Functionalized Carbon Nanotubes for Highly Active and Metal-Free Electrocatalysts in Hydrogen Evolution Reaction

Six kinds of functionalized multiwalled carbon nanotubes (FCNTs) with different functional moieties were utilized as metal-free electrocatalysts towards the hydrogen evolution reaction for the first time. Ethylenediamine-functionalized multiwalled carbon nanotubes (EDA-CNTs) delivered the best HER activity holding a low-onset overpotential of 150 mV, a Tafel slope of 116 mV dec−1, and a Faradaic efficiency (FE) of 94% with a good stability. This HER activity of EDA-CNTs is superior or quite comparable to other reported metal-free HER catalysts, while the preparation of this electrocatalyst is simple, quick, and inexpensive. This good HER performance of EDA-CNTs can be resulted from the high electrical conductivity and its high grafting yield to form more amide groups for enhancement of proton adsorption. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) were successfully used to elucidate the HER process promoted by EDA-CNTs, in which the amide groups were demonstrated to improve the proton adsorption.