Sunlight-Driven CO <sub>2</sub>-to-Fuel Conversion: Exploring Thermal and Electrical Coupling between Photovoltaic and Electrochemical Systems for Optimum Solar-Methane Production

Abstract

A novel Photovoltaic-Electrochemical (PV-EC) integrated system is designed, capable of converting CO2 into carbon-based fuels, in which “smart” synergetic effects between the two technologies are explored, such as thermal coupling (TC) and electronic regulation (DC-DC), that can strongly improve the energetic performance. We show that, when thermally-coupled, the PV and EC cells exhibit a symbiotic behaviour: the solar-to-fuel efficiency stays almost temperature-independent due to improved reaction kinetics, which compensates for photovoltaic thermal losses. The electronic regulation is equally important, because it guarantees that all power provided by PV generation is channelled to the EC load. When conjugated with TC, the DC-DC converter can boost production up to 50% beyond the TC improvement. For operating temperatures in the 40-90°C range, combined TC and DC-DC can boost production by up to 586% and 42.9% for Perovskite/Si double-junction and mono-crystalline Si solar cells, respectively. These solutions are tested in two PV-powered pathways for methane production: 1-step, CO2 →CH4, and 2-step, CO2 →Syngas→CH4; where in the latter the intermediate syngas is converted to methane through catalytic hydrogenation. Despite the advantageous simplicity of the direct production (1-step) of methane, the comparison between the two paths showed that the second route achieves close to 20% higher annual yield.