(4gh) Enhance CO2-to-C2+ Products Yield through Spatial Management of CO Concentration Profile on Layered Gas Diffusion Electrode

The electrochemical carbon dioxide (CO₂)-to-multi-carbon (C₂₊) products conversion provides a promising strategy to mitigate the ever-increasing carbon emission. However, the C-C coupling, which is the rate-determining step of the CO₂-to-C₂₊ products conversion, is restricted by the limited *CO surface coverage. The sequential CO₂ reduction, integrating the consecutive CO₂-to-CO and CO-to-C₂₊ products conversion steps on two complementary catalysts, raises the *CO coverage and thus increases the partial current density of C₂₊ products (j_C2+). The tandem catalysts have been widely reported to exhibit an enhanced j_C2+ at reduced overpotential. However, the j_C2+ remains moderate (~ -300 mA cm^-2), primarily due to the insufficient *CO coverage. Improving the j_C2+ demands further increased *CO coverage, which translates to enhanced local CO partial pressure (P_CO). Nevertheless, many sequential CO₂ reduction experiments already illustrate a higher CO Faradaic efficiency (FE) relative to the bare Cu catalyst.Further increasing CO supply would result in a low CO utilization efficiency, which sacrifices the FE of C₂₊ products. Therefore, it runs into a dilemma between improving the j_C2+ and enhancing the FE of C₂₊ products in sequential CO₂ reduction simultaneously.

Here, we design a layered gas diffusion electrode (LGDE) structure, which piles a CO-selective catalyst layer (CL, such as Ag, ZnO) and a C₂₊-selective CL (Cu), as shown in Figure 1. The concept of LGDE comes from the more efficient reactant conversion in the plug flow reactor (PFR) than the continuum stirred tank reactor (CSTR) for reactions with positive reaction order, such as CO-to-C₂₊ products conversion. During the CO₂ reduction, the CO-selective CL builds up the P_CO at the Cu CL/electrolyte interface, imitating the “inlet region” of PFR. Concentrating the CO locally at the Cu CL/electrolyte interface boosts the *CO coverage on Cu for higher j_C2+ and magnifies the CO residence time in the Cu CL for more efficient CO utilization. As a proof-of-concept, the commercial ZnO and Cu nanoparticles were used as the CO- and C₂₊-selective catalysts, respectively. The Cu/ZnO LGDE exhibits a j_C2+ of 1.8 times as high as the CSTR-analogous one-layer electrode composed of physically mixed Cu and ZnO nanoparticles and 3.4 times as high as the bare Cu electrode. This work provides insight into the design principle for tandem electrodes to achieve simultaneously high selectivity and productivity towards C₂₊ products.