Prussian Blue Analogue-assisted Preparation Of Bifunctional Carbon Catalytic Materials For Zinc-air Batteries

Serious environmental crisis and growing energy demand have prompted people to pursue renewable energy equipment.Among many energy storage/conversion systems,rechargeable zinc-air batteries（ZABs）are considered to be one of the most promising candidates for next-generation advanced energy devices owing to their high energy density,low cost,environmental protection and excellent safety.However,due to the slow kinetics of oxygen reaction,the charge-discharge process of ZABs must be catalyzed by bifunctional catalysts that are active for both oxygen reduction and oxygen evolution reaction.Although precious metal-based materials are considered as the benchmark catalysts for ZABs,their high cost and limited resources seriously hinder their potential applications.Therefore,it is very important to design and develop highly active bifunctional oxygen electrocatalysts with cost advantages.Among various non-noble metal catalysts,transition metal nitrogen-doped carbon component（M-N-C）has been proved to be an ideal electrocatalyst due to the synergistic effect between metal and nitrogen,porous structure and graphite carbon.However,they still have problems such as uncontrollable structural uniformity,uncontrollable pore structure,and low density of active sites.As a representative material of Metal-Organic Frameworks（MOFs）,Prussian blue derivative（PBA）has become a suitable precursor for the preparation of M-N-C materials due to its porous three-dimensional structure,high stability and wide variety.The high-density M-N_x sites contained in the precursor are the key factors for deriving bifunctional catalysts.However,the N and C contents of PBA calcined products are low,and the exposed active sites are less.It has been reported that the construction of composite catalysts is one of the effective strategies for the preparation of PBA-based bifunctional catalysts.Therefore,in this paper,a PBA precursor Co₃[Co（CN）₆]₂ was prepared by hydrothermal method,and three bifunctional electrocatalysts were constructed with Mn,Bi and P successively.Firstly,Co₃[Co（CN）₆]₂ was combined with metal salt Mn,carbon powder（Vulcan XC-72R）and melamine to prepare Co Mn-PBA/NC by pyrolysis,which was used for the study of ZABs.Then,Mn was replaced by Bi and the composite electrocatalyst Co Bi-PBA/NC was obtained by high temperature carbonization,which was used to drive ZABs.Finally,Co P-PBA/NC was obtained by coupling non-metallic P with PBA,and used as an electrode material to study the performance of ZABs.The three catalysts have good bifunctional catalytic activity and perform well in ZABs.The specific research contents are as follows:Part I:Preparation of Co,Mn composite nitrogen-doped carbon materials and application of zinc-air batteryMn is widely used as a dopant due to its large radius and low electronegativity,which can weaken the strength of Co-O bonds and promote the formation of lattice defects.Therefore,C₄H₆Mn O₄·4H₂O was used as Mn source,which was combined with Co₃[Co（CN）₆]₂,Vulcan XC-72R（C source）and melamine（N source）by stirring and ball milling,and was then pyrolyzed at high temperature in a tube furnace to produce Co Mn-PBA/NC.Meanwhile,optimized pyrolysis temperature and molar ratio of PBA to C₄H₆Mn O₄·4H₂O were used to obtain target catalysts with excellent performance.The catalyst shows good bi-functional catalytic activity,with a half-wave potential（0.859 V）similar to Pt/C and a potential of 1.901 V at 10 m A cm^-2.The peak power density of 101.83m W cm^-2 can be achieved by using it as cathode catalyst for ZABs.Part II:Preparation of Co,Bi composite nitrogen-doped carbon materials and application of zinc-air batteryAs an environmentally friendly and inexpensive element,Bi can improve the overall oxygen vacancy mobility of catalysts,which is a promising electrode material.Therefore,（Bi NO₃）₃·5H₂O was used as a Bi source,which was carbonized after composite with PBA,N and C materials to prepare Co Bi-PBA/NC.During the experiment,the optimum conditions for the preparation of target catalyst were determined to be the pyrolysis temperature of600℃and the mass ratio of Co₃[Co（CN）₆]₂ to（Bi NO₃）₃·5H₂O of 1:1.The catalyst shows good half-wave potential（0.843 V）and overpotential（707 m V）,and displays open circuit voltage of 1.54 V and peak power density of 71.80 m W cm^-2 in ZABs.Part III:Preparation of Co,P composite nitrogen-doped carbon materials and application of zinc-air batteryThe binding of negatively charged P to the transition metal can limit electron delocalization of the metal,resulting in co-valence and ionic characteristics of the M-P bond.At the same time,P can also reduce the energy gap of molecular orbitals,which plays an important role in electrocatalysis.Therefore,Co P-PBA/NC can be prepared by using triphenylphosphine as P source and introducing it into PBA by ball milling.In addition,by changing the calcination temperature in the preparation process and adjusting the ratio of PBA and P,bifunctional catalysts with good performance can be obtained.Moreover,ZABs driven by the catalyst have an open-circuit voltage of 1.62 V,a peak power density of 119.33m W cm^-2,and a specific capacity of 924.86 m Ah g _Zn^-1(10 m A cm^-2).