Efficient bifunctional catalysts synthesized from three-dimensional Ni/Fe bimetallic organic frameworks for overall urea electrolysis

Abstract

Herein, a three-dimensional (3D) Ni/Fe bimetallic organic framework (MOF-Ni@MOF-Fe) with a structure of rhombus blocks on nanosheets is synthesized on Ni foam by a 2-step solvothermal method. After sulfide reaction, MOF-Ni@MOF-Fe–S is vulcanized by MOF-Ni@MOF-Fe with a structure of interwoven and folding nanosheets. Meanwhile, Ni₃S₂ is formed under the influence of iron. This special structure makes MOF-Ni@MOF-Fe–S to expose more active sites. MOF-Ni@MOF-Fe–S shows superior urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) performance. When MOF-Ni@MOF-Fe–S is used as UOR and HER catalysts, it has low potentials of 1.347 V (vs. RHE) at 10 mA cm⁻² and 0.145 V (vs. RHE) at 10 mA cm⁻² in 1.0 M KOH with 0.5 M urea, respectively. MOF-Ni@MOF-Fe–S as a bifunctional electrode is assembled as an alkaline urea electrolyzer, showing catalytic activity at a low cell voltage of 1.539 V at 10 mA cm⁻² and excellent stability during 10 h chronopotentiometry analysis.