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[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]

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]

The insufficient durability of Pt‐based catalysts and the sluggish kinetics of oxygen reduction reaction (ORR) is hampering the development of proton exchange membrane fuel cells (PEMFCs) for commercialization. Herein, a single atom Ti‐modified activated nitrogen‐doped porous carbon (Ti‐a‐NPC) is designed to equalize O2‐activation/*OH‐removal through regulating the charge rearrangement of ultra‐small L12‐Pt3Co for efficient and durable oxygen reduction. The Ti single‐atom modified in the surface/pore of Ti‐a‐NPC can anchor the Pt‐based intermetallic nanoparticles (NPs) not only guarantees Pt‐based intermetallics’ ultra‐fine size (≈2.62 nm) but also maintains Pt‐based intermetallics during ORR process. The enhanced catalyst (L12‐Pt3Co/Ti‐a‐NPC) achieves 11‐fold mass activity (1.765 A mgPt−1) compared to commercial Pt/C. Notably, after 30 000 cycles of accelerated durability tests, the mass activity of the L12‐Pt3Co/Ti‐a‐NPC only decreased by 3.7%, while that of commercial Pt/C decreased by 37.1%. Rationalized by theoretical simulation, the introduction of Ti atoms can form charge channels between L12‐Pt3Co NPs and Ti‐a‐NPC, accelerating the charge transfer in the ORR process. Furthermore, the charge of L12‐Pt3Co will accumulate to Ti atoms and buffer the electron transfer of L12‐Pt3Co to the N atoms, thus optimizing the adsorption performance of the active site to the oxygen‐containing intermediate and improving the intrinsic activity of the catalyst. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) represents a cornerstone for many clean energy conversion technologies such as fuel cells and metal‐air batteries. Nevertheless, the commercialization of these technologies is largely impeded by the slow kinetics of ORR, for which active, durable and cost‐effective ORR catalysts are needed. In recent years, zeolitic imidazolate framework (ZIF) derived carbon materials emerge as a new class of non‐precious metal catalysts (NPMCs) toward ORR, largely benefiting from their high surface area, abundant porosity, tunable chemical/electronic structure, and superior ORR activity which is comparable or even surpasses those state‐of‐the‐art Pt‐based ORR catalysts. This review offers a comprehensive overview of the recent advances in ZIF‐derived carbons for ORR. The synthesis strategies and the key factors affecting the ORR performance of ZIF‐derived carbon materials are discussed. Future research directions and perspectives on exploring ZIF derived carbons as efficient ORR catalysts are highlighted, with a focus on the principles of rationally engineering the coordination structures of active sites. [ABSTRACT FROM AUTHOR]

Developing efficient and anti‐corrosive oxygen reduction reaction (ORR) catalysts is of great importance for the applications of proton exchange membrane fuel cells (PEMFCs). Herein, we report a novel approach to prepare metal oxides supported intermetallic Pt alloy nanoparticles (NPs) via the reactive metal‐support interaction (RMSI) as ORR catalysts, using Ni‐doped cubic ZrO2 (Ni/ZrO2) supported L10−PtNi NPs as a proof of concept. Benefiting from the Ni migration during RMSI, the oxygen vacancy concentrations in the support are increased, leading to an electron enrichment of Pt. The optimal L10−PtNi−Ni/ZrO2−RMSI catalyst achieves remarkably low mass activity (MA) loss (17.8 %) after 400,000 accelerated durability test cycles in a half‐cell and exceptional PEMFC performance (MA=0.76 A mgPt−1 at 0.9 V, peak power density=1.52/0.92 W cm−2 in H2−O2/−air, and 18.4 % MA decay after 30,000 cycles), representing the best reported Pt‐based ORR catalysts without carbon supports. Density functional theory (DFT) calculations reveal that L10−PtNi−Ni/ZrO2−RMSI requires a lower energetic barrier for ORR than L10−PtNi−Ni/ZrO2 (direct loading), which is ascribed to a decreased Bader charge transfer between Pt and *OH, and the improved stability of L10−PtNi−Ni/ZrO2−RMSI compared to L10−PtNi−C can be contributed to the increased adhesion energy and Ni vacancy formation energy within the PtNi alloy. [ABSTRACT FROM AUTHOR]

Atomically dispersed iron–nitrogen–carbon catalysts are promised, low‐cost, and high‐performance electrocatalysts for the Oxygen Reduction Reaction (ORR) in fuel cells. However, most Fe–N–C materials are produced via pyrolysis at a high temperature and it is difficult to characterise the precise Fe–N configurations. This can lead to confusion surrounding the best chemical and coordination environment for Fe and understanding the subsequent ORR mechanisms. In this work, Fe porphyrin is used to produce a specific Fe–N environment, therefore allowing the role and activity of this environment to be studied. Carbon nanotubes (CNTs) are covalently functionalized with iron 5,10,15,20‐triphenylporphyrin (FeTPP) motifs via aryl diazonium methodology, enabling the exact role of only the Fe‐Pyrrolic N4 configuration of FeTPP in ORR to be studied and better understood. Upon covalent functionalization, a high electrochemical active site density of 1.12 × 1015 sites cm−2, approximately six‐fold more than that of noncovalently functionalized samples with 12.7% electrochemical active site. The heightened active site density and superior electrochemical active site utilization (12.7%) lead to the more favorable 4‐electron pathway for the ORR. Furthermore, a preliminary discussion regarding the selectivity of the ORR pathway is initiated. [ABSTRACT FROM AUTHOR]

