Table 2.
Fe concentrations (the cobalt concentration is CCo = 100-CFe) as a percentage of the total metal content for the prepared Co1+δFe2−δO4(111) films before and after oxygen evolution reaction (OER) experiments
| θ = 0° | θ = 70° | θ = 0° | θ = 70° | θ = 0° | θ = 70° | ||
|---|---|---|---|---|---|---|---|
| No | δ before OER | Fe concentration before OER | Fe concentration after OER | Difference (‘after’-‘before’) | |||
| 1 | 0.20 | 60% | 64% | 52% | 49% | 8% | 15% |
| 2 | 0.08 | 64% | 70% | 55% | 48% | 9% | 22% |
| 3 | 0.05 | 65% | 70% | not measured | not measured | ||
| 4 | 0.02 | 66% | 70% | 58% | 53% | 8% | 17% |
| 5 | −0.04 | 68% | 76% | 62% | 62% | 6% | 14% |
Concentrations are calculated from the areas of the Fe 2p and Co 2p peaks in the XPS spectra (see Fig. 3). The electron detection angles θ are given relative to the surface normal. The XPS sampling depths are: λ = 12.0 Å and 4.1 Å for Fe and 10.9 Å and 3.7 Å for Co, considering 0° and 70° as respective detection angles. For more details, see the SI.