Alkaline Water Splitting Over RuO₂@phosphomolybednic Acid Encased Multi-Walled Carbon Nanotubes

Rational design of active and stable bifunctional electrocatalysts for the generation of hydrogen and oxygen is crucial for clean and renewable energy. Herein, we developed a robust method for the preparation of electrocatalysts from RuO 2 and phosphomolybdic acid (PMA)-encapsulated multi-walled carbon nanotubes (MWCNT). It involves a low-temperature thermal encapsulation of PMA followed by anchoring of RuO 2 at phosphomolybdic acid sites by ion exchange. RuO 2 @PMA/MWCNTs showed an exceptionally low overpotential of 41 mV for the hydrogen evolution reaction (HER) with a Tafel slope of 71 mV d −1 ec −1 in an alkaline medium. Thermal sintering of RuO 2 @PMA/MWCNTs resulted in rutile T-RuO 2 @PMA/MWCNTs. It showed an overpotential of 320 mV for the oxygen evolution reaction (OER) with an 81 mV/dec Tafel slope in 1 M KOH solution. In continuous operation for 24 h, the electrocatalyst exhibited good stability for HER and OER. The electrocatalytic activity was supported by density functional theory (DFT) simulations. The electronic state near the Fermi level exhibits the metallic character of the RuO 2 @PMA/MWCNTs system, supporting charge transfer from the PMA/MWCNTs to RuO 2 . The qualitative magnitude of the simulated overpotential for the HER and OER matching the experimental data suggests that the combined effect of RuO 2 and PMA on the MWCNTs host offers efficient water splitting activity.