Investigation On Structural Design And Electrocatalytic Performance Of Low-Dimensional Nanomaterials

The energy crisis and environmental pollution have made people pay more attention to utilize clean energy and sustainable biomass.As one of the most promising methods to realize the industrial production of clean energy and the conversion of renewable biomass energy,electrocatalysis technology has be intensively focused in recent years.Hydrogen energy is the hottest topic nowadays due to its high energy density and non-polluting energy features,but there are still some problems in the hydrogen production by water electrolysis.On the one hand,the catalytic activity and stability of current catalysts for cathodic hydrogen evolution reaction（HER）still can meet the industrial demands,and therefore it is of great significance to develop catalysts with better HER performance.On the other hand,oxygen evolution reaction（OER）occurs at anodic side of water electrolysis,which shows sluggish kinetics and low economic value.Therefore,it is urgent to seek oxidation alternatives at anode and design corresponding catalyst,so as to markedly enhance the energy efficiency and economic benefit of water electrolysis.In response to these problems,we start from the following two aspects.On the one hand,we focus on the composition engineering and morphology controlling of a one-dimensional low platinum-based catalyst to greatly improve its HER activity,with further emphasis on in-depth correlation between atomic structure and catalytic performance.On the other hand,towards replacing anodic OER with more valuable oxidation reactions,a transition metal nickel-based catalyst is developed to efficiently convert 5-hydroxymethylfurfural（HMF）biomass to value-added 2,5-furandicarboxylic acid（FDCA）.The detailed researches are as follows:1.Firstly,one-dimensional"candied fruit shape"platinum-nickel alloy nanowires（Pt Ni NWs）were accurately synthesized by a two-step liquid phase method,followed by phosphorous doping using sodium hypophosphite as phosphorous source to obtain platinum-nickel-phosphorus alloy nanowires（Pt Ni P NWs）for alkaline HER.Electrochemical tests demonstrate that one-dimensional Pt Ni P NWs exhibit much higher catalytic performance than commercial platinum-carbon catalysts,that Pt Ni P-0.11 NWs with moderate phosphorus content exhibit an overpotential as low as 12 m V at a current density of 10 m A cm^-2in 1 M KOH,an overpotential of only 67 m V at 100 m A cm^-2,and a Tafel slope of only 28.6 m V dec^-1.Moreover at an overpotential of 70 m V,the turnover frequency（TOF）of Pt Ni P-0.11 NWs is as high as 28.6 s^-1,while the mass activity（MA）and specific activity（SA）is 5.79 A mg_Pt^-1 and 14.22 m A cm^-2,respectively,which is 10.6 times and 15.3 times of commercial platinum-carbon.Based on theoretical calculation and electrochemical analysis studies,we found that nickel atoms reduced the water dissociation barrier on Pt,while the introduction of phosphorus further optimized the electronic structure of platinum and nickel,which thermodynamically and kinetically promoted interfacial hydrogen spillover and overall HER activity.2.To address the issues of OER such as high overpotential and low economic value,this chapter aims to replace OER by electrooxidation reaction of HMF biomass to produce value-added FDCA compound at anode.However,HMF oxidation suffers from challenges like complicated reaction pathways and low selectivity.In order to achieve high selectivity for FDCA production,we prepared the two-dimensional hexagonal Ni_1-xCu_x（OH）₂ nanosheets via using a one-step hydrothermal method.Electrochemical tests show that the HMF conversion over Ni_0.9Cu_0.1（OH）₂ catalyst reaches 100%,and the Faradaic efficiency of FDCA reaches 91.2%with corresponding overpotentials are also markedly lower than that of OER.Mechanism studies show that the excellent performance of Ni_1-xCu_x（OH）₂ nanosheets is due to the controllable introduction of amorphous island-like copper on the surface of nickel hydroxide nanosheets,which improves the local electronic structure of nickel and makes it easier to form more active Ni OOH species,On the other hand,the amorphous island-like copper structure makes the coordination of copper atoms on nickel more flexible,which leads to the better coordination with the oxidation intermediates of HMF.As a result,HMF electrooxidation to FDCA is significant boosted with high conversion and selectivity.This paper can provide insights for designing HER catalysts,and exploring coupled electrooxidation in water electrolysis.