Phosphorus-induced Cobalt Based Oxide Coupling To 3D Carbon For Zn-air Batteries

With the increasing energy crisis and serious environmental pollution,a large number of researchers are committed to making efficient use of renewable energy by developing conversion and energy storage technologies.Energy conversion technology based on a rechargeable Zn-air battery(RZAB)has been increasingly studied because of its high theoretical energy density,high safety and low manufacturing cost.However,the energy conversion efficiency of this technology is limited by the slow oxygen reduction reaction/oxygen evolution reaction(ORR/OER)on the air electrode.In addition,most of porous carbon electrodes made by research inevitably have to decompose and reconstruct the catalyst,which leads to low energy utilization efficiency.Therefore,there is an urgent need to design and synthesize highly efficient and mechanically integrated bifunctional electrocatalysts for electrochemical energy devices.Studies have shown that the biomass derived carbon materials retain the cross-linking network and natural ion transport channel,which is conducive to the construction of the three-phase interface structure,promote the efficient mass transfer and conduction of oxygen electrocatalysis,thus improve the energy conversion efficiency of equipment such as metal-air batteries and fuel cells,which is worthy of in-depth study.In this thesis,we rationally designed the strategy of surface phosphorus atom induction,improved the activity of in-situ synthesized three-dimensional(3D)air cathode,and systematically studied the effect mechanism of heteroatom induction on catalytic performance.The specific work is as follows:(1)Using paulownia wood as 3D carbon substrate,the surface phosphorus-induced CoO nanoparticles embedded in paulownia wood carbon plate(P-CoO@PWC)were directly used as 3D air cathode by carbonization,evaporation induction,low temperature oxidative phosphating and so on.By controlling the phosphating time,a series of P-CoO@PWC catalysts induced by phosphorus atoms were obtained.The activity evaluation showed that the P-CoO@PWC-2 with 2.26%phosphorus content had the best catalytic performance.The prepared electrode exhibits remarkable catalytic activities for both ORR and OER with a small overpotential gap(EOER-EORR=0.68 V).At the same time,the catalytic stability and methanol tolerance of the catalyst are better than those of 20%Pt/C and RuO2.The 3D electrode of P-CoO@PWC-2 used in aqueous or solid-state Zn-air battery has excellent specific power,low charge-discharge voltage gap(0.84 V)and long-term cycle stability(700 cycles).(2)On the basis of exploring the optimal phosphating time in the first chapter,we designed a more convenient and green method to synthesize phosphorus-induced CoMnO spinel nanoparticles anchored on paulownia wood carbon plate(P-CoMnO@PWC)and directly used as 3D air cathode.The strong coupling between P-CoMnO and PWC promotes the multiphase charge transfer process.At the same time,the conductive carbon network contributes to the overall stability by protecting P-CoMnO from corrosion and aggregation.Structural analysis shows that the structure has mesoporous morphology,and the low temperature phosphating does not destroy the cobalt manganese oxide spinel structure with a size of about 30 nm.Through the precise regulation of the electronic properties of CoMnO by phosphorus atoms,the efficient electrocatalytic activity of the catalysts was achieved.P-CoMnO@PWC families have multi-stage pore structure and rich edge defects.The nanocomposite exhibits better ORR activity(initial/half-wave potential 1.01/0.86 V)and high OER activity(300 mV under 10 mA cm-2)than 20%Pt/C and RuO2.The catalytic stability and methanol tolerance of the nanocomposites are better than those of 20%Pt/C and RuO2.The water-based or solid-state Zn-air battery assembled with P-CoMnO@PWC family has an open-circuit voltage of 1.56 V and a peak power density of 160 mW cm-2,with a low charge-discharge voltage gap(0.80 V)and long-term cycle stability(1200 cycles).In summary,considering the feasibility of the integrated strategy of surface phosphating,we think that the combination of heteroatoms and non-precious metal oxides will arouse great interest in the rational design of new electrocatalysts.In addition,the strategy can be further extended to other 3D composites for different energy conversion and storage systems,such as other metal-air batteries,sodium ion batteries and supercapacitors.