The role of oxygen-permeable ionomer for polymer electrolyte fuel cells

Abstract

In recent years, considerable research and development efforts are devoted to improving the performance of polymer electrolyte fuel cells. However, the power density and catalytic activities of these energy conversion devices are still far from being satisfactory for large-scale operation. Here we report performance enhancement via incorporation, in the cathode catalyst layers, of a ring-structured backbone matrix into ionomers. Electrochemical characterizations of single cells and microelectrodes reveal that high power density is obtained using an ionomer with high oxygen solubility. The high solubility allows oxygen to permeate the ionomer/catalyst interface and react with protons and electrons on the catalyst surfaces. Furthermore, characterizations of single cells and single-crystal surfaces reveal that the oxygen reduction reaction activity is enhanced owing to the mitigation of catalyst poisoning by sulfonate anion groups. Molecular dynamics simulations indicate that both the high permeation and poisoning mitigation are due to the suppression of densely layered folding of polymer backbones near the catalyst surfaces by the incorporated ring-structured matrix. These experimental and theoretical observations demonstrate that ionomer’s tailored molecular design promotes local oxygen transport and catalytic reactions.

PtCo/C catalysts with narrow particle size distribution improve high current density operation in PEM fuel cells

“…As it is most likely that ReCatalyst PtCo/C features a higher fraction of exterior PtCo on carbon than the references (as discussed earlier), the chance for ionomer-induced poisoning for ReCatalyst catalyst is higher compared to the UM catalysts. [72][73][74][75] This hypothesis is further supported by other prior fundamental studies in the liquid electrolyte by N. Marković et al on single crystal surfaces of Pt. 76,77 The authors have shown that the variations in activity for oxygen reduction with crystal facets arise from the different structural sensitivity on the adsorption of anions in the electrolyte.…”

Fully Hydrocarbon Membrane Electrode Assemblies for Proton Exchange Membrane Fuel Cells and Electrolyzers: An Engineering Perspective

“…The oxygen diffusivity of state‐of‐the‐art highly oxygen‐permeable ionomer (HOPI) is ≈3 × 10 −10 m 2 s −1 at 30% RH and ≈5 × 10 −10 m 2 s −1 at 90% RH, both at 80 °C. [ 12 ] As a rough comparison, the oxygen diffusivity of SPEEK (1.4 × 10 −10 m 2 s −1 ) and that of SPSU (0.25 × 10 −10 m 2 s −1 ) was observed to be lower than that of the Nafion reference (6.2 × 10 −10 m 2 s −1 ) at the same conditions (80 °C, 75% RH, and 166 kPa abs ). [ 156 ]…”

“…Those materials include increased catalytic active sites and intrinsic activity [5,6] and catalyst layers with mesoporous Pt/C from GM R&D. [7] The optimal electrode ionomer should provide high proton conductivity at high temperatures (>100 °C) and low humidity (<50% relative humidity (RH)), thus high ion exchange capacity (IEC) [8] without poisoning the catalyst [9,10] and finally a high oxygen permeability. [11,12] The gas diffusion layers should also be improved to significantly reduce the gas transport losses. [13] The desired high operating temperatures (>100 °C) are a bottleneck for state-of-the-art PFSA membrane-electrode assemblies (MEAs), while being highly attractive to boost efficiency, increase cooling gradients, and increase CO tolerance.…”

UV-crosslinkable anthracene-based ionomer derived gas “Expressway” for anion exchange membrane fuel cells

“…S7, † and the blue part of the diagram represents the free volume produced by polymer chain stacking. 26 The migration and rotation of the polymer chain segments were severely restricted by the crosslinked network of rigid steric hindrance anthracene groups, resulting in a lower polymer chain packing degree. The free volume of CPPOAN is approximately 30% higher than PPOAN via mathematical statistics, 294 nm 3 and 382 nm 3 for PPOAN@Pt/C and CPPOAN@Pt/C, respectively; this provided convincing evidence of the crosslinked rigid steric hindrance anthracene group-induced formation of the porous morphology.…”