Nature of Highly Active Electrocatalytic Sites for the Hydrogen Evolution Reaction at Pt Electrodes in Acidic Media

The hydrogen evolution reaction (HER) is one of the two processes in electrolytic water splitting. Known for more than two centuries, the HER still receives great attention in fundamental and applied science in view of its apparent simplicity (only two electrons are transferred), fast kinetics in acidic media, and promising technological applications in electrolyzers. However, the exact nature of active catalytic sites for this reaction is often uncertain, especially at nonuniform metal electrodes. Identification of such centers is important, as the HER will probably be central in future energy provision schemes, and it is simultaneously a convenient model reaction to study structure-composition-activity relations in catalysis. In this work, using simple coordination-activity considerations, we outline the location and geometric configuration of the active sites at various model Pt single-crystal electrodes. We show that when the coordination of such surface sites is optimized and their density at the surface is maximized, the experimental-specific HER activities are among the highest reported in the literature for pure platinum with a well-defined surface structure under similar conditions.

Electrochemical cell design for the impedance studies of chlorine evolution at DSA(®) anodes

A new electrochemical cell design suitable for the electrochemical impedance spectroscopy (EIS) studies of chlorine evolution on Dimensionally Stable Anodes (DSA(®)) has been developed. Despite being considered a powerful tool, EIS has rarely been used to study the kinetics of chlorine evolution at DSA anodes. Cell designs in the open literature are unsuitable for the EIS analysis at high DSA anode current densities for chlorine evolution because they allow gas accumulation at the electrode surface. Using the new cell, the impedance spectra of the DSA anode during chlorine evolution at high sodium chloride concentration (5 mol dm(-3) NaCl) and high current densities (up to 140 mA cm(-2)) were recorded. Additionally, polarization curves and voltammograms were obtained showing little or no noise. EIS and polarization curves evidence the role of the adsorption step in the chlorine evolution reaction, compatible with the Volmer-Heyrovsky and Volmer-Tafel mechanisms.

Making the hydrogen evolution reaction in polymer electrolyte membrane electrolysers even faster

Although the hydrogen evolution reaction (HER) is one of the fastest electrocatalytic reactions, modern polymer electrolyte membrane (PEM) electrolysers require larger platinum loadings (∼0.5–1.0 mg cm⁻²) than those in PEM fuel cell anodes and cathodes altogether (∼0.5 mg cm⁻²). Thus, catalyst optimization would help in substantially reducing the costs for hydrogen production using this technology. Here we show that the activity of platinum(111) electrodes towards HER is significantly enhanced with just monolayer amounts of copper. Positioning copper atoms into the subsurface layer of platinum weakens the surface binding of adsorbed H-intermediates and provides a twofold activity increase, surpassing the highest specific HER activities reported for acidic media under similar conditions, to the best of our knowledge. These improvements are rationalized using a simple model based on structure-sensitive hydrogen adsorption at platinum and copper-modified platinum surfaces. This model also solves a long-lasting puzzle in electrocatalysis, namely why polycrystalline platinum electrodes are more active than platinum(111) for the HER.

There is substantial research into minimizing platinum use in polymer electrolyte membrane electrolyzers. Here, the authors report that the hydrogen evolution activity of platinum(111) electrodes can be significantly enhanced by monolayer amounts of copper, which weaken the binding of hydrogen intermediates.

Non-covalent interactions in water electrolysis: influence on the activity of Pt(111) and iridium oxide catalysts in acidic media

Electrolyte components, which are typically not considered to be directly involved in catalytic processes at solid–liquid electrified interfaces, often demonstrate a significant or even drastic influence on the activity, stability and selectivity of electrocatalysts.