Efficient Recovery of Silver from Crystalline Silicon Solar Cells by Controlling the Viscosity of Electrolyte Solvent in an Electrochemical Process

We present electrowinning of silver (Ag) from crystalline silicon (c-Si) solar cells using a solution of methanesulfonic acid (MSA) as the electrolyte. Ag dissolved effectively in MSA because of its high solubility in MSA; however, the electrochemical recovery of Ag from MSA solutions was found to be inefficient because of the low mobility of Ag ions in MSA, owing to its high viscosity. Therefore, we decreased the viscosity of MSA by adding deionized (DI) water, as a possible method for enhancing the mobility of Ag ions. The concentrations of added DI water were 0, 1.1, 5.0, 9.3, and 20.8 M, respectively. Further, we performed cyclic voltammetry for each solution to calculate the diffusion coefficient using the Randles–Sevcik equation, and analyzed the viscosity of MSA solutions depending on the concentration of added water using a rheometer. The morphologies of the electrochemically recovered Ag particles changed with variations in the amount of the added water, from branch-like structures to dendritic structures with a decreasing size. Moreover, the cathodic current efficiency increased considerably with increasing concentration of the added DI water. Finally, we recovered Ag with >99.9% (3N) purity from c-Si solar cells by electrowinning, as determined by glow discharge mass spectrometry.