Study On The Preparation And Catalytic Performance Of Carbon-based O₂/CO₂ Electrochemical Reduction Catalysts Derived From N-containted Biomass

Microbial fuel cell(MFC)is a promising biotechnology that utilizes microorganisms as catalysts to decompose organic or inorganic matter and simultaneously harvest electricity.However,the poor MFCs performance and low organic pollutants removal rate restrict its reality application.Previous studies showed that adding effective cathode catalyst to overcome the high energy barrier of oxygen reduction reaction(ORR)was one of the important methods to improve MFCs performance.In addition,the CO2 concentration in the atmosphere increases day by day,its efficient resource and energy utilization become a research focus in the field of environment and energy.Carbon dioxide reduction reaction(CDRR)is considered a promising method of recycling carbon,but because of the chemical inert of CO2,the development of high efficient electrochemical reduction catalyst plays an important role in improving CO2 reduction efficiency.Many studies indicated that low cost heteroatom doped carbon nano-materials have excellent ORR or CDRR catalytic activity,which have been regarded as important candidates for the metal catalysts especial for noble-metal catalysts.In other hand,nitrogenous biomass is the only renewable energy source with available carbon products.The natural features of including N,P and S heteroatom make itself to be an ideal material for the preparation of in situ heteroatom-doped carbon nano-materials.In this paper,Alfalfa Leaf with low nitrogen content was used as raw materials to prepare carbon-based materials,and then the effects of different chemical activators on structure and performance of the materials were investigated.Results demonstrated that KOH was an outstanding chemical activator,and carbon sheet ALC-K prepared under KOH showed fine structure and stable performance,which were proved to be efficient cathode oxygen reduction catalysts.When it was used as the cathode catalyst of MFCs,a maximum power density of 1328.9 mW/m2 was obtained,which was only 9 mW/m2 lower than that of Pt/C.However its stability was much better than that of Pt/C cathode.The MFCs performance was positively correlated to the nitrogen content in carbon sheet,especially the content of pyridinic-N and graphitie-N.Then.the inner membrane of passion fruit with a higher nitrogen was used as raw material to prepare carbon-based material(BXG-AC)under the same preparalion and activation method.The linear voltammetry scan results showed that BXG-AC.exhibited a comparable onset potentials to that of Pt/C,but the half-wave potential of 0.11 V was slightly more positive than that of Pt/C(0.02 V),which was regarded as important candidates for the commercial Pt/C catalyst.When it was used as the cathode catalyst of MFCs,a maximum power density of 1153.3 mW/m2 was obtained.lower than that of ALC-K.It was demonstrated that catalytic properties of the as-prepared carbon-based materials was not positively correlated with the nitrogen content,and the reason may be associated with the larger difference of specific surface area between ALC-K and BXG-AC.In addition,Alfalfa Leaf and the inner membrane of passion fruit are low pollution biomass.livestock sewage sludge with relatively high pollution and nitrogen content was brought into focus.LSC-A with high nitrogen in situ doping was successfully prepared under the same preparation and activation method as former,which shows similar specific surface area but much higher nitrogen content than that of BXG-AC.It was found that LSC-A was an oxygen reduction catalyst with excellent performance.When used as the cathode catalyst of MFCs,a maximum power density of 1273.3 mW/m2 was obtained,higher than that of BXG-AC.In conclusion,nitrogen-containing biomass can be used as raw material to successfully prepare N heteroatom in situ doped carbon-based materials catalysts,which exhibits excellent catalytic performance,the specific surface area and nitrogen content in carbon-based materials are all important factors affecting its catalyst activity.On the other hand,electroplating sludge and municipal sludge,which are rich of transition metals,especially in electroplating sludge,are relatively hard to be disposed.Due to the high catalytic activity of transition metal on CO2 electrochemical reduction.electroplating sludge was direct pyrolysis to prepare porous carbon TES,and then the as-prepared sample was used to catalyst the electrochemical reduction of CO2 subsequently.In MECs system with TES as catalyst,CO2 was reduced to methane,ethylene,carbon monoxide,formic acid and acetate with the help of Cu2O?NiO?Ni(OH)2?FeONi?CuNi?CuFeS and FexNiy as catalytic active sites in TES,and their production rates are 42.6±0.6?29.5±0.2?35.4±0.5 and 3.1±0.04?0.6±0.05 mg·L-1·h-1.But carbon material derived from municipal sludge by direct pyrolysis show feeblish CO2 electrochemical reduction activity.On the contrary,MSC-HA porous carbon modified by coupled hydrothermal reaction still exhibited excellent CO2 electrochemical catalytic activity even after removal of transition metals,and its catalytic performance shows best under-1.3 V external potential,under which CO2 could be reduced to acetate,formic acid and methane with the help of carbon quantum dots,pyridine-N and P element catalytic active sites in MSC-HA,and its production rates are 103.36 u g h-1 cm-2,37.15 A g h-1 cm-2 and 12.88 u g h-1 cm-2,with the total faraday efficiency was about 31.73%.The possible CO2 reduction mechanism is that CO2 molecules are initially adsorbed onto the electrode surface and reduced to CO2-radicals first,then the CO2-radicals are protonated by HCO3-ions and finally,reduced to CO,CH4 or C2H4.In contrast,the CO2-radicals could combine to generate-OOC-COO-groups.Then,these groups are protonated and further reduced to acetate.This study employed natural N-rich biomasses(Alfalfa Leaf,the inner membrane of passion fruit,livestock sewage,electroplating sludge and municipal sludge)as raw materials and utilized facile heat-treatment techniques to prepare efficient and stable carbon-based material catalysts toward ORR or CDRR.The preparation methods were low-cost,environmental benign and convenience.The results of these thesis provided new approaches for preparing carbon-based catalysts for high-performance O2/CO2 electrochemical reduction,and provided a new direction for the source and energy recycling of waste biomasses.