped porous carbons containing atomically dispersed iron are prime candidates for substituting platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. These carbon catalysts are classically synthesized via complicated routes involving multiple heat-treatment steps to form the desired Fe-N x sites. We herein developed a highly active Fe N C catalyst comprising of exclusive Fe-N x sites by a simplified solid-state synthesis protocol involving only a single heat-treatment. Imidazole is pyrolyzed in the presence of an inorganic salt-melt resulting in highly porous carbon sheets decorated with abundant Fe-N x centers, which yielded a high density of electrochemically accessible active sites (1.36 × 1019 sites g−1) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E 1/2) of 0.905 V RHE in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E 1/2 of 0.760 V RHE is achieved at a low loading level (0.29 mg cm−2). In PEMFC tests, a current density of 2.3 mA cm−2 is achieved at 0.90 V iR-free under H 2 –O 2 conditions, reflecting high kinetic activity of the optimized catalyst. [ABSTRACT FROM AUTHOR]

Transition metal- and N-codoped carbon nanotubes (CNTs) have superior catalytic activity because the curling surface enhances the bonding ability of atoms within CNTs to other species. However, it is a great challenge to prepare CNTs with transition metal- and N-doped at high level during the growth of CNTs. Here, (Fe,N-codoped CNT)/(Fe-based nanoparticle) (Fe,N-CNT/FeNP) hybrid nanostructures are for the first time prepared through the carbonization of Fe-doped g-C 3 N 4. The doping of Fe and N is simultaneously realized during the formation of CNTs. Meanwhile, the abundant and homogeneous Fe and N in Fe-doped g-C 3 N 4 ensure high-level and uniform doping of Fe and N in CNTs. The Fe,N-CNT/FeNP hybrid nanostructures have several types of active components, including homogeneously distributed coordinating Fe moieties (FeC x N y or FeN x) and CFe 15.1 nanoparticles embedded in Fe,N-CNTs, towards oxygen reduction reaction (ORR). A superior ORR electrocatalytic performance is therefore obtained on the Fe,N-CNT/FeNP nanohybrids. Our preparation method opens an avenue to preparation of CNTs with transition metal- and N-doping at high-level, and the superior performance of Fe,N-CNT/FeNP nanostructures for ORR will be very helpful to the development of fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

• FeNC is a promising cathode catalyst for phosphoric acid fuel cells. • ORR activity of FeNC is projected to be comparable to Pt/C at higher temperatures. • Unlike Pt/C, FeNC is unexpectedly resistant to poisoning by phosphate anions. • A "size-related hindrance effect" is observed during phosphate exposure on FeNC. • Phosphate poisoning of FeNC depends strongly on the nature of carbon support. The greatest challenges facing the large – scale commercialization of the intermediate temperature phosphoric acid fuel cell (PAFC) technology are: (i) the high cost of Pt catalyst that is required to overcome the slow kinetics of oxygen reduction reaction (ORR) on the PAFC cathode, and (ii) deactivation of the Pt catalyst by exposure to the phosphoric acid electrolyte. Inexpensive carbon-based materials, particularly iron-nitrogen-coordinated carbon supported catalysts (FeNC), are promising cathodes for PAFCs. The higher ORR activation energy and phosphate poisoning resistance of FeNC present a clear advantage over the Pt-based commercial catalysts that are easily susceptible to deactivation after exposure to phosphate anions. While the immunity of FeNC catalysts to phosphate anion poisoning has been reported previously, this work explores the counter-intuitive and conditional nature of this poisoning resistance based on the properties of the carbon support used in the preparation of the FeNC catalyst. A combination of electrochemical measurements with characterization experiments performed using X-ray photoelectron spectroscopy, infrared spectroscopy and in-situ X-ray absorption spectroscopy is used to explore the phenomenon of phosphate poisoning on FeNC catalysts synthesized from two different carbon supports. Results from these studies reveal a "size-related hindrance effect" wherein the ORR active Fe centers in FeNC remain inaccessible to larger anions such as phosphate when the Fe sites are present deeper inside the pores of a carbon support with high porosity. However, FeNC catalyst is poisoned by phosphate anions when synthesized using a carbon support with low porosity. This work helps gain insights into the nature of active sites in FeNC catalysts that will be useful in designing precious-metal free ORR catalysts for intermediate temperature fuel cell technologies. [ABSTRACT FROM AUTHOR]

