Preparation Of Porous Carbon Derived From Rice Bran And Performance In Energy Storage

With the social development,energy shortage and environmental pollution problems have become increasingly prominent.The development of clean and efficient energy for sustainable development has become a necessary requirement,among which,energy storage technology is a vital part of new energy industry.Electric double layer supercapacitors and lithium-ion batteries as efficient energy storage and conversion devices,attract much attention.However,either electric double layer supercapacitors or lithium-ion batteries can well meet the practical application for low energy density.Currently,the researches on electric double layer supercapacitors mainly focus on improving the energy density;researches on lithium-ion battery focus to develop a new type of high specific energy batteries-lithium-sulfur battery(theoretical specific energy 1675mAh g^-1).Poor electrical conductivity and the presence of shuttle effect,severely restricted the commercial applications of lithium-sulfur batteries.The electrode material has a decisive role on the performance of the energy storage device.Porous carbon material has excellent electrical conductivity,porosity and chemical stability and is widely used as supercapacitors and lithium-sulfur battery electrode materials.To further develop an excellent porous carbon material?ultra-high specific surface area,pore/mesoporous hierarchical porous structure,hetero atoms N,O doped?has a very important significance.Numerous studies reported that excellent porous carbon material can be effectively prepared from biomass as a carbon source,expecially nitrogen-containing biomass.Rice bran as agricultural by-products produces 2.93×10⁷ tons in China every year.Rice bran is rich in nitrogen?12%-16%?,while less than 10%utilization and only few studies are related to exploration in the field of energy storage.The previous outstanding studies on porous carbon materials with high SSA,hierarchical porous structures and heteroatom doped are based on complex preparation method,small production or high production cost.In this work,porous carbon materials based on rice bran with above advantages can be prepared in large scale by simple direct activation method at low cost.In fact,we take NaOH as activating agent and successfully prepare N-doped porous carbon materials with high specific surface area up to 3465 m² g^-1 at a low temperature of 600 ^oC.Activation temperature and the amount of activator can effect materials properties,and the specific surface area and pore volume ranges 1525-3465 m²g^-1,0.629-1.466 cm³ g^-1,respectively.The final samples were dominated by micropores with a small amount of mesopores.The electrochemical characterization was performed in the system of 6 M KOH and 1.5M Li₂SO₄.The results indicate excellent electrochemical stability?up to 91.3%?and high specific capacity in the KOH electrolyte(the highest up to 372 F g^-1 at 0.1 A g^-1,231 F g^-1at 60 A g^-1),superior than most of previously reported biomass-based porous carbon.In order to broaden the application in the field of high energy density,we took 1.5 M Li₂SO₄as the electrolyte.Experimental results showed the specific capacity up to 286F g^-1 in a current density of 0.1 A g^-1,and still more than 150 F g^-1 even at 50 A g^-1.The maximum energy density of porous carbon is more than the 25 Wh kg^-1,far more than the commercial activated carbon(3-5 Wh kg^-1),and still 6.8 Wh kg^-1 even at the energy power density of up to 12483 W kg^-1.As the cathode materials of lithium-sulfur battery,specific capacity is up to 971mAh g^-1,and the capacity retention rate is 87.6%after 100 cycles,indicating that rice bran-based porous carbon can effectively suppress sulfide dissolved in the electrolyte.The cheap raw materials?rice bran?,simple preparation method,high specific capacitance is conducive to industrialization production.