Study On Solid Oxide Fuel Cells Operating On Biochars

Fuel cells directly convert the chemical energy stored in fuels to electric energy with high efficiency and low emissions,and is the next generation technology instead of the conventional combustion-based power generation technology.Compared with all other types of fuel cells,the direct carbon fuel cells?DCFCs?possess the highest energy conversion efficiency in theory?100%?,and extensive availability of solid carbon fuels,indicating great potential for application.Biomass energy is a type of important carbon-neutral and renewable energy source.Biochar is one of the common products of thermochemical conversion of biomass.The direct use of biochar as fuel for DCFCs is of great significance for an efficient and clean utilization of biochar and alleviating energy shortage.The Boudouard gasification reaction is one of the key factors that restricts the output performance of DCFCs when directly using biochar as fuel.The metal elements that biochar contains naturally,such as K,Ca,Mg and Fe,which are essential for the photosynthesis and other metabolic processes of plants,and usually have strong catalytic activity for the Boudouard gasification reaction of carbon fuels.In this thesis,the feasibility of direct utilization of bamboo biochar?BC?as fuel for direct carbon solid oxide fuel cells?SO-DCFCs?is studied by comparing BC to de-ashed BC?DC?and activated BC?AC?in terms of Boudouard reactivity and the performance of the fuel cells.The results show that the inherent metal elements in BC play a crucial role in enhancing its Boudouard reactivity.BC has noticeably higher Boudouard reactivity than DC.The performance of the cell when using BC fuel is markedly superior to that using DC fuel under the same conditions.The comparative experiments of catalyst-loaded AC and DC to catalyst-loaded BC reveal that the microstructure of carbon is an important factor impacting its catalyst loading efficiency and further the Boudouard reactivity.Catalyst-loaded BC has an improved gasification reactivity,and the PPD of the related cells reaches approximately 191 mW cm^-22 at 850?.Activated carbon has large specific surface areas,high porosity,stable physicochemical properties and excellent surface reactivity,and is widely used as a variety of functional materials.Biomass activated carbon is mainly obtained by taking agricultural and forest biomass as low cost and renewable raw materials.Herein,the physicochemical properties of the walnut shell charcoal?WSC?and KOH activated WSC?WSC-B?and their effect on the electrochemical performance of fuel cells are studied.The results show that at 850?using WSC as fuel for SO-DCFCs,the power density can reach 237mW cm^-2,and the fuel conversion efficiency is 42.6%.The WSC-B fuel has an increased degree of carbon disorder and a rich porous structure,which greatly accelerates the rate of the Boudouard gasification reaction of carbon.As a result,the output performance of DCFCs is increased to 364 mW cm^-2,and the discharge stability is enhanced.Pomelo peel has the unique advantages of being a fuel for DCFCs,such as its loose and porous structure,and the containing of catalytic ingredients for carbon gasification.The experimental results show that the pomelo peel char?PC?exhibits superior Boudouard gasification reactivity due to its unique reticulated carbon foam with homogenously distributed inherent catalysts?K and Ca?.The power densities of fuel cells operating on PC and catalyst-loaded PC?PCC?achieves 309 and 518 mW cm^-22 at 850oC,respectively.The stability tests conducted at a current density of 50 mA cm^-2and 825?indicate that the fuel availability rates of PC and PCC are 47.25%and 34.71%,respectively,and the cell using PC fuel has a more stable running than that using PCC.The results suggest that PC is a promising solid carbonaceous fuel for SO-DCFCs.