Phytic acid-guided ultra-thin N,P co-doped carbon coated carbon nanotubes for efficient all-pH electrocatalytic hydrogen evolution

Abstract

Nanostructure engineering of heteroatom-doped carbon catalysts can greatly enhance their electrocatalytic activity by increasing the accessible active sites and beneficial physical properties (e.g., surface area, conductivity, etc.). Herein, we successfully constructed ultra-thin N,P co-doped carbon (NPC) on the surface of multi-walled carbon nanotubes (CNT) by using phytic acid (PA) as a “guide”. The rich phosphate groups in PA allow them to be covalently modified on the surface of CNT by the condensation reaction and to further attract large aniline monomers through acid–base interactions, resulting in the uniform and tight bonding between polyaniline and CNT after the polymerization process. During the subsequent thermal reaction, PA also serves as a self-sacrificial dopant for the formation of ultra-thin NPC and the doping amount of P in NPC can be easily adjusted by changing the amount of PA. Due to the abundance of active sites, large electrochemically active surface area and rapid electron transfer, the developed CNT@NPC presents remarkable electrocatalytic activities for the hydrogen evolution reaction (HER) with an overpotential of 167, 440 and 304 mV to reach a current density of 10 mA cm⁻² in acidic, neutral, and alkaline electrolytes, respectively. In particular, its acidic HER activity exceeds that of most reported metal-free electrocatalysts and is comparable to that of some excellent transition metal-based catalysts. The approach proposed here is of potential importance for the preparation of ideal heteroatom-doped carbon/nanocarbon composites for use in a variety of future energy conversion systems.