Influence Of Mass Transfer Process On Electrocatalytic Properties Of Multi-Scale Porous Materials

The nitrogen-doped graphene has good electrochemical performance.The microsphere structure prepared by it has a large specific surface area and excellent electrocatalytic performance,and it has wide application prospect as a supercapacitor electrode material.Rotating disk electrodes are a common method for measuring the electrochemical intrinsic reaction rate of materials.By rotating the electrode to generate forced convection,so that concentration polarization can be eliminated within a certain range.However,the reaction rate obtained using the classical electrode kinetic model(Koutecky-Levich formula)is still affected by the mass transfer process.The nitrogen-doped graphene microsphere electrode is not a traditional flat-plate electrode,and the hierarchical porous structures on the surface will also generate mass transfer limitation,which leads to great deviation in the calculation of the intrinsic reaction dynamic characteristics.In this paper,because it's hard to calculate the kinetic characteristics of intrinsic reaction,the computational fluid dynamics(CFD)method is used to simulate the competition between mass transfer and reaction dynamic process to reproduce the current density with voltage to obtain parameters closer to the intrinsic reaction kinetics.The main research contents are as follows:The numerical simulation of the velocity field inside the rotating disk electrode was carried out to study the hydrodynamic characteristics of the electrode.The mass transfer ability of the electrolyte was characterized by the axial velocity of the center of the rotating disk electrode.The influence of electrode size and position on the mass transfer efficiency of the rotating disk electrode was analyzed.By discussing the four dimensionless numbers,the optimization criteria for the design of disc electrode structures.is givenThe numerical simulation of the concentration field on the surface of the rotating disk electrode and its vicinity was carried out to study the effect of external mass transfer on the electrocatalytic performance.Based on the NS equation,an electrode dynamics model with detailed mass transfer process was established.The velocity field of the electrode surface and its surrounding fluid and the concentration field of the component were refined calculated.The intrinsic reaction kinetic parameters of the electrode were obtained by reproducing the experimental curve of current density versus voltage.The reaction kinetic parameters obtained by the classical K-L formula are compared with the input parameters.The K-L formula application range of the voltage and the correctness of reaction rate constant is givenThe numerical simulation of the internal concentration field of the hierarchical porous structure electrodes were carried out to study the effect of mass transfer inside the electrode on the electrocatalytic performance.Four idealized geometric models were constructed,and the competition between mass transfer and reaction was characterized by the dimensionless number Thiele Modulus.The form of the different structural features of the Thiele modulus is analyzed,and the improved formula of the external hierarchical porous structure of Thiele modulus is given.