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

Abstract

In this study, it is revealed that carbon-free gas diffusion electrodes (CF-GDEs) with macropore sizes outperform the a carbon-based GDE (GDE_ref). These CF-GDEs exhibit notably reduced overpotentials and increased electrochemical stability. By combining three distinct macropore-sized substrates, coated with MnO_x and hydrophobized with polytetrafluorethylen, a range of CF-GDEs with distinct porosity gradients is designed. In the results, the pivotal role of substrate layers and their hydrophilic/hydrophobic attributes in steering the formation of the electrolyte thin film are unveiled. Specifically, one CF-GDE shows a reduction by one-third of the η_OER (0.24 V) compared to GDE_ref at 10 mA cm⁻². Noteworthy, this CF-GDE also displays excellent long-term stability without degradation, which is a common issue with carbon-based GDEs due to carbon corrosion. Impressively, the stability measurement conditions the active catalyst sites of the CF-GDE and leads to the formation of NiO_x, Ni₆MnO₈, and NiMn layered double hydroxides. This results in a doubling of the current densities.