Strain Effects on the Oxidation of CO and HCOOH at Au-Pd Core-Shell Nanoparticles

The mechanism of CO and HCOOH electrooxidation in an acidic solution on carbon-supported Au–Pd core–shell nanoparticles was investigated by differential electrochemical mass spectrometry and in situ Fourier transform infrared (FTIR) spectroscopy. Analysis performed in nanostructures with 1.3 ± 0.1 nm (CS1) and 9.9 ± 1.1 nm (CS10) Pd shells provides compelling evidence that the mechanism of adsorbed CO (COads) oxidation is affected by structural and electronic effects introduced by the Au cores. In the case of CS10, a band associated with adsorbed OH species (OHads) is observed in the potential range of CO oxidation. This feature is not detected in the case of CS1, suggesting that the reaction follows an alternative mechanism involving COOHads species. The faradaic charge associated with COads oxidation as well as the Stark slope measured from FTIR indicates that the overall affinity and orbital coupling of CO to Pd are weaker for CS1 shells. FTIR spectroscopy also revealed the presence of HCOOads intermediate species only in the case of CS1. This observation allowed us to conclude that the higher activity of CS10 toward this reaction is due to a fast HCOOads oxidation step, probably involving OHads, to generate CO2. Density functional theory calculations are used to estimate the contributions of the so-called ligand and strain effects on the local density of states of the Pd d-band. The calculations strongly suggest that the key parameter contributing to the change in mechanism is the effective lattice strain

Electrochemical Behavior of TiOxCy as Catalyst Support for Direct Ethanol Fuel Cells at Intermediate Temperature: From Planar Systems to Powders

To achieve complete oxidation of ethanol (EOR) to CO₂, higher operating temperatures (often called intermediate-<i>T</i>, 150–200 °C) and appropriate catalysts are required. We examine here titanium oxycarbide (hereafter TiO_<i>x</i>C_<i>y</i>) as a possible alternative to standard carbon-based supports to enhance the stability of the catalyst/support assembly at intermediate-<i>T</i>. To test this material as electrocatalyst support, a systematic study of its behavior under electrochemical conditions was carried out. To have a clear description of the chemical changes of TiO_<i>x</i>C_<i>y</i> induced by electrochemical polarization of the material, a special setup that allows the combination of X-ray photoelectron spectroscopy and electrochemical measurements was used. Subsequently, an electrochemical study was carried out on TiO_<i>x</i>C_<i>y</i> powders, both at room temperature and at 150 °C. The present study has revealed that TiO_<i>x</i>C_<i>y</i> is a sufficiently conductive material whose surface is passivated by a TiO₂ film under working conditions, which prevents the full oxidation of the TiO_<i>x</i>C_<i>y</i> and can thus be considered a stable electrode material for EOR working conditions. This result has also been confirmed through density functional theory (DFT) calculations on a simplified model system. Furthermore, it has been experimentally observed that ethanol molecules adsorb on the TiO_<i>x</i>C_<i>y</i> surface, inhibiting its oxidation. This result has been confirmed by using in situ Fourier transform infrared spectroscopy (FTIRS). The adsorption of ethanol is expected to favor the EOR in the presence of suitable catalyst nanoparticles supported on TiO_<i>x</i>C_<i>y</i>

Electrochemical Behavior of TiO_<i>x</i>C_<i>y</i> as Catalyst Support for Direct Ethanol Fuel Cells at Intermediate Temperature: From Planar Systems to Powders

To achieve complete oxidation of ethanol (EOR) to CO₂, higher operating temperatures (often called intermediate-<i>T</i>, 150–200 °C) and appropriate catalysts are required. We examine here titanium oxycarbide (hereafter TiO_<i>x</i>C_<i>y</i>) as a possible alternative to standard carbon-based supports to enhance the stability of the catalyst/support assembly at intermediate-<i>T</i>. To test this material as electrocatalyst support, a systematic study of its behavior under electrochemical conditions was carried out. To have a clear description of the chemical changes of TiO_<i>x</i>C_<i>y</i> induced by electrochemical polarization of the material, a special setup that allows the combination of X-ray photoelectron spectroscopy and electrochemical measurements was used. Subsequently, an electrochemical study was carried out on TiO_<i>x</i>C_<i>y</i> powders, both at room temperature and at 150 °C. The present study has revealed that TiO_<i>x</i>C_<i>y</i> is a sufficiently conductive material whose surface is passivated by a TiO₂ film under working conditions, which prevents the full oxidation of the TiO_<i>x</i>C_<i>y</i> and can thus be considered a stable electrode material for EOR working conditions. This result has also been confirmed through density functional theory (DFT) calculations on a simplified model system. Furthermore, it has been experimentally observed that ethanol molecules adsorb on the TiO_<i>x</i>C_<i>y</i> surface, inhibiting its oxidation. This result has been confirmed by using in situ Fourier transform infrared spectroscopy (FTIRS). The adsorption of ethanol is expected to favor the EOR in the presence of suitable catalyst nanoparticles supported on TiO_<i>x</i>C_<i>y</i>