Investigation into the electrolysis performance of a novel directly solar irradiated solid oxide electrolysis cell

• A novel direct solar irradiated solid oxide electrolysis cell (DSiSOEC) is developed and experimentally demonstrated. • The DSiSOEC exhibits significantly higher efficiency than conventional electrical heating SOEC. • Direct solar irradiation increases the SOEC heating rate by 12 times compared to electric heating. • DSiSOEC saves about 76% of energy and shows promising energy saving prospects. Current coupling methods linking solar energy to solid oxide electrolysis cell (SOEC) mostly involve indirect coupling, with limited studies exploring direct coupling. This study is the first to evaluate a novel directly solar irradiated solid oxide electrolysis cell, anticipating a reduction in polarization loss incurred during the electrolysis process and improving the electrochemical performance of the system through direct solar irradiation. Additionally, it aims to reduce electric energy consumption required to maintain the high-temperature environment for the reaction and enhance the energy conversion efficiency of the electrolysis system, presenting a unique coupling technology. Hence, this paper proposes and develops the inaugural solar SOEC system, directly harnessing sunlight on the SOEC electrode surface, achieving stable and continuous hydrogen production through experimental methods. Experimental results demonstrate that direct solar irradiation increases the SOEC system’s heating rate by 12 times compared to electric heating, with a notably swifter response time. Under identical electrolysis voltages, the system exhibits significantly higher efficiency under direct solar irradiation than under electric heating. Moreover, for equivalent hydrogen production, the total energy input from solar energy is lower than that from electric heating, saving about 76 % of energy. Under specific conditions—solar radiation power of 123.2 W, electrolysis temperature of 655 °C, cathode-side gas input maintaining a water-hydrogen molar ratio of 8:2, and an electrolysis voltage of 1.5 V—the SOEC system sustains a nearly constant current density of about 359 mA/cm 2 for 3 h. Comparative experiments conducted under identical working conditions, both in solar and electrically heated environments, reveal that the electrochemical impedance spectroscopy indicates inhibited mass transfer processes during electrolysis under direct solar irradiation. Consequently, the electrochemical performance of the SOEC system operating under direct solar irradiation was lower than that under electrically heated environments, across varying electrolysis temperatures and water contents. This study uncovers the pivotal influence of direct solar irradiation on concentration losses during the electrolysis process. The corresponding concentration losses can be subsequently mitigated by optimizing the reactor structure of the solar SOEC system.