Application of similarity theory in the study of proton exchange membrane fuel cells: a comprehensive review of recent developments and future research requirements

The diversity and complexity of the parameters involved in the modeling of proton exchange membrane fuel cells (PEMFCs) have restricted further research and applications of such cells, and the similarity theory is a promising solution to this problem. The similarity theory is an effective tool to obtain compact and generalized results with the same precision as that of the basic mathematical model. This paper presents a comprehensive review of the application of the similarity theory to most aspects of PEMFCs. The advantages of using the similarity theory, such as generality, reduction in the test effort, convenient comparisons and guidance to scale up the experiment, are discussed and analyzed. Although a number of similarity criteria have been proposed in recent years, the similarity theory is not as widely applied or well accepted in PEMFC research as in the heat transfer and fluid flow domain. The objective of this paper is to demonstrate the feasibility of performing a similarity analysis for such complex systems and encourage researchers to present a dimensionless expression of their results in the follow-up PEMFC research. A key challenge is to use the similarity analysis for a complete gas-water-electricity-heat-mechanics coupled with PEMFC system and obtain the correlation between the dimensionless output voltage/current and input similarity criteria. This review indicates that none of the existing models can achieve this objective, and further research pertaining to this aspect must be performed. Several recommendations to achieve this aim, including a hierarchical classification of the criteria, are provided.