Photo-stimulated hydrogen desorption from magnesium nanoparticles

Hydrogen remains an attractive energy carrier because it is abundant, environmentally friendly and has the highest gravimetric energy density of any known substance. Despite this high gravimetric energy density, hydrogen suffers from a low volumetric energy density as a room-temperature gas. To maximize volumetric energy density, storing hydrogen as a magnesium hydride is an efficient and economically viable route, owing to the low weight and high earth abundance of magnesium. A long-lasting obstacle for using magnesium is the high temperature required to release hydrogen once absorbed by magnesium. Although nanoscale magnesium is known to have a favorable effect on the hydrogen desorption temperature, it is not sufficient. In this work, hydrogen absorption and release was investigated by measuring optical changes, which correspond to certain hydrogen concentrations in magnesium nanoparticles. Remarkably, hydrogen desorption from the magnesium nanoparticle assembled thin films at room temperature could be achieved by illumination. This photo-stimulated hydrogen desorption introduces an effective and simple method to enable reversible hydrogen storage in magnesium. The sensitivity of the optical method here used is demonstrated by the fact that even hydrogen absorption from ambient air at 1 ppm has been measured. This work demonstrates that hydrogen can be efficiently stored and released from magnesium nanoparticles using only photons.