Stability of vapor phase water electrolysis cell with anion exchange membrane

The production of renewable hydrogen gas with a vapor-fed solar hydrogen generator is an appealing strategy. In such all solid-state standalone device no liquid electrolyte is required. The use of an anion exchange membrane separating cathode and anode compartments is particularly advantageous and its performance matches the performance of liquid phase electrolysis. In this work, a vapor-fed water electrolyzer was investigated comprising a poly(vinyl alcohol) anion exchange membrane impregnated with 4M KOH solution and Ni-based catalysts. The performance was evaluated over time periods of hours to days. The vapor fed device showed similar initial activity as an electrolysis setup with the same electrodes immersed in 1M KOH liquid electrolyte. To sustain a current density of 10 mA/cm(2), it was observed that the required potential initially increased but eventually reached a steady state at ca. 1.9 V. From a D2O isotope labelling experiment of the vapor phase, it was noticed that the system initially consumed H2O absorbed in the membrane to produce H-2. After this water of the membrane was consumed, water to be split is taken from the vapor phase and water mass transfer limitation starts occurring. Once water mass transfer and splitting reactions are matched, a steady state potential is reached. The results of this work are encouraging and pave the way to efficient stable operation of vapor-fed solar hydrogen generators.