Modified Carbon-based Oxygen Functional Electrocatalyst:Preparation And Applications In Energy Conversion

With the increasingly serious environmental problems caused by the predatory exploitation of fossil fuels and combustion products,the development of new energy conversion technology is one of the important measures to realize the concept of green,economic,and sustainable development.Among them,hydrogen production by electrolysis of water and zinc-air batteries have attracted much attention as two typical energy conversion technologies that realize the mutual conversion between electrical and chemical energy,and the slow kinetic oxygen functional reaction(including OER and ORR)restricts the above two technologies to large-scale application of energy conversion technology.The development of efficient oxygen functional catalysts can effectively reduce the overpotential of OER and ORR,improve energy conversion efficiency,and solve the problem of slow oxygen functional reaction kinetics.Among many catalysts,carbon-based materials stand out in the field of energy conversion technology due to their wide-ranging sources,good electrical conductivity,diverse morphologies,and easy functional modification,and present broad application prospects.The construction of carbon-based oxygen functional catalyst,which is cheap and has excellent catalytic performance,is of great significance to promote the process of water splitting to produce hydrogen and the industrialization of zinc-air batteries.In order to reduce the cost of carbon-based oxygen functional catalysts and improve catalytic activity and stability,based on the analysis of existing research reports,this paper proposes modified strategies such as loading transition metals and their derivatives,heteroatom doping,and coating.The precise control of the surface microstructure of the material enriches the types of active sites,improves the versatility of the carbon-based oxygen functional catalyst,and obtains a series of excellent performance OER,ORR and OER/ORR bifunctional carbon-based oxygen functional catalysts,and explore the application of these materials in electrolyzed water and zinc-air batteries,the main research contents are as follows:(1)The nickel-iron phosphide(Ni2.3FeP3.4)was grafted on the carbon nanotube(CNTs)substrate by the hydrothermal method and the high-temperature pyrolysis phosphating method,and a kind of nickel-iron with a "shuttle" structure was prepared.Phosphide/carbon nanotube OER composite catalyst(Ni2.3FeP3.4/CNTs).Among them,CNTs act as a support for the growth of Ni2.3FeP3.4,so that Ni2.3FeP3.4 particles are uniformly dispersed and the active sites are fully exposed.The three-dimensional structure formed by CNTs entanglement can not only accelerate electron transfer,improve the conductivity of the catalyst,and accelerate the diffusion of electrolyte,but also can effectively prevent material deformation and structural collapse during the continuous precipitation of oxygen bubbles.The prepared Ni2.3FeP3.4/CNTs has good OER catalytic performance.When the current density is 10 mA cm-2 and 100 mA cm-2,the OER overpotential of Ni2.3FeP3.4/CNTs drops to 239 mV respectively and 282 mV(1 M KOH),the performance exceeds most literature reports and commercial Ir/C,RuO2 catalysts.Ni2.3FeP3.4/CNTs exhibits high-efficiency catalytic performance and good stability in electrolyzed water applications.(2)Using inert biomass as a carbon source,a three-dimensional nitrogen-doped porous graphitic carbon ORR catalyst(MS-NPC)was prepared by high-temperature pyrolysis.Among them,the nitrogen atom doping causes the surrounding carbon atoms charge rearrangement,creating abundant active sites for the catalyst;the large specific surface area promotes the full exposure of the active center;the loose and porous three-dimensional structure is conducive to the diffusion and transfer of OH-and O2;high degree of graphitization is conducive to accelerating electron transfer and enhancing the conductivity of the catalyst.The prepared MS-NPC not only has the ideal structure characteristics such as obvious graphite structure,large specific surface area(1483 m2 g-1),and rich nitrogen content(4.70%),but also the ORR catalytic performance has been greatly improved,and the ORR onset potential up to 0.985 V,limiting current density up to 5.8 mA cm-2(0.1 M KOH),has good stability and methanol and CO toxicity resistance,its performance exceeds most literature reports and precious metal catalysts.Density functional theory(DFT)calculations further reveal the electrocatalytic activity and potential catalytic mechanism of ORR,and the calculation results are consistent with the experimental rules.In addition,the primary liquid zinc-air battery assembled with MS-NPC as the cathode catalyst has superior performance,surpassing the precious metal Pt/C-based zinc-air battery,and shows certain application prospects in solid-state flexible zinc-air batteries.(3)The nickel-iron alloy(Ni3Fe)is anchored on the nitrogen-doped porous graphene(NPG)substrate by the hydrothermal method and the high-temperature phase transfer method.The surface folds and loose sponge-like network structure of the NPG are beneficial to dispersedly growth of NisFe alloy particles.It provides sufficient growth sites to effectively control the size of Ni3Fe alloy particles.At the same time,the two phases of NPG and NisFe alloy are closely combined to form a strong interfacial interaction and synergistic strengthening produces more active sites.The three-dimensional integrated structure of nickel-iron alloy/nitrogen-doped porous graphene composite material(Ni3Fe/NPG-1)has excellent OER and ORR performance.Under the current density of 10 mA cm-2,the OER overpotential of Ni3Fe/NPG-1 is 329 mV(0.1 M KOH),the ORR onset potential and half-wave potential are 0.874 V and 0.83 V,respectively,and the performance is comparable to commercial 20%Pt/C.In addition,the secondary liquid zinc-air battery assembled from Ni3Fe/NPG-1 exhibits the advantages of high open circuit potential,high energy density and good cycle stability,and shows good application prospects in secondary flexible all-solid-state batteries.(4)The iron-cobalt alloy(FeCo)is embedded in nitrogen-doped carbon nanotubes(NCNT)by high-temperature pyrolysis,and the outer surface of the nanotubes is further coated with a nitrogen-phosphorus-doped carbon layer(NPC).A new OER/ORR bifunctional catalyst(NPC/FeCo@NCNT)was prepared with novel structure:nitrogen/phosphorus co-doped carbon nano tubes embedded with iron-cobalt alloy.Among them,the synergistic effect by the heterogeneous interface between the alloy particles and the carbon nanotubes helps to accelerate the reaction kinetics;heteroatom doping can further optimize the oxygen adsorption energy and reduce the reaction energy barrier by changing the electronic structure of the carbon atoms.The structure is gradually optimized,and the bifunctional catalytic performance is gradually improved,so that the prepared NPC/FeCo@NCNT catalyst exhibits excellent OER/ORR bifunctional catalytic performance.When the current density is 10 mA cm-2,the OER overpotential of NPC/FeCo@NCNT is 339.5 mV(0.1 M KOH),and the ORR onset potential is 0.92 V.In addition,the catalyst has certain application prospects in secondary liquid and solid and flexible solid-state zinc-air batteries,and can be used in devices such as LED lights and electric models.All in all,this research proposes four new ideas for improving the catalytic performance of carbon-based oxygen functional catalysts,we systematically study the internal relations between the preparation conditions and the catalyst microstructure,the interaction between the components,and the catalytic performance.Based on high-efficiency,stable and cheap carbon material,we design and develop new oxygen-based functional catalysts and provide basic data and theoretical references,and further promote the application process of carbon-based oxygen functional catalysts from the laboratory to large-scale applications.