Crystalline NiFex nanoparticles homogeneously embedded in ordered mesoporous carbon for improved electrochemical hydrogen storage performance

Abstract

Hybrids of bimetallic NiFex crystalline nanoparticles homogeneously embedded in ordered mesoporous carbon (OMC) for electrochemical hydrogen storage applications were fabricated through wet impregnation and H2 reduction techniques. The size and distribution of NiFex nanoparticles of NiFex/OMC hybrids can be tuned by controlling the molar ratio of Ni : Fe, with the smallest diameter of 4.7 nm for the NiFe2 alloy nanoparticles. The effects of NiFex nanoparticle incorporation into the OMC matrix on the surface area, pore volume, pore size and electrochemical hydrogen storage performances were comparatively investigated using adsorption isotherms of nitrogen, electrochemical impedance spectroscopy, potentiodynamic polarization, cyclic voltammetry and galvanostatic charge–discharge techniques. With the molar ratio of Ni : Fe decreasing, the discharge capacity and the cycle performance of the NiFex/OMC hybrids display a notable improvement due to the homogenous dispersion of NiFex nanoparticles, higher surface area, larger mesopore volume, lower defect ration, and smaller charge-transfer resistance. The NiFe2/OMC samples display greatly improved electrochemical hydrogen storage discharge capacity of 418 mA h g−1, which is about four times as high as that of the pure OMC electrode.