Rotating thin‐film method for supported catalysts

Abstract In this chapter, the thin‐film R(R)DE (TFR(R)DE) method is described, i.e., a method for the quantitative evaluation of the electrocatalytic activity of high‐surface area catalysts in a true R(R)DE configuration. The method offers complete catalyst utilization combined with a high reproducibility with respect to the catalyst loading on the electrodes. It is further proven that both catalyst agglomerate and film diffusion effects, respectively, are negligible in the thin catalyst/Nafion layers. That means the thin‐film electrodes can be treated like smooth rotating electrodes with the well‐known hydrodynamics and defined mass‐transport conditions. In other words, kinetic parameters such as kinetic current densities, activation energies, Tafel slopes etc. can directly be determined from the measured current densities without applying any mathematical modeling of the mass transport in the catalyst/Nafion layer. Furthermore, this method allows the determination of electrode kinetics under fuel cell relevant mass‐specific current densities of 1–2 A . The suitability of the TFRDE method is demonstrated by discussing results from different kinetic studies on the oxidation of CO and CO/H 2 mixtures on high‐surface area Pt, PtRu, PtSn and PdAu electrocatalysts. Additionally, it is illustrated how thin‐film electrodes can be successfully used for measurements with a differential electrochemical mass spectrometry (DEMS) setup for the mass‐spectrometrical determination of the electrochemically formed products. In the last section, the adaptation of the TFRDE method for ring‐disk measurements is described. The potential‐ and rotation‐rate independent, well‐defined collection efficiency for the thin film RRDE configuration enables the quantification of the molar fraction of H 2 O 2 produced during oxygen reduction. In general, the TFR(R)DE method can be seen as an easy‐to‐use tool for the screening and characterization of high‐surface area electrocatalysts under low temperature fuel cell relevant conditions.