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

Suppression of hydrogen evolution in acidic electrolytes by electrochemical CO2 reduction

In this article we investigate the electrochemical reduction of CO2 at gold electrodes under mildly acidic conditions. Differential electrochemical mass spectroscopy (DEMS) is used to quantify the amounts of formed hydrogen and carbon monoxide as well as the consumed amount of CO2. We investigate how the Faradaic efficiency of CO formation is affected by the CO2 partial pressure (0.1-0.5 bar) and the proton concentration (1-0.25 mM). Increasing the former enhances the rate of CO2 reduction and suppresses hydrogen evolution from proton reduction, leading to Faradaic efficiencies close to 100%. Hydrogen evolution is suppressed by CO2 reduction as all protons at the electrode surfaces are used to support the formation of water (CO2 + 2H(+) + 2e(-) -> CO + H2O). Under conditions of slow mass transport, this leaves no protons to support hydrogen evolution. On the basis of our results, we derive a general design principle for acid CO2 electrolyzers to suppress hydrogen evolution from proton reduction: the rate of CO/OH- formation must be high enough to match/compensate the mass transfer of protons to the electrode surface.Catalysis and Surface Chemistr

Effect of pore diameter and length on electrochemical CO2 reduction reaction at nanoporous gold catalysts

Catalysis and Surface Chemistr

Structural principles to steer the selectivity of the electrocatalytic reduction of aliphatic ketones on platinum

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 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.Catalysis and Surface Chemistr

A DEMS approach for the direct detection of CO formed during electrochemical CO2 reduction

Observation of CO formed during electrochemical CO2 reduction using Differential Electrochemical Mass Spectrometry (DEMS) is complicated by the fragmentation of CO2 in the course of the ionization process. Since much more CO2 than CO enters the vacuum of the mass spectrometer, the ion current for mass 28 is dominated by the CO+-fragment of CO2. By reducing the cathode potential of the ion source of the mass spectrometer from-70 V to-27.5 V, fragmentation of CO2 is reduced to a negligible degree. This allows direct observation of electrochemically formed CO by measuring the ionic current for mass 28. We show that this method is superior to matrix calibration in which the ionic current for mass 44 corrected by the CO+/CO2+-intensity ratio is subtracted from the ionic current for mass 28. Using this method, we compare DEMS results for the electrochemical reduction of CO2 at gold electrodes obtained in two different cells, a conventional DEMS cell with the working electrode sputtered onto the membrane in contact with the vacuum and a flow cell where the interface to the vacuum is separated from the working electrode. We show that in the conventional cell at the interface between electrolyte and vacuum, the local CO2 concentration is reduced as the nearby vacuum interferes with the equilibria of reactions involving gases, and the local pH is increased. Therefore, in DEMS cells where the working electrode is positioned in the vicinity of the interface, the onset potential for CO2 reduction and hydrogen evolution are shifted and the observed faradaic efficiency for CO2 reduction are considerably reduced compared to literature values. This can be rectified by using flow cells that allow a spatial separation between vacuum/electrolyte interface and working electrode. We describe how the Dual Thin Layer Cell can be calibrated for detecting CO, thus allowing quantification of evolved amounts of CO from the ionic current for mass 28. (C) 2020 The Authors. Published by Elsevier B.V.Catalysis and Surface Chemistr

A mechanistic investigation on the electrocatalytic reduction of aliphatic ketones at platinum

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.Catalysis and Surface Chemistr