ELECTROCHEMICAL PROMOTION OF CATALYSIS AT METAL SURFACES

摘要

It is now well-established [1] that the catalytic activity of metal films deposited on solid electrolytes can be promoted dramatically and in a reversible way under potential (or current) application between the catalyst and a counter electrode (also deposited on the electrolyte). The enhancement of reaction rate may be several orders of magnitude higher than that predicted by Faraday's law alone. This phenomenon is known as the Non-Faradaic Modification of Catalytic Activity (NEMCA) or Electrochemical Promotion (EP). Recent models to describe the electrochemical promotion of catalysis involve describing the spillover of ionic species onto an active catalyst surface. The stability of these ionic species results in the formation of a surface double layer on the gas-exposed catalyst surface. In turn, this surface double layer causes a modification of the catalyst work function. The work function modification is then believed to influence surface adsorption/desorption equilibria [2] or surface kinetic rate constants [3,4]. To date these models have solely been applied to describe the electrochemical promotion of working electrodes in solid state electrochemical cells where the support can be considered to be a pure ion conductor. Here we will extend such models to account for the behaviour of mixed-conducting (electronic and ionic) supports. This has implications for the behaviour of conventional supported-metal catalysts. These implications will be discussed within the framework of such an 'extended' model of electrochemical promotion.