Practical solar powered aircraft require an efficient energy storage system to store energy during the day for use at night. Hydrogen and oxygen, generated by electrolyzing water during the day and recombined at night to generate electricity, has a theoretical energy density of 3.73 kWh/kg. Harnessing this potential has been approached with a combination of a lightweight PEM electrolyzer and a lightweight PEM fuel cell with a new stack structure utilizing metallurgical bonding to assemble thin metal gas barriers with lightweight metal flow fields. This design minimizes size, weight, electrical resistance, and part count. This technology has been demonstrated to produce efficient and effective stacks.