The global average concentration of CO2 in the atmosphere has been rising rapidly for past several decades and has already crossed the 400 ppm mark for the first time in recorded history. An effective way to tackle this problem is to capture CO2 and convert it into fuels or chemicals. A solid oxide electrolysis cell (SOEC) can efficiently convert CO2 and H2O into a mixture of CO and H2 (synthesis gas). If the energy needed for this process is obtained from a renewable source, SOEC can become an attractive sustainable technology for CO2 utilization. In the current study, Ni and Co- doped A-site deficient perovskite materials of the composition La0.7Sr0.2NixCoyFe1-x-yO3 (x,y=0; x=0, y=0.2; x=0.1, y=0.1; x=0.2, y=0) are studied as SOEC cathodes for co-electrolysis of CO2 and H2O at 800°C, with a focus on the tunability of the product synthesis gas composition. In-situ XRD, XPS, Raman spectroscopy, electronic conductivity measurements, oxygen mobility test, in-situ DRIFTS and XANES were used to investigate the effect of dopants on the structural and chemical properties of the perovskite materials. During CO2 and H2O co-electrolysis, Faradaic efficiency for synthesis gas production was the lowest for the Co- doped sample and highest for the Ni- doped sample, and the H2/CO ratio in the produced syngas increased with increasing Ni content in the cathode material. This ratio could be controlled by adjusting the B-site dopant levels, cell voltage and H2O/CO2 ratio in the cathode feed stream. In-situ XANES data collected from the cathodes during CO2 and H2O co-electrolysis suggest that the Co ions in La0.7Sr0.2Co0.2Fe0.8O3 get oxidized during current flow, which can diminish the number of oxygen vacancies in the material and thus lowers the electrochemical performance. Formation of graphitic carbon was detected on post-electrolysis Co- doped cathode which is another reason behind the lower Faradaic efficiency obtained from this cathode. The Ni- doped cathodes did not lead to any such carbon formation during the electrolysis process. A long-term co-electrolysis test performed on a La0.7Sr0.2Ni0.1Co0.1Fe0.8O3 cathode for more than 100 hours showed stable electrochemical performance, high Faradaic efficiency and resistance to carbon formation.

Production of syngas with controllable H2/CO ratio by high temperature co-electrolysis of CO2 and H2O over Ni and Co- doped lanthanum strontium ferrite perovskite cathodes

2019 Fall National Meeting

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