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

Jun-Kyu Lee,Young-Soo Ahn,Gi-Hwan Kang,Jin-Seok Lee

doi:10.3390/app8112131

Abstract

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.

Highlights

Demand for photovoltaic (PV) systems, that have been installed since the 1990s, has grown exponentially [1]
Ag has excellent solubility in methanesulfonic acid (MSA), the electrochemical efficiency of MSA is not expected to be good, owing to its high viscosity, because the Ag ions have lower mobility in a high-viscosity electrolyte [18], which is related to diffusion [19,20]
The recovery of Ag from crystalline silicon (c-Si) solar cells using MSA, rather than inorganic acids, is advantageous from an environmental point of view, as MSA does not give rise to typical problems associated with the generation of waste acid solutions and toxic fumes

Summary

Introduction

Demand for photovoltaic (PV) systems, that have been installed since the 1990s, has grown exponentially [1]. A significant number of end-of-life (EoL) modules are expected to be generated, and this number is growing exponentially because the lifetime of a PV module is approximately 20–30 years [2]. PV modules have been included in the European Waste. Electrical and Electronic Equipment (WEEE) directive for electronic waste in 2012 [3], as well as in the domestic laws of European countries. According to the WEEE directive, the annual collection target is 65% (by mass) of all equipment in the market, or 85% of waste generated starting from 2018. The recovery target is 85%, and recycling is 80% over the same period [4]. Among the PV module components, silver (Ag), which is used as a front electrode of a solar cell, is one of the precious materials.

Methods

Results

Conclusion