Oxygen Reduction Activity Indicator for Fuel Cell Catalysts at Rated Voltage

The fuel cell performance is generally affected by the catalytic activities. Considering the advancement in technology and increased demand for fuel cells, commercialization of fuel cells is inevitable. Therefore, the development of catalysts with high catalytic activities is highly desirable to meet the newly proposed technical targets of electrocatalysts. Even though pure Pt catalysts can meet the target requirements especially in the rotating disc electrode systems at 0.9V, the performance of the membrane electrode assemblies is still considerably low. On the other hand, the low performance of Pt/C catalysts as compared to the pure Pt catalysts has raised concerns on the effects of Pt on the fuel cell performance.

Presently, the focus has majorly shifted on the development of high-performance catalysts with high oxygen reduction reaction activities at rated voltages of 0.6V-0.8V. Unfortunately, the available indicators for these catalysts are not favorable to use due to several challenges like the difficulty in the characterization of the catalytic activities of oxygen reduction catalyst in the rated voltage range of 0.6V-0.8V. This is attributed to the challenges in distinguishing the key types of polarization: activation polarization, mass transfer polarization, and ohm polarization. Recently, electrochemical impedance microscopy has shown the potential of distinguishing the aforementioned polarization to give relevant insights about the catalytic activities i.e. charge transfer resistance.

Wuhan University of Technology researchers: Yan Rao, Chao Cai, Jinting Tan, and Professor Mu Pan investigated the charge transfer resistance of Pt/C catalysts in membrane electrode assemblies at different potentials. In particular, they evaluated the oxygen reduction reaction activities of catalysts for fuel cells at the rated voltage of 0.8V-0.6V. The team commenced their work by measuring the charge transfer resistance of the membrane electrode assemblies with Pt/C catalysts in the range of 0.68V-0.92V using a Tafel slope. Eventually, they compared the charge-transfer resistance of the membrane electrode assemblies with PtCo/C catalysts to that with Pt/C catalysts. The research work is currently published in the research journal, Journal of The Electrochemical Society.

At high potentials, the authors recorded approximately 80mV/decade for the Tefel slopes calculated from the charge transfer resistance. However, this value decreased with the decrease in the potentials below 0.8V. On the other hand, the charge-transfer resistance of the PtCo/C catalysts was relatively lower than that for Pt/C catalysts in the high potential regions due to the low oxygen reduction reaction of the Pt/C catalysts at high potentials. Additionally, almost similar oxygen reduction reaction activities were exhibited in the rated potential region.

In summary, the Wuhan University of Technology scientists proposed a charge-transfer resistance to evaluating the oxygen reduction reaction activity of catalysts for fuel cells at the rated voltage. To actualize their study, they performed durability tests and monitored the charge-transfer resistance of the membrane electrode assemblies with Pt/C catalysts. Interestingly, a 125.6% increase in the charge-transfer resistance was recorded after 900hrs. Altogether, the study paves the way for various improvements that will enable determination of the factors influencing the increase in the charge-transfer resistance. Such improvements may lead to the development of high-performance fuel cell catalysts for various applications.