(433g) Oxide-Encapsulated Electrocataysts for Selective and Stable CO2 Upgrading from Reactive Carbon Capture Solutions

The direct upgrading of CO₂ from bicarbonate-laden reactive carbon capture solutions is a promising approach for lowering energy consumption and enhancing CO₂ utilization of the process.¹ However, the high concentration of bicarbonate ions in reactive carbon capture solutions promote the bicarbonate-mediated hydrogen evolution (HER) reaction, thus lowering the selectivity towards CO.² Additionally, the trace amounts of metal impurities present in the electrolyte can deposit on the cathode and further shift the selectivity towards HER.³ In this work, we demonstrate a simple yet effective strategy to overcome these challenges by encapsulating Ag nanoparticle electrocatalysts with a semi-permeable TiO₂ nano-membrane to block bicarbonate ions from accessing the buried Ag active sites and therefore mitigate the bicarbonate-mediated HER. The TiO₂-encapsulted Ag (Ag@TiO₂) electrocatalyst showed a 50% lower HER partial current density at potentials more negative than -0.7 V vs. RHE, resulting in a 15% increase in CO faradaic efficiency. In situ surface-enhanced Raman spectroscopy (SERS) further revealed the absence of bicarbonate ions and the presence of CO₂ reduction intermediates near the buried interface, confirming the bicarbonate-blocking ability of the TiO₂ overlayer. During electrode stability evaluation conducted in the presence of 5 ppm Fe and 0.02 M ethylene diamine tetra-acetic acid (EDTA), Ag@TiO₂ demonstrated 15% higher steady-state faradaic efficiency than bare Ag. X-ray fluorescence (XRF) characterization results on spent electrodes indicated that the Fe deposition rate on Ag@TiO₂ was significantly lower than that on bare Ag, showing the positive effect of the TiO₂ overlayer in blocking Fe impurities. This work demonstrates the combination of oxide encapsulation and impurity scavenging with EDTA as an effective strategy for selective and stable syngas production in reactive carbon capture solutions.

References

1. Lee, G.; Rasouli, A. S.; Lee, B.-H.; Zhang, J.; Won, D. H.; Xiao, Y. C.; Edwards, J. P.; Lee, M. G.; Jung, E. D.; Arabyarmohammadi, F.; Liu, H.; Grigioni, I.; Abed, J.; Alkayyali, T.; Liu, S.; Xie, K.; Miao, R. K.; Park, S.; Dorakhan, R.; Zhao, Y.; O’Brien, C. P.; Chen, Z.; Sinton, D.; Sargent, E., CO₂ electroreduction to multicarbon products from carbonate capture liquid. Joule 2023, 7 (6), 1277-1288.

2. Marcandalli, G.; Goyal, A.; Koper, M. T. M., Electrolyte Effects on the Faradaic Efficiency of CO₂ Reduction to CO on a Gold Electrode. ACS Catalysis 2021, 11 (9), 4936-4945.

3. Hori, Y.; Konishi, H.; Futamura, T.; Murata, A.; Koga, O.; Sakurai, H.; Oguma, K., “Deactivation of copper electrode” in electrochemical reduction of CO₂. Electrochimica Acta 2005, 50 (27), 5354-5369.