• Ternary Ni/Co/N co-doped porous carbon film (Ni-Co-N@CF) is fabricated by a simple controllable and scalable strategy. • The Ni-Co-N@CF catalyst exhibits a large electrochemically active surface area and maximum diffusion limited current density. • The catalyst demonstrates a superior anti-poisoning capacity and long-term stability. • The excellent ORR activities are attributed to the synergetic interactions of ternary doping of Ni/Co/N in the film skeleton. • The ternary Ni/Co/N in the film can enhance electron conductivity and provide more Co-N active sites. Rational design of a stable, highly active non-precious metal-based electrocatalysts for oxygen reduction reaction (ORR) is vitally important for industrial application of fuel cells technology. As a potential alternative of Pt/C catalyst, two-dimensional (2D) porous carbon materials are widely investigated due to the highly accessible surface area and active sites, wherein carbon films doped with a plurality of metals and non-metal elements are rarely reported due to an uncontrollable synthesis process. Here, a bi-metallic (NiCo alloy nanoparticles) and nonmetallic (N) co-doped porous carbon film (Ni-Co-N@CF) is fabricated by a simple controllable and scalable strategy comprising the synthesis of NiCo alloy nanoparticles, modification of organic molecules, and high-temperature carbonization process. The optimized Ni-Co-N@CF catalyst shows an excellent ORR electrocatalytic activity with a larger electrochemically active surface area (2.31 m2 g−1), a higher half-wave potential (0.86 V) and a lower diffusion limited current density (−4.43 mA cm−2) than all the prepared control catalysts. Moreover, the designated catalyst also exhibits high durability and superior methanol tolerance in alkaline media, significantly better than the commercial Pt/C (20 wt%). The superior ORR performance is attributed to the synergetic interactions of ternary doping of Ni/Co/N in the 2D film skeleton, which not only greatly enhances conductivity but also provides more Co-N active sites. [ABSTRACT FROM AUTHOR]

PtCu hollow octahedral nanoparticles with wall thickness of ~2.1 nm have been successfully achieved to be as efficient bifunctional electrocatalysts toward oxygen reduction reaction and methanol oxidation reaction. • PtCu hollow octahedrons (HOs) with wall thickness of ~2.1 nm have been achieved. • The MA of PtCu/C HOs toward ORR boosts to 2.60 A mg Pt -1. • After 10,000 voltage cycles, the MA of Pt 44.1 Cu 55.9 /C HONs remains 1.63 A mg Pt -1. • The optimum MA of methanol electrooxidation on PtCu/C HONs is 1.94 A mg Pt -1. In response to the scarcity of precious metals, the development of precious-metal-saving electrocatalysts exhibiting high mass activity (MA) and durability towards oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) for both proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) has aroused increasing attention. In this study, octahedral Cu-rich PtCu alloy is seeded to fabricate near-surface composition-tunable PtCu hollow octahedral nanoparticles (HONs) with the wall thickness of ~2.1 nm. Due to both the alloying effects of near surface and the special hollow octahedral structure, the PtCu/C HONs exhibit significantly higher MA and durability than commercial Pt/C towards both ORR in alkaline medium and MOR in sulfuric acid electrolyte. The ORR MA of Pt 44.1 Cu 55.9 /C HONs are up to 2.60 A mg Pt −1 that is 18.5-fold enhancement compared with that of Pt/C. Besides, after 10,000 voltage cycles, the MA of Pt 44.1 Cu 55.9 /C HONs remains to be 1.61 A mg Pt −1, a datum 53.7 times that of Pt/C. The in situ CO polarization curves exhibit that the Pt 44.1 Cu 55.9 HONs/C own high resistance to CO poisoning. For MOR in sulfuric acid electrolyte, the optimum SA/MA of PtCu/C HONs is 5.33 mA cm−2/1.94 A mg Pt −1, which is 10.25/5.87 times higher than that of Pt/C. This study provides effective bifunctional cathode and anode electrocatalysts for both PEMFCs and DMFCs. [ABSTRACT FROM AUTHOR]

The development of cost-effective and highly-efficient electro-catalysts is essential for the advancement of proton exchange membrane fuel cells (PEMFC). We present a novel nitrogen-sulphur co-doped carbon nanotubes-few layer graphene1D-2D hybrid support formed by partially exfoliating multiwall carbon nanotubes (PECNT), to improve interface bonding to catalyst nanoparticles. Detailed Raman spectroscopy and STEM-EDS analyses demonstrate that active sites on the co-doped hybrid support ensure both uniform distribution and improved bonding of the catalyst nanoparticles to the support. Electrochemical studies show that Pt nanoparticles decorated on nitrogen-sulphur co-doped PECNT (Pt/NS-PECNT) have higher electrochemical active surface area and mass activity accompanied by low H 2 O 2 formation and improved positive half-wave potential, as compared to those decorated on co-doped rGO-incorporated PECNT hybrid structure (Pt/NS-(rGO-PECNT)). Fuel cell measurements demonstrate a higher power density for our novel (Pt/NS-PECNT) electro-catalyst when compared to both Pt/NS-(rGO + PECNT), and commercial Pt/C electro-catalyst. We demonstrate in this work that the interconnectivity between Pt-nanoparticles and the dopant or defect sites on the support play a crucial role in enhancing the ORR activity, fuel cell performance, and durability of the catalyst. [ABSTRACT FROM AUTHOR]

