Synthesis And Application Of Core-Shell Structure Nano Electrocatalysts Loaded On Reduced Graphene Oxide

Recently,researchers pay more attention on fuel cell and the involving center electrochemical reactions.The direct ethanol fuel cell as the represent of fuel cell,and the related reactions as oxygen reduction reaction(ORR),oxygen evolution reaction(OER)and ethanol oxidation reaction(EOR)have getted achievement gradually,but the activity and cost of electrocatalyst are still the limiting factors of their development.This article aims to synthesis core-shell structure electrocatalysts,based on the high activity of nobel metals,the electronic effect and geometric effect between nobel metals and transition metals.Then the as-prepared electrocatalysts are studied on element analysis and characteristic tests,then in application on ORR,OER,EOR and the anode of DEFC.We hope researchers can draw inspiration for development of catalyst of high activity and low cost from this article.We synthesized the electrocatalyst named Ni@Au@Pd-rGO that contains Ni as the core,Au as the interlayer and Pd as the shell,with reduction graphene oxide(rGO)loaded,through the in-situ reduction replacement method.By the similar way,we also synthesized another electrocatalyst named Co@Pd-rGO with Co as core and Pd as shell.Ni@Au@Pd-rGO and Co@Pd-rGO were applied on ORR,OER,EOR and DEFC as the anode catalyst.There are mostly Ni,Au,Pd metal existing in Ni@Au@Pd-rGO,but also a little Au Pd alloy and Ni-Au solid solution.Ni@Au@Pd-rGO has high performance as the bifunctional catalyst in ORR and OER.In ORRs,the onset potential(E_onset)and limiting current density are 0.961 V vs.RHE and 5.6 m A/cm².Accroding to the K-L plots,the ORR catalyzed by Ni@Au@Pd-rGO is a 4-electron transfer process.In OERs,the E_onset is 1.5663 V vs.RHE which is the lowest potential,companying the lowest overpotential and Tafel slope,which are 0.52 V and 0.180 V/decade,respectively.In EOR test,the E_onset of Ni@Au@Pd-rGO moves to lower potential,is-0.5 V vs.MMO,and the peak current density is as high as 11.85m A/cm².Ni@Au@Pd-rGO has good stability in i-t test.At optimum operation temperature80?,Ni@Au@Pd-rGO owns the highest open-circuit voltage and power density,are 0.62V and 126 m W/cm² as the anode catalyst in DEFC.These results indicate that Ni@Au@Pd-rGO with high property is a potential catalyst in DEFC.Co@Pd-rGO is as wonderful as Ni@Au@Pd-rGO in ORRs and OERs.In ORRs,the E_onset and half-wave potential are positive.The current density is as high as 5.22 m A/cm²,and the whole process confirms to first-order kinetic equation and is a 4-electron transfer process.In OERs,the overpotential and Tafel slope are 0.263 V and 0.138 V/decade,which are the lowest.The conclusion is that Co@Pd-rGO is a promising bifunctional electrocatalyst in ORRs and OERs.In EOR test,Co@Pd-rGO is better than Ni@Au@Pd-rGO.Its E_onset is at-0.6 V/vs.MMO,and the peak current density is 18.99 m A/cm².In addition,the value of I_F/I_B is 1.055,indicating the wonderful ability to resistant to toxication.When as the anode catalyst in DEFC at 80?,Co@Pd-rGO owns the highest open-circuit voltage and power density,are 0.71 V and 231.9 m W/cm².The high properties of Ni@Au@Pd-rGO and Co@Pd-rGO in ORR,OER,EOR and DEFC are due to the electronic effects and geometic effects between metals.Furthermore,the advantages of rGO and core-shell structure also play a significant role.