The weak adsorption energy of oxygen-containing intermediates on Co center leads to a considerable performance disparity between Co-N-C and costly Pt benchmark in catalyzing oxygen reduction reaction (ORR). In this work, we strategically engineer the active site structure of Co-N-C via B substitution, which is accomplished by the pyrolysis of ammonium borate. During this process, the in-situ generated NH₃ gas plays a critical role in creating surface defects and boron atoms substituting nitrogen atoms in the carbon structure. The well-designed CoB₁N₃ active site endows Co with higher charge density and stronger adsorption energy toward oxygen species, potentially accelerating ORR kinetics. As expected, the resulting Co-B/N-C catalyst exhibited superior ORR performance over Co-N-C counterpart, with 40 mV, and fivefold enhancement in half-wave potential and turnover frequency (TOF). More importantly, the excellent ORR performance could be translated into membrane electrode assembly (MEA) in a fuel cell test, delivering an impressive peak power density of 824 mW·cm^–2, which is currently the best among Co-based catalysts under the same conditions. This work not only demonstrates an effective method for designing advanced catalysts, but also affords a highly promising non-precious metal ORR electrocatalyst for fuel cell applications.

The reactant concentration at the catalytic interface holds the key to the activity of electrocatalytic hydrogen evolution reaction (HER), mainly referring to the capacity of adsorbing hydrogen and electron accessibility. With hydrogen adsorption free energy (ΔG_H) as a reactivity descriptor, the volcano curve based on Sabatier principle is established to evaluate the hydrogen evolution activity of catalysts. However, the role of electron as reactant received insufficient attention, especially for noble metal-free compound catalysts with poor conductivity, leading to cognitive gap between electronic conductivity and apparent catalytic activity. Herein we successfully construct a series of catalyst models with gradient conductivities by regulating molybdenum disulfide (MoS₂) electronic bandgap via a simple solvothermal method. We demonstrate that the conductivity of catalysts greatly affects the overall catalytic activity. We further elucidate the key role of intrinsic conductivity of catalyst towards water electrolysis, mainly concentrating on the electron transport from electrode to catalyst, the electron accumulation process at the catalyst layer, and the charge transfer progress from catalyst to reactant. Theoretical and experimental evidence demonstrates that, with the enhancement in electron accessibility at the catalytic interface, the dominant parameter governing overall HER activity gradually converts from electron accessibility to combination of electron accessibility and hydrogen adsorbing energy. Our results provide the insight from various perspective for developing noble metal-free catalysts in electrocatalysis beyond HER.

The scale-up deployment of ruthenium (Ru)-based oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane water electrolysis (PEMWE) is greatly restricted by the poor stability. As the lattice-oxygen-mediated mechanism (LOM) has been identified as the major contributor to the fast performance degradation, impeding lattice oxygen diffusion to inhibit lattice oxygen participation is imperative, yet remains challenging due to the lack of efficient approaches. Herein, we strategically regulate the bonding nature of Ru–O towards suppressed LOM via Ru-based high-entropy oxide (HEO) construction. The lattice disorder in HEOs is believed to increase migration energy barrier of lattice oxygen. As a result, the screened Ti₂₃Nb₉Hf₁₃W₁₂Ru₄₃O_x exhibits 11.7 times slower lattice oxygen diffusion rate, 84% reduction in LOM ratio, and 29 times lifespan extension compared with the state-of-the-art RuO₂ catalyst. Our work opens up a feasible avenue to constructing stabilized Ru-based OER catalysts towards scalable application.

The development of cost-effective, robust, and durable electrocatalysts to replace the expensive Pt-based catalysts towards oxygen reduction reaction (ORR) is the trending frontier research topic in renewable energy and electrocatalysis. Particular attention has been paid to metal-nitrogen-carbon (M-N-C) single atom catalysts (SACs) due to their maximized atom utilization efficiency, biomimetic active site, and distinct electronic structure. More importantly, their catalytic properties can be further tailored by rationally regulating the microenvironment of active sites (i.e., M–N coordination number, heteroatom doping and substitution. Herein, we present a comprehensive summary of the recent advancement in the microenvironment regulation of M-N-C SACs towards improved ORR performance. The coordination environment manipulation regarding central metal and coordinated atoms is first discussed, focusing on the structure–function relationship. Apart from the near-range coordination, long-range substrate modulation including heteroatom doping, defect engineering is discussed as well. Besides, the synergy mechanism of nanoparticles and single atom sites to tune the electron cloud density at the active sites is summarized. Finally, we provide the challenges and outlook of the development of M-N-C SACs.