This PEM fuel cell has H2 storage built-in

Conventional hydrogen-based systems designed to store electrical energy (from solar arrays, for example) typically feed electricity to a proton-exchange-membrane (PEM) electrolyzer to generate H2 from water. This H2 is then compressed and stored in a cylinder, or as a metal hydride in a canister containing a powdered metallic alloy. When electricity is required, H2 is supplied from the storage cylinder to a PEM fuel cell, along with O2 from air, and electricity is generated again. The conversion efficiencies in the various stages of such a system lead to an overall energy efficiency of less than 50%. To improve this efficiency, a reversible PEM fuel cell with integrated metal-hydride hydrogen storage — a “proton flow battery” — has been designed by researchers from RMIT University (Melbourne, Australia; www.rmit.edu.au), led by professor John Andrews. In the proton flow battery, many steps in the conventional process that incur net energy losses and irreversible entropy gains are completely avoided. The researchers claim their system’s roundtrip energy efficiency can be comparable with that of the best battery types, such as lithium ion (about 70 to 80%), while storing more energy per unit mass and volume.…