Advanced Catalysts for the Oxygen Evolution Reaction Fabricated By Reactive Spray Deposition Technology: Degradation Mechanisms Governing the Performance Loss during the Long-Term Steady State Operation

Development of novel and improved catalysts and membrane electrode assemblies (MEAs) for proton exchange membrane (PEM) based energy conversion devices is of crucial importance for widespread application of the PEM fuel cells and electrolyzers. These PEM based devices are critical for the Hydrogen Economy (HE) implementation. The HE is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. Currently, the main challenges that the state-of-the-art MEAs are facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers and time consuming and expensive multi-step fabrication processes; and (ii) poor durability caused by the instability of the catalysts and the materials [1, 2].

Herein, we demonstrate the capabilities of the unique Reactive Spray Deposition Technology (RSDT) for fabrication of advanced catalysts for the oxygen evolution reaction (OER) and MEAs that could overcome these challenges. The RSDT is a flame assisted method [3, 4] that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large (up to 1000 cm²) MEAs for application in PEM fuel cells and electrolyzers [4]. In addition, this technology allows precise control of the composition, morphology, and particle size distribution of wide range of nanoparticles supported and unsupported on carbon, and thus ensures fine tuning of the catalysts' activity and durability. Ir/IrO_x unsupported catalysts fabricated by RSDT have been studied in half cell configuration by rotating disc electrode (RDE) technique in 0.1 M HClO₄ and showed improved activity towards the OER in comparison to the state-of-the-art commercial IrO₂ catalyst. Furthermore, MEAs with geometric area of 86 cm² and one order of magnitude lower Ir loading in the anode catalyst layer in comparison to the state-of-the-art MEAs for PEM water electrolyzers [5], were fabricated by the RSDT and tested for 5000 hours at current density of 1.8 A cm^-2, 50 ^oC, and 400 psi differential hydrogen pressure. Diagnostic tests that include polarization curves, electrochemical impedance spectroscopy, linear sweep voltammetry, and hydrogen crossover measurements were performed periodically in order to evaluate the cell performance change during the long-term durability test. After the test, the MEAs were disassembled and subjected to comprehensive post test analysis. A wide range of techniques including high-resolution TEM, STEM, EDS, SEM, ICP, XCT, XPS, and digital optical microscopy, have been used to study the degradation mechanisms governing the performance loss in the MEAs during the long-term steady state operation, and the results will be presented and discussed in detail in this talk.

References

1. https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf

2. https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf

3. Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).

4. Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).

5. Ayers, K. Current Opinion in Electrochemistry, 18, 9–15 (2019).