Spirited talk

A new methanol fuel cell for use in mobile phones will allow 3G handset users up to eight hours of continuous talk time, its Japanese developers said this week. The power system has been developed jointly by telecoms firm NTT DoCoMo and Fujitsu Laboratories.

NTT DoCoMo first unveiled a prototype micro-fuel cell using methanol as an inexpensive source of power last year. This was designed to meet user demands for handsets with greater power capacity but reduced environmental impact.

The new design is aimed at users of 3G FOMA handsets, and has three times the energy capacity of the early prototype while weighing exactly the same: 190g.

The fuel cell’s life has been extended by increasing the methanol concentration from 30 per cent to more than 99 per cent. This enables the prototype device to charge up to three FOMA handset batteries with just 18 cubic centilitres of methanol.

The fuel cell produces energy through the reaction between methanol and oxygen present in the air. It consists of a ‘passive’ cell in which no mechanical components such as pumps or fans are employed.

However, when high-concentration fuel is used such devices have previously been susceptible to a phenomenon known as methanol crossover. This is where fuel permeation occurs between battery electrodes, resulting in lower generation efficiency.

Researchers at Fujitsu developed a new material to reduce the methanol crossover effect to what it claims is one-twentieth that of other commercially available devices. Water that occurs as a by-product during the power generation is used to dilute the fuel, also limiting the decline of power generation efficiency.

In theory, micro-fuel cells offer up to 10 times the performance of lithium ion batteries. The performance of micro-fuel cells depends on how compact they can be made, and how much energy can be created from a given volume of fuel. So DoCoMo and Fujitsu are now hoping to make the device even smaller.

Customers’ power consumption demands are rising as 3G users take advantage of features such as videophone. Unlike in Europe, where their take-up has been hampered by the high cost of handsets, 3G services have proved widely popular in Japan, with the result that NTT DoCoMo plans to phase out 2G subscriptions altogether by 2012.

As well as producing micro-fuel cells, DoCoMo is also working to increase the capacity of conventional lithium-ion batteries, used to power the current generation of handsets.