VATIS UPDATE Article

A collaboration led by Kyushu University, Japan, has recently developed a catalyst that can oxidize both hydrogen and carbon monoxide depending on the pH of the reaction system. The catalyst mimics the behavior of two enzymes: hydrogenase in acidic media (pH 4-7) and carbon monoxide dehydrogenase in basic media (pH 7-10). The catalyst is a water-soluble complex containing nickel and iridium metal atoms with a unique “butterfly” structure.

The researchers investigated the ability of their catalyst to oxidize hydrogen and carbon monoxide in a 1:1 mixture. Importantly, they were able to isolate various intermediates in the oxidation processes to confirm the mechanisms of hydrogen and carbon monoxide oxidation by the catalyst. “We found that the catalyst reacted with hydrogen to form a hydride complex under acidic conditions,” said Professor Seiji, at Kyushu University.

The team then investigated the resistance of their catalyst to poisoning by carbon monoxide in a prototype fuel cell using feed gases of hydrogen, carbon monoxide, and a 1:1 mixture of the two. The power density of the fuel cell containing the catalyst depended on the system pH and feed gas composition. Oxidation of hydrogen by the catalyst was facilitated at low pH (acidic conditions) and oxidation of carbon monoxide was faster at high pH (basic conditions); these trends correspond well with the behavior observed for the related enzymes.