Bifunctional and regenerable molecular electrode for water electrolysis at neutral pH

The instability of molecular electrodes under oxidative/reductive conditions and insufficient understanding of the metal oxide-based systems have slowed down the progress of H-2-based fuels. Efficient regeneration of the electrode's performance after prolonged use is another bottleneck of this research. This work represents the first example of a bifunctional and electrochemically regenerable molecular electrode which can be used for the unperturbed production of H-2 from water. Pyridyl linkers with flexible arms (-CH2-CH2-) on modified fluorine-doped carbon cloth (FCC) were used to anchor a highly active ruthenium electrocatalyst [Ru-II(mcbp)(H2O)(2)] (1) [mcbp(2-) = 2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine]. The pyridine unit of the linker replaces one of the water molecules of 1, which resulted in RuPFCC (ruthenium electrocatalyst anchored on -CH2-CH2-pyridine modified FCC), a high-performing electrode for oxygen evolution reaction [OER, overpotential of similar to 215 mV] as well as hydrogen evolution reaction (HER, overpotential of similar to 330 mV) at pH 7. A current density of similar to 8 mA cm(-2) at 2.06 V (vs. RHE) and similar to-6 mA cm(-2) at -0.84 V (vs. RHE) with only 0.04 wt% loading of ruthenium was obtained. OER turnover of >7.4 x 10(3) at 1.81 V in 48 h and HER turnover of >3.6 x 10(3) at -0.79 V in 3 h were calculated. The activity of the OER anode after 48 h use could be electrochemically regenerated to similar to 98% of its original activity while it serves as a HE cathode (evolving hydrogen) for 8 h. This electrode design can also be used for developing ultra-stable molecular electrodes with exciting electrochemical regeneration features, for other proton-dependent electrochemical processes.