Investigation of the Hydrogen Evolution Reaction and Hydrogen Oxidation Reaction on Nickel Single Crystal Electrodes in Alkaline Media

Abstract

Ni materials have become increasingly important with the push to develop renewable energy technologies, specifically water electrolysis and fuel cell technology. This is because Ni serves as a much cheaper alternative to commonly used noble metals such as platinum while still delivering strong catalytic activity and durability in alkaline media. As a result there have been several studies probing the fundamental interfacial electrochemical behaviour of polycrystalline Ni to further facilitate the development of these technologies. However, there are very few works involving the study of monocrystalline Ni electrodes, which are critical for the development and understanding of nanoparticle materials used in water electrolysers and fuel cells. This work aims to address this gap in the literature by providing a systematic study of both the hydrogen evolution and oxidation reactions (HER & HOR) on Ni(111), Ni(100), and Ni(110) electrodes. To study the HER, the monocrystalline electrodes are first characterized through cyclic voltammetry (CV) measurements in 0.10 M aqueous NaOH solution saturated with N2 gas at a scan rate of 50 mV sec1. After characterizing the electrodes, the activity of the HER on the Ni(hkl) electrodes was analyzed by linear sweep voltammetry (LSV) measurements at a potential scan rate of s = 0.10 V s–1 ensuring steady-state conditions. Unlike polycrystalline Ni the constructed Tafel plots display two distinct linear regions, and the general trend for the electrochemical activity towards the HER of the Ni(hkl) electrodes was found to be Ni(111) > Ni(110) > Ni(100). To study the HOR the electrodes again had to be characterized by CV measurements in 0.10 M aqueous NaOH solution that was instead saturated with H2 gas. To determine the activity of the Ni(hkl) electrodes towards the HOR, linear sweep voltammetry (LSV) measurements were performed, and from them Tafel plots were constructed. The general trend determined for the Tafel slopes in the HOR region were as follows: Ni(110) > Ni(100) > Ni(111). After completing the LSV experiments further CV measurements were performed to characterize the Ni(hkl) electrode surfaces after a long exposure to oxidative conditions. It was determined that the long range order of the monocrystalline surface was affected by the oxidation and subsequent reduction that took place.