Anion modulate the morphological and electronic structure of NiFe-based electrocatalyst for efficient urea oxidation-assisted water electrolysis

Renewable energy-driven water electrolysis is considered as an environmentally friendly hydrogen (H2) production technology. Replacing the oxygen evolution reaction (OER) with the urea oxidation reaction (UOR) is a more effective way to improve the energy efficiency of H2 generation. Herein, a highly efficient 2D NiFeMo-based UOR catalyst and 1D NiFeMo-based HER catalyst are prepared by adjusting the concentration of MoO4‒. The MoO4‒ can serve as the key regulator to adjust the balance between the electrolytic dissociation (α) of the reactants and the supersaturation (S) to modulate the morphological and electronic structure. The prepared 2D NiFeMo nanosheet UOR catalyst and 1D NiFeMo nanorod HER catalyst can achieve a current density of 100 mA cm−2 at a potential of 1.36 and 0.062 V, respectively. In a HER/UOR system, a cell voltage of 1.58 V is needed to achieve a current density of 100 mA cm−2. The HER/UOR system operated stably for over 60 h with 3 times the direct water electrolysis current density. Moreover, the in situ Raman characterization coupled with XPS analysis clarifies that the addition of high-valence Mo can lower the transition energy barrier between the low and high oxidation state of Ni, which in turn lowers the overpotential of UOR. This work provides a novel strategy for synthesizing morphology-dependent electrocatalysts for different catalytic systems.