Low-temperature methane oxidation: Harnessing electrochemically induced oxygen ions for enhanced Pd nano-catalyst performance

Abstract

The electrochemical promotion of nano-sized Pd catalysis deposited on yttria-stabilized zirconia (YSZ) solid electrolyte (Pd/YSZ) was studied for complete methane oxidation in excess of oxygen. The as-prepared and used Pd/YSZ catalysts were characterized using TEM, SEM, and XRD techniques. In this study, for the first time, we demonstrated the electrochemical promotion of complete methane oxidation over Pd at temperatures as low as 300 °C. The electrochemical promotion of Pd/YSZ was carried out at different cathodic and anodic polarization values in excess of oxygen (p_O2 = 6 kPa) in temperatures ranging from 300—420 °C. Upon anodic and cathodic polarization the highest rate increase of 17.7 and 1.4 was observed at 420 °C, respectively. Chronoamperometric rate transients showed continuous rate increase with the polarization time indicating continuous activation of Pd/YSZ and formation of PdO_x active phase. When polarization was stopped the reaction rate slowly returned to its initial state showing the persistent EPOC, i.e., the open-circuit reaction rate after polarization was enhanced compared to initial open-circuit conditions (γ = 1.6 after 29 h of polarization). The changes occurring in the Pd catalyst during the polarization were studied using electrochemical techniques, such as cyclic voltammetry, steady-state polarization and electrochemical impedance spectroscopy (EIS).

Graphical Abstract