Investigation On The Modification And Hydrogen Evolution Performance Of Three-Dimensional Carbon Matrix Composites

Electrocatalytic hydrogen evolution is the main way to utilize hydrogen energy,so the development of high-efficiency electrocatalysts has become a research hotspot.In this paper,a series of novel carbon-based composite catalysts were prepared by using melamine foam as the support material and MoS₂ as the main catalyst.The melamine foam was carbonized at 600°C,700°C and 800°C under argon atmosphere,respectively.The carbonized foam still maintains the original three-dimensional network and has good hydrophilicity?Solid-Liquid contact angle?is less than 90o?.At the same time,the graphitization of the carbonized foam gradually decreases with the rise of the carbonization temperature.The BET test showed that the foam carbonized at 800°C had the largest specific surface area of 252.36 m² g^-1.After compounding MoS₂,only CM-800 can maintain its original shape under hydrothermal treatment,while the other two groups are collapsed into debris.Electrochemical test results show that the performance of the composite with 800°C carbonized foam is the best,and the overpotential at the current density of 10 mA cm^-2 is the lowest among all examples.Regulating precursor concentration for hydrothermal compounding with carbonized foam CM-800 as the carrier,the MoS₂ sheet could be uniformly attached to the carbon-based skeleton,and the thickness of the sheet was measured about 15-20 nm.It can be seen from the microscopic morphology that the stacked pattern of the MoS₂ sheet gradually changes from a spherical cluster at low concentrations to a vertically compact arrangement under high concentration conditions.The results of electrochemical hydrogen evolution characterization and impedance spectroscopy showed that the performance of CMMS-800 synthesized at high concentration was the best(the overpotential at 10 mA cm^-2 was 218 mV),mainly because the vertical alignment of the sheets exposing more active sites,while the carbon-based backbone provides a fast migration channel for carriers.Carbonized melamine foam/graphene/MoS₂ composites have little difference in microscopic morphology compared to no graphene-coated samples,and all of the dense sheets are arranged vertically on the carbon-based skeleton.The incorporation of graphene further affects the crystal growth of the catalyst.It can be seen from the unit cell parameters that under relative low and high concentration coating conditions,the unit cell of MoS₂ will grow abnormally,and when the coating concentration is 25 mg/L,the unit cell of MoS₂ is the smallest.and then the packing factor?PF?model was introduced to analyze the issue.It is found that the decrease of the crystal cell volume directly leads to the increase of?002?crystal plane lamella under the same volume condition,causing the sheets to squeeze each other to expose more?100?crystal facets.At the same time,the electrochemical performance of R&CMMS-25 is also optimal under this condition,the overpotential at 10 mA cm^-2 is 167 mV and the Tafel slope is reduced to 76 mV/dec compared to samples without coating graphene.The hydrogen evolution performance of composite material has been greatly improved.Similarly,the characterization of the electron transport efficiency of the material was indirectly characterized by impedance spectroscopy,R&CMMS-25 has the lowest impedance value,which is sufficient to demonstrate that coating the appropriate amount of reduced graphene oxide can accelerate the electron migration efficiency and further enhance the hydrogen evolution performance.