Enhanced electrocatalytic performance for overall water splitting: exploring heterojunctions and vacancy-engineered nanosheets

Abstract

This study presents a novel approach to enhancing electrocatalytic performance for overall water splitting (OWS) through the strategic construction of distinct catalytic structures. We propose an in situ transformation method that partly converts ultrathin, two-dimensional zeolitic imidazolate framework (ZIF-67) nanosheets into layered double hydroxide (LDH) nanosheets, resulting in catalysts with tailored properties. The in situ construction of 2D ZIF-67/CoNi LDH heterojunctions with optimization of metal–oxygen bonds and oxygen vacancies significantly increases the number of accessible catalytic active sites and enhances charge transport efficiency; the reaction intermediates are more easily adsorbed and desorbed during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) processes. Characterization studies, including the use of polarization curves, electrochemical active surface area (EASA), and X-ray photoelectron spectroscopy (XPS), reveal abundant accessible active sites and enhanced charge/mass transfer capabilities. Notably, the Co/Ni-LZ-24 NTs achieved an overpotential of only 80.50 mV for the HER, while Co/Ni-LZ-36 NTs demonstrated a low overpotential of 289.59 mV for the OER at a current density of 10 mA cm⁻² in 1.0 M KOH solution. Furthermore, the coupled catalyst system yields an impressive OWS performance, requiring a minimal cell voltage of 1.59 V at the same current density. This work underscores the importance of synergistic design principles in advancing efficient and sustainable OWS technologies.