Engineering strategies toward efficient CO2 electrochemical reduction to C1 products
Creators: Sui, Pengfei
Publisher: name: University of Alberta Library
Year: 2023

<p>Electrochemical CO2 reduction reaction (CO2RR) is regarded as an attractive technology to lower the CO2 emission level and achieve sustainable carbon neutrality by converting CO2 to valuable chemicals. CO and HCOOH/formate are the promising products in terms of their commercial viability based on technoeconomic analysis. However, the present electrocatalysts still suffer from the high overpotential and sluggish reaction kinetics. The low solubility of CO2 in aqueous media and broad distributions of the conversion products also account for the unsatisfactory CO2RR performance, which needs to be overcome to meet the requirement for practical implementations of CO2RR technologies. Given that the reaction pathways for CO2RR to C1 products can be generalized to three key points: CO2 adsorption ability, reaction intermediates, and proton-coupled electron transfer (PCET) steps. In this thesis, various engineering strategies were investigated to have focused on these points by designing highly active, selective, and stable p-block metal-based electrocatalysts to achieve desirable CO2RR performance.<br>
Firstly, to effectively optimize the binding strength of the reaction intermediates, a bimetallic engineering strategy is used to improve the selectivity toward the target product. The designed electrocatalyst InOx@CuO shows high Faradaic efficiency (FE) and ultralow onset potential for CO formation. The introduced In species on Cu successfully tune the binding strength of *COOH intermediate and effectively suppress the competing hydrogen evolution reaction as revealed by computational results. Given the importance of PCET steps during CO2RR, an interface engineering strategy is applied to synthesize interface-rich Bi2S3-Bi2O3 heterostructure. The desirable current density and selectivity towards formate with a wide potential range of FEformate over 90 % are achieved in a flow cell system, which is attributed to the strengthened charge transfer ability induced by the electronic interaction between the Bi2S3 and Bi2O3 at the interface.<br>
Considering the limited solubility of gaseous CO2 in aqueous media, the electrocatalyst Bi2O2CO3 nanoflowers with self-reinforced CO2 adsorption properties are designed and demonstrate efficient formate electrosynthesis. The in situ measurements and theoretical calculation results reveal the self-reinforced CO2 adsorption properties and rapid CO2 adsorption-desorption kinetics on the catalyst surface, significantly facilitating the CO2RR process. In addition, phase engineering has shown great potential for improving CO2RR performance since the unconventional phase of nanomaterials usually delivers different physicochemical properties and functionalities. To this end, the stable α-Bi2O3 and metastable β-Bi2O3 phases are prepared for CO2RR. Compared to α-Bi2O3, β-Bi2O3 possesses better abilities for CO2 adsorption and charge transfer that consequently lead to faster reaction kinetics. Further computational results point out that the exothermic process of the key intermediate *OCHO formation on β-Bi2O3 benefits high formate selectivity.<br>
Finally, the defective ultrathin Bi5O7I nanotubes are synthesized for the efficient CO2RR to formate. The abundant defects offer massive uncoordinated active sites for CO2RR to proceed and increase the CO2 adsorption capability. Benefiting from the prominent capillary and confinement effects, the unique nanotube channel structure significantly enhances the charge transfer ability and the mass transport in aqueous media as well as stabilizes the reaction intermediates. All of these merits collectively contribute to the improved electrocatalytic performance and highlight the great potential of defect engineering for CO2RR performance improvement.</p>