Construction Of Non-Precious Metal Bifunctional Electrocatalysts And Their Performance In Zinc-Air Batteries

The energy crisis and environmental pollution caused by the consumption of traditional fossil fuels have prompted people to vigorously develop clean and sustainable energy conversion technologies.Recently,rechargeable zinc-air batteries（ZABs）have been considered as promising energy storage devices due to their natural abundance,high theoretical specific energy density,and environmental friendliness.The oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）are crucial for the charge-discharge process of ZABs,determining their overall energy efficiency and cycle life.However,the slow kinetics and multiple complex processes involved in ORR and OER require highly active and durable electrocatalysts for practical applications.At present,noble metal Pt-based and Ru/Ir-based catalysts have shown good catalytic activities for ORR and OER,respectively.However,the high cost,natural scarcity and single catalytic activity seriously hinder its large-scale application.Therefore,it is of great significance to explore low-cost,highly active,and durable non-noble metal bifunctional electrocatalysts for rechargeable ZABs.In response to the above problems,based on the strategies of encapsulation confinement,dianion-induced electron delocalization,and aerophilic three-phase interface design,a series of non-precious transition metal-based catalysts were designed and constructed to explore the microstructure of the catalyst reaction interface.The structure-activity relationship with the catalytic performance further reveals the catalytic reaction mechanism.Finally,their performance in rechargeable ZABs were investigated.（1）A peapod-like Co Se₂@NC bifunctional electrocatalyst was successfully fabricated by confining Co Se₂ nanoparticles（NPs）to one-dimensional（1D）N-doped carbon（NC）nanorods based on a polyaniline encapsulation strategy.The electronic coupling role between Co Se₂ and NC was revealed via X-ray photoelectron spectroscopy and synchrotron radiation X-ray absorption spectroscopy.In situ Raman spectroscopy was conducted to examine the structure of Co Se₂@NC under the OER in an alkaline electrolyte.The Co Se₂@NC electrocatalyst exhibit superior activity towards the ORR(E_1/2=0.83 V)and OER(η=340 m V@10 m A cm^-2)in a 0.1 mol L^-1 KOH solution.The as-assembled rechargeable ZAB achieves a large peak power density of 137.1 m W cm^-2 and outstanding stability for 500 cycles at 10 m A cm^-2.The encapsulation of Co Se₂ NPs in the NC shells impedes their aggregation and corrosion during the ORR and OER processes.Experimental and DFT-based computational analyses assist in ascribing the outstanding bifunctional catalytic performance to the formation of N-Co Se₂ active sites.This study provides a convenient strategy for the construction of non-noble metal bifunctional catalysts,which may be used in zinc-air batteries and other sustainable energy conversion devices.（2）Guided by theoretical calculations,a bifunctional Ni(S_0.51Se_0.49)₂@NC catalyst was designed and fabricated using dianionic regulation strategy.Synchrotron radiation X-ray absorption spectroscopy and density functional theory calculations revealed that synchronous sulfidation and selenization can induce the electronic delocalization of N-Ni(S_0.51Se_0.49)₂ active sites to enhance the adsorption of*OOH/*OH intermediate for ORR/OER.In situ Raman spectroscopy revealed indicate that the partial N-Ni(S_0.51Se_0.49)₂ active species may be transformed into theβ-Ni OOH species under the harsh oxidation environment,which can potentially induce the oxygen evolution and resist the destruction of Ni(S_0.51Se_0.49)₂@NC.The Ni(S_0.51Se_0.49)₂@NC electrocatalyst exhibited bifunctional catalytic activity for the ORR（half-wave potential of 0.83 V）and OER(320 m V at 10 m A cm^-2).The rechargeable ZABs exhibited an open-circuit voltage of 1.46 V,a specific capacity of 799.1 m Ah g^-1,and an excellent stability for 1000 cycles.These findings provide a feasible strategy for developing low-cost and efficient non-noble metal multifunctional catalysts.（3）Based on the calculation of density functional theory（DFT）,a facile carbon dots（CDs）-assisted synthesis strategy was proposed to fabricate Co nanoparticles（NPs）embedded porous sponge with oxygen-containing active sites（P-Co@O-CS）for both ORR and OER.The hydrophilicity and aerophilicity of P-Co@O-CS are beneficial to O₂diffusion and mass transfer.The density functional theory calculations and experimental studies revealed that the Co-C-COC active sites modulates the local charge density,lowers the reaction energy barrier,and enhances the ORR/OER activity.The P-Co@O-CS-1000 displays superior bifunctional catalytic performance with a half-wave potential of 0.82 V for ORR and a small overpotential of 294 m V at 10 m A cm^-2 for OER in alkaline media.Moreover,the bifunctional P-Co@O-CS-1000 catalyst can drive the liquid ZABs with high peak power density(106.4 m W cm^-2),specific capacity(720.7 m Ah g^-1),and outstanding long-term cycle stability（over 750 cycles）,and exhibits potential feasibility in flexible all-solid-state ZABs.These findings provide new insights into the rational design of efficient bifunctional oxygen catalysts in rechargeable metal-air batteries.（4）Based on a simple and cost-effective method,the synthetic diamond catalyst was converted into high-performance highly graphitized carbon sheet-coated Fe Ni alloy catalyst（Fe Ni@GC-8）for ORR and OER.The bulk material with a large amount of carbon wrapped in Fe Ni alloy was dissected into a 2D lamellar structure with a high degree of graphitized carbon wrapped in an appropriate amount of Fe Ni alloy by high-energy ball milling and magnetic separation.The Fe Ni@GC-8 catalyst shows excellent bifunctional catalytic performance for ORR(E_1/2=0.81 V)and OER(η=310 m V@10 m A cm^-2)in alkaline medium.The assembled Fe Ni@GC-8 based rechargeable zinc-air battery has an open-circuit voltage of 1.43 V,a peak power density of 115.2 m W cm^-2,a specific capacity of 786.9 m Ah g^-1,and a cycle stability of more than 1200 cycles.In situ Raman test showed that the formation of Fe OOH and Fe（OH）₂intermediate promots the ORR of Fe Ni@GC-8 catalyst,and the formation ofβ-Ni OOH intermediate is conducive to the improvement of the OER performance of Fe Ni@GC-8 catalyst.The DFT results showed that the synergistic interaction of Fe*Ni@GC and Fe Ni*@GC active sites promotes the rapid adsorption/desorption capacity of oxygenated intermediates,thus enhancing the ORR/OER performance of Fe Ni@GC-8catalyst.As a green method,this study provides a new opportunity for low-cost and large-scale preparation and utilization of spent catalyst.