Rational Preparation And Mechanism Investigation Towards CO-Tolerant PEMFC Anodes

The technological advancement of proton exchange membrane fuel cells(PEMFCs)marks a significant breakthrough in the industrialization of hydrogen energy.Notably,hydrogen-oxygen fuel cells,direct formic acid fuel cells(DFAFCs)and direct methanol fuel cells are the most representative types of PEMFCs.Currently,CO poisoning is a common challenge faced by PEMFC anodes.This thesis conducts a series of studies focusing on the problem of CO poisoning in hydrogen oxygen fuel cells and DFAFC.Based on the differences in the origin of poisoning,innovative anti-poisoning mechanisms are proposed,providing a basis for the design of reasonable catalytic systems,achieving the breakthrough in CO tolerance.At the same time,combined with spectroscopic evidences and computational simulations,in-depth exploration of the reaction mechanism was conducted,and new insights and discoveries were obtained.1.Construction of CO tolerant PEMFC anode based on the synergistic effect of Ir single atom and Ir nanoparticles.In this chapter,a new anti-poisoning mechanism is proposed for hydrogen fuel cell anodes:single atom and nanoparticle synergistic catalysis.Based on this,a catalytic structure was designed and prepared,wherein iridium(Ir)single atoms and Ir nanoparticles coexist in proximity.Ir nanoparticles are the active source of HOR.The Ir single sites not only electrooxidize CO quickly at low potential,but they also make it easier for neighboring Ir nanoparticles to desorb CO,thereby providing effective protection to the hydrogen oxidation sites on Ir nanoparticles.The synergistic effect between the two active centers enables the catalyst to exhibit superior CO tolerance in fuel cells,as evidenced by peak power densities of 353 mW cm-2 and 209 mW cm-2 in the presence of 100 ppm and 1000 ppm CO,respectively.These values are more than twice that of the commercial PtRu/C anti-CO poisoning catalyst.2.Preparation of Rh/Pt synergistic catalyst using ultra-small particle size ZIF-8.Through the optimization of active site selection and material synthesis techniques,we have improved the synergistic anti-poisoning strategy in this chapter.We discovered that NaBH4 can significantly improve the growth rate and yield of ZIFs materials(close to 100%),minimize the particle size of ZIF-8 to approximately 25 nm,and achieve a single batch preparation of 100 g.The RhSA-N-C monoatomic catalyst,prepared using ultra-small particle size ZIF-8 as the support,exhibits the highest CO electrooxidation activity known to date,achieving a peak power density of 330 mW cm-2 in PEMFCs fueled by pure CO and operating continuously for over 440 hours without degradation.Building on this success,we developed a synergistic anti-poisoning system,RhSA-PtNC,composed of rhodium(Rh)single atoms and Pt nanoclusters.The outstanding COOR activity of Rh single atoms renders the catalyst highly CO-tolerant in fuel cells.Remarkably,the peak power density of Rh/Pt synergistic catalysts reaches 874 W cm-2 in an H2/100 ppm CO mixture,significantly outperforming traditional commercial PtRu/C catalysts.3.Development and Mechanism Analysis of FAOR Anti-poisoning Catalyst.In this study,we developed a monoatomic Rh-based catalyst,denoted as Czif-Rh N-C,for the anode of direct formic acid fuel cells(DFAFCs).The catalyst exhibited a remarkable mass power density of 1531 mW mg-1 in DFAFCs,which is 20 times higher than that of commercial Pd/C.Furthermore,the Czif-Rh-N-C catalyst demonstrated excellent activity towards CO electrochemical oxidation,which enables the CO intermediates originating from indirect pathway can be effectively converted to CO2.This mechanism not only eliminates the toxic effect of CO in the FAOR but also prolongs the operation time of DFAFCs which can exceed 130 hours,while commercial Pd/C stops working within 12 hours.Additionally,employing Czif-Rh-N-C as a model catalyst,we uncovered an unconventional dissociation recombination mechanism through isotope labeling and in situ electrochemical mass spectrometry during CO electrooxidation and formic acid electrooxidation,enhancing our understanding of the underlying reaction mechanism.4.A new pathway for FAOR with hydrogen as an intermediate.The mechanism of formic acid oxidation(FAOR)in DFAFC was further investigated.Using in situ electrochemical mass spectrometry as the main technical means,combined with isotope tracing methods,the real-time monitoring of the FAOR on Pt/C catalyst and two single atom catalysts(Rh-N-C and Ir-N-C)was carried out,and it was the first time that hydrogen molecules were captured as the intermediates of FAOR.Based on this,we proposed a new FAOR reaction pathway and named it"hydrogen oxidation pathway".This mechanism not only further explores the anodic reaction of DFAFCs and echoes the dissociation-reformation mechanism,but also provides us with a new idea for understanding other PEMFCs anode reactions.