[Follow-up] Sony Explains High Output of Ultra-small Fuel-Cell System

May 7, 2008
Kouji Kariatsumari, Nikkei Electronics
Demonstration of watching TV on mobile phone: The image on the screen is blurred for copyright reasons.
Demonstration of watching TV on mobile phone: The image on the screen is blurred for copyright reasons.
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Fullerene-based electrolyte film
Fullerene-based electrolyte film
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Catalyst on fuel electrode
Catalyst on fuel electrode
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Catalyst on air electrode
Catalyst on air electrode
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Sony Corp delivered a lecture on a fuel-cell system for use in mobile devices at Small Fuel Cells 2008. The lecture was titled "Micro Fuel Cell System for Mobile Consumer Electronic Devices" (See related article).

The prototyped fuel-cell system measures about 50 x 30 x 20mm and consists of a fue-cell unit, a micropump (referred to as "regulator" in the lecture) to supply fuel, a Li-polymer rechargeable battery and a control circuit.

The fuel-cell unit is composed of six cells and uses methanol with a purity of 99%. In addition to the power management of the fuel cell and the Li-polymer rechargeable battery, the control circuit controls the micropump and protects the Li-polymer rechargeable battery.

As a result of hybridization with the Li-polymer rechargeable battery, the latest fuel-cell system reportedly enables the maximum output of 3W or higher, although the fuel-cell unit by itself can only output about 1W.

The fuel-cell unit generates power at a constant output in a high efficiency range. And the load change in the device is handled by an output from the Li-polymer rechargeable battery.

Thus, when the electric load is light, the battery is charged by the fuel-cell unit. And when the load is heavy, the power is supplied from both the fuel cell unit and the Li-polymer rechargeable battery.

In the lecture, Sony showed a video clip demonstrating how a mobile phone powered by the latest fuel cell system displays TV broadcasts. The user can watch TV for about 14 hours with 10mL methanol, the company said. The energy generated by the fuel-cell unit with 1mL methanol is 1.1Wh, which is more than three times higher than the company's 2005 prototype and about double that of the 2006 prototype.

The high energy efficiency results from a high-density, low-crossover membrane electrode assembly (MEA) using a fullerene-based electrolyte film and a platinum-based new catalyst material. Sony has promoted the development of a fullerene-based electrolyte film for years.

Moreover, the energy efficiency was improved by the regulator, which can properly control the amount of methanol flow, the company said.

Regarding the durability, Sony suggested that the output of the latest system decreased by only 5% after the continuous operation of 900 hours. According to the company, the control circuit has functions unnecessary for the actual product, such as a data collection function, because the latest fuel cell system is a prototype used for R&D. Therefore, the actual system may be much smaller, the company said.