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

Abstract

To achieve complete oxidation of ethanol (EOR) to CO2, higher operating temperatures (often called intermediate-T, 150-200 °C) and appropriate catalysts are required. We examine here titanium oxycarbide (hereafter TiOxCy) as a possible alternative to standard carbon-based supports to enhance the stability of the catalyst/support assembly at intermediate-T. 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 TiOxCy 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 TiOxCy powders, both at room temperature and at 150 °C. The present study has revealed that TiOxCy is a sufficiently conductive material whose surface is passivated by a TiO2 film under working conditions, which prevents the full oxidation of the TiOxCy 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 TiOxCy 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 TiOxCy.

Ultrathin layered double hydroxide nanosheets with Ni(III) active species obtained by exfoliation for highly efficient ethanol electrooxidation

“…S6, the ultrathin NiAl-LDH-NSs have a good catalytic activity for acetaldehyde while have no catalytic performance for acetic acid, demonstrating the acetic acid is the final product in this reaction process. Combine the results in our work and the general reported EOR reaction mechanism by Ni-based catalysts in the literature [12,13], the EOR reaction process by ultrathin NiAl-LDH-NSs in this work is as follows: $$\text{Ni}{\left(\text{OH}\right)}_2+{\text{OH}}^{-}\to \text{NiOOH}+{\mathrm{H}}_2{\text{O+e}}^{-}$$ $$\text{NiOOH}+{\text{CH}}_3{\text{CH}}_2\text{OH}\to {\text{CH}}_3\text{CHO}+\text{Ni}{\left(\text{OH}\right)}_2$$ $$\text{NiOOH}+{\text{CH}}_3\text{CHO}\to {\text{CH}}_3\text{COOH}+\text{Ni}{\left(\text{OH}\right)}_2$$…”

“…However, high cost, low abundance and catalytic poisoning by the carbon monoxide produced in electrooxidation have severely restricted the practical usage of Pt-based electro-catalysts in direct ethanol fuel cells (DEFCs) [10,11]. To overcome these problems, a broad range of non-precious metal catalysts have been actively pursued including metal [12], metal oxides [13], hydroxides [14] and sulfides [15]. Recently, layered double hydroxides (LDHs) have been reported as a promising candidate for various electrocatalytic systems [16–19] including EOR [18,19] owing to their novel structure and desirable properties.…”

“…For EOR based on Ni-based electrocatalysts, Ni(III) species (NiOOH) play an authentic catalytic role [12,13,20]. While generally synthesized Ni oxides and hydroxides need undergo progressive oxidation from low valence states (Ni(II)) to high valence states (Ni(III)) during electrochemical process prior to the EOR [13,14]. Previous report [21] has testified that chemically oxidized NiOOH is extremely active in electrochemical reactions.…”

Effect of Air‐Aging on the Electrochemical Characteristics of TiOxCy Films for Electrocatalysis Applications

“…The titanium substrate stabilizes the Ti−O−C film and provides the electrical contact, which is essential for electrochemical investigations. However, the optimal film composition with regard to interfacial electrical conductivity and catalytic performance of deposited Pt has not been identified yet ,,. TiO x C y films are prone to surface reoxidation (to TiO 2 ) when exposed to air or during anodic polarization, which is due to the intrinsic thermodynamic instability of the oxycarbide phase ,.…”

“…However, the optimal film composition with regard to interfacial electrical conductivity and catalytic performance of deposited Pt has not been identified yet ,,. TiO x C y films are prone to surface reoxidation (to TiO 2 ) when exposed to air or during anodic polarization, which is due to the intrinsic thermodynamic instability of the oxycarbide phase ,. Moreover, and interestingly for the development of (intermediate temperature) direct ethanol fuel cell electrodes, it was shown that the addition of ethanol inhibits anodic oxidation of TiO x C y .…”