Controllable Construction Of Graphene-based Hybrids And Their Electrocatalytic Performance

With the progress of human civilization,environment pollution and energy shortage in the contemporary world has become urgent issues,which imminently need new energy forms and new technologies.The fast development of nanomaterials and nanotechnologies promotes the progress of new technologies,which makes human society enter an era of new materials.Due to its excellent electronic transmission performance(electron mobility as high as 2 × 105 cm² V-1 s^-1),high specific surface area(?2630 m² g^-1 of theoretical value),as well as good mechanical and transparent property,graphene has caused great attention among researchers and common people,which shows strong application potential in various fields.However,due to the aggregation behavior of two-dimensional graphene,even if the graphene layers are loaded nanocatalysts,it still tends to face-to-face stacking,causing a large number of catalytic active sites sandwiched between the graphene layers and making them unable to be contacted by the reactant molecules,so that the catalytic performance is far from full play.Therefore,it is necessary to control the morphologies of graphene-based electrocatalysts.Reasonable design and simple preparation of graphene-based electrocatalysts with exposed active sites,can not only improve the catalyst utilization efficiency significantly,but also accelerate the reactant mass transfer in the process and improve the electrochemical reaction kinetics.In addition,the catalytic performance is closely related to the microstructure of size,composition and shape.The control and optimization of catalyst microstructure in the presence of graphene support will further enhance the activity and stability of graphene-based electrocatalysts.However,related research work is rare and deserve to be explored.Aiming at the above scientific problems,this paper reasonably design and simply prepare some highly active and durable graphene-based electrocatalysts,and they were applied into the direct alcohol fuel cell application with a high efficiency and a low cost.Moreover,this paper presents some new morphologies of graphene-based electrocatalysts with high efficiency,some new technologies of electrochemical in situ controllable preparation,and some new train thought of how to load the electrocatalyst with high stability.These will be an effective approach to improve the performance of graphene-based electrocatalysts,and provide a reference for other researchers.The detailed research is as follows:?1?Conventional stacking arrangement of rGO sheets makes the electrocatalysts confine between the rGO sheets and therefore catalytic active sites are not fully exposed.We report here a facile synthesis of vertically oriented open reduced graphene oxide?VrGO?through one-step cyclic voltammetric electrolysis of graphene oxide?GO?in the presence of Na₂PdCl₄,where GO and Na₂PdCl₄ are simultaneously electrochemically reduced and the resultant enough Pd nanoparticles sandwiching the rGO sheets are found to play a key role in enabling the rGO to vertically stand on the electrode.Without Pd nanoparticles or with low-loading amount of Pd nanoparticles results in a deposition of rGO parallel to the electrode.The vertical orientation of Pd/rGO nanoflake units brings the Pd/VrGO composite a remarkably enhanced catalytic activity toward methanol electrooxidation.The mass activity(620.1 A g^-1)of Pd/VrGO is 1.9 and 6.2 times of Pd/LrGO(331.8 Ag^-1)and commercial Pd/C catalyst(100.5 A g^-1).Furthermore,the Pd/VrGO catalyst shows excellent resistance to CO poisoning.?2?Although vertically oriented graphene-based hybrids represent an emerging class of electrocatalysts,its catalytic performance still need to be further improved.Herein,we report a vertically oriented reduced graphene oxide supported dealloyed Pd-Cu nanoparticle catalyst?PdCu/VrGO?synthesized by a facile cyclic voltammetric electrodeposition of GO in the presence of Na₂PdCl₄ and copper ethylenediamine tetraacetate.The structure and composition are characterized by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,Raman spectroscopy,and X-ray photoelectron spectroscopy.Meanwhile,the electrochemical properties are measured by cyclic voltammetry and chronoamperometry.The PdCu/VrGO catalyst exhibits excellent electrocatalytic activity towards methanol oxidation,with the mass activity of 762.8 A g^-1,which is 7.1 times that of a commercial Pd/C catalyst.In addition,PdCu/VrGO shows good chemical stability and superior tolerance to CO poisoning.?3?The limited active site exposure and the easy aggregation tendency result in unsatisfying catalytic activity and durability of metal nanoparticle-based electrocatalysts.Herein,we construct a completely open support of polyaniline-coupled vertically oriented reduced graphene oxide?PANI@VrGO?through a facile and green cyclic voltammetric electrodeposition approach,and Pd nanoparticles are crystallised upon in situ reduction to realize the full exposure and the tight immobilization.The structure and composition are characterized by electron microscopy,Raman spectroscopy,Fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopy.Cyclic voltammetry and chronoamperometry techniques reveal that the resulting hybrid exhibits high electrocatalytic activity?3.6 times that of a commercial Pd/C catalyst for methanol oxidation?and excellent catalytic durability.These results demonstrate that the hybrid is a superior electrocatalyst for large-scale application in direct alcohol fuel cells and the synthetic method offers a new avenue for building other highly active and durable nanoparticle-based catalysts.?4?We report the fabrication of a three-dimensional?3D?reduced graphene oxide-carbon nanotubes network?rGO@CNTs?by one-step electrodeposition and utilized as a highly efficient metal-free ORR electrocatalyst.Graphene oxide?GO?is used as a surfactant to well disperse pristine CNTs for the preparation of stable colloid GO-CNTs solution,and subsequently one-step electrodeposition to obtain 3D rGO@CNTs hybrid.The structure and composition are characterized by electron microscopy,X-ray diffraction,and Raman spectroscopy.Meanwhile,the ORR performance is tested through cyclic voltammetry,linear sweep voltammetry and chronoamperometry techniques,which shows high electrocatalytic activity and superior durability.The catalyst is modified onto the cathode electrode of microbial fuel cells,and the power density is much closer to that of commercial Pt/C catalyst,which shows a promising practical application.