Pitfalls and Protocols: Evaluating Catalysts for CO₂ Reduction in Electrolyzers Based on Gas Diffusion Electrodes

Abstract

The evaluation of catalysts on gas diffusion electrodes (GDEs) have propelled the progress of electrochemical CO 2 reduction reaction (CO 2 RR) at industry-relevant activities. However, high experimental complexities exist in GDE-based flow electrolyzers, whereby various experimental factors can influence the evaluation of catalytic CO 2 RR performances. Not accounting for these experimental factors could result in inconsistent conclusions and thus hinder rational catalyst developments. This Perspective highlights a range of experimental factors that can affect the performance metrics for electrocatalysts. Specifically, the product faradaic efficiency can be influenced by the overestimation of the effluent gas flow rate, unaccounted losses of products, and unintended alteration of microenvironments. In addition, cathodic voltage can be inaccurately determined due to the unaccounted dynamic changes in uncompensated resistance. By raising awareness of these potential pitfalls and establishing appropriate protocols, we foresee a more meaningful benchmarking of catalytic performances across the literature.

CO2electrolysis towards large scale operation: rational catalyst and electrolyte design for efficient flow-cell

“…Thus far, the intrinsic activity of different electrocatalysts in a particular electrolyte varies significantly in literature. [147][148][149] The major contributor to this discrepancy is the inaccurate calculation of cathodic voltage, FE and catalyst deposition. This discrepancy in the literature data is mainly because of the different types of GDE cells used by different groups and the protocols followed during CO 2 RR operation.…”

Benchmarking of commercial Cu catalysts in CO2electro-reduction using a gas-diffusion type microfluidic flow electrolyzer

“…3,[11][12][13][14] In recent CO 2 RR studies, gas-diffusion type flow electrolyzers were widely employed to deliver industrially relevant reaction rate and selectivity by improving the mass transport of CO 2 from the gas phase to the catalyst surface. 5,[15][16][17] CO 2 RR performance with over 60% faradaic efficiency of C 2+ products at current densities 4100 mA cm À2 has been achieved in numerous recent reports. [18][19][20][21][22][23] Owing to the structural complexity of the gas-diffusion electrode (GDE) and varied configurations of flow electrolyzers employed in the literature, it is unclear whether the reported CO 2 RR performance reflects the intrinsic activity of the catalysts, as it is commonly assumed, or features of flow reactors.…”

“…[18][19][20][21][22][23] Owing to the structural complexity of the gas-diffusion electrode (GDE) and varied configurations of flow electrolyzers employed in the literature, it is unclear whether the reported CO 2 RR performance reflects the intrinsic activity of the catalysts, as it is commonly assumed, or features of flow reactors. 5,15,24,25 In this work, we evaluated the CO 2 RR performance of three commercial Cu catalysts, i.e., nanoparticle Cu (NP Cu, purchased from Sigma-Aldrich), spherical Cu (Sph Cu, purchased from Macklin), and copper oxide (CuO, purchased from Alfa Aesar), using a gas-diffusion type microfluidic flow electrolyzer that has been widely employed in CO 2 electrolysis. We showed that all three commercial catalysts were able to deliver FE of C 2+ products above 70% at 200 mA cm À2 , and notably, NP Cu could achieve near 80% FE of C 2+ products at 300 mA cm À2 .…”

“…[26][27][28] The results reported in this work highlight that commercial Cu catalysts can achieve similar or better performances compared to many reported Cu-based CO 2 RR catalysts with designed compositions, well-defined shapes or controlled nanostructures in terms of both C 2+ product selectivity and current density. 15,29,30 Thus, selectivity control toward specific target product(s) could be a fruitful direction in the future design of CO (2) RR catalysts.…”

“…18–23 Owing to the structural complexity of the gas-diffusion electrode (GDE) and varied configurations of flow electrolyzers employed in the literature, it is unclear whether the reported CO 2 RR performance reflects the intrinsic activity of the catalysts, as it is commonly assumed, or features of flow reactors. 5,15,24,25…”