Development of Metal Organic Framework Based Nanomaterials for Electrocatalytic Applications

Abstract

This research work emphasizes the development of novel and cost-effective transition metalbased anode electrocatalysts composites with rGO and CNTs. The material was studied for their application in oxygen evolution reaction (OER), and methanol oxidation reaction (MOR) which are the core electrochemical reactions of a fuel cell. Economical and abundant transition metal-based MOFs and MOFs/Carbon-Based composites are potential candidates as electrode materials for electrochemical reactions in an alkaline medium. The sonicationassisted solvothermal approach was employed for materials fabrication while characterization was performed by FTIR, XRD, SEM, EDX, BET, Elemental Mapping, XPS, and Raman Spectroscopy. The first part of this thesis describes the electrocatalytic activities of low-cost Ni-BTC MOF/1-5 wt % rGO composites (0.85 mg cm-2) for MOR in an alkaline medium. The electrocatalytic behavior was systematically studied by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), Tafel slope, and Chronoamperometry while product analysis was performed by Nuclear Magnetic Resonance (NMR) Spectroscopy and Gas Chromatography (GC). The Ni-BTC/4 wt % rGO composite with four times less loaded amount than the state-of-the-art Pt metal delivers a current density of 200 mA/cm2 at a peak potential of 1.65 V vs. RHE. It also possesses a low Tafel slope (33.3 mV/dec), minimal resistance (16.79 Ohm) along with an affinity to retain 83 % of the original current density for 3600 seconds during stability test. However, the response of the same samples towards OER was not satisfactory giving considerably low current density at the same potential. In the second phase of this work, Co BTC MOF and its rGO composites were studied for MOR and OER in an alkaline medium. In the case of MOR, among the synthesized samples, 1 wt % rGO/Co BTC composite (1.07 mg cm-2) parade promising current density of 130 mA cm-2 at 1.65 V vs. RHE, Tafel slope 83.6 mV dec-1, the resistance of 14.75 Ω, good stability for 3600 seconds in chronoamperometry and minor change in current response after 1000 cycles in cyclic stability test (CV) in 1M NaOH/2 M methanol solution. On the other hand, for the OER process, Co BTC MOF-rGO composites were tested in 1 M KOH solution. Among the tested samples, Co BTC-5 wt % rGO composite electrocatalytic response was comparable to other cobalt-based systems as 10 mA cm-2 current density was generated at Vonset 1.45 V and overpotential (η) 0.29 V vs. RHE. The observed Tafel slope, resistance, Turn Over Frequency (TOF), Mass Activity (MA) were 71.41 mV/dec, 18.02 Ω, 1.07 s-1, and 58.9 mA/mg, respectively along with long term stability for 3600 seconds. In the third part of this study, FeNiNH2BDC MOF and its 2-6 wt % CNTs composites were tested for the OER in a 1 M KOH solution. Among the synthesized samples, FeNiNH2BDC-5 wt % CNTs composite display excellent performance as 10 mA cm-2 current density was delivered at overpotential of 0.22 V vs. RHE for OER. Moreover, minimum Tafel slope (68.50 mV/dec), high TOF (0.67 s-1), inferior resistance (20.72 Ω), huge Electrochemically Active Surface Area (EASA) 1500 cm2 and 56 % retention of current density after 3600 seconds are the salient features of 5 wt % CNTs composite and prove it to be an appropriate alternative for noble metal-based electrocatalyst for OER.