Effect of Electrolyte and Adsorbates on Charging Rates in Mesoporous Gold Electrodes

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The classical model for porous electrodes reported by De Levie several decades ago (and expanded upon since then) was developed mainly to describe pores with micrometer-scale diameters. Presumably it will break down as pore diameters approach atomic dimensions. Mesoporous gold formed by dealloying is a valuable test platform for this because its 10 nm pores are on the boundary of this expected breakdown and because the electrochemical and surface properties of gold are relatively well understood. The De Levie model works for these electrodes at high salt concentrations, but under dilute conditions, there is not enough salt locally to charge the interface, increasing real impedance on intermediate time scales. Specific adsorption on pore walls can cause a similar increase and also cause an effective mobility decrease, tunable through electrolyte choice and the use of alkanethiol monolayers. These effects are not expected in micrometer-scale pores and are important considerations when designing devices with nanoporous electrodes.