Unraveling Hybrid Energy Pathways for Solar-Driven CO ₂ Reduction toward Efficient Fuel Production

Efficient solar-to-fuel conversion demands the integration of multiple energy inputs to overcome the thermodynamic barrier for CO 2 reduction. Here, we develop and validate a unified modeling framework for a solar-driven membrane reactor that couples thermal, electrical, and mechanical driving forces within a solid oxide electrolysis cell (SOEC)-type configuration. The model is benchmarked against experimental polarization data over a wide range of temperatures and oxygen partial pressures, showing agreement within ±5%. Mapping this hybrid operating space identifies an optimal window (1473–1673 K, p O 2 > 10 –2 atm) that achieves peak solar-to-fuel efficiency of 30.4%. While higher temperatures reduce voltage requirements, radiative and enthalpy penalties dominate at elevated temperature. The analysis quantifies trade-offs associated with the operating voltage, gas separation work, and mass transport limitations. These findings define practical efficiency limits and offer experimentally grounded design principles for scalable, high-performance solar fuel systems enabled by hybrid energy pathways.