Solar thermochemical splitting of CO2 into separate streams of CO and O2 with high selectivity, stability, conversion, and efficiency

Abstract

Developing solar technologies for converting CO2 into fuels has become a great energy challenge, as it closes the anthropogenic carbon cycle and leads to the production of sustainable transportation fuels on a global scale. However, the low mass conversion, poor selectivity, and/or low energy efficiency of current approaches have hindered their industrial implementation. Here, we experimentally demonstrate the solar-driven thermochemical splitting of CO2 into separate streams of CO and O2 with 100% selectivity, 83% molar conversion, and 5.25% solar-to-fuel energy efficiency. This benchmark performance was accomplished using a 4 kW solar reactor featuring a reticulated porous structure, made of ceria, directly exposed to 3000× flux irradiation and undergoing redox cycling via temperature/pressure-swing operation. The dual-scale interconnected porosity (mm and μm-sized pores) of the ceria structure provided volumetric radiative absorption and enhanced heat/mass transport for rapid redox kinetics, while 500 consecutive redox cycles further validated material stability and structure robustness. A detailed energy balance elucidates viable paths for achieving higher efficiencies and for large-scale industrial implementation using an array of modular solar reactors integrated into the established solar concentrating infrastructure.