Metal-organic framework derived core-shell nanoparticles as high performance bifunctional electrocatalysts for HER and OER

Abstract

Development of an affordable, stable, and efficient electrocatalyst using nonprecious material to generate green H2 and O2 is still a challenging research problem. This research demonstrates the development of an efficient bifunctional electrocatalyst for HER as well as OER. Self-sacrificial nickel-based MOF acted as a precursor in facile pyrolysis carried out at 600, 700, and 800 °C temperatures to yield three bifunctional electrocatalysts viz Ni@NCS-600, Ni@NCS-700, and Ni@NCS-800, respectively. A blend of metallic Ni-nanoparticles and heteroatoms (N, S, & O) doped graphitic matrix has shown a synergistic effect for efficient electrocatalysis. The facile transformation of Ni-MOF into core-shell structure imparts stability to metal electrocatalyst by preventing direct exposure to the electrolytes during water splitting. After systematic characterization by various analytical techniques, their electrocatalytic performances were evaluated for OER and HER in alkaline and acidic medium, respectively. Bifunctional electrocatalytic activity of Ni@NCS-800 was found to be highly efficient, and comparable to precious state-of-the-art catalysts (RuO2 and Pt/C). Ni@NCS-800 exhibits extremely low overpotential, which needs only 330 mV and 366 mV to reach 10 mAcm−2 current density in OER and HER, respectively. The Tafel slope has been derived from the EIS also, imparting the alternating current. Thereby, a superior electrokinetic activity of Ni@NCS-800 has been observed, due to the elimination of non-faradaic current, with a Tafel slope of 32 mV/dec. The stability was evaluated by potentiostatic and potentiodynamic techniques. Therefore, this study explores a suitable pathway for the fabrication of simple, nonprecious, stable, yet catalytically efficient material for HER and OER activity.