The Preparation Of Polyacid-based Nanocomposite And Its Electrocatalytic Water Splitting Performance

With the rapid social and economy development,we are facing the serious environmental pollution and energy crisis.Hydrogen(H2)is widely recognized as the potential clean and renewable energy since the 21st century because of the advantages of the abundant source,high energy density and so on.Electrolysis of water to produce H2 and oxygen(O2)is an efficient way to resolve the energy problems.However,decreasing the high overpotential is required to improve the electrocatalytic activity in kenetics.Therefore,we are urgent to produce highly active electrocatalysts to decrease the energy barrier for water splitting reaction.To date,commercial noble metal(Pt and Ir)-based materials are the high-efficient electrocatalysts for water splitting.However,the low crustal abundances and high costs severely limit the commercial applications of these noble metal-based catalysts.Therefore,the development of low-cost and high-efficient non-precious metal electrocatalysts is a major research goal for scientific researchers.Polyoxometalates(POMs)are a series of the metal-oxygen clusters with many advantages,such as small size,water solubility and high redox ability.POMs have various structures and transition metal sources(e.g.,Mo,W,V),which have potential advantages in the development of non-precious metal-based electrocatalysts.In order to improve the poor conductivity and dispersity,POMs can be hybridized with other materials including conductive substrates and metal-organic frameworks(MOFs).The as-prepared POMs/substrates or POMs/MOFs can be directly carbonized to obtain POMs-based nanocomposites with unique structures and multiple active species as the efficient electrocatalysts for water splitting.In this paper,we have synthesized a series of POMs-based nanocomposites using POMs precursors coupled with GO,MOFs or carbon cloth.POMs-based nanocomposites exhibit excellent performance for hydrogen evolution reaction(HER),oxygen evolution reaction(OER)and overall water splitting(OWS).The detailed works are as follows:(1)MoS2/N-RGO nanocomposite was prepared using PMo12 as Mo sources and GO as substrates by a facile one-pot hydrothermal method.The PMo12 particles are uniformly dispersed between the GO layers by electrostatic tension,ensuring the uniform growth of the MoS2 nanosheets on the RGO surface.Through controlling the reaction temperature,MoS2/N-RGO with enlarged interlayer spacing of 9.5 A is obtained and shows excellent HER performance in acid medium.MoS2/N-RGO has an onset potential of ca.5 mV,Tafel slope of 41.3 mV dec-1,high exchange current density of 7.4 ×10O-4 A cm-2 as well as good stability.(2)A series of MoS2-based bimetallic sulfides on carbon cloth(M-Mo-S/CC,M=Co,Ni,Fe)were synthesized by a one-pot hydrothermal method using three Anderson-typed POMs as the bimetallic precursors.The growth process of M-Mo-S/CC can be studied through the nucleation-doping competition mechanism.Owing to the different metal nucleation reaction rates,Co-Mo-S and Ni-Mo-S nanospheres show the heterostructures with CoS2 or NiS inside and MoS2 outside,while Fe-Mo-S nanosheets grow on CC without stacking.Besides,M-Mo-S/CC can be directly used as the working electrodes and show different activity for HER,OER and OWS in 1 M KOH.Co-Mo-S/CC shows the best catalytic performance among M-Mo-S/CC.(3)POMOFs/GO composite was successfully synthesized by a simple solution method at the room temperature using PMo12,HKUST-1 and GO as precursors.MoO2@PC-RGO composite was obtained by carbonizing POMOFs/GO precursor.Due to the synergistic effects among MoO2 particles,phosphorus-doped carbon skeleton and conductive graphene films,MoO2@PC-RGO composite shows the high HER activity in acid electrolyte with the ultra-small onset potential close to 0 mV,a small Tafel slope of 41 mV dec-1 and a high exchange current density of 4.83×10-4 A cm-2.(4)A powerful solid-phase hot-pressing method was applied to synthesize POMOFs on CC.After phosphidation of POMOFs on CC,the carbon coated bimetallic phosphides can be obtained and used as the electrocatalysts for electrolysis of water.The solid-phase hot-pressing method ensures the bimetallic phosphides grow on substrates uniformly and tightly,which increases the stability of the electrocatalysts in harsh electrolytes.Moreover,PMo12@HKUST-1/CC derived Cu-Mo-P/CC shows the excellent all-pH values HER performance.PMo12/ZIF-8/ZIF-67/CC derived CoP/MoP@NC/CC demonstrates outstanding overall water splitting in alkaline medium.