Understanding the Enhancement of Electrocatalytic Activity toward Hydrogen Evolution in Alkaline Water Splitting by Anodically Formed Oxides on Ni and C‐containing Ni

Abstract

AbstractNickel oxides/hydroxides are active electrocatalysts for the hydrogen evolution reaction (HER) in alkaline water electrolysis. A durable activity of Ni with Ni(OH)2 was observed mainly on porous substrates, such as nickel foam or carbon cloth. Herein, we examined the effect of anodic oxidation on the HER using smooth samples of Ni, Ni with graphene, and Ni with C introduced by a low‐temperature plasma treatment. Electrochemical measurements in 1.0 M KOH showed that a strong activation toward HER was achieved by voltammetric cycling to potentials of the formation of Ni3O4, Ni2O3, and/or NiO2. The presence of C enhanced this activation. The effect of C was explained by the accumulation of larger amounts of these products as a result of a deteriorated passivity, their higher compactness (demonstrated by higher impedance), and the longer durability under conditions of HER (revealed by a slower cathodic reduction). The durability of oxides in porous C structures can be explained by anodic potentials in pores owing to the ohmic potential drop. It is proposed that anodic oxidation might be used for the reactivation of Ni cathodes for water electrolysis.