Tandem Electrocatalytic CO₂ Reduction with Efficient Intermediate Conversion over Pyramid-Textured Cu–Ag Catalysts

Abstract

If combined with renewably generated electricity, electrochemical CO2 reduction (E-CO2R) could be used as a sustainable source of chemicals and fuels. Tandem catalysis approaches are attractive for providing the product selectivity which would be required for commercial application. Here we demonstrate two-step tandem electrocatalytic E-CO2R with efficient conversion of the intermediate species. The catalyst scaffold is Si (100) which is etched to form a textured surface consisting of micron-sized pyramid structures with {111} facets. Two metals are used in the electrocatalytic cascade: Ag is employed to perform two-electron reduction 2 of CO2 to the intermediate CO and Cu performs conversion to more reduced products. Using high angle physical vapor deposition, we form separated, micron-scale areas of the two electrocatalysts on opposite sides of the pyramids, with their relative surface coverages being tunable with deposition angle. Compared to textured scaffolds with blanket Ag and Cu used as controls, bimetallic pyramid tandem catalysts have higher current densities and much lower faradaic efficiencies for CO. These effects are due to efficient conversion of the CO formed on Ag to more reduced products on the Cu. Methane is the main product to be enhanced by the cascade pathway: a bimetallic catalyst with approximately equal coverages of Ag and Cu produces methane with a FE of 62% at -1.1 VRHE, corresponding to a partial current density of 12.7 mA cm -2 . We estimate an intermediate conversion yield for the CO intermediate of 80-90%, which is close to the masstransport limited value predicted by reaction-diffusion simulations.

Boosting CO2 electroreduction towards C2+ products via CO* intermediate manipulation on copper-based catalysts

“…39 Besides, when the distance between the CO formation sites and CO deep reduction sites in the cascade do not match the CO diffusion distance and moderate coverage, the C 2+ production will be dominated by C 1 . 161,212…”

Catalysis for e-Chemistry: Need and Gaps for a Future De-Fossilized Chemical Production, with Focus on the Role of Complex (Direct) Syntheses by Electrocatalysis

“… 130 , 131 Exploring more systematically the many possible new paths, offering also process intensification, given by tandem and/or paired electrocatalytic reactions. 132 , 133 We have cited the examples of direct (one-step) glucose conversion to adipic acid, or the production of the monomers for PEF polymer synthesis on both sides of the electrocatalytic cell, a greener polymer substituting PET (polyethylene terephthalate), one of the largest in market volume polymers in current use. Intensifying research on the direct synthesis of ethylene or methanol/ethanol by electrocatalytic reduction of CO 2 , which were not discussed here having been already discussed in many reviews, for example by Zhao et al 2 and Ra et al 16 Ethylene or methanol/ethanol can be then used as such or as a building block for further e -chemistry.…”

Scale Effect on Producing Gaseous and Liquid Chemical Fuels via CO2 Reduction

“…The mass transfer performances of CO 2 and CO in catholyte were simulated with a commercial finite element software, COMSOL. The diffusion coefficients of CO were set at 2.03 × 10 −9 m 2 /s [9]. The initial concentration of CO in the bulk electrolyte was set at 0 mM.…”

“…Among these products, CO and HCOOH are produced via two-electron CO 2 electrochemical reduction, which means that producing 1 mole of CO or HCCOH requires the minimum amount of electrons. Moreover, CO and HCOOH are primary products/intermediates, and other C1, C2, and C3 products would be subsequently generated after CO [9]. Since only a few reaction steps are needed, it is easier to get a high selectivity for producing CO or HCOOH than other products.…”