The effect of number of layers of nanoporous gold films on their electrochemical behaviour

Nanostructured material based electrodes are frequently used in electrochemical analysis and catalysis for their multifarious favourable properties. The deep interior surfaces of these electrodes are, however, not often well addressed due to diffusion constrains, leading to a poor materials economy. The present work demonstrates thickness control and manipulation of dealloyed nanoporous gold (NPG) electrodes using a layer-by-layer method. The viability of the method is confirmed by electron microscopy and electrochemical characterisation. The effect of the number of NPG layers (from one to five, leading to a thicknesses range of 100-500 nm) on the electrochemical behaviour is evaluated, based on the 1) redox behaviour of a diffusing redox probe ferrocenemethanol, 2) dopamine undergoing proton-coupled two-electron transfer, 3) surface-confined osmium complex modified redox polymer, and 4) the bioelectrocatalysis of an enzyme, fructose dehydrogenase (FDH). Notably, the results show that the best performance is achieved for an intermediate number of NPG layers, suggesting that the tedious efforts in fabricating deep/ thick nanostructures can be optimised.