Part One-Chapter4 -Mass transport 11-13课件.ppt

Chapter 4;Mass transport : the movement of species in the media (liquid, gas or solid). Rate of mass transport: the flux of species i, Ji (mol s-1 cm-2) --- the amount of material passing through a unit area within an interval of unit time ;Diffusion ------ Movement of a species driven by a gradient of chemical potential (i.e., concentration gradient). (c1 ? c2);The mass transport in electrochemical systems ;The changes on the local concentration of solution species due to mass transport;The relationship between the current density and the mass transport rate ;Transient and Steady-state mass transport processes;Semi-empirical treatment of steady-state mass transport (稳态传质的半经验处理);mass transport coefficient; A stagnant layer of thickness ? exists in the vicinity the electrode surface, while the natural or forced convection maintains the concentration uniformly equal to its bulk value beyond x = ?ib;Steady-state mass transport in real electrochemical cells due to natural and forced convection (层流);The velocity parallel to solid surface ;The effective diffusion layer and its thickness有效扩散层及其厚度;The limiting diffusion current density;(1) 考虑有效扩散层;The strategies to increase the mass transport rate;Rotating disk electrode (RDE);Microelectrodes;Steady-state current density on Microelectrodes;Steady-state current – potential curves (polarization curves) for Nernst (reversible) electrochemical reactions (可逆体系稳态极化曲线);Case 1 --- both O and R are initially present;Case 2 --- only O is initially present;Case 3 --- R is insoluble产物 R 为独立相（气体或固相沉积层）;The diffusion layer and its effective thickness;Mixed mass transport by diffusion and migration;Mixed mass transport by diffusion and migration;Mixed mass transport by diffusion and migration;Steady-state polarization curves under mixed mass transport and interfacial reaction kinetics control (传质动力学+电极反应动力学); When there is concentration polarization, we have;轿染承嘱尼眨律努级率悯盐列蔫泊骄份幽缚核敷熬造恳保挺扮采虱迂按呀Part One-Chapter4 -Mass transport