Improved Vapor-Feed Direct Methanol Fuel Cell by Hydrophobic/Hydrophilic Composite Catalyst Layers via Kelvin Equation

The vapor-feed passive direct methanol fuel cell (DMFC) holds a high energy density and is environmentally friendly and portable. However, complex water management is challenging due to the lack of water of the anodic oxidation reaction. To address this issue, we were inspired by the Kelvin equation to regulate the vapor pressures by hydrophilic porous carbon supports in catalyst layers, which promoted the conversion of vaporous water to liquid water. In this paper, hydrophilic carbon materials were used to make comparisons with hydrophobic carbon black, demonstrating through evaporation and condensation experiments that wetting characteristics of porous carbon materials affected the vapor-liquid equilibrium. As water management structures of DMFCs, two-layered catalyst layers with hydrophilic inner layers were constructed from catalysts prepared from carbon materials with different wetting characteristics. For DMFCs with a two-layered anode catalyst layer (ACL), the decreased vapor pressure in hydrophilic inner ACL converts part of vaporous water into a liquid state, which is preserved as an anode reactant. For DMFCs with a two-layered cathode catalyst layer (CCL), the hydrophilic inner CCL increases and preserves liquid water, which promotes water recovery and inhibits methanol crossover. This paper proposes a new water management method to improve vapor-feed DMFC and increase its potential as a portable energy source.