Preparation Of Coffee Grounds Based Biochar Catalytic Materials And Its Performance Study For Hydrogen Production Of Sodium Borohydride

Hydrogen energy is one of the most promising clean energy carriers due to its cleanliness,efficiency and high calorific value.Sodium borohydride（Na BH₄）is an ideal hydrogen energy donor with high energy density,good safety and recyclability for hydrogen storage.At present,the preparation of low-cost and efficient catalysts is the focus of hydrogen production from sodium borohydride.In this paper,Co/C_SCG,Co/C@g-C₃N₄ and BC_SCG-SO₃H catalysts were prepared using coffee spent grounds（SCG）as raw materials to catalyze the hydrogen production reaction of sodium borohydride.The main work of the thesis is as follows:（1）Coffee carbon(C_SCG)with a flake structure was obtained by high-temperature carbonization using coffee spent grounds as a raw material,and Co/C_SCG catalysts were prepared by liquid-phase reduction using C_SCG as a carrier and evaluated for their activity in catalytic hydrogen production by sodium borohydride hydrolysis.The amorphous Co nanoparticles were uniformly dispersed on the C_SCG with an average particle size of 3.94nm.The hydrogen generation rate（HGR）of sodium borohydride hydrolysis was 6263m L·min^-1·g _Co^-1,in 5 m L sodium borohydride alkali solution with reaction temperature of 30 ℃,sodium borohydride concentration of 0.02 g·m L^-1,Na OH concentration of 4wt.%,and catalyst dosage of 57.2 mg.The optimal reaction conditions predicted by the response surface method were as follows:Na OH concentration was 5 wt.%,reaction temperature was 35 ℃,catalyst dosage was 4.57 mg·m L^-1,and HGR of 6082 m L·min^-1·g _Co^-1 under this reaction condition.（2）C@g-C₃N₄ composite carrier was synthesized by pyrolysis using the mixture of SCG and melamine as raw materials.Then,Co/C@g-C₃N₄ catalysts were prepared by liquid phase reduction,and their catalytic performance in catalyzing the hydrolysis dehydrogenation of sodium borohydride was evaluated.The composite of biomass carbon and g-C₃N₄ increased the number of micropores and mesopores of the material and improved the specific surface area of the composite.Electrochemical impedance analysis showed that the composite of biomass carbon and g-C₃N₄ could also reduce the electron transfer resistance of the catalyst,resulting in a high catalytic activity.The HGR of sodium borohydride hydrolysis was 17857 m L·min^-1·g _Co^-1,in 5 m L sodium borohydride alkali solution with reaction temperature of 30 ℃,sodium borohydride concentration of 0.02 g·m L^-1,Na OH concentration of 6 wt.%,and catalyst dosage of14.3 mg.And it also had good photocatalytic ability about hydrolysis dehydrogenation of sodium borohydride,and the HGR under light conditions was increased by 14%compared with the no light conditions.（3）Coffee spent grounds were used as raw material and activated by Na HCO₃ at high temperature to generate porous carbon precursor(BC_SCG),which was then sulfated by sulfuric acid to prepare a solid acid catalyst(BC_SCG-SO₃H)for catalytic hydrogen production by methanolysis of sodium borohydride.The catalyst has an abundant acid center and suitable acid strength and shows excellent catalytic activity for the alcoholysis reaction of sodium borohydride.The HGR of sodium borohydride hydrolysis was 15432 m L·min^-1·g_cat.^-1,in 5 m L methanol solution with reaction temperature of 30 ℃,sodium borohydride concentration of 0.02 g·m L^-1,and catalyst dosage of 15 mg,and the hydrogen production activity of 1488 m L·min^-1·g_cat.^-1was maintained at 0 ℃.