Influence of pore size on mass transport: Bifunctional MnOx-coated nickel foam vs carbon corrosion prone commercial GDE in alkaline electrolyte

Abstract

A promising step towards a carbon-free gas diffusion electrode (CF-GDE) design for alkaline applications is shown in this work. MnOx´s are electrodeposited on nickel foam by varying the settings, and then they were annealed at 300 °C. These CF-GDEs were characterized and compared with a commercial carbon-based GDE (GDEref). Samples were analyzed by XRD, SEM, X-ray tomography, contact angle method, nitrogen sorption, and electrochemical methods. Electrochemical impedance spectroscopy confirmed the higher reactant transport of CF-GDEs during OER and ORR. The large pore size of the CF-GDE substrate (nickel foam) results in a high supply of catalyst sites deep inside the CF-GDE. The transport distance of gaseous O2 is also reduced since the thin electrolyte film is at the gas bulk of the CF-GDE. The catalytic bifunctionality was additionally examined by galvanostatic measurements at 5 and 10 mA cm− 2. A promising CF-GDE exhibited 0.43 V ηOER and −2.43 V ηORR at 10 mA cm−2. Lastly, long-term stability measurements of 2100 cycles at 1.5 V (OER) and −0.75 V (ORR) vs. Hg/HgO in 1 M NaOH show the carbon corrosion of GDEref (60% current density loss) and a stable current density of CF-GDE.