Environmentally Benign Synthesis of Copper Benzenetricarboxylic Acid MOF as an Electrocatalyst for Overall Water Splitting and CO2 Reduction

Abstract

As a class of porous coordination polymers, metal organic frameworks (MOFs) have potential applications in many fields. In this work, a novel synthetic method, without using toxic solvents, has been developed to prepare HKUST-1 MOF nanoparticles from coprecipitation reaction of copper (II) chloride and 1,3,5-benzenetricarboxylic acid (trimesic acid) in distilled water. The synthesized nanoparticles were first characterized by X–ray diffraction (XRD), Fourier–transform infrared spectroscopy (FT–IR), and scanning electron microscopy (SEM). The flat–band potential, conduction band, and valence band edges of HKUST-1 nanoparticles were experimentally determined in alkaline solution, and UV–Vis diffuse reflectance spectra (DRS) analysis showed the band gap energy to be 2.5 eV. Electrochemical working electrodes were prepared by electrophoretic deposition of HKUST-1 on the surface of a stainless steel electrode for electrochemical voltammetry and impedance measurements. For the first time the prepared HKUST-1 nanoparticles were investigated as multifunctional electrocatalysts for both overall water splitting and CO2 reduction in alkaline solution. The Tafel plot was used to show the relationship between the over–potential (η) and the logarithmic current density, revealing the kinetic parameters of the electrochemical reactions. Furthermore, the Tafel slope was determined to be 190 mVdec−1, indicating that the Volmer mechanism with electrochemical desorption of hydrogen acts as the rate–determining step (RDS).