Asymmetric rectified electric and concentration fields in multicomponent electrolytes with surface reactions

Asymmetric rectified electric fields (AREFs) are time-averaged residual electric fields that form upon the application of an AC field to a two-electrode cell. AREFs have been used to explain discrepancies between experimental and theoretical results of directed colloidal assembly. Current understanding in the literature states that AREFs can arise only due to asymmetric ion diffusivities. While recent experimental literature has employed electrochemical reactions to drive directed colloidal assembly, the effects of surface electrochemical reactions on AREF theory remain unexplored.

Here, we solve the Poisson-Nernst-Planck equations for multicomponent electrolytes with surface reactions in the limit of low applied potentials. Crucially, we find that in addition to diffusivity asymmetry, surface reactions can also give rise to the formation of AREFs. Furthermore, we discover that the strength of AREFs induced by electrochemical reactions can be higher than that resulting from diffusivity asymmetry alone. Additionally, we report the emergence of asymmetric rectified concentration fields, which can lead to the directed assembly of colloids via diffusiophoresis, in agreement with the recently proposed mechanism of electrodiffusiophoresis in the literature.