Modelling, design and validation of a laminar flow channel electrochemical cell set up for elevated temperature studies of fuel cell electrocatalysts

Proton Exchange Membrane Fuel Cells (PEMFCs) are often run at a high temperature T (80-100°C) and pressure P (2 bar). Thin-film rotating (ring) disk electrodes (TF-R(R)DEs) are the half-cell electrochemical setup of choice for a rapid screening of the oxygen reduction reaction (ORR) activity of Pt supported on carbon black supports (Pt/C) electrocatalysts. Unfortunately, when considering high T and P, it suffers some limitations. On the other hand, a channel flow electrode (CFE) cell constructed with polyetheretherketone (PEEK), a high performance polymer, can be operated in closed systems with controlled oxygen concentration while maintaining a high level of cleanliness. These characteristics are necessary for measuring the maximum mass activity MAmax of the catalyst material under conditions close to operando PEMFCs in order to establish the Pt effectiveness in fuel cell membrane electrode assemblies. Herein the modeling, material selection, design, and testing of a versatile CFE cell developed from scratch is presented since only little technical details are usually given on the experimental setup developed by other research groups. Furthermore, this cell is compatible with commercially available parts and special care has been devoted to the cell design in order to ease the overall assembling of the experimental setup. Well-defined hydrodynamics, low dead volume, high mass-transfer rate and high signal/noise have also been implemented as general requirements. The working electrodes used in this cell are a circular polycrystalline Pt or a circular thin and homogenous film of three different loadings L of a Pt/C catalyst covering a glassy carbon current collector. The kinetically controlled ORR MA has been investigated under potentiodynamic conditions at various potential scan rate dE/dt and at varied laminar flow rates Ū (0.1-18.6 mL·min-1) of an oxygen-saturated 0.1 M HClO4 electrolyte solution at ambient T. One loading was also tested at three different T (20, 40 e 60 °C). From the analyses a linear relationship between O2 mass transport limiting current and cubic root of the electrolyte flow has been determined at all tested temperatures, and it matches the expectations from modelling. Although Pt disk manifested currents lower than theoretical one due to its low active surface area, no major impurities were found. The MA gained with the CFE cell are in accordance with the literature for electrocatalyst material activity. A MAmax of 1155 mA·mg-1Pt has been obtained at ambient temperature for Pt catalyst with the following experimental parameters: L of 14 μgPt·cm-2, dE/dt of 5 mV·s-1 and Ū higher than 4 mL·min-1. From the results it has been possible to conclude that this new CFE cell is valid at both ambient and at high temperature. Still, the cell and the surrounding flow-controlling equipment require additional fine-tuning for even more precise and repeatable data acquisition.