Electrospun NiMn2O4 and NiCo2O4 spinel oxides supported on carbon nanofibers as electrocatalysts for the oxygen evolution reaction in an anion exchange membrane-based electrolysis cell

Spinel oxide electrocatalysts supported on carbon nanofibers (CNFs), denoted as and NiMnO/CNF and NiCoO/CNF, are investigated for the oxygen evolution reaction (OER) in alkaline electrolyte. NiCoO/CNF and NiMnO/CNF are prepared according to an optimized electrospinning method using polyacrylonitrile (PAN) as carbon nanofibers precursor. After the thermal treatment at 900 °C for 1 h in the presence of helium and the subsequent one at 350 °C for 1 h in air, nanosized metal oxides with a spinel structure supported on carbon nanofibers are obtained. The physico-chemical investigation shows relevant difference in the crystallite size (9 nm for the NiCoO/CNF and 20 nm for the NiMnO/CNF) and a more homogeneous distribution for NiMnO supported on carbon nanofibers. These characteristics derive from the different catalytic effects of Co and Mn during the thermal treatment as demonstrated by thermal analysis. The OER activity of NiCoO/CNF and NiMnO/CNF is studied in a single cell based on a zero gap anion-exchange membrane-electrode assembly (MEA). The NiMnO/CNF shows a better mass activity than NiCoO/CNF at 50 °C (116 A g @ 1.5 V and 362 A g @ 1.8 V vs. 39 A g @ 1.5 V and 253 A g @ 1.8 V) but lower current density at specific potentials. This is the consequence of a lower concentration of the active phase on the support resulting from the need to mitigate the particle growth in NiMnO/CNF.