Research On Electrochemical Properties Of The Ginkgo Leaf-Based Porous Carbons And Its Derivatives

With the challenge of excessive fossil fuel consumption and environmental pollution,renewable and green energy technologies have been developed for future energy generation,storage and usage.In practical applications,the cost,environmental friendliness and sustainability of the energy storage and conversion devices are three main factors we care about.Supercapacitors are the most potential energy storage devices because of good stability,long life cycle,high pow er density,reasonable energy density and environmental protection.Water-splitting reaction device is the most environmentally friendly and efficient way to produce hydrogen.Electrochemical energy storage and conversion devices are primarily reliant on the development of advanced electrode materials and catalysts.Carbon materials make it the best choice for electrode materials of electrochemical energy storage and conversion devices due to high specific surface area,electronic conductivity,high specific capacitance and low-cost.In this work,porous carbon materials and its derivatives have been designed and prepared using the source of biomass ginkgo leaves and cobalt precursor.Their electrochemical performances were studied.The main contents are summarized as follows:?1?Nitrogen/sulfur co-doped hierarchically porous carbons were designed for high-performance supercapacitor electrode materials in a one-step process,in which ginkgo leaves used as carbon source and S source,and ammonium nitrate used as activating agent and N source.During the activation process,the using of ammonium nitrate generated large amount of mesopores and micropores through chemical etching of the carbon skeletons by redox reactions,and released massive gaseous by-products which further promoted the formation of hierarchical pores.The results show that the prepared porous carbon possesses a specific surface area of 672 m² g^–1,exhibits a high specific capacitance of 330.5 F g^–1 at a current density of 0.5 A g^–1 and a capacitance of 252 F g^–1 even at current density of 10 A g^–1 with an excellent capacitance retention of 85.8%after 10000 cycles in a three-electrode system.Moreover,the assembled symmetric supercapacitor displays a high energy density of43.6 Wh kg^–1 at a power density of 400 W kg^–1.?2?Co nanoparticles capsuled by N,S-doped porous carbon?Co/NSPC?were prepared by a simple one-step method via low temperature pyrolysis of the raw materials of ginkgo leaves,ammonium nitrate,and cobalt nitrate.It has been found that the addition of ammonium nitrate can significantly reduce the synthesis temperature,the energy loss,and save energy.The catalyst exhibits excellent hydrogen and oxygen evolution ability in alkaline electrolyte.The electrode material Co/NSPC shows good hydrogen evolution catalytic activity with the overpotential of295.1 mV and Tafel slop of 106.38 mV dec^–1 at the current density 10 mA cm^–2.During the oxygen evolution reaction,the overpotential and tafel slope of Co/NSPC are 376.9 mV and 98.4 mV dec^–1,respectively.?3?On the basis of content?2?,CoP/NSPC was treated with NaH₂PO₂ as phosphorus source in situ growth method to form CoP/NSPC composite for electrode material of water splitting.The effects of various carbonization temperatures and cobalt on the properties of the materials were investigated.The results show that in the acid electrolyte,the electrode material shows good hydrogen evolution catalytic activity with the overpotential of 129 mV at the current density 10 mA cm^–2.In the alkaline electrolyte,the oxygen evolution overpotential of the electrode material is286.4 mV at the current density 10 mA cm^–2.This means that CoP/NSPC can be used as a dual function catalyst for water splitting.