Sustainable and energy-saving hydrogen production via binder-free and in situ electrodeposited Ni–Mn–S nanowires on Ni–Cu 3-D substrates

Abstract

Electrochemical water splitting, with its oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), is undoubtedly the most eco-friendly and sustainable method to produce hydrogen. However, water splitting still requires improvement due to the high energy consumption caused by the slow kinetics and large thermodynamic potential requirements of OER. Urea–water electrolysis has become increasingly appealing compared to water-splitting because of the remarkable decline in the cell potential in the hydrogen production process and less energy consumption; it also offers a favorable opportunity to efficiently treat wastewater containing a significant amount of urea. In this work, Ni–Mn–S/Ni–Cu nano–micro array electrocatalysts were synthesized by a two-step and binder-free electrochemical deposition technique and investigated as an effective electrode for the HER and urea oxidation reaction (UOR). According to the electrochemical results, the optimized electrode (Ni–Mn–S/Ni–Cu/10) showed excellent electrocatalytic activity for the HER (64 mV overpotential to achieve the current density of 10 mA cm⁻² and Tafel slope of 81 mV dec⁻¹) in alkaline solution. When Ni–Mn–S/Ni–Cu/10 is employed as a UOR anode in an alkaline solution containing urea, it achieves a current density of 10 mA cm⁻² at 1.247 V vs. RHE. In addition, when the optimized sample was utilized as a bi-functional electrode for overall urea–water electrolysis (HER-UOR), the cell voltage reached 1.302 V at 10 mA cm⁻² (which is 141 mV less than that for HER-OER). The electrocatalytic stability results unequivocally revealed small changes in voltage during a 24 h test and showed good durability. This non-noble metal electrocatalyst, prepared by the electrodeposition synthesis method, is a promising solution to implement low-cost hydrogen production and wastewater treatment.