ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDE ON ZINC ANTIMONIDE AND DEVELOPING OF CATALYTIC CONDUCTANCE FOR BENCHMARKING ELECTROCATALYSTS

Abstract

Inspired by the nickel-based intermetallic catalysts for electrochemically reducing carbon dioxide (CO2) to highly reduced products; here I explored the possibility of electrochemical reduction of CO2 on zinc-based intermetallic compounds. Zinc antimonide (ZnSb) was found to be able to reduce CO2 to carbon monoxide and formate. H/D isotopic experiments found that the competing water reduction reaction can be suppressed by switching the electrolyte solvent from hydrogen oxide to deuterium oxide. The zinc antimonide electrode was found to exhibit significant differences in electroconductivity upon illumination. Thus, the electrochemical behaviors were observed to be sensitive to the ambient light intensity.

The evaluation and benchmarking of electrocatalysts is challenging since existing catalyst parameters fail to capture the energetic and kinetic landscape associated with heterogeneous charge transfer processes. Recent work has attempted to utilize a modification of the homogeneous parameters turnover number (TON) and turnover frequency (TOF) in order to parameterize electrocatalytic reactivity. However, here, we experimentally demonstrate that electrocatalytic TON is a parameter that is not intrinsic to the catalyst, but an extrinsic property related to the design of the electrochemical cell employed, and as such is not a molecularly-valid descriptor of catalysis. Classic TOF values can be modified to make them more electrochemically meaningful by including overpotential effects. However, these values are still limited as descriptors of an electrocatalytic process. To overcome existing limitations, a new metric - catalytic conductance (), which integrates current density, overpotential, and Faradaic efficiency, is proposed. As a mechanism-insensitive metric, catalytic conductance is capable of balancing the goals of high reaction productivity and low power input. Catalytic conductance per unit concentration of catalyst (homo) was adopted for benchmarking homogeneous catalysts. Case studies of electrochemical reduction of carbon dioxide demonstrate the value of  for benchmarking electrocatalysts.