Interface engineering for boosting electrocatalytic performance of CoP-Co2P polymorphs for all-pH hydrogen evolution reaction and alkaline overall water splitting

Abstract

Exploring cobalt phosphide catalysts with abundant active sites and outstanding intrinsic activity for active and robust hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is highly desirable. Herein, by the fine-tuning thermal-reduction treatment of cobalt phosphonates with spherical shape, the novel carbon-wrapped CoP-Co2P polymorphs are rationally constructed. The unique hierarchical porous architecture and heterointerface of CoP-Co2P not only increase active sites but also ensure intrinsic activity. The resultant catalyst exhibits significantly boosted HER activity in a wide pH range, for instance, a current density of 10 mA cm−2 at the overpotential of 81 mV in 0.5 mol L−1 H2SO4, 109 mV in 1.0 mol L−1 KOH, and 227 mV in 1.0 mol L−1 phosphate buffer saline, and remarkable OER activity (1.53 V@10 mA cm−2 in 1.0 mol L−1 KOH), associated with the impressive stability for each reaction. Moreover, serving as the bifunctional electrocatalysts in a two-electrode electrolyzer for overall water splitting, a low cell voltage of 1.60 V can deliver a current density of 10 mA cm−2 in 1.0 mol L−1 KOH. The structural evolution process of the CoP-Co2P catalyst during electrolysis is thoroughly investigated. This work presents a new approach for designing and fabricating efficient and affordable metal phosphides for various electrochemical technologies.