Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants.Kinetic current density at certain overpotential cal...Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants.Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts.However,it is frequently found that the diffusion limiting current density is not correctly identified in the literatures.Instead of kinetic current density,the measured current density normalized by diffusion limiting current density(j/jL)has also been frequently under circumstance where its validity is not justified.By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples,we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density.Our analysis reveals that j/jLis a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same.In addition,if one wants to use j/jLto compare the intrinsic activity,the concentration overpotential should be eliminated.展开更多
The ring current,one of the most important current systems around the Earth,intensifies during geomagnetic storms and is believed to be the main reason for large-scale magnetic field perturbations in the geospace envi...The ring current,one of the most important current systems around the Earth,intensifies during geomagnetic storms and is believed to be the main reason for large-scale magnetic field perturbations in the geospace environment.Understanding how the ring current builds up and evolves during geomagnetic storms is of great importance not only for advancing the knowledge of the Sun-Earth system but also for improving the modeling capability of predicting hazardous space weather events.Focusing on the national strategic needs in the space weather prediction,in this study,we establish a ring current model named storm time ring current model(STRIM).The STRIM comprehensively embraces key physical processes in association with ring current dynamics,including plasma source injections from the nightside plasmasheet and transport around the Earth,charge-exchange with neutral hydrogens,Coulomb collisions with thermal plasma,wave-particle interactions,field line curvature scattering,and precipitation loss down to the upper atmosphere.The electric fields needed for particle motion can be optionally taken from empirical models or self-consistently calculated,while the magnetic field configuration is obtained from Tsyganenko 2005 model.Simulation results are verified against the published literature and validated with in-situ satellite or ground-based observations and are found to have the same high-level capability and fidelity as other well-known published models.We also discuss future tasks of fostering the model's performance and potential applications.展开更多
基金supported by the National Natural Science Foundation of China(No.91545124,No.21972131,and No.21832004)。
文摘Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants.Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts.However,it is frequently found that the diffusion limiting current density is not correctly identified in the literatures.Instead of kinetic current density,the measured current density normalized by diffusion limiting current density(j/jL)has also been frequently under circumstance where its validity is not justified.By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples,we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density.Our analysis reveals that j/jLis a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same.In addition,if one wants to use j/jLto compare the intrinsic activity,the concentration overpotential should be eliminated.
基金supported by the National Natural Science Foundation of China(Grant Nos.41821003 and 41974192)the Fundamental Research Funds for the Central Universities。
文摘The ring current,one of the most important current systems around the Earth,intensifies during geomagnetic storms and is believed to be the main reason for large-scale magnetic field perturbations in the geospace environment.Understanding how the ring current builds up and evolves during geomagnetic storms is of great importance not only for advancing the knowledge of the Sun-Earth system but also for improving the modeling capability of predicting hazardous space weather events.Focusing on the national strategic needs in the space weather prediction,in this study,we establish a ring current model named storm time ring current model(STRIM).The STRIM comprehensively embraces key physical processes in association with ring current dynamics,including plasma source injections from the nightside plasmasheet and transport around the Earth,charge-exchange with neutral hydrogens,Coulomb collisions with thermal plasma,wave-particle interactions,field line curvature scattering,and precipitation loss down to the upper atmosphere.The electric fields needed for particle motion can be optionally taken from empirical models or self-consistently calculated,while the magnetic field configuration is obtained from Tsyganenko 2005 model.Simulation results are verified against the published literature and validated with in-situ satellite or ground-based observations and are found to have the same high-level capability and fidelity as other well-known published models.We also discuss future tasks of fostering the model's performance and potential applications.
