Electrochemical CO2 reduction (CO2RR) is one of the most promising methods for decreasing the concentration of CO2, meanwhile, converting them into the high value-added chemicals, which has been more and more investigated and developed recently. Imidazolium ionic liquids (ILs) have been widely used as electrolytes in CO2RR and shown satisfactory performance. While the function of ILs is still unclear. Besides, the economic feasibility and potential of CO2RR with ILs-based electrolytes as well as the environmental effects are also unclear. Therefore, this work focuses on the technology evaluation and exploration for CO2RR-to-CO with ILs-based electrolyte.

Firstly, a literature review about CO2RR to CO, CH4, CH3OH, and syngas (H2/CO=1:1 and 1:2) in ILs-based electrolytes was conducted. Then the processes to obtain these C1-products were analyzed from both economic and environmental aspects based on the state-of-the-art technology and the rationally hypothetical future cases. The results show that CO is the most valuable product considering both the economic benefits and environmental impact, which will be more lucrative in the future with the improvement of CO2RR performance. 

Then, based on 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), a series of imidazolium ILs with various proton in the group (-CH3, -CH3OH and -SH, noted as [BMMIM][PF6], [BMOHIM][PF6] and [BMSHIM][PF6], respectively) at C2 site of the imidazole ring were synthesized and used as electrolyte to perform CO2RR over a commercial Ag foil. As a result, the more inert the active proton, the more favorable for the production of CO. Notably, nearly 100% CO was obtained when [BMMIM][PF6] with the most inert proton. This confirms that the C2-H of the imidazole ring has an important influence on CO2RR performance and may be involved in the reaction.

Finally, [BMMIM][PF6] and [BMIM][PF6] were selected as the electrolytes to conduct CO2RR over a bimetallic catalyst. As a result, the product from 99.69% HCOOH switched into 98.85% CO only via changing the electrolyte from [BMIM][PF6] into [BMMIM][PF6]. Mechanistic studies reveal that the CO2 adsorption configuration on the surface of the catalyst was altered when switching to another IL with a different CO2 active site, resulting in two distinct pathways for the generation of HCOOH and CO, respectively. 

Combining CO2 electrochemical reduction (CO2R) and biomass gasification for producing methanol (CH3OH) is a promising option to increase the carbon efficiency, reduce total production cost (TPC), and realize the utilization of byproducts of CO2R system, but its viability has not been studied. In this work, systematic techno-economic assessments for the processes that combined CO2R to produce CO/syngas/CH3OH with biomass gasification were conducted and compared to stand-alone biomass gasification and CO2R processes, to identify the benefits and analyze the commercialization potential of different pathways under current and future conditions. The results demonstrated that the process that combined biomass gasification with CO2R to CO represents a viable pathway with a competitive TPC of 0.39 €/kg-CH3OH under the current condition. For all the combined cases, electricity usage for CO2R accounts for 36–76% of total operating cost, which plays a key role for TPC. Sensitivity analysis confirmed that the process that combined biomass gasification with CO2R to CO is sensitive to the price of electricity, while both CO2R performance and prices of stack and electricity are important for the processes that combined with CO2R to syngas/CH3OH.

The increasing CO2 emission, as the chief culprit causing numerous environmental problems, could be addressed by the electrochemical CO2 reduction (CO2R) to the added-value carbon-based chemicals. Ionic liquids (ILs) as electrolytes and co-catalysts have been widely studied to promote CO2R owing to their unique advantages. Among the potential products of CO2R, those only containing one carbon atom, named C1 products, including CO, CH3OH, CH4, and syngas, are easier to achieve than others. In this study, we first summarized the research status on CO2R to these C1 products, and then, the state-of-the-art experimental results were used to evaluate the economic potential and environmental impact. Considering the rapid development in CO2R, future scenarios with better CO2R performances were reasonably assumed to predict the future business for each product. Among the studied C1 products, the research focuses on CO, where satisfactory results have been achieved. The evaluation shows that producing CO via CO2R is the only profitable route at present. CH3OH and syngas of H2/CO (1 : 1) as the targeted products can become profitable in the foreseen future. In addition, the life cycle assessment (LCA) was used to evaluate the environmental impact, showing that CO2R to CH4 is the most environmentally friendly pathway, followed by the syngas of H2/CO (2 : 1) and CO, and the further improvement of the CO2R performance can make all the studied C1 products more environmentally friendly. Overall, CO is the most promising product from both economic and environmental impact aspects.