Preparation And Properties Of Non-metallic Oxygen Reduction Catalysts

The exhaustion of fossil fuels and the deterioration of the ecological environment have inspired us to develop new types of clean energy.Fuel cells have the advantages of high energy density and clean and environmental protection,and are considered the most likely to be commercialized.In addition,hydrogen peroxide（H₂O₂）is also a green oxidant and has great potential in chemical production.The main problems that limit the large-scale commercialization of fuel cells and H₂O₂ are the expensive Pt-based catalysts and the complicated H₂O₂ synthesis process and high energy consumption.In order to solve the above two problems,it is urgent to develop metal-free oxygen reduction reaction catalysts instead of Pt-based catalysts.However,H₂O₂can be produced through a 2-electron oxygen reduction reaction route.Therefore,metal-free oxygen reduction reaction catalysts have become the focus of research.The article focuses on the selection and preparation of oxygen reduction reaction catalyst,ORR catalytic performance and reaction pathways.It mainly includes the following aspects:In this paper,benzimidazole phosphate ionic liquid[HBimi]DHP was prepared by the reaction of benzimidazole rich inπ-electron aromatic ring with phosphoric acid,which was used as precursor and calcined at high temperature to obtain N,P co-doped carbon catalyst for oxygen reduction reaction.The effect of pyrolysis temperature on the electrochemical performance was studied.The results showed that the electrochemical performance was the best at 900℃in N₂ atmosphere.The initial potential(～1.00 V_RHE)and half wave potential(～0.81 V_RHE)were higher than those of[Hmim]DHP,and the initial potential was close to commercial Pt/C.The results of RDE and RRDE indicated that oxygen reduction reaction is a 4-electron pathway.XPS and TEM results confirmed the effective doping of N and P elements.The high catalytic activity is mainly due to the presence of moreπ-electron groups in the precursor.The presence of aromatic rings promotes the redistribution ofπ-electrons,which helps to improve ORR catalytic performance.Using biomass waste litchi shells as the precursor,N and P co-doped carbon material with high surface area was synthesized.The results showed that the catalyst(C₉₀₀)obtained by calcination in N₂ atmosphere at 900℃has the best electrochemical performance.The initial potential was as high as～0.98 V_RHE.When XC-72 was loaded,the catalytic performance was significantly improved.The limiting current was increased from 2.5 m A cm^-2 to 3.7 m A cm^-2.The stability test results showed that C₉₀₀ and C₉₀₀/XC-72 show more than 90%initial current after 3600 s continuous operation.Both of RDE and RRDE test results indicated that the oxygen reduction reaction is a 2-electron pathway,which can produce H₂O₂.The BET surface area and total pore volume of C₉₀₀ were 693.3 m² g^-1 and 0.405 cm³ g^-1.TEM energy spectrum indicated uniform doping of N and P elements.