Preparation And Properties Of Metal Phosphide And Biomass-Based Porous Carbon Composites

With the development of world economy,energy shortage and ecological crisis have become increasingly serious.There is a high demand for the development of green,renewable and efficient energy conversion methods as well as new energy storage materials.Porous carbon materials have gained important applications in fields of energy storage and electrochemistry due to their high specific surface area,excellent thermal stability and high electrical conductivity.Biomass-based heteroatom-doped porous carbon materials were prepared by using biomass or its derivatives as carbon source,nitrogen source,phosphorus source,and using freeze-drying,high-temperature carbonization/activation process.Metal phosphide/biomass-based heteroatom-doped porous carbon composites were prepared by adding metal salts to the synthesized biomass-based heteroatom-doped porous carbon materials.The supercapacitor performance and electrocatalytic performance of the prepared composites were investigated.The followings are the results of the study:?1?The content of phytic acid and the carbonization temperature have a great influence on the specific surface area and pore volume of the porous carbon.When the mass ratio of phytic acid and chitin is 3:1 at carbonization temperature of 900?,the maximum of specific surface area and pore volume of the material are 1626 cm² g^-1 and0.91 cm³ g^-1,respectively.The surface morphology and structural characteristics of nitrogen-phosphorus co-doped porous carbon materials were characterized by SEM,TEM,XRD,BET.The results show that the nitrogen-phosphorus co-doped porous carbon materials have high specific surface area and abundant micro/mesoporous pores.In the electrochemical performance test,at a sweep rate of 2 mV/s the capacitance is 157 mAh g^-1,and the capacitance is still 128 mAh g^-1 even at a high sweep speed of 5 mVs^-1.?2?The metal salt ammonium heptamolybdate was added in the process of synthesizing biomass-based heteroatoms doped porous carbon materials,and carbonizing to form molybdenum phosphide after high temperature carbonization to obtain molybdenum phosphide and biomass-based heteroatom-doped porous carbon composites?NPPC?MoP?.Nitrogen adsorption and desorption tests show that the material still has a high specific surface area(1200 cm² g^-1)and pore volume(0.67 cm³ g^-1).XPS and EDS test results show that N and P are successfully doped into porous materials.The HER activity of NPPC?MoP was tested in acidic or alkaline electrolytes.The results show that NPPC?MoP materials exhibit high catalytic activity for hydrogen evolution in acidic or alkaline media.At current density of 10 mA cm^-2 the overpotential are 121 mV and 219mV,respectively.Cyclic stability test show that NPPC?MoP still maintains efficient hydrogen evolution catalytic activity after 12 hours of circulation.?3?The metal phosphide alloy of phosphide-iron-cobalt and biomass-based heteroatom-doped porous carbon composite?NPPC?FeCoP?was synthesized by the same method as?2?.The XRD test results show that the metal phosphide alloy is successfully synthesized.The catalytic performance of HER in acidic medium shows that the catalytic performance of NPPC?FeCoP?114 mV?material is better than that of its corresponding single metal phosphide NPPC?CoP?143 mV?and NPPC?FeP?218 mV?,at current density of 10 mA cm^-2.It is proved that cobalt doping in NPPC?CoP material or cobalt doping in NPPC?FeP plays a synergistic role in HER performance.Cyclic stability tests is carry out on NPPC?FeCoP,the results show that NPPC?FeCoP maintains efficient hydrogen evolution catalytic activity after 12 hours of circulation.