Nitrogen-doped porous carbon materials show excellent water adsorption ability by forming strong hydrogen bonding between water molecules and the doped atoms. When these porous carbon materials are used to construct a water management layer (WML) of a passive direct methanol fuel cell (DMFC), high water concentration and hydraulic pressure formed inside the cathode catalyst layer would facilitate the water recovery from cathode to anode. In this paper, a highly hydrophilic nitrogen-doped carbon aerogel was synthesized by the carbonization of hydrogel precursors composed of resorcinol, formaldehyde, and graphene oxide under ammonia, and it was used for the first time to construct the WML for liquid-feed and vapor-feed passive DMFCs. The results show that the WML significantly improves the output performance of the liquid-feed DMFC by enhancing the water recovery, which is characterized and proved by the smaller cathode polarization, the slightly increased anode polarization, and a released cathode water flooding situation. A new method was also proposed to study the in situ methanol crossover of DMFCs, which confirmed that the methanol crossover during the discharge was reduced by the WML. As for the vapor-feed DMFCs, the WML reduces both the cathode and anode polarizations significantly, which increases the output performance greatly. This study opens a new window for the design and optimization of the membrane assembly electrode of DMFCs.
Keywords: carbon aerogel; catalyst layer; direct methanol fuel cell; water adsorption; water management.