Electrooxidation of d- and l-Glucose at Well-Defined Chiral Bimetallic Electrodes

Abstract

The electrooxidation of D-and L-glucose at chiral Pt{321} r/s single crystal electrodes modified with Au, Ag and Bi adatoms up to a coverage of one monolayer (ML) is reported. All adatoms investigated are found to selectively decorate kink and step sites. Only at higher coverages is adsorption onto the narrow {111} terrace sites observed for Bi, Ag and Au, consistent with previously reported adsorption behaviour on stepped surfaces vicinal to the {111} plane for chemisorbates exhibiting a lower work function than platinum. However, silver is found to block {111} terrace sites even when Pt step sites are still available on Pt{321}. This behaviour is ascribed to the propensity of silver to undergo place-exchange to form a surface alloy. The selective decoration of chiral kink sites has a profound influence on the voltammetric response of Pt{321} towards glucose electrooxidation. For bismuth adsorption, the electrooxidation current density initially increases and reaches a maximum when bismuth adsorption at {111} terraces commences. This is because the reaction pathways at step/kink sites leading to the formation of adsorbed CO (a surface poison for the clean surface reaction) and other strongly adsorbed intermediates, are either blocked by adsorbed bismuth or their electrooxidation and subsequent removal promoted. Once all step/kink sites are blocked by bismuth, hardly any chiral discrimination can be discerned between r-/s-electrodes towards D-/L-glucose. Silver adsorption does not cause any increase in glucose electrooxidation current density but rather induces a continual attenuation in glucose electrooxidation activity, particular (in contrast to bismuth) electrooxidation current at potentials in excess of 0.35 V. Therefore, unlike for bismuth, the initial glucose adsorption and electrooxidation processes associated with chiral kink sites appear to be preserved even though silver adsorbs at these sites. It is speculated that spontaneous place-exchange of silver with platinum to form a PtAg surface alloy at steps is responsible for this difference in behaviour between silver and bismuth. Finally, gold neither promotes reaction rate nor preserves chiral discrimination and is therefore deduced to act as an inert site blocker (no alloying, no promotion of CO electrooxidation) leading to complete attenuation of glucose electrooxidation current at a coverage of one ML.

Insights into Self-Poisoning during Catalytic Hydrogenation on Platinum Surfaces Using ATR-IR Spectroelectrochemistry

“…This suggests that adsorbed CD impedes EP dissociation, consistent with previous reports that CD suppresses CO formation by blocking the necessary decomposition sites in the Pt surface. 31,52 3.4. EP Injection Analysis.…”

Tailoring the catalytic activity of electrodes with monolayer amounts of foreign metals

“…Nowadays, typical implementation strategies for engineering electrocatalysts with submonolayer and monolayer amounts of foreign atoms involve modification of model single crystal surfaces, [113][114][115][116][117][118] extended polycrystalline surfaces 104 and nanoparticles. 37,119,120 One can distinguish (i) ''pure'' surface science approaches in which samples are prepared under ultra-high vacuum (UHV), 121,122 and (ii) approaches which use electrochemical steps, [123][124][125][126] including underpotential deposition. The surface science approaches have the advantage of exhaustive surface characterisation with advanced UHVtechniques directly after the sample preparation, 127 without accounting for random contaminations from the environment and electrolytes.…”

Active Porous Electrodes Prepared by Ultrasonic‐bath and their Application in Glucose/O2 Electrochemical Reactions

“…However, some challenges must be surpassed to make feasible the use of DGFCs with abiotic anodes, namely: controlled output power, limited activity and biocompatibility. Furthermore, most of the works regarding abiotic anodes report investigations in acidic or alkaline media, which makes impossible the application in physiological conditions [25, 26]. Another important issue is the glucose concentration, which changes the output power.…”