H2/CO production via high temperature electrolysis of H2O/CO2 coupling with solar spectral splitting at a tunable cut-off wavelength.

Solar driven CO 2 /H 2 O splitting is a promising path for large-scale and long-term solar energy conversion and storage. In this work, a thermodynamic model of solar driven high-temperature CO 2 /H 2 O electrolysis was established, with the full solar spectrum split at a tunable cut-off wavelength for meeting the electrical and thermal energy demands of the process at a high efficiency. Compared with the system without spectral splitting, the solar-to-H 2 efficiency can be significantly improved from 36.0 % to 45.5 % by introducing spectral splitting. Besides, the optimal electrolysis temperature can be largely lowered, from 1623 K to 1323 K due to the significant reduction of the solar radiation input for electricity generation. The exergy efficiency of CO 2 electrolysis was shown to be higher than that of H 2 O electrolysis due to the higher molar exergy of CO compared to H 2 , although the first-law efficiency of H 2 O electrolysis is higher at T ele < ∼1200 K. A high concentration ratio of the solar-thermal process can lead to both high solar-to-fuel efficiency and high optimal electrolysis temperature because of the reduction of reradiation loss. The electrolysis temperature and the use of excessive CO 2 /H 2 O were shown to have an important effect on both the efficiency and the optimal cut-off wavelength because they are closely related with the thermal and electrical energy demands of the whole process. The optimal cut-off wavelength can be as low as 540 nm at electrolysis temperature of 1873 K (T ele = 1873 K) and excessive H 2 O coefficient of 6 (r = 6), and increases to the working limit of the photovoltaic material (900 nm in this work) as the electrolysis temperature and excessive coefficient decrease to T ele < 1023 K and r < 2. [Display omitted] • A thermodynamic model coupling the full solar spectrum with high temperature electrolysis of H 2 O/CO 2 was established. • Solar spectral splitting at a tunable cut-off wavelength was employed. • Solar-to-fuel efficiency can be significantly improved by the introduction of spectral splitting. • H 2 O and CO 2 electrolysis were compared and effects of various key parameters were investigated. • The model can be extended to other solar-driven hydrogen production processes with hybrid driving forces. [ABSTRACT FROM AUTHOR]