Electrochemical – chemical cycle for high-efficiency decoupled water splitting in a near-neutral electrolyte

Green hydrogen produced by water splitting using renewable electricity is essential to achieve net-zero carbon emissions. Present water electrolysis technologies are uncompetitive with low-cost grey hydrogen produced from fossil fuels, limiting their scale-up potential. Disruptive processes that decouple the hydrogen and oxygen evolution reactions and produce them in separate cells or different stages emerge as a prospective route to reduce system cost by enabling operation without expensive membranes and sealing components. Some of them divide the hydrogen or oxygen evolution reactions into electrochemical and chemical sub-reactions, leading the way to high efficiency. However, high efficiency was demonstrated only in a batch process with thermal swings that present operational challenges. This work introduces a breakthrough process that produces hydrogen and oxygen in separate cells and supports high-efficiency continuous operation in a membraneless system. We demonstrate high Faradaic and electrolytic efficiency and high-rate operation in a near-neutral electrolyte of NaBr in water.