Electrochemical water-splitting reactions (hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)) and oxygen redox reactions (oxygen reduction reaction (ORR) and OER) are core processes for electrochemical water-splitting devices, rechargeable metal–air batteries, and regenerative fuel cells. Developing highly efficient non-noble multifunctional catalysts in the same electrolyte is an open challenge. Herein, efficient Co–N–C electrocatalysts with a mixed structure comprising Co–N moieties and Co nanoparticles encapsulated in a N-doped carbon layer were prepared via pyrolysis of a new structure of Co-coordinated bis­(imino)­pyridine polymer constructed by 2,6-diacetylpyridine and 3,3′-diaminobenzidine. Results demonstrate that Co ion sources have a remarkable impact on the final Co–N–C performance. The Co–N–C catalyst prepared using cobalt acetate as a precursor displays remarkable overall multifunctional performance. It needs only a cell voltage of 1.66 V (obtained from the half-cell test) for the water-splitting reaction (HER/OER) to reach 10 mA·cm–2 in 1.0 M KOH, and the overall oxygen redox activity (OER/ORR) is 0.72 V in 0.1 M KOH, outperforming the reported nonprecious metal catalysts. The excellent activity is attributable to the synergistic effects between active sites with encapsulated metallic Co for HER and OER and Co–N moieties for ORR.

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Developing photoanodes that can split water with low (or even without) externally applied bias is a critical challenge for achieving efficient solar-driven photoelectrochemical water oxidation. Here, we proposed a flux-assisted oriented crystal growth route to minimize the drawbacks of Ta 3 N 5 photoanode, including the following: (1) Crystallographic-oriented growth minimizes the negative effect of electronic structure anisotropy of the Ta 3 N 5 , facilitating the directional fast charge transfer in having lighter carrier effective mass of (b,c)-axes directions. (2) Reducing crystal defects suppressed surface recombination of carriers and released the surface Fermi level pinning effect. (3) Increment of oxygen-impurity electron donor by Sc doping improved the electrical conductivity, promoting the bulk charge separation and transfer. Specifically, the onset potential of Ta 3 N 5 photoanode was dramatically negatively shifted to 0.4 V RHE , and thereby afforded a 0.82% half-cell solar-to-hydrogen efficiency.