Designing an electrocatalyst with low Pt content is an immediate need for essential reactions in low temperature fuel cell systems. In the present work, La0.9925Ba0.0075Al0.995Pt0.005O3 is aimed at using with low (only 0.5%) Pt doping as an electrocatalyst for oxygen reduction reaction (ORR). The low doping level renders exsolution of 1–2 nm nanoparticles with uniform dispersion upon reduction in H2/N2 at low temperatures. Pt exsolved perovskite oxides deliver significantly enhanced catalytic activity for ORR and improved stability in alkaline media. This study demonstrates that LaAlO3 with low noble metal content holds immense potential as an electrocatalyst in real fuel cell systems. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is the bottleneck of metal‐air batteries and fuel cells. Strain regulation can change the geometry and adjust the surface charge distribution of catalysts, which is a powerful strategy to optimize the ORR activity. The introduction of controlled strain to the material is still difficult to achieve. Herein, we present a temperature‐pressure‐induced strategy to achieve the controlled lattice strain for metal coordination polymers. Through the systematic study of the strain effect on ORR performance, the relationship between geometric and electronic effects is further understood and confirmed. The strained Co‐DABDT (DABDT=2,5‐diaminobenzene‐1,4‐dithiol) with 2 % lattice compression exhibits a superior half‐wave potential of 0.81 V. Theoretical analysis reveals that the lattice strain changes spin‐charge densities around S atoms for Co‐DABDT, and then regulates the hydrogen bond interaction with intermediates to promote the ORR catalytic process. This work helps to understand the catalytic mechanism from the atomic level. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is the bottleneck of metal‐air batteries and fuel cells. Strain regulation can change the geometry and adjust the surface charge distribution of catalysts, which is a powerful strategy to optimize the ORR activity. The introduction of controlled strain to the material is still difficult to achieve. Herein, we present a temperature‐pressure‐induced strategy to achieve the controlled lattice strain for metal coordination polymers. Through the systematic study of the strain effect on ORR performance, the relationship between geometric and electronic effects is further understood and confirmed. The strained Co‐DABDT (DABDT=2,5‐diaminobenzene‐1,4‐dithiol) with 2 % lattice compression exhibits a superior half‐wave potential of 0.81 V. Theoretical analysis reveals that the lattice strain changes spin‐charge densities around S atoms for Co‐DABDT, and then regulates the hydrogen bond interaction with intermediates to promote the ORR catalytic process. This work helps to understand the catalytic mechanism from the atomic level. [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]

The development of effective and stable cathode electrocatalysts is highly desired for fuel cells. Controlling the composition and morphology of Pd-based materials can provide a great opportunity to improve their oxygen reduction reaction (ORR) performance. Here, we report the synthesis of hexagonal close-packed (hcp) Pd2B nanosheet assemblies (Pd2B NAs) via the boronation reaction between as-synthesized Pd NAs and N,N-dimethylformamide. The hcp Pd2B NAs with uniform pore distribution can provide sufficient active sites for ORRs. The insertion of B atoms can induce the phase transition from face-centered cubic structure to hcp structure, as the most thermodynamically stable phase in the Pd-B alloy, which is beneficial for enhancing the ORR stability and toxicity resistance. Therefore, the hcp Pd2B NAs exhibit superior mass activity, specific activity and excellent stability for ORR. The present strategy of boron-intercalation-triggered crystalline transition of Pd-based nanomaterials is valuable for the design of metal–nonmetal catalysts with enhanced performance. [ABSTRACT FROM AUTHOR]

Samaria-doped ceria (SDC) overlayers were deposited on Ag cathodes by sputtering. The SDC sputtering time was varied to investigate the properties of the Ag–SDC overlayer cathode-coated fuel cells depending on the thickness of the SDC overlayers. Among the fabricated fuel cells, Ag with a 10-nm-thick SDC overlayer (Ag-SDC10) cathode-coated fuel cell exhibited the highest peak power density of 6.587 mW/cm2 at 450 °C, showing higher performance than a pristine Pt-coated fuel cell. Moreover, electrochemical impedance spectroscopy revealed that the Ag-SDC10 cathode-coated fuel cell significantly mitigated polarization loss originating from enhanced oxygen reduction reaction kinetics compared to the pristine Ag-coated fuel cell. [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]

