Spectrometric Study of Electrochemical CO2 Reduction on Pd and Pd-B Electrodes

The electrochemical CO2 reduction reaction (CO2RR) on Pd-based electrodes to dissolved formate and/or gaseous CO is largely dependent on potential and the electrode material, yet there is a lack of molecular-level insights into this dependence. Herein, in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) in conjunction with differential electrochemical mass spectrometry (DEMS), gas chromatography (GC), and nuclear magnetic resonance (NMR) measurements is applied to investigate the CO2RR on Pd and Pd-B film electrodes, providing a direct observation of the role of surface CO as well as the B-doping effect at varied potentials. Comprehensive spectrometric results reveal that at lower overpotentials, CO gradually accumulates on both Pd electrode surfaces poisoning the dominant formate pathway, while at higher overpotentials, surface CO forms facilely with linearly bonded CO (the minor surface CO species) acting as an active precursor and bridge-bonded CO (the major surface CO species) as a spectator toward the gaseous CO product. Moreover, B-doping in Pd hinders CO formation and promotes formate production on the Pd-B electrode for the CO2RR as compared to that on the pristine Pd electrode at all of the overpotentials under investigation.