Research On Electrochemical Properties Of The Lotus Pollen-derived Porous Carbons And Its Composites

The existence of energy shortage and environmental pollution has caused researchers to pay more attention to the development of electrode materials for energy storage and conversion equipment.Supercapacitors are considered to be a potential energy storage device due to their fast-charging speed,high energy conversion efficiency and long cycle life.Hydrogen production by electrochemical water splitting is an efficient and clean energy conversion method.Biomass carbon materials are widely applied in the preparation of electrode materials because of their high specific surface area,rich pore structure,and good stability.Herein,based on the biomass carbon material,the lotus pollen carbon-based supercapacitor and its molybdenum electrolyzed water catalytic electrodes were synthesized by ammonium nitrate pyrolysis method,aiming to improve their electrochemical performance and discuss the performance improvement mechanism.The main research contents are as follows:(1)Using lotus pollen as a carbon source,ammonium nitrate as an activator and N dopant,N-doped lotus pollen-based biomass porous carbon(N-PC)was prepared through a one-step carbonization method.Among all the pollen-derived porous carbons,the specific surface area of the prepared N-PC700 can be as high as 3106 m²g^-1.In a three-electrode system,in the 6 mol L^-1 KOH electrolyte,the specific capacitance at a current density of 0.5 A g^-1 is as high as 373.3 F g^-1.In addition,in the assembled symmetrical capacitor exhibited a high energy density of 53.5 Wh kg^-1,at the power density of 640 W kg^-1,After 10000 cycles of testing,the specific capacitance retention rate of the symmetrical device retain 96.4%,showing high cycle stability.This provides a simple method for the preparation of biomass-based carbon materials.(2)Using lotus pollen,ammonium nitrate and ammonium molybdate as carbon source,active agent and molybdenum source,respectively,N-doped Mo₂C-supported lotus pollen-based porous carbon composite(Mo NC/PC)was prepared by the one-step carbonization/activation method.In an acidic electrolyte,Mo NC/PC has a minimum overpotential of only 155 m V at a current density of 10 m A cm^-2,and the corresponding Tafel slope is 64.1 m V dec^-1.Among alkaline electrolytes,Mo NC/PC can provide an overpotential of 182 m V and a corresponding Tafel slope of 76.3 m V dec^-1.After 10 h of stability performance test in acid electrolyte,the current density remained basically unchanged,showing good catalytic hydrogen evolution reaction performance and good stability.In addition,the composite material also has certain electrochemical performance under the neutral electrolyte,indicating the superiority of the composite material to split water in the whole p H range(0?14).(3)On the basis of(2),using sublimated sulfur as the sulfur source,through chemical vapor deposition(CVD)treatment on Mo NC/PC,we synthesized a pollen-based porous carbon composite co-supported by MoS₂/Mo₂C(MoNCS).In the full range of p H(0?14),MoNCS composites exhibited excellent electrocatalytic hydrogen evolution performance.In acidic and alkaline electrolytes,at a current density is 10 m A cm^-2,MoNCS can provide the smallest overpotential 106 m V and198 m V,respectively.Their corresponding Tafel slopes are 36.3 m V dec^-1and 99.4m V dec^-1,respectively.After 100 h of stable performance test,the current density remained basically unchanged.In the neutral electrolyte,the composite material can also provide a certain overpotential.This result indicates that the prepared MoNCS electrode material exhibited excellent electrocatalytic hydrogen evolution reaction performance and good stability in the full p H range.