Unveiling the Favorable Synergy of ZIF-9 and Borocarbonitride on rGO as a Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution Reactions in Alkaline Media

Abstract

Exploitation of the reaction of hydrogen with oxygen as an energy source requires energy storage and conversion devices, such as metal-air batteries and fuel cells, which, in turn, require the development of low-cost materials with high electrocatalytic performance for hydrogen/oxygen evolution reactions (HER/OER).o develop highly efficient, bifunctional HER/OER electrocatalysts, the imidazole-substituted benzimidazole precursor 3 was used to synthesize a cobalt(II)-MOF (ZIF-9). Synthesized ZIF-9 was used as a sacrificial precursor, where the pyrolysis temperature and Co doping of the benzimidazole framework were tuned. Composites of ZIF-9 with boron carbon nitride (BCN) and graphene oxide (rGO) on carbon cloth (CC), denoted as ZIF-9 + BCN + rGO/CC, were prepared by varying the amounts of BCN and rGO in a ratio of 1:1, respectively, immobilized on the electrode surfaces. The nanocomposite catalysts were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis, Brunauer-Emmett-Teller analysis, and Raman spectroscopy. The efficacy of the composite electrocatalysts as the working electrode for electrochemical water electrolysis via hydrogen and oxygen evolution reactions was evaluated by using spectroscopic and analytical techniques. The composite catalyst ZIF-9 + BCN + rGO/CC exhibited impressive performance, indicated by the overpotential, onset potential, and Tafel values in 1 M KOH electrolyte at a scan rate of 5 mV and overpotential of 10 mA cm^-2. ZIF-9 + BCN + rGO/CC afforded η₁₀ values of less than -222 mV (HER) and 374 mV (OER). The Tafel values were 39 mV/dec (HER) and 73 mV/dec (OER). The ZIF-9 + BCN + rGO/CC catalyst showed remarkable stability for approximately 50 h and was durable in basic media for both the hydrogen and oxygen evolution reactions. ZIF-9 + BCN + rGO/CC as a cathode and anode catalyst exhibited excellent performance in terms of overall electrocatalysis, superior to that of state-of-the-art catalysts.