Ultrafine VN nanodots induced generation of abundant cobalt single-atom active sites on nitrogen-doped carbon nanotube for efficient hydrogen evolution

Development of highly active and stable non-noble electrocatalysts with well-defined nanostructures is crucial for efficient hydrogen evolution reaction(HER). Herein, a novel three-dimensional(3D) selfsupported electrode consists of vanadium nitride(VN) nanodots and Co nanoparticles co-embedded and highly active single Co atoms anchored in N-doped carbon nanotubes supported on carbon cloth(VN-Co@CoSAs-NCNTs/CC) is fabricated via a one-step in situ nanoconfined pyrolysis strategy, which shows remarkable enhanced HER electrocatalytic activity in acidic medium. During pyrolysis, the formed VN nanodots induce the generation of atomic Co Nxsites in NCNTs, contributing to superior electrocatalytic activity. Experimental and density functional theory(DFT) calculation results reveal that the electrode has multiple accessible active sites, fast reaction kinetics, low charge/mass transfer resistances,high conductivity, as well as downshifted d-band center with a thermodynamically favorable hydrogen adsorption free energy(△G_(H·)), all of which greatly boost the HER performance. As a result, the VNCo@CoSAs-NCNTs/CC electrode displays superb catalytic performance toward HER with a low overpotential of 29 mV at 10 mA cm^(-2) in acidic medium, which could maintain for at least 60 h of stable performance. This work opens a facile avenue to explore low-cost, high performance, but inexpensive metals/nitrogen-doped carbon composite electrocatalysts for HER.

Cobalt atoms dispersed on hierarchical carbon nitride support as the cathode electrocatalyst for high-performance lithium-polysulfide batteries

Lithium-sulfur batteries are promising candidates for next-generation energy storage but are confronted with several challenges. One of the possible solutions is to design proper cathode electrocatalysts to accelerate the redox interconversion of solvated polysulfide intermediates. Herein, we report cobalt atoms dispersed on hierarchical carbon nitride support as an effective cathode electrocatalyst for lithium-polysulfide batteries. The electrocatalyst material is prepared from the simple reaction between melamine and cyanuric acid in the presence of Co^2+, followed by the Ar annealing. The product has a unique hierarchical structure consisting of many thin and porous C3 N4 nanosheets finely dispersed with Co atoms. The atomic dispersion of Co species is confirmed by X-ray absorption experiments.Electrochemical measurements reveal that it can promote the interconversion of polysulfides. As a result,batteries using this cathode electrocatalyst achieve large capacity($1400 mAh/g at 1.6 mA/cm^2), good rate performance($800 mAh/g at 12.8 mA/cm^2) and impressive cycling stability under different current densities and different sulfur loadings.