Advances in chemistry hold promise for solar generation and hydrogen storage

Recent work at MIT, in the Nocera Group headed by Daniel Nocera, have given a much needed boost to proponents of the solar and hydrogen energy economy by providing some breakthrough technology allowing the use of solar energy to electrolytically crack water into hydrogen and oxygen gases with low cost and low energy investment.

Until now, both solar and hydrogen energy have been considered marginal in terms of their actual economic potential – solar because of basic efficiency issues and location/climate dependencies, and hydrogen because of the energy and money cost of producing hydrogen to charge fuel cells.

Converting sunlight into energy using the most modern of solar cells has produced a maximum efficiency of around 40%, and commercially produced cells are generally below 20% efficiency. The cost of making the solar cells with highest efficiency, their life-span, and their durability are all issues as well. Another critical issue facing solar energy technology is the question of what to do with the energy once it is produced: until now the two best means of taking advantage of solar-produced energy are 1) storage in deep-cycle lead-acid batteries, or 2) direct conversion to heat. Neither of these are economic at large, societal-level scale.

The challenges facing advocates and researchers in the field of hydrogen energy storage (hydrogen is not an energy source, it is a storage mechanism) are similarly daunting. While many generations, styles, and implementations of the basic hydrogen fuel cell have been developed, and are now working quite well as energy storage devices for cars, homes, or etc, the main problem with the proposed “Hydrogen Economy” is the generation of hydrogen, which is not found in its elemental or gaseous state on Earth's surface. Generating hydrogen gas or elemental hydrogen requires a significant amount of energy, either to “crack” water into hydrogen and oxygen gas, or to “crack” hydrocarbons, producing hydrogen, carbon dioxide, and assorted other chemical species, depending on the type of hydrocarbon used. In either case, the benefits of “clean” hydrogen storage and use are significantly reduced, either by the requirement to use a lot of energy to make the hydrogen to charge the cell, or by the release of CO2 during the hydrogen production process.

This is where the MIT team's work becomes so interesting. Nocera and his colleagues initially posited that the best way to produce hydrogen (and oxygen) was to somehow mimic the photosynthetic process used by plants to “crack” water using sunlight, producing oxygen gas and hydrogen (plants use this hydrogen by combining it with carbon to make cellulose and sugar). The MIT group's work has paid off, and along with several other research groups, they are now developing means of reproducing the photosynthetic process using chemical reactions in an electrolytic bath powered by sunlight.

In a nutshell, the process uses cobalt and phosphate in thin films on electrodes. The electrodes are charged via solar power, and when immersed in water, catalyze the oxidation of water into hydrogen and oxygen gas. The research is still in its early stages, and there are many skeptics and many challenges ahead... but there seems to be a lot of ”>promise in the technology – enough so that government-run and -funded labs in the US and Japan are beginning to commit resources to investigating the potential.