Hong-Sung Chang

Materials and processes for small fuel cells

Abstract Materials and processes for water management electrode, efficient flow field, low cost ionomer membrane and stack design for proton exchange membrane fuel cell (PEMFC) also with methanol oxidation catalyst, liquid diffusion electrode, low methanol cross-over membrane and efficient monopolar cell pack design for direct methanol fuel cell (DMFC) are discussed. These include the technical achievements of small PEMFC (Membrane and Electrode Assembly (MEA): 400 mW/cm 2 with non-humidified H 2 /air, 1 Bar, 30 °C; membrane: 0.1 S/cm; stack: 40 and 200 W with no peripheral) and miniaturized DMFC (MEA: 50 mW/cm 2 with 2 M methanol and 1 Bar air at 30 °C; membrane: hybrid; cell pack: 600 mW). Further studies for the realization of these technologies are also suggested.

Performance comparison of 802.16d OFDMA, TD-CDMA, cdma2000 1xEV-D0 and 802.11a WLAN on voice over IP service

We analyzed four systems designed for high-data rate transmission such as IEEE 802.16d OFDMA5 3GPP TD-CDMA, 3GPP2 cdma2000 1xEV-DO, and IEEE 802.11a WLAN, and compared their efficiency, the number of VoIP user, and the normalized number of VoIP user per 1 MHz. It is shown that the 802.16 system serves the most number of VoIP user, and the normalized number of user per 1 MHz is also the most. Even though 802.11a system is operated over the widest band, it supports the less number of user compared to the 802.16 system with smaller bandwidth, due to the inefficiency of CSMA/CA scheme. TD-CDMA and 1xEV-DO serve the same number of VoIP user per 1 MHz bandwidth, and TD-CDMA performs with the best efficiency among four systems. Comparing with TD-CDMA and 1xEV-DO, we concluded that 802.16d OFDMA system is the most flexible to assign its resource to users due to its finest granularity among three systems.