Study on the water transport phenomena onto the direct methanol fuel cell performance: control of the electrode structure and the electrochemical analysis

Abstract

Direct methanol fuel cells (DMFCs) have been investigated as portable power system due to their high-energy efficiency and simple system configuration. However there is a limit to commercialize it as the small consumer electronics. Slow kinetics of methanol electro-oxidation on present catalyst and methanol crossover are the main problem resulting in low power density and fuel efficiency. And there is water flooding as a critical problem for performance improvement. Water in the DMFCs is moved from anode to cathode or generated at the cathode. Excess water, however, falls down cell voltage for water prevents cathode reaction by blocking reaction sites. Hence water transport and the degree of cathode flooding in DMFCs appears to be significantly in the cell performance and long-term stability. Herein we focused on the characteristic of water discharge with the changes of structure and hydrophobicity of electrode. And water flooding phenomena is analyzed from three points of view: 1) water flux and pressure drop in the channel, 2) resistance in the electrode with the electrochemical impedance spectroscopy, and 3) calculations of water distribution by computational program. Within this work, outer Micro Porous Layer (MPL) is introduced to investigate the characteristic of water discharge which is placed on the Gas Diffusion Layer (GDL) and is the last interfacial layer between a channel and Membrane Electrode Assembly (MEA). Its advantage of outer MPL is to investigate water behaviors clearly according to the property of MPL. Normal MPL is placed inside as interface between catalyst layer and GDL to help water drained out easily into GDL. However its effect is ambiguous due to GDL. And the relatively hydrophobic MPL and the relatively hydrophobic MPL are used into anode and cathode by turns. Three kinds of MEAs are composed according to the combination of MPL. AICI means the anode with the relatively hydrophilic outer MPL and the cathode with the relatively hydr...