Search for a Platinum metal-free catalyst for Proton Exchange Membrane Fuel Cells (PEMFCs) is a concern to scientists as the Pt-catalyzed electrode comprises about 45% of the entire fuel cell stack cost. Due to layered structure, Two-dimensional (2D) MoS2 nanostructured materials have recently drawn attention as effective catalysts for oxygen reduction reaction (ORR). The 1T-phase of MoS2 (1T-MoS2) has higher electronic conductivity than the 2H-phase (2H-MoS2); high surface area 1T-MoS2 can have high electrocatalytic activity towards PEFFCs. Here, we report hydrothermally synthesized 2H-MoS2 and solvothermally synthesized mixed 1T/2H-MoS2 phases as a catalyst for ORR in PEM Fuel Cells. Owing to the high BET-specific surface area, hybrid 1T/2H-MoS2 showed better ORR activity than 2H-MoS2. The limiting current density of the 1T/2H-MoS2 hybrid structure is ‒7.1 mA cm−2 compared to Pt/C (‒8.2 mA cm−2) at 1600 rpm. The Tafel slope values of 2H-MoS2, 1T/2H-MoS2, and Pt/C are 92.7 mV dec−1, 57.5 mV dec−1, and 39.3 mV dec−1, respectively. The electron transferred during ORR are 3.8 and 1.8, respectively, for 1T/2H-MoS2 and 2H-MoS2 (in 0.1 M KOH) ; suggesting less formation of undesirable peroxide formation than 2H-MoS2. The 1T/2H-MoS2 displays better electrochemical durability compared to 2H-MoS2 (after 2000 CV cycles). [ABSTRACT FROM AUTHOR]

Fe─N─C materials with Fe─N4 sites are considered as most promising non‐precious metal‐based electrocatalysts for low‐cost proton‐exchange‐membrane fuel cells (PEMFCs). Breaking the trade‐off between activity and stability has been a long‐standing challenge in the field of acidic oxygen reduction reaction (ORR). Herein, a "top‐down" thermally‐driven strategy is developed to achieve highly active pyrrolic N‐coordinated Fe sites in a high spin state with Fe atomic cluster (Fen@Fe─Npyrr─C) and discover that the neighboring Fen cluster can synergistically stabilize such vulnerable Fe─N4 sites by inhibiting their protonation. Consequently, the Fen@Fe─Npyrr─C catalysts exhibit much enhanced ORR activity and stability, endowing PEMFCs with a high power density of 804.6 mW cm−2 (testing conditions: 80 °C, 100% RH, 2.0 bar) and over 100 h durability (at 0.5 V). These findings open up opportunities for the exploration of durable Fe─N─C ORR electrocatalysts for non‐precious metal‐based PEMFCs and other applications. [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]

Engineering the electronic configuration and intermediates adsorption behaviors of high‐performance non‐noble‐metal‐based catalysts for the sluggish oxygen reduction reaction (ORR) kinetics at the cathode is highly imperative for the development of anion exchange membrane fuel cells (AEMFCs), yet remains an enormous challenge. Herein, a rare‐earth metal oxide engineering tactic through the formation of Fe3O4/La2O3 heterostructures in N,O‐doped carbon nanospheres (Fe3O4/La2O3@N,O‐CNSs) for efficient oxygen reduction electrocatalysis is reported. The theoretical calculations reveal that the interfacial bonds formed by the La─O─Fe heterogeneous interface effectively optimize the electronic structure of the Fe d‐band center relative to the Fermi level, which results in a significant reduction of the reaction barriers of rate‐limiting steps during the ORR. The modulation in intermediates chemisorption enables Fe3O4/La2O3@N,O‐CNSs an outstanding ORR performance and improved stability, with a significantly higher half‐wave potential value (0.88 V). More impressively, this integrated catalyst delivers a remarkable power density of 148.7 mW cm−2 in practical AEMFC operating conditions, along with negligible performance degradation over 100 h using an H2‐air atmosphere, which is higher than commercial Pt/C‐coupled electrodes. The results presented here are believed to provide guidelines for fabricating high‐performance AEMFCs electrocatalysts in terms of heterointerface engineering and strong electronic coupling effect induced by rare‐earth oxides. [ABSTRACT FROM AUTHOR]

The development of precious metal-free (M-N-C) catalysts for the oxygen reduction reaction (ORR) is considered crucial for reducing fuel cell costs. Herein, Co-Zn/NC interconnected frameworks with uniformly dispersed Co nanoparticles and graphitic carbon are designed and successfully synthesized through the in situ growth of zeolitic imidazolate frameworks (ZIF67 and ZIF8) along with biomass nano-microfibrillar cellulose (MFC), followed by pyrolysis. A Co-Zn/NC composite is prepared by combining Co-Zn/NC with a perfluorosulfonic acid polymer. The Co-Zn/NC composite catalyst exhibits excellent ORR catalytic activity (E0 = 0.974 V vs. RHE, E1/2 = 0.858 V vs. RHE) and good long-term durability, with 90% current retention after 10000s, surpassing that of commercial Pt/C in alkaline media. The hierarchical porous structure, coupled with the uniform distribution of Co nanoparticles and nitrogen doping, contributes to superior electrocatalytic performance, while the interconnected frameworks and graphitic carbon ensure good stability. Additionally, the Co-Zn/NC composite demonstrates promising applications in acidic media. This strategy offers significant guidance to develop advanced non-precious metal carbon-based catalysts for highly efficient and stable ORR. [ABSTRACT FROM AUTHOR]

