Ink optimization for the fabrication of Cu2O-CeO2 gas diffusion electrodes

Abstract

CO2 emissions are a very famous problematic nowadays because it is what causes the greenhouse effect and the climate change. One way for reducing these emissions is doing an electrochemical reaction and convert CO2 into other products like: ethylene (C2H4), methane (CH4), methanol (CH3OH), carbon monoxide (CO), et al. In this project, this problematic was treated, and we studied the CO2 conversion into ethylene, because it is the product that has more uses in the plastic industry, it is a polymer and it can synthetize polyethylene, also it is the best product because does not contribute into the greenhouse effect how it can do methane or carbon monoxide. At industrial level, ethyne production can be performed on an electrochemical flow cell, whose design requires the implementation of a gas diffusion electrode (GDE). Under this configuration, the electrochemical reaction will take place when the CO2 flow is activated on the electrode. The GDEs are usually composed by a support (carbon paper), a microporous layer, and a catalyst layer (cooper-based catalyst). For the catalyst layer deposition, a stable ink formulation (solvent+ ionomer + catalyst + PTFE) is required to guarantee a hydrophobic catalyst layer. In this context, the main goal of this work is to optimize the ink composition for the fabrication of an active Cu2O-5 wt.%CeO2 GDE of 5 cm2. With this aim, the catalytic material was first scaledup. Then, the stability of the ink composition was studied using different catalyst/solvent and nafion/solvent ratios. Sequentially, the stability of the ink was also evaluated using different solvents (ethanol, water, isopropanol). Finally, for the most promising ink formulation, the addition of 5wt% of polytetrafluoroethylene (PTFE) was evaluated in order to improve the hydrophobicity properties of the electrodes. In all prepared GDEs, catalyst characterization and CO2 electrochemical evaluation were performed to select the optimum GDE able to produce efficient C2H4. The results of stability suggested that the ink formulation composed by isopropanol as solvent (10 mL), nafion as ionomer (280 μL) and Cu2O-5 wt.%CeO2 (40 mg) as catalyst is the most promising for scale-up GDE of 5 cm2. In this electrode, the faradaic efficiency (FE) to ethylene achieved was close to 56%. urthermore, the addition of PTFE was found to be positive since a more hydrophobic GDE was fabricated, and thus an improved FE to ethylene was achieved (60%). The high GDE performance was attributed to the use of the solvent. Isopropanol appears to create rougher surfaces, smaller cubic particles, and a thin catalyst layer.