Nowadays environmental deterioration and global warming are among the principal concerns for humankind. One of the upstanding technologies to settle them is proton exchange membrane fuel cells (PEMFCs), where through an electrochemical reaction, oxygen and fuel (as hydrogen) are transformed into electric energy, water and heat, usually using carbon supported platinum (Pt/C) as catalyst and Nafion as proton conductive ionomer. PEMFC production at the laboratory scale is mainly done by spray method, having some counterbacks such as catalyst wasting and slow deposition rate. Recently, the screen print method has caught attention worldwide for industrial-scale production of PEMFC since it was successfully employed in a variety of applications, such as solar cells, microelectronics, etc. This method consists of preparing a catalyst paste dispersing the catalyst with ionomer and solvents, once homogenized the paste is passed through a mesh and then deposited on a substrate in a single quick step avoiding material waste. For an effective screen print process, a stable and workable catalyst paste is needed, being rheological properties and drying time the most important features to fit those needs. Despite water and low molecular weight alcohols being the typical solvents used for catalyst paste fabrication and the rheological properties of resulting pastes using these solvents are already reported [1], they do not fit the requirements for screen print industrial production. On the other hand, cyclohexanol has a high viscosity and long drying time, being a promising alternative to obtain a paste suitable for the industry's needs, however, the rheological properties of a catalyst paste containing cyclohexanol remain unclear. In addition, it has been reported that this solvent has positive effects on the catalyst and ionomer interactions, enhancing the catalyst activity and improving mass transport [2]. In this research, several screen print catalyst pastes having the same final volume and different solvent proportions of water, 1 propanol, and cyclohexanol (W:1PA:CHN) were prepared. The same proportion of water and 1 propanol was kept but the proportion of cyclohexanol was gradually increased for each sample: (1:1:0), (1:1:0.5), (1:1:1), (1:1:2) and (1:1:3). Additionally, a sample containing only cyclohexanol was prepared (0,0,1) to discern the isolated effect of this solvent. From the resulting pastes, PEMFC were produced by the screen print method. The relation between cyclohexanol content and catalyst paste rheological properties was investigated using a cone/plate rheometer, while the screen printed PEMFC electrochemical characteristics by the polarization curve, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), especially for evaluating proton conductivity.
Read full abstract