Developing highly active and durable catalyst is of pivotal importance in fuel cells, owing to excessive consumption of fossil fuels. Herein, porous dendritic PtRuPd nanospheres (PtRuPd NSs) were synthesized by a facile hexadecylpyridinium chloride (HDPC)-mediated one-pot aqueous method with ascorbic acid (AA) as the reducing agent. The as-obtained PtRuPd NSs displayed high-efficient catalytic activity and durability for ethylene glycol oxidation reaction (EGOR) and oxygen reduction reaction (ORR). It exhibited enlarged mass activity (MA, 1.368 A mg−1) compared to commercial Pt/C (1.100 A mg−1) for EGOR. Besides, the onset potential (E onset , 0.930 V) and half-wave potential (E 1/2 , 0.852 V) of PtRuPd NSs were more positive relative to homemade PtPd NSs (0.905 and 0.840 V), PdRu NSs (0.895 and 0.839 V), and commercial Pt/C (0.910 and 0.822 V) toward ORR. This work provides some valuable guidelines for producing novel trimetallic nanocatalysts in fuel cells. [ABSTRACT FROM AUTHOR]

Co nanoparticles supported on three-dimensionally (3D) N-doped holey graphene aerogels (Co/N-GA-h) hybrids were successfully synthesized by simple high-temperature pyrolysis method. As a non-noble metal electrocatalyst, the Co/N-GA-h hybrids displayed the excellent activity and durability for the ORR in alkaline media. The reactive and stable catalysts for the oxygen reduction reaction are highly desirable for low temperature fuel cells. The commercial oxygen reduction reaction electrocatalysts generally reply on noble metal based nanomaterials, which suffer from inherent cost and selectivity issues. At present, it still remains challenge for designing efficient non-noble metal-based oxygen reduction reaction electrocatalysts. Herein, we successfully synthesize Co nanoparticles supported on three-dimensionally N-doped holey graphene aerogels hybrids by the high-temperature calcination of the graphene aerogels-polyallylamine-CoII hybrids. The component optimized hybrids show the excellent electrocatalytic activity for oxygen reduction reaction in alkaline media, which is comparable to commercial Pt/C electrocatalyst. Meanwhile, the hybrids also show eminent tolerance for CO and methanol, attributing to their excellent oxygen reduction reaction selectivity. The three-dimensionally interconnected structure of graphene aerogels, N-doping, uniform dispersion and high crystallinity of Co nanoparticles, and holey structure of graphene contribute to the striking oxygen reduction reaction activity of hybrids. [ABSTRACT FROM AUTHOR]

Non-precious metal doped carbonaceous materials are currently the most promising alternative towards oxygen reduction reaction (ORR) electrocatalysts in terms of cost, accessibility, efficiency and durability. In this work, a simple one-step pyrolysis process was used for the synthesis of copper doped graphitic carbon nitride (Cu-g-C 3 N 4) as electrocatalyst. The as-synthesized Cu-g-C 3 N 4 material is displaying excellent electrocatalytic response towards ORR in alkaline medium. In comparison to commercial Pt/C catalyst, Cu-g-C 3 N 4 exhibits high methanol tolerance, long term stability, without compromising (4e−) electron transfer pathway process and attaining less than 4% H 2 O 2 formation. The enhanced electrocatalytic behaviour may be ascribed to the formation of active sites strongly coupled into the nitrogen-rich carbon matrix. Such a low-cost, extremely durable and stable electrocatalyst can therefore be regarded as an efficient cathodic material, which can be utilized for several renewable energy conversion technologies such as fuel cell, biofuel cell and metal-air battery. [ABSTRACT FROM AUTHOR]

For the development of metal-air batteries and fuel cells, highly efficient and inexpensive electrocatalysts are one of the main issues for scalable applications of these advanced energy devices. Herein, based on the in situ conversion of FeS to γ-FeOOH with a two-dimensional (2D) layered structure, a special nanohybrid, N, S co-doped porous carbon nanosheets loaded with γ-FeOOH, is fabricated by carbonization of Fe3+-coordinated polydopamine, which uniformly coats the surface of bacterial cellulose. The nanocomposites exhibit high activity towards the cathodic oxygen reduction reaction (ORR), characterized by a more positive half-wave potential (10 mV) than the commercial Pt/C (20 wt%) electrocatalyst in alkaline medium. Additionally, the nanohybrid has excellent stability and a high methanol tolerance towards the ORR. Further experiments and density functional theory (DFT) calculations demonstrate that the doped N, S in the carbon matrix and the (0 1 0) plane of γ-FeOOH are the ORR active sites. A zinc-air battery equipped with this nanohybrid presents better a power density (92 mW cm−2) and specific capacity (740 mA h g−1) than the Pt/C electrocatalyst, demonstrating its promising potential for application in energy conversion devices. [ABSTRACT FROM AUTHOR]

