Elucidation the relationship between electrode potentials and heterogeneous electrocatalytic reactions has attracted widespread attention. Herein we construct the well-defined Mn single-atom (MnSA) catalyst with four N-coordination through a simple thermal pyrolysis preparation method to investigate the electrode potential micro-environments effect on carbon dioxide reduction reactions (CO₂RR) and oxygen reduction reactions (ORR). MnSA catalysts generate higher CO production Faradaic efficiency of exceeding 90% at −0.9 V for CO₂RR and higher H₂O₂ yield from 0.1 to 0.6 V with excellent ORR activity. Density functional theory (DFT) calculations based on constant potential models were performed to study the mechanism of MnSA on CO₂RR. The thermodynamic energy barrier of CO₂RR is lowest at −0.9 V vs. reversible hydrogen electrode (RHE). Similar DFT calculations on the H₂O₂ yield of ORR showed that the H₂O₂ yield at 0.2 V was higher. This study provides a reasonable explanation for the role of electrode potential micro-environments.

Design of catalyst layers (CLs) with high proton conductivity in membrane electrode assemblies (MEAs) is an important issue for proton exchange membrane fuel cells (PEMFCs). Herein, an ultrathin catalyst layer was constructed based on Pt-decorated nanoporous gold (NPG-Pt) with sub-Debye-length thickness for proton transfer. In the absence of ionomer incorporation in the CLs, these integrated carbon-free electrodes can deliver maximum mass-specific power density of 198.21 and 25.91 kW·g_Pt^-1 when serving individually as the anode and cathode, at a Pt loading of 5.6 and 22.0 μg·cm^-2, respectively, comparable to the best reported nano-catalysts for PEMFCs. In-depth quantitative experimental measurements and finite-element analyses indicate that improved proton conduction plays a critical role in activation, ohmic and mass transfer polarizations.

An effective electrocatalyst being highly active in all pH range for oxygen reduction reaction (ORR) is crucial for energy conversion and storage devices. However, most of the high-efficiency ORR catalysis was reported in alkaline conditions. Herein, we demonstrated the preparation of atomically dispersed Fe-Zn pairs anchored on porous N-doped carbon frameworks (Fe-Zn-SA/NC), which works efficiently as ORR catalyst in the whole pH range. It achieves high half-wave potentials of 0.78, 0.85 and 0.72 V in 0.1 M HClO₄, 0.1 M KOH and 0.1 M phosphate buffer saline (PBS) solutions, respectively, as well as respectable stability. The performances are even comparable to Pt/C. Furthermore, when assembled into a Zn-air battery, the high power density of 167.2 mW·cm^-2 and 120 h durability reveal the feasibility of Fe-Zn-SA/NC in real energy-related devices. Theoretical calculations demonstrate that the superior catalytic activity of Fe-Zn-SA/NC can be contributed to the lower energy barriers of ORR at the Fe-Zn-N₆ centers. This work demonstrates the potential of Fe-Zn pairs as alternatives to the Pt catalysts for efficient catalytic ORR and provides new insights of dual-atom catalysts for other energy conversion related catalytic reactions.