A 2D Co-MOF nanosheet for boosting the alkaline water splitting through electrocatalytic urea oxidation

Abstract

Alkaline hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) is gaining considerable interest for boosting the overall water splitting in the context of green hydrogen production with simultaneous deurefication from wastewater. In this work, we have successfully synthesized a novel cobalt based two dimensional (2D) metal–organic framework (MOF), (named as Co-IDBA-MOF) by solvothermal method using mixed ligand system consisting of 2,2′-iminodibenzoic acid (IDBA) and 4,4′-bipyridine (Bpy). The single crystal X-ray analysis of Co-IDBA-MOF confirms its layered 2D structure. The bulk specimen of MOF was further characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric (TG) analysis, UV-Visible spectroscopic analysis. Field emission scanning electron microscopic (FE-SEM), field emission gun transmission electron microscopic (FEG-TEM) and atomic force microscopic (AFM) analyses uncovered its ultrathin 2D nanosheet-type morphology, which facilitates the fabrication of 2D material for potential fabrication of real device. This Co-IDBA-MOF shows a good performance in alkaline HER at -0.241 V w.r.t RHE for 10 mA cm-2 current density (ȵ10) and a modest oxygen evolution reaction (OER) activity (1.66 V for 10 mA cm-2 w.r.t RHE) in alkaline water medium. However, the anodic potential gets drastically reduced to 1.55 V after 0.33 (M) of urea addition due to urea oxidation reaction (UOR). Further modification over the Ni-foam (NF) reduced this potential to 1.59 V in the case of UOR. The lowering of Tafel slope and a concomitant increase of double layer capacitance for alkaline hydrogen evolution reaction (HER) and concomitant urea oxidation reaction (UOR) suggested the better kinetics for overall water splitting after urea addition. Further variation of urea concentration and the concentration of electrode material tunes the UOR activity. This work aims to design a novel Co-MOF based electrode material for bifunctinal activity and large-scale green hydrogen production via UOR.