Quantitative analysis of electrochemical diffusion layers using synchrotron infrared radiation

The high spatial resolution provided by synchrotron generated infrared (IR) radiation has been used to map spatiotemporal concentration profiles in the diffusion layer around a working electrode. An IR spectroelectrochemcial cell employing an inlaid band electrode has been developed that eliminates geometric issues with previous designs. The new cell was used to follow the diffusion layers produced by the reduction of ferricyanide and the oxidation of hydroquinone. Differences between the diffusion coefficients of ferricyanide and ferrocyanide determined here and the accepted literature are caused by the water-structure forming properties of different supporting electrolytes. The diffusion coefficients of hydroquinone and p- benzoquinone determined by diffusion layer mapping have been shown to be self-consistent with independently determined diffusion coefficients as measured using hydrodynamic linear sweep voltammetry. The consistency of the diffusion coefficients achieved for all species demonstrates that the spectroelectrochemical cell design allows for accurate monitoring of concentration profiles of species within electrochemical diffusion layers.