Mass transport overpotential

See also - diffusion overpotential, -> diffusion time, -> fractals in electrochemistry, -> mass transport overpotential, -> mass transport processes. 

Mass transport overpotential (or concentration polarization (overpotential)) tjc — is a departure of the - electrode potential (or cell potential), E, from the - equilibrium electrode potential (or zero-current potential), Eeq, caused by a -> faradaic current flow and the associated surface concentration, Cox(x = 0), deviation from the bulk concentration, Cox(°°)> of the reacting redox species, Ox... 

Wood, D. L. and Borup, I. R. L. 2010a. Estimation of mass-transport overpotentials during long-term PEMFC operation. Journal of the Electrochemical Society 157 B1251-B1262. 

Fig. 7 CeU G2 cathode catalyst-layer and GDL mass-transport overpotentials, oxygen reduction reaction (ORR) overpotential, and iR-corrected cell voltage as a function of current density at different durability testing times (1,054 total hours at constant 0.90 A cm Gore PRIMEA series 5620 MEA (50.0-cm active area, 0.40/0.60mg Pt cm, 35- am Gore SELECT membrane) SGL SIGRACET GDL 24BC (5wt%/23wt% PTFE substrate/MPL) at both sides. See the Appendix for durability testing conditions. RH Relative humidity, A Anode, C Cathode...

Wood, D., Davey, J., Atanassov, P. and Borup, R. (2006) PEMFC component characterization and its relationship to mass-transport overpotentials during long-term testing. ECS Trans. 3 (1), 753-763. 

Fig. 9 (a) Cell impedance measurements (1-kHz high-frequency resistance) of the continuously operated cell and the start/stop-cycled cell, (b) Changes in oxygen reduction overpotentials versus lifetime for a MEA in constant operation (circles) and start/stop cycling mode (squares). (c) Changes in mass-transport overpotentials in Hj/air operation versus lifetime for a MEA in constant operation (circles) and start/stop cycling mode (squares) at 0.2 and 0.8 A cm , respectively... 

Cathode mass transport Higher mass-transport overpotentials in start/stop-cycled ceU Electrolyte fiooding due to carbon corrosion and resulting changes in hydrophobicity Significant increase of mass-transport overpotentials Severe corrosion of carbon results in loss of structural integrity of cathode catalyst layer and void volume loss... 

In order to quantify changes in the mass transport overpotentials, additional H2-air polarization curves (stoichiometries 1.2/I.3 for H2/air) were recorded. In Fig. 2 la (white squares), the cell potential at 0.2 A cm is plotted, showing a total reduction of 47 mV after 1800 h, compared to beginning of life. The additional 17 mV of degradation were due to increased mass transport overpotentials, which resulted from changes in the hydrophobic-... 

Fig. 25 Mass transport overpotentials in mV as a function of current density and MEA runtime...

---