The efficiency and performance of proton exchange membrane fuel cells (PEMFCs) are primarily influenced by ORR electrocatalysts. In recent years, atomically dispersed metal–nitrogen–carbon (M-N-C) catalysts have gained significant attention due to their high active center density, high atomic utilization, and high activity. These catalysts are now considered the preferred alternative to traditional noble metal electrocatalysts. The unique properties of M-N-C catalysts are anticipated to enhance the energy conversion efficiency and lower the manufacturing cost of the entire system, thereby facilitating the commercialization and widespread application of fuel cell technology. This article initially delves into the origin of performance and degradation mechanisms of Fe-N-C catalysts from both experimental and theoretical perspectives. Building on this foundation, the focus shifts to strategies aimed at enhancing the activity and durability of atomically dispersed Fe-N-C catalysts. These strategies encompass the use of bimetallic atoms, atomic clusters, heteroatoms (B, S, and P), and morphology regulation to optimize catalytic active sites. This article concludes by detailing the current challenges and future prospects of atomically dispersed Fe-N-C catalysts. [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]

Alleviating the degradation issue of Pt based alloy catalysts, thereby simultaneously achieving high mass activity and high durability in proton exchange membrane fuel cells (PEMFCs), is highly challenging. Herein, we provide a new paradigm to address this issue via delaying the place exchange between adsorbed oxygen species and surface Pt atoms, thereby inhibiting Pt dissolution, through introducing rare earth bonded subsurface oxygen atoms. We have succeeded in introducing Gd−O dipoles into Pt3Ni via a high temperature entropy‐driven process, with direct spectral evidence attained from both soft and hard X‐ray absorption spectroscopies. The higher rated power of 0.93 W cm−2 and superior current density of 562.2 mA cm−2 at 0.8 V than DOE target for heavy‐duty vehicles in H2‐air mode suggest the great potential of Gd−O−Pt3Ni towards practical application in heavy‐duty transportation. Moreover, the mass activity retention (1.04 A mgPt−1) after 40 k cycles accelerated durability tests is even 2.4 times of the initial mass activity goal for DOE 2025 (0.44 A mgPt−1), due to the weakened Pt−Oads bond interaction and the delayed place exchange process, via repulsive forces between surface O atoms and those in the sublayer. This work addresses the critical roadblocks to the widespread adoption of PEMFCs. [ABSTRACT FROM AUTHOR]

Alleviating the degradation issue of Pt based alloy catalysts, thereby simultaneously achieving high mass activity and high durability in proton exchange membrane fuel cells (PEMFCs), is highly challenging. Herein, we provide a new paradigm to address this issue via delaying the place exchange between adsorbed oxygen species and surface Pt atoms, thereby inhibiting Pt dissolution, through introducing rare earth bonded subsurface oxygen atoms. We have succeeded in introducing Gd−O dipoles into Pt3Ni via a high temperature entropy‐driven process, with direct spectral evidence attained from both soft and hard X‐ray absorption spectroscopies. The higher rated power of 0.93 W cm−2 and superior current density of 562.2 mA cm−2 at 0.8 V than DOE target for heavy‐duty vehicles in H2‐air mode suggest the great potential of Gd−O−Pt3Ni towards practical application in heavy‐duty transportation. Moreover, the mass activity retention (1.04 A mgPt−1) after 40 k cycles accelerated durability tests is even 2.4 times of the initial mass activity goal for DOE 2025 (0.44 A mgPt−1), due to the weakened Pt−Oads bond interaction and the delayed place exchange process, via repulsive forces between surface O atoms and those in the sublayer. This work addresses the critical roadblocks to the widespread adoption of PEMFCs. [ABSTRACT FROM AUTHOR]

