The need to regularly recharge batteries in mobile phones, laptops and other portable terminals may be eliminated in the future, according to the latest developments by leading silicon chip manufacturer STMicroelectronics. ST, which has long been one of the major suppliers of the silicon chips used in mobile phones, has reported progress by one of its advanced R&D teams in developing tiny fuel cells, small enough to fit inside a mobile handset, that could generate all the electrical energy needed to power the phone from cheap and easily available organic fuels.
A fuel cell is a device that generates energy using electrochemical reactions instead of fuel combustion. In recent years, there has been enormous interest in fuel cells because they promise to deliver cheap, clean energy. Although much of the work in the emerging field of fuel cell technology has been aimed at automotive applications, ST researchers have also been investigating the replacement of the rechargeable batteries used in mobile phones by tiny fuel cells that can be refilled with fuel whenever needed, just like refillable cigarette lighters.
“Using fuel cells instead of batteries would make mobile phones lighter and much more convenient to use as they could be simply topped up with fuel whenever necessary. In addition, there would be significant environmental benefits as the fuel can be derived from sustainable organic sources, while the by-products are mainly water and a much lower level of carbon dioxide than is produced by burning fossil fuels,” says Dr. Salvo Coffa, who leads the Corporate Technology R&D team that is researching the micro fuel cell technology.
The operation of a fuel cell involves the chemical interaction between hydrogen and oxygen to produce water, heat and electrical energy. Typically, a fuel cell consists of a pair of electrodes (the ‘anode’ and the ‘cathode’) separated by a membrane that allows protons (hydrogen ions) to pass through the membrane but does not allow an electric current to pass. In addition, catalysts such as platinum are used to increase the rate of the reaction and therefore the amount of electrical energy produced.
The main problem with applying fuel cell concepts to mobile phones is that the power source (battery or fuel cell) must be able to deliver around 300mA of current at 3.6V and it must not occupy a volume of more than around 12 cubic centimeters. However, the output current of a fuel cell is directly related to the common surface area between the electrodes and the membrane and to obtain 300mA of current using conventional fuel cell technologies would require a surface area of around 60 square centimeters, much larger than is available in a mobile phone.
ST has made important progress in overcoming this problem by developing new technologies in which the fuel cell could be implemented as a 3D structure containing thousands of buried microchannels that maximize the contact area between the gases, the catalysts and the electrodes.
The ST research team has also succeeded in fabricating a special nanoporous layer, consisting of a layer of silicon containing millions of pores, each measuring just a few nanometers in diameter. The small pore sizes give the layer a very large effective surface area, thus increasing the efficiency of the catalysis. In addition, the ST team is working with the University of Naples to develop novel membranes that exhibit high proton conductivity and lower cost compared to the membrane materials that are commercially available today.
“ST is committed to researching new technologies that could help to minimize the impact of industrial and consumer products on the global environment. Although there is still further work to do before these developments can be integrated into a commercial technology, we are very excited about their potential,” says Coffa.
The ST work on micro fuel cells is partially supported by a National Research Project, aimed at developing small fuel cells for portable electronic applications, in which several other Italian institutions participate (CNR-IMM, CNR-ITAE, CNR-ITS and Pirelli labs). In the project, ST leads and coordinates the activity related to micro-fuel cell fabrication and integration.