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

Abstract

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 CO ad 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 CO 2 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.

Adsorbed Intermediates in Oxygen Reduction on Platinum Nanoparticles Observed by In Situ IR Spectroscopy

“…Infrared (IR) spectroscopy, in particular, has proved to be a very powerful experimental technique to study in situ or operando electrocatalytic reactions on metal surfaces, and detect various adsorbed oxygenated species . However, thus far, most reports of in situ spectroscopic studies have been restricted to thin‐film metal surfaces, which cannot replicate features of nanoparticle catalysts, such as size dependence .…”

Adsorbed Intermediates in Oxygen Reduction on Platinum Nanoparticles Observed by In Situ IR Spectroscopy

“…Infrared (IR) spectroscopy,inparticular, has proved to be av ery powerful experimental technique to study in situ or operando electrocatalytic reactions on metal surfaces, [24][25][26][27][28][29][30][31] and detect various adsorbed oxygenated species. [32][33][34][35] However,t hus far,m ost reports of in situ spectroscopic studies have been restricted to thin-film metal surfaces,which cannot replicate features of nanoparticle catalysts,s uch as size dependence.…”

Insight into the Electrooxidation Mechanism of Ethylene Glycol on Palladium‐Based Nanocatalysts: In Situ FTIRS and LC‐MS Analysis

“…In the same way the bands corresponding to the COO À symmetrical vibration (ν sym OÀ C-O), all appearing in a rather narrow interval, make their differentiation difficult. However, based on previously reported work [20,42] the bands at 1076 cm À 1 , 1236 cm À 1 , 1326 cm À 1 , 1361 cm À 1 and 1410 cm À 1 can be assigned to glycolate, which seems to be the main observed product. Indeed, the typical bands of glyoxylate and oxalate at 1107 cm À 1 and 1308 cm À 1 are not observed.…”