Covalent Molecular Anchoring of Metal-Free Porphyrin on Graphitic Surfaces toward Improved Electrocatalytic Activities in Acidic Medium

Abstract

Robust engineering of two-dimensional (2D) materials via covalent grafting of organic molecules has been a great strategy for permanently tuningtheir physicochemical behaviors toward electrochemical energy applications. Herein, we demonstrated that a covalent functionalization approach of graphitic surfaces including graphene by a graftable porphyrin (g-Por) derivative, abbreviated as g-Por/HOPG or g-Por/G, is realizable. The efficiency of this approach is determined at both the molecular and global scales by using a state-of-the-art toolbox including cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). Consequently, g-Por molecules were proven to covalently graft on graphitic surfaces via C-C bonds, resulting in the formation of a robust novel hybrid 2D material visualized by AFM and STM imaging. Interestingly, the resulting robust molecular material was elucidated as a novel bifunctional catalyst for both the oxygen evolution (OER) and the hydrogen evolution reactions (HER) in acidic medium with highly catalytic stability and examined at the molecular level. These findings contribute to an in-depth understanding at the molecular level ofthe contribution of the synergetic effects of molecular structures toward the water-splitting process.