Study The Performance Of Phosphoric Acid Anti-poisoning Of Electrocatalysts For High Temperature Polymer Electrolyte Membrane Fuel Cell

With the increasing crisis of energy and environment,the development of efficient and clean energy is of great significance to the sustainable development of mankind.Compared with traditional low-temperature polymer electrolyte membrane fuel cell（LT-PEMFC,operating temperature～80℃）,high-temperature polymer electrolyte membrane fuel cell（HT-PEMFC,operating temperature 120～250℃）have many advantages that low dependence of hydrogen purity and simplified system management,which is an important direction for the development of fuel cell in the future.Phosphoric acid,as proton conductor,can adsorb on the Pt surface to transfer proton.However,too much phosphoric acid adsorption occupied the catalytic active sites,would lead to serious poisoning of catalysts and hinder the reactant to contact with the catalyst.In addition,due to the thermal evaporation and fluidity of phosphoric acid,the uneven distribution and loss of phosphoric acid in catalytic layer lead to the occurrence of dead zone of reation in catalytic layer,which reduces the activity expression and durability of the catalysts.The cost of HT-PEMFC remains high due to the related problems of HT-PEMFC,resulting in the large quantity of precious metal（Pt）catalysts that should be used to maintain the performance of fuel cell.In view of the problems of proton conductors,it is of practical significance to design catalysts specifically to improve the activity expression and durability of catalysts.The key problems of the phosphoric acid poisoning and poor durability of catalysts for HT-PEMFC,we aim to solve the related problems by means of microenvironment regulation on catalyst surface,introduction of efficient binder and solid organic phosphoric acid,and CO prepositioning.To realize the low consumption of precious metal and high output power and long life for HT-PEMFC,the main research contents of this paper are as follows:（1）To solve the problems that free phosphoric acid adsorbed the catalyst surface to poison the catalyst and block reactant transport channel,sodium alginate with rich groups of hydrogen bond,as the catalytic layer binder,was introduced into the catalytic layer.The hydrogen bond groups of sodium alginate can effectively adsorb and then fix phosphoric acid,reducing the adsorption amount of phosphoric acid on the catalyst surface and preventing phosphoric acid accumulation in the pore of the catalytic layer.Therefore,improving the activity utilization of catalysts and the stability of catalytic layer.In addition,the proton transport network can be constructed in the catalytic layer after the adsorption of phosphoric acid by sodium alginate,which can improve the proton transport of catalytic layer.Sodium alginate as binder,0.85 mg _Pt cm^-2,the fuel cell shows the high peak power density of 675 m W cm^-2,which is 1.5 times higher that that of the fuel cell with PTFE as binder.（2）Based on the impact of sodium alginate addition on fuel cell performance,this paper further introduced the rich-amine defect C₃N₄ to change the adsorption amount of phosphoric acid on the catalyst surface,so as to improve the performance of fuel cell.The rich amine groups in defective C₃N₄ can generate acid-base interaction with phosphoric acid,and thus transfer phosphoric acid on the catalyst surface to defective C₃N₄,which achieve the purpose of improving performance of fuel cell.By introducing defects C₃N₄ to the membrane electrode of fuel cell,the anode(0.20 mg _Pt cm^-2)and cathode(0.40 mg _Pt cm^-2)with lower Pt load,HT-PEMFC show the high peak power density of 672 m W cm^-2 and superior durability of high performance(about 620 m W cm^-2 with stability of acceleration 3 500 cycles),the performance is better than the current reported most of the performance of HT-PEMFC.（3）In view of the problem,phosphoric acid,as proton conductor,has strong fluidity and easy evaporation.Organic phosphoric acid（ethylenediamine tetramethylene phosphonic acid,EDTMPA）,higher melting point,is further introduced to reduce the evaporation of phosphoric acid and improve/maintain the proton transmission capacity of fuel cell.The CO dissolution experiment and in-situ electrochemical impedance study showed that the introduction of EDTMPA could effectively reduce the poisoning and proton transport resistance of phosphoric acid on Pt surface.Adding EDTMPA in the cathode(0.4 mg _Pt cm^-2),the fuel cell show the high peak power density of 820 m W cm^-2,which is 28%higher than that of the fuel cell without EDTMPA.In addition,EDTMPA added in both anode(0.20 mg _Pt cm^-2)and cathode(0.40 mg _Pt cm^-2),the fuel cell,H₂/O₂ and H₂/Air conditions,have showed better peak power density and stability in the accelerated aging experiments with 10000 cycle,which is also better than the most of the reported work so far.（4）Phosphoric acid in membrane electrode woule be redistributed under the action of electric field and concentration difference during the assembly and operation of fuel cell.Based on the characteristics of phosphoric acid redistribution,this paper innovatively introduced CO adsorption to preoccupy Pt.Due to the strong interaction between Pt atom and CO on the Pt surface,the adsorption poisoning of phosphoric acid to Pt in the redistribution process can be effectively reduced,and atomic level modification can regulate the adsorption poisoning of phosphoric acid.This paper has systematically studied that the different operating temperature and catalyst layer thickness take effect on the performance of fuel cell.The results show that the highest utilization of catalysts under 160℃and thin layer of catalyst layer(0.20 mg _Pt cm^-2).Meanwhile,this paper also compares the defective C₃N₄ and EDTMPA modified fuel cells,showing that the fuel cell of the CO preoccupation modification has the best performance.