The Role of TiO2 Doping on RuO2-Coated Electrodes for the Water Oxidation Reaction

Electrochemical water splitting into H2 and O2 presents a significant and challenging energy loss due to the high overpotential required at the anode. Today, in industrially relevant applications, dimensionally stable anodes (DSA) based on the electrocatalytic active RuO2 are conventionally utilized. To enhance the resistance against corrosion, incorporation of TiO2 in the RuO2-coated electrodes is widely employed. In the present work we have used scanning electrochemical microscopy (SECM) to demonstrate that TiO2-doped RuO2-coated electrodes, in addition to being more durable, also show an electrocatalytic activity that is, on average, 13% higher as compared to the pure RuO2-coated electrodes. We also demonstrate that cracks in the pure RuO2 coating are the most active zones, probably because Ti from the Ti support has diffused into the first applied layer of the RuO2 coating. To reveal the nature of this enhanced activity for water oxidation displayed on TiO2-doped RuO2 electrodes, we have employed X-ray photoelectron spectroscopy (XPS) for material characterization. The results show that the electrocatalytic activity enhancement displayed on the mixed (Ru1–x:Tix)O2 coating is promoted through a charge transfer from the RuO2 to the TiO2, which provides new and more reactive sites designated as activated RuO2δ+.This study has partly been carried out in the framework of the European Commission FP7 Initial Training Network “ELCAT”, Grant Agreement No. 214936-2. Portions of this research were performed at SPring-8 with the approval of Japan Synchrotron Radiation Research Institute as Nanotechnology Support Project of the Ministry of Education, Culture, Sports, Science and Technology (Proposal No. 2007A2005 and 2008A1671/BL-47XU)

Electrocatalysis, Fundamentals - Electron Transfer Process; Current-Potential Relationship; Volcano Plots

Electrocatalysis is the science exploring the rates of electrochemical reactions as a function of the electrode surface properties. In these heterogeneous reactions, the electrode does not only accepts or supplies electrons (electron transfer), as in simple redox reactions, but affects the reaction rates interacting with reactants, intermediates, and reaction products, i.e., acts as a catalyst remaining unchanged upon its completion. The term electrocatalysis, an extension to electrochemistry of the term catalysis (Greek kata (down) and lyein (to let)), was apparently first used in 1934[1]. The beginning of intensive research in this area can be traced back to early 1960s in connection with the broadening fuel cell research. Many electrocatalytic reactions have great importance. These include hydrogen, oxygen, and chlorine evolution; oxygen reduction oxidation of small organic molecules suitable for energy conversion (methanol, ethanol, formic acid); and reactions of organic syntheses. Important features of electrocatalytic reactions, facilitated by the application of the electrode potential, include (i) high reaction rates that can be achieved, (ii) high selectivity at defined potentials, and (iii) the unique direct energy conversion in fuel cells that are likely to become one of the major sources of clean energy. The main events in an electrocatalytic reaction are adsorption/desorption, electron transfer, and bond breaking/formation