N-Doped Carbon-Incorporated Cobalt–Iron Mixed-Metal Phosphide Nanoboxes as Efficient Bifunctional Catalysts for Overall Water Splitting

Optimizing the composition and structure of nanocatalysts is an efficient approach to achieving the top electrocatalytic performance. However, the construction of hollow nanocomposites composed of metal phosphides and highly conductive carbon to promote the electrocatalytic performance of metal phosphide-based catalysts is rarely reported. Herein, a CoFeP/C nanobox nanocomposite consisting of Co-Fe mixed-metal phosphides and N-doped carbon was successfully fabricated through an ion-exchange phosphidation strategy derived from ZIF-67 nanocubes. Benefiting from the synergistic effects between multiple components and the unique hollow structure, CoFeP/C nanoboxes can catalyze the alkaline oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with high activity and stability. Furthermore, in the construction of an alkaline water electrolyzer using CoFeP/C nanoboxes as both OER and HER catalysts, they were capable of efficiently splitting water with a current density of 10 mA cm^-2 achieved by applying only 1.62 V of cell voltage and exhibited outstanding durability. Density functional theory calculations demonstrate that synergistic effects among multiple components in CoFeP/C nanoboxes can lower the hydrogen adsorption free energy of the HER and OER energy barrier of the rate-determining step, thus promoting the catalytic reactions. The design and synthesis of CoFeP/C nanoboxes highlight the importance of the composition and structural characteristics in achieving high-performance water electrolysis.