Electrochemical reduction of noble metal species in ethylene glycol at platinum and glassy carbon rotating disk electrodes

Linear sweep voltammetry has been used to delineate the electrochemical beh avior of ethylene glycol, and to determine the reduction potential of sever al noble metal species in this solvent at room temperature. Ethylene glycol was found to be electrochemically inactive between -1.15 and 1.65 V at a g lassy carbon electrode, and between -0.82 and 2.0 V at a Pt electrode. Meta l reduction potentials determined using both rotating electrodes follow the sequence: AuCl4- >Ag+ > PtCl62- > Pd(NH3)(4)(2+). Under all conditions tes ted, ethylene glycol oxidation began at potentials more positive than metal reduction ones, thus suggesting that ethylene glycol cannot reduce these n oble metal species. However, finely divided Ag and Au, were synthesized at room temperature by reduction of their corresponding ions with ethylene gly col (the basis of the polyol process). This observed difference between ele ctrochemical results and chemical synthesis can be explained by recognizing that measured potentials are the sum of a thermodynamic potential and over potential. Comparison between metal reduction potentials and temperature fo r metal particle synthesis indicates that the potential becomes more negati ve as the temperature increases. These results may provide useful informati on to better understand the fundamentals of the polyol process. (C) 1999 El sevier Science B.V. All rights reserved.