An inexpensive cobalt-based catalyst efficiently evolves hydrogen in pH-neutral water at ambient temperature and in the presence of atmospheric oxygen, report researchers at the University of Cambridge, U.K. "… Our finding provides a first step to produce 'green hydrogen' under relevant conditions," notes Erwin Reisner, head of the Christian Doppler Laboratory for Sustainable SynGas Chemistry at the university. Work already has started on developing a solar-driven water-splitting device to produce H2 and O2 simultaneously, he adds.
"Until now, no inexpensive molecular catalyst was known to evolve H2 efficiently in water and under aerobic conditions. However, such conditions are essential for use in developing green hydrogen as a future energy source under industrially relevant conditions," he explains.
The homogeneous cobaloxime-type material evolves H2 both electro- and photocatalytically. It provides a Farradaic efficiency of about 43% and a photo-induced H2-evolution relative activity of about 70% under those conditions. More details appear in an article in Angewandte Chemie International.
Platinum also evolves H2. "The issue with platinum is that it's very rare and therefore expensive. It also is a good O2-reduction catalyst, which limits its operation for H2 evolution in the presence of O2," notes Reisner. "We will do a direct comparison with platinum soon."
"Problems of the cobaloxime catalyst are the limited lifetime (several hours) and a small turnover number (it only produces about 100 molecules of H2 per molecule of catalyst). We need numbers in the millions here," he admits. "Development of more inexpensive and efficient systems is still required."