Pt‐based intermetallics are recognized as effective catalysts for oxygen reduction reaction (ORR) in fuel cells. However, the synthesis of intermetallics often requires prolonged annealing and the effect of different crystal structures on ORR still need to be investigated. Herein, L12‐Pt3Mn and L10‐PtMn intermetallics with Pt‐skin are rapidly synthesized through an emerging periodic carbothermal shock method to investigate their ORR‐activity difference. The formation of L12‐Pt3Mn and L10‐PtMn can be well‐controlled by the Pt/Mn feeding ratio, pulse cycles, and temperature. Electrocatalytic investigations show that L12‐Pt3Mn presents a more positive half‐wave potential (0.91 V vs RHE) and onset potential (1.02 V vs RHE) than those of L10‐PtMn. The mass activity and specific activity of L12‐Pt3Mn are respectively fourfold and threefold greater than those of L10‐PtMn. Theoretical calculations indicate that the L12‐Pt3Mn has a more substantial work function than L10‐PtMn, thereby conferring L12‐Pt3Mn with an increased electron density allocation for catalytic involvement. This electron confinement imparts L12‐Pt3Mn with a Pt d‐band center lower than that of L10‐PtMn, consequently attenuating the adsorption of strongly bonded *O intermediates during the rate‐determining step. This study not only employs a straightforward method for intermetallic preparation but also elucidates the discrepancies in ORR activity across intermetallics with distinct structures. [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 oxygen reduction reaction (ORR) is the key reaction in metal air and fuel cells. Among the catalysts that promote ORR, carbon‐based metal‐free catalysts are getting more attention because of their maximum atom utilization, effective active sites and satisfactory catalytic activity and stability. However, the pyrolysis synthesis of these carbons resulted in disordered porosities and uncontrolled catalytic sites, which hindered us in realizing the catalysts' design, the optimization of catalyst performance and the elucidation of structure–property relationship at the molecular level. Covalent organic frameworks (COFs) constructed with designable building blocks have been employed as metal‐free electrocatalysts for the ORR due to their controlled skeletons, tailored pores size and environments, as well as well‐defined location and kinds of catalytic sites. In this Concept article, the development of metal‐free COFs for the ORR is summarized, and different strategies including skeletons regulation, linkages engineering and edge‐sites modulation to improve the catalytic selectivity and activity are discussed. Furthermore, this Concept provides prospectives for designing and constructing powerful electrocatalysts based on the catalytic COFs. [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]

It is essential for the widespread application of proton exchange membrane fuel cells (PEMFCs) to investigate low‐cost, extremely active, and long‐lasting oxygen reduction catalysts. Initial performance of PGM‐free metal‐nitrogen‐carbon (M−N−C) catalysts for oxygen reduction reaction (ORR) has advanced significantly, particularly for Fe−N−C‐based catalysts. However, the insufficient stability of M−N−C catalysts still impedes their use in practical fuel cells. In this review, we focus on the understanding of the structure‐stability relationship of M−N−C ORR catalysts and summarize valuable guidance for the rational design of durable M−N−C catalysts. In the first section of this review, we discuss the inherent degrading mechanisms of M−N−C catalysts, such as carbon corrosion, demetallation, H2O2 attack, etc. As we gain a thorough comprehension of these deterioration mechanisms, we shift our attention to the investigation of strategies that can mitigate catalyst deterioration and increase its stability. These strategies include enhancing the anti‐oxidation of carbon, fortifying M−N bonds, and maximizing the effectiveness of free radical scavengers. This review offers a prospective view on the enhancement of the stability of non‐noble metal catalysts. [ABSTRACT FROM AUTHOR]

Atomically dispersed Fe-N-C catalysts for the oxygen reduction reaction (ORR) have been synthesized with a template-free method using carbon xerogels (CXG) as a porous matrix. The porosity of the CXGs is easily tunable through slight variations in the synthesis procedure. In this work, CXGs are prepared by formaldehyde and resorcinol polymerization, modifying the pH during the process. Materials with a broad range of porous structures are obtained: from non-porous to micro-/meso-/macroporous materials. The porous properties of CXG have a direct effect on Fe-N-CXG activity against ORR in an acidic medium (0.5 M H2SO4). Macropores and wide mesopores are vital to favor the mass transport of reagents to the active sites available in the micropores, while narrower mesopores can generate additional tortuosity. The role of microporosity is investigated by comparing two Fe-N-C catalysts using the same CXG as the matrix but following a different Fe and N doping procedure. In one case, the carbonization of CXG occurs rapidly and simultaneously with Fe and N doping, whereas in the other case it proceeds slowly, under controlled conditions and before the doping process, resulting in the formation of more micropores and active sites and achieving higher activity in a three-electrode cell and a better durability during fuel cell measurements. This work proves the feasibility of the template-free method using CXG as a carbon matrix for Fe-N-C catalysts, with the novelty of the controlled porous properties of the carbon material and its effect on the catalytic activity of the Fe-N-C catalyst. Moreover, the results obtained highlight the importance of the carbon matrix's porous structure in influencing the activity of Fe-N-C catalysts against ORR. [ABSTRACT FROM AUTHOR]

An oxygen reduction reaction (ORR) is the key half reaction of proton exchange membrane fuel cells (PEMFCs), and is highly dependent on Pt-based nanocrystals as core electrocatalysts. Despite the exceptional ORR activity from adjusting the electronic structures of surface or near-surface atoms, several serious issues, including the corrosion of carbon supports, the preferential leaching of active metal elements, the instability of surface low-coordinated atoms and the sintering/agglomeration of nanocrystals, still exist, challenging the ORR durability of developed Pt-based ORR catalysts. From the point of view of the catalyst structure design, in this review, we summarized the state-of-the-art structural regulation strategies for improving the ORR durability of Pt-based catalysts. The current limitation of Pt-based binary catalysts for ORR electrocatalysis is firstly discussed, and the detailed strategies are further classified into the optimization of supports, metal-doped alloys, core/shell structures, intermetallics and high-entropy alloys, etc. The structure–performance relationship is detailedly explained, especially emphasizing the elimination of the above restrictions. Finally, the existing challenges and future research direction are further presented, aiming at practicing the PEMFC devices of the ultradurable Pt-based catalysts. [ABSTRACT FROM AUTHOR]

