Hollow CoP Encapsulated in an N-Doped Carbon Nanocage as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Abstract

Exploring high-efficiency and earth-abundant bifunctional electrocatalysts for overall water splitting is of great significance to meet the requirement of the hydrogen economy, but still faces many challenges. In this work, we propose the chemical etching, successive carbonization, and phosphorization treatment strategy of solid ZIF-67 (ZIF = zeolitic imidazole framework), constructing a hybrid nanostructure with CoP nanoparticles embedded in a hollow N-doped carbon nanocage (h-CoP@NC). The elaborate hollow porous structure is conducive to effectively exposing more active sites and shortening mass-transportation pathways. The nitrogen-doped carbon layer would protect the active CoP units from agglomeration and enhance the conductivity. These structural factors synergistically contribute to the enhanced electrocatalytic performance. As a result, the carbonization-temperature-optimized h-CoP@NC-900-300 catalyst can efficiently catalyze both hydrogen and oxygen evolution reactions with respective overpotentials of 196 and 339 mV to afford a current density of 10 mA cm–2, outperforming other contrast catalysts. Impressively, to comprise this optimal electrocatalyst into both an anode and cathode of the alkaline electrolyzer, a cell voltage of 1.764 V is needed for achieving a current density of 10 mA cm–2 with continuously operational ability. This present study would shed light on the exploration of advanced transition-metal-based electrocatalysts by composition and structure design for energy conversion applications.