Construction And Performance Study Of Manganese-based Oxygen Electrode Catalyst

The development of clean energy has significant influence on the sustainable development of society,which causes the hot research for clean energy conversion devices such as metal-air batteries and water splitting devices.However,their development is hindered by the slow kinetic process of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）on the oxygen electrode.Besides,the high cost of catalysts could not meet the market demand.Therefore,the research of ORR/OER catalysts with low cost and excellent performance has become one of the main challenges for the development of new energy conversion devices in the future.In this thesis,the high-abundance transition metal Mn is chosen as a raw material to construct a single-atom dispersed Mn-N_xembedded in nitrogen-doped amorphous carbon（Mn NC）ORR catalyst and a three-dimensional（3D）nano-flower-sphere structure with Mnⁿ⁺and Ti₆C_3.75doped into the Ni Fe layered double hydroxides(Ni Fe Mn LDH-Ti₆C_3.75)catalyst for OER.Their physical characterizations and catalytic performances are further systematically studied by modern spectroscopic microscopy technologies and electrochemical methods.The detail contents are as follows:（1）A Mn NC catalyst with atomically dispersed Mn-N_xembedded in nitrogen-doped amorphous carbon was constructed by a coordination-pyrolysis strategy.In this part,a Mn-N_x-containing complex precursor was synthesized by using the coordination reaction between phenanthroline and manganese nitrate,and then pyrolyzed to obtain the single-atomic Mn NC catalyst.Synchrotron radiation X-ray absorption spectroscopy（XAS）and X-ray photoelectron spectroscopy（XPS）demonstrated that the coordination reaction not only prevented the agglomeration of manganese-based precursors efficiently,but also ensured the formation of single-atom dispersed Mn-N_xspecies.At the same time,thanks to its large specific surface area(738 m²g^-1)and suitable mesoporous structure,Mn NC exhibited excellent ORR catalytic performance in alkaline media.Electrochemical tests presented that the ORR half-wave potential(E_1/2)of Mn NC catalyst was 0.86 V,which was comparable to that of 20 wt.%Pt/C.Besides,after catalyzing ORR for 20000 s at 0.57 V,the current density still retained 90.40%of the initial value.Furthermore,the Mn NC based Zn-air battery（ZAB）delivered excellent performance including a peak power density of 130.0 m W cm^-2and a specific capacity of 819.0 m Ah g _Zn^?1,as well as prominent durability which could continuously discharge for 60 h.All of the above performances for Mn NC based ZAB were superior to those of commercial Pt/C-based ZAB.（2）A Ni Fe Mn LDH-Ti₆C_3.75OER electrocatalyst with a 3D nano-flower-sphere structure was prepared by a simple and scalable one-pot hydrothermal method.Physical characterizations showed that the addition of Ti₆C_3.75could prevent LDH from aggregating and promoted the growth of LDH into a nano-flower-sphere structure,which was more conducive to mass transfer.XPS results and operando Raman tests showed that the presence of Mnⁿ⁺would modulate the Ni²⁺electron structure,forming an electron-rich state Ni²⁺,making it easier to adsorb oxygen-containing intermediates,thereby improving the OER catalytic performance.The OER overpotential of Ni Fe Mn LDH-Ti₆C_3.75at 10 m A cm^-2in 1 M KOH was only 210 m V.After 6000 cycles of accelerated aging test,the overpotential decreased by only 10 m V.All the above results proved that Ni Fe Mn LDH-Ti₆C_3.75showed excellent activity and stability towards OER.