Transition-metal Sulfide/Phosphide Materials:Synthesis,Characterization And Electrocatalytic Activity

With the growing demand for clean and sustainable energy,the development of renewable energy technologies such as zinc-air baterries and water splitting?low-cost,highly active and durable?is a major challenge and opportunity for modern social science.Addtionally,these advanced technologies are closely related to a series of electrochemical reactions.Zinc-air batteries involve oxygen evolution reaction?OER?and oxygen reduction reaction?ORR?,while electrocatalytic water splitting contain hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.However,these hydrogen-based and oxygen-based electrical reactions are hindered by their own slow kinetic and require the use of favorable catalyst to make them feasible for practical application.So far,the noble metal catalysts Pt/C are the most effective ORR and HER electrocatalysts,while IrO2/RuO2 are the state-of-the-art catalysts for OER.Unfortunately,these noble-metal catalysts limit their widespread commercialization due to their high cost,scarcity and poor durability.There is an urgent need to explore advanced electrodes with precisely regulated nanostructures to improve energy and power density,catalytic activity and catalytic stability.As highly active electrocatalysts,the nanomaterials' size,shape,dimension and morphology significantly affect the performance of electrochemical conversion reactions.Doping of metal nanoparticles by heteroatoms such as phosphorus and sulfur is known to be an interesting tool for improving their catalytic properties?activity and stability?since the varied active-sites and electron-reconfigured interfaces.Due the transition metal sulfides and phosphides exhibit good corrosion resistance,excellent durability,high melting point and strong mechanical strength,they exhibit great potential as electrocatalysts,catalyst carriers and battery materials.Herein,I had prepared transition metal sulfides and phosphides which were used as electric catalyst?mainly applied for zinc air battery and water splitting?.Transition metal phosphide mainly include noble metal palladium phosphide and non-noble metal NiCoP,while transition metal sulfide mainly include precious metals palladium sulfide and non-noble metal NiMoS.According to the catalyst synthesis method,this work is mainly divided into two parts as follow.1.We have reported the colloidal synthesis of palladium sulphides?including Pd16S7,Pd4S,and PdS?via a facile one-pot hot-solution synthetic route.Among the different palladium sulfides tested,monodisperse Pd4S nanoparticles?NPs?exhibited much enhanced electrocatalytic activity toward ORR in alkaline medium,with the half-wave potential of 0.877 V,ca.47 mV more positive than that of commercial Pt/C.The as-prepared Pd4S catalyst also demonstrated enhanced tolerance against methanol and significant improvement in terms of stability in comparison to Pt/C catalyst.Furthermore,when employed as the air cathode,the performance of the primary Zn-air battery made with Pd4S exhibited better performance and long-term stability than those with commercial Pt/C.Density functional theory?DFT?calculations indicated the existence of oxygen absorption sites in Pd4S surface was able to trap atomic oxygen moderately and desorb O2 facilely,and thus led to its superior ORR activity.Pd₃P nanoparticals were prepared using TOPO and TPP as phosphorus source,respectively.When using TPP as phosphorus source,the as-prepared Pd₃P was relatively well dispersed and had much smaller size.Under acidic conditions,Pd₃P/C exhibited much better catalytic activity and superior stability for HER than Pd/C.The enhanced performance of HER activity might be attributed to the binary composition,good conductivity and more active sites of Pd₃P/C.2.In the aqueous solution,NiCoP/CC and Ni-Mo-S/NF with different morphologies were obtained by hydrothermal method.The 3D nest-like NiCoP have been successfully prepared on CC by a successive hydrothermal,oxidation and phosphidation process for the first time.The nest-like structure of NiCoP greatly increased the active sites and fast facile transport of electrons throughout the entire electrode,as well as the facile release of the evolved gas during HER and OER catalysis.The as-synthesized nest-like NiCoP/CC exhibits excellent HER catalytic performance and durability at both acidic and alkaline conditions.Furthermore,it also shows superior OER performance in basic media,which enables the NiCoP/CC as the bifunctional electrocatalysts for the overall water splitting.The use of NiCoP/CC as both cathode and anode will significantly simplify the electrode design,and thereby promote their widespread deployment in the future.We obtained a 3D network-like Mo-doped Ni3S2 catalyst by low temperature hydrothermal and further sulfidation process.We had introduced the influence of the addition ratio of Mo and Ni precursors on the morphology,composition and catalytic activity.Due to the high surface area,three-dimensional mesh morphology,appropriate composition and enhanced charge transport,the obtained Ni-Mo-S/NF?5:5?exhibited high catalytic activity and stability in 1 M KOH medium for both HER and OER.Furthermore,when used as the anode and the cathode for overall water splitting in basic solution,Ni-Mo-S/NF?5:5?also performed excellent activity and durability.This stable,inexpensive,earth abundant three-dimensional electrocatalyst can be used in commercial applications.