were obtained for the two techniques, with little bubble formation observed up to 0.17-0.20 A cm -2 . At higher current densities, up to around 0.6 A cm -2 , bubbles were formed predominantly at the cathode. Given that commercial alkaline electrolysers typically operate at current densities up to 0.6 A cm -2 , this suggests that minimizing bubble formation at the cathode offers the key opportunity for further performance improvements in the capillary-fed cell. The cathode and anode produced bubbles at similar rates at still higher current densities, to 1 A cm-2. Even at 1 A cm -2 , the rate of bubble formation on the electrodes was substantially lower than in conventional, 'bubbled' electrolysis cells. In the course of this work, the previously reported high electrochemical performance of the capillary-fed cell was independently confirmed.