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

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 per-formance 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.

Automated summary

In this study, a crystalline nickel-cobalt phosphides/amorphous phosphorous-incorporated manganese oxides composite was developed as an efficient, durable, and multifunctional catalyst for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) in alkaline solution. The composite exhibited excellent UOR activity and HER performance, as well as long-term stability. The outstanding catalytic performance was attributed to the incorporation of Co into the NiPx system, which lowered the oxidation potential of Ni2+, leading to the enrichment of UOR-oriented active component on the electrode surface. In addition, the excellent electrical conductivity and electron-transfer ability of CoNiPx, along with the unique configuration of a-P-MnOy and c-CoNiPx, contributed to enhanced reactant adsorption and long-term stabilities towards UOR and HER.