Electroconvection-driven fractal pattern diversification in electrodeposition

Abstract

Electrodeposition, the growth of metal films from electrolytes under an electric current, commonly produces a variety of intricate and often fractal patterns. While such morphologies have long fascinated researchers, predicting the transitions between them and their fractal dimensions remains a significant challenge. In this work, we identify electroconvection (EC), an electrokinetic instability near ion-selective electrodes, as a previously unrecognized yet dominant driver of pattern diversification. Through direct visualization and scaling analysis, we demonstrate that the resulting morphology depends critically on the competition between EC flow development and electrodeposit growth. At low voltages and/or high ion concentrations, classical growth modes emerge: migration-dominant, and diffusion-limited aggregation. However, at high voltages and/or low ion concentrations, we uncover two distinct EC-induced regimes: (i) EC-affected branch (electrodeposit-first) and (ii) EC-driven branch (EC-first). This newly proposed classification enables accurate prediction of both pattern bifurcation and fractal dimension, surpassing traditional diffusion- and reaction-limited models. Our findings provide the first direct evidence of electroconvection as a key mechanism shaping electrodeposition morphology, offering fresh insight into the complex dynamics of metal growth under electric fields.