Insights over the in-situ grown copper sulfide/NiFe-LDH composites for alkaline and urea water electrolysis

Abstract

Harnessing hydrogen fuel through electrocatalytic water splitting offers an eco-friendly alternative to the traditional fossil fuels. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are the two half-cell reactions, that make up the electrocatalytic water splitting. Replacing the sluggish OER in the electrocatalytic water splitting with less energy demanding urea oxidation reaction (UOR) might benefit overall water splitting with reduced cell voltages. On the other hand, developing electrodes based on non-precious metals is essential for cost-effective and efficient water splitting. Herein, composites comprising non-precious nickel iron layered double hydroxide (NiFe-LDH) and copper (II) sulfide (CuS) are grown over the nickel foam and subjected to electrochemical measurements for alkaline water electrolysis (AWE) and urea water electrolysis (UWE). Structural and morphological investigations reveal that the 10 wt% CuS composited NiFe-LDH (NFCS10) is supposed to have effective catalytic features for water electrolysis. The electrochemical investigations in the three-electrode system with silver/silver chloride (Ag/AgCl, reference electrode) and platinum (Pt, counter electrode) revealed that the NFCS10 requires only a minimal overpotential (Ƞ50) of 235 mV for UOR and 400 mV for OER respectively. For bifunctional performance, NFCS10 requires an overall cell potential (OCP) of 1.65 V and 1.50 V to reach 10 mA/cm2 current density in AWE and UWE, respectively. X-ray photoelectron spectroscopy identifies the enrichment of oxygen vacancies in NiFe-LDH:CuS heterostructure, which could influence the charge transport and stability of the proposed electrode. This study emphasizes the interfacial interactions between the LDH and metallic sulfide, as well as their impact on the electrocatalytic activity in alkaline and urea water splitting.