Electrochemical atomic force microscopy study of proton conductivity in a Nafion membrane

Abstract

High membrane conductivity is one of the key parameters in polymer electrolyte fuel cell applications. We introduce an electrochemical atomic force microscopy method that provides simultaneously the surface topography of a Nafion 112 membrane and the conductivity of ion channels with an unprecedented resolution of ca. 10 nm. For given conditions, a large fraction of the channel ports is found to conduct exactly the same number of protons per unit time. This is taken as evidence for an optimum pore size and structure for proton conduction, or alternatively, for an efficient connectivity of the ion channel network, so that the same conductivity is measured at all exit pores. The time response following a potential step and the influence of the relative humidity on the transport properties is investigated. The method will be of relevance for tailoring the production technology to yield an optimised micromorphology, and it permits detailed tests of membrane models and provides data for theoretical modelling of proton conductivity.

Correlating Humidity-Dependent Ionically Conductive Surface Area with Transport Phenomena in Proton-Exchange Membranes

“…An increase in the fraction of the membrane active area with humidity is consistent with earlier observations. 28,40 However, the fraction of conductive area of Nafion shows a large area of low-current domain.…”

“…In addition, the surface structure can affect water absorption into the membrane and influence the rate of mass-transfer processes, and thereby limit PEMFC performance. Contact angle measurements 38 and AFM imaging 17,24,25,27,[39][40][41][42] showed that the surface of the PFSA membrane is predominantly hydrophobic or non-wetting, especially at low relative humidity (RH) levels.…”

Atomic force microscopy and infrared analysis of aging processes of polymer electrolyte membrane fuel cell components

“…There is no general correlation between a higher voltage loss and a low PTFE content at the electrode. The PTFE content at the interface of the last row (segments [13][14][15][16], represented by the energy dissipation values, is almost parallel to the voltage loss. A higher dissipation value is correlated to a higher PTFE content and correlated here to a smaller voltage loss.…”

“…12b the energy dissipation of anode and cathode MPL is compared for the same segments. Even though the gas diffusion media at anode and cathode are of different nature from two suppliers, the energy dissipation of gas inlet (1) and outlet (16) and those of segments 14-16 of the last row close to the outlet have a comparable value. A large difference, more precisely an almost anti-parallel behavior, is visible in the other segments analyzed by AFM (diagonal of fuel cell).…”

“…With AFM the surface topography as well as different properties such as i.e. conductivity, adhesion force, elasticity, and dissipation energy can be measured and statistically analyzed [16][17][18]. Two main reasons for degradation of the PEMFC GDL are known, namely changes of GDL wetting behavior and GDL structural changes.…”