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Controllable CO₂ conversion in high performance proton conducting solid oxide electrolysis cells and the possible mechanisms
- Shi, Nai, Xie, Yun, Huan, Daoming, Yang, Yi, Xue, Shuangshuang, Qi, Zeming, Pan, Yang, Peng, Ranran, Xia, Changrong, Lu, Yalin
- Journal of materials chemistry A 2019 v.7 no.9 pp. 4855-4864
- Fourier transform infrared spectroscopy, Raman spectroscopy, adsorption, anodes, carbon cycle, carbon dioxide, carbon monoxide, carbonates, cathodes, electrochemistry, electrolysis, electrolytes, greenhouses, methane, protons, reflectance, steam, thermodynamics
- To solve the increasing greenhouse problem and to achieve sustainable carbon cycling, effective conversion of CO₂ through chemical or electrochemical ways is key. In this study, efficient and controllable conversion of CO₂ mainly to CO and CH₄ has been demonstrated in a proton conducting solid oxide electrolysis cell (P-SOEC) using BaZr₀.₈Y₀.₂O₃₋δ (BZY) as the electrolyte and SrEu₂Fe₁.₈Co₀.₂O₇₋δ as the anode, in which an excellent current density of 1.23 A cm⁻² at 1.5 V was achieved at 550 °C and 100 hours of smooth operation is demonstrated. Compared with the pure steam electrolysis, impedance spectral investigations indicate that the presence of CO₂ in the cathode actually accelerates the electrode reactions, in contrast with that in a regular O-SOEC. This may be attributed to the higher adsorption of CO₂ and more effective conversion of protons over the BZY electrolyte. With the increase of electrolysis current, formation of both CO and CH₄ are enhanced, contradictory to the deduction based on thermodynamic calculations in which the concentration of CH₄ increases while that of CO reduces. In situ Raman and in situ diffuse reflectance FTIR spectroscopy (in situ DRIFTS) was conducted, and reaction routes for CO₂ were then proposed. Continuously replenished protons, which steadily and efficiently react with CO₃²⁻ to form–OCO– and finally CO, are suggested to play a critical role in the conversion of CO₂ and the formation of CO in the P-SOEC. Our results shed new light on future effective conversion of CO₂.