Nickel Sulfide-Based Nanocomposites:Synthesis,Characterizations And Applications In Energy Conversion And Storage

As convenient,efficient and cost-effective renewable energy technologies,the photo-,electrochemical-based energy conversion and storage systems,especially the hydrogen generation and electrochemical energy storage techniques,have been regarded as a key to solve the new energy problems.Nickel sulfides have been widely used in electrochemical catalysis and energy storage applications due to their high electrical conductivity,high electrochemical activity,low-cost,and non-toxicity.However,the practical applications of nickel sulfides are still facing many problems.Therefore,in this dissertation,a variety of nickel based transition metal sulfide nanocomposites with special structure have been developed based on the design and modification of hetero-nanostructures.In addition,combining with various analysis and characterization methods,their practical application performances in photo-and electrocatalytic water splitting,supercapacitors,and sodium ion batteries are also investigated.The main research results of this study are listed as follows:?1?Based on the electroless plating process assisted by sodium hypophosphite,a hybrid photocatalyst consisting of ?-NiS modified CdS nanowires has been synthesized via a simple and green hydrothermal route using CdS NWs as the template.Such a technique facilitates the uniform and tight growth of co-catalyst(??-NiS?onto the CdS NWs.With the optimal loading amount of NiS,the obtained NiS/CdS NWs presents a record-high photocatalytic activity for H2 evolution in lactic acid aqueous solutions under visible light irradiation.Under the room temperature,the rate of H2 evolution is measured as 158.7 mmol h-1 g-1,which is nearly 250-fold higher than that over pure CdS NWs,and the apparent quantum yield reached an exceptionally high value of 74.1%at 420 nm,as well as high catalytic stability.The mechanism for the photocatalytic H2 evolution over the present NiS/CdS NWs is also proposed.This strategy would provide new insight into the design and development of high-performance heterostructured photocatalysts.?2?For the first time,NiS-MoS2 hetero-nanosheet arrays are directly constructed onto the carbon cloth via a one-step hydrothermal method by introducing sodium dodecyl sulfate as surfactant to control the systematic growth of NiS and MoS2.Benefiting from the well-exposed electroactive sites and numerous conductive channels for the fast transport of ions and electrons,the as-prepared NiS-MoS2 electrode exhibits excellent performance for electrochemical catalysis and energy storage.When used as a bifunctional electrocatalyst for overall water splitting,a current density of 10 mA cm-2 at a low cell voltage of 1.54 V can be achieved,superior to most of the recently reported noble-metal free electrocatalysts under similar conditions.Moreover,when used as positive electrode for aqueous supercapacitors,it shows a high areal capacity of 0.76 mA h cm-2,and the assembled flexible devices exhibit high energy density and power density.?3?A porous NiS/SnS2 core-shell heteronanowall arrays on carbon cloth are synthesized via controlling the cation-exchange reaction between Ni2+ions and Sn4+in SnS2 nanosheet arrays template.Such a hetero nano wall arrays shows high specific surface area to well expose the active sites,and the porous surface can facilitate the diffusion of electrolyte ions.In addition,due to the abundant hetero-interfaces between the in-situ grown NiS shell and SnS2 core,the charge transfer rate and redox activity of NiS are greatly elevated.Moreover,the inert SnS2 core can serve as an internal "skeleton" to prevent the decomposition and/or destruction of external redox active species.Consequently,the NiS/SnS2@CC delivers a ultrahigh specific capacity of 430.4 mA h g-1 at a current density of 1.16 A-1.Moreover,the all-solid-state flexible hybrid supercapacitors assembled with Fe2O₃/rGO negative electrode exhibit a very high energy density of 104.23 W h kg-1 at a power density of 301 W kg-1 with excellent cycling stability.?4?A novel coherent SnS2/NiS2 hetero-nanosheet arrays on carbon cloth is fabricated through a simple one-step solvothermal method by controlling the synchronous growth of SnS2 and NiS2.Such a unique heteronanosheet can trigger strong coupling effect between SnS2 and NiS2,and thus can markedly elevate electric conductivity and charge transfer rate for sodiation/desodiation reaction.Compared with pure SnS2,the Na+diffusion coefficient for such SnS2/NiS2 composite increases almost two orders of magnitude.In addition,the coherent integration of SnS2 and NiS2 also creates a strong restriction effect to reduce the aggregation and volume variation during the long-term cycling,keeping the integrity of the heterostructure with high stability.Thus,such a coherent hetero-nanosheet arrays,exhibits outstanding performance when used as the anode for sodium-ion battery,presenting a high reversible capacity?909.2 mA h g-1 of the fifth cycle at 200 mA g-1?,excellent rate capability?360 mA h g-1 at 5 A g-1?and satisfying.cycling stability.Such strategy to design and synthesis coherent heteronanostructures could offer an effectively alternative way for the development of advanced electrode materials for energy storage devices.