Energy Storage And Conversion Performance For Co/Ni-Based Nanomaterials

Due to the increasing exhaustion of traditional fossil resource and the deterioration of global environment,the conversion and storage of clean new energy has become a hot research topic.As an energy storage device,supercapacitor has been widely studied because of its high power density,long cycle life and fast charge and discharge capacity.Electrode material has a great influence on the overall supercapacitor performance.In addition,electrocatalytic water splitting is an effective way to obtain clean hydrogen energy.The catalytic performance of the electrocatalyst plays a crucial role in catalytic efficiency.In this paper,a series of Co/Ni based nanocomposites were prepared on the foam nickel and graphene substrates,and then the supercapacitor and electrocatalytic water splitting performance were studied.The specific studies are as follows:(1)A series of Ni0.37Co0.63S2-Reduced Graphene Oxide nanocomposites with different graphene contents(NCS@rGO-x)has been successfully prepared via a facile one-step hydrothermal method.The transmission electron microscopy results revealed that the morphology and size of transition metal sulfides change with the content of graphene.The research results of the electrocatalytic water oxidation and the photocatalytic degradation of methylene blue showed that the catalytic performance of the catalyst was also greatly dependent on the content of graphene.On the one hand,a stable current density of 10 mA/cm2 at a small overpotential of ~276 mV(vs.RHE)could be obtained for the optimum sample in electrocatalytic water oxidation process.The outstanding catalytic activity is mainly due to its unique three-dimensional structure and high electrical conductivity.On the other hand,the optimal sample also showed excellent photocatalytic degradation performance for methylene blue.(2)Homologous Ni/Co-based overall water splitting catalyst has been fabricated by a low temperature hydrogenation treatment and subsequent facile chemical bath deposition process.The direct hydrogenation treatment catalyst(H-NiCo)consists of crystalline Ni/Co alloy core and amorphous nickel cobalt oxide shell around 5nm exhibits excellent catalytic activity for hydrogen evolution in 1M KOH.Then the OER catalyst(H-NiCo@FeOOH)with excellent performance is synthesized by the growth of ultrathin,amorphous and interconnected FeOOH nanosheets on hydrogenated Ni/Co nanorods through chemical bath deposition.In electrocatalytic oxygen evolution process,a low overpotential of 278 mV is required to achieve a current density of 10 mA/cm2,and the Tafel slope is only 47.5 mV/dec.When integrated in an alkaline electrolyzer,a full water splitting current density of 10 mA/cm2 can be obtained at 1.65 V.(3)Three-dimensional(3D)hierarchical NixCo1-x O/NiyCo2-yP@C(denoted as NiCoOP@C)hybrids have been successfully prepared by a phosphorization treatment of hierarchical Nix Co1-xO@C grown on nickel foam.The resulting NiCoOP@C hybrids exhibited excellent supercapacitor performance such as long cycle life and high specific capacitance due to the synergistic effects of NixCo1-xO and NiyCo2-yP and the 3D hierarchical structure.Then an asymmetric ultracapacitor(ASC)was assembled through using NiCoOP@C hybrids as positive electrode and activated carbon as negative electrode,respectively.The as-prepared ASC obtained a maximum energy density of 39.4 Wh/kg at a power density of 394 W/kg and still holds 21 Wh/kg at 7500 W/kg.The experimental results showed that the NiCo OP@C hybrids as electrode material have great pratical application prospect for supercapacitors.