Abstract
Improving cell performance is the most demanded task in direct methanol fuel cell (DMFC) research, although this fuel cell has several intrinsic features like high energy density, moderate operating temperature and environmentally friendly operation. The catalyst layer (CL) is the site of electrochemical reactions directly affecting the cell performance. Accordingly, the structure and preparation of the CL are crucial in optimizing performance. In this study, a novel gradient catalyst layer (G-CL) for the anode of DMFC is developed and better performance is obtained compared with that of single catalyst layer (S-CL) anode. A G-CL anode is composed of an outer CL of covalent organic framework (COF) materials-mixed catalyst near the microporous layer (MPL) and a conventional inner CL near the membrane side. Different loading of Pt catalyst in the two layers. Therefore, in the G-CL structure, there existed a catalyst concentration gradient and porosity gradient. Anode electrodes are characterized morphologically and electrochemically and the performance of individual cells containing such G-CL designs is measured. The results indicate that incorporation of the appropriate amount of COF materials enables the outer CL not only to have a larger electrochemical surface area (ECSA) and expose more catalytic active sites but also holds a strong proton transfer ability to improve the methanol oxidation reaction (MOR) performance. Due to the presence of the inner layer of the CL formed the methanol gradient oxidation process. With the same platinum-ruthenium (Pt–Ru) catalyst loading, the 5 wt.% COF G-CL anode structure exhibited lower methanol crossover and higher power density (nearly 11% increment) compared with that of the S-CL anode with high methanol concentration (8 M) at 60 °C, showing the promising potential in further applications.
•Construction of gradient catalyst layer by incorporating COF in anode CL.•Gradient CL anode structure with larger electrochemically active surface area and strong catalytic activity.•Gradient CL anode structure effectively reduces the adverse effect of MeOH crossover and improve the DMFC performance.