Influence of the NaOH Concentration on the Hydrogen Electrode Reaction Kinetics of Ni and NiCu Electrodes

Abstract

Nickel is a promising electrocatalyst for hydrogen electrode reactions in alkaline media. Its electrocatalytic activity for hydrogen oxidation and evolution reactions can be enhanced when its surface is partially covered by Ni (hydr)oxides or by associating it with Cu. In this work, the influence of the NaOH concentration on the hydrogen electrode kinetics on various Ni electrodes is investigated. On metallic Ni, the electrocatalytic activity (measured as an exchange current density normalized to the surface area of Ni) is almost constant between pH 12 and 14, whereas it decreases by a factor of two on partially oxidized Ni and on the NiCu/C electrode. Analyzing the current potential curves with the help of microkinetic modeling reveals that the Had and OHad binding energies on Ni do not depend on pH, whereas the rate constants of the Volmer and Heyrovsky reactions decrease with pH. The pH effect on the electron transfer elementary act is briefly discussed in the framework of a quantum mechanical theory.

Recent Advances in the Understanding of Nickel-Based Catalysts for the Oxidation of Hydrogen-Containing Fuels in Alkaline Media

“…While further (preferably in situ spectroscopic) studies are required to unveil the surface state of Ni electrodes during the HOR and thus unambiguously confirm its influence on the reaction kinetics, it should be emphasized that the model proposed by Oshchepkov et al currently presents the most consistent explanation of the available literature data. [48][49][50][51][52] Armed with this knowledge, Oshchepkov et al have recently reported a partially oxidized Ni-NiOx/XC-72 electrocatalyst prepared by electrodeposition technique, which possesses HOR specific activity at the level of a commercial Pd/C electrocatalyst (Table 1). 137 It has been demonstrated that the conductivity.…”

“…In addition, Oshchepkov et al have recently pointed out to the influence of the surface state of Ni electrodes on their HOR/HER activity in the potential interval -0.2 < E < 0.5 V vs RHE. [48][49][50][51][52] Below the most relevant information regarding electrochemistry of Ni electrodes in alkaline media is briefly summarized.…”

“…The behavior of nickel in alkaline media has been recently summarized by the groups of MacDougall , and Jerkiewicz, − who discussed in detail various potential-dependent processes taking place on the surface of Ni electrodes. In addition, Oshchepkov et al have recently reported on the influence of the surface state of Ni electrodes on their HOR/HER activity in the potential interval −0.2 V < E < 0.5 V vs RHE. − Below, the most relevant information regarding the electrochemistry of Ni electrodes in alkaline media is briefly summarized.…”

“…14%, based on the data presented in ref ), which goes along with the increase of the HOR current. While further (preferably in situ spectroscopic) studies are required to unveil the surface state of Ni electrodes during the HOR and thus unambiguously confirm its influence on the reaction kinetics, it should be emphasized that the model proposed by Oshchepkov et al currently presents the most consistent explanation of the available literature data. − …”

In Situ Sonoactivation of Polycrystalline Ni for the Hydrogen Evolution Reaction in Alkaline Media

“…In addition, our light microscopy and SEM analyses of the surface of the Ni­(poly) electrode demonstrate that there is no noticeable surface roughening that could be attributed to the ultrasonic treatment (this is unique to the cell employed in this research). Consequently, the smaller size of this anodic CV peak as the duration of ultrasonication increases provides evidence that the Ni­(poly) electrode undergoes gradual partial oxidation, the mechanism of which is discussed below. − …”