Preparation And Hydrogen Evolution Properties Of Ni-based Alloy/Graphene Composites

With the large-scale use of fossil energy,the problems such as environmental pollution and energy crisis have been caused.Hydrogen energy has attracted more attention due to its green,environmental friendly and renewable characteristics.Among them,the production of hydrogen by water splitting has become the focus of research because the product is green and environmental friendly.In the hydrogen production system of catalytic water splitting,the addition of co-catalyst can effectively reduce the overpotential of hydrogen evolution,thereby improving the hydrogen production efficiency.However,the scarcity and high price of precious metals limit their large-scale production and application,so we turn our attention to cheap,readily available and abundant non-precious metals instead.The transition metal Niis abundant in the earth’s crust and has high catalytic activity,and has been widely used as a co-catalyst in hydrogen production systems in recent years.The single metal Niis easy to agglomerate,resulting in a low active site and a large adsorption energy with hydrogen,resulting in an unbalanced adsorption and desorption,which is very different from the metal Pt.Metal alloying can change the electron cloud density of single metal and regulate hydrogen adsorption,which is beneficial to the improvement of catalytic performance.At the same time,graphene is widely used as catalyst carrier and co-catalyst due to its huge specific surface area and excellent electron transport function.Due to the existence of a large number of oxygen-containing functional groups on the surface of graphene,the semiconductor or metal ions act directly,and themselves will be reduced to RGO to synthesize graphene-based composites.In this paper,by directly calcining graphene oxide and metal chloride precursors,Ni-based alloy nanoparticles supported by graphene were synthesized and as a co-catalyst for catalyzing the hydrogen evolution reaction.This thesis mainly consists of the following two parts:（1）Graphene oxide（GO）was first prepared,then Ni（Ⅱ）salts and Cu（Ⅱ）salts were added in different proportions,and the precursors were calcined in N₂+H₂atmosphere to synthesize NiCu alloy/graphene composite（N_xC_yG）,and as a co-catalyst for dye-sensitized photocatalytic hydrogen production.Because of the modulation of metal-support interaction（MSI）is of particular interest in improving the catalytic performance of metal nanocatalysts.Herein,Here,an alloying strategy is employed to tune the MSI in graphene-supported Nicatalyst by introducing Cu.The results reveal the introduction of Cu significantly affects the MSI in N_xC_yG cocatalysts,and a reasonable Ni/Cu ratio（4:1）significantly enhances the MSI in N₄C₁G cocatalyst.Such an enhanced MSI facilitates the electron injection from excited dye to RGO and further transfer to the NiCu alloy,and leads to smaller size of NiCu alloy nanoparticles（NPs）with sufficient active sites.Moreover,the synergetic effect between Niand Cu is conducive to optimize the hydrogen adsorption on NiCu surface.As a result,the N₄C₁G cocatalyst shows much improved electrocatalytic and photocatalytic HER performance compared with monometallic Ni/graphene and Cu/graphene.The apparent quantum yield（AQY）at 420 nm reaches up to 67.7%in the dye-sensitization system.（2）Different proportions of Ni（Ⅱ）salt and Fe（Ⅲ）salt were added to the graphene sol,and then a certain amount of urea was added.After drying,the precursors were calcined in N₂atmosphere,and the gas generated by the pyrolysis of urea at high temperature was used as a reducing gas to reduce the metal ions,the NiFe alloy/graphene composite（N_xF_yG）was prepared and used as a co-catalyst for catalytic hydrogen evolution reaction.The introduction of Fe makes electrons transfer to carbon atoms,and the hydrogen adsorption energy of Niis controlled by the adjustment of the under-electron d orbital.Due to the stability of hydrogen adsorption during the hydrogen evolution reaction,the carbon atoms near the metal particles have a higher charge density,which is conducive to hydrogen evolution.The reaction showed good hydrogen evolution activity under alkaline conditions.