Scalable engineering of the active NiMoO4/MoO2 catalyst by rapid Joule heating for industrial pre-treated seawater electrolysis

Abstract

Adopting reverse osmosis (RO) for seawater desalination is well established and suitable for coupling with alkaline water electrolysis (ALK) systems. The progressive accumulation of residual ions during the reaction, along with the limited energy efficiency of industrial ALK cells, drives the requirement to explore scalable strategies for engineering highly active catalysts. Herein, a facile water bath followed by a rapid Joule heating method has been reported for scalable fabrication of large-scale electrodes. Typically, a NiMoO₄/MoO₂ cathode with a size of 10 cm × 10 cm was grown on a nickel mesh (NM) substrate. NiMoO₄/MoO₂ achieved an overpotential of 345.2/349.2 mV at 500 mA cm⁻² in alkaline freshwater/seawater, with stability at 1 A cm⁻² for 1000 h. Further experiments on the ALK device adopting quasi-industrial conditions (6 M KOH RO seawater, 60 °C) showed that NiMoO₄/MoO₂∥NM delivered a current density of 500 mA cm⁻² with a reduction of the required voltage by 1 V in comparison with NM∥NM, displaying an impressive Faraday efficiency of 90.2% and electricity consumption of 4.48 kW h Nm⁻³ H₂, demonstrating the potential for industrial applications. The characterization and experimental results verified the vital role of Joule heating and the optimised electronic structure in the NiMoO₄/MoO₂ heterostructure, resulting in an efficient hydrogen evolution reaction (HER).