Water Splitting in Brine: Engineering Electrolytes for Active, Stable, and Tunable Photoelectrochemical Cells

Abstract

Solar-driven water splitting is a promising source of renewable energy, but faces several obstacles to widespread implementation, including photoelectrocatalyst activity, stability, and control. While current remedies focus on improving catalysts themselves (e.g., fabricating protective layers, modifying surfaces for higher activity), engineering electrolyte remains an underutilized strategy for tuning properties of photoelectrochemical cells (PECs). The goal of this project is to leverage aqueous chemistry to increase activity, stability, and control of photoelectrocatalysis. We demonstrate that saline waters increase activity (as cathodic H2 and anodic O2 production) through increased conductivity, and employ varying concentrations of NaCl electrolyte. To increase stability, we add aqueous buffer species such as carbonate, acetate, and ammonia to resist extreme pH changes that can degrade electrodes. We investigate tunability of PEC performance by changing electrolyte pH, organic content, and silica concentrations. Ultimately, we investigate mechanistic impacts of aqueous species in a TiO2/MoS2 PEC (standard photoelectrodes) through experiments with synthetic electrolytes of controlled composition; we also aim to establish proof-of-concept for photoelectrocatalytic energy production in desalination brines, an underutilized waste stream.