• Catalytic partial oxidation (CPOX) processing experimentally investigated to use Methane in SOFC. • Reynolds number effects on electrochemical performance of the SOFCs. • Carbon deposition prevented by utilizing oxygen with methane in favorable operating conditions. • Investigation of the carbon deposition through the NiO-YSZ anode by EDAX and SEM. The development of high-performance non-precious metal electrocatalysts is of great importance for construction of next generation fuel cells. Herein, we report for the first time the creation of new metal-free porous carbon framework catalysts derived from N -rich hypercrosslinked polymers (HCPs) using pyrrole as building blocks for oxygen reduction reaction (ORR) (denoted as PCF-HCPs). The PCF-HCPs obtained at the pyrolysis temperature of 900 °C (PCF-HCP-900), displayed outstanding catalytic activity towards the ORR compared with other PCF-HCPs pyrolysis temperature. Due to PCF-HCP-900 with large specific surface, excellent porosity and, importantly, exposed active sites caused by N doping with high density, the catalysts exhibited outstanding ORR activity in alkaline medium, i.e., the PCF-HCP-900 yielded a half-wave potential of 0.84 V, which was 10 mV higher than that of the state of-the-art Pt/C catalyst (0.83 V), and onset potential of 0.95 V (vs. RHE), a high diffusion limiting current density of 4.8 mA cm−2, better methanol tolerance and long-term stability (2 mV negative shift after 3000 potential cycles) than commercial Pt/C. Furthermore, PCF-HCP-900 shows a favorable 4-electron transfer process (n ≈ 3.96) and lower H 2 O 2 yield. Based on these merits, the PCF-HCP-900 may open a new possibility for design of ORR metal-free catalyst of fuel-cell technologies. [ABSTRACT FROM AUTHOR]

Green and efficient non-precious metal electrocatalysts for oxygen reduction reaction (ORR) are prepared to meet the increasing demand for clean, secure and sustainable energy. Herein, we report a novel and environmentally friendly strategy for synthesis of graphene-wrapped iron carbide (Fe 7 C 3) nanoparticles supported on hierarchical fibrous N-doped graphene with open-mesoporous structures (Fe 7 C 3 /NG) by simply annealing the mixture of melamine, iron (II) phthalocyanine (FePc) and Fe 2 O 3. The effects of the pyrolysis temperature and the molar ratio of FePc to melamine were critically examined in the controls. Remarkably, the Fe 7 C 3 /NG obtained at 800 °C (i.e. Fe 7 C 3 /NG-800) manifested the forward shifts in the onset potential (0.98 V) and half-wave potential (0.85 V) with respective to commercial Pt/C (50 wt %) in 0.1 M KOH, coupled with the great enhancement in the durability (still remained 92.11% of its initial current density even after 40,000 s) and strong methanol tolerance. This research presents a promising strategy for developing Pt-free non-precious efficient ORR electrocatalysts in fuel cells. [ABSTRACT FROM AUTHOR]

The schematic diagram representation favourable active site of oxygen reduction reaction on BCN composites catalyst. • The BCN catalyst contains B B bonding explored as an active site for ORR. • BCN composite with carbonaceous materials enhances for ORR activity. • An ORR activity with E onset of 1.01 V and current density of 5.0 mA/cm2 is seen. • A better methanol tolerance and improved durability has been observed. Unmanageable of oxygen electrochemistry on cathode side of fuel cells creates a major hindrance to designing a cell device. Effectively, Platinum alone cannot afford the oxygen reduction reaction (ORR) due to several worries such as unaffordable cost, stability, scarcity and intermediate tolerance etc. that would hurdle the development of fuel cell technology. In order to demonstrate similar efforts, we discuss a synthesis of boron carbon nitride (BCN) nanosheets and its composite by thermal and solvothermal method respectively. The BCN nanosheets also show the formation of a homonuclear B B bond, which are important for enhancing oxygen affinity. Since the chemistry of B B bond involves higher bond energy, more reactivity or unusual gas adsorption behavior, thus making such sites promising towards stronger electrophilic interactions such as oxygen adsorption followed by its reduction. As synthesized BCN exhibits an interesting onset potential of ∼0.94 V in electroreduction of oxygen. More importantly, upon composite formation with carbon black, BCN shows further enhancement in the ORR kinetics with an onset potential of 1.01 V and a current density of 5 mA/cm2, which is very much comparable with Pt/C. An interesting phenomenon of activating O 2 reduction using BCN has been systematically studied to unravel noble metal-free electrocatalysis. [ABSTRACT FROM AUTHOR]

By using methyl orange template, polypyrrole nanotubes were obtained by the oxidative polymerization of pyrrole. The nanotubes were carbonized in inert atmosphere to nitrogen-enriched carbon nanotubes. These were subsequently coated with 20 wt% of polypyrrole prepared in the absence or the presence of anionic dyes (methyl orange or Acid Blue 25). The morphology of all the samples was examined by the electron microscopies, FTIR and Raman spectroscopies. Moreover, X-ray photoelectron spectroscopy and elemental analysis were used to prove the chemical structure and the successful coating process. Electron paramagnetic resonance analysis was used to calculate the spin concentrations. Significant impact of coating method is evidenced with neat polypyrrole coating providing a two-fold capacitance increase compared to uncoated nanotubes, while coating in the presence of Acid Blue 25 decreasing it slightly. With respect to oxygen reduction reaction, coatings irreversibly transformed in the first few cycles in the presence of the products of O 2 reduction, presumably hydrogen peroxide, altering the oxygen reduction mechanism. This transformation allows the tailoring of the polymeric shell, over ORR active carbonaceous core, and tuning of the catalyst selectivity and optimization of materials performance for a given application – from alkaline fuel cells to hydrogen peroxide generation. [ABSTRACT FROM AUTHOR]

