The impact of flue gas impurities and concentrations on the photoelectrochemical CO2 reduction

Reactive carbon capture using electrochemical reactors

The electrolytic upgrading of CO2 presents a promising strategy to mitigate global CO2 emissions while generating valuable carbon-based products such as carbon monoxide, formate, and ethylene. However, the adoption of industrial-scale CO2 electrolyzers is hindered by the high energy and capital costs associated with the purification and pressurization of captured CO2 prior to electrolysis. One promising solution is "reactive carbon capture," which involves the electrolytic conversion of the eluent from CO2 capture units, or the "reactive carbon solution," directly into valuable products. This approach circumvents the energy-intensive processes required for electrolyzers fed with gaseous CO2. This Tutorial Review highlights recent advances for reactive carbon capture, showcasing its potential as a scalable solution for electrolyzers that upgrade CO2 into fuels and products.

Direct low concentration CO2 electroreduction to multicarbon products via rate-determining step tuning

Direct converting low concentration CO2 in industrial exhaust gases to high-value multi-carbon products via renewable-energy-powered electrochemical catalysis provides a sustainable strategy for CO2 utilization with minimized CO2 separation and purification capital and energy cost. Nonetheless, the electrocatalytic conversion of dilute CO2 into value-added chemicals (C2+ products, e.g., ethylene) is frequently impeded by low CO2 conversion rate and weak carbon intermediates' surface adsorption strength. Here, we fabricate a range of Cu catalysts comprising fine-tuned Cu(111)/Cu2O(111) interface boundary density crystal structures aimed at optimizing rate-determining step and decreasing the thermodynamic barriers of intermediates' adsorption. Utilizing interface boundary engineering, we attain a Faradaic efficiency of (51.9 ± 2.8) % and a partial current density of (34.5 ± 6.4) mA·cm-2 for C2+ products at a dilute CO2 feed condition (5% CO2 v/v), comparing to the state-of-art low concentration CO2 electrolysis. In contrast to the prevailing belief that the CO2 activation step (C O 2 + e - + * → C O 2 - * ) governs the reaction rate, we discover that, under dilute CO2 feed conditions, the rate-determining step shifts to the generation of *COOH (C O 2 - * + H 2 O → C * O O H + O H - ( a q ) ) at the Cu0/Cu1+ interface boundary, resulting in a better C2+ production performance.

Simultaneous Capture of CO2 Boosting Its Electroreduction in the Micropores of a Metal-organic Framework

Integration of CO2 capture capability from simulated flue gas and electrochemical CO2 reduction reaction (eCO2 RR) active sites into a catalyst is a promising cost-effective strategy for carbon neutrality, but is of great difficulty. Herein, combining the mixed gas breakthrough experiments and eCO2 RR tests, we showed that an Ag12 cluster-based metal-organic framework (1-NH2 , aka Ag12 bpy-NH2 ), simultaneously possessing CO2 capture sites as "CO2 relays" and eCO2 RR active sites, can not only utilize its micropores to efficiently capture CO2 from simulated flue gas (CO2  : N2 =15 : 85, at 298 K), but also catalyze eCO2 RR of the adsorbed CO2 into CO with an ultra-high CO2 conversion of 60 %. More importantly, its eCO2 RR performance (a Faradaic efficiency (CO) of 96 % with a commercial current density of 120 mA cm-2 at a very low cell voltage of -2.3 V for 300 hours and the full-cell energy conversion efficiency of 56 %) under simulated flue gas atmosphere is close to that under 100 % CO2 atmosphere, and higher than those of all reported catalysts at higher potentials under 100 % CO2 atmosphere. This work bridges the gap between CO2 enrichment/capture and eCO2 RR.

Oxide-Derived Bismuth as an Efficient Catalyst for Electrochemical Reduction of Flue Gas

Post-combustion flue gas (mainly containing 5-40% CO₂ balanced by N₂ ) accounts for about 60% global CO₂ emission. Rational conversion of flue gas into value-added chemicals is still a formidable challenge. Herein, this work reports a β-Bi₂ O₃ -derived bismuth (OD-Bi) catalyst with surface coordinated oxygen for efficient electroreduction of pure CO₂ , N_2, and flue gas. During pure CO₂ electroreduction, the maximum Faradaic efficiency (FE) of formate reaches 98.0% and stays above 90% in a broad potential of 600 mV with a long-term stability of 50 h. Additionally, OD-Bi achieves an ammonia (NH₃ ) FE of 18.53% and yield rate of 11.5 µg h^-1 mg_cat ^-1 in pure N₂ atmosphere. Noticeably, in simulated flue gas (15% CO₂ balanced by N₂ with trace impurities), a maximum formate FE of 97.3% is delivered within a flow cell, meanwhile above 90% formate FEs are obtained in a wide potential range of 700 mV. In-situ Raman combined with theory calculations reveals that the surface coordinated oxygen species in OD-Bi can drastically activate CO₂ and N₂ molecules by selectively favors the adsorption of *OCHO and *NNH intermediates, respectively. This work provides a surface oxygen modulation strategy to develop efficient bismuth-based electrocatalysts for directly reducing commercially relevant flue gas into valuable chemicals.