Mg/seawater batteries driven self-powered direct seawater electrolysis systems for hydrogen production

Direct seawater electrolysis to sustainable production of hydrogen fuel is attractive, given the abundant seawater resource on Earth. Nevertheless, current seawater electrolysis systems necessarily require external power grid to drive the electrolysis process, which are neither able to achieve continuous hydrogen production nor applicable to mobile and undersea apparatuses. Herein, we demonstrate a self-powered, direct seawater electrolysis system driven by Mg/seawater batteries for continuous hydrogen production. For a case study, a heterostructured MoNi/NiMoO4 is prepared to catalyze the hydrogen evolution reaction (HER) at the cathodes of both the Mg/seawater battery and the seawater electrolysis, displaying a superior performance surpassing a commercial Pt/C with the overpotential as low as 256 mV at 10 mA cm−2 in seawater. The Mg/seawater battery achieves a peak power density of 21.08 mW cm−2, serving as a power source to drive seawater electrolysis. The self-powered system yields a total hydrogen evolution rate of 12.11 mL cm−2 h−1 and conversion efficiency of Mg-to-hydrogen up to 83.97%. Such a self-powered direct seawater electrolysis system provides an intriguing strategy for the continuous acquisition of hydrogen fuel from infinite seawater without any external power grids.