NF is widely used as a 3-dimensional support for OER catalysts , but its intrinsic activity is modest (Fig. ). Since it has been shown that iron incorporation is required to enhance the OER activity of NiOx-based catalysts , we hypothesized that the activity of NF might be increased in a similar way by iron incorporation. Fe ions were incorporated by potential cycling in commercial KOH, as it was previously shown that such a process led to the incorporation of Fe ions into NiOx films . Indeed when NF was subjected to 100 repetitive cyclic voltammetric (CV) scans from 1.21 to 1.54 V vs. RHE in a 1 M commercial KOH solution (with a Fe concentration of 0.18 mg L -1 according to measurements using Inductively Coupled Plasma Mass Spectrometry (ICP-MS)), a layer of Fe-containing nickel oxide (NiOx-Fe) was formed. A NF-NiOx-Fe electrode (loading of iron oxide: 4.3 g cm -2 ) exhibits much higher OER activity than NF (Fig. ). The as-received NF was then immersed into a solution containing 10 wt% hydrochloric acid (HCl) for 30 minutes, which resulted in a NF-AC (AC = acid cleaned) electrode with a rougher surface than NF according to the scanning electron microscopy images (Supplementary Fig. ). After repetitive CV or linear sweep voltammetric (LSV) scans from 1.21 to 1.54 V vs. RHE in a 1 M commercial KOH solution, NF-AC-NiOx-Fe electrodes were prepared. According to ICP-MS, the iron oxide loadings were in the range of 1.0-14.1 g cm -2 depending on the preparation procedure (details are provided in Supplementary Information).