Factors Affecting the Performance of CLs

Analyzing the factors affecting the performance of CL is complex. In this section, we only describe the primary factors affecting the performance of the CLs. 

2) Binder type and content in CL. PTFE and ionic conducting polymers like PFSA ionomer are commonly used as binders in CLs. The content of binders in the CL affects simultaneously the gas permeability, the catalytic activity, and the ionic conductivity [22]. Hence, optimizing binder content in the CL is necessary for better performance. The resistance of the CL could be reduced at the optimized binder content, increasing the utilization of the catalysts. 

The amount of polyelectrolyte binder used in CLs is not as large as that in membranes [18] however, the amount is important because it is closely related to CL performance, catalyst utilization, and MEA durability [23, 24]. In current PEMFCs, PFSA ionomers are employed in the CL as binders and in the proton conducting electrolyte to extend the formation of the electrochemical three-phase interface [3]. The latter is important for obtaining desirable catalyst utilization and, thus, high performance of MEA. Since the reactant must be transported through the proton conducting electrolyte before it arrives at the reaction sites to carry out reactions, the binder in the CL must be reactant-permeable to avoid reactant mass transport limitations [25]. The reactant-permeable property of the binder is 

Song et al. found that the optimal amount of ionomer in the CL is approximately 0.8 mg cm when Pt loadings are kept at 0.4 mg cm [28]. These values are rationalized in terms of the catalyst active area and the transport of the involved species for the electrode reaction. Previous studies looking at the influence of PFSA content on cell performance revealed that the optimal amount of the PFSA ionomer is about 0.8 mg cm in the case of the carbon-supported Pt catalyst [5, 29, 30]. But the optimal amount should depend on the Pt catalyst loadings in the CL [31]. Investigations of CLs with alternative ionomers, and their application in MEAs, have recently been reported [25, 32, 33]. 

The surface of the Pt particles could also be oxidized, according to Equations 7.13 and 7.14  

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