Defect engineering and electronic modulation of heterostructured CoP/CoO/N-doped carbon nanofibers as efficient bifunctional electrocatalysts for water splitting.

The development of efficient bifunctional electrocatalysts for overall water splitting is crucial for sustainable hydrogen production. In this work, we introduce a novel CoP/CoO/N-doped carbon nanofiber (CoP/CoO/N-CNFs) catalyst, synthesized through a combination of electrospinning, carbonization, oxidation, and phosphorization. The resulting heterostructure exhibits outstanding bifunctional electrocatalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The key innovations include the interface effect and synergistic interactions between CoP and CoO, enhanced by nitrogen doping and abundant oxygen vacancies, which significantly improve the catalyst's intrinsic activity, electrochemical surface area, stability, and near-unity Faraday efficiency. In situ structural evolution during electrolysis leads to the formation of active Co(OH) and CoOOH species, further enhancing catalytic performance. The optimal CoP/CoO/N-CNFs-370-1:40 catalyst demonstrates exceptional HER and OER performances, requiring overpotentials of just 79 mV and 287 mV at 10 mA·cm respectively, which is superior to many analogous non-noble electrocatalysts reported. Density functional theory (DFT) calculations reveal that the CoP/CoO heterojunction facilitates efficient charge transfer and optimizes the adsorption of reaction intermediates by modulating the d-band center, which accounts for the superior catalytic activity. This work offers a promising strategy for designing efficient non-precious bifunctional electrocatalysts for water splitting.