Preparation Of Oxygen Electrode Catalyst And Research On Its Electrocatalytic Performance

The development of the chemical industry has provided a variety of new materials and products for people’s basic necessities of life,and has also derived many new directions.Among these new directions,how to use renewable energy to produce green hydrogen and use hydrogen efficiently and safely has become a hot topic in recent years,driven by China’s“carbon peak”and“carbon neutrality”policies.It involves a variety of energy storage and conversion devices:energy storage devices-Zinc-Air batteries,hydrogen production devices-Water electrolysis equipment,and high-efficiency hydrogen devices-Hydrogen fuel cells.In these devices,the reaction kinetics of oxygen reduction（ORR）and oxygen precipitation（OER）reactions occurring at the cathode or anode are slow due to their complex multi-electron reaction processes,which are heavily dependent on precious metal catalysts such as Pt,Ru,Ir,etc.,resulting in high catalyst cost and hindering the development of corresponding energy devices.Therefore,the development of oxygen reduction and oxygen evolution catalysts with high activity and low cost is of great significance for hydrogen energy conversion devices.Aiming at the key core issues of the above energy conversion devices,this paper develops a series of ORR and OER catalysts with high activity and stability,such as Sb-SeNC,Ru-VO₂,FeSb-NC and Pt_ey/NC,and conducts in-depth research on their mechanism and device applications.The main contents and innovations are as follows:For the ORR catalysts in the cathode of Zn-Air battery,the dual-atom Sb-SeNC catalysis was synthesized by asorption-pyrolysis strategy.The fine structure of SbN₂C₂ and SeC₂ in Sb-SeNC was identified by X-ray absorption spectroscopy.The synergistic effect between them makes the Sb-SeNC catalyst reach a half-wave potential(E_1/2)of 0.865V in 0.1 M KOH.After 400 h continuous charging and discharging cycle,the voltage efficiency the Sb-SeNC+RuO₂-based liquid Zn-Air battery assembled with Sb-SeNC and RuO₂catalysts as cathode catalysts only decreased by 8.7%.In addition,at-40℃,the peak power density of the solid-state Zinc-Air battery assembled with Sb-SeNC reached 54.1 mW cm^-2,which was higher than Pt/C and Sb-NC.And after continuous discharge for 44 h under different currents,the voltage only attenuated 7.4%,demonstrating excellent low-temperature discharge performance.To solve the problem that catalysts need to be changed frequently in electrolytic water devises under different conditions（pH）,Ru-VO₂ catalyst with excellent overall water splitting（OWS）performance and stability at all pH conditions was prepared by hydrogen peroxide reduction method.The detailed experimental characterization shows that Ru-VO₂ has Ru nanoparticle（NP）and Ru-doped VO₂ composite structures.The acidic OER mechanism of Ru-VO₂follows the adsorption evolution mechanism（AEM）,which was identified by in situ Raman,TMA⁺labeling experiments and in situ DEMS.Using Ru-VO₂as anode and cathode catalysts,the Ru-VO₂||Ru-VO₂ two-electrode electrolyzer only need a splitting voltage of 1.515 V,1.540 V and 1.630 V(at 10m A cm^-2)in 0.5 M H₂SO₄,1 M PBS and 1 M KOH.Among them,under acidic conditions,Ru-VO₂||Ru-VO₂ two-electrode electrolyzer can operate stably for 125 h at 10 mA cm^-2,which is at the top list of acid bifunctional acid OWS catalysts.Subsequent density functional theory（DFT）calculations further revealed that the presence of Ru NP can break the hydrogen bonds formed between the active intermediates（*OH）adsorbed on Ru single atoms and the O atom in the VO₂ surface,thereby improving the OER activity.To solve the problem of high cost of cathode catalyst for proton exchange membrane fuel cell（PEMFC）,non-precious metal dual-atom FeSb-NC catalyst was prepared by adsorption-pyrolysis method.The coordination structures of Feand Sb were determined as FeN₄OH and SbN₄ by X-ray absorption spectroscopy.In 0.1 M HClO₄ and 0.1 M KOH,the E_1/2 of FeSb-NC reaches 0.795 V and 0.905 V respectively.The peak power density of PEMFC assembled with FeSb-NC catalyst reached 0.4 W cm^-2 under 1 bar H₂-Air condition.Similarly,the solid-state Zinc-Air battery assembled with FeSb-NC catalyst had a peak power density of 57.5 mW cm^-2 at-40℃,and also can discharge continuously for 30 h under different current densities.The DFT calculation further revealed the catalytic mechanism of SbN4 as a lateral coordination to enhance the ORR activity of FeN4OH.In order to solve the problem of poor performance in PEMFC when the cathode has low Pt loading(<0.1 A mg _Pt^-1),a new idea of using high specific surface area ORR catalyst to achieve low Pt in the fuel cell cathode was proposed.Pt_ey/NC catalyst with“Yolk-like”structure was prepared by using high specific surface area N doped porous carbon as support by ethylene glycol reduction method.The catalyst has a specific surface area of 2271 m² g^-1 and abundant mesoporous structure.The ICP results show that the Pt content of Pt_ey/NC is only 5.48 wt.%,which is about 1/4 of the Pt content in commercial Pt/C.Nonetheless,the E_1/2 of Pt_ey/NC is 10 mV higher than that of commercial Pt/C in 0.1 M HClO₄.In the PEMFC test,under the test condition of 2.5 bar H₂-O₂,the peak power density reached 1.15 W cm^-2 when the cathode loading was 0.075 mg _Pt cm^-2.It is equivalent to the peak power density of 40 wt.%Pt/C(1.22W cm^-2)with a cathode load of 0.2 mg _Pt cm^-2 under the same conditions.In addition,at a loading of 0.03 mg _Pt cm^-2,the mass activity at 0.9 V reached 1.63A mg _Pt^-1 and 1.10 A mg _Pt^-1 at 2.5 bar and 1.5 bar,respectively.The structure-activity relationship between the catalyst specific surface area,catalytic layer thickness,and fuel cell mass activity was further systematically analyzed.There is an approximately linear relationship between the specific surface area and the catalytic layer thickness,which makes the Pt_ey/NC catalyst assembly with a high specific surface area The PEMFC cathode Pt loading can be reduced to 0.03mg _Pt cm^-2,and the catalytic layer thickness reaches 6.7μm,while commercial Pt/C cannot form a continuous catalytic layer at the same loading.DFT calculations further revealed the influence of the carrier on the Pt（111）crystal face.When the adsorption site is close to the carrier,the ORR activity is the best,and the onset reaches 1.04 V,which is higher than the onset potential of the pure Pt（111）crystal face.（0.705 V）.This work provides a new idea for reducing the cathode Pt loading in PEMFC.