| As an efficient and clean energy conversion device,fuel cell is an important development direction of future energy utilization.Low temperature proton exchange membrane fuel cells（LT-PEMFCs,operating temperature～80℃）are the most promising class of fuel cells,but they suffer from difficulties in the preparation,storage,and transportation of high-purity hydrogen,as well as complex water and thermal management systems for fuel cells,etc.High temperature proton exchange membrane fuel cells（HT-PEMFCs）have a series of advantages that LT-PEMFCs do not have:with the increase of reaction temperature,the kinetic rate of catalytic reaction is greatly improved,and the catalyst is highly tolerant to fuel impurities,and the system water,thermal management system is simple and can be used in combination with a variety of hydrogen supply methods,which is expected to break through the application bottleneck of LT-PEMFCs.However,HT-PEMFCs mainly use phosphoric acid as a proton conductor,and phosphoric acid is strongly adsorbed on the Pt surface to block the catalytic active sites,which greatly reduces the catalytic activity utilization rate.At the same time,problems such as uneven distribution and loss of phosphoric acid in the catalytic layer lead to poor proton transport and limit the output performance of HT-PEMFCs.In addition,the high temperature and strong acid conditions of HT-PEMFCs put forward higher requirements for the stability of the catalyst in the case of fuel starvation.Finally,the high concentration of CO gas impurity in commercial hydrogen or in-situ reformed hydrogen used in HT-PEMFCs to reduce hydrogen cost still greatly limits the performance of commercial Pt/C catalysts.In view of the series of problems faced by HT-PEMFCs,this thesis focuses on the catalysts’anti-phosphoric acid poisoning,efficient proton transport,catalyst stabilization under fuel starvation conditions,and high-concentration CO poisoning resistance.The specific research contents are as follows:（1）In order to solve the problem of serious poisoning of Pt-based catalysts by phosphoric acid,CNT@Si O2-Pt cathode catalysts were prepared by modifying carbon nanotubes with Si O2 and further supporting Pt nanoparticles.Chemical tests and device performance tests of HT-PEMFCs show that Si O2 in the CNT@Si O2-Pt catalyst has a stronger phosphate ion adsorption capacity than the adjacent Pt active site,which greatly inhibits the adsorption of phosphoric acid on the active site Pt of the oxygen reduction catalyst.At the same time,the immobilization of phosphoric acid by Si O 2promotes the uniform distribution of phosphoric acid in the catalytic layer,and builds an efficient and fast proton transport network.HT-PEMFCs with CNT@Si O2-Pt as cathode catalyst exhibited performances of 765 m W cm-2（H2/O2）and 486 m W cm-2（H2/Air）at 160℃,and operated stably for more than 200 hours.At 220℃,a peak power density（H2/O2）of 1061 m W cm-2 was exhibited.The introduction of Si O2 in the cathode catalytic layer provides a high-speed reaction path for the oxygen reduction process of proton-coupled electrons,thereby achieving ultra-high output power density and stability of HT-PEMFCs.（2）In order to solve the problems of poor proto n conductivity and low oxygen solubility of reactants in the catalytic layer containing phosphoric acid,we synthesized Ti O2-x,Ti P2O7 cocatalysts,and mixed them uniformly with Pt/C for HT-PEMFCs cathode catalysis.layer.Compared with Ti O2-x,Ti P2O7 itself has better proton conductivity and electrical conductivity,so further solution electrochemical tests found that Ti P2O7 co-catalyst did not affect the ORR performance of Pt/C in solution,followed by HT-PEMFCs device The test results show that the unifo rm introduction of Ti P2O7into the catalytic layer of HT-PEMFCs can greatly increase the proton conductivity of the catalytic layer.At the same time,the enrichment of oxygen by Ti P 2O7 increases the concentration of reactant oxygen in the catalytic layer,which accelerates the concentration of oxygen in the cathode catalytic layer of the fuel cell.The three-phase interfacial reaction rate of the HT-PEMFCs showed an ultra-high power density of 965m W cm-2（H2/O2,no back pressure）at 160℃.Excellent stability is maintained during operation.Studies have shown that the introduction of a cocatalyst with intrinsic proton conductivity in the catalytic layer can accelerate the cathodic proton transport and the three-phase interfacial reaction rate,thereby achieving ultra-high output power density of HT-PEMFCs.（3）In order to solve the problems of current reversal decay and catalytic layer instability during fuel starvation of HT-PEMFCs,we propose an ingenious strategy by screening non-Pt catalysts at the anode,which combines the operating temperature（120～240℃）of HT-PEMFCs with the temperature of HT-PEMFCs.The hydrogen release temperature（106～300℃）in the lattice gap of Pd is matched with the significantly enhanced hydrogen oxidation activity of Pd at high temperature,which achieves the highest performance of fuel cells using Pd/C as anode and far exceeds that of HT-PEMFCs.Ultra-long fuel starvation durability of single commercialized Pt/C.Specifically,Pd acts as a hydrogen buffer layer and ox ygen absorber in the anode to provide additional in-situ hydrogen and absorb oxygen permeating from the cathode or the environment during the fuel starvation of HT-PEMFCs,maintaining a fast hydrogen oxidation reaction and The reverse current degradation p rocess was delayed by more than 1 hour（whereas conventional strategies can only reach seconds or minutes）.Compared with the conventional single Pt/C anode,the Pd-containing anode catalyst layer delayed the reversal current degradation time by 37 times a nd retained peak power density by 40 times.Therefore,a strategy that combines the reversibility of metal and hydrogen storage/release with the characteristics of PEMFCs operating conditions can provide new guidance for fuel cell durability and lifetime i mprovement.（4）In view of the problem that high concentration of CO in HT-PEMFCs still has a large poisoning effect on the anode Pt/C catalyst,firstly,we took three single-metal catalysts with hydrogen oxidation activity as the research objects,and scr eened out the best catalysts at high temperature.The monometallic catalyst Pd/C with strong resistance to CO poisoning,and the research results clarified the different anti-CO poisoning mechanisms at low temperature and high temperature.Finally,Pt Pd bimetallic catalyst was prepared by solvothermal reduction method.The interaction between Pt and Pd optimize the electronic structure,the hydrogen adsorption energy and promote the hydrogen oxidation reaction kinetics through bimetallic sites.The prepared Pt Pd alloy catalyst has very good CO tolerance in the full temperature range of HT-PEMFCs,while maintaining a higher output power density of HT-PEMFCs.The development of anode catalysts resistant to high concentrations of CO poisoning in HT-PEMFCs provides an efficient route for the direct utilization of industrial hydrogen. |
