Researchers at Massachusetts Institute of Technology in Cambridge have demonstrated that light can be used to produce molecular hydrogen. If the catalytic technique can be optimized, it may yield a cost-effective means of producing environmentally friendly energy.The group, which reported the work in the Aug. 31 issue of Science, built on prior research into the use of dimeric rhodium complexes as a catalyst, which led to a stoichiometric process. It instead excites the precursor of the dirhodium catalyst with UV light. The catalyst then reacts with hydrohalic acid to yield H2. Currently, the conversion efficiency of the technique is too low to be practical.