Studying the ORR activity of platinum-based electrocatalysts is an urgent task in the development of materials for proton-exchange membrane fuel cells. The catalytic ink composition and the formation technique of a thin layer at the RDE play a significant role in studying ORR activity. The use of a polymer ionomer in the catalytic ink provides viscosity as well as proton conductivity. Nafion is widely used as an ionomer for research both at the RDE and in the MEA. The search for ionomers is a priority task in the development of the MEA components to replace Nafion. The study also considers the possibility of using the LF4-SK polymer as an alternative ionomer. The comparative results on the composition and techniques of applying the catalytic layer using LF4-SK and Nafion ionomers are presented, and the influence of the catalytic ink composition on the electrochemical characteristics of commercial platinum–carbon catalysts and a highly efficient platinum catalyst based on an N-doped carbon support is assessed. [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]

Currently, the development of nonmetallic oxygen reduction reaction (ORR) catalysts based on heteroatomic-doped carbon materials is receiving increaseing attention in the field of fuel cells. Here, we used enzymolytic lignin (EL), melamine, and thiourea as carbon, nitrogen, and sulfur sources and NH4Cl as an activator to prepare N- and S-codoped lignin-based polyporous carbon (ELC) by one-step pyrolysis. The prepared lignin-derived biocarbon material (ELC-1-900) possessed a high specific surface area (844 m2 g−1), abundant mesoporous structure, and a large pore volume (0.587 cm3 g−1). The XPS results showed that ELC-1-900 was successfully doped with N and S. ELC-1-900 exhibited extremely high activity and stability in alkaline media for the ORR, with a half-wave potential (E1/2 = 0.88 V) and starting potential (Eonset = 0.98 V) superior to those of Pt/C catalysts and most non-noble-metal catalysts reported in recent studies. In addition, ELC-1-900 showed better ORR stability and methanol tolerance in alkaline media than commercial Pt/C catalysts. [ABSTRACT FROM AUTHOR]

Precisely designing asymmetric diatomic configurations and studying their electronic regulation effect for improving the oxygen reduction reaction (ORR) performance are important for anion exchange membrane fuel cells (AEMFCs). Here, a Fe, Cu co‐doped 2D crystalline IISERP‐MOF27 nanosheet derived FeN3O‐CuN4 diatomic site nanocatalyst (named as FeCu‐NC) is synthesized for the cathodes of AEMFCs. Thanks to the optimal electronic structure of FeN3O‐CuN4 in the FeCu‐NC catalyst, it shows enhanced half‐wave potential (0.910 V), turnover frequency (0.165e s−1 site−1), and decreased activation energy (19.96 kJ mol−1) in KOH. The FeCu‐NC‐based AEMFC achieves extremely high kinetic current (0.138 A cm−2 at 0.9 V) and rated power density (1.09 W cm−2), surpassing the best‐reported transition metal‐based cathodes. Density functional theory calculations further demonstrate that the Cu‐N4 can break the localization of Fe‐3d orbitals, accelerate the electron transport, and optimize the OH adsorption, thus facilitating the ORR process. [ABSTRACT FROM AUTHOR]

The use of platinum-free (Pt) cathode electrocatalysts for oxygen reduction reactions (ORRs) has been significantly studied over the past decade, improving slow reaction mechanisms. For many significant energy conversion and storage technologies, including fuel cells and metal–air batteries, the ORR is a crucial process. These have motivated the development of highly active and long-lasting platinum-free electrocatalysts, which cost less than proton exchange membrane fuel cells (PEMFCs). Researchers have identified a novel, non-precious carbon-based electrocatalyst material as the most effective substitute for platinum (Pt) electrocatalysts. Rich sources, outstanding electrical conductivity, adaptable molecular structures, and environmental compatibility are just a few of its benefits. Additionally, the increased surface area and the simplicity of regulating its structure can significantly improve the electrocatalyst's reactive sites and mass transport. Other benefits include the use of heteroatoms and single or multiple metal atoms, which are capable of acting as extremely effective ORR electrocatalysts. The rapid innovations in non-precious carbon-based nanomaterials in the ORR electrocatalyst field are the main topics of this review. As a result, this review provides an overview of the basic ORR reaction and the mechanism of the active sites in non-precious carbon-based electrocatalysts. Further analysis of the development, performance, and evaluation of these systems is provided in more detail. Furthermore, the significance of doping is highlighted and discussed, which shows how researchers can enhance the properties of electrocatalysts. Finally, this review discusses the existing challenges and expectations for the development of highly efficient and inexpensive electrocatalysts that are linked to crucial technologies in this expanding field. [ABSTRACT FROM AUTHOR]

