Controllable Synthesis Of Transition Metal-based Hybrid Nanomaterials,Electronic Structure Regulation And Their Electrocatalytic Performance

Transition metal-based hybrid nanocatalysts are widely used in catalytic materials for various reactions due to its special physical and chemical properties.With a rising global population in recent years,increasing energy demands and impending climate change,water splitting reaction and metal-air batteries has attracted great attention in recent years.At present,noble metal-based electrocatalysts are still the most widely commercial used in oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?.Unfortunately,their scarcity and high cost may cause significant obstacles to limit their further development.Therefore,it is highly urgent to develop highly efficient noble metal-free electrocatalysts.Motivated by the above consideration,the synthesis conditions for transition metal-based hybrid nanomaterials and their electrocatalytic performance toward the ORR and OER were systematically investigated in this study.The main work of this paper include following aspects:?1?In this chapter,novel hierarchical heteroatoms-co-doped Fe₂M/graphene?M=P,N,S?nanocomposites were developed by a facile strategy,including hydrothermal and subsequent calcination methods.The hydrothermal treatment of thiourea and an ionic liquid not only supplied heteroatom sources but also promoted the formation of iron nitride and iron phosphide and improved their catalytic performances.The electrochemical results indicated that the as-obtained hybrid catalysts manifested enhanced electrocatalytic activity toward the ORR due to the strong synergistic effects.The high content of heteroatoms distributed on the surface and interface of the hybrids and the density functional theory calculations?DFT?suggested that Fe-N-C,Fe-P-C,and Fe-S-C multiple active surface sites were formed at the hybrids interfaces.Moreover,these results demonstrated that heteroatom-doped catalysts could effectively form chargetransfer channels and thus modify the charge distribution in the hybrids interfaces.The as-prepared heteroatoms-doped Fe₂M/graphene hybrids would be developed into highly efficient catalysts as ideal alternatives for noble metal catalysts in commercial applications.?2?Over the past decade,transition metal phosphide?TMP?has been demonstrated to be one of the most active,stable,and cost-effective OER electrocatalysts in a wide pH range.It has been established that the P content in TMP is critical to OER performance.The TMP nanocatalysts doped with heteroatoms were synthesized using hydrothermal-assisted calcination method by ionic liquid-dopant,namely,NPF/Ni₁₂P₅,NPF/Co₂P and NPF/Fe₂P.The results indicate that the prepared NPF-TMP exhibits excellent OER catalytic performance and stability.Different from the traditional high-temperature calcining NaH₂PO₂ to provide a phosphorus source,this chapter developed a simple and safe method to achieve transition metal phosphide by using ionic liquid-dopant.This facile method offers the possibility of developing other transition metal phosphide nanocatalytic materials.?3?In this chapter,a series of surface N,P,and F tri-doped Cu_0.81Ni_0.19.19 alloy nanoflowers with tunable composition and morphology were in situ grafted onto nickel foam?NF?by a one-step hydrothermal method using ionic liquid-dopant.Notably,the optimized NPF-Cu_0.81Ni_0.19/NF?NCN?hybrid catalyst manifests superior OER performance in alkaline solution,which only requires an ultralow overpotential of 200 mV to initiate the OER at the current density of 10 mA cm^-2,which is the most efficient Cu-based electrocatalysts reported to date.It is demonstrated that heteroatoms doping can simultaneously regulate the electron structure,3D flowers morphology feature,and release more accessible active surface sites to promote the OER catalytic performance and stability.The NCN exhibits a large electrochemically active area.Sufficient contact areas between the catalyst surface and the conductive substrate can be achieved to avoid the influence of resistance to electron transport.Oxygen can be more easily released from the catalyst surface and desorbed on the electrode,reducing ohmic losses and accelerating the OER kinetics.The surface heteroatoms doping strategy may open up further opportunities to design other morphologies catalysts and optimize their electrocatalytic performance.