Peak power Micro

Yu et al. from the Hong Kong University described a miniature FC consisting in a MEA between two micro-machined Si substrates [8]. By sandwiching Cu between layers of gold, they were able to decrease the internal resistance of the thin-film current collectors, which involved an increase performance of the FC, achieving a peak power density of 193 mW cm with H2 and O. ... 

Different technologies have been developed which allows the fabrication of PEM micro fuel cells based on commercially available MEAs. Planar micro fuel cells with size of 1 cm x 1 cm and 200 pm thickness with 40 mA output current at 1.5 V (=120 mW cm, 25°C, 50% RH) has been successfully demonstrated. Cell performance was validated under varying ambient conditions. A peak power of 210 mW cm was demonstrated with dry H2 as fuel and with natural convection on the air side. 

A maximum peak power density at optimal conditions of 210 mW cm and stable long-term operation at 80 mW cm was achieved at different ambient conditions. The total performance of the micro fuel cells is in the same range of current and power density compared to the best conventional planar PEM fuel cells. At the same time this technology offers a high degree of miniaturisation and the capability for mass production which is a clear success of our micro-patterning approach. 

Pavel N, Tsunekane M, Taira T (2011) Composite, all-ceramics, high-peak power Nd YAG/ Cr YAG monolithic micro-laser with multiple-beam output for engine ignition. Opt Express 19 9378-9384... 

The best performance levels achieved to date are for micro fuel cells based on traditional membranes and electrodes and using forced convection [6, 7]. For example, power levels of over 300 mW/cm have been shown for pure pressurized oxygen, whereas 130 mW/cm was achieved for free convection of ambient air. Significant efficiencies, or voltages, have also been demonstrated at the peak power values, ranging from 0.4 to 0.7 V for various implementations. Most demonstrations were, however, done in a laboratory setting with external control and monitoring. 

Chan et al. (2005), have realised micro fuel cells through an approach that combines thin film materials with MEMS (micro-electro-mechanical system) technology. The membrane electrode assembly was embedded in a polymeric substrate (PMMA) which was micromachined through laser ablation to form gas flow channels. The micro gas channels were sputtered with gold to serve as current collectors. This cell utilized the water generated by the reaction for the humidification of dry reactants (H2 and O2). The peak power density achieved was 315 mW cm (901 mA cm" at 0.35 V) for the H2-O2 system with 20 ml min" O2 supply and H2 at 10 psi in dead ended mode of operation. A Y shaped microfluidic channel is depicted in Fig. 21. 

Micro fuel cell system faces numerous challenges for its widespread application in mobile devices. The electrical interfaces and the size of the fuel cell system should be maintained same as that of batteries. Fuel cells lack size-related standards similar to the one available for batteries. There is no standard fuel cell product that can be used as a power pack for all brands of the same electronic device. Currently micro fuel cells are quite expensive due to the use of noble metal catalyst and tiny pumps, fans, valves etc. for the reactant supply, recirculation, thermal, water management and product handling. Air traffic regulation could prohibit use and transportation devices fitted with micro fuel cells due to the flammable nature of most of the fuels used in these devices. The peak power rating of many of the micro fuel cells are inferior to that of batteries resulting in their inability to meet some of the functional requirement of microelectronic devices. 

Due to the limited peak capacity of the 15 cm analytical column utilized in 2-D nano LC-MS, several elution steps are required to achieve the required separation. The 15 cm analytical column can be replaced with a 100 cm nano LC column to increase the resolution of sample in each step. As shown by Yang,20 a 100 cm column allows the one-step separation of more than 2000 polypeptides from trypsin digest of mouse brain lysate, P2 fraction using XtremeSimple ultrahigh pressure nano LC (Micro-Tech Scientific, Vista, California) and LTQ MS (Thermo Electron, San Jose, California) in 6 hr (Figure 14.16). In addition to the improvement of resolving power with a 100 cm column, it... 

Table 1 PEM micro-fuel cell prototypes, incorporating mesoporous silicon as the proton exchange membrane in the core system, are reported in the literature. The performance of the membranes (proton conductivity) and the FC, i.e., the open circuit voltage (OCV) and the power density peak during the test, is reported...

Table 2 Micro-FC prototypes, incorporating mesoporous silicon in the core system, reported in the hterature for DHFC (direct hydrogen fuel cell), DMFC (direct methanol fuel cell), and RHFC (reformed hydrogen fuel cell). Aacttve is the active surface, OCV the open circuit voltage of the cell, PP the power peak during the test, fuel A and K are the fuels provided at anode (A) and cathode (K), T° is the temperature during the test, RT is the room temperature, MeOH is methanol and EtOFI is ethanol...

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