Synthesis of diverse stable MOFs and their electro catalytic capabilities towards desulfurization, water splitting and various nitrophenol reduction reactions

Abstract

Metal–organic frameworks are a novel class of crystalline porous materials with enormous application potential, consisting of metal nodes and organic linkers. Because of their adjustable porosity, significant surface area and adaptability to various ligands and metal centers for functionalization, MOFs are considered to be highly promising electrocatalytic materials in different fields. This work explains the simple synthesis of carbonized MOFs (Al, Ni and Co–C MOFs) by a hydrothermal method, and their characterization for functional moieties and morphological structures by different surface analytical methods, followed by exploring them as model catalysts for water splitting, electrooxidation of thiophene (TP), benzothiophene (BT) and dibenzothiophene (DBT) and reduction of p-nitrophenol (p-NP), 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP). Co–C MOF shows the lowest onset potential of 1.54, 1.52 and 1.55 V with a lower Tafel slope value of 69, 126 and 126 mV dec⁻¹ with a charge transfer resistance value (R_ct) of 4238, 4864 and 6327 Ω for the electrooxidation of TP, BT and DBT, respectively. Interestingly, the synthesized Ni–C MOF exhibits the best hydrogen evolution reaction (HER) activity when compared to Al and Co–C MOFs, bearing the lowest value of overpotential (225 mV), Tafel slope (114 mV dec⁻¹) and charge transfer resistance (130 Ω). Furthermore, the synthesized Co–C MOF also provides the best oxygen evolution reaction (OER) activity and displays the lowermost overpotential, Tafel slope and charge transfer resistance values of 220 mV, 169 mV dec⁻¹ and 149 Ω, respectively. In addition, all three nitro compounds were totally reduced by synthesized Ni–C MOF, providing excellent performance with minimum reduction time. The outstanding activity of the synthesized Co and Ni–C MOFs towards desulfurisation and OER activity as well as the HER and nitrophenol reduction, respectively, is associated with high electrochemical active surface area (ECSA) and enlarged pore volume leading to innumerable active sites, resulting in enhanced performance.