Sunlight-driven CO2-to-fuel conversion: exploring thermal and electrical coupling between photovoltaic and electrochemical systems for optimum solar-methane production

Abstract

Artificial photosynthesis is regarded as the best way to protect the environment while producing carbon-based fuels, because it closes the anthropogenic carbon cycle. Herein we simulate a Photovoltaics-Electrochemical (PV-EC) system capable of converting CO2 into usable carbon-based fuels, in order to analyse the implementation of synergetic techniques such as intermediate electronic regulation and thermal coupling on the improvement of the energetic performance. We proved that, when thermally coupled, the two cells of the system 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 to enhance efficiency because it guarantees that we make use of the full PV power output to the EC load. These solutions are tested in two pathways for methane production: 1-step, CO2→CH4, and 2-step, CO2→Syngas→CH4, exhibiting solar-to-fuel efficiency gains up to 586% and 43%, respectively, when compared with the systems without both the thermal coupling and the DC-to-DC converter. Lastly, an energetic comparison of the two pathways was made. The direct production (1-step) of methane showed to provide 20% less energy than the second path, where syngas is produced and converted to methane through a Fischer-Tropsch synthesis at 350 °C and 10 atm.