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

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 omega 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.