Impact of Alkali Metal Cations and Iron Impurities on the Evolution of Hydrogen on Cu Electrodes in Alkaline Electrolytes

Abstract

is key to the development of processes that can convert CO and CO 2 to hydrocarbons, and nitrate to ammonia. The hydrogen evolution reaction (HER) often competes with these processes. Few studies studied this reaction on Cu under alkaline conditions. Herein, we examined the HER on Cu electrodes under alkaline conditions in Na + -and Cs + -containing electrolytes. We found that in 0.1 M solutions of NaOH and CsOH of the highest commercially available purity grades, trace impurities of iron deposit on the Cu electrode during electrolysis. As a result, the rate of the HER is enhanced by up to a factor of ≈5 over the course of eleven cyclic voltammograms (CV) from 0.15 to −0.65 V vs the reversible hydrogen electrode. After removal of the iron impurities, the CVs are stable as a function of cycle number. Comparison of the CVs in pre-electrolyzed 0.1 M NaOH and CsOH reveals that changing the cation from Na + to Cs + has no measurable effect on the HER. With density functional theory (DFT), we further rationalized our experimental findings. We discuss the implications of our results for electrocatalytic processes on Cu electrodes.

Understanding Cation Trends for Hydrogen Evolution on Platinum and Gold Electrodes in Alkaline Media

“…It is important to point out that although the electrolytes in this study were used as received, no metal contaminants are expected to affect our measurements as evidenced by the overlapping consecutive CVs shown in Figure S6 in the Supporting Information. 22 As shown in Figure 5a,b, similar to gold, on platinum, increasing the concentration of Li + cations promotes HER both at pH 11 and 13. In contrast, for the K + electrolyte, at pH 9 and 10, we observe a positive reaction order at a low K + concentration and at the highest concentrations, HER starts to be inhibited, confirming the relationship between local alkalinity and the concentration of weakly hydrated cations at the reaction interface.…”

“…The cyclic voltammetry is shown in Figure S5, and the corresponding reaction order plots are shown in Figure . It is important to point out that although the electrolytes in this study were used as received, no metal contaminants are expected to affect our measurements as evidenced by the overlapping consecutive CVs shown in Figure S6 in the Supporting Information . As shown in Figure a,b, similar to gold, on platinum, increasing the concentration of Li + cations promotes HER both at pH 11 and 13.…”

The Role of Cation Acidity on the Competition between Hydrogen Evolution and CO2 Reduction on Gold Electrodes

“…Two large surface area gold electrodes were used, and a potential of −2 V was applied for 12 h, similarly to the procedure reported elsewhere. 31 The sulfates and perchlorates were used as received, as these are high-purity salts, ≥99.99%. The pH of the prepared electrolyte was certified using a glass-electrode pH meter (Lab 855, SI Analytics) calibrated with standard buffer solutions (Radiometer Analytical).…”

The Pivotal Role of s‐, p‐, and f‐Block Metals in Water Electrolysis: Status Quo and Perspectives

“…Currently, the alkali metals are basically introduced into three material systems including NNTM‐based oxides, hydroxides, and chalcogenides to modify their OER and/or HER activity. [ 108–132 ] The aims of introducing alkali metals mainly contain the following three aspects. [ 111–128 ] First, the appropriate introduction of alkali metal ions into NNTM‐based compound can enhance the oxidation state of NNTM species, by which the electrophilicity of NNTM toward the adsorbed O is effectively increased, and thus accordingly promoting the reaction of one OH‐anion with one adsorbed O atom on NNTM to form the adsorbed OOH‐intermediate.…”

“…[ 108–132 ] The aims of introducing alkali metals mainly contain the following three aspects. [ 111–128 ] First, the appropriate introduction of alkali metal ions into NNTM‐based compound can enhance the oxidation state of NNTM species, by which the electrophilicity of NNTM toward the adsorbed O is effectively increased, and thus accordingly promoting the reaction of one OH‐anion with one adsorbed O atom on NNTM to form the adsorbed OOH‐intermediate. Second, the NNTM–O(S) bond becomes more covalent upon the incorporation of appropriate alkali metal ions, by which a hole state near the Fermi level is created and the hybridization of O(S) 2p–NNTM 3d is enhanced, enabling the catalyst more electrophilic and even activating lattice oxygen as active sites.…”