At the nuvera fuel cells lab in Cambridge, Massachusetts, 25-year-old chemical engineer Darryl Pollica stands in front of a prototype 5-kilowatt fuel cell -- a miniature powerplant that can make most of the electricity needed by a family of four. Its metal skin has been removed to reveal a cubical frame about 5 feet on each side, packed with tanks, valves, and electronics. Conspicuously taped to the outside of the frame is a Nokia cellphone.