Improving Performance of PEM Water Electrolysis Utilizing Nanofiber-Enhanced Porous Transport Electrodes with Low Iridium Content
Authors: Wen Xin , Penninckx Bastien , Sasidharan Sankar , Wenger Fabian , Ehrnberg Ellinor 
Published: December 2024

As the world strives to reduce its reliance on fossil fuels and transition towards cleaner energy sources, Membrane Water Electrolysis (PEMWE) emerges as a promising solution for generating clean hydrogen with its ability to utilize renewable energy sources such as solar and wind power. It is essential to select the appropriate materials for PEMWE for enhancing its efficiency, lifetime, and cost-effectiveness. A common PEMWE cell consists of a Membrane Electrode Assembly (MEA), which includes a proton exchange membrane coated with platinum (Pt) as the catalyst for Hydrogen Evolution Reaction (HER) and iridium (Ir) as the catalyst for Oxygen Evolution Reaction (OER), along with a carbon-based material and a Porous Transport Layer (PTL) as gas diffusion layers on the cathode and anode sides, respectively. A primary challenge within this cell structure lies in minimizing the usage of the rare and precious metal, Ir. As outlined by the U.S. Department of Energy (DOE), the target Ir content in electrodes should be reduced to less than 0.5 mg/cm2 by 2026 [1].

Smoltek Hydrogen is committed to reducing Ir catalyst loading on the anode side by developing a unique Porous Transport Electrode (PTE) with its patented nanofiber structure [2]. By growing these nanofibers vertically on the PTLs, surface area is significantly enhanced. Through the electrodeposition method, Ir catalyst can form a thin layer along the nanostructure. This not only maximizes Ir catalyst utilization, achieving loading levels as low as 0.1 mg/cm2 but also reduces contact resistance between the catalyst layer and PTL substrates.

The performance of PEMWE depends significantly on the materials utilized in each layer and the quality of their interfaces. A key strategy to enhance cell conductivity and minimize energy loss is to reduce cell thickness while improving interfacial contact [3].

In our investigation, we explored various parameters to boost the performance of PEMWE utilizing our specialized PTE. The results demonstrate that incorporating Nafion ionomer between the OER catalyst layer and the membrane, along with assembling the PTE with the membrane using the hot-pressing method, greatly improves interfacial contact and enhances the initial performance of PEMWE. Additionally, reducing the thickness of the PTL and membrane can further optimize cell conductivity. Moreover, factors such as cell pressure, parameters of the cell pre-conditioning step, as well as testing conditions such as temperature and water flow rates in the electrolyzer test systems, significantly influence performance. This study is focused on identifying the optimal cell conditions for Smoltek Hydrogen's PTEs.

References

https://www.energy.gov/eere/fuelcells/technical-targets-proton-exchange-membrane-electrolysis

https://www.smoltek.com/hydrogen/

Katherine Ayers. Current Opinion in Chemical Engineering, 2021, 33, 100719.

https://publications.jrc.ec.europa.eu/repository/handle/JRC10404

Figure 1. (a) SEM cross-section image of Smoltek PEMWE single cell. (b) SEM cross-section observation zooming in the Ir-coated nanofibers. (c) SEM image of nanofibers with Ir catalyst. (d) Polarization Curves observed at 80˚C, following the JRC Protocol [4], comparing the performance between PTEs with and without ionomers

Figure 1