Effect of metal ad-layers on Au(1 1 1) electrodes on electrocatalytic oxidation of glucose in an alkaline solution

Abstract

Glucose oxidation in a 0.1 M NaOH solution at Au(1 1 1) single crystal electrodes modified with various ad-metals (Cu, Ag, Ru, Pt, Pd and Cd) by underpotential deposition (upd) was investigated. Ag ad-atoms of 1/3 monolayer (ML) onto the Au(1 1 1) surface showed the highest catalytic activity for glucose oxidation: The peak potential for glucose oxidation to gluconolactone (two-electron oxidation) was around −0.40 V vs. Ag|AgCl|KCl(sat), and the catalytic effect of this electrode on the oxidation of gluconolactone was also observed around −0.1 V vs. Ag|AgCl|KCl(sat) to give formate as the main product in a 0.1 M NaOH solution. Full coverage of Ag ad-atoms, however, led to a decrease in peak current with no marked shift in potential for glucose oxidation, but suppressed the oxidation of gluconolactone significantly. Cu ad-atoms modified Au(1 1 1) electrodes showed a slight negative shift of the pre-peak in the oxidation of glucose with a small oxidation current and a main oxidation peak appeared around −0.04 V vs. Ag|AgCl|KCl(sat). Cd ad-atoms gave similar activity at a bare Au(1 1 1) electrode, whereas Ru and Pt ad-atoms showed a considerable decrease in oxidation current. Pd ad-atoms gave negative catalytic activity. Double layer capacitance measurements revealed that the shift of the potential of zero charge (pzc) between bare Au(1 1 1) and Ag ad-atom modified Au(1 1 1) electrodes (the pzc shifted negatively by modification of Ag) was of great help in the explanation of the observed catalytic activities, where the number of AuOH sites on the Au(1 1 1) surface would be important for the oxidation of glucose and gluconolactone.