Durability Degradation, PEFC

In this chapter, centered on such specific factors for residential application, degradation phenomena observed in long-term operation experiments assuming residential cogeneration systems at Osaka Gas are reviewed and analyzed. In addition, the present status and the potential of the durability of PEFCs for residential use are briefly reported. 

This volume of Modern Aspects of Electrochemistry is intended to provide an overview of advancements in experimental diagnostics and modeling of polymer electrolyte fuel cells. Chapters by Huang and Reifsnider and Gu et al. provide an in-depth review of the durability issues in PEFCs as well as recent developments in understanding and mitigation of degradation in the polymer membrane and electrocatalyst. 

The durability and lifetime are important factors for the commercialization of fuel cells. Therefore, the degradation of fuel-cell components has been subjected to an increasing number of studies, mainly focused on PEFCs [56-67]. For AFCs,... 

To reach the requirements of performance and durability for both automotive and stationary PEFC appUcations [20], catalyst durability has become an important issue both for of academic and industrial R D. Cathode degradation in operating PEFCs mainly occurs tmder transient conditions, leading both to Pt dissolu-tion/degradation and carbon-support corrosion. At typical operational pH conditions and above 0.9 V, two main mechanisms lead to Pt degradation (i) diffusion of dissolved Pt species... 

Durability testing (2700 h) of a PEFC at 300 mA cm and fully humidified conditions were conducted by Yu et al. (2005a). The rate of PEM degradation was accelerated after 1900 h of continuous operation resulting in a significant increase of the hydrogen crossover current (from -1.4 to -28 mA cm at the end of durability experiment) and electrochemically active surface area loss. 

The major degradation factors of the MEA for the residential PEFC system discussed in the previous sections are based on the results of long-term durability tests. However, during such long-term tests, the improvement of materials used in the... 

System Humidification A natural question for a student to ask is Why do we need to humidify the PEFC at all After all, it is a net water generation device, and yet so much of the design is ultimately meant to remove water from the cell. Since the fuel cell has a precarious balance between a moist electrolyte needed for high ionic conductivity and a flooded cell that degrades performance, it is entirely possible that some sections of the same fuel cell or individual plates in a stack will be overly dry and other sections in the cell or different plates in a stack will be flooded. Because of this, some humidification is typically needed at the inlet of the fuel cell to ensure adequate performance. Addition-aly, strong humidity gradients in the electrolyte can result in internal stresses that limit durability. 

Chapter 6 is devoted entirely to PEFC systems, including hydrogen- and direct alcohol-based apphcations, issues, and degradation concerns. The specific devotion to PEFCs is based on my personal expertise and the fact the PEFC is the most broadly studied system and most likely to have future ubiquitous application in various applications. From a student perspective, the automotive application tends to draw students into the class, so that the PEFC tends to be the system of greatest student interest. Additionally, multiphase management for PEFCs is especially complex compared to other systems where only single phase flow is present in the reactant and product mixture. Due to its importance in stability, performance, and durability, special attention is taken to detail the water balance and flooding in PEFCs. 

---