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

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.