Maximizing Bifunctionality for Overall Water Splitting by Integrating H₂ Spillover and Oxygen Vacancies in CoPBO/Co₃O₄ Composite Catalyst

In the pursuit of utilizing renewable energy sources for green hydrogen (H₂) production, alkaline water electrolysis has emerged as a key technology. To improve the reaction rates of overall water electrolysis and simplify electrode manufacturing, development of bifunctional electrocatalysts is of great relevance. Herein, CoPBO/Co₃O₄ is reported as a binary composite catalyst comprising amorphous (CoPBO) and crystalline (Co₃O₄) phases as a high-performing bifunctional electrocatalyst for alkaline water electrolysis. Owing to the peculiar properties of CoPBO and Co₃O₄, such as complementing Gibbs free energy values for H-adsorption (Δ<i>G</i> _H) and relatively smaller difference in their work functions (ΔΦ), the composite exhibits H₂ spillover (HS) mechanism to facilitate the hydrogen evolution reaction (HER). The outcome is manifested in the form of a low HER overpotential of 65 mV (at 10 mA cm^-2). Moreover, an abundant amount of surface oxygen vacancies (O_v) are observed in the same CoPBO/Co₃O₄ composite that facilitates oxygen evolution reaction (OER) as well, leading to a mere 270 mV OER overpotential (at 10 mA cm^-2). The present work showcases the possibilities to strategically design non-noble composite catalysts that combine the advantages of HS phenomenon as well as O_v to achieve new record performances in alkaline water electrolysis.