Preparation Of Three-dimensional Graphene Cobalt Sulfide Composite Material And Exploration Of Its Oxygen Reduction And Total Hydrolysis Properties

The three-dimensional graphene material has broad application prospects in the field of electrocatalysis due to its high specific surface area,fast electron transport rate and low density.However,due to the poor catalytic performance of the simple graphene material,it is usually combined with transition metal materials or non-metal element to obtain three-dimensional graphene composite material with synergistic enhancement of catalytic performance.This three-dimensional graphene composite has become an ideal material for building next-generation energy storage and conversion devices such as supercapacitors,batteries and fuel cells.Among them,oxygen reduction reaction?ORR?is a key reaction of many energy conversion devices,which plays a decisive role in the performance of these devices.At the same time,electrocatalytic overall water splitting as a promising hydrogen production method has also been extensively studied.Therefore,this paper mainly explores the preparation of composite materials of three-dimensional graphene and cobalt sulfide and its application in oxygen reduction and total hydrolysis.It mainly includes the following two aspects.Firstly,melamine foam is used as template to obtain porous sulfur and nitrogen-codoped graphene/carbon foam with uniformly distributed cobalt sulfide nanoparticles(Co_1-xS/SNG/CF)which is prepared by a simple infiltration-drying-sulfuration method.It is noteworthy that melamine foam not only works as a three-dimensional support skeleton,but also provides a nitrogen source without any environmental pollution.Such Co_1-xS/SNG/CF catalyst shows excellent oxygen reduction catalytic performance with an onset potential of only 0.99 V,which is the same as that of Pt/C catalyst?Eonset=0.99 V?.Furthermore,the stability and methanol tolerance of Co_1-xS/SNG/CF are more outstanding than those of Pt/C catalyst.Our work manifests a facile method to prepare S and N-codoped 3D graphene network decorated with Co_1-xS nanoparticles,which may be utilized as potential alternative to the expensive Pt/C catalysts toward ORR.Secondly,the design and development of highly efficient and durable non-precious metal catalysts are of great significance for the HER and the OER,especially bifunctional catalysts for overall water splitting.Here,a series of novel composites of 3D nitrogen-doped graphene foams with homogeneously dispersed CoS_1.097 nanoparticles?NPs?are synthesized through hydrazine-induced foaming and thermal-treatment process at different temperatures.Notably,the composite thermally treated at 750?(CoS_1.097/NGF-750)which possesses continuous 3D porous structures exhibits super-hydrophilic properties and ultrahigh catalytic activity,providing a current density of10 mA cm^-2 at a low overpotential of 240 mV for the OER and 124 mV for the HER,respectively.In addition,a self-supported two-electrode electrolyzer assembled using CoS_1.097/NGF-750 as both the cathode and anode exhibits the current densities of 10 and20 mA cm^-2 at potentials of 1.56 V and 1.65 V,respectively,and long-term stability?95%of the activity remained after 45 h?.Furthermore,this novel catalyst can be produced on a large scale;therefore it could be promising for practical applications in overall water splitting.