Preparation And Bifuntional Electrochemical Performance Research Of Pd/NiMo(NiCr)/C Nano Electrocatalysts

Among the many electrochemical new energy technologies,rechargeable fuel cells and metal-air secondary batteries have attracted much attention because of their cleanliness,environment-friendly and high energy conversion rates.Oxygen reduction(ORR)and oxygen precipitation(OER)are the key electrode reactions that occur at the oxygen electrode when they are discharged and charged.The high overpotential,slow kinetic characteristics of the ORR and OER processes are key causes of energy efficiency and power degradation of them.Therefore,it is important to study a bifunctional catalyst with both high ORR and OER electrocatalytic activity.Pt and its alloy catalysts are currently recognized as highly active ORR catalysts,and Ru-based and Ir-based catalysts are excellent highly active OER catalysts.Pt + Ir or Ru multicomponent catalysts are good to achieve efficient dual-function of electrocatalytic ORR&OER.Considering that resources of Pt,Ru,Ir are rare and expensive,how to reduce its precious metal load or use alternative elements is the direction of scientific research efforts.In this paper,Pd/NiMo/C and Pd/NiCr/C,which are low precious metal loading bifunctional oxygen electrode electrocatalysts,are designed and prepared by using the NiMo or NiCr component as the OER activity center,and then loading a small amount of Pd noble metal(the price is relatively cheap for Pt)as the ORR activity center.In this paper,different Pd/C catalysts in different carbon carriers(biochar,template carbon,graphene oxide,and oxidized commercial conductive carbon black),which were prepared by ethylene glycol back-flow method,were investigated.Based on the characterization of the morphology and electrochemical properties of the materials,we can find that the commercial conductive carbon blacks through the deal of oxidation is optimal for the carbon base of the noble metal.This is mainly because of the high degree of graphitization of commercial carbon that contributes to the high electron transfer capacity,and the oxide-treated surface-rich oxygen-containing functional groups that contributes to subsequent metal ion adsorption and uniform loading of metal ions,which has been proved by XRD and HRTEM test.Then,a series of Pd/NixCry/C catalysts were prepared and the optimum NiCr ratio was determined.The results show that the electron transfer number of Pd/Ni19Cr1/C catalytic oxygen reduction is 3.79.The ratio about the transfer process of four electrons is as high as 94%.And its starting potential and half-wave potential about ORR were-0.023 V(vs.SCE,same below)and-0.116 V,respectively.The half-wave potential is more positive compared to the commercial Pt/C and commercial PtRu/C.For the OER reaction,its electrocatalytic oxygen current density at 0.7 V is 7 times for the commercial Pt/C and 3 times for the commercial PtRu/C,respectively.In this paper,we studied in detail if the preparing condition in the preparing process of Pd/NiMo/C about the non noble metal NiMo loading method(hydrazine hydrate reduction method and impregnation-hydrogen thermal reduction method),NiMo content,hydrogen reduction temperature and noble Pd content on the Pd/NiMo/C catalyst,affected the morphology and electrochemical properties of the catalyst.XPS indicates that the interaction between NiMo and the noble metal leads to the change of the electronic structure of the Pd surface,which shows the higher catalyst oxygen reduction activity in the electrochemical test.On the other hand,Pd/NiMo/C has limited exposure to non-noble metal NiMo alloy and its oxides,which improves the oxygen evolution and anti-methanol poisoning of the catalyst to a certain extent.Moreover,the Pd loading on NiMo improves the surface utilization of Pd.The half-wave potential of the best catalyst Pd/Ni4Mo1/C is 0.13 V,whic is 36 mV higher than Pt/C half-wave potential whose precious metal load is twice than its.For the OER process,NiMo @ Pd/C has an 5.5 times oxygen current density of commercial Pt/C at 0.7 V and 2.7 times of commercial PtRu/C(its noble metal load is three times as Pd/NiMo/C).In this paper,the Pd/NiMo/C bifunctional catalyst with high activity,anti-poisoning and low precious metal load is designed to reduce the energy loss and cost of rechargeable fuel cell and metal air battery.