Pore-scale study of effects of relative humidity on reactive transport processes in catalyst layers in PEMFC

• High surface area carbon (HSC) particles can be adopted to increase the specific surface area of catalyst layer (CL) in proton exchange membrane fuel cells. Relative humidity (RH) has a significant effect on the Pt activity inside HSC particles, and the underlying mechanisms need to be further investigated. In this study, a pore-scale model considering the effects of RH on the reactive transport processes inside the CLs is developed. Two kinds of liquid water distributions affected by the RH, including capillary condensation in pores and ultra-thin liquid film on Pt surface, are considered. The liquid water distribution, Pt activity and local oxygen transport resistance (Rlocal) under different RH are studied in detail. It is found that as RH increases from 0.3 to 1.0, the condensed water in micropores of HSC particles increases, resulting in an increase in reactive surface area by about 43 %. Combined effect of the RH, Pt loading, I/C ratio and different kinds of carbon particles is investigated. It is found that due to the lack of sufficient reaction sites, compared with that under a high Pt loading, Rlocal under a low Pt loading is more sensitive to the RH. Besides, since the Pt activity inside HSC particles depends on the condensed water, the Rlocal of HSC particles is more sensitive to the RH than solid carbon particles. Finally, the Rlocal at low ionomer content is more sensitive to RH due to low ionomer coverage on Pt particles. The present study provides a pore-scale model for investigating the coupled effects of RH and CL porous structures on local transport processes, and can facilitate the optimization of CL nanoscale structures for better cell performance. 

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Naturresursteknik -- Annan naturresursteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Environmental Engineering -- Other Environmental Engineering (hsv//eng)

Nyckelord

Capillary condensation

Catalyst layer

High surface area carbon

Local transport resistance

Low platinum loading

Carbon

Catalysts

Condensation

Liquid films

Platinum

Proton exchange membrane fuel cells (PEMFC)

Water supply systems

Carbon particle

Catalysts layers

High surface area

Local transport

Platinum loadings

Transport resistance

Ionomers

catalyst

fuel cell

ion exchange

membrane

optimization

reactive transport

relative humidity

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)