Interface-driven electrocatalysis: Highlighting the role of NdNiO₃-NiO heterointerface in urea electro-oxidation

Abstract

Enhancing the activity of Ni-based catalysts for the electrochemical urea oxidation reaction (UOR) through the construction of heterojunctions or by heteroatom doping primarily involves the generation of polarized and/or high-valent Ni sites. However, systematic investigations of the impact of this strategy on the formation of UOR-active NiOOH species and its influence on UOR activity are scarce. Herein, we have chosen NdNiO3-NiO catalysts to systematically vary the average oxidation of Ni from + 2 to + 3 by adjusting the stoichiometric ratio of NdNiO3 to NiO. Detailed electrochemical analysis and in situ X-ray absorption spectroscopy have revealed that the catalyst systems rich in NdNiO3-NiO heterointerfaces exhibit more favourable formation of NiOOH species and, subsequently, better UOR activity. Interestingly, this enhanced UOR activity does not show an obvious positive correlation with the increase in the average oxidation state of Ni. The UOR current density follows the trend NNO2NO8 (20 % NdNiO3 and 80 % NiO) > NNO8NO2 > NNO6NO4 > NNO4NO6 > NiO > NdNiO3. The higher UOR activity of NNO2NO8 and NNO8NO2 is attributed to the more effective formation of surface-exposed heterointerfaces, thereby establishing the dependence of UOR activity on these active heterointerfaces. In situ Raman spectroscopy substantiates the formation and sustained presence of NiOOH in NdNiO3-NiO heterointerface during UOR. Theoretical studies indicate that the modulation of electronic structure through charge redistribution at the heterointerface optimizes hydroxylation, urea adsorption, and CO2 desorption, consequently leading to enhanced UOR performance. These insights bring attention to the importance of heterointerface engineering in enhancing Ni-based UOR electrocatalysts.