Regenerable and Bifunctional Electrode for Hydrogen Production from Water at Neutral Ph

Abstract

The instability of the molecular electrodes under oxidative/reductive conditions and insufficient understanding of the metal oxide-based systems have slowed down the progress of H2-based fuels. Efficient regeneration of the electrode’s performance after prolonged use is another unavoidable bottle-neck of this research. This study presents the development of an efficient, and reusable electrode suitable for use as both anode and cathode in electrochemical cells for H2 production. Pyridyl units with flexible arms (-CH2-CH2-) were used to anchor a highly active ruthenium electrocatalyst [RuII(mcbp)(H2O)2] (1) [mcbp2− = 2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine] onto fluorine-doped carbon cloth. This resulted in RuPFCC, a high-performing electrode for oxygen evolution [OE, overpotential of   ̴ 215 mV] as well as hydrogen evolution reaction (HER, overpotential of  ̴ 330 mV) at pH 7. Current density of   ̴ 8 mA/cm2 at 1.65 V (vs NHE) and   ̴ -6 mA/cm2 at -1.25 V (vs NHE) with only 0.04 w% loading of ruthenium was obtained. OER turnover of > 7.4 × 103 at 1.4 V in 48 h and HER turnover of > 3.6 × 103 at -1.2 V in 3 h were calculated. The activity of the OE anode after 48 h use could be electrochemically regenerated to  ̴ 98% of its original activity while using it as a HE cathode (i.e., while evolving hydrogen) for 6 h. This work provides efficient strategies for developing ultra-stable molecular electrodes with exciting electrochemical regeneration, that can be used in electrochemical cells.

Keywords: hydrogen, oxygen, Molecular electrode, Regenerable, Dual function, water