Jung-Je Woo

Hydrogen bonding: a channel for protons to transfer through acid-base pairs.

Different from H(3)O(+) transport as in the vehicle mechanism, protons find another channel to transfer through the poorly hydrophilic interlayers in a hydrated multiphase membrane. This membrane was prepared from poly(phthalazinone ether sulfone kentone) (SPPESK) and H(+)-form perfluorosulfonic resin (FSP), and poorly hydrophilic electrostatically interacted acid-base pairs constitute the interlayer between two hydrophilic phases (FSP and SPPESK). By hydrogen bonds forming and breaking between acid-base pairs and water molecules, protons transport directly through these poorly hydrophilic zones. The multiphase membrane, due to this unique transfer mechanism, exhibits better electrochemical performances during fuel cell tests than those of pure FSP and Nafion-112 membranes: 0.09-0.12 S cm(-1) of proton conductivity at 25 degrees C and 990 mW cm(-2) of the maximum power density at a current density of 2600 mA cm(-2) and a cell voltage of 0.38 V.

Improvement of an enzyme electrode by poly(vinyl alcohol) coating for amperometric measurement of phenol

A poly(vinyl alcohol) film cross-linked with glutaraldehyde (PVA-GA) was introduced to the surface of a tyrosinase-based carbon paste electrode. The coated PVA-GA film was beneficial in terms of increasing the stability and reproducibility of the enzyme electrode. The electrode showed a sensitive current response to the reduction of the o-quinone, which was the oxidation product of phenol, by the tyrosinase, in the presence of oxygen. The effects of the PVA and PVA-GA coating, the pH, and the GA:PVA ratio on the current response were investigated. The sensitivity of the PVA-GA-Tyr electrode was 130.56microA/mM (1.8microA/microM cm(2)) and the linear range of phenol was 0.5-100microM. At a higher concentration of phenol (>100microM), the current response showed the Michaelis-Menten behavior. Using the PVA-GA-Tyr electrode, a two-electrode system was tested as a prototype sensor for portable applications.

End-group cross-linked large-size composite membranes via a lab-made continuous caster: enhanced oxidative stability and scale-up feasibility in a 50 cm2 single-cell and a 220 W class 5-cell PEFC stack

We present successful scaling-up feasibility of a large-size membrane-electrode assembly (MEA) using a newly developed thin composite polymer electrolyte membrane for fuel cell applications. The highly sulfonated end-group cross-linkable polymer electrolytes were synthesized and reinforced using a porous polytetrafluoroethylene (pPTFE) substrate of 15 μm thickness. Here, a lab-scale continuous caster was developed in order to fabricate thin composite membranes with a uniform thickness of 25 μm. The reinforced thin composite membranes exhibit an efficiently reduced water uptake and swelling ratio, and improved oxidative stability in Fentons reagent compared to normal cast membranes. The optimized composite membrane was subsequently tested in a single-cell and a five-cell stack to demonstrate their feasibility for the scaled-up polymer electrolyte fuel cells (PEFCs). Eventually, the composite membrane successfully performed in the stack with low scale-up losses of about 2–3%. As a preliminary investigation, an in situ accelerated degradation test (ADT) is performed to evaluate the relative chemical durability of the composite MEA in a 50 cm2 single cell (at 100 °C with approximate relative humidity of 10%), and the degradation kinetic of the MEA (1.47 mV h−1) is comparable to Nafion®212 (1.45 mV h−1) during 24 h ADT.

Estimation of approximate activation energy loss and mass transfer coefficient from a polarization curve of a polymer electrolyte fuel cell

A simple electrochemical approach is presented to quantitatively predict activation energy and mass transfer coefficient from a polarization curve of polymer electrolyte fuel cells to examine the membrane-electrode assembly (MEA) performance. It is assumed that the initial voltage drop at open circuit voltage is due to kinetic activation energy and that the current loss at short circuit current is due to mass transfer resistance. Accordingly, voltage drop in the activation polarization is converted into a change in the Gibbs free energy to determine the activation energy requirement. The mass transfer coefficient for current losses is derived from Fick’s law, based on the mass transfer limitation of oxygen at the oxygen reduction reaction sites. Case studies from the literature show reasonable correlations to the operating conditions, thereby providing a useful tool for prediction of the preliminary values of the activation energy and mass transfer coefficient for an MEA under various conditions.