All chemicals used were of analytical grade from Sigma Aldrich and were without need of any further purification. The Fe3P powder (product code: 691593; Sigma Aldrich, UK) and Fe2P powder (product code: 691658; Sigma Aldrich, UK) utilised were of 99.5% purity (trace metals basis, −40 mesh avg. part. size). These are referred to in the text with a subscript “raw” to indicate that they were used, raw, without any treatment.
The Fe3P powder was wet ball milled in a Retsch PM 100 planetary ball mill over the following time intervals: 5, 10, 20 and 50 h in a 50 mL zirconium oxide (ZrO2) grinding jar (Retsch, Germany). Ball milling was carried out with 2 mm yttrium stabilized zirconia beads (Retsch, Germany) at 150 rpm, where 2 g Fe3P was placed in 30 mL methanol to form a milling slurry. The 2 mm diameter of the zirconia beads and milling speed have been previously shown to result in the finest powder dispersion.42 (link) Electrochemical measurements were performed in 0.5 M H2SO4, which was of the highest possible purity from Sigma Aldrich (99.999%, double distilled for trace metal analysis).
The Fe3P powder was wet ball milled in a Retsch PM 100 planetary ball mill over the following time intervals: 5, 10, 20 and 50 h in a 50 mL zirconium oxide (ZrO2) grinding jar (Retsch, Germany). Ball milling was carried out with 2 mm yttrium stabilized zirconia beads (Retsch, Germany) at 150 rpm, where 2 g Fe3P was placed in 30 mL methanol to form a milling slurry. The 2 mm diameter of the zirconia beads and milling speed have been previously shown to result in the finest powder dispersion.42 (link) Electrochemical measurements were performed in 0.5 M H2SO4, which was of the highest possible purity from Sigma Aldrich (99.999%, double distilled for trace metal analysis).