Protected Oxidation Catalyst

A new catalyst that breaks water into its oxygen and hydrogen constituents avoids a problem that has plagued previous cobalt-based water-oxidation catalysts—the propensity of the released O₂ to destroy the catalyst. Chemists have been avidly searching for photosynthetic mimics that catalyze the oxidation of water, with the goal of creating H₂ to power fuel cells. The new catalyst, a bulky complex with the formula [Co₄(H₂O)₂(PW₉O₃₄)₂]^10–, comes from the lab of Craig L. Hill at Emory University (Science, DOI:10.1126/science.1185372 ). Hill and coworkers say this complex is now the fastest known homogeneous water-oxidation catalyst and is an improvement over popular heterogeneous cobalt-based water-oxidation catalysts. Hill’s group surrounded the catalyst’s cobalt oxide core with bulky polytungstate ligands that resist oxidation. Not only is the catalyst free of carbon-based ligands, which are also vulnerable to oxidation, but it also self-assembles in boiling water. That the elements in the catalyst—cobalt, tungsten, phosphorus, and oxygen—are cheap and abundant is another plus. The researchers say their work prompts the examination of other polyoxometalate-stabilized multi-transition-metal oxide clusters as water-oxidation catalysts.