Revealing a hidden superpower: Sulfur doping triggers reconstruction of MnCr LDH for efficient water splitting and Mg/seawater batteries

Electrolyzing seawater presents a promising strategy to address the energy crisis. The optimally sulfur-doped S 0.45 -MnCr layered double hydroxide (LDH) catalyst demonstrates exceptional hydrogen evolution reaction (HER) performance in alkaline seawater at 50 °C, requiring overpotentials of only 57.9 mV and 245.4 mV to achieve 10 and 500 mA cm −2 , respectively. For overall seawater splitting, it requires only 1.72 V to deliver 100 mA cm −2 . When used as a cathode in a magnesium-seawater batteries (MSBs), it delivers a power density of 7.80 mW cm −2 . Sulfur doping simultaneously triggers the formation of highly active MnCO 3 during synthesis. Characterization confirms that sulfur doping promotes chromium leaching, thereby enlarging the electrochemical active surface area (ECSA). In situ XRD analysis at various potentials verifies the formation of additional active MnCO 3 species during HER, consistent with the activity enhancement observed in chronopotentiometric measurements. This work offers novel insights for designing bifunctional catalysts for direct seawater electrolysis.