Correlation of hierarchical porosity in nanoporous gold with the mass transport of electron transfer-coupled-chemical reactions

Optimization of mass transfer within a porous material is a highly promising strategy to improve the efficiency of electrode reactions. Herein, nanoporous gold (NPG) modified gold electrode is investigated to study the mass transport of ascorbic acid (AA), which oxidation process is characterized by an electrochemical coupled 1st order chemical reaction, commonly termed as EC1 reaction. The template-assisted synthesis of NPG results into the formation of a highly pure and porous film of gold. However, the surface porosity of NPG depends on the choice of electrodeposition parameters, such as deposition time (td) and potential (Ed) and the size of the substrate. Such porosity variation of NPG strongly influences the voltammetric profile of AA anodic reaction, displaying sigmoidal, non-symmetric and symmetric peak features. The analysis of mass transport behaviour of AA reveals a combination of diffusion and thin layer EC1 mechanism, predominance of which is determined by the Ed and td selected for NPG synthesis, as well as the size of the Au substrate. The mass transport of AA on NPG prepared on Au microelectrodes experienced a significant diffusion from bulk solution, owing to the larger pores, which permits the easier exchange of redox species between the NPG volume and the bulk solution. On the contrary, mass transport of AA on NPG deposited on big Au electrode has a significant contribution of thin layer diffusion, attributed to the smaller surface pores of NPG, which limits the exchange of AA and its oxidized form from the bulk solution