Investigating Anodic Catalyst-Ionomer Interactions in Anion Exchange Membrane Water Electrolysis (AEMWE)

Molecular hydrogen has an energy density per mass three times higher than gasoline and produces no carbon dioxide when burned, making it a useful alternative to polluting fossil fuels. However, over 99% of hydrogen currently comes from fossil fuels and therefore negates the carbon benefits of powering vehicles and power systems with hydrogen. Water electrolysis is a clean, alternative hydrogen production method that could be coupled with renewable energy to produce carbon-neutral hydrogen. While proton exchange membrane water electrolysis and alkaline water electrolysis are well-established technologies, the former relies on expensive titanium parts and scarce catalyst materials, and the latter suffers from poor efficiency and membrane stability, limiting their widespread adoption. Anion exchange membrane water electrolysis (AEMWE) is a promising candidate to reduce the cost of producing hydrogen, as it doesn’t require expensive platinum-group metal catalysts and acid-resistant metals such as titanium for parts, yet it has reasonably good efficiency. AEMWE must further improve in efficiency and increase its lifetime for large-scale use. The anode contains higher overpotentials than the cathode; thus, much research focuses on reducing anodic overpotentials to increase efficiency. Ionomer-catalyst interactions govern the kinetics and transport through the catalyst layer, yet little research has studied these interactions. In this poster, PiperION ionomer particles were ground into various sizes before being combined with Co₃O₄ catalyst particles and solvents. The different inks were then sprayed onto nickel foam substrates to synthesize anodes with different microstructures. Cells were assembled using a Pt/C cathode and a PiperION membrane, and electrochemical tests, including electrochemical impedance spectroscopy and potentiostatic polarization curves, were used to evaluate electrolyzer performance. Overpotentials were broken down using high frequency resistance and Tafel slope analysis, while scanning electron microscopy was used to study catalyst layer morphology. Depending on KOH electrolyte concentration, ionomer particle size had different levels of influence on electrolyzer performance: with 1M KOH, ionomer particle size had little effect on performance. However, with 0.1M KOH, larger ionomer particle size in the anodic catalyst layer decreased kinetic, catalyst layer resistance, and residual—often attributed to mass transport—overpotentials, therefore increasing cell efficiency. The reductions in overpotentials were attributed to increased electrochemically active surface area, increased electronic conductivity, and increased porosity. The increase in efficiency, though, came with a tradeoff of increased degradation in the form of voltage gain after conducting a degradation test. This increased degradation was caused by significant delamination of catalyst and therefore decreased electrochemically active surface area, seen via electron microscope imaging. The results indicate that understanding ionomer-catalyst interactions is important to improving AEMWE performance, especially at low electrolyte concentrations. Future research should go into optimizing catalyst and ionomer loading simultaneously with ionomer particle size to minimize overpotentials attributed to kinetics, catalyst layer resistance, and mass transport.