Investigation of Efficient Electrochemical Reduction of CO2 to CO over Zn- and Cd-based Catalysts

  • Author / Creator
    Xiao, Jing
  • Electrochemical CO2 reduction reaction (CO2RR), powered by renewable electricity sources, is an attractive approach to mitigating CO2 emissions and to storing intermittent renewable energy in the form of high-value carbon-neutral fuels. Among the various CO2RR products, CO, as an important feedstock for Fischer-Tropsch process, is the most kinetically accessible product. However, the sluggish kinetics for initial CO2 activation and the inevitable competitive hydrogen evolution reaction (HER) in aqueous electrolytes lead to the insufficient selectivity and energy efficiency of CO production. Although noble metals, such as Au, Ag and Pt, have been recognized as the most efficient catalysts for CO production, their low abundances and the associated high costs hinder their large-scale applications. Therefore, it is highly imperative to develop inexpensive electrocatalysts capable of efficiently promoting CO2RR to CO with high selectivity.
    Among the possible candidate non-noble metals, Zn holds the promise as a potential alternative to noble metals due to its earth-abundance and intrinsic selectivity for CO production. Hence, hexagonal Zn nanoplates (H-Zn-NPs) enclosed by Zn(100) and Zn(002) facets were synthesized and studied for their feasibility to catalyze CO2RR. Compared with the similarly sized Zn nanoparticles (S-Zn-NPs), the H-Zn-NPs exhibited remarkably enhanced current density, together with an improved CO Faradaic efficiency (FE) of over 85% in a wide potential window. Theoretical calculations revealed that the exposed Zn(100) facets and edge sites on H-Zn-NPs were energetically favorable for CO2RR to CO, which directly results in the enhanced CO2RR performance.
    Recently, CdCO3 was found to possess high CO selectivity because of the strong binding affinity with CO2. However, the reported current density (< 1 mA cm‒2) is far from being satisfactory. Therefore, CdCO3 nanoparticles decorated carbon nanofibers (CdCO3-CNFs) were synthesized to boost CO2RR by a strong catalyst-support interaction. As expected, the obtained CdCO3-CNFs displayed a high FE of 93.4% and a good partial current density (~10 mA cm‒2) at a potential of ‒0.83 V. Moreover, the local pH effect on CO2RR was investigated based on the in-situ synthesis of CdCO3 from porous CdO nanosheets, which would release OHˉ at the electrode/electrolyte interface. Compared with the pre-synthesized CdCO3 having similar morphology, the in-situ grown CdCO3 exhibited considerably increased FEs of CO in a wide potential range and achieved the maximum value of 99.2% at a potential of −0.86 V. The enhancement in CO selectivity was demonstrated to benefit from the higher local pH at the catalyst surface which significantly promoted CO2RR while inhibiting HER. This work provides new insights into the design strategy for cost-effective and efficient electrocatalysts for CO2RR to CO.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.