Electrocatalyst Performance at the Gas/Electrolyte Interface under High-Mass-Transport Conditions: Optimization of the “Floating Electrode” Method

Abstract

The thin-film rotating disk electrode (TF-RDE) is a well-developed, conventional ex situ electrochemical method that is limited by poor mass transport in the dissolved phase and hence can only measure the kinetic response for Pt-based catalysts in a narrow overpotential range. Thus, the applicability of TF-RDE results in assessing how catalysts perform in fuel cells has been questioned. To address this problem, we use the floating electrode (FE) technique, which can facilitate high-mass transport to a catalyst layer composed of an ultralow loading of catalyst (1–15 μgPt cmgeo –2) at the gas/electrolyte interface. In this paper, the aspects that have critical effects on the performance of the FE system are measured and parametrized. We find that, in order to obtain reproducible results with high performance, the following factors need to be taken into account: system cleanliness, break-in procedure, hydrophobic agent, ionomer type, and the measurements of catalyst surface area and loading. For some of these parameters, we examined a range of different approaches/materials and determined the optimum configuration. We find that the gas permeability of the hydrophobic agent is an important factor for improving the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) performance. We provide evidence that the suppression of the HOR and ORR introduced by the Nafion ionomers is more than a local mass transport barrier but that a mechanism involving the adsorption of the sulfonate on Pt also plays a significant role. The work provides intriguing insights into how to manufacture and optimize electrocatalyst systems that must function at the gas/electrolyte interface.

Resolving the nanoparticles' structure-property relationships at the atomic level: a study of Pt-based electrocatalysts

“…MFE allows using a TEM grid as a working electrode and thus is synergistic with the IL-TEM methodology ( Hodnik and Cherevko, 2019 ; Hrnjić et al., 2020 ). The main characteristic of the MFE setup is that the working electrode operates in the so-called floating mode ( Lin et al., 2020 ; Zalitis et al, 2013 , 2015 , 2020 ). This means that the electrode is not dipped in the electrolyte solution, as is the case with TF-RDE, but is instead placed on its surface.…”

How to appropriately assess the oxygen reduction reaction activity of platinum group metal catalysts with rotating disk electrode

“…The following proposals are urgently to be motivated: (1) RHE should be used as RE as far as possible, and if other REs are adopted, their details of potential conversion vs. RHE should be illustrated, and there is no need to conduct iR-drop correction if Luggin capillary is placed correctly in TF-RDE test; (2) To simulate the standard MEA polarization protocol proposed by DOE and narrow the gap of ORR activities obtained via TF-RDE and MEA, reciprocating LSV/SCV should be performed to characterize the ORR performances of PGMs; (3) Connotations like M A and S A should be defined precisely, and K-L equation as well as the selection of j L should be emphasized; (4) The details of calculation processes, such as m Pt , j A , j L , and ECSA et al., should be listed in article or supplemental information for the better readability for readers. Furthermore, considering the limited mass transport in TF-RDE and its discrepancy in test conditions with respect to MEA, whose fabrication process is very much an art, floating electrode ( Lin et al., 2020 ; Zalitis et al., 2013 ) and gas diffusion electrode ( Inaba et al., 2018 ; Mardle et al., 2020 ; Roudbari et al., 2020 ) techniques have been proposed in recent years and are under rapid development to bridge the activity gap between TF-RDE and MEA while maintaining its simplicity, convenience, and controllability.…”

Anion Exchange Ionomers: Impact of Chemistry on Thin‐Film Properties

“…In addition, the high mobility of the side chain of the perfluorinated ionomers may form an optimal three‐phase interface during the cell break‐in process to improve cell performance. [ 33 ] On the other hand, the catalyst nanoparticle aggregation in the perfluorinated ionomer bonded electrodes may occur more significantly as the concentration of the ionic groups in the vicinity of the electrocatalysts is higher. [ 34 ]…”