Toward a Practical Solar-Driven CO2 Flow Cell Electrolyzer: Design and Optimization

A first-of-its-kind solar CO2 flow cell electrolyzer is reported here with a solar-to-fuel efficiency (SFE) of 6.5% at high operating currents (>1 A), orders of magnitude greater than those of other reported solar-driven devices that typically operate at currents of a few milliamperes. The approach of solar module-driven electrolysis, compared to monolithic photoelectrochemical cells, allows simpler manufacture, use of commercially available components, and optimization of the power transfer between the photovoltaic and the electrochemical systems. Employing commercial high-efficiency crystalline silicon solar cells with a large area flow cell CO2 electrolyzer (25 cm2), we present a procedure for optimizing the SFE of a decoupled photovoltaic electrolyzer by impedance matching the source and the load using their independent current–voltage characteristics. The importance of the voltage-dependent Faradaic efficiency of the electrolyzer on device performance and optimization is highlighted.