This study is led by Dr. Houfu Lv, Prof. Guoxiong Wang and Prof. Xinhe Bao (Dalian Institute of Chemical Physics, Chinese Academy of Sciences). Solid oxide electrolysis cells provide a practical solution for direct conversion of CO 2 to chemicals, however, an in-depth mechanistic understanding of the dynamic reconstruction of active sites for perovskite cathodes during CO 2 electrolysis remains a great challenge. Herein, the team identify that iridium-doped Sr 2 Fe 1.45 Ir 0.05 Mo 0.5 O 6-δ (SFIrM) perovskite displays a dynamic electrochemical reconstruction feature during CO 2 electrolysis with abundant exsolution of highly dispersed IrFe alloy nanoparticles (NPs) on the SFIrM surface, which is well investigated using in situ electrochemical X-ray diffraction (XRD), near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), and X-ray absorption spectroscopy (XAS).
During the electrochemical reconstruction and activation process under a constant voltage mode at 1.0 V for ~4 000 s, the current density gradually increased and finally approached a steady state. The exsolved IrFe alloy NPs display high dispersion with an average diameter of ~1.0 nm and a density above 80 000 μm -2 on the SFIrM surface. Moreover, the activation time was reduced rapidly with increasing applied voltage (constant voltage: 1.2 V, activation time: within 250 s), with similar particle size and density of the exsolved metal NPs during CO 2 electrolysis.
In addition, in situ NAP-XPS measurements were employed to monitor their catalytic process during CO 2 electrolysis to reveal the intrinsic reaction mechanism. Upon application of electrochemical polarization, a broader peak appeared at ca. 290 eV in the C 1 s spectra, which could be attributed to carbonate species and was most probably decisive for CO 2 electrolysis. The peak area of carbonate species on the Sr 2 Fe 1.5 Mo 0.5 O 6-δ (SFM) cathode was weaker than that on the SFIrM cathode. The enhanced carbonate intermediate species signal confirmed that the in situ reconstructed IrFe@SFIrM interfaces facilitated CO 2 adsorption and activation. IrFe@SFIrM interfaces were thus proposed as the catalytically active sites that devoted to a higher CO 2 electrolysis performance than SFM.
The initial exsolved IrFe alloy NPs could be re-dispersed sufficiently into smaller nanoclusters via a brief oxidation treatment in air. IrFe alloy NPs were regenerated when the applied voltage was switched on again, and the appearance of the intermediate carbonate peak could be further obtained. The oxidative re-dispersion strategy could efficiently improve the stability by delaying particle aggregation.
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See the article:
In situ electrochemical reconstruction of Sr 2 Fe 1.45 Ir 0.05 Mo 0.5 O 6-δ perovskite cathode for CO 2 electrolysis in solid oxide electrolysis cells
https://doi.org/10.1093/nsr/nwad078
National Science Review