Degradation study on tin- and bismuth-based gas-diffusion electrodes during electrochemical CO_(2) reduction in highly alkaline media

This work investigated the degradation of tin – based gas-diffusion electrodes (GDE) and also a promising Bi2O3 GDE in electrochemical CO_(2) reduction in highly alkaline media which has not been studied before. The contributions of the electrode wetting (or flooding, if excessively) and catalyst leaching on the degradation were analyzed. Therefore, electrochemical impedance spectroscopy was used to monitor the wetted surface area of the GDE in combination with post-mortem analysis of the penetration depth by visualizing the electrolyte’s cation in the GDE cross-section. Furthermore, to reveal a possible degradation of the electrocatalyst, its distribution was mapped in the GDEs cross-section after operation while the catholyte was additionally analyzed via ICP-MS. The results clearly demonstrate that the SnO_(2) catalyst dissolves in the reaction zone inside the GDE and might be partially redeposited near the GDEs surface. Since the redeposition process occurs only partially a steady loss of catalyst was observed impeding a clear distinction of the two degradation phenomena. Nevertheless, the deterioration of the electrode performance measured as faraday efficiency (FE) of the parasitic hydrogen evolution reaction (HER) qualitatively correlates with the differential double layer capacitance (Cdl). A significant difference of the rate of increase for the hydrogen FE and Cdl can be ascribed to the superposition of both above-mentioned degradation mechanisms. The demonstrated instability of SnO_(2) contrasts with the behavior of Bi2O3 GDE which is stabilized during CO_(2) conversion by redeposition of the diluted dissolved species as metallic Bi which is active for the CO_(2) reduction reaction.

Valorizing carbon dioxide via electrochemical reduction on gas-diffusion electrodes

The electrochemical carbon dioxide(CO_(2))reduction provides a means to upgrade CO_(2)into value-added chemicals.When powered by renewable electric-ity,CO_(2)electroreduction holds the promise of chemical manufacturing with carbon neutrality.A commercially relevant CO_(2)electroreduction process should be highly selective and productive toward desired products,energetically efficient for power conversion,and stable for long-term operation.To achieve these goals,designing gas-diffusion catalytic electrodes and prototyping reactors built upon in-depth understandings of the reaction mechanisms are of para-mount importance.In this review,the fundamentals of gas-diffusion electrodes are briefly presented.Then,the most recent advances in developing high-performance CO_(2)reduction using gas-diffusion electrodes are overviewed.Reactor engineering aiming at enhancing productivity,energy efficiency,CO_(2)single-pass utilization,and operating lifetime is further discussed.Challenges in developing CO_(2)electroreduction systems are included.The prospects for advancing CO_(2)electroreduction toward practical applications are also narrated.

Surface engineering of ZnO electrocatalyst by N doping towards electrochemical CO_(2) reduction

The discovery of efficient,selective,and stable electrocatalysts can be a key point to produce the largescale chemical fuels via electrochemical CO_(2) reduction(ECR).In this study,an earth-abundant and nontoxic ZnO-based electrocatalyst was developed for use in gas-diffusion electrodes(GDE),and the effect of nitrogen(N)doping on the ECR activity of ZnO electrocatalysts was investigated.Initially,a ZnO nanosheet was prepared via the hydrothermal method,and nitridation was performed at different times to control the N-doping content.With an increase in the N-doping content,the morphological properties of the nanosheet changed significantly,namely,the 2D nanosheets transformed into irregularly shaped nanoparticles.Furthermore,the ECR performance of Zn O electrocatalysts with different N-doping content was assessed in 1.0 M KHCO_(3) electrolyte using a gas-diffusion electrode-based ECR cell.While the ECR activity increased after a small amount of N doping,it decreased for higher N doping content.Among them,the N:ZnO-1 h electrocatalysts showed the best CO selectivity,with a faradaic efficiency(FE_(CO))of 92.7%at-0.73 V vs.reversible hydrogen electrode(RHE),which was greater than that of an undoped Zn O electrocatalyst(FE_(CO)of 63.4%at-0.78 V_(RHE)).Also,the N:ZnO-1 h electrocatalyst exhibited outstanding durability for 16 h,with a partial current density of-92.1 mA cm^(-2).This improvement of N:ZnO-1 h electrocatalyst can be explained by density functional theory calculations,demonstrating that this improvement of N:ZnO-1 h electrocatalyst comes from(ⅰ)the optimized active sites lowering the free energy barrier for the rate-determining step(RDS),and(ⅱ)the modification of electronic structure enhancing the electron transfer rate by N doping.

Beyond catalytic materials:Controlling local gas/liquid environment in the catalyst layer for CO_(2)electrolysis

Electrochemical reduction of CO_(2)to value-added chemicals using renewable electricity provides a promising strategy to achieve sustainable fuel production and carbon neutrality.Along with the development of electrocatalysts,fow cells with gas-diffusion electrodes(GDEs)have been used to reach commercially viable current densities for CO_(2)electrolysis,while the local environment and CO_(2)mass transport in the electrodes remain to be elucidated.In this review article,we highlight some insights into the microenvironment in the catalyst layer for CO_(2)electrolysis,including typical mass transport models for CO_(2)reduction in H-type cells and GDE fow cells,the effect of a hydrophobic microenvironment on CO_(2)mass transport and catalytic performance,and the formation of a gas/liquid balance and solid–liquid–gas interfaces for CO_(2)electrolysis.The insights and discussions in this article can provide important guidelines on the design of catalysts,electrodes,and electrolyzers for CO_(2)electrolysis,as well as other gas-involving electrocatalytic reactions.