Preparation And Electrocatalytic Performance Of Pd/TM@TM_xO_y-rGO (TM=Ni, Co, Mn) Composite Structure Materials

Direct methanol fuel cells?DMFC?have been extensively studied recently because of their simple operation,low pollution,and high energy density.Among all the components of DMFC,anode catalysts cost the most and play a significant role in the development of DMFC.Pt-based and Pd-based catalysts have become the most popular anode catalysts.However,high cost and worse poisoning resistance confine their development and application.Pd-based catalysts have better poisoning resistance than Pt-based ones under alkaline condition.Therefore,lots of works are focus on Pd-based catalysts.In this paper,the core-shell transition metal modified reduction graphene oxide loading Pd nano-short chain is studied.The reducing agent are sodium borohydride?NaBH₄?,N,N-dimethylformamide?DMF?and glucose,and the obtained catalysts are represented as Pd/TM@TM_x O_y-rGO?B?,Pd/TM@TM_x O_y-rGO?D?and Pd/TM@TM_x O_y-rGO?G?,respectively.The strong reducing agent NaBH₄ is used as a reducing agent,the transition metal of core-shell structure is modify on the surface of the reduced graphene oxide by hydrothermal and high heat treatment.The Pd nano-short chain is reduced by photochemical reduction,then the Pd/TM@TM_x O_y-rGO?B??TM=Ni,Co?composite catalyst with core-shell structure was obtained.Due to the core-shell structure,the specific surface area of the graphene has increased,thereby the Pd nano-short chain is well dispersed on the surface of the transition metal modify reduced graphene oxide.The experimental results show that Pd/Co@CoO-rGO?B?and Pd/Ni@NiO-rGO?B?catalysts have good activity and stability for catalytic oxidation of methanol.Compared with commercial Pd/C,the catalytic activity of Pd/Co@CoO-rGO?B?,Pd/Ni@NiO-rGO?B?and Pd/rGO?B?was increased 7.01,5.2 and 3.39 times,respectively.The best activity of Pd/Co@CoO-rGO?B?has increased 1.5 times compared with commercial Pt/C.The core-shell transition metal modify reduced graphene oxide was prepared with hydrothermal and high temperature treatment by using a weak reducing agent glucose as reducing agent,and then Pd nano-short chain was loaded onto the composite by photochemical reduction,then got the Pd/TM@TM_x O_y-rGO?G?composite catalyst.Combined with SEM,TEM,XRD and Raman tests,results display that Mn@Mn₃O₄,Ni@NiO,Co@CoO particles are uniformly modify on the surface of graphene,and Pd nano-short chains have no obvious agglomeration.Electrochemical test results show that Pd/Mn@Mn₃O₄-rGO?G?,Pd/Ni@NiO-rGO?G?and Pd/Co@CoO-rGO?G?have good catalytic activity and stability.And the Pd/Mn@Mn₃O₄-rGO?G?catalyst has highest catalytic activity,which is 6.28 times than that of the commercial Pd/C catalyst.The weak reducing agent NaBH₄ is used as a reducing agent,the transition metal of core-shell structure is modify on the surface of the reduced graphene oxide by hydrothermal and high heat treatment,and the Pd nano-short chain is reduced by photochemical reduction,then the Pd/TM@TM_x O_y-rGO?B??TM=Ni,Co?composite catalyst with core-shell structure was obtained.The results of TEM and SEM show that the transition metal is indeed modify on the surface of graphene in the form of core-shell structure,and the Pd nano-short chain is evenly distributed on the graphene sheets.The electrochemical properties of the catalysts were carried out.The results show that Pd/Ni@NiO-rGO?D?and Pd/Co@CoO-rGO?D?catalysts have high activity for methanol catalysis,and increased 2.83 and 2.77 times than commercial Pd/C.The results show that the Pd/Co@CoO-rGO?B?catalyst reduced by NaBH₄ can achieve methanol electrocatalytic activity up to 1786 mA/mg,while the elctrocatalytic activity for Pd/Co@CoO-rGO?G?catalyst reduced by glucose was only 695 mA/mg,and the Pd/Co@CoO-rGO?D?catalyst reduced by DMF had an electrocatalytic activity of 717 mA/mg for methanol.This indicates that different reducing agents have different reduction degrees for the same transition metal.Among the catalysts reduced by NaBH₄,Pd/Co@CoO-rGO?B?shows best activity.Among the catalysts reduced by DMF,Pd/Ni@NiO-rGO?D?is the best.Among the catalysts reduced by glucose,Pd/Mn@Mn₃O₄-rGO?G?is the promising one.This indicates that the reducing agent has a great influence on the growth of the metal particles.In this paper,to deal with the issues of easy agglomeration and poor stablity for fuel cell catalysts.TM@TM_x O_y modified rGO introduced can not only induce the anchoring site of nanaopartides,but also enhance the electron effect of support and noble metal particles.