Hydrogen Evolution Reaction on Ultra-Smooth Sputtered Nanocrystalline Ni Thin Films in Alkaline Media—From Intrinsic Activity to the Effects of Surface Oxidation

Abstract

Highly effective yet affordable non-noble metal catalysts are a key component for advances in hydrogen generation via electrolysis. The synthesis of catalytic heterostructures containing established Ni in combination with surface NiO, Ni(OH)2, and NiOOH domains gives rise to a synergistic effect between the surface components and is highly beneficial for water splitting and the hydrogen evolution reaction (HER). Herein, the intrinsic catalytic activity of pure Ni and the effect of partial electrochemical oxidation of ultra-smooth magnetron sputter-deposited Ni surfaces are analyzed by combining electrochemical measurements with transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The experimental investigations are supplemented by Density Functional Theory and Kinetic Monte Carlo simulations. Kinetic parameters for the HER are evaluated while surface roughening is carefully monitored during different Ni film treatment and operation stages. Surface oxidation results in the dominant formation of Ni(OH)2, practically negligible surface roughening, and 3–5 times increased HER exchange current densities. Higher levels of surface roughening are observed during prolonged cycling to deep negative potentials, while surface oxidation slows down the HER activity losses compared to as-deposited films. Thus, surface oxidation increases the intrinsic HER activity of nickel and is also a viable strategy to improve catalyst durability.

Kinetics of Hydrogen Evolution Reaction on Monometallic Bulk Electrodes in Various Electrolytic Solutions

“…We could argue that oxidation could increase ESA and, thus, lead to enhanced activity. However, our recent work on sputtered smooth Ni films demonstrated that such changes are negligible (~1% increase in ESA) [45].…”

Influence of Substrate Preparation on the Catalytic Activity of Conical Ni Catalysts

“…Nickel and its alloys are commonly used catalysts in many reactions, such as watersplitting [8][9][10], ethanol oxidation [11,12], and CO 2 reforming of methane [13,14]. They can be synthesized in several forms, e.g., bulk coatings [15,16], thin films [17,18], micropatterned electrodes [19,20], nanosheets [21,22], and sponges [23,24]. However, the substrate used is also essential in enhancing catalytic performance [25].…”