Controlled synthesis of nickel phosphides: Mechanistic insights and catalytic activity in hydrogen peroxide production

Abstract

Strategically designing oxygen reduction reaction (ORR) electrocatalysts based on electronic structure is a pivotal method for enhancing the electrocatalytic activity and selectivity of two-electron (2e) reactions. While many transition metal phosphides, including Ni_xP_y, have demonstrated activity in electrocatalytic reactions, their effectiveness in 2e ORR electrocatalysis is still uncertain. In this study, guided by the theoretical insights into high electroactivity unveiled by the d-band center (E_d) theory, we engineered and synthesized Ni₂P/Ni₅P₄ nanosheets (NSs). Functioning as 2e ORR electrocatalysts in alkaline environments, the Ni₂P/Ni₅P₄ NSs exhibited outstanding 2e selectivity of up to 95%, with an electron transfer number close to two. Demonstrating a Faradaic efficiency exceeding 95% over a wide potential range (0.2–0.5 V), these NSs displayed extended stability for over 48 h, outperforming most transition metal-based catalysts reported in literature. By employing density functional theory (DFT) calculations, the increased activity is ascribed to the adjustment of the d-band center at the engineered heterostructure interface, effectively regulating the adsorption energy of oxygen-containing intermediates (*OOH). This study offers crucial insights into the methodical design and production of effective transition metal phosphide electrocatalysts guided by the d-band center theory.