The increasing demand for energy and the harmful effects fossil fuels have on the environment make it necessary to develop alternative energy sources, such as artificial photosynthesis systems. These systems require efficient water oxidation catalysts. The goal of this project was to study how adding a hydroxyl ligand in different positions to the water oxidation catalyst [Cp*Ir(pic)NO3] (pic=κ2-pyridine-2-carboxylic acid, ion(−1)) affects its catalytic performance. The catalytic activity of five complexes was compared using two sacrificial oxidants, cerium (IV) ammonium nitrate (CAN) and NaIO4, at different pH levels (pH = 1 for CAN and pH = 5 - 7 for NaIO4). The presence of the hydroxyl group increased the turnover frequency (TOF) of the catalysts when CAN was used as the oxidant, but it decreased the TOF when NaIO4 was used, suggesting that the mechanism of water oxidation is different with different oxidants. With NaIO4, the performance increased as the pH increased. The highest TOF value observed in this study was obtained with [Cp*Ir(pic)NO3] and NaIO4 at pH 7 (maximum TOF = 270 min-1). These results demonstrate how adjusting the ligand groups, the oxidant, and the pH can optimize the performance of these water oxidation catalysts, so they could be used in an efficient artificial photosynthesis system.

Hydroxy-pyridine-carboxylate iridium complexes as extremely active, tunable and pH-responsive water oxidation catalysts

253rd National Meeting (2017)

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