Dong-Ryul Shin

Performance of a polymer electrolyte membrane fuel cell with thin film catalyst electrodes

In order to develop a kW-class polymer electrolyte membrane fuel cell (PEMFC), several electrodes have been fabricated by different catalyst layer preparation procedures and evaluated based on the cell performance. Conventional carbon paper and carbon cloth electrodes were fabricated using a ptfe-bonded Pt/C electrocatalyst by coating and rolling methods. Thin-film catalyst/ionomer composite layers were also formed on the membrane by direct coating and transfer printing techniques. The performance evaluation with catalyst layer preparation methods was carried out using a large or small electrode single cell. Conventional and thin film membrane and electrode assemblies (MEAs) with small electrode area showed a performance of 350 and 650 mA/cm2 at 0.6 V, respectively. The performance of direct coated thin film catalyst layer with 300 cm2 MEAs was higher than those of the conventional and transfer printing technique MEAs. The influence of some characteristic parameters of the thin film electrode on electrochemical performance was examined. Various other aspects of overall operation of PEMFC stacks were also discussed.

Water transport in polymer membranes for PEMFC

To determine the net electro-osmotic drag coefficient of Nafion 115 and Hanwha membrane, we measured the fluxes of water discharged from anode and cathode at different current densities. Also, we investigated the contribution of water supply for membrane from anode and cathode. When the cathode was humidified, water supply for membrane at low current densities was achieved via the cathode, but the contribution of the anode became more important as current density gradually increased. The net electro-osmotic drag coefficient decreased sharply with current density, but it had a nearly constant value over 200 mA cm−2. When the cathode was not humidified, at low current densities, most of water generated at cathode was supplied for membrane, but water supply from cathode at high current densities decreased proportionately, and the net electro-osmotic drag coefficient showed larger value.

A novel process to fabricate membrane electrode assemblies for proton exchange membrane fuel cells

A new fabrication method of membrane electrode assembly (MEA) for proton exchange membrane fuel cells is developed by using perfluorosulfonyl fluoride copolymer powder and Pt/C catalyst. The perfluorosulfonyl fluoride copolymer powder is pressed into a sheet at 230°C by hot pressing. The Pt/C catalyst is then coated on to either side of the sheet by screen printing, followed by hot pressing. During this process, due to the melt-fabricable property of the pre-formed sheet, the coated catalyst layer is embedded into the membrane. The resultant MEA is converted into perfluorosulfonate polymer by hydrolysis of NaOH solution. The thermal property of the copolymer powder has been analyzed by DTA-TGA, and the interfacial contact of the catalyst with the membrane has been also investigated by SEM. The performance characteristics of the MEA have been evaluated in a single cell.

A study on the formation of surface functional groups during oxygen reduction on a platinum-dispersed carbon electrode in an 85% H3PO4 solution at elevated temperature

Abstract The formation of the surface functional group during oxygen reduction on a platinumdispersed carbon (Pt/C) electrode has been investigated in an 85% H 3 PO 4 solution at 145 °C with concurrent blowings of a mixture of oxygen and nitrogen by using Fourier transform infrared (FTIR) spectroscopy supplemented by AC-impedance spectroscopy. AC-impedance spectra indicated that the reactivity of H 2 O 2 towards the chemical and electrochemical decomposition increases with increasing oxygen partial pressure. From the results of FTIR spectroscopy, the surface functional group formed during oxygen reduction proved to be composed mainly of quinone and carboxyl groups. By comparison of the FTIR spectra obtained from the pure and Pt/C powders treated in a H 2 O 2 -containing aqueous solution with those from the Pt/C powder treated in H 3 PO 4 solution, it is concluded that the carboxyl group formation dominates over the quinone group generation in the low oxygen partial pressure range; however, it is quite the opposite in the high oxygen partial pressure range.

Characterization and performance analysis of silicon carbide electrolyte matrix of phosphoric acid fuel cell prepared by ball- milling method.

Abstract The effect of ball milling in making a silicon carbide slurry for the electrolyte matrix of a phosphoric acid fuel cell (PAFC) was studied by measuring the zeta potential and the particle-size distribution, and by analyzing cell performance. The ball-milled slurry gives a better particle distribution than the conventional mechanical-stirring method, and the particle distribution of the slurry depends on balling time and pH, which is confirmed by zeta potential. A single cell with a ball-milled electrolyte matrix also displays high performance. It is concluded that the ball-milling method is preferable to the mechanical-stirring procedure for preparing silicon carbide slurries.

Microstructure of PTFE and acid absorption behavior in PTFE-bonded carbon electrodes

The microstructure of PTFE and acid absorption characteristics of the electrocatalyst layer of PTFE-bonded gas diffusion electrodes have been investigated. Before sintering, PTFE was in the form of spherical particles and fibrils and was transformed to a lump or honeycomb network of thin film or filaments. By the formation of a high temperature structure of PTFE, the hydrophobicity of the electrocatalyst layer increased and hydrogen chemisorbed Pt fraction and utilization of Pt decreased.

La 0.8 Ca 0.2 CrO 3 Interconnect Materials for Solid Oxide Fuel Cells: Combustion Synthesis and Reduced-Temperature Sintering

Sub-micrometer powders for ceramic interconnects of solid oxide fuel cells were synthesized by the aqueous combustion process. The materials were prepared from the precursor solutions with different glycine (fuel)-to-nitrate (oxidant) ratios (). Single-phase powders with a perovskite structure were obtained after combustion when was equal to or larger than 0.480. Especially, the stoichiometric precursor with

Development of Two-layer Electrode for Direct Methanol Fuel Cell

The performance of the Direct Methanol Fuel Cell (DMFC) using multi-layer electrode, which prepared by various anode catalysts and Nafion membranes, was studied for reducing the amount of the metal catalyst loaded in the MEA system. The amount of the catalyst used in this experiment was in cathode and in anode, respectively. The best performance was to be of MEA3 at and 2 bar in this experiment. However, the overall performance of the DMFC was maintained almost the same compared to the general commercial catalyst systems.

Development of LSM-Coated Crofer Mesh for Current Collectors in Solid Oxide Fuel Cells

A Crofer 22 APU mesh coated with a conductive ceramic material was developed as an alternative cathode current collector to Ag-based materials for solid oxide fuel cells. (LSM) layer was deposited onto the Crofer mesh using a spray-coating technique, in an attempt to mitigate the degradation of electrical properties due to surface oxidation at high temperatures. The oxidation experiments at in air indicated that the areaspecific resistance (ASR) of the LSM-coated Crofer mesh was strongly dependent on the wire diameter and the contact morphology between mesh and cell. In addition, the post-heat-treatment in resulted in a reduced thickness of Cr-containing oxide scales at the interface between Crofer mesh and LSM layer, leading to a decreased ASR.

High Temperature Sealing Method: Induction Brazing for SOFCs

The nickel based brazing alloys (BN-2, BNi-4) modified by reactive TiH2 have been studied for their gas sealing properties of anode-supported tubular SOFCs to ferritic stainless steel by induction brazing process. BNi-2 and BNi-4 are not wetted in YSZ electrolyte, but the brazing alloy with added TiH2 showed good wettability with YSZ electrolyte due to formation of a TiOX layer. Among the tested brazing alloys (BNi-2, BNi-4, modified BNi-2, modified BNi-4), all except modified BNi-4 did not join with YSZ. The gas tightness of a brazed cell was confirmed by OCV value, and it was stayed nearly the same as the theoretical value for 600h at 750 °C. Based on these experimental results, it is concluded that the BNi-4 modified by TiH2 is suitable as a sealing material in SOFCs operating at 750 °C.Copyright