Micro-reformed hydrogen fuel cell

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...

Typically, micro fuel cells use methanol as fuel alfhough hydrogen-fed micro fuel cells have also been developed. The choice of the type of fuel cell to use in portable devices may be limited to low-temperature fuel cells such as PEMFC (proton exchange membrane fuel cell/polymer electrolyte membrane fuel cell) and DMFC. However, micro reformed methanol fuel cells and miniature SOFCs have also been developed. 

Accordingly, serious commercially oriented attempts are currently being made to develop special gas-phase micro and mini reactors for reformer technology [91, 247-259], This is a complex task since the reaction step itself, hydrogen formation, covers several individual processes. Additionally, heat exchangers are required to optimize the energy balance and the use of liquid reactants demands micro evaporators [254, 260, 261], Moreover, further systems are required to reduce the CO content to a level that is no longer poisonous for a fuel cell. Overall, three to six micro-reactor components are typically needed to construct a complete, ready-to-use micro-reformer system. 

High system efficiency levels can be achieved only with intensive heat integration within the fuel cell micro CHP systems. Hence, heat integration system studies are of utmost importance along with the development of novel reforming catalysts, cleanup systems, and PEM fuel cell components if on-site hydrogen production is desired for micro CHP applications. 

However, most fuel cell systems can tolerate methane concentrations up to at least 1% in the reformate, no special purification reactions are required. In contrast, hence, removing small residual amounts of carbon monoxide from pre-purifled reformate applying the methanation reaction may be considered as an alternative to the preferential oxidation of carbon monoxide, provided that the CO concentration is low enough to have no significant impact on the hydrogen yield. However, no applications of methanation for CO clean-up in micro structured devices appear to have been reported, hence the issue is not discussed in depth. Finally, during hydrocarbon reforming all hydrocarbon species (saturated and unsaturated) smaller than the feed molecule may be formed. 

Enzymes have been considered in bio fuel cells as anode electrocatalysts since their use avoids the problem of poisoning the anode with carbon monoxide present in reforming gas, allowing the use of cheap hydrogen-containing fuels such as methanol. Even though enzymatic fuel cells have been reported to have power output and stability limitations, some of them are currently being used to produce electricity to power small electrical devices with power demands in the order of micro- and milh- Watts as power output limitations are overcome. 

Roses, L., Manzolini, G. and Campanari, S. (2010) CFD simulation of Pd-based membrane reformer when thermally coupled within a fuel cell micro-CHP system. International Journal of Hydrogen Energy, 35, 12668-12679. 

Kim, T. (2009) Micro methanol reformer combined with a catalytic combustor for a PEM fuel cell. Int.J. Hydrogen Energy, 34 (16), 6790-6798. 

Metal foam (see, for example. Figure 3.5) has already been discussed in the context of heat exchangers. Micro-reactors, highly relevant to the subject of small fuel cells, have also been introduced in earlier chapters. The construction of metal foam based methanol steam micro-reformers to generate hydrogen for polymer electrolyte membrane fuel cells (PEMFCs) has been reported and in Guangzhou, Chinese researchers have looked at laminated micro-reactors in which copper-based catalysts have been supported by metal foams (see Figure 11.11 Yu et al., 2007). 

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