Chen Jia

Advancing Fe–N–C single-atom catalysts is paramount for sustainable proton-exchange membrane fuel cells. Dual-atom catalysts offer the most transformative strategy, as they are inherently more active than single-atom catalysts. However, controlling their local coordination environment during synthesis to a desired structure remains a formidable challenge, restricting current high-impact studies to heuristic methods for designing efficient dual-atom catalysts. Studying the promising Fe–Cu–N–C catalyst, we theoretically identify that the most active and stable site for the oxygen reduction reaction features an Fe–Cu bond in N4-coordination environments, N4 Fe–Cu–N–C. By combining X-ray absorption spectroscopy (XAS) with density functional theory, we determine that the synthesis step creating metal-vacant N–C ligands is essential for yielding the desired N4 Fe–Cu–N–C sites. In H2–O2 fuel cells, N4 Fe–Cu–N–C exhibits superior stability with 34.5% voltage loss in 156 h, whereas Fe–N–C loses 50.0% in 90 h. Mechanistic insights reveal that the formation of an Fe–Cu bond induces a charge redistribution effect, strengthening the neighboring bonds in the dual-atom moiety to boost catalyst durability. Aligning with theoretical findings, operando cyclic voltammetry and XAS elucidate that the N4 Fe–Cu–N–C fuel cells effectively suppress detrimental Fe2+/Fe3+ redox processes, thereby preventing carbon corrosion and demetalation, the two major degradation pathways. This rational protocol for catalyst design can enable greater control over the synthesis of intricate local coordination environments in dual-atom sites, thereby contributing to the development of stable, low-cost hydrogen fuel cells.

Single-atom catalysts (SACs) are promising for the electrochemical carbon dioxide reduction reaction (CO2RR) owing to their maximum metal utilization and well-defined active sites. However, the low density of active sites and inadequate mass transport limit their electrocatalytic performance. Here, we report a highly ordered hierarchical porous Ni SAC incorporating nanoconfined ionic liquids (ILs) for CO2RR. The interconnected macropores and mesopores provide efficient transport pathways, while hydrophobic ILs nanoconfined within the microporous network enhance local CO2 availability. The hybrid catalyst delivers nearly unity CO Faradaic efficiency and enhanced partial current densities up to 32 mA cm–2, outperforming conventional Ni–N–C catalysts by 220%. Moreover, its ability to maintain high activity under diluted CO2 conditions further supports enhanced local CO2 availability enabled by the nanoconfined ILs. Operando and in situ spectroscopies suggest enhanced catalytic engagement of Ni sites and significantly enhanced mass transfer enabled by the hierarchical porous structure and nanoconfinement of ILs. Density functional theory calculations further reveal that the ILs modulate the electronic structure of Ni sites and lower the formation energy of the key intermediates. This synergistic integration of hierarchical porosity and local microenvironment engineering offers a viable pathway for advancing high-performance electrocatalysis.

Dual-atom catalysts are highly promising for advancing the benchmark Fe-N-C single-atom catalysts for proton exchange membrane fuel cells. However, controlling the local coordination in synthesis to a desired structure remains a formidable challenge. Studying the promising Fe-Cu-N-C, we theoretically identify that the most active and stable dual-atomic structure features a Fe-Cu bond in N₄-coordinations, N₄ Fe-Cu-N-C. We then combine X-ray absorption spectroscopy and computational chemistry to design a facile synthesis route, finding that the synthesis step creating metal-vacant N-C ligands is essential for yielding N₄ Fe-Cu-N-C. In a H₂-O₂ fuel cell, N₄ Fe-Cu-N-C exhibits improved stability with 34.5% voltage loss in 156 hours, whereas Fe-N-C loses 50.0% in 90 hours. Detailed investigations show that a charge redistribution effect induced by the electroactive Fe-Cu bond strengthens N-C ligands to boost the catalyst durability. Operando cyclic voltammetry reveals that N₄ Fe-Cu-N-C suppresses Fe²⁺/Fe³⁺ redox processes, which prevents Fenton reaction-induced carbon corrosion. This theory-guided synthesis paves the way for more stable, low-cost hydrogen fuel cells.

Ammonia is a vital chemical feedstock for agriculture and energy storage. However, conventional ammonia synthesis via the Haber–Bosch process is both energy‐intensive and carbon‐intensive, and therefore, developing sustainable alternatives is critical. This review discusses recent progress for the electrochemical production of ammonia from various nitrogen sources under ambient conditions. Both nitrogen conversion and the conversion of reactive nitrogen oxides (nitrate, nitrite, and nitric oxide) have been explored but face major drawbacks, such as low yields, competing side reactions, such as hydrogen evolution, a high activation barrier, and complex multi‐electron/proton pathways. This review first discusses the recent progress in this field from a material standpoint to improve the selectivity and yield towards ammonia. Then, the improvements in critical areas beyond material development are discussed in depth, such as ammonia detection and reactor design. Finally, nitrogen, nitrate/nitrite, and nitric oxide reduction routes are assessed to identify the most promising path to sustainable, scalable green ammonia production. Altogether, more innovations are needed to develop efficient and scalable electrochemical NH ₃ synthesis technologies that can supplement, or eventually replace, the Haber–Bosch process.

This review summarized recent advances in CO ₂ RR/CORR at ampere-level current density (>500 mA cm ⁻² ), including mechanisms, and principles for rational catalyst design and mass transport manipulation, along with the challenges and future directions.

Simultaneous reduction of concentration and activation overpotentials at hierarchically porous Ni/CeO_x interfaces in anion-exchange membrane water electrolysers.