Development of novel electrode materials for the electrocatalysis of oxygen-transfer and hydrogen-transfer reactions

摘要

The fundamental aspects involved in the electrocatalysis of anodic O-transfer reactions and cathodic H-transfer reactions are studied. The main focus of the study is to increase our knowledge of the processes controlling the transfer reactions and apply this knowledge to the development of novel electrode materials for use as electrochemical sensors. The transfer reactions have prerequisite steps of reactant adsorption at the electrode surface as well as adsorption of O atoms, for O-transfer reactions, and H atoms, for H-transfer reactions. Investigations of anodic O-transfer reactions reveal that MnO2 film electrodes show improved response for dimethyl sulfoxide (DMSO) oxidation as compared to the Au substrate. Doping of the MnO2 film electrodes with Fe(III) enhances electrocatalytic activity for DMSO oxidation. Thermally prepared RuO2 films provide an electrode material that not only exhibits electrocatalytic activity for O-transfer reactions but shows mechanical and chemical stability as well. Doping of the RuO2 film electrodes with Fe(III) further increases activity and provides an electrochemical sensor with detection capabilities for DMSO, methionine, and cysteine in the range of 3.2 x 10-4 mM. Reasons for the increase in activity, caused by doping of the metal oxide films with Fe(III), are attributed to separation of surface sites involved in the adsorption processes required for O-transfer reactions. An investigation of H-transfer reactions, specifically nitrate reduction, initially examines various metals for activity to determine candidates for use in alloy electrodes. The Sb10Sn20Ti 70, Cu63Zn37, and the Cu25Ni75 alloy electrodes all show improved response for nitrate reduction as compared to their pure component metals. Reasons for the improved activity are speculated to involve the separation of surface adsorption sites for the processes involved in nitrate reduction. Further examination of Cu-Ni alloys reveals that the nitrate reduction occurs via an 8 e- process at the Cu75Ni25 alloy electrode and a 6 e - process at the Cu50Ni50 and the Cu 25Ni75 alloy electrodes. Flow injection data obtained using Cu50Ni50 and Cu25Ni75 electrodes exhibit detection limits for nitrate of 0.95 muM and 0.60 muM, respectively.