Facile Protocol for Alkaline Electrolyte Purification and Its Influence on a Ni–Co Oxide Catalyst for the Oxygen Evolution Reaction

We report a simple and effective electrochemical method to remove Fe impurities from commercial KOH electrolyte. We therefore utilize a MoS₂ catalyst deposited on porous Ni foam as both the anode and cathode in a two-electrode electrolysis setup. After 12 h of constant galvanostatic electrolysis at 100 mA, the Fe impurities from the KOH electrolyte were successfully removed, as confirmed by means of inductively coupled plasma optical emission spectroscopy analysis. In the purified KOH, a Ni–Co₃O₄ composite oxide catalyst showed no Fe-induced activation. In contrast, we directly observed the uptake of Fe on the Ni–Co₃O₄ catalyst from the nontreated electrolyte during catalyst operation using a coupled spectroelectrochemical setup. Interestingly, we further identified an influence on the dissolution behavior of Ni and Co in the presence of Fe impurities. Whereas hitherto mainly the activation effect of Fe impurities has been discussed, we hereby show that they additionally suppress corrosion under reaction conditions. Using our fast and low-cost method for the purification of large amounts of electrolyte, catalyst materials can be widely studied without these additional effects induced by Fe impurities in commercial KOH.