Assessment of Solar-to-Fuels Strategies: Photocatalysis and Electrocatalytic Reduction

The production of fuels in a solar refinery by the nonbiological conversion of CO₂ and water is a potential sustainable solution to meet our future energy needs. We develop a general process model for a solar refinery that allows us to assess the energetic and economic feasibility of a specific process. We demonstrate the utility of this model by analyzing two specific cases: 1) the photocatalytic conversion and 2) the photovoltaic-powered electrocatalytic reduction of CO₂ to yield a methanol product. From the analysis, we posit specific catalytic, reaction engineering, process engineering, and solar utilities targets to compete with industrial methanol production. For the photocatalytic process, the most important challenge is to improve the solar-to-fuels efficiency to at least 15 %, whereas for the electrocatalytic reduction process, even with much improved current density, cell potential, and reaction selectivity, the process will be ultimately limited by the price of solar (or other renewable) electricity.