New electrolyzer principles: decoupled water splitting

As we move away from fossil fuels toward renewable energies, green hydrogen produced by water electrolysis becomes a promising and tangible solution for the storage of excess energy for power generation and grid balancing, and for the production of decarbonized fuel for transportation, heating, and other applications. To compete with the price set by steam methane reforming and other carbon-based hydrogen production technologies, a true paradigm shift in water electrolysis technologies is required. In this chapter, we discuss disruptive decoupled water splitting schemes, in which the concurrent production of hydrogen and oxygen in close proximity to each other in conventional electrolysis is replaced by time- or space-separated hydrogen and oxygen production steps. We present the main decoupling strategies, including electrolytic and electrochemical—chemical water splitting cycles, and the redox materials that facilitate them by mediating the ion exchange between the hydrogen and oxygen evolution reactions. Decoupled water splitting offers increased flexibility and robustness and provides new opportunities for hydrogen production from renewable sources.