Impact of the Carbon Substrate for Gas Diffusion Electrodes on the Electroreduction of CO₂ to Formate

Abstract

Aiming to advance the technical maturity of CO2 electrolysis to formic acid, various gas diffusion layers (GDLs) are investigated for their suitability as carbon‐based substrate for gas diffusion electrodes (GDEs) and their effect on the electroreduction of CO2 to formate. Particular attention lies on the elucidation for the effect of the GDL thickness, hydrophobic treatment, and presence of a microporous layer (MPL) on the GDE performance in terms of Faradaic efficiency. Based on the investigation it is found that the GDL thickness has no discernible influence on the Faradaic efficiency, while a GDE with a hydrophobic treatment of 10 % PTFE outperforms a GDE based on a GDL with 30 % PTFE. Furthermore, the presence of a MPL is found to be of marked importance to achieve relevant current densities given its effect on the focus of the catalyst layer on the GDE surface after spray coating, the wetting, and the electrical conductivity.

Early-stage performance change of gas diffusion electrodes for CO2 electroreduction to formate

“…S9 † it can be stated that next to the catalyst agglomeration also catalyst migration into deeper GDL layers occurs for electrodes with a catalyst loading > 2.3 mg cm −2 , leading to a loss of catalyst nanoparticles in contact with the electrolyte. 7 Hence, the observed agglomeration and the catalyst migration lead to changes in the catalyst layer topography, which initiates a change in the available active surface area of the catalyst. This becomes especially evident in the results of Fig.…”

“…Moreover, an additional carbonaceous microporous layer may or may not be sandwiched in between them. 6,7 Although the technology for GDEs is quite advanced, as its usage in several electrochemical processes such as chlorine electrolysis, [8][9][10] water electrolysis [11][12][13][14] and PEM fuel cells [15][16][17] is mature, the GDEs for electroreduction of CO 2 face severe problems concerning long-term stability and electrode degradation. The uniqueness of GDEs for the electroreduction of CO 2 stems from their bifunctionality and makes it difficult to directly compare them to GDEs for other electrochemical processes.…”

“…11,18 Furthermore, the nature of evolving products such as formic acid and ethanol alters surface wetting, which may lead to electrode ooding due to the enrichment of low-surface-tension liquid products. 19 It is, therefore, all the more important to investigate the stability of GDEs, but until today, the focus mostly lay on catalyst design, [20][21][22][23] the composition of the gas diffusion electrodes (GDEs) 7,[24][25][26][27] and process studies on a laboratory scale. [28][29][30] Moreover, those publications that do consider GDE degradation [31][32][33] mostly investigate electrode ooding 19,[34][35][36] and carbonate formation.…”

“…S1, all gure numbers preceded by an S can be found in the ESI †), despite a yet absent microporous layer (MPL). 7…”

Impact of the PiperION Anion Exchange Membrane Thickness on the Performance of a CO2-to-HCOOH Three-Compartment Electrolyzer

“…For CO 2 -to-CO electrolysis, scaling up and stacking into multiple cells are under investigation. − In contrast, the current focus for the CO 2 -to-C 2+ electrolysis focuses on the development of highly active and selective catalyst materials for application in batch reactors or single flow cells. − Selective and durable catalysts, particularly those based on bismuth and tin materials, have gained significant attention in the field of CO 2 -to-HCOOH electroreduction. Moreover, their potential application in advanced electrolyzer configurations is of growing interest. − …”