Renewable, or green, hydrogen will play a critical role in the decarbonisation of hard-to-abate sectors and will therefore be important in limiting global warming. However, renewable hydrogen is not cost-competitive with fossil fuels, due to the moderate energy efficiency and high capital costs of traditional water electrolysers. Here a unique concept of water electrolysis is introduced, wherein water is supplied to hydrogen- and oxygen-evolving electrodes via capillary-induced transport along a porous inter-electrode separator, leading to inherently bubble-free operation at the electrodes. An alkaline capillary-fed electrolysis cell of this type demonstrates water electrolysis performance exceeding commercial electrolysis cells, with a cell voltage at 0.5 A cm−2 and 85 °C of only 1.51 V, equating to 98% energy efficiency, with an energy consumption of 40.4 kWh/kg hydrogen (vs. ~47.5 kWh/kg in commercial electrolysis cells). High energy efficiency, combined with the promise of a simplified balance-of-plant, brings cost-competitive renewable hydrogen closer to reality.

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‘Green’ hydrogen produced from water electrolysis powered by renewable energy will play a critical role in the future global energy transition to ‘net zero’ carbon emissions. To this end, intensive...

Physical properties of aqueous KOH solutions are crucial to the design and operation of alkaline electrolyzers but have been scarcely and sometimes unreliably reported. Obtaining published data for various properties currently requires timeconsuming searches and subsequent interpretation, interpolation, and extrapolation. This work collates and critically analyzes published data for a range of physical properties relevant to alkaline electrolysis, including the density, viscosity, conductivity, surface tension, oxygen/hydrogen solubility, oxygen/hydrogen diffusivity, and water vapor pressures of aqueous KOH solutions, as a function of temperature, KOH molarity, and pressure. Correlation functions, in the form of excel spreadsheets, have been developed to allow interpolation of the most reliable data and computation of desired quantities at specific temperatures, pressures, and KOH concentrations. Composite models incorporating these properties have been developed for automated computation of (i) diffusive gas crossover and (ii) gas production volumes, including (iii) water vapor content, and associated (iv) dissolved gas concentrations in the liquid electrolyte, as a function of KOH concentration, temperature, pressure, current density, and separator thickness and porosity. These spreadsheets are provided in the Supporting Information, as tools and reference points for researchers and practitioners in alkaline electrolysis.