Experimental syngas production via co-electrolysis with AC:DC operated solid oxide cells for downstream fuel synthesis

Solid oxide cells enable syngas production from renewable electricity via co-electrolysis of H 2 O and CO 2 . Because co-electrolysis requires substantial energy to sustain operating temperature, electrothermally balanced operation through AC:DC modulation has been proposed as a strategy to improve thermal management. In this work, co-electrolysis performance was experimentally investigated on commercial fuel-supported single cells operating isothermally at 750 °C, analysing the effects of AC:DC frequency (0.1–1000 Hz) and long-term stability. AC:DC operation reduced the cell voltage by 20-23 mV compared to DC mode. At 0.1 Hz, oscillations in outlet gas composition were observed, whereas increasing frequency suppressed composition fluctuations and led to a slight decrease in methane formation, suggesting partial inhibition of methanation in the electrochemically active fuel electrode region. Long-term operation in DC and AC:DC mode (30 Hz, −0.5 A/cm 2 , 70% conversion) produced syngas with a (H 2 −CO 2 )/(CO + CO 2 ) ratio of 2.25, while AC:DC exhibited a low degradation rate throughout the test duration. These results demonstrate that AC:DC operation enables stable co-electrolysis with minimal degradation and reduced methane formation, indicating its potential to enhance both thermal management and process selectivity for downstream fuel synthesis. • AC:DC lowers co-electrolysis cell voltage compared to DC. • High frequencies provide stable composition and might reduce methane formation. • Long-term AC:DC tests showed stable syngas production and low degradation rates.