Understanding the performance of a bisphosphonate Ru water oxidation catalyst
Jesús Antonio Luque‐Urrutia, Jayneil M. Kamdar, Douglas B. Grotjahn, Miquel Solà, Albert Poater
Abstract
Water oxidation catalysts (WOCs) create electrons that allow generating H2 from water and sunlight, a promising process for the production of clean energy. The mechanism of water oxidation mediated by Ru(2,2'-bipyridine-6,6'-diphosphonato)(4-picoline)2 has been studied computationally to comprehend the results obtained in the experiments performed by the Concepcion and Grotjahn groups. Our study was performed at pH = 8 and 1. At pH = 8, the phosphonates are fully deprotonated and the catalysis, which is shown to be more energetically costly than that of the dicarboxylato Ru catalyst counterpart, takes place through a mechanism that involves a bimolecular interaction between two metal-oxo units (I2M). At pH = 1, only one of the phosphonates of the catalyst can deprotonate. After testing all possible pathways and comparing with experimental data, we conclude that the catalysis proceeds neither through a water nucleophilic attack nor via I2M, but rather we hypothesize that the rate-determining step involves both the catalyst and the ceric ammonium nitrate.