Review—Electrochemistry for Sustainable Solar Photovoltaics

Electrochemistry and solar photovoltaics are traditionally considered to be in two different domains of science and technology. However, electrochemistry will play an indispensable role in sustaining the production and deployment of solar panels in the coming decades. This paper presents three examples on how electrochemistry will lead to solutions to several roadblocks to sustainable solar photovoltaics. The first example is storage of intermittent solar electricity through a zinc↔zinc oxide loop which requires two technologies: (1) solar electroreduction of zinc oxide and (2) a mechanically-recharged zinc/air battery. Compared to the hydrogen↔water loop, the zinc↔zinc oxide loop is advantageous for long-term (seasonal to multiyear) storage and global trade of solar electricity. The second example is electrorefining to produce solar-grade silicon from metallurgical-grade silicon. Ultrapure materials by electrolysis is an unanswered challenge in electrochemistry. A two-step three-electrode electrorefining process is proposed. Practical challenges in achieving ultrapure silicon by molten-salt electrorefining are outlined. The final example is metal recovery from waste solar panels. Four metals in silicon panels are worth recovery: silver, lead, tin, and copper. They can be leached out in nitric acid and the leachate contains multiple metals. Sequential electrowinning can recover the metals one by one based on their different reduction potentials. The remaining issues in this process are discussed.