The ORR mechanism of PMSEPE/MIL-101(Fe)-800. In this work, a novel catalyst of oxygen reduction reaction (ORR) was designed and fabricated by electrospinning, photo-curing and carbonization, based on polymer poly(dimethylsilylene ethynylenephenyleneethynylene) (PMSEPE) and metal organic frameworks (MOFs)—Materiaux de l'Institute Lavosier-101(Fe) (MIL-101(Fe)). The optimal catalyst PMSEPE/MIL-101(Fe)-800, which was carbonized at 800 °C, presented a bamboo-like nanofiber structure with a high degree of graphitization, a high specific surface area (302.3 m2/g) and a high yield (64.17%). Fe 3 C particles were found to be encapsulated into the Fe-Si-N co-doped carbon nanofibers. In the electrochemical tests, PMSEPE/MIL-101(Fe)-800 showed an onset potential of 0.935 V (vs. RHE) and a diffusion limit current of 6.01 mA/cm2 (vs. RHE) in 0.1 M KOH aqueous solution, of which performances are competitive to commercial 20 wt% Pt/C. PMSEPE/MIL-101(Fe)-800 also exhibited a higher methanol tolerance and duration stability. Further Zn-air battery test used by PMSEPE/MIL-101(Fe)-800 suggested its potential for the application of fuel cell. [ABSTRACT FROM AUTHOR]

• A new precursor of Fe-dual pyridine coordination complexes was designed to synthesize Fe-N-C catalyst with hybrid structure of Fe-Nx moieties and exposed Fe carbides/nitrides nanodots. • This characteristic of hybrid active sites contributes the catalyst's excellent electrochemical performance and durability for ORR. • The new dual-pyridine based polymer could be extended to coordinate with various divalent metal ions for exploring non-precious metal ORR catalysts. Iron-nitrogen-carbon (Fe-N-C) materials as the most promising non-precious metal catalysts for oxygen reduction reaction (ORR) to replace Pt-based catalysts are in high demand for large scale application of fuel cells. However, their activity and durability are still critical issues. Development of Fe/N/C-containing precursors is a straightforward strategy for obtaining advanced Fe-N-C ORR catalysts to address these issues. Herein, we report an advanced Fe-N-C catalyst with a hybrid structure of single Fe atom sites (Fe-N x moieties) and exposed Fe carbides/nitrides nanodots with diameters <2 nm embedded onto highly graphitic N-doped carbon matrix. The catalyst is synthesized by pyrolysis of a new kind of Fe-dual pyridine coordinated complex as the precursor. This facile chemical route results in a non-conventional Fe-N-C catalyst with encapsulated Fe-metallic phase nanoparticles or Fe-Nx moieties. The catalyst exhibits excellent ORR activity and remarkable durability in both acidic and alkaline media. Its onset and half-wave potentials are 1.08 V and 0.88 V vs. (RHE) in 0.1 M KOH, respectively, and 0.95 V and 0.81 V vs. RHE, respectively, in 0.5 M H 2 SO 4. Furthermore, a single proton exchange membrane (PEM) fuel cell fabricated by our catalyst generates the output power of 0.65 W cm−2, which indicates great potential of our hybrid structured Fe-N-C catalyst for the practical application in fuel cells. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract High activity and good durability of electrocatalysts are of significance in practical applications of fuel cells. Among them, multi-component metallic hollow nanocages/nanoframes show great potential as advanced catalysts because of their highly open structures, large surface area and good stability. Herein, we report a general uric acid-mediated solvothermal method for shape-controlled synthesis of rhombic-like Pt 35 Cu 65 hollow nanocages (HNCs) with uric acid as co-reductant and co-structure-directing agent. Uric acid and cetyltrimethylammonium chloride (CTAC) played important roles in the hollow cages. The specific architectures showed remarkably enhanced catalytic properties towards glycerol oxidation reaction (GOR), ethylene glycol oxidation reaction (EGOR) and oxygen reduction reaction (ORR) with the enhanced specific activity, outperforming commercial Pt/C (20 wt%). This work provides a new avenue for rational design of novel bimetallic nanocatalysts with enhanced characters in energy storage and conversion. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract How to reduce the usage of precious metals in electrocatalysts is a big challenge for the development of fuel cells. Metal nanoclusters (NCs) are highly desirable as active catalysts, but palladium nanoclusters (Pd NCs) have been less well developed than other metal clusters, such as gold, silver and copper, owing partly to the difficulties in size-controlled synthesis. Here, based on N, N-dimethylformamide (DMF)-mediation and ligand-exchange reaction, atomically precise Pd 5 (C 12 H 25 S) 13 nanoclusters are successfully synthesized. By loading the as-prepared Pd 5 nanoclusters on multiwalled carbon nanotubes (MWCNTs) and the following pyrolysis to remove the thiolate ligands, the surface-cleaned Pd 5 clusters (Pd 5 NCs/MWCNTs) can serve as efficient electrocatalysts for the oxygen reduction reaction (ORR) and the ethanol oxidation reaction (EOR). With ultra-low mass loading of Pd (2%), the Pd 5 NCs showed higher mass and specific activities and better durability than the commercial Pd/C catalyst (5 wt%) for the ORR. At 0.8 V, the mass and specific activities of Pd 5 NCs/MWCNTs are 5.70 and 4.53 times higher than the commercial Pd/C catalyst, respectively. As for the EOR, the Pd 5 NCs/MWCNTs exhibited lower onset potential (0.39 V) and peak potential (0.81 V) than the commercial Pd/C catalyst (0.44 and 0.89 V). Electrochemical impedance spectroscopy (EIS) measurements indicated that for the EOR, the Pd 5 nanoclusters have a much smaller charge transfer resistance (R ct) than the commercial Pd/C. The high-performance electrocatalytic properties of Pd 5 NCs for the ORR and EOR could be ascribed to the relatively high surface area-to-volume ratio and high density of exposed surface atoms of the Pd 5 nanoclusters. [ABSTRACT FROM AUTHOR]

