The Preparation Of Transition Metal Phosphides-based Composites For The Performance Of Supercapacitors

Supercapacitors?SCs?have attracted extensively research interest due to their advantages such as fast charge and discharge,long lifespan,high power density,and good safety in use.However,the widespread use of supercapacitors has been severely limited because of the low energy density.How to further optimize the reaction kinetics performance of the electrode material without sacrificing its power density and cyclic stability to achieve high energy storage capacity still remains one of the challenging problems that need to be solved urgently.Transition metal phosphides?TMPs?exhibit the metalloid characteristics or rapid electron transport ability induced by strong electron delocalization in the sublattices of TMPs,making them attractive potential electrode candidates for high performance SCs.However,TMPs are generally limited by relatively poor electrochemical stability and lower specific capacity.To this end,this paper in-situ assembles highly conductive arrayed NiCoP nanowires on flexible conductive carbon cloth substrate?CC?and subsequently decorates the nanowires with NiCo-layered double hydroxides?NiCo-LDH?and MoSe₂ special nanostructures to form binder-free,self-supporting hybrid electrode,significantly improving the performance of the electrode material.The details are summarized as follows:?1?Preparation of a special NiCoP@NiCo-LDH structure on the surface of flexible conductive CC,and multi-dimensional collaboration comprehensively improves the electrochemical energy-storage characteristics.we assemble one-dimensional?1D?highly conductive arrayed NiCoP nanowires on flexible carbon cloth substrate?CC?by hydrothermal-phosphorization treatment and subsequently decorate the NWs with two-dimensional?2D?highly interconnected NSs of NiCo-LDH by a simple chemical bath deposition to form a 3D open NiCoP@NiCo-LDH heterostructure,which realizes the optimal combination of 1D,2D,3D.Such special structure integrates the advantages of the high stability of interconnected NiCo-LDH NSs,the high conductivity of the arrayed NiCoP NWs,excellent mechanical strength of CC,and the 3D hierarchical open structure.Density functional theory?DFT?calculations reveal that the introduction of the NiCoP core improves the conductivity of the overall heterostructure and the powerful affinity for OH^-of NiCo-LDH shell,which provide additional theoretical assistance for the improved electrochemical performance.In a three-electrode system with 6M KOH as the electrolyte,NiCoP@NiCo-LDH electrode exhibits excellent electrochemical performance(4683 mF cm^-2(1951 F g^-1)at the current density of 1 mA cm^-2 and an excellent rate capability of 89.3%at 20 mA cm^-2)and outstanding cyclic stability(81.1%of the capacity remains after 5000 cycles at a current density of 10 mA cm^-2).?2?Preparation of a special NiCoP@MoSe₂ structure on the surface of flexible conductive CC,interlayer-expanded few-laye MoSe₂ NSs provide more active sites and the NiCoP NWs array improves the electron transfer efficiency,which significantly improve the electrochemical energy storage characteristicsWe assemble highly conductive arrayed NiCoP nanowires on flexible CC substrate by hydrothermal-phosphorization treatment and subsequently decorate the NWs with MoSe₂ NSs by a hydrothermal treatment,forming a 3D multi-stage composite of NiCoP@MoSe₂ for high performance SCs.The interaction between tightly bound NiCoP and MoSe₂ result in the reduction of the number of MoSe₂ layers from more than 15 to 2-3,and expansion of the interplanar spacing from 0.65 nm to0.76 nm.Such novel multi-stage composite integrate the advantages of more accessible active sites of the interlayer-expanded few-layer MoSe₂ nanosheet,the high conductivity of the arrayed NiCoP nanowires,and the 3D open nanostructures,achieving the synergistic effects of the directionally efficient electron transfer and efficient utilization of active sites.Consequently,the synthesized 3D NiCoP@MoSe₂multi-stage composite has fast Faraday redox kinetics and excellent energy storage properties(5611 mF cm^-2(2244 Fg^-1)at a current density of 1 mA cm^-2,still has 79.2%capacity retention at a current density of up to 40 mA cm^-2 and 91.9%retention after8000 cycles at a high current density of 20 mA cm^-2).?3?Optimized combination of positive and negative electrodes and assembled high-efficiency flexible all-solid-state supercapacitors?FASC?to achieve high energy and power density energy storage devices.FASCs were assembled using the prepared electrodes?NiCoP@NiCo-LDH and NiCoP@MoSe₂?as the positive electrode,activated carbon?AC?as the negative electrode,and PVA/KOH as the gel electrolyte.NiCoP@NiCo-LDH//AC device has an energy density of 57 Wh kg^-1 at a power density of 850 W kg^-1,and NiCoP@MoSe₂//AC device has an energy density of 55.1 Wh kg^-1 at a power density of 799.8 W kg^-1.The assembled FASCs all possess high specific capacitance and long lifespan.The two FASCs in series are able to power 21 LEDs,a thermohygrometer and an electronic watch,respectively,demonstrating its viability and potential applicability.In summary,decoration of the arrayed NiCoP with highly interconnected NiCo-LDH NSs and interlayer-expanded few-layer MoSe₂ NSs to form two unique composite.Benefiting from the advantages of appropriate components and unique structure,the as-prepared composite materials show excellent electrochemical performance for supercapacitor.Our work provides a new idea for the synthesis and application of TMPs-based composites.