fig3

Figure 3. XPS spectra, (A) Ni 2p XPS spectrum for Ni2P nanoflake; (B) Ni 2p XPS spectrum for β-Ni(OH)₂; (C) p 2p XPS spectrum for Ni2P nanoflakes; (D) O 1s XPS spectrum for Ni2P nanoflakes; (E) RRDE polarization curves in 1 M KOH solution at 1,600 rpm with and without 0.5 M urea at 5 mV s^-1 and the ring potential is set as 0.2 V (vs. RHE) to detect the as-generated O₂; (F) Polarization curves of the two-electrode water splitting systems with Pt mesh||Ni₂P electrodes in 1 M KOH solution with and without 0.5 M urea at 5 mV s^-1 (G) UOR mechanism on Ni₂P and β-Ni(OH)₂ nanoflakes in alkaline media^[100]. This figure is quoted with permission from Liu et al. XPS: X-ray photoelectron spectroscopy; RRDE: rotating ring-disk electrode; UOR: urea oxidation reaction; RHE: reversible hydrogen electrode.