Systematic analysis of the direct methanol fuel cell

Abstract

The dynamic operating behaviour of the direct methanol fuel cell (DMFC) is governed by several physico-chemical phenomena which occur simultaneously: double layer charging, electrode kinetics, mass transport inside the porous structures, reactant distributions in the anode and cathode flowbeds etc. Therefore it is essential to analyse the interactions of these phenomena in order to fully understand the DMFC. These phenomena were initially analysed independently by systematic experiments and model formulations. Electrode kinetics were determined by fitting models of varying complexity to electrochemical impedance spectroscopy (EIS) measurements. Reaction intermediates adsorbed on the catalyst seem to play a key role here. To describe mass transport across the DMFC a onedimensional model was formulated applying the generalised Maxwell-Stefan equations for multi-component mass transport and a Flory-Huggins model for the activities of mobile species inside the membrane (PEM). Also swelling of the PEM as well as heat production and transport were considered. Finally, the anode flowbed was analysed by observing flow patterns in different flowbed designs and measuring residence time distributions (RTDs). Detailed CFD models as well as simpler CSTR network representations were used to compare to the experimental results. Even the simpler models showed good agreement with the experiments. After these investigations the results were combined: the electrode kinetics model was implemented in the mass transport model as well as in the CSTR network flowbed model. In both cases, good agreement, even to dynamic experiments, was obtained. List of SymbolsMolar concentration d (m) Thickness i (mA cm )2 ) Current density n (mol m )2 s )1 ) Overall molar flux density r (mol m )3 s )1 ) Reaction rate t (s)

An overview of unsolved deficiencies of direct methanol fuel cell technology: factors and parameters affecting its widespread use

“…A number of works have been performed to analyze the anodic oxidation of CH 3 OH , and these resulted in the postulations of its reaction mechanism . The most accepted of these postulates follow a bifunctional mechanism , comprising of C–H bond activation (Reactions 4 and 5) and H 2 O adsorption (Reaction 6). The important steps of this postulate are represented as follows: CH 3 OH adsorption: C–H bond activation: H 2 O adsorption: …”

Mass transport phenomena in direct methanol fuel cells

“…Since the two-phase flow behavior in the flow field affects not only the mass transport of methanol to the anode CL, but also the removal of gas CO 2 from the cell, it is directly related to cell performance [2,. To gain better understanding of the mass transport of methanol and gas CO 2 on the DMFC anode, twophase flow behaviors in different anode flow fields have been extensively studied [2,10,14,[31][32][33][34][35][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54]. The commonly used flow fields are sketched in Fig.…”

“…Mass transport not only affects the performance and operating stability of the DMFC, but also influences the volumetric energy density of the DMFC system [7][8][9][10][11][12][13][14]. Over the past decade, the mass transport of methanol, gas CO 2 , oxygen and water has been extensively studied [2][3][4][5][6][7][8][9][10][11][12][13][14]. The purpose of this article is to present a comprehensive review of the advances in the study of mass transport of different species in DMFCs and to discuss about the future research directions.…”

Solid Electrolyte Membrane Reactors

“…A detailed mathematical analysis of methanol cross -over and the transport mechanisms in PEM was reported by Sundmacher et al . ( 2001 ) and Schultz et al . ( 2007 ).…”