Lowering water oxidation overpotential of a mononuclear ruthenium(II) complex bearing ionizable imidazole moieties

The search for alternative and carbon-free source of energy is now of paramount importance for a sustainable development. The use of solar energy appears as one of the most promising alternatives through photoelectrochemical cells, and ruthenium-based water oxygen catalysts (WOC) are among the most used catalysts to achieve this goal. In this work we present the synthesis and characterization by UV-vis, 1H-NMR, ESI-MS, single crystal XRD, and cyclic voltammetry of a new mononuclear ruthenium complex, [Ru(H2dimpy)(bpy)OH2](PF6)2, bearing dissociable protons. Upon deprotonation at pH > 9, the RuIII/RuII redox couples are largely shifted to lower potentials. Cyclic voltammetry at pH = 13 showed that the complex displays catalytic current towards water oxidation at low overpotential (1.0 V), being a potential molecule to be used as a catalyst for water oxidation. Figure 1 shows CV’s measurements in both acid and basic media. Even in acid conditions, when the imidazole moieties are protonated, the complex shows a lower RuIII/RuII redox couple (0.61 V) when compared to analogous [Ru(tpy)(bpy)OH2](PF6)2 in pH = 1 (0.81 V)1.