Water-Splitting Catalyst Likes All pH Values

The possibility of splitting water to liberate hydrogen, a clean-burning fuel, has spurred an intense search for catalysts to make that process feasible and energy efficient. Most of the promising inexpensive catalysts mediate only half of the chemistry—either the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER). Coupling those halves in a single water-splitting system has remained challenging, in part because of each half’s pH preference. HER catalysts prefer acidic media, whereas OER catalysts typically prefer alkaline or neutral solutions. A team led by Tewodros Asefa of Rutgers University may have sidestepped that problem by developing a HER catalyst that works well at any pH (Angew. Chem. Int. Ed. 2014, DOI: 10.1002/ange.201311111). In a series of electrocatalysis experiments ranging in pH value from 0 to 14, the researchers found that cobalt-doped, nitrogen-rich carbon nanotubes, which they prepared from inexpensive dicyandiamide and CoCl₂, are nearly as active in producing hydrogen as costly platinum reference catalysts. Initial tests lasting 10 hours showed that the cobalt-based catalyst remains stable under all pH conditions.