Amine-functionalized multi-walled carbon nanotubes (EDA-MWCNTs) for electrochemical water splitting reactions

Abstract

Herein, this study presents the highly efficient and inexpensive metal-free multifunctional electrocatalyst demonstrated for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) effectively for all pH. This current study also presents the in situ decoration of ethylenediamine (EDA) on acid-functionalized multi-walled carbon nanotubes (O-MWCNTs). Moreover, an ethylene diamine is known to form a stable nitrogen source to make nitrogen rich MWCNTs as a metal-free electrocatalytic system. Those as-synthesised nanomaterials were characterised via scanning electron microscopy (SEM), high resolution-transmission electron microscopy (HRTEM), Fourier-transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) surface area analysis, which suggested the presence of N-containing active sites/defects in the lattice of the nanotubes. It is of great interest to the scientific community and still an impressive challenge; H₂ is a perfect candidate for the replacement of fossil fuels in the upcoming era due to the zero emission of carbon dioxide (CO₂) species during its combustion. O-MWCNTs and EDA-MWCNTs nanomaterials exhibit OER with ultra-small overpotentials of 0.27 V and 0.19 V at 10 mA cm⁻², respectively, having lower Tafel slopes of 49 and 40 mV dec⁻¹, respectively, in 0.5 M KOH. Moreover, the HER exhibits lower Tafel slopes of O-MWCNTs and EDA-MWCNTs 90 and 75 mV dec⁻¹, respectively, in 0.5 M H₂SO₄. These efforts further demonstrate the high potential of the as-synthesized nanocatalyst towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This metal-free electrocatalyst offers a novel, efficient, highly stable, environmentally friendly and inexpensive process for its fabrication. The catalytic activity exhibits that the ethylene diamine decorated on a multi-walled carbon nanotube EDA-MWCNTs composite could be an encouraging electrocatalyst towards HER and OER from their supportive interfaces.