Fuel cells have emerged as a promising clean electrochemical energy technology with a great potential in various sectors, including transportation and power generation. However, the high cost and scarcity of the noble metals currently used to synthesise electrocatalysts for low‐temperature fuel cells has hindered their widespread commercialisation. In recent decades, the development of non‐precious metal electrocatalysts for the cathodic oxygen reduction reaction (ORR) have gained significant attention. Among those, electrocatalysts with atomically dispersed active sites, referred to as single‐atom catalysts (SACs), are gaining more interest. Nanocarbon materials containing single transition metal atoms coordinated to nitrogen atoms are active electrocatalysts for the ORR in both acidic and alkaline conditions and thus have a great promise to be utilised as non‐precious metal cathode electrocatalysts in low‐temperature fuel cells. This review article provides an overview of the recent advancements in the utilisation of transition metal‐based SACs in proton exchange membrane fuel cells (PEMFCs) and anion exchange membrane fuel cells (AEMFCs). We highlight the main strategies and synthetic approaches for tailoring the properties of SACs to enhance their ORR activity and durability. Based on the already achieved results, it is evident that SACs indeed could be suitable for the cathode of the low‐temperature 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]

Transition metal single atoms anchored on nitrogen‐doped carbon (M‐N‐C) matrix with M‐N‐C active sites have shown to be promising catalysts for both hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Herein, a hybrid catalyst with low‐level loading of atomic Pt and Co species encapsulated in nitrogen‐doped graphene (Pt@CoN4‐G) is developed. The Pt@CoN4‐G shows low overpotential for HER in wide‐pH electrolyte and manifests improved mass activity with almost eight times greater than that of Pt/C at an overpotential of 50 mV. The Pt@CoN4‐G also exhibits a top‐level ORR activity (half‐wave potential, E1/2 = 0.893 V) and robust stability (>200 h) in alkaline medium. Using theoretical calculations and comprehensive characterizations , the strong metal–support interactions between Pt species and CoN4‐G support and synergistical cooperation of multiple active sites are clarified. A flow alkali‐Al/acid hybrid fuel cell using Pt@CoN4‐G as cathode catalyst delivers a large power density of 222 mW cm−2 with excellent stability to achieve simultaneously hydrogen evolution and electricity generation. In addition, Pt@CoN4‐G endows a flow Zn‐air battery with high power density (316 mW cm−2), good stability under large current density (>100 h at 100 mA cm−2), and long cycle life (over 600 h at 5 mA cm−2). [ABSTRACT FROM AUTHOR]

In light of the depletion of conventional energy sources, it is imperative to conduct research and development on sustainable alternative energy sources. Currently, electrochemical energy storage and conversion technologies such as fuel cells and metal-air batteries rely heavily on precious metal catalysts like Pt/C and IrO2, which hinders their sustainable commercial development. Therefore, researchers have devoted significant attention to non-precious metal-based catalysts that exhibit high efficiency, low cost, and environmental friendliness. Among them, perovskite oxides possess low-cost and abundant reserves, as well as flexible oxidation valence states and a multi-defect surface. Due to their advantageous structural characteristics and easily adjustable physicochemical properties, extensive research has been conducted on perovskite-based oxides. However, these materials also exhibit drawbacks such as poor intrinsic activity, limited specific surface area, and relatively low apparent catalytic activity compared to precious metal catalysts. To address these limitations, current research is focused on enhancing the physicochemical properties of perovskite-based oxides. The catalytic activity and stability of perovskite-based oxides in Oxygen Reduction Reaction/Oxygen Evolution Reaction (ORR/OER) can be enhanced using crystallographic structure tuning, cationic regulation, anionic regulation, and nano-processing. Furthermore, extensive research has been conducted on the composite processing of perovskite oxides with other materials, which has demonstrated enhanced catalytic performance. Based on these different ORR/OER modification strategies, the future challenges of perovskite-based bifunctional oxygen electrocatalysts are discussed alongside their development prospects. [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]

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]

Solid oxide fuel cells (SOFCs) represent a breed of eco-friendly, weather-independent, decentralized power generation technologies, distinguished for their broad fuel versatility and superior electricity generation efficiency. At present, SOFCs are impeded by a lack of highly efficient oxygen reduction catalysts, a factor that significantly constrains their performance. The double perovskites LnBaCo2O5+δ (Ln = Lanthanide), renowned for their accelerated oxygen exchange and conductivity features, are widely acclaimed as a promising category of cathode catalysts for SOFCs. This manuscript offers a novel perspective on the physicochemical attributes of LnBaCo2O5+δ accumulated over the past two decades and delineates the latest advancements in fine-tuning the composition and nanostructure for SOFC applications. It highlights surface chemistry under operational conditions and microstructure as emerging research focal points towards achieving high-performance LnBaCo2O5+δ catalysts. This review offers a comprehensive insight into the latest advancements in utilizing LnBaCo2O5+δ in the field of SOFCs, presenting a clear roadmap for future developmental trajectories. Furthermore, it provides valuable insights for the application of double perovskite materials in domains such as water electrolysis, CO2 electrolysis, chemical sensors, and metal–air batteries. [ABSTRACT FROM AUTHOR]

