Abstract
To reduce the usage of Pt in polymer electrolyte membrane fuel cell electrocatalysts, an increase of the Pt utilization efficiency is crucial. In this study, the effect of polybenzimidazole (PBI) wrapping on carbon blacks (CBs) for the improvement of the Pt utilization efficiency in polymer electrolyte membrane fuel cells is investigated using CBs having a high surface area (HSA) and a low surface area (LSA). Subsequently, the structure-efficiency relationship is determined. A comparison study of the single-cell measurements using PBI-coated and non-coated HSA and LSA electrocatalysts reveals that HSA CB is more effective to improve the Pt utilization efficiency, where an improvement of 33% for the power density is achieved, while LSA CB shows an improvement of 10% under conditions of 80 °C at a relative humidity of 100%. The mechanism behind the greater improvement, especially for HSA CB, is mainly related to the micropore capping by the PBI wrapping, which increases the electrochemical active surface area as well as the proton conductivity and O2 diffusion. However, even though the degree of improvement is lower for LSA CB, an increase of the Pt utilization efficiency is realized mainly owing to the loading of uniformly dispersed smaller Pt.
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