Preparation And Electrocatalytic Properties Of Boron-doped Carbon Materials By Electrochemical Deposition

Fuel cells,with high energy density,low operating temperature,various fuels,clean exhaust gas,and low noise,have rapidly developed into alternatives to traditional power sources.There are many factors affecting the performance of fuel cells,and the loss in cathodic oxygen reduction reaction is one of them.Cathodic oxygen reduction reaction mainly includes one-step four-electron and two-step two-electron reaction.Considering the energy conversion efficiency and output voltage of fuel cell,the two-electron reaction mechanism should be avoided as far as possible.The number of electron transfer depends mainly on the catalysts in the reaction process,so it is necessary to study highly active catalytic materials.Carbon material catalysts doped with non-metallic heteroatoms?including nitrogen,phosphorus,sulfur,iodine,boron and other elements?have attracted wide attention due to their excellent catalytic activity,stability,methanol permeability resistance and low cost.In this paper,boron-doped carbon materials have been successfully prepared by a simple and effective liquid-phase electrochemical deposition technology.The boron-doped amount can be controlled by adding different quality boron sources.At the same time,the effects of different process parameters on the samples of boron-doped carbon materials have been explored.The carbon materials were firstly prepared by liquid phase electrochemical deposition with or without boron source.The results of scanning electron microscopy?SEM?and transmission electron microscopy?TEM?show that the carbon materials prepared by liquid phase electrochemical method distribute around the silicon matrix in the form of small fragments.FTIR and XPS analysis show that boron can be successfully doped into carbon lattices by liquid phase electrochemical method,which confirms the feasibility of this method.The boron doping can increase the internal defects of carbon materials from XPS analysis,and the boron-carbon elements in boron-doped carbon materials mainly exist in BCO₂,BC₄,and B₄C.The boron-doped carbon materials prepared by liquid-phase electrochemical deposition have obvious oxygen reduction peaks at near-0.4 V,and the oxygen reduction activity of the samples doped with boron is higher.LSV tests show that the number of transfer electrons before and after boron doping increases from 2.2 to 3.7,which indicates that boron doping is beneficial to the selection of four-electron reaction path for carbon materials.Compared with the undoped boron samples,the methanol resistance and durability of the doped boron carbon materials increase by 26.5%and 10%respectively.The liquid phase electrochemical deposition technology can be used for boron doping,and the electrochemical properties of the samples doped with boron are significantly improved,which paves the way for the follow-up research.By changing the amount of boron source,boron-doped carbon materials with the doping degree of 0.60%,0.75%,0.81%and 0.93%were prepared.The controllable concentration of boron-doped carbon materials was realized by liquid-phase electrochemical technology.The results of electrochemical analysis showed that the electrocatalytic activity,anti-methanol toxicity and stability of the samples increased in turn with the increase of boron doping content.Scanning,Raman and XPS analysis show that the main reason for the above results is that the increase of boron source enhanced the conductivity of the solution system,accelerated the reaction rate in the solution,and increased the boron doped into carbon lattice,resulting in more defects in carbon lattice,thus increasing the active site of oxygen reduction reaction.In order to explore the optimum technological parameters for preparing boron-doped carbon materials,a series of boron-doped carbon materials were prepared by controlling variable method under the conditions of different substrate size,power supply voltage,power supply frequency and duty cycle.The electrochemical tests showed that the smaller the particle size of silicon powder,the better the electrocatalytic activity.Under the conditions of2.5 kV,3 kHz and 90%duty cycle,the prepared boron-doped carbon material has better performance.Comprehensive analysis shows that the liquid phase electrochemical deposition technology can be used for boron doping,and the concentration of boron doping can be controlled.Good process parameters are more conducive to improving the electrocatalytic activity of catalyst materials.The prepared boron-doped carbon material has good electrocatalytic activity,methanol resistance and durability,low cost and easy preparation.It can be used as cathode catalyst for fuel cell.