To achieve the Fe−N−C materials with both high activity and durability in proton exchange membrane fuel cells, the attack of free radicals on Fe−N4 sites must be overcome. Herein, we report a strategy to effectively eliminate radicals at the source to mitigate the degradation by anchoring CeO2 nanoparticles as radicals scavengers adjacent (Scaad‐CeO2) to the Fe−N4 sites. Radicals such as ⋅OH and HO2⋅ that form at Fe−N4 sites can be instantaneously eliminated by adjacent CeO2, which shortens the survival time of radicals and the regional space of their damage. As a result, the CeO2 scavengers in Fe−NC/Scaad‐CeO2 achieved ~80 % elimination of the radicals generated at the Fe−N4 sites. A fuel cell prepared with the Fe−NC/Scaad‐CeO2 showed a smaller peak power density decay after 30,000 cycles determined with US DOE PGM‐relevant AST, increasing the decay of Fe−NCPhen from 69 % to 28 % decay. [ABSTRACT FROM AUTHOR]

To achieve the Fe−N−C materials with both high activity and durability in proton exchange membrane fuel cells, the attack of free radicals on Fe−N4 sites must be overcome. Herein, we report a strategy to effectively eliminate radicals at the source to mitigate the degradation by anchoring CeO2 nanoparticles as radicals scavengers adjacent (Scaad‐CeO2) to the Fe−N4 sites. Radicals such as ⋅OH and HO2⋅ that form at Fe−N4 sites can be instantaneously eliminated by adjacent CeO2, which shortens the survival time of radicals and the regional space of their damage. As a result, the CeO2 scavengers in Fe−NC/Scaad‐CeO2 achieved ∼80 % elimination of the radicals generated at the Fe−N4 sites. A fuel cell prepared with the Fe−NC/Scaad‐CeO2 showed a smaller peak power density decay after 30,000 cycles determined with US DOE PGM‐relevant AST, increasing the decay of Fe−NCPhen from 69 % to 28 % decay. [ABSTRACT FROM AUTHOR]

The anion‐exchange membrane direct ammonia fuel cell, as a carbon‐free fuel cell type, has recently received increasing attention albeit suffering from high cost of using the platinum‐group metal oxygen reduction reaction (ORR) catalysts. To pave the development of this promising power source, the atomically dispersed transition metal‐nitrogen‐carbon (M‐N‐C) materials with low cost and high ORR performance have allured to investigate their ammonia tolerance during the ORR. Herein, it is initially deconvoluted how compositional and structural elements of FeN4 sites modulate catalyst's performance. Furthermore, ORR catalytic activities of the M‐N‐C (M = Fe, Co or Mn) and Pt/C catalysts are investigated in ammonia‐containing electrolytes, showing that M‐N‐C catalysts have better ammonia tolerance than Pt/C. Among others, the Fe‐N‐C exhibits the best ammonia tolerance with only 4 mV negative shifts of half‐wave potential, 2.7% decrease of current, and negligibly irreversible activity loss. The superior ammonia tolerance of MN4 sites to Pt (111) surface is further confirmed by density functional theory calculations. The adsorption capacity of MN4 for O2 is higher than NH3 and the bonding force between MN4 and O2 is stronger than NH3, whereas opposite adsorption capacity and bonding force trends are observed on Pt (111) surface. [ABSTRACT FROM AUTHOR]

The oxygen reduction and evolution reactions are considered the bottleneck in many electrochemical devices, i. e. fuel cells, water electrolyzers, and metal‐air batteries. The continuous focus has been on inventing and exploring cost‐effective and robust electrocatalysts. Few developed non‐precious metal/metal‐free materials, in fact, outperformed state‐of‐the‐art catalysts during the half‐cell study. However, most of these materials show limited activity during the full cell demonstration, restricting their deployment in commercial energy devices. In this direction, transition metal nitrides (TMNs) have emerged as a potential alternative with peculiar electronic properties and the ease of tuning their intrinsic as well as extrinsic properties. High hardness, refractory nature, d‐band modulation ability and comparatively lower energy for the nitride formation are the other motivations to explore their effectiveness in oxygen electrocatalysis. Considering this, the minireview attempts first to present the properties of catalytic interest, followed by the most viable synthesis approaches in nanoengineering of the TMNs. Next, we provide key trends toward catalytic property modulation for oxygen electrocatalysis, the role of TMNs as potential catalytic support, followed by the effect of TMNs′ in situ autoxidation on the performance. Finally, we state the current limitations of TMNs toward oxygen electrocatalysis, followed by our vision for further advancements. [ABSTRACT FROM AUTHOR]