Thermodynamics and proton transport in Nafion -: III.: Proton transport in Nafion/sulfated ZrO2 nanocomposite membranes

A proton transport model is proposed to describe proton diffusion in Nafion/(ZrO2/SO42-) nanocomposite membranes. The model considers the water content which could be determined by thermodynamics, dissociation of protons near the acid surface, stabilization of protons in water, and the strength and concentration of acid sites from Nafion as well as ZrO2/SO42-. The transport of proton occurs via a sluggish hopping process through the membrane surface, and relatively fast structural and ordinary mass diffusion of hydronium ions in the bulk of the membrane pores. The conductivity of the in situ sol-gel prepared Nafion/(ZrO2/SO42-) nanocomposite membranes is accurately predicted as a function of relative humidity without any fitted parameters. Nafion/(ZrO2/SO42-) nanocomposite membrane shows higher proton conductivity compared with Nafion at the same temperature and humidity conditions due to the improved water uptake and provision of strong acid sites. The model provides a theoretical framework for understanding proton conduction in nanocomposite membranes and can be successfully used to develop high-conducting membranes for fuel cell applications. (c) 2005 The Electrochemical Society.