Preparation And Electrochemical Performance Of Hollow Carbon-based Metal Materials

Owing to its high energy density,cleanliness and wide resources,Hydrogen becomes an ideal alternative carrier.At present,electrochemical water splitting for HER and the hydrolysis of ammonia borane?AB?are sustainable,efficient and low carbon emissions to produce hydrogen among various methods.To date,Pt-based electrocatalysts are considered as the most efficient catalysts for the hydrogen evolution reaction?HER?.However,the commercial application of Pt-based electrocatalysts is hindered by its less reserves and high cost.Furthermore,ammonia borane is one of most promising chemical hydrogen storage materials,which benefits from its high hydrogen storage density?19.6 wt%?,security,non-toxicity and stability at room temperature.In the presence of a catalyst,1 mol of ammoniaborane?AB?can be hydrolyzed to release 3 mol hydrogen.Consequently,exploiting efficient and inexpensive bifunctional electrocatalyst for HER and releasing hydrogen from ammonoborane hydrolysis are of great significance for the development of sustainable energy.Hollow carbon materials have extraordinary specific surface areas,good mechanical properties and conductivities.Compositing metal and carbon materials is an effective way to improve activity and stability of catalysts.Based on this,we have prepared hollow carbon materials and metal composites for HER and the hydrolysis of AB,respectively.Meanwhile,their catalytic activity and reaction mechanism are also investigated.All above have provided a novel method to develop metal-based carbon composite bifunctional catalysts with low cost,high activity and good stability,and the main content is as follows:Firstly,hollow carbon sphereencapsulate Ru nanoparticles?HCRNs?and hollow carbon sphere encapsulate Ru layers?HCRLs?were prepared via hydrothermal and high-temperature roasting method with modified SiO₂ microspheres as hard templates.HCRN?Ru:4.8 wt%?and HCRL?Ru:23.5 wt%?showed excellent electrocatalytic performance for HER in 1.0 M KOH,which indicated the overpotential of 33 and 18mV at current density of 10 mA cm^-2(?₁₀),respectively,which is better than other Ru/C catalysts and commercial Pt/C catalysts?Pt:20 wt%??38 mV?.In addition,the TOF values of HCRN and HCRLare 0.77 and 0.25 s^-11 at the overpotential was 15 mV,respectively,which is also superior to commercial Pt/C catalyst(0.19 s^-1).After 10000cycles of CV,the catalytic activity of the catalyst remained almost unchanged,indicating that the catalyst has excellent cyclic stability.In the other hand,HCRLs850exhibited high catalytic activity and stability in the ammonioborane hydrolysis for releasing hydrogen,and its TOF and activation energy is 716 mol_H2 min^-1 mol^-1_cat and30.2 kJ mol^-1,respectively.After 8 cycles of CV,the catalytic activity of the catalyst did not decrease obviously.Density functional theory?DFT?calculations and toxication experiments revealed that the carbon shells were activated by electrons transfered from the encapsulated Ru,and the active sites is located on the metal-modified carbon surface,especially at the defect site.Secondly,on the basis of the above work,the carbon sphere is used as the carrier and prepared RuCo alloy embedded in hollow carbon spheres catalyst?RuCo@HCSs?via the method of vacuum impregnation and high temperature roasting.The RuCo@HCSs catalyst extremely well catalytic activity and stability for HER in acid,basic and neutral solution.It displays overpotentials of 57,21 and 49 mV at 10mA cm^-2??10?in 0.5 M H₂SO₄,1.0 M KOH and 1.0 M PBS solution,respectively,and high turnover frequencies?TOF?of 1.79,3.28,and 1.24 s^-1 at 100 mV,respectively,which were even larger than that of Pt/C(39,40,and 58 mV,respectively;1.10,2.12,and 0.84 s^-1,respectively).In addition,RuCo@HCSs showed high catalytic activity and stability in the ammonioborane hydrolysis for releasing hydrogen,its TOF and activation energy is 784 mol_H2 min^-1 mol^-1_cat and 27.4 kJ mol^-1,respectively.After 8cycles of CV,the catalytic activity of the catalyst remained barely changed.