Oxygen vacancies and surface reconstruction on NiFe LDH@Ni(OH)2 heterojunction synergistically triggering oxygen evolution and urea oxidation reaction

Abstract

The combination of heterostructure and oxygen vacancy is one of the effective strategies to enhance the performance of oxygen evolution reaction (OER) and urea oxidation reaction (UOR). Herein, NiFe LDH@Ni(OH)2-z p-n heterostructure with abundant oxygen vacancies was successfully fabricated by multi-step strategy as electrodeposition and in-situ etching. NiFe LDH@Ni(OH)2-z p-n heterostructure can modulate the d-band center to optimize the adsorption energies of hydroxides, while oxygen vacancies also contributed to increasing the amount of active sites and reducing charge transfer resistance during OER and UOR. In-situ UV–vis spectroscopy and Fourier transform a.c. voltammetry (FTACV) unveiled the surface reconstruction of NiFe LDH to generate Ni/FeOOH which facilitated the adsorption of the reaction intermediates and accelerated charge transfer during OER and UOR. As a result, NiFe LDH@Ni(OH)2-z presented the low overpotential of 250/290 mV at 100/200 mA cm−2, small Tafel slope (43.6 mV dec−1) and excellent stability. The reaction order of OER with nearly unity indicated the fast adsorption process of OH-. NiFe LDH@Ni(OH)2-z also shows excellent electrocatalytic performance for UOR with 1.44 V at 100 mA cm−2 and Tafel slope of 37 mV dec−1. This work offers a novel approach for the formation of p-n heterostructure with rich oxygen vacancies to engineer the electronic modulation and surface reconstruction for synergistically triggering OER and UOR.