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

Abstract

The reduction of CO 2 to CO from a bicarbonate feedstock offers an opportunity to directly use aqueous carbon capture solutions, while bypassing ex-situ energy-intensive gaseous CO 2 regeneration. In this study, we resolved how the electrolyte cation identity (Li + , Na + , K + , Cs + ) affects the two reactions that make bicarbonate electrolysis possible: (i) the production of insitu CO 2 formed through reaction of HCO 3 À (from the catholyte) with H + (sourced from the membrane); and (ii) the electroreduction of CO 2 into CO. Our results show that cation identity does not change the rate of in-situ CO 2 formation, but it does enhance the rate of the CO 2 reduction reaction (CO2RR).Electrolysis experiments performed with a constant [HCO 3 À ] showed that CO selectivities progressively increased for the series Li + , Na + , K + , and Cs + , respectively. Optimization of the electrolyte composition yielded a CO selectivity of~80 % during electrolysis of 1.5 M CsHCO 3 solutions at 100 mA cm À 2 , while saturated LiHCO 3 solutions (0.84 M) yielded CO selectivities values of merely 30 % at the same current density. This study demonstrates a quantitative relationship between CO product selectivity and the cation radius, which provides a pathway to integrate bicarbonate electrolysis to carbon capture.

The insensitive cation effect on a single atom Ni catalyst allows selective electrochemical conversion of captured CO2 in universal media

“…1a). [16][17][18][19][20][21][22][23][24][25][26][27] However, inferior selectivity toward CO or formate has been exhibited compared with that of the conventional CO 2 -fed electrochemical reduction reaction (CO 2 RR). 28 The electrocatalytic activity is determined by the charge transfer at the electrode-electrolyte interface, which necessitates the thorough investigation of cCO 2 RR in terms of the interactions with the absorbent medium to improve the conversion activity.…”

Cation-Driven Increases of CO2 Utilization in a Bipolar Membrane Electrode Assembly for CO2 Electrolysis

“…In all of the above scenarios, however, researchers have separately determined the importance of having alkali cations present at the electrode–electrolyte interface when performing ECO2R. Unlike alkaline conditions where high ECO2R Faradaic efficiencies can be achieved over a range of cation concentrations, recent work in acidic or neutral pH cathode conditions highlights that a special consideration of cation concentrations is required to achieve high CO 2 reduction selectivities. − Combining these observations with previous BPMEA demonstrations that have traditionally suffered from poor CO 2 reduction selectivities, we hypothesized that the low selectivity in a BPMEA system could be overcome by increasing cation concentrations at the cathode. ,, Thus, if the low parasitic CO 2 loss of BPM’s can be achieved simultaneously with improved CO 2 reduction performance, high CO 2 utilization efficiencies would be possible as a result.…”

Development of catalysts and electrolyzers toward industrial-scale CO2electroreduction

“…163,164 Actually, it has been shown that cation crossover from the anode to the cathode can improve the electroreduction performance, but the formation of a precipitate makes the flow cell unstable during long-term operation. 165–168 To overcome this contradiction, Janáky et al 169 proposed an operando activation and regeneration process, where the cathode of a membrane zero-gap flow cell was periodically infused with alkali cation-containing solutions with good wetting properties. The activation was repeatable and the flow cell obtained a high performance with a CO partial current density of nearly 420 mA cm −2 for over 200 h.…”