Abstract
Herein, we demonstrate an easy way to improve the hydrogen evolution reaction (HER) activity of Pt electrodes in alkaline media by introducing Ni–Fe clusters. As a result, the overpotential needed to achieve a current density of 10 mA cm−2 in H2‐saturated 0.1 m KOH is reduced for the model single‐crystal electrodes down to about 70 mV. To our knowledge, these modified electrodes outperform any other reported electrocatalysts tested under similar conditions. Moreover, the influence of 1) Ni to Fe ratio, 2) cluster coverage, and 3) the nature of the alkali‐metal cations present in the electrolyte on the HER activity has been investigated. The observed catalytic performance likely originates from both the improved water dissociation at the Ni–Fe clusters and the subsequent optimal hydrogen adsorption and recombination at Pt atoms present at the Ni–Fe/Pt boundary.
Highlights
Improving the kinetics of the rate-determining step, water dissociation, which is correlated with the OH-adsorption energy, is nowadays recognized as a promising strategy to improve the hydrogen evolution reaction (HER) activity in alkaline solutions.[4,11]
Various studies on Ni–Fe hydroxides, which are among the best catalysts for the oxygen evolution reaction (OER), showed that relative to pure Ni hydroxide films, the addition of Fe can enhance their conductivity more than 30 times.[15]
X-ray absorption spectroscopy and coulometric titration indicated that the addition of Fe can increase the oxidation state of Ni atoms in its vicinity,[16,17] which implies an improved water dissociation ability due to the increased *OH binding energy (* corresponds to an adsorption site).[18]
Summary
The current understanding of the origin of such high activity is that the Ni hydroxides provide an optimal water dissociation, while at the same time Pt promotes H2 generation.[14] various studies on Ni–Fe hydroxides, which are among the best catalysts for the oxygen evolution reaction (OER), showed that relative to pure Ni hydroxide films, the addition of Fe can enhance their conductivity more than 30 times.[15] X-ray absorption spectroscopy and coulometric titration indicated that the addition of Fe can increase the oxidation state of Ni atoms in its vicinity,[16,17] which implies an improved water dissociation ability due to the increased *OH binding energy (* corresponds to an adsorption site).[18] we introduced both Fe and Ni clusters to a Pt surface and investigated the resulting HER activity in various alkaline electrolytes. Typical CVs of NiFe@Pt(111) electrodes resemble that of Ni@Pt(111); the OH adsorption peaks are slightly negatively shifted (see the direct comparison in Figure S1 in the Supporting Information).
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