The catalytic conversion of CO2 can reduce its impact in the atmosphere and produce chemicals of industrial interest. Based on this, herein, ethanol formation from CO2 hydrogenation with water was... Show moreThe catalytic conversion of CO2 can reduce its impact in the atmosphere and produce chemicals of industrial interest. Based on this, herein, ethanol formation from CO2 hydrogenation with water was studied. Inspired by CO2 electroreduction results, we show that ethanol can be formed at atmospheric pressure, using metallic Cu catalysts in the CO2 hydrogenation with water steam (CO2 + H-2 + H2O) with selectivity of 84% and productivity of similar to 2 mu mol.gcat(-1) .h(-1) at 190 degrees C. When only H2O is used (without H-2), the same trend was observed. To the best of our knowledge, ethanol is reported for the first time to be synthesized at atmospheric pressure, using only CO2 and water as reactants in a thermocatalytic process. H-1 NMR results showed that water (and deuterated water) hydrogenate CO2 to form ethanol. CO-DRIFTS analyses revealed that water enhances the carbon-metal strengthening and this can explain why ethanol production is favored during the CO2 hydrogenation. Show less
Molecular-level insight into interfacial water at a buried electrode interface is essential in electrochemistry, but spectroscopic probing of the interface remains challenging. Here, using surface... Show moreMolecular-level insight into interfacial water at a buried electrode interface is essential in electrochemistry, but spectroscopic probing of the interface remains challenging. Here, using surface-specific heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy, we directly access the interfacial water in contact with the graphene electrode supported on calcium fluoride (CaF2). We find phase transition-like variations of the HD-SFG spectra vs. applied potentials, which arises not from the charging/discharging of graphene but from the charging/discharging of the CaF2 substrate through the pseudocapacitive process. The potential-dependent spectra are nearly identical to the pH-dependent spectra, evidencing that the pseudocapacitive behavior is associated with a substantial local pH change induced by water dissociation between the CaF2 and graphene. Our work evidences the local molecular-level effects of pseudocapacitive charging at an electrode/aqueous electrolyte interface. Show less
The Angstrom-scale space between graphene and its substrate provides an attractive playground for scientific exploration and can lead to breakthrough applications. Here, we report the energetics... Show moreThe Angstrom-scale space between graphene and its substrate provides an attractive playground for scientific exploration and can lead to breakthrough applications. Here, we report the energetics and kinetics of hydrogen electrosorption on a graphene-covered Pt(111) electrode using electrochemical experiments, in situ spectroscopy, and density functional theory calculations. The graphene overlayer influences the hydrogen adsorption on Pt(111) by shielding the ions from the interface and weakening the Pt-H bond energy. Analysis of the proton permeation resistance with controlled graphene defect density proves that the domain boundary defects and point defects are the pathways for proton permeation in the graphene layer, in agreement with density functional theory (DFT) calculations of the lowest energy proton permeation pathways. Although graphene blocks the interaction of anions with the Pt(111) surfaces, anions do adsorb near the defects: the rate constant for hydrogen permeation is sensitively dependent on anion identity and concentration. Show less
Liu, X.; Cecilio de Oliveira Monteiro, M.; Koper, M.T.M. 2023
Insights into how to control the activity and selectivity of the electrochemical CO2 reduction reaction are still limited because of insufficient knowledge of the reaction mechanism and kinetics,... Show moreInsights into how to control the activity and selectivity of the electrochemical CO2 reduction reaction are still limited because of insufficient knowledge of the reaction mechanism and kinetics, which is partially due to the lack of information on the interfacial pH, an important parameter for proton-coupled reactions like CO2 reduction. Here, we used a reliable and sensitive pH sensor combined with the rotating ring-disk electrode technique, in which a functionalized Au ring electrode works as a real-time detector of the OH- generated during the CO2 reduction reaction at a gold disk electrode. Variations of the interfacial pH due to both electrochemical and homogeneous reactions are mapped and the correlation of the interfacial pH with these reactions is inferred. The interfacial pH near the disk electrode increases from 7 to 12 with increasing current density, with a sharp increase at around -0.5 V vs. RHE, which indicates a change of the dominant buffering species. Through scan rate-dependent voltammetry and chronopotentiometry experiments, the homogenous reactions are shown to reach equilibrium within the time scale of the pH measurements, so that the interfacial concentrations of different carbonaceous species can be calculated using equilibrium constants. Furthermore, pH measurements were also performed under different conditions to disentangle the relationship between the interfacial pH and other electrolyte effects. The buffer effect of alkali metal cations is confirmed, showing that weakly hydrated cations lead to less pronounced pH gradients. Finally, we probe to which extent increasing mass transport and the electrolyte buffer capacity can aid in suppressing the increase of the interfacial pH, showing that the buffer capacity is the dominant factor in suppressing interfacial pH variations. Show less
Solvent-adsorbate interactions have a great impact on catalytic processes in aqueous systems. Implicit solvent calculations are inexpensive but inaccurate toward hydrogen bonds, while a full... Show moreSolvent-adsorbate interactions have a great impact on catalytic processes in aqueous systems. Implicit solvent calculations are inexpensive but inaccurate toward hydrogen bonds, while a full incorporation of explicit solvation is computationally demanding. Micro-solvation attempts to break this dilemma by including only those solvent molecules directly interacting with the solute and any nearby interfaces, thereby providing a compromise between accuracy and computational expenses. Here, we show that micro-solvation of *OH and its relation to adsorption sites is largely transferable across late transition metal nanoparticles. Solvation energies for *OH on nanoparticles of Ir, Pd, and Pt range from -0.63 +/- 0.04 eV to -0.67 +/- 0.12 eV, while those on Au and Ag are -0.75 +/- 0.07 eV and -1.01 +/- 0.05 eV, respectively. These results enable the use of average solvation corrections for *OH on late transition metal nanostructures. Show less
