Efficient production of hydrogen via water splitting is an important goal that would represent a significant step towards truly sustainable supplies of energy. However, currently available catalysts for water electrolysis are either too low in efficiency or too unstable to be practical in this context. Recognizing the very high stability of manganese phosphate, we describe here a novel catalyst material based on manganese oxide that is both stabilized and sensitized by a surface phosphorylation reaction in an ionic liquid electrodeposition process. XPS and EXAFS data show that the surface of the MnOx contains phosphorous at P to Mn ratio of similar to 1:2, indicating that the surface layer contains both phosphate characteristics and oxide characteristics. The catalyst stability was significantly enhanced compared to the previously reported manganese oxide catalysts and more than 25 h of continuous water oxidation is demonstrated. (c) 2012 Elsevier B.V. All rights reserved.