Scalable Gas Diffusion Electrode Fabrication for Electrochemical CO₂ Reduction Using Physical Vapor Deposition Methods

Abstract

Electrochemical CO 2 reduction (ECR) promises the replacement of fossil fuels as the source of feedstock chemicals and seasonal storage of renewable energy. While much progress has been made in catalyst development and electrochemical reactor design, few studies have addressed the effect of catalyst integration on device performance. Using a microfluidic gas diffusion electrolyzer, we systematically studied the effect of thickness and the morphology of electron beam (EB) and magnetron-sputtered (MS) Cu catalyst coatings on ECR performance. We observed that EB-Cu outperforms MS-Cu in current density, selectivity, and energy efficiency, with 400 nm thick catalyst coatings performing the best. The superior performance of EB-Cu catalysts is assigned to their faceted surface morphology and sharper Cu/gas diffusion layer interface, which increases their hydrophobicity. Tests in a large-scale zero-gap electrolyzer yielded similar product selectivity distributions with an ethylene Faradaic efficiency of 39% at 200 mA/cm 2 , demonstrating the scalability for industrial ECR applications.

Effect of Gold Catalyst Surface Morphology on Wetting Behavior and Electrochemical CO2 Reduction Performance in a Large-Area Zero-Gap Gas Diffusion Electrolyzer

“…In the same study, however, the wetting angle of a 300 nm EB npAu coating (∼59°) was significantly smaller than that of the corresponding 300 nm EB pure Au coating (∼106°) prepared on a GDL . The more hydrophobic character of the 300 nm EB Au coating (∼106°) compared to our 400 MS Au coating (∼20°) is consistent with our previous work on EB and MS Cu coatings where we observed that the wetting angle on 400 nm EB Cu coatings (∼124°) is much higher than that of the corresponding 400 nm MS Cu coatings (∼65°), which makes the latter more prone to electrode flooding at high current densities . The different wetting behavior seems to be related to the different surface morphologies produced by EB and MS techniques with a more well-defined faceted nature of EB Cu coatings compared to the very rough and serrated appearance of MS Cu coatings .…”

“…The coatings are very uniform in thickness and have the same mesoscale porosity and nanoscale morphology consisting of faceted, 50–100 nm wide primary particles that form larger agglomerates which grow in size with increasing film thickness (Figure S1b,d). In general, while the morphologies of the MS Au and Ag 0.7 Au 0.3 coatings are very similar to that of the MS Cu catalyst coatings studied in our previous work, the MS Au coatings exhibit a more faceted appearance than the corresponding Cu MS coatings …”

“…As shown in our recent study on MS and EB Cu catalyst coatings, the ECR current density increases linearly with the mesoscale surface area. 34 We hypothesize that the increase in mesoscale surface area of the thicker 800 nm Au coating dominates over the effects of the lower wetting angle compared to the 400 nm npAu coating, thus enabling higher CO faradaic efficiencies and partial current densities compared to the 400 nm npAu coating while still providing a sufficiently hydrophobic surface.…”

“…In general, while the morphologies of the MS Au and Ag 0.7 Au 0.3 coatings are very similar to that of the MS Cu catalyst coatings studied in our previous work, the MS Au coatings exhibit a more faceted appearance than the corresponding Cu MS coatings. 34 Dealloying of the 400/800 nm MS Ag 0.7 Au 0.3 alloy coatings for 1 h in concentrated nitric acid did not change their mesoscale morphology but introduced additional nanoscale porosity consisting of ∼10 nm Au ligaments and pores characteristic for npAu (Figure 1b,c). We note that the resulting Au catalyst loading obtained by dealloying the 400/ 800 nm thick Ag 0.7 Au 0.3 alloy coatings is equivalent to 120/240 nm thick pure Au coatings.…”

Electrochemical Reduction of CO2 With Good Efficiency on a Nanostructured Cu-Al Catalyst

“…Despite significant prospect, the electrochemical CO 2 reduction reaction (CO 2 RR) encounters many challenges associated to high energy barriers, multiple parallel reactions and competitive hydrogen evolution reaction (HER) ( Yin et al, 2019 ). Consequently, a wide range of chemicals such as carbon monoxide (CO), formate (HCOO − ), methane (CH 4 ), methanol (CH 3 OH), ethane (C 2 H 6 ), ethylene (C 2 H 4 ) and ethanol (C 2 H 5 OH) is identified as the CO 2 RR products, and the formation of H 2 is almost inevitable in aqueous electrolytes ( Bagger et al, 2017 ; Zhao et al, 2018 ; Ren et al, 2019 ; Zeng et al, 2021a ; Zeng et al, 2021b ; Jeng et al, 2022 ; Zhou et al, 2022 ). Among these species, CO and its mixture with H 2 (H 2 /CO syngas) have high relevance for the chemical industry ( Nielsen et al, 2018 ; Zeng et al, 2020a ).…”