One pot synthesis and characterization of binary and ternary metal organic frameworks (MOFs) as tri-modal catalysts for thiophene electrooxidation, water splitting and 4-nitrophenol reduction

Abstract

Because of their large specific surface area, high porosity, changeable pore size, and ordered pore arrangement, metal–organic frameworks (MOFs) are emerging as electrocatalysts in various fields of energy resources and bio-sensors. In this work, we report a one-pot synthesis of trimetallic MOFs (Co–Ni–Al-MOFs), as well as bimetallic MOFs (Co–Ni-MOFs, Co–Al-MOFs, and Ni–Al-MOFs) using Co, Ni, and Al metal salts and BTC and 4,4′-bipyridine as linkers, their characterization for surface morphology, functional group and elemental analysis using various analytical techniques and explored them as tri-modal catalysts for thiophene electrooxidation, water splitting and chemical reduction of 4-nitrophenol (4-NP). Electrochemical studies using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) on Co–Ni–Al-MOFs showed the lowest onset potential of 1.36 V with a lower Tafel slope of 181 mV dec⁻¹ and charge transfer resistance value (R_ct) of 447 Ω for the effective electrooxidation of thiophene. Further catalytic activity studies towards water splitting revealed that Co–Ni–Al-MOFs displayed superior catalytic activity towards the HER and the OER at lower overpotentials of 174 and 220 mV with Tafel slopes of 108 and 97 mV dec⁻¹ respectively, compared to other bimetallic MOFs with excellent long-term stability, as revealed by chronoamperometry (CA). The high catalytic activity of Co–Ni–Al-MOFs may be associated with their larger surface area and higher pore volume than those of the other bi-metallic MOFs, as studied by BET analysis, leading to innumerable redox-active sites towards electrochemical processes. Moreover, the catalytic activity of the as prepared catalysts was assessed towards the reduction of 4-NP to 4-aminophenol (4-AP), where Co–Ni–Al-MOFs exhibited exceptional activity with a minimum reduction time of 8 min bearing a high rate constant value.