Speaker: Dr. Yun Wang

Electrochemical Engine Center (ECEC)

Department of Mechanical and Nuclear Engineering

Pennsylvania State University

Abstract:

Owing to their high energy efficiency, low pollution, and low noise, fuel cells are widely regarded as 21^st century energy-conversion devices for mobile, stationary, and portable power.  Among all types of fuel cells, the polymer electrolyte fuel cell (PEFC) has reached “center stage”, particularly for mobile and portable applications.  Besides providing high power capability, the PEFC works at low temperatures and can be compactly assembled, making it a premiere candidate as the power source for vehicles and portable electronics.  

In this talk, I will summarize the current status of fundamental research in PEFCs and indicate where this burgeoning field is heading.  Particularly, discussions will focus on the following three areas: multi-phase multi-component transport, transient analysis, and large-scale operation/simulations, which are mostly covered by my research:

1.  The importance of multi-phase multi-component transport is that fuel cells rely on liquid water transport to remove the excess byproduct water from electrodes in two-phase regions.  In addition, liquid water may block the porous media and gas channels, hampering the reactant access to the catalyst sites.  This blockage may severely reduce cell performance and durability.

2.  Transient phenomena in automotive fuel cells are poorly understood at present. In addition to the complex dynamic response involving various time scales, severe degradation of the membrane electrode assembly (MEA) in a PEFC has been observed and attributed to the transient operation; these include fuel/oxidant starvation, membrane dryout, electrode flooding, and voltage reversal. 

3.  The need for high power requires large-size fuel cells (for high current) or a number of fuel cells assembled in a stack (for high cell voltage).  One challenge in large-scale operations is that the heat/water management is complex therefore hard to control.  Numerical simulations are preferred in studying large-scale cells due to the low cost of numerical investigation.  Particularly, large-scale calculations are needed for industry designs as well as academic interests in heat/mass transport in large-scale systems.

In addition, my presentation will cover the fundamentals of electrochemical kinetics, mass/heat transfer, and fluid mechanics, and apply these principles to explain the physics in some practical issues, such as carbon corrosion in electrodes, over- or under-shoot of cell voltage during transients, heat pipe effect in gas diffusion layers (GDLs), and functions of micro-porous layers (MPLs).