Preparation And Electrocatalytic Properties Of Biomass Carbon Materials Based On Ionic Liquids

With the rapid development of human society,various non-renewable fossil fuels were being consumed gradually,which brought about resource depletion and a series of environmental problems.As a green and pollution-free renewable energy,hydrogen energy is an ideal substitute for fossil energy.At present,electrolysis of water is a relatively simple method for hydrogen production.As we all know,noble metal catalysts have high catalytic activity and can significantly reduce the overpotential of water splitting.However,the rarity and high cost of noble metals limit its industrialization application.So it is very necessary to develop efficient and inexpensive non-noble metal catalysts.Biomass is widely available and cheap,and can be used as precursors for the preparation of porous carbon materials.And low-cost and easily agglomerated transition metals have high water splitting activity.The combination of carbon materials and transition metals can make up for each other’s shortcomings,so that developing transition metal biomass carbon-based electrocatalysts shows huge potentials.The synthetic biomass based ionic liquid and wood chips were used as raw materials to synthesize biomass carbon-based materials based on ionic liquids by pretreatment carbonization,electrodeposition and phosphorization in this thesis.The electrocatalytic properties of hydrogen production,oxygen production and water splitting of catalysts were measured in acid and alkaline solution.The specific contents are as follows:1.A simple one-step carbonization process was used to synthesize nitrogen-phosphorus-cobalt co-doped porous carbon electrocatalyst with cobblestone-like morphology using synthetic biomass-based ionic liquid.Without the addition of activators,the specific surface area of CoP@NPC-900 was as high as 979.67 m² g^-1.At the current density of 10 m A cm^-2,the overpotentials of CoP@NPC-900 in acid-base solution were 181 and 238 m V,respectively,and Tafel slopes were 59 and 88 m V dec^-1.As the proton donor of ionic liquid,gluconic acid can adjust the pore structure,increase the specific surface area and pore volume of the catalyst during the carbonization process.In addition,temperature also played a key role,when the temperature reached 900℃,CoP crystal phase and porous cobblestone-like morphology were formed.The teheoretical calculation results also showed that CoP@NPC has the ideal free energy of adsorption,which is beneficial to the transition from intermediate H*state to the catalyst-1/2 H₂ state.In addition,there is a synergistic effect between CoP nanocrystals and porous carbon（NPC）,which enhances the density state near the Fermi level and accelerates electrons transfer.Therefore,CoP@NPC-900 had high hydrogen evolution performance in a wide range.2.The wood chips were treated by synthetic ionic liquid solution,and then nickle-cobalt phosphate supported self-supporting electrode（CoNi P@TCW）were prepared through carbonization,electrodeposition,and phosphorization processes.CoNi P@TCW-2 still maintains a stable three-dimensional nanosheet morphology after phosphating,which is condutive to exposing more active sites and gas release.CoNi P@TCW-2 had the best hydrogen evolution reaction（HER）performance in acid and base solution.The overpotentials were 71.93and 107.62 m V(10 m A cm^-2),respectively,and Tafel slopes were 60.09 and 79.52 m V dec^-1.Besides,CoNi P@TCW-2 had lower oxygen evolution reaction（OER）overpotential(η₁₀=320m V)in 1 M KOH solution,which was better than noble metal Ir O₂.In the assembled two-electrode electrolyzer,the water splitting voltage was only 1.66 V at the current density of 10m A cm^-2,which exhibited excellent water splitting performance.