Drs. Haile (CalTech) and Steinfeld (ETH, Zurich) led a small international team that developed a new solar energy machine. Their results, published in Science, employ cerium oxide to break down carbon dioxide and/or water into fuels.

They reported on a prototype that concentrates the solar energy through a quartz window, into a cerium oxide (ceria) lined cylinder (with alumina for insulation). What intrigued the researchers is that, while cerium oxide is a rare earth, it is among the most abundant (0.0046% of the earth;s crust,  by weight).

Cerium oxide has been used in fuel cells for years because of its high oxygen ion conductivity and in multiple step processes to remove oxygen from water, liberating hydrogen for use as fuel.  Chem E researchers at MIT were examining this in the early 70’s, and, more to the point,  Drs. Chung and Park ,  reported in Catalysis Today, that cerium oxide effected the photocatalytic decomposition of water, yielding hydrogen (the oxygen was preferentially absorbed by the catalyst).

Using these principles, along with the knowledge that when cerium oxide is heated, it releases oxygen; it reabsorbs same as it cools, Drs. Haile and Steinfeld chose this as the basis for the development.  When water is in the chamber and the sunlight is focused on the device, oxygen is stripped out, leaving hydrogen to serve as fuel.  If water and carbon dioxide are in the chamber, syn gas (a low heat value fuel, similar to natural gas).

The prototype only proves the concept; it is highly inefficient in converting the solar energy collected (some 0.7%).  They hope to augment this efficiency to 19%, via smaller apertures and better insulation, since most of the energy is radiated back to the atmosphere or lost as heat through the walls of the device.

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