Designing a Zn–Ag Catalyst Matrix and Electrolyzer System for CO₂ Conversion to CO and Beyond

Abstract

year, [2] however carbon capture without utilization represents a purely sunken cost. Alternatively, CO 2 electrolysis provides a route to both environmental sustainability and economic viability by using clean electricity to electrochemically reduce waste CO 2 to generate a valueadded commodity. The field has made substantial breakthroughs in this area in recent years through adoption of gas diffusion electrodes (GDEs); [3] gas-porous supports that promote the mass transport of CO 2 from the gas phase to the surface of a metal-based catalyst that undertakes the electrochemical conversion. Amongst the targeted products, carbon monoxide, CO, has been identified as the most readily profitable by technoeconomic models. [4][5][6] It is directly applicable in the steel, petrochemical and food industries and is amenable for upconversion to higher value commodities by other processes, for example, methanol synthesis, Fischer-Tropsch synthesis, or microbial systems. [7,8] Contemporary CO 2 -to-CO electrolyzers demonstrate >50% energy efficiency (EE) at >400 mA cm −2 , [9] in line with technoeconomic targets CO 2 emissions can be transformed into high-added-value commodities through CO 2 electrocatalysis; however, efficient low-cost electrocatalysts are needed for global scale-up. Inspired by other emerging technologies, the authors report the development of a gas diffusion electrode containing highly dispersed Ag sites in a low-cost Zn matrix. This catalyst shows unprecedented Ag mass activity for CO production: −614 mA cm −2 at 0.17 mg of Ag. Subsequent electrolyte engineering demonstrates that halide anions can further improve stability and activity of the Zn-Ag catalyst, outperforming pure Ag and Au. Membrane electrode assemblies are constructed and coupled to a microbial process that converts the CO to acetate and ethanol. Combined, these concepts present pathways to design catalysts and systems for CO 2 conversion toward sought-after products.

Analyzing Production Rate and Carbon Utilization Trade-offs in CO2RR Electrolyzers

“…Furthermore, these values only represent the conditions at a local slice in the gas channel, whereas experiments represent the average consumption over the entire channel (see SI Figure S7 for calculated internal CO 2(g) and electric current density profiles). In any case, it is encouraging that a rough comparison of Figure b to values experimentally extracted in Figure c and Figure c at similar current densities shows reasonable agreement without adjusting any parameters from Weng et al In terms of the functional dependence of the calculated k MT on CO 2 concentration in the gas channel, we hypothesize that the predicted rise in k MT at lower values of external CO 2(g) concentration in Figure b is due to increased (bi)­carbonate formation caused by an increase in pH at the cathode . In other words, as the CO 2(g) supply becomes limited, the pH-decreasing effect of CO 2 dissolution is lessened, which drives up the pH at the cathode and increases (bi)­carbonate formation.…”

Probing the Catalytically Active Region in a Nanoporous Gold Gas Diffusion Electrode for Highly Selective Carbon Dioxide Reduction

“…At low flow rates the electrolyte floods the entire GDE, resulting in mass transport limitations and increased HER. It is unlikely that this flooding is occurring in the catalyst layer alone, as previous literature has demonstrated that the CO 2 diffusion layer thickness is on the order of microns rather than nanometers. − We present in Figure the three idealized states in which a catalyst layer can exist. In reality it is likely that the true wetting of the catalyst layer occurs as a combination of all three idealized states.…”

Concentration Optimization of Localized Cu0 and Cu+ on Cu-Based Electrodes for Improving Electrochemical Generation of Ethanol from Carbon Dioxide

“…An electrochemical CO 2 reduction reaction (CO 2 RR) uses electrical energy to convert CO 2 molecules into hydrocarbon products, which can store the intermediate electricity as chemical energy in the form of fuels [ 1 ]. Various products, such as carbon monoxide [ 2 , 3 , 4 ], formic acid [ 5 , 6 ], methane [ 7 ], methanol [ 8 ], ethylene [ 9 , 10 ], acetic acid [ 11 ], ethanol [ 12 , 13 ], and minor C 3+ products [ 14 ], have been acquired from direct and homogeneously catalyzed CO 2 reduction. The selectivity of a specific product of the CO 2 RR is heavily dependent on the electrocatalysts.…”

“…The selectivity of a specific product of the CO 2 RR is heavily dependent on the electrocatalysts. Generally, Zn [ 4 ], Ag [ 2 ], and Pd [ 3 ] metals are extensively explored to produce CO, while Sn [ 5 ], Bi [ 5 ], and Pb [ 6 ] metals have been studied to generate HCOOH from the CO 2 RR. Other high-value products containing alcohols and olefins are difficult to obtain from the CO 2 RR owing to their multi-electron requirement, which is provided by the surface atomic arrangement of electrocatalysts.…”