Nickel Cathode Passivation in Alkaline Water Electrolysis

Abstract

During water electrolysis in alkaline electrolytes, nickel cathodes deactivate over time. The presence of soluble iron species in the alkaline electrolyte mitigates the deactivation. Congruently, iron deposits are observed on the Ni electrodes. The role of the iron deposits in preventing deactivation is explored in this work. Nickel deactivation has been proposed to be due to the formation of a surface Ni hydride phase. A complete coating of metallic iron is known to prevent nickel electrode deactivation. In industrial electrolysis, however, there is never complete coverage of the Ni electrode by iron deposition. In this work, we focused on determining the extent of iron surface coverage required to prevent nickel deactivation. A metallic grid placed over the nickel electrodes during iron vacuum sputtering was used to achieve iron coverages ranging from 20 to 100%.