Membraneless water electrolysis enabled by flow and porous electrode design for bubble separation

Intensification of water electrolysers is essential to lower the cost of green hydrogen. In this study we design and test a novel alkaline water electrolyser operating without a separator diaphragm (membraneless), using instead a convective flow barrier between electrodes, saving material and energy cost. For the first time, high-speed imaging has confirmed conditions required for a clear electrode gap, with bubble separation up to high current density > 4 A cm −2 . This design was enabled through computational fluid dynamics simulations (OpenFOAM) developed for coupling ionic and kinetic charge transport in the electrolyte and electrodes with the insulating effect of bubble two-phase flow. A pseudo-2D, 3D-printed transparent electrolyser cells validated the fluid flow vectors using particle image velocimetry of bubbles, as well as tracking bubble transport inside the cell. The simulated current density distribution on the electrodes, along with the two-phase flow simulations showed membraneless separation of bubbles was possible and later proven in the experiments using an inactive porous barrier layer with pore diameter of < 51 μ m. Modelling at larger scale detailed that two-phase flow of bubbles effects charge-transfer instead of ohmic transport in this system. Theoretical single-phase flow and transport models predict at 50 cm scale it can operate at low current density with low crossover ( < % 1 with minimum Reynolds number of 80) but experimental measurements indicated precise control of electrolyte mixing is required to acheive this in practice. Scenarios investigated in this study de-risk the next steps of reducing the electrode gap and growth of catalyst, enabling predictions of 1 A cm −2 at 1.8 – 2.5 V. • PIV and transparent 3D-printed electrolysers used to study bubble, flow patterns. • Porous electrode and flow design achieve electrolysis with no crossover at 4 A/cm 2 . • Coupled two-phase flow and electrochemistry models used to predict cell potential. • Hydrophilic barrier layer with small pores enables gas separation in electrodes. • Convective flow barrier yields low crossover ( < 0.1 %vol) at 0.5 m, 0.1 A/cm 2 .