Robust bifunctional catalytic activities of N-doped carbon aerogel-nickel composites for electrocatalytic hydrogen evolution and hydrogenation of nitrocompounds

Abstract

Nitrogen doped carbonaceous aerogel (NCA) was prepared by a simple hydrothermal treatment of cotton and ovalbumin as a carbon and nitrogen source. Magnetic Ni/NCA composite was prepared by simple chemical reduction method using hydrazine hydrate. The similar method was used in the preparation of various Ni/NCA composites with Ni percentage in the composites ranging from 45% to 75%. The magnetically active Ni/NCA catalysts so-fabricated were characterized by different analytical techniques, viz., X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDS). The as-prepared pure Ni nanoparticles (Ni NPs) and Ni/NCA composites were employed as a prospective electrocatalysts for hydrogen evolution reaction (HER) and reduction of 4-nitrophenol. Various electrochemical parameters of Ni NPs and Ni/NCA electrocatalysts were determined and studied extensively through voltammetric and impedance methods. Electrochemical studies reveal that the prepared Ni/NCA composites show high catalytic performances and good recyclability. Particularly, Ni/NCA-60 exhibited best electro-catalytic activity among the investigated electrocatalysts in alkaline medium. Tafel slopes and constants determined for the investigated electrocatalysts revealed superior electrocatalytic performance of Ni/NCA composites over Ni NPs. From the mechanistic view point, HER likely operates through Volmer-Heyrovsky mechanism with electrochemical hydrogen adsorption as the rate determining step. Furthermore, accelerated durability test (ADT) experiments showed that Ni NPs retained about 75% of the initial activity while Ni/NCA consistently retained about 90% of the initial activity after ADT. The high catalytic activities and good durability of the Ni/NCA materials can be of potential use in the fields of electrocatalysis for hydrogen production and catalytic reduction of organic toxic pollutant. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.