Synthesis Of Transition Metal Phosphide/pyrophosphate Based Hybrid Nanostructures And Their Electrocatalytic Performance For Total Water Splitting

Hydrogen(H₂)is the clean fuel with light weight and high energy density.High-efficient production and utilization of H₂ facilitate to alleviate current energy crisis and environmental pollution problems.Electrocatalytic overall water splitting(OWS)has been considered to be one of most ideal avenues for mass production of high-purity H₂.However,the high energy barrier of water dissociation and hydrogen desorption of the cathode hydrogen evolution reaction(HER)in alkaline media and the sluggish kinetics of the anode oxygen evolution reaction(OER)greatly hinder the development of OWS technology.Based on current research status of OWS electrocatalysts,this dissertation will focus on phase engineering,crystal-status modulation,doping,hybridization and interface engineering strategies,and controllably synthesize some transition metal phosphide/pyrophosphate nanohybrid structures,such as Fe/Ni phosphides nanocrystals“armored”with porous P-doped carbon(PC)and anchored on P-doped graphene(PG)nanohybrids,Ni₂P/V-PO_xcrystalline-amorphous heterogeneous porous nanosheets-based 3D flower-like super-structures and amorphous Co₂P₂O₇ nanosheet/r GO,by utilizing supramolecular gel precursors thermal conversion,hydrothermal and wet chemical methods.The electrocatalytic HER and OER performances of those nanohybrid catalysts were systematically investigated and evaluated,and further assembly of OWS device.Moreover,based on a series of advanced spectra and electrochemical analyses,the origins of the excellent catalytic activities for those catalysts were also suggested.Some preliminary results have been achieved at present.The details are as follows:(1)The phase-controlled synthesis of Fe/Ni phosphides nanocrystals that“armored”with porous P-doped carbon and anchored on P-doped graphene nanohybrids(NHs),including(Ni_xFe_1-x)₂P@PC/PG,Fe P-(Ni_xFe_1-x)₂P@PC/PG,Fe P-Fe₂P@PC/PG and Ni₂P@PC/PG,has been realized for the first time by controllable thermal conversion of skillfully designed supramolecular gel precursors that containing containing phytic acid,graphene oxides(GO),iron/nickel salt and polyethylene glycol monocetyl ether(Brij 58),and simply tuning the molar ratio of Fe/Ni in the gel precursors.Electrochemical tests disclose that those iron/nickel phosphides based NHs show phase-dependent catalytic behaviors.Among them,the pure-phase(Ni_xFe_1-x)₂P@PC/PG manifests the highest electrocatalytic HER and OER activity.Using it as bifunctional catalyst,the constructed device only needs a cell voltage of 1.45 V for driving OWS to reach 10 m A cm^-2 current density,superior to their mixed-phase and monometallic phosphides counterparts,and recently reported bifunctional catalysts based devices as well as the Pt/C||Ir O₂ electrolyzer.This work not only offers a facile strategy for phase-controlled synthesis of iron/nickel phosphides nanocrystals NHs but also screens out pure-phase(Ni_xFe_1-x)₂P@PC/PG as unprecedented bifunctional catalyst to use in alkaline OWS,which may shed light on rational design of advanced TMPs-based NHs and promote their applications in OWS or other renewable energy options.(2)The 3D flower-like superstructures derived from Ni V-LDH were firstly in-situ grown on a carbon cloth substrate via a ficle hydrothermal method,which were then subjected to oxidation-phosphation for forming the Ni₂P/V-PO_xcrystalline-amorphous heterogeneous porous nanosheet-based flower-like superstructures(Ni₂P/V-PO_xPNFSs).Based on this,Ni₂P/V-PO_x PNFSs exhibits excellent HER,OER and OWS catalytic performance,and its performance is better than single-component Ni₂P or V-PO_x.With Ni₂P/V-PO_x PNFSs as the anode and cathode of the OWS device,the cell voltage for driving the current density of 10 m A cm^-2 only needs 1.444 V.Its performance is mainly derived from the heterogeneous structure between crystalline Ni₂P and amorphous V-PO_x.This work demonstrates that synthesis of crystalline-amorphous heterostructual structures is expected to boost the bifunctional electro-catalytic performances of TMPs nanostructures,and promote their application in OWS or other renewable energy options.(3)The ultra-thin Co₂P₂O₇ nanosheets were grown in situ on the GO substrate by the wet chemical method,and then tempered in an Ar/H₂(15%)reducing atmosphere to prepare amorphous Co₂P₂O₇ nanosheet/r GO nanohybrid(a-Co₂P₂O₇/r GO).a-Co₂P₂O₇/r GO shows good OER electrocatalytic activity,and only need an overpotential of 303 m V to reach the current density of 10 m A cm^-2.The amorphous structure of a-Co₂P₂O₇/r GO enables strong electronic coupling between Co₂P₂O₇nanosheets and r GO substrate.This work has constructed a nano-hybrid material with high active sites,which is expected to develop high-performance OER catalysts for applying in OWS or metal-air batteries fields.