Controllable Construction Of Transition-metal-based Nanocomposites On Substrate For Electrocatalysis

The exploitation of traditional fossil energy has brought about increasingly severe energy shortage and environmental deterioration.It is urgent to develop new renewable clean energy.Hydrogen energy has a broad application prospects in the field of reducing energy crisis and controlling environmental pollution for its advantages of environmental protection,high calorific value of combustion,renewable and so on.Due to the rich raw materials,clean products and simple equipment,electrocatalytic water splitting stands out in many hydrogen production methods.However,due to the sluggish kinetics of the oxygen evolution reaction?OER?which is a complex four electron reaction,the efficiency of electrolysis is greatly inhibited and the energy consumption is increased.Urea oxidation reaction?UOR?is considered as an ideal alternative to OER because it can not only reduce the energy consumption of hydrogen production due to its low theoretical cell potential,but also help to purify the urea-rich wastewater.However,the practical application of energy-saving hydrogen production still needs the promotion of electrocatalyst.Currently,noble-metal-based materials,especially Pt-based compounds,are the state-of-the-art electrocatalysts,but their high price and scarce reserves problems seriously limit the practical applications.Therefore,it is of great significance to develop the electrocatalysts with low cost,high efficiency and stability.This paper controllable construct transition metal nanocomposites based on substrate for electrocatalysis.The main works were as follows:1.One-step electrodeposition method to synthesize transition-metal surface decorated with metal sulfide nanoparticles?M_xS_y/M/NF,M=Ni,Co,Fe?for hydrogen generation.In this chapter,we have developed a simple one-step electrodeposition method to realize the preparation of M_x S_y/M/NF.The prepared Ni₃S₂/Ni/NF,Co_xS_y/Co/NF and Fe_xS_y/Fe/NF show the greatly improved HER performance,whose overpotential at the current density of10 mA cm^-2 decreased from 196 mV?Ni/NF?,271 mV?Co/NF?and 288 mV?Fe/NF?to 45mV,89 mV and 128 mV,respectively,after the modification of metal sulfide nanoparticles.A series of experimental characterizations and density functional theory calculations show that the excellent HER performance can be attributed to the synergistic effect of transition metals and metal sulfides,that is,the former promotes water dissociation and the latter accelerates hydrogen production.2.A facile shaking reaction strategy to in-situ grow Ni₂P/Fe₂P nanohybrids on Ni foam?Ni₂P/Fe₂P/NF?for HER,UOR and urea electrolysis.In this chapter,we reported a simple and rapid strategy to obtain in-situ grow 3D electrode by use nickel foam as the substrate and the metal source.The Ni,Fe-PBA precursor can be obtained firstly via the combination of K₃[Fe?CN?₆]and the Ni²⁺which is obtained by the oxidation of nickel from nickel foam by Fe³⁺,followed by a simple phosphorization treatment,the Ni₂P/Fe₂P/NF can be obtained.The urea oxidation reaction?UOR?instead of oxygen evolution reaction?OER?was studied to reduce the energy consumption of hydrogen production.Benefitting from the 3D conductive network,rapid electron transition and synergistic effect of the Ni₂P and Fe₂P,the obtained Ni₂P/Fe₂P electrode shows excellent electrocatalytic performance,whose cathodic?HER?overpotential,anodic?UOR?voltage and cell voltage is only 115 mV,1.36 V and 1.47 V at the current density of 10 mA cm^-2,respectively.3.A one-pot“shielding-to-etching”strategy to construct amorphous MoS₂ modified CoS/Co_0.85Se heterostructured nanotube arrays(a-MoS₂/CoS/Co_0.85Se HNTs)for highly efficient HER,UOR and urea electrolysis.In this chapter,amorphous MoS₂ modified CoS/Co_0.85Se heterostructure nanotube arrays have been synthesized by a unique one-step"shielding-to-etching"strategy using the cobalt carbonate hydroxide nanorods based on foam nickel as template.Through the characterization of the products under different reaction time,the formation process of hollow structure named"shielding to etching"was clearly revealed,in which the nanorods with shielding layers were firstly obtained and then converted into nanotubes through further etching reaction.The a-MoS₂/CoS/Co_0.85Se heterostructure nanotube arrays show excellent electrocatalytic activity due to the abundant active sites,shortened ion diffusion and electron transfer pathways and optimized electronic structure brought by the hollow heterostructure.A two-electrode electrolyzer was assembled by using a-MoS₂/CoS/Co_0.85Se HNTs electrode as both anode and cathode,which achieved the current density of 10 mA cm^-2 with a voltage of only 1.42 V and surpassing most reported transition-metal-based electrocatalysts.Moreover,only a commercial 1.5 V battery as the electric source drive the total urea electrolysis system to produce hydrogen.