Preparation And Electrochemical Properties Of Self-supported Transition Metal Phosphide Nanoporous Electrode With Carbon Cloth

Rational designing of the electrocatalysts and energy storage materials is of great signifcance for achieving highly effcient energy conversion and storage in electrochemical energy devices.In recent years,transition metal phosphides（TMPs）have drawn great attention,which brings more opportunities for the designing of the materials.Compared to other traditional metal materials,TMPs materials usually have good electrical conductivities and outstanding electrochemical properties due to their unique nanostructure.This not only displays a feasible solution to fabricate materials for efficient energy storage and conversion,but also provides a new platform for designing and performance optimization of functional materials.It is an ultimate goal to design the efficient non-nobel metal electrocatalysts for efficient hydrogen evolution reactions（HER）and the efficient electrode materials for supercapacitor in our works.The author highlights the systematic and optimizing design of the non-platinum hydrogen-evolution electrocatalysts and the electrode materials for supercapacitor by means of constructing hierarchically porous structure,element doping,choosing substrate material and phosphorization.The design and optimization strategies for TMPs materials in this paper will provide new ideas for the design and preparation of high performance energy conversion and storage materials in the future.The content of this research is as follows:1.Different amounts of Zn-doped Co-based phosphides were grown on titanium foil（Zn-CoP/CoP₂/Ti）and CC（Zn-CoP/Co₂P/CC）wre prepared respectively,which were tested for electrocatalytic performance.The microstructure of Zn-CoP/CoP₂/Ti is open nano-flower-like,which can facilitate the diffusion of electrolyte ions and exposes more active sites.The HER and OER performance tests were performed in 1M KOH,and the overpotentials were 225 and 370 mV at a current density of 10 mA cm^-2,respectively.The microstructure of Zn-CoP/Co₂P/CC is a hierarchical structure,which consists of nanospheres and rhombic nanoarrays.The hierarchical structure has a large surface area and more ion transport channels,which is beneficial to improve the catalytic performance.In acidic and alkaline conditions,the overpotential of HER is as low as 81 and 92 mV at a current density of 10 mA cm^-2,respectively.In addition,the activity stability tests of Zn-CoP/Co₂P/CC were maintained for more than 24 h.2.Novel rhombic arrays of porous CoP₂ nanowires on carbon cloth（CoP₂/CC）are designed and synthesized via a four-step strategy,and as a highly efficient catalyst for HER.The four-steps involves hydrothermal synthesis of the Co_xZn_1-xOHF precursor,the formation of Co₂O₃-ZnO through thermal treatment,alkaline etching of ZnO and phosphorization.Specifically,the ratio of Co to Zn（1:1—1:5）in the precursor affects significantly morphology and HER performances of CoP₂/CC.The CoP₂/CC-4（which was obtained at the optimal Co-Zn ratio 1:4）,as a self-supported and binder-free electrode,exhibits superior catalytic performance toward HER in both acid and alkaline media.The overpotential of HER is as low as 56 mV in 0.5 M H₂SO₄ and 72 mV in 1 M KOH at a current density of 10 mA cm^-2,respectively.Correspondingly,the Tafel slope of the electrode reaction is not larger than 67 mV dec^-1 and 88 mV dec^-1 in acid and alkaline solution respectively.Furthermore,the catalyst maintained high stability for HER.This work displays a new idea to fabricate efficient electrocatalysts for HER or other electrochemical reactions.3.Carbon cloth supported lamellar nickel-cobalt-molybdenum ternary phosphide（NCMP）are prepared by a simple method including a hydrothermal and subsequent phosphorization process.The NCMP nanosheets are grown vertically on carbon cloth（CC）to form a threedimensional（3D）thin-wall cell structure with open pores（NCMP/CC）,which can be directly acted as working electrode without other binders or conductive additions,and achieves a specific capacitance as high as 433 F g^-1 at a current density of 1 A g^-1.Meanwhile,in order to match the capacitive behaviors of NCMP/CC in the two-electrode systems,hierarchically porous,nitrogen-doped,and interconnected carbon nanosheets（HPN-CNS）are also prepared from agaric through a one-step method.An asymmetric supercapacitor device（ASC）is assembled successfully by employing the self-supported thin-wall cell structure NCMP/CC as positive electrode and the HPN-CNS as the negative electrodes,respectively.More importantly,the device exhibits not only high energy density of 43.83 Wh kg^-1 along with power density of 0.89 kW kg^-1,but also an excellent cycle stability（82.4%after10000 cycles）under a cell voltage of 1.8V.