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... Show moreProton-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. Show less
Combining computational and experimental methods is a powerful approach to understand the variables that govern catalyst performance and ultimately design improved materials. However, the... Show moreCombining computational and experimental methods is a powerful approach to understand the variables that govern catalyst performance and ultimately design improved materials. However, the effectiveness of this approach rests on the strength of the relationships between calculated parameters and experimental measurements. These relationships are complicated by the intricacy and dynamic behaviour of catalytic active sites, and by the non-trivial relationship between calculated reaction energetics and observed rates. In this Perspective, we highlight opportunities to enhance the connection between computation and experiment in electrocatalysis. These include measuring the intrinsic kinetic behaviour of catalysts, creating precise models for the active site and its environment, and forming clear relationships between calculated reaction energetics and observed rates. As experimental and computational methods continue to become more powerful, clear connections between the two will maximize their utility to guide the design of efficient and selective electrocatalysts. Show less
The electrocatalytic reduction of carbon dioxide is widely studied for the sustainable production of fuels and chemicals. Metal ions in the electrolyte influence the reaction performance, although... Show moreThe electrocatalytic reduction of carbon dioxide is widely studied for the sustainable production of fuels and chemicals. Metal ions in the electrolyte influence the reaction performance, although their main role is under discussion. Here we studied CO2 reduction on gold electrodes through cyclic voltammetry and showed that, without a metal cation, the reaction does not take place in a pure 1 mM H2SO4 electrolyte. We further investigated the CO2 reduction with and without metal cations in solution using scanning electrochemical microscopy in the surface-generation tip-collection mode with a platinum ultramicroelectrode as a CO and H2 sensor. CO is only produced on gold, silver or copper if a metal cation is added to the electrolyte. Density functional theory simulations confirmed that partially desolvated metal cations stabilize the CO2– intermediate via a short-range electrostatic interaction, which enables its reduction. Overall, our results redefine the reaction mechanism and provide definitive evidence that positively charged species from the electrolyte are key to stabilize the crucial reaction intermediate. Show less
Bondü, C.J.; Calle Vallejo, F.; Costa Figueiredo, M.; Koper, M.T.M. 2019
Due to a general feedstock shift, the chemical industry is charged with the task of finding ways to transform renewable ketones into value-added products. A viable route to do so is the... Show moreDue to a general feedstock shift, the chemical industry is charged with the task of finding ways to transform renewable ketones into value-added products. A viable route to do so is the electrochemical hydrogenation of the carbonyl functional group. Here we report a study on acetone reduction at platinum single-crystal electrodes using online electrochemical mass spectroscopy, in situ Fourier transform infrared spectroscopy and density functional theory calculations. Acetone reduction at platinum displays a remarkable structural sensitivity: not only the activity, but also the product distribution depends on the surface crystallographic orientation. At Pt(111) neither adsorption nor hydrogenation occur. A decomposition reaction that deactivates the electrode happens at Pt(100). Acetone reduction proceeds at the (110) steps: Pt[(n – 1)(111) × (110)] electrodes produce 2-propanol and Pt[(n + 1)(100) × (110)] electrodes produce propane. Using density functional theory calculations, we built a selectivity map to explain the intricacies of the acetone reduction on platinum. Finally, we extend our conclusions to the reduction of higher aliphatic ketones. Show less
