The Construction And Electrocatalyzed Performance Of Metal Oxides/Carbon Nitride-Based Materials

The development of fuel cells has always been concerned by the community since the1960s.Fuel cells,which possess special features of low operating temperature and zero emission,can efficiently convert chemical energy into electric energy with high energy density and high current density.However,the sluggish oxygen reduction reaction?ORR?in cathode obstructed their rapid development.As far as we know,noble metal-based materials?Pt and Pd?are still the state-of-the-art ORR catalysts.However,its high cost,scarce resources,and vulnerability to methanol poisoning have limited their widespread commercialization.Therefore,exploiting non-precious metal ORR electrocatalysts with high efficiency,low cost and good resistansis to methanol is an efficient and meaningful strategy for the widespread application of fuel cells.Transition metal oxides,which were widely used in electrocatalytic areas due to their advantages of abundant precursur reserves and low cost,have been considered as promising non-precious metal ORR electrocatalysts.However,pure transition metal oxides often exhibit ultra low ORR activity due to their low conductivity and shortage of active sites.Their ORR activity can be promoted by compounded with two-dimensional layered materials to expose more active sites.Graphitic carbon nitride?g-C₃N₄?has a typical two-dimensional layered structure similar to graphite.It is highly desirable in electrocatalytic reactions for the sake of abundant nitrogen content and excellent chemical stability.Hence,layered g-C₃N₄ is introduced to boost ORR activity of transition metal oxides.The specific contents of this paper are as follows:?1?NiO/g-C₃N₄ composites were successfully fabricated throught a two-step method.And the ORR catalytic performance was tested in O₂ saturated 0.1 M KOH electrolyte.The results showed that the NiO/g-C₃N₄-400 composites calcined at 400°C exhibited the best ORR activity with good stability and excellent resistance to methanol.RRDE test showed that the transferred electron number of NiO/g-C₃N₄-400 composites is 2.7 and the yield of H₂O₂?%?is higher than70%.This indicated that the ORR was dominated by the 2-electron path.Consuming a large overpotential to catalyze ORR is not optimistic.So,developing other metal oxides/carbon nitride composites to efficiently catalyze ORR cannot be put off.?2?Fe₂O₃/A-C₃N₄ composites were successfully fabricated by a simple calcination step,before which,two-dimensional carbon nitride?denoted as A-C₃N₄?alkalized by KOH and1-octyl-3-methylimidazolium tetrachloroiron?[Omim]FeCl₄?ion liquid were mixed formly to be further calcined.The ORR activity test in O₂ saturated 0.1 M KOH electrolyte showed that,0.5Fe₂O₃/A-C₃N₄-300 composites calcined at 300°C with the[Omim]FeCl₄ amount of 0.5 g,showed the best ORR activity with a limiting current density of 5.2 mA/cm².RRDE test showed that the number of transferred electron was 3.7,and the yield of H₂O₂?%?was less than 20%.In addition,0.5 Fe₂O₃/A-C₃N₄-300 composites had the good stability and excellent resistance to methanol.?3?The C dots/Co₃O₄ composites were prepared through a simple two-step strategy.Graphitic carbon nitride?g-C₃N₄?,cobalt nitrate hexahydrate and organic base of1,8-diazabicyclo[5.4.0]undec-7-ene were used as raw materials.The ORR test under O₂ saturated0.1 M KOH electrolyte showed that the limiting current density of the C dots/Co₃O₄ was 5.1mA/cm²,1.6 mA/cm² higher than that of the pure Co₃O₄ material.The RRDE test showed that the transferred electron number of C dots/Co₃O₄ composites was 3.8 and the yield of H₂O₂?%?was less than 15%.In addition,it possessed good anti-interference ability to methanol,and the residual current retention rate was as high as 85%after a long period of accelerated decay stability test.All of the electrocatalytic tests showed that the C dots/Co₃O₄ composites had excellent ORR catalytic activity.