Electrodes Designed for Converting Bicarbonate into CO

Abstract

The deployment of electrolyzers that convert CO2 into chemicals and fuels requires appropriate integration with upstream carbon capture processes. To this end, the electrolytic conversion of aqueous (bi)­carbonate offers the opportunity to avoid the energy-intensive steps currently used to extract pressurized CO2 from carbon capture solutions. We demonstrate here that an optimized silver gas diffusion electrode (GDE) architecture enables conversion of model carbon capture solutions (i.e., 3 M KHCO3) into CO at partial current densities (J CO) greater than 100 mA cm–2 with CO2 utilization rates of ∼70%. These results exceed the performance of any previously reported liquid-fed CO2 electrolyzers and rival gas-fed devices. We were able to hit these metrics through the systematic design of gas diffusion layer (GDL) components (e.g., polytetrafluoroethylene) and catalyst layer constituents (i.e., Nafion, silver) on CO production. A key finding of this work is that hydrophobic GDE components (which are common to gas-fed CO2RR electrolyzers) decrease in situ CO2 generation and thus the formation of the final CO product. These findings show a clear path toward industrially relevant reactors that couple electrolytic CO2 conversion with carbon capture.

Electrolytic Conversion of Bicarbonate Solutions to CO at >500 mA cm-2 and 2.2 V

“…We sought to bypass these challenges by developing a CO2RR electrolyzer that uses a liquid bicarbonate feed instead of gaseous CO 2 [23][24][25][26] . The efficient electrolysis of bicarbonate solutions (e.g., KHCO 3(aq) ), a common eluant of carbon capture units, can form the same CO2RR products as an electrolyzer fed with gaseous CO 2 , but without the need for CO 2 regeneration and pressurization (Fig.…”

“…Bicarbonate electrolyzers are also proven to yield CO 2 utilization values (the fraction of the CO 2 feedstock that is converted into the desired product) >40%; these values are much higher than the 1-20% typically reported for gaseous CO 2 -fed electrolyzers 21,24,27 All reports of bicarbonate electrolysis to date use bipolar membranes (BPMs) 23,24,26,[28][29][30] . These…”

Electrochemical carbon dioxide capture to close the carbon cycle

“…An example is the modular, sequential CO 2 capture and conversion system that uses the pH-swing concept to produce CO electrochemically [45,46]. In addition, reactive CO 2 capture, in which the CO 2 capturing medium pre-concentrates the dilute feed and produces favorable local micro-environments, has become an emerging field for integrated CO 2 capture and conversion using electrochemical techniques [47,48].…”

Impact of Alkali Cation Identity on the Conversion of HCO3− to CO in Bicarbonate Electrolyzers

“…[13][14][15] These challenges with gaseous feedstocks prompted us to design bicarbonate electrolyzers that directly convert aqueous carbon capture solutions (e. g., KHCO 3(aq) ) into CO while also producing OH À to regenerate the carbon capture sorbent (Figure S2). [16][17][18][19] Bicarbonate electrolysis is made possible by using a flow cell architecture with a bipolar membrane (BPM) that separates the anode and cathode compartments (Figure 1). Water dissociates in the BPM under a reverse bias to provide H + to the cathode and OH À to the anode compartments [Equation (1)].…”