Electrocatalysis of Ethylene Glycol Oxidation on Bare and Bi-Modified Pd Concave Nanocubes in Alkaline Solution: An Interfacial Infrared Spectroscopic Investigation

Electrocatalysis of ethylene glycol oxidation (EGO) on shape-controlled Pd nanocrystals is of great interest in the pursuit of efficient biomass fuel utilization and nanomaterial application. The present work is aimed at a mechanistic study of electrocatalytic EGO in alkaline media on surface-cleaned high-index Pd concave nanocubes (Pd CNCs) with and without surface Bi modification. CO-adsorption displacement effectively removes the surfactants on as-synthesized Pd CNCs, facilitating controlled Bi adatom formation. EGO on the Pd CNCs is notably enhanced as a result of Bi modification, with the activity peak at a Bi coverage of ca. 0.31 in terms of apparent and specific oxidation current densities. Internal (ATR-SEIRAS) and external (IRRAS) reflection modes of in situ infrared spectroscopy have been used to probe the EGO process at a molecular level. High surface sensitivity ATR-SEIRAS enabled ready identification of the formation and removal of CO and 2-hydroxyacetyl surface species during EGO on Pd CNCs and Bi-modified Pd (Bi/Pd) CNCs. In comparison to that on bare Pd CNCs, the COad band is significantly stronger on Bi/Pd CNCs, suggestive of a promoted C–C bond cleavage. IRRAS results further reveal that glycolate and glyoxal are the main products of EGO on both pristine and Bi/Pd CNCs. In addition, formations of glyoxal, CO, and CO2 on Bi/Pd CNCs are relatively enhanced, in comparison to those on bare Pd CNCs. On the basis of the comprehensive spectral results and literature reports, relevant reaction pathways are proposed for EGO at Pd and Bi/Pd CNCs in alkaline media.