Graphical abstract Functionalized Fe-TCNQ monolayers serve as high-performance bifunctional ORR/OER catalysts. Highlights • A low limiting overpotential of 0.33 V for Fe-TCNQ is predicted toward ORR. • The catalytic performance of Ni-TCNQs monolayer is identified as the highest for OER. • By grafting ligands and applying strain, the adsorption strengths can be optimized. • Fe-TCNQ-Cl is predicted as high-activity bifunctional ORR/OER catalysts. Abstract The identification of catalytically active and stable bifunctional electrocatalysts for the oxygen reduction and evolution reaction (ORR/OER) would revolutionize rechargeable metal-air batteries and regenerative fuel cell technologies. In this study, we use density functional theory (DFT) calculations to systemically investigate 2D transition metal based tetracyanoquinodimethane (TM–TCNQ, TM = Cr-Cu, Ru-Ag, Pt, Ir) monolayers with single TM atoms catalysts (SACs) distributed periodically with high density. We calculate a lower limiting overpotential of η lim = 0.33 V for Fe-TCNQ yielding a higher expected activity than that of Pt metal (0.48 V) for the ORR under acidic conditions. The catalytic performance of Fe-TCNQ for OER is, however, surpassed by Ni-TCNQs (η lim = 0.46 V), which is identified as the highest among the candidates. By applying grafting axial ligands and external strain, the adsorption strength of reaction intermediates on TM reactive sites can be further optimized and enhances the activities of Mn-, Fe- and Ni-TCNQs for the ORR or the OER. Here, Fe-TCNQ-Cl (η lim = 0.27/0.55 V), followed by Fe-TCNQ-CO (η lim = 0.67/0.43 V), are predicted as novel, high-performance bifunctional ORR/OER catalysts with comparable limiting overpotentials to those of the best commercially used electrocatalysts, Pt (ORR: η lim = 0.48 V) and RuO 2 (OER: η lim = 0.42 V). In addition, the recently synthesized Fe-TCNQ possess excellent conductivity with fast electron transfer during the catalytic reactions. These results show 2D TM-TCNQ monolayers are durable, low-cost, and efficient catalysts for the ORR and the OER in metal-air batteries and fuel cells. [ABSTRACT FROM AUTHOR]

Abstract Due to the depletion of fossil fuels and severe environmental pollution problems, the urgent demand for clean and sustainable energy sources is constantly emphasized. In recent decades, platinum (Pt)-based fuel cells have achieved tremendous advances as a green energy source, but there is still a need to further improve energy production efficiency in order to realize practical applications. Conventional Pt electrocatalysts are usually insufficient in catalytic activity and the selectivity of electrochemical reactions due to sluggish kinetics and surface poisoning. In contrast, metal alloy nanocatalysts exhibit exceptional electrocatalytic performance on fuel cells, more than pure Pt catalysts, owing to the synergistic effect by systematic modification of the surface geometry and electronic structure of the catalytically active metal component. This review provides overviews and advances in the applications of metal alloy nanohybrid particles enabling the improvement of electrocatalytic efficiency and discusses the challenges and outlooks in the fields of green energy production based on metal alloy nanocatalysts. Graphical abstract Synergistic effects (d -band shift, surface-lattice strain and surface-defects formation) of metal alloy nanocatalysts for the improvement of electrochemical activity. fx1 Highlights • Metal alloy nanocatalysts exhibit exceptional electrocatalytic activity on fuel cell. • Advances of metal alloy particles enhancing electrocatalytic activity are reviewed. • Outlooks in the field of fuel cell based on metal alloy nanocatalysts are discussed. [ABSTRACT FROM AUTHOR]

