Challenges in Product Selectivity for Electrocatalytic Reduction of Amine-Captured CO2: Implications for Reactive Carbon Capture
CO2 is a potential feedstock for carbon-based fuels or materials, but is only available in dilute streams. Integrated processes for CO2 capture and conversion directly valorize the CO2 captured by sorbent materials, skipping the energetically expensive sorbent regeneration step. Amines are the most heavily studied liquid-phase sorbent materials for CO2 capture from dilute streams. Amines react with CO2 in a 2:1 ratio to form the corresponding ammonium carbamate. Ammonium carbamate [NH4][H2NCO2] was tested as the substrate using the highly selective and robust CO2-to-formate reduction electrocatalyst [(tBuPOCOP)Ir(H)(NCCH3)2], where (tBuPOCOP) is the tridentate pincer ligand 2,6-bis(ditert-butyl-phosphonito). When ammonium carbamate was used as the substrate instead of CO2, only hydrogen was produced. An equivalent electrolysis with ammonium hexafluorophosphate with CO2 also resulted in primarily hydrogen. Methyl carbamate and urea were also tested as substrates as proxies for carbamate that do not contain an equivalent of ammonium, and there was also negligible reduction to carbon-based products. These results indicate that the loss of selectivity observed for aminecaptured CO2, or ammonium carbamate, is likely due to the generation of the acidic ammonium equivalent as well as the greater challenge of reducing carbamate compared to CO2. This study illustrates that catalysts with high selectivity for concentrated CO2 can favor hydrogen evolution and loss of carbon-based products when amine-captured CO2 is used instead.
- Research Organization:
- Univ. of California, Irvine, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- SC0020275
- OSTI ID:
- 2567114
- Journal Information:
- ACS Omega, Journal Name: ACS Omega Journal Issue: 21 Vol. 10; ISSN 2470-1343
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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