Degradation Study by Start-Up/Shut-Down Cycling of Superhydrophobic Electrosprayed Catalyst Layers Using a Localized Reference Electrode Technique

Abstract

Degradation of a polymer electrolyte membrane fuel cell (PEMFC) with electrosprayed cathode catalyst layers is investigated during cyclic start-up and shut-down events. The study is carried out within a single cell incorporating an array of reference electrodes that enables measurement of cell current as a function of local cathode potential (localized polarization curves). Accelerated degradation of the cell by start-up/shut-down cycling gives rise to inhomogeneous performance loss, which is more severe close to the gas outlet and occurs predominantly during start-up. The degradation consists primarily of loss of cathode catalyst activity and increase in cell internal resistance, which is attributed to carbon corrosion and Pt aggregation in both anode and cathode. Cells with an electrosprayed cathode catalyst layer show lower degradation rates during the first 100 cycles, compared with those of a conventional gas diffusion electrode. This difference in behavior is attributed to the high hydrophobicity of the electrosprayed catalyst layer microstructure, which retards the kinetics of corrosion of the carbon support. In the long term, however, the degradation rate is dominated by the Pt/C ratio in the cathode catalyst layer.

Stability of CoPx Electrocatalysts in Continuous and Interrupted Acidic Electrolysis of Water

“…This might be explained by the fact that such a frequent change of load (i. e. j start ≈0 mA/cm 2 , j end ≈−5 mA/cm 2 ) creates additional stress to the electrode by forming reverse currents upon repeated sweeping. A similar phenomenon is widely observed in commercial electrolyzers and fuel cells which suffer from reverse (or shunt) currents created by the shut‐down/start‐up of electrolyzer ,. Reverse currents might originate from the oxidation of H 2 produced during the preceding HER and accompanied by anodic degradation of the electrode.…”

An opinion on catalyst degradation mechanisms during catalyst support focused accelerated stress test (AST) for proton exchange membrane fuel cells (PEMFCs)

“…takes place mainly during startup/shutdown due to development of potentials ranging between 1.4 and 1.75 V [7][8][9][10][11]. Modifications of catalyst composition, surface structure, etc.…”

Single Cell Study of Water Transport in PEMFCs with Electrosprayed Catalyst Layers

“…Mercury porosimetry shows 12 cm 3 g −1 carbon pore volume for electrosprayed layers, compared with 2.5 cm 3 g −1 carbon of films prepared by airbrushing with the same composition . The total pore volume fraction of the electrosprayed layers is normally above 90%, compared with 80% for layers deposited with airbrush and commercial layers . The results of pore size distribution are shown in Figure for electrosprayed and airbrushed films with two different Nafion concentrations (results extracted from Fig.…”

“…The beneficial effect is attributed to faster water transport and more homogeneous response induced by a superhydrophobic cathode catalyst layer [8]. The durability of the cell is also positively affected by the dry and homogeneous conditions imposed within the electrosprayed cathodic layer [12]. On the other hand, catalyst activity is slightly unfavored by the electrosprayed morphology, probably due to the dryer conditions, as shown by impedance analysis in single cells and rotating disk electrode [8,13], although with a minor impact on the performance of the PEMFC.…”