Direct methanol fuel cells powered portable devices

The electrocatalytic oxidation of methanol has been widely investigated for exploitation in the so-called direct methanol fuel cell (DMFC). The most likely type of DMFC to be commercialized in the near future seems to be the polymer electrolyte membrane DMFC using proton exchange membrane, a special form of low-temperature fuel cell based on PEM technology. In this cell, methanol (a liquid fuel available at low cost, easily handled, stored, and transported) is dissolved in an acid electrolyte and burned directly by air to carbon dioxide. The prominence of the DMFCs with respect to safety, simple device fabrication, and low cost has rendered them promising candidates for applications ranging from portable power sources to secondary cells for prospective electric vehicles. Notwithstanding, DMFCs were... 

Fuel cells are electrochemical devices that convert the chemical energy of the fuels directly into electrical energy, and are considered to be the key technology for power generation in stationary, automotive, portable and even microscale systems. Among all kinds of fuel cells, direct methanol fuel cells have really exhibited the potential to replace current portable power sources and micropower sources in the market (Yao et al., 2006). 

Shipments of fuel cell-equipped mobile devices could grow very rapidly if they can eliminate the need for frequent recharging of current battery-powered models. The Medis 24/7 Power Pack in April 2007. It is a portable, disposable power source for small electronic devices such as cell phones and MP3 players. Manufactured by Medis Technologies, it is based on Direct Liquid Fuel cell technology, and may be of particular utility in military applications. Elsewhere, MTI MicroFuel Cells manufactures a power pack for portable electronics that is based on direct methanol fuel cell technology that it calls Mobion. 

Carbon aerogels and xerogels have been used as supports for Pt and Pt-based electrocatalysts for proton-exchange membrane fuel cells (PEMFCs), also known as polymer-electrolyte fuel cells [56,58,83-90], These fuel cells are convenient and environmentally acceptable power sources for portable and stationary devices and electric vehicle applications [91], These PEMFC systems can use H2 or methanol as fuel. This last type of fuel cell is sometimes called a DMFC (direct methanol fuel cell). 

The main applications of direct methanol fuel cells in the near future will be the power supply of various portable electronic devices with civil, commercial, or military uses. In the future, power plants for electric vehicles and other transportation will join the above-mentioned applications. All these applications have specific, different features ... 

Polymer electrolyte and direct methanol fuel cells (PEFCs and DMFCs) are the most promising power sources for applications such as electric vehicles and electronic portable devices, due to their high power density, relatively quick startup, rapid response to varying loading, and low operating temperature [131]. Pt-based catalysts are the most important electrocatalysts in these fuel cells [132]. It has been widely reported that the catalytic activity of a Pt-based catalyst for the oxygen reduction reaction (ORR) and the methanol oxidation reaction in fuel cells is highly dependent on the oxidation states of the Pt crystallites on the surface of the catalyst [133, 134]. The oxidation states of Pt and the crystallites contents can... 

It is the aim of this chapter to review recent progress on nano-structured electro-catalysts for application to PEMFCs and direct methanol fuel cells (DMFCs). As one of the most important PEMFCs, DMFCs have been recognized as a potential future power source for portable electronic devices (Arico etal, 2001 Basri etal, 2010 Guo etal, 2008 Hamnett, 2003 Kamarudinef a/., 2009 Zhao et al, 2011). In particular, the relationships between nano-structure and electrocatalysis, and the catalytic mechanisms are discussed. Special attention has been paid in the latest avenues for making low-cost and effective catalysts such as novel nano-structures of Pt, binary and ternary platinum-based catalysts, new cost-effective synthesis routes, and new catalyst... 

However, considering the portable market, efficiency and cost are less important than system size, so these trade-offs are acceptable. The most developed DAFC is the direct methanol fuel cell (DMFC). Many prototype and nearly commercial DMFC systems exist for powering small electronics, laptop computers, cell phones, hand-held electronics, and other devices. Direct alcohol fuel cells are expected to occupy a growing market for portable power for years into the future. 

Portable power—Many companies (MTI, Motorola, NEC, Fuji, Matsushita, Medis, Manhattan Scientific, Polyfuel) are developing miniature fuel cells as battery replacements for various consumer and military electronic devices. Because of fuel storage issues, most of them use methanol in either direct methanol fuel cells or through microreformer in regular PEM fuel cells. 

Interestingly, the PEMFC may also operate directly on methanol. Naturally, the problems associated with high coverage of various intermediates will be present, as mentioned above, as well as additional problems such as loss of methanol over the membrane. Nevertheless, it is possible to operate a methanol fuel cell with a voltage around 0.4 V and a reasonable current, to power small mobile devices such as portable computers and cell phones and make them independent of connection to the conventional power net. For more details on fuel cells we refer the reader to L. Carr-ette, K.A. Friedrich and U. Stimming, Fuel Cells 1(1) (2001) 5-39. 

In recent decades, direct alcohol fuel cells (DAFCs) have been extensively studied and considered as possible power sources for portable electronic devices and vehicles in the near future. The application of methanol is limited due to its high volatility and toxicity, although it is relatively easily oxidized to CO2 and protons. So other short chain organic chemicals especially ethanol, ethylene glycol, propanol, and dimethyl... 

Apart from hydrocarbons and gasoline, other possible fuels include hydrazine, ammonia, and methanol, to mention just a few. Fuel cells powered by direct conversion of liquid methanol have promise as a possible alternative to batteries for portable electronic devices (cf. below). These considerations already indicate that fuel cells are not stand-alone devices, but need many supporting accessories, which consume current produced by the cell and thus lower the overall electrical efficiencies. The schematic of the major components of a so-called fuel cell system is shown in Figure 22. Fuel cell systems require sophisticated control systems to provide accurate metering of the fuel and air and to exhaust the reaction products. Important operational factors include stoichiometry of the reactants, pressure balance across the separator membrane, and freedom from impurities that shorten life (i.e., poison the catalysts). Depending on the application, a power-conditioning unit may be added to convert the direct current from the fuel cell into alternating current. 

---