Ultra compact direct hydrogen fuel cell prototype using a metal hydride hydrogen storage tank for a mobile phone

Sung Han Kim, Craig M. Miesse, Hee Bum Lee, Ik Whang Chang, Yong Sheen Hwang, Jae Hyuk Jang, Suk Won Cha

The small fuel cell is being researched as an alternative power source to the Li-ion battery in mobile phone. In this paper, a direct hydrogen fuel cell system which powers a mobile phone without a supplementary battery is compactly integrated below 25 ml volume at the backside of the phone. The system consists of a small (8 ml) metal hydride hydrogen storage tank with 4 L hydrogen storage or an energy density of ∼640 W h/L, a thin air-breathing planar polymer electrolyte membrane fuel cell (PEMFC) stack (13.44 cm2 × 3 mm for a volumetric power density of 335 W/L), miniature pressure regulator, and a high efficiency DC–DC voltage converting circuitry. The hydrogen storage tank is packed with the AB5 type metal hydride alloy. The eight-cell air-breathing planar stack (8 ml) is very thin (3 mm) due to a thin flexible printed circuit board current collectors as well as a unique riveting assembly and is capable of a robust performance of 2.68 W (200 mW/cm2). A miniature pressure regulator is compact with fluidic and electrical connections within 4 ml. A miniature DC–DC voltage converter operates at an overall efficiency of 90%. Consequently, the estimated energy density of a fully integrated fuel cell system is 205 W h/L (70.5 W h/kg).