Tailoring the d-band center of N-doped carbon nanotube arrays with Co4N nanoparticles and single-atom Co for a superior hydrogen evolution reaction

Abstract

A 3D self-supported integrated electrode, consisting of heteroatomic nitrogen-doped carbon nanotube arrays on carbon cloth with confined ultrafine Co₄N nanoparticles and a distribution of anchored single-atom Co, is fabricated via a cobalt-catalyzed growth strategy using dicyandiamide as the nitrogen and carbon source and a layered cobalt hydroxide-nitrate salt as the precursor. The abundance of exposed active sites, namely, the Co₄N nanoparticles, single-atom Co, and heteroatomic N-doped carbon nanotubes, and multiple synergistic effects among these components provide suitable tailoring of the d-band center for facilitating vectorial electron transfer and efficient electrocatalysis. Benefiting from the merits of its structural features and electronic configuration, the prepared electrode exhibits robust performance toward the hydrogen evolution reaction with overpotentials of only 78 and 86 mV at 10 mA cm⁻² in acidic and basic electrolytes, respectively. Density functional theory calculations and X-ray photoelectron spectroscopy valence band measurements reveal that the effective tailoring of the d-band center by Co₄N nanoparticles plays a crucial role in optimizing the hydrogen adsorption free energy to a more thermoneutral value for efficient electrocatalysis.

Catalysis: A green route to water splitting

A carbon-based, environmentally friendly catalyst for enhancing the extraction of hydrogen from water has been synthesized by researchers in China. Separating water into its constituent atoms is a scalable method for producing hydrogen and therefore a source of clean energy. Platinum catalysts can enhance electrochemical splitting, but platinum is rare and expensive. Bo Cao from Inner Mongolia University, Hohhot, and co-workers have developed an alternative carbon nanotube-based catalyst that can be fabricated using a “green” process. Carbon nanotubes have been used previously, often in a powder form, from which it is difficult to make the electrodes required in practical applications. The researchers created three-dimensional electrodes on carbon cloth using arrays of nitrogen-doped carbon nanotubes containing cobalt nitride nanoparticles, and confirmed the excellent electrocatalytic properties of the material.