Ordered Array Electrodes Fabricated by a Mask-Assisted Electron-Beam Method as Platforms for Studying Kinetic and Mass-Transport Phenomena on Electrocatalysts

Abstract

This work describes a method for fabrication of extensive ordered arrays of microelectrodes with varied geometries, surrounded either by an insulating surface of poly(methyl methacrylate) (PMMA) or by a conductive material such as gold or glassy carbon (GC). The method is based on procedures from electron beam lithography (EBL) but, in contrast to classic EBL, it can be applied by using widely available conventional SEM instruments that are not specifically tailored for EBL operation. The electron gun of the SEM is used to irradiate and modify a PMMA film that is covered by a micro- or nano-structured mask (i.e., a TEM grid), which is further selectively revealed. Each array can be evaluated in two configurations, when it is surrounded by the PMMA film, and when it is in contact with the exposed support after PMMA removal. The first configuration is useful to evaluate the electrochemical behavior of pure microelectrode arrays for correlating it with model equations. The second configuration is particularly useful when the substrate material by itself is inactive for the studied reaction. In the latter case, any detected differences between the electrochemical behavior of the PMMA-coated array and that of the bi-component array should come from the contributions of the microelectrode boundaries. These arrays were employed for studying the hydrogen oxidation reaction in alkaline medium on Au/Rh and on GC/Rh in order to detect possible kinetic interactions of both components at the heterojunctions.