Preparation and electrochemical properties of Fe3 O4 / ammonium⁃humate based carbon composites

The preparation of Fe3 O4 / carbon composites can not only effectively solve the problems of the agglomeration and poor electrical conductivity of Fe3O4particles，but also take advantage of the high capacity of Fe3O4，and provide some excellent electrochemical properties. In this study， the Fe3 O4 / ammonium⁃humate based carbon composites (Fe3O4 /SHAC⁃X)were prepared by hydrothermal⁃carbonization process using coal⁃based ammonium humate and fer⁃ ric chloride as raw materials. Scanning electron microscopy(SEM)，transmission electron microscopy(TEM)，X⁃ ray diffraction(XRD)，nitrogen adsorption/desorption and X⁃ray photoelectron spectroscopy(XPS)were used to characterize the morphology，pore structure and surface chemistry of the samples. The electrochemical properties of the cor⁃ responding supercapacitor electrode materials were evaluated by constant current charge⁃discharge，cyclic voltammetry and alternating⁃current impedance measurements. The results show that the pore structure of Fe3 O4 / SHAC⁃X main⁃ ly consists of mesopores，the mesopore volume and average pore size increase gradually with the increase of the dosage of FeCl3·6H2O，which are also closely related to the mass loading and distribution characteristics of Fe3O4 particles. The Fe3 O4 / SHAC⁃3 has the highest Fe content among three samples，and the Fe3 O4 particles exhibit good dispersivity with uniform particle size. The corresponding electrode material has obvious pseudocapacitance effect in the 3 mol / L KOH electrolyte，showing a small electrochemical impedance and high volumetric capacitance of 253 F / cm3 at the cur⁃ rent density of 42.5 mA/g based on its high forming density(1.48 g/cm3). Moreover，the Fe3O4 /SHAC⁃2 displays a better rate performance，delivering a high capacitance retention of 73.1% with the current density increasing from 42.5 to 4 250 mA / g. The specific capacitance can still maintain 88.3% after 10 000 cycles at 2 125 mA / g，indicating a superior cycle performance. This work is conducive to promote the clean and efficient utilization of coal based humic acid，and also has reference significance for the research and application of the Fe3 O4 / carbon composites.