Electronic Structure Modulation And Electrocatalytic Oxygen Reduction Reaction Performance Of Iron Phthalocyanine

The growing energy demand has spurred a strong interest in developing low-cost,renewable,clean energy,such as metal-air batteries and fuel cells.Oxygen reduction reaction?ORR?as a half-reaction cathode in these clean energy devices strictly determines the performance of these energy devices to some extent.However,the complex four-electron reaction mechanism of the ORR leads to a sluggish kinetic feature,which seriously affects the energy conversion efficiency of chemical energy devices.Therefore,it is necessary to develop a highly efficient oxygen reduction catalyst to increase the efficiency of there energy devices.Emerging as an inexpensive alternative with highly Pt-like activity,Fe–N–C materials have recently aroused giant expectations.Although the electron configuration of catalytically active FeN4 moiety greatly determines the ORR kinetics on Fe–N–C catalysts,its further modification for activity optimization still suffers from efficient strategies.As a new two-dimensional material,MXenes have excellent conductivity,high surface hydrophilicity and electronegativity as well as high mechanical stability.In particular,by changing the crystal structure and surface terminations of MXenes,the unique electronic structure can be regulated,which gives MXenes a near-surface chemical environment to adjust the electronic structure of the catalyst.Moreover,they can also serve as charge storage host in the electrocatalytic reaction process due to the special morphological structure,ensuring efficient and continuous electrochemical reactions.Therefore,MXenes can be serve as attractive electrocatalyst support.In this thesis,iron phthalocyanine?FePc?with typical FeN4 moieties was selected as the Fe-N-C catalyst model,and two-dimensional layered Ti3C2Tx Mxene was used as the substrate.We first achieves FePc/Ti3C2Tx hybrid catalyst by coupling FePc with Ti3C2Tx.The morphology and structure of the related materials were characterized by a series of testing methods.The ORR performence of FePc and FePc/Ti3C2Tx electrocatalysts were studied.In addition,the structure-activity relationship between the electronic structure and ORR intrinsic activity of the FeN4 moiety of Fe-N-C were further explored by means of spectroscopy and magnetic testing techniques.The main results are as follows:?1?Ti3C2Tx with accordion-like structure was obtained by simple solid-state reaction and selective etching process.Then,FePc/Ti3C2Tx hybrids were successfully obtained by coupling Ti3C2Tx with FePc.The structural changes of the composites before and after compounding were analyzed by means of electron microscopy,X-ray diffraction and infrared spectroscopy.?2?After introducing Ti3C2Tx support,the FePc/Ti3C2Tx catalyst exhibits two-fold and fve-fold ORR acyivity higher than that of FePc and commercial Pt/C by introducing Ti3C2Tx respectivity,and even exceeded most of the reported Fe–N–C catalysts.In addition,its turnover frequency?TOF?is also accelerated to four-fold than pure FePc,as well as the electron transfer numbers?n?and the yield of hydrogen peroxide have been significantly optimized.?3?Since Ti3C2Tx possesses rich surface terminations,including hydroxyl and fluorine,they can interact with four-coordinated Fe?II?and weaken Fe–N bonding when FeN4 moiety adheres to Ti3C2Tx surface.The electronic structure of the active sites of catalysts was studied by means of spectroscopy and magnetic measurement.The results reveal that this interaction leads to remarkable Fe 3d electron delocalization and spin-state transition of Fe?II?ions.Particularly,the local electron density of FeN4moiety greatly redistributes,and more unpaired d electrons are generated through a change in electron configuration from dxy2dyz2dxz1dz21 to dxy2dyz1dxz1dz21dx2-y21,yielding an easier dioxygen adsorption and reduction.