Analysis of MEA’s durability under Accelerated Stress Tests that mimic realistic automotive operations

This work aims at studying MEA’s ageing under single operational “mode” accelerated stress tests (AST), that were specifically designed to replicate under hydrogen/air feeding the main stressors of realistic operations in the automotive sector. A methodology for developing AST is here presented and preliminary results about the activity included. In particular, low power and high power functioning have been mimicked in a Zero-Gradient hardware, which allows a reliable materials comparison. Quantities, measurable in-situ and operando, have been tracked during ageing, like cell power, polarization curves, Pt active area, oxygen mass transport resistance, Electrochemical Impedance Spectra. The final objective is to clarify the underlying ageing mechanisms and assess the contribution of each specific operation to the MEA lifetime, focusing in particular on the cathode catalyst layer durability. Moreover, the rate of voltage loss for the new ASTs has been successfully correlated to the degradation observed under a complete driving cycle protocol.

Aromatic ionomer in the anode catalyst layer improves start-up durability of polymer electrolyte fuel cells

Sulfonated polyphenylene ionomer (SPP-QP) was used as a catalyst layer binder in polymer electrolyte fuel cells. SPP-QP functioned well in the proton-conducting thin layers to show high electrochemically active surface...

Ionomer Films Impact on The Structure, Flow Regime, and The Wettability of The Catalyst Layer of PEMFC

Percolation testing and contact angle measurements have been used to investigate the role of relative humidity on structure, mass transport, and wettability of a PEM fuel cell catalyst layer and membrane. Four samples were tested, two catalyst layers and two membranes. Structure and mass transport changes in the catalyst layers resulting from RH changes were studied in terms of percolation pressure. A clear change in the structure between low and high RH conditioning was observed. Relative humidity (RH) cycling also impacted percolation pressures with an indication of catalyst layer cracking. In addition, RH effect on wettability of both catalyst layers and membranes was studied by measuring contact angles of sessile drops.

Impedance-based Performance Analysis of Micropatterned Polymer Electrolyte Membrane Fuel Cells

Micropatterns applied to proton exchange membranes can improve the performance of polymer electrolyte fuel cells; however, the mechanism underlying this improvement is yet to be clarified. In this study, a patterned membrane electrode assembly (MEA) was compared with a flat one using electrochemical impedance spectroscopy and distribution of relaxation time analysis. The micropattern positively affects the oxygen reduction reaction by increasing the reaction area. However, simultaneously, the pattern negatively affects the gas diffusion because it lengthens the average oxygen transport path through the catalyst layer. In addition, the patterned MEA is more vulnerable to flooding, but performs better than the flat MEA in low-humidity conditions. Therefore, the composition, geometry, and operating conditions of the micropatterned MEA should be comprehensively optimized to achieve optimal performance.

Modeling of three-phase continuously operating open-cell foam catalyst packings: sugar hydrogenation to sugar alcohols

An advanced comprehensive and transient multiphase model for a trickle bed reactor with solid foam packings was developed. A new simulation model for isothermal three-phase (gas–liquid–solid) catalytic tubular reactor models was presented where axial, radial and catalyst layer effects were included. The gas, liquid and solid phase mass balances included most of the individual terms for solid foam packing (e.g. kinetics, liquid-solid and intraparticle mass transfer effects). Hydrogenation of arabinose and galactose mixture on a ruthenium catalyst supported by carbon-coated aluminum foams was applied as a fundamentally and industrially relevant case study. Parameter estimations allowed to obtain reliable and significant parameters. To test the model performance, a sensitivity analysis was performed and the effect of the kinetic parameters and the operation conditions on the arabinose and galactose conversions was studied in detail. The model described here is applicable for other three-phase continuous catalytic reactors with solid foam packings.

Optimization of the Interface Between Catalyst Layer and Proton Exchange Membrane via rolled technique

Optimization of the interface between the catalyst layer (CL) and the proton exchange membrane (PEM) plays an important role in performance enhancement in proton exchange membrane fuel cells (PEMFCs). Here, a rolled technique was used to optimize the PEM|CL interface to obtain a smooth CL surface with decreased roughness from 0.347 to 0.266 μm due to the reduction of protrusions after the rolled process. Advantages of the optimized PEM|CL interface formed after decal transfer method were carefully evaluated. First, the internal resistance of the rolled CL is significantly reduced from 61.5 to 47.5 mΩ cm2@2000 mA/cm2, which is ascribed to the higher contact area between CL and PEM. Meanwhile, owning to the alleviation of liquid water accumulation at the interface, the oxygen transport resistance at no back pressure of CL dropped from 0.21 to 0.15 s/cm. The relieved ohm polarization and mass transfer polarization promote a 28.5% increase of performance. Rolled technique with proper calendrer roll space could result in an optimized interface with well-maintained internal structural integrity of CL. However, a lower calendrer roll gap will damage the structure of CL and have a negative effect on the interface optimization.

Optimizing the use of a “Zero-Gap” Gas Diffusion Electrode Setup for Electrochemical Reduction of CO2

The lack of a robust and standardized experimental test bed to investigate the performance of catalyst materials for the electrochemical CO2 reduction reaction (ECO2RR) is one of the major challenges in this field of research. To best reproduce and mimic commercially relevant conditions for catalyst screening and testing, gas diffusion electrode (GDE) setups attract a rising attention as an alternative to conventional aqueous-based setups such as the H-cell configuration. In particular a zero-gap design shows promising features for upscaling to the commercial scale. In this study, we develop further our recently introduced zero-gap GDE setup for the CO2RR using an Au electrocatalyst as model system and identify/report the key experimental parameters to control in the catalyst layer preparation in order to optimize the activity and selectivity of the catalyst.