NiCo2O4 and NiMn2O4 spinel oxides supported on CNF as electrocatalysts for the OER

Spinel electrocatalysts supported on carbon nanofibers (CNFs) denoted as NiCo2O4/CNF and NiMn2O4/CNF were investigated for oxygen evolution reaction (OER) in alkaline electrolyte. NiCo2O4/CNF and NiMn2O4/CNF were 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 1h in air, nanosized metal oxides with a spinel structure supported on carbon nanofibers were obtained. The physico-chemical investigation showed relevant difference in crystallite sizes (9 nm for the NiCo2O4/CNF and 20 nm for the NiMn2O4/CNF) and more homogeneous distribution for NiMn2O4 supported on carbon nanofibers. These characteristics derived from the different catalytic effects of Co and Mn during the thermal treatment as demonstrated by the TG-DSC analysis. The OER activity of NiCo2O4/CNF and NiMn2O4/CNF was studied in a single cell based on a zero gap anion-excange membrane-electrode assembly (MEA). The NiMn2O4/CNF showed a better mass activity than NiCo2O4/CNF at 50 °C (116 A g-1 @ 1.5 V and 383 A g-1 @ 1.8 V vs. 39 A g-1 @ 1.5 V and 272 A g-1 @ 1.8 V) but lower current density at specific potentials. This was the consequence of a lower concentration of the active phase on the support resulting from the need to mitigate the particle growth in NiMn2O4/CNF.