The sluggish kinetics of Oxygen Reduction Reaction (ORR) at the cathode in proton exchange membrane fuel cells or metal-air batteries requires highly effective and stable electrocatalysts to boost the reaction. The low abundance and high price of Pt-based electrocatalysts hamper the widespread application of proton exchange membrane fuel cells and metal-air batteries. As promising alternatives, metal-free carbon materials, especially upon doping heteroatoms or creating defects demonstrated excellent ORR activity, which is as efficient as or even superior to commercial platinum on carbon. Significant progress on the development of advanced carbon materials as highly stable and durable catalysts has been achieved, but the catalytic mechanisms of these materials still remain undistinguished. In present review, we summarized the up-to-date progress in the studies of carbon materials, and emphasized on the combination of experiment and theory to clarify the underlying mechanisms of these materials. At last, we proposed the perspectives on the proper strategies of elucidating the mechanisms of carbon materials as electrocatalysts towards ORR.

To achieve zero-carbon economy, advanced anode catalysts are desirable for hydrogen production and biomass upgrading powered by renewable energy. Ni-based non-precious electrocatalysts are considered as potential candidates because of intrinsic redox attributes, but in-depth understanding and rational design of Ni site coordination still remain challenging. Here, we perform anodic electrochemical oxidation of Ni-metalloids (NiP_x, NiS_x, and NiSe_x) to in-situ construct different oxyanion-coordinated amorphous nickel oxyhydroxides (NiOOH-TO_x), among which NiOOH-PO_x shows optimal local coordination environment and boosts electrocatalytic activity of Ni sites towards selective oxidation of methanol to formate. Experiments and theoretical results demonstrate that NiOOH-PO_x possesses improved adsorption of OH* and methanol, and favors the formation of CH₃O* intermediates. The coordinated phosphate oxyanions effectively tailor the d band center of Ni sites and increases Ni-O covalency, promoting the catalytic activity. This study provides additional insights into modulation of active-center coordination environment via oxyanions for organic molecules transformation.

A paired electrochemical refinery toward the cathodic nitrate reduction reaction (NO₃RR) and anodic glycerol oxidation reaction (GOR) driven by renewable electricity could generate high value-added ammonia and formic acid simultaneously. However, both cathode and anode electrocatalysts often suffer from low efficiency and unclear reconstruction. Herein, we prepare a non-noble NiCu–OH nanocomposite precatalyst composed of crystalline Cu₂(OH)₃(NO₃) and amorphous Ni(OH)₂, which can be reconstructed into high-activity and stable cathodic NO₃RR and anodic GOR electrocatalysts under operating conditions. Various in situ and ex situ experiments demonstrate that NiCu–OH could convert into active Cu nanoparticles coupled with amorphous Ni(OH)₂ under cathodic NO₃RR conditions. Meanwhile, under anodic GOR conditions, NiCu–OH-derived bimetal oxide (NiCuO) changes into active NiOOH species composited with Cu vacancy-rich CuO. Furthermore, an actual paired electrochemical refinery with the reconstructed NiCu-based catalysts toward the NO₃RR and GOR shows a low potential of 1.37 V at a current density of 100 mA cm⁻² to continuously produce ammonium and formate. This study provides a new paradigm for the design of an electrochemical refinery with reconstructed non-noble electrocatalysts toward chemical upgradation.