Electrocatalytic Oxidation Decarboxylation Of Fatty Acids On The Surface Of Carbon-based Electrodes

According to the 2022 China Sustainable Aviation Fuel Development Research Report,the global demand for aviation kerosene,an essential fuel for aircraft,is expected to grow rapidly until 2019.The global market of aviation has seen a sharp decline due to the pandemic in the last three years.However,global aviation traffic continues to grow as the world economy recovers.Currently,the production of aviation fuel is largely dependent on fossil fuels,which cannot be replaced by electricity or hydrogen energy.The use of sustainable aviation fuel(SAF)to replace aircraft fuel produced from fossil fuels is a promising approach in the present and the future,with the China’s goal of"carbon peaking and carbon neutrality"in September 2020 and the International Air Transport Association’s(IATA)goal of achieving net zero emissions in the global aviation industry by 2050 in 2021.Among the promising commercial production processes for SAFs,the hydrogenation process(HEFA)of esters and fatty acids(waste oil(swill-cooked dirty oil,etc.)is relatively mature,but traditional thermal catalytic synthesis requires the reaction conditions of high temperature and high-pressure hydrogen.Therefore,the use of electrocatalytic technology to synthesize aviation fuel from fatty acids under mild conditions is a new path for the production of SAF in the future.Carbon material is the most common electrode material for the synthesis of hydrocarbons by electrocatalytic decarboxylated fatty acids except precious metals Pt and Ru.Carbon material has the advantages of preferable electrical conductivity,high surface area,low cost and easy modification.However,there are few researches on the catalytic activity,product selectivity and stability of carbon materials in aqueous system,which the application of carbon materials in the electrocatalytic oxidation decarboxylation of fatty acids is limited.Therefore,it is very important to study the adsorption and transformation of fatty acid on the surface of carbon-based electrode for the activity of electrocatalytic decarboxylation of fatty acids,product selectivity and electrode stability.The following work was carried out in this paper:(1)In order to explore the potential effect of physicochemical properties of carbon-based electrode materials on decarboxylation of fatty acid(in chapter 3),this paper carried out physical and chemical characterization of six different characteristics of carbon-based electrodes(hydrophilic(hydrophobic)carbon paper,hydrophilic(hydrophobic)carbon cloth,carbon felt,graphite sheet).It was found that hydrophilic carbon paper(cloth)and carbon felt have hydroxyl groups on the surface,and hydrophilic and hydrophobic carbon paper and graphite sheet have significant graphite structure,while carbon cloth and carbon felt show graphite structure by XRD and ATR-FTIR.And hydrophilic carbon paper and graphite sheet have a large electrochemically active surface area.In addition,through the analysis of LSV and Tafel slope,six carbon-based electrodes can inhibit oxygen evolution reaction(OER)with the addition of caprylic acid.By comparing the catalytic performance of the six carbon-based electrodes in electrocatalytic decarboxylation of fatty acids,it was found that the hydrophilic carbon paper and hydrophilic carbon cloth had good conversion of octanoic acid and yield of hydrocarbon due to its hydrophilic properties and easy adsorption of carboxylic acid on the electrode surface at higher currents,and the best decarboxylation performance of hydrophilic carbon cloth(conversion of 32.9%,total yield of 18.5%,selectivity of 51.3%and Faraday efficiency of 42.0%),which may be due to the large specific surface area of carbon cloth.In the process of reaction,the electrodes have different degrees of oxidation off,and heat release occurs at high current density.This may be due to the adsorption of the reactants on the electrode surface,which requires higher voltage to desorb the product and thus release heat.(2)In Chapter 4,in order to study the influence of different conditions on the electrocatalytic decarboxylation of fatty acids by carbon-based electrode,the catalytic decarboxylation performance of fatty acids with different current density,voltage,concentration of reactants and electrolyte and different chain lengths of fatty acids was compared.With the time-voltage/current density curves and the stability of the electrodes under different conditions,it was found that the carbon-based electrodes had higher conversion(17.9%),selectivity(48.6%)and Faraday efficiency(35.1%)at 100 m A/cm~2,and higher conversion(13.1%),selectivity(81.8%)and Faraday efficiency(49.3%)at 10V.And the electrocatalytic decarboxylation reaction is more favorable under neutral or weakly acidic.At room temperature and pressure,fatty acids with shorter carbon chains(hexanoic acid)or longer carbon chains(nonanoic acid)were not favored for the conversion of electrocatalytic decarboxylation of fatty acid at carbon-based electrodes.Furthermore,by treating the electrode by different ways during the reaction,it was found that the rise of voltage and the fall of current are due to the adsorption of the reactants and the products of hydrocarbon on the electrode surface,which blocks the active site.