Crystalline phosphides/amorphous oxides composite for energy-saving hydrogen production assisted by efficient urea oxidation reaction

Abstract

Developing active and stable electrocatalysts for urea oxidation reaction (UOR) is of great significance to energy-saving hydrogen production. Herein, we report a crystalline nickel–cobalt phosphides/amorphous phosphorous-incorporated manganese oxides composite (c-CoNiPx/a-P-MnOy) with a hierarchical structure as an efficient, durable, and multifunctional catalyst for both UOR and hydrogen evolution reaction (HER) in alkaline solution. The c-CoNiPx/a-P-MnOy electrode shows excellent UOR activity (by indirect mechanism) with the low potentials of 1.24 and 1.35 V at 10 and 100 mA cm−2, respectively, long-term stability (300 h), and excellent HER performance with a hydrogen production rate of 0.18 mmol h−1 and an average Faraday efficiency (FE) of 97.2 % at 20 mA cm−2 and high stability at 50 mA cm−2 as assisted by UOR. The outstanding catalytic performance is attributed to that: (1) the Co-incorporation into NiPx system lowers the oxidation potential of Ni2+ to Ni3+, leading to the enrichment of UOR-oriented active component (NiOOH) on the surface of the electrode; (2) CoNiPx with excellent electrical conductivity and electron-transfer ability serves as the active phase for HER; and (3) the unique configuration of a-P-MnOy and c-CoNiPx not only boosts the adsorption of reactant molecules to enhance the activity, but also enables long-term stabilities towards UOR and HER. This work highlights that the crystalline/amorphous configuration and the Mn/Co-incorporation greatly optimize the catalytic activity and stability towards both UOR and HER, which opens a new avenue to develop high-performance catalysts for the energy-saving hydrogen production.