| Summary: | The intermittent and volatile nature of renewable energy sources threatens the stable operation of power grids, necessitating dynamically operated energy storage. Power-to-gas technology is a promising method for managing electricity variations on a large gigawatt (GW) scale. The electrolyzer is a key component that can convert excess electricity into hydrogen with high flexibility. Recently, organic/inorganic composite separators have been widely used as diaphragm membranes; however, they are prone to increase ohmic resistance and gas crossover, which inhibit electrolyzer efficiency. Here, we show that the ceria nanoparticle and polysulfone composite separator exhibits a low area resistance of 0.16 Ω cm<sup>2</sup> and a hydrogen permeability of 1.2 × 10<sup>–12</sup> mol cm<sup>–1</sup> s<sup>–1</sup> bar<sup>–1</sup> in 30 wt% potassium hydroxide (KOH) electrolyte, which outperformed the commercial separator, the Zirfon PERL separator. The cell using a 100 nm ceria nanoparticle/polysulfone separator and advanced catalysts has a remarkable capability of 1.84 V at 800 mA cm<sup>−2</sup> at 30 wt% and 80 °C. The decrease in the average pore size of 77 nm and high wettability (contact angle 75°) contributed to the reduced ohmic resistance and low gas crossover. These results demonstrate that the use of ceria nanoparticle-based separators can achieve high performance compared to commercial zirconia-based separators.
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