Polyoxometalate‐Derived Hexagonal Molybdenum Nitrides (MXenes) Supported by Boron, Nitrogen Codoped Carbon Nanotubes for Efficient Electrochemical Hydrogen Evolution from Seawater

MXenes and doped carbon nanotubes (CNTs) have entered into research arenas for high‐rate energy storage and conversion. Herein, a method of postsynthesis of MXenes in boron, nitrogen codoped CNTs (BNCNTs) is reported with their electrocatalytical hydrogen evolution performance. The encapsulation of hexagonal molybdenum nitrate nanoparticles (h‐MoN NPs) into BNCNTs protects h‐MoN NPs from agglomeration and poisoning in the complex environment. In principle, the synergism of B and N dopants on the doped CNTs and confined h‐MoN NPs produces extremely active sites for electrochemical hydrogen evolution. Density functional theory calculations reveal that the active sites for hydrogen evolution originate from the synergistic effect of h‐MoN(001)/CN (graphitic N doping) and h‐MoN(001)/BNC. The h‐MoN@BNCNT electrocatalyst exhibits a small overpotential of 78 mV at 10 mA cm−2 and Tafel slope of 46 mV per decade, which are dramatically improved over all reported MoN‐based materials and doped CNTs. Additionally, it also exhibits outstanding electrochemical stability in environments with various pH values and seawater media from South China Sea. Nanoflakes of hexagonal molybdenum nitrate are synthesized in the matrix of boron, nitrogen codoped carbon nanotubes with efficient electrocatalytic hydrogen evolution performance in acidic, neutral, and alkaline solutions. Electrolysis of seawater can also be operated by using as‐obtained catalysts because doped carbon nanotubes can protect hexagonal molybdenum nitrate from agglomeration and poisoning in the complex environment.