Developing efficient bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for producing hydrogen and utilizing hydrogen effectively to promote electrochemical energy storage in proton membrane exchange fuel cells (PEMFCs). Herein, we report Co@Pd core-shell nanoparticles encapsulated in porous carbon derived from zeolitic imidazolate framework 67 (ZIF-67) for both ORR and HER. The controlled pyrolysis of ZIF-67 can lead to the formation of Co nanoparticles encapsulated in nitrogen-doped porous carbon (Co NC), which subsequently underwent galvanic replacement with Na 2 PdCl 4 to form Co@Pd core-shell nanoparticles embedded in nitrogen-doped porous carbon (Co@Pd NC). The Co@Pd NC exhibited outperformance in ORR and HER than commercial Pd/C, as manifested by more positive onset potential and larger diffusion-limited current density in ORR tests, as well as a small overpotential to drive a current density of 10 mA cm −2 , and much lower Tafel slope in HER tests. It also demonstrated more robust long-term stability than commercial Pd/C for both ORR and HER. Multiple techniques inter-confirmed that the Pd loading in the sample was very low. The findings can pave a path for fabricating a core-shell structured nanocomposite with ultralow noble metal usage as a bifunctional catalyst for electrochemical energy storage and conversion with high-efficiency and remarkable longevity. [ABSTRACT FROM AUTHOR]

Pt-based bimetallic nanostructures with low content of Pt were considered as one of the attractive nanocatalysts for their high Pt utilization efficiency, remarkable catalytic characters and cost-effectiveness in facilitating the sluggish cathodic reactions in fuel cells. Herein, three-dimensional Pt 47 Ni 53 nanopolyhedrons (NPHs) with abundant active sites were constructed by a facile one-pot solvothermal strategy, in which cytosine and cetyltrimethylammonium chloride (CTAC) worked as the co-structure directing agents. The Pt 47 Ni 53 NPHs were mainly characterized by a series of techniques, showing the high catalytic activity and stability towards oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in comparison to Pt 13 Ni 87 nanocrystals (NCs), Pt 63 Ni 37 NCs, commercial Pt black and/or Pt/C catalysts. Impressively, the mass activity of Pt 47 Ni 53 NPHs was about 215.80 mA mg Pt −1 for ORR, approximately 4-time increase relative to Pt black (49.60 mA mg Pt −1 ). These results demonstrate the promising applications of the synthesized nanocatalysts in energy storage and transformation. [ABSTRACT FROM AUTHOR]

A carbon supported Pt catalyst with tetradecyltrimethylammonium bromide (TTAB) adsorbed to the nanoparticle surface was operated and tested as a cathode in a polymer electrolyte membrane fuel cell. The fuel cell with the TTAB@Pt/C catalyst showed a higher current relative to the amount of Pt used than the fuel cell with a commercial Pt/C catalyst. Besides, CO stripping evidenced that for the TTAB@Pt/C electrode large parts of the Pt surface were covered by TTAB. Hence, the fuel cell with the TTAB@Pt/C cathode showed a larger current related to the electrochemical active surface area as compared to the fuel cell with the commercial Pt/C cathode. This improvement in the ORR kinetics was further investigated by X-ray photoelectron and in-situ X-ray absorption spectroscopy, and was found to have been caused by two effects: (1) the presence of a metal-ligand charge transfer in the TTAB@Pt/C electrode and (2) the prevention of oxygen containing adsorbates which were being formed in large amounts on the Pt/C electrode. Furthermore, the latter effect also explains the higher stability observed for the TTAB@Pt/C compared to the Pt/C electrode. [ABSTRACT FROM AUTHOR]

The preparation of highly efficient and cheap electrocatalysts toward oxygen reduction reaction is significant for many electrochemical cells. Here we facilely synthesized nitrogen doped carbon nanotube by pyrolyzing melamine formaldehyde resin and Fe loading on MgO. There were mainly three morphologies observed, slender bamboo-like CNT, thick bamboo-like CNT, surface smooth, hollow CNT. The content of Fe loading on MgO had little influence on morphologies of CNT, however, when no MgO as support, only carbon ribbon obtained. The MgO as support was also significant for the formation of CNT. The samples with CNT formed represented better catalytic activity than control samples with no-CNT obtained, the morphology of CNT was beneficial for catalytic process. The sample C 1 -CNT with lowest content of Fe on support represented best catalytic activity which was competitive with 20% Pt/C in half-wave potential. The C 1 -CNT also showed outstanding stability and improved selectivity towards ORR, making it a promising alternative to Pt in application of fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

Non-precious Fe/N/S-composited hierarchically porous carbon materials (Fe(x)/N/S-PAD, PAD: poly(acrylamide-co-diallyldimethyl ammonium chlor), x : the weight ratio of FeSO 4 7H 2 O/PAD) are synthesized using a facile silica colloid template approach with FeSO 4 7H 2 O as Fe and S sources, and PAD as N source, respectively. A simultaneous creation of porous structures and surface functionalities (Fe, N and S) of such catalysts is realized just by simply tuning the weight ratio of FeSO 4 7H 2 O and PAD in the synthetic precursors. As a result, a series of catalyst samples with high oxygen reduction reaction (ORR) activity/stability are obtained, demonstrating the promotion role of FeSO 4 /PAD ratio in synthesizing high-performing catalysts. Particularly, a catalyst (Fe(1.5)/N/S-PAD) with a trace Fe content down to 1.0 wt.% is tested to be superior to a commercial Pt/C catalyst in alkaline media and exhibits impressive ORR performance in acidic media. Combined with characterization results such as TEM, Raman spectra, BET and XPS analysis, it is found that the well-defined micro- and meso-porous structure play the key role in enhancing catalytic ORR performance rather than the final total N contents in the carbon. Regarding the stability of such a catalyst, test using cyclic voltammetry for 5000 cycles in O 2 -saturated solution shows a negligible degradation rate when compared with Pt/C one, suggesting that this catalyst could be used for catalyzing the high-performing cathode ORR in proton-exchange membrane fuel cells, alkaline fuel cells and metal–air batteries. [ABSTRACT FROM AUTHOR]

