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

Abstract

The direct electroconversion of captured CO2 is attracting attention as the streamlined manner for the carbon capture and utilization, omitting energy-demanding CO2 separation processes. In amine-based conventional capturing media, however,...

Ammonia-Mediated CO2 Capture and Direct Electroreduction to Formate

“…Apart from the KOH solution, amines such as monoethanolamine (MEA) solution are commonly used for capturing CO 2 due to the facile kinetics of the formation of amine-CO 2 adducts (RXN ). − Conversion of the MEA-CO 2 adduct to CO has been reported in previous studies but only at low current densities (<50 mA cm –2 ). ,, In addition to the insufficient i -CO 2 concentration, the bulky carbamate (RNHCOO – ) and ethanolammonium (RNH 3 + ) ions may hinder the mass transport at the electrode double layer, which limits the i -CO2RR performance.…”

“…The total i -CO 2 produced from NH 4 HCO 3 was 3.4 or 10.8 times that of KHCO 3 or MEA-CO 2 , respectively. The poor CO2RR performance with MEA-CO 2 could be attributed to the bulky ions of MEA-CO 2 that inhibit i -CO 2 formation and transportation . Furthermore, by comparing the results with the corresponding control cells without applied current (Table S1), we found the portion of produced i -CO 2 from thermal decomposition was 93% for NH 4 HCO 3 , much higher than that for KHCO 3 (52%), highlighting the ease of CO 2 release from NH 4 HCO 3 .…”

“…As a suitable alternative, CO 2 can be captured by ammonium (NH 4 + ) solution to form ammonia bicarbonate (NH 4 HCO 3 ) (RXN ). , Compared to MEA, NH 3 has a higher CO 2 -capturing capacity because it doubles the stoichiometric ratio of CO 2 to the capturing agent (RXN and ) . More importantly, release of CO 2 from NH 4 HCO 3 requires much lower energy than that from MEA-CO 2 or KHCO 3 , as illustrated by their decomposition temperatures: 36, 120, and 150 °C for NH 4 HCO 3 , MEA-CO 2 , and KHCO 3 , respectively .…”

Uncovering the active species in amine-mediated CO2 reduction to CO on Ag

“…To address these vital open questions, we herein study the influence of accessible solution-state handles-CO2 partial pressure, pH, the properties of the amine and the resulting solution speciation-on CO2R to CO on Ag catalysts. While other products may in theory be possible, prior efforts have focused mainly on CO2-to-CO formation in amine capture solutions [11][12][13] , making this reaction of highest relevance at present. Additionally, the simple 2ereduction of CO2 to CO on weakly binding catalysts like Ag and Au 14,15 is well-understood in aqueous, amine-free CO2R, enabling us to better isolate the influence of the amine on the reaction.…”

“…carbamate which forms from the enthalpically favorable reaction (~ -80 to -100 kJ/mol 21 ) between the free amine and CO2, bears CO2 to the electrode surface and therefore functions as an active species. On the one hand, both Chen et al 22 and Kim et al 12 proposed that the CO2R reaction occurred via electron transfer to dissolved CO2,aq in aqueous MEA-containing electrolytes. Alternatively, Lee et al 11 proposed that aqueous amine-coordinated-CO2 (carbamate) was responsible for the formation of CO, as the electrolytes in their study were sparged with N2 to reduce the concentration of dissolved CO2 in the bulk electrolyte.…”