Volcano Activity Relationships for Proton-Coupled Electron Transfer Reactions in Electrocatalysis

Catalysis and Surface Chemistr

Activity volcanoes for the electrocatalysis of homolytic and heterolytic hydrogen evolution

Catalysis and Surface Chemistr

Hydrogen-Induced Step-Edge Roughening of Platinum Electrode Surfaces

Electrode surfaces may change their surface structure as a result of the adsorption of chemical species, impacting their catalytic activity. Using density functional theory, we find that the strong adsorption of hydrogen at low electrode potentials promotes the thermodynamics and kinetics of a unique type of roughening of 110-type Pt step edges. This change in surface structure causes the appearance of the so-called "third hydrogen peak" in voltammograms measured on Pt electrodes, an observation that has eluded explanation for over 50 years. Understanding this roughening process is important for structure-sensitive (electro)catalysis and the development of active and stable catalysts.Article / Letter to editorLIC/ES/Catalysis and Surface Chemistr

Selective electrocatalytic hydrogenation of α,β-unsaturated ketone on (111)-oriented Pd and Pt electrodes

In this paper, we study the electrocatalytic reduction of methyl vinyl ketone on Pt(111) and Pd-modified Pt(111) electrodes, as well as some of its expected hydrogenation derivatives and isolated functional moieties. The selectivity and Faraday efficiency have been calculated via sampling the catholyte solution after two hours of electrolysis. Furthermore, the adsorbates involved in the deactivation process on both surfaces were studied by means of potential opening experiments and in situ infrared spectroscopy. The Pd-modified Pt(111) electrode is very active (even mass transport limited) for the selective electrochemical hydrogenation of the C=C to 2-butanone, in the hydrogen underpotential deposition potential window (between 0 and 0.2 VRHE), with limited poisoning. Pt(111) is much less active, and poisons rapidly with adsorbed CO. The poison is formed from the C=C bond, not from the C=O moiety, as evidenced by the same poisoning occurring for ethylene. Further hydrogenation to the saturated alcohol happens at more negative potentials, but with 2-butenol as intermediate, not 2butanone, as the latter species interacts too weakly with the (111) surface.Catalysis and Surface Chemistr

Examination and Prevention of Ring Collection Failure During Gas-Evolving Reactions on a Rotating Ring-Disk Electrode

Use of a rotating ring-disk electrode during gas-evolving reactions has been shown liable to errors under higher current densities, since product collection on the ring is vulnerable to the formation of gas bubbles at the disk-ring interspace. In this study, we explored methods of reducing such bubble-related errors and improving the reliability of the collection factor under high-intensity gas evolution. We attempted the mounting of a thin wire close to the surface, to dislodge bubbles that formed specifically on the interface between the disk and the disk-ring spacer. This approach was tested for the detection of chlorine during parallel chlorine and oxygen evolution, and resulted in a notable alteration of the collection efficiency; its value became lower than theoretical expectations and also quite stable, even under higher current densities. We also coated the RRDE tip in a hydrophilic polymer, to reduce the tendency of bubble formation; this was tested for the collection of hydrogen and oxygen gas, and led to a mild increase in overall performance. The coating allowed for approximately 50% higher hydrogen evolution current density without ring failure, and for oxygen collection led to an overall improvement in behaviour.Catalysis and Surface Chemistr

A kinetic descriptor for the electrolyte effect on the oxygen reduction kinetics on Pt(111)

Proton-exchange membrane fuel cells demand efficient electrode-electrolyte interfaces to catalyse the oxygen reduction reaction (ORR), the kinetics of which depends on the energetics of surface adsorption and on electrolyte environment. Here we show an unanticipated effect of non-specifically adsorbed anions on the ORR kinetics on a Pt(111) electrode; these trends do not follow the usual ORR descriptor, that is *OH binding energy. We propose a voltammetry-accessible descriptor, namely reversibility of the *O *OH transition. This descriptor tracks the dependence of ORR rates on electrolyte, including the concentration/identity of anions in acidic media, cations in alkaline media and the effect of ionomers. We propose a model that relates the ORR rate on Pt(111) to the rate of the *O to *OH transition, in addition to the thermodynamic *OH binding energy descriptor. Our model also rationalizes different trends for the ORR rate on stepped Pt surfaces in acidic versus alkaline media.Catalysis and Surface Chemistr

The effect of temperature on the cation‐promoted electrochemical CO2 reduction on gold

Abstract Electrochemical reactions in general, and the CO2 reduction reaction (CO2RR) in particular, are commonly studied at room temperature. However, practical electrolysers may use elevated temperatures. There is currently a lack of fundamental understanding of the effect of temperature on the CO2RR. Here, we performed temperature-dependent studies on the CO2RR on a relatively simple electrode material, namely gold, to obtain insights into how temperature influences this reaction and the competing hydrogen evolution reaction. A rotating ring disk electrode setup was used to show that the CO2RR activity and selectivity increased with temperature, and to obtain kinetic parameters such as the apparent activation energy and transfer coefficient. The magnitude of the temperature effect and the activation energy was affected by both the cation identity and concentration in the electrolyte. Moreover, the positive effect of temperature on the kinetics of the CO2RR was counteracted by the lower CO2 solubility, making efficient mass transport even more important at higher temperatures.Catalysis and Surface Chemistr

Measurement of competition between oxygen evolution and chlorine evolution using rotating ring-disk electrode voltammetry

Catalysis and Surface Chemistr

The Importance of Cannizzaro-Type Reactions during Electrocatalytic Reduction of Carbon Dioxide

Catalysis and Surface Chemistr

Effect of Saturating the Electrolyte with Oxygen on the Activity for the Oxygen Evolution Reaction

Catalysis and Surface Chemistr