Fabrication of low-cost and efficient electrocatalyst for oxygen reduction reaction (ORR) is highly desirable. Herein, Zinc ferrite/reduced graphene oxide (ZnFe 2 O 4 /rGO) is prepared by a quite simple and environmentally benign approach and applied as a high performance ORR electrocatalyst for the first time. The surface morphology and chemical composition of ZnFe 2 O 4 /rGO are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. Cyclic voltammetry, linear sweep voltammetry and chronoamperometry are used to evaluate the electrochemical activities and stabilities of ZnFe 2 O 4 /rGO catalysts in alkaline media. Among ZnFe 2 O 4 /rGO with different mass ratios, the catalyst with 69.8 wt% ZnFe 2 O 4 (called ZnFe 2 O 4 /rGO (3)) has the best catalytic activities and it shows much superior methanol tolerance and better durability than the commercial Pt/C catalyst. Due to the synergistic effect, the ZnFe 2 O 4 /rGO (3) nanohybrid exhibits high ORR catalytic performance and durability, which follows a desirable four electron transfer mechanism in alkaline media. Therefore, it may be a highly competitive catalyst for fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

Mass-selected platinum–gadolinium alloy nanoparticles (Pt x Gd NPs) are synthesized for the first time as oxygen reduction reaction (ORR) electrocatalysts using the gas aggregation technique, under ultrahigh vacuum (UHV) conditions. The morphology of the Pt x Gd catalysts is characterized, and their catalytic performance toward the ORR is assessed in acidic media using a half-cell configuration. The Pt x Gd 8-nm catalyst shows a high activity (3.6 A (mg Pt) −1 ), surpassing the highest activity reached so far with Pt x Y NP catalysts. In addition, the optimum Pt x Gd catalyst also presents high stability, as suggested by the accelerated stability tests under ORR potential cycling. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements confirm that as-prepared Pt x Gd NPs are compressively strained, relative to pure Pt, and that a Pt x Gd core/Pt-rich shell structure is adopted after partial Gd leaching. The activity correlates strongly with the compressive strain. On that basis, we propose that the ORR enhancement is due to the compressive strain within the Pt shell induced by the alloy core. The results herein confirm the suitability of Pt x Gd NPs as cathode nanocatalysts for proton exchange membrane fuel cells (PEMFCs). [ABSTRACT FROM AUTHOR]

Highlights: [•] There was a linear relation between the binding energy of OOH* and OH* for the N-GNRs. [•] The most OER and ORR active sites were identified near the edge but not exactly on the edge of the armchair nanoribbons. [•] The minimum theoretic OER and ORR overpotential was calculated. [•] The calculations suggested that N-GNRs were a highly promising OER/ORR catalyst. [ABSTRACT FROM AUTHOR]

Highlights: [•] FePc/SWNT heterojunction nanowires are prepared via a self-assembly approach. [•] FePc/SWNT performs much better than Pt/C in the ORR in alkaline media. [•] DFT and experimental results are combined to understand the ORR at FePc/SWNT. [•] The O2–FePc interaction is facilitated with fast electron transfer to the surface. [ABSTRACT FROM AUTHOR]

Abstract: The shape and structure of electrocatalysts at the nanoscale level have a decisive effect on their activity and durability in low-temperature fuel cells. Herein, we report the discovery of unexpected structural phenomena in exotic nanostructures: the anomalous compressive strain and superior electron retention properties of highly porous Pt (HP-Pt) nanoparticles synthesized using a weakly interacting organic capping agent, tetradecyl trimethyl ammonium bromide. Even though the particle size of the HP-Pt nanoparticles was much larger than those of commercial electrocatalysts, bond length shortening occurred anomalously, and the downshifted d-band center eventually led to increased oxygen reduction reaction activity. This is because the HP-Pt nanoparticles had a highly porous urchin-like dendritic structure, interestingly in the single-crystalline phase, despite the large particle size. In addition, their electron retention properties were superior to those of commercial samples, which led to drastically enhanced stability against Pt dissolution at high potentials. [Copyright &y& Elsevier]

Abstract: Nanoporous gold (NPG) made by dealloying silver/gold alloys is a mesoporous metal combining high surface area and high conductivity. Recently, NPG has been shown to exhibit some of the high catalytic activity previously associated only with supported gold nanoparticles. Here we describe how NPG acts as a catalyst for the oxygen reduction reaction in both gas phase (in fuel cells) and aqueous environments (using rotating disk electrochemistry). NPG was found to reduce oxygen via an effectively 4-four electron route comprised of a first reduction of oxygen to hydrogen peroxide, and then an unusually active further catalytic reduction of hydrogen peroxide to water. [Copyright &y& Elsevier]