Influence of process conditions on gas purity in alkaline water electrolysis

In this paper the influence of operating conditions on the product gas purity of a zero-gap alkaline water electrolyzer was examined. Precise knowledge of the resulting gas purity is of special importance to prevent safety shutdown when the electrolyzer is dynamically operated using a renewable energy source. The investigation in this study involves variation of temperature, electrolyte concentration and flow rate as well as different electrolyte management concepts. The experiments were carried out in a fully automated lab-scale electrolyzer with a 150 cm² zero-gap cell and approximately 31 wt% KOH at ambient and balanced cathodic and anodic pressure. The purity of the evolved gases was measured via online gas chromatography. It can be seen from the experiments that a temperature increase and flow rate decrease reduces the gas impurity when mixing catholyte and anolyte. A further reduction of gas impurity can be achieved when both cycles are being separated and a dynamic cycling strategy is applied.