Alternative Gas Diffusion Electrode Designs: Influence of Porosity Gradients on the Electrochemical Activity

Gas diffusion electrodes (GDEs) are essential in various electrochemical applications aimed at reducing CO2 emissions and combating climate change, such as fuel cells, electrolyzers and metal-air batteries. However, carbon-based GDEs often face issues with corrosion in alkaline environments during OER and ORR, necessitating metal-based materials as viable alternatives. Nickel foam is an attractive solution due to its high OER electrochemical activity and stability in alkaline media. This study explores carbon-free gas diffusion electrodes (CF-GDEs) with distinct porosity gradients, made from MnOx-coated macroporous substrates and hydrophobized with PTFE. The research demonstrates that these CF-GDEs significantly outperform a commercial carbon-based GDE (GDEref) by showing reduced overpotentials and enhanced electrochemical stability. In particular, the layered design Fop|Fop*|Fle* exhibited a one-third reduction in ηOER (0.24 V) compared to GDEref at 10 mA cm-2. Noteworthy, this CF-GDE also shows excellent long-term stability without degradation, which is a common issue in carbon-based GDEs due to carbon corrosion. Stability tests revealed the formation of electrochemically active NiOx, Ni6MnO8, and NiMn layered double hydroxides, resulting in a doubling of current densities. These findings highlight the potential of CF-GDEs with optimized porosity gradients for advanced applications in sustainable energy technologies.