A Study of Anodically Grown Hydroxide Films on an Amorphous Ni[sub 78]Si[sub 8]B[sub 14] Alloy

Abstract

Films grown on amorphous Ni 78 Si 8 B 14 alloy and on polycrystalline Ni by polarization in 1 M KOH solution were analyzed by X-ray photoelectron spectroscopy ͑XPS͒ and scanning tunneling spectroscopy ͑STS͒. XPS investigations showed that the films formed on both the amorphous Ni 78 Si 8 B 14 alloy and polycrystalline Ni at open-circuit potential and after polarization at 0.4 V RHE consist of Ni͑OH͒ 2 , while the films formed after polarization at 0.5 V RHE consist of NiOOH. No traces of B or Si in the uppermost of the hydroxide films produced on the amorphous Ni 78 Si 8 B 14 alloy were found. STS showed that all films formed on the amorphous Ni 78 Si 8 B 14 had more n-type semiconductor character than those formed on polycrystalline Ni. Electrochemical investigations indicated that the amorphous Ni 78 Si 8 B 14 alloy is a better electrocatalyst for the oxygen evolution reaction than polycrystalline Ni. We discuss whether this can be attributed to an enhanced electron density on the Ni sites in the alloy leading to an increase in the tunneling probability of the electrons on the surface film. This can subsequently enhance its catalytic action towards the oxygen evolution reaction.

An experimental study of the electronic structure of anodically grown films on an amorphous Ni78Si8B14 alloy

“…semi-conducting behaviour compared to Ni(OH) 2 and compared to the (oxy)hydroxides formed on pure Ni. [3] The 3d component in the valence band spectra of the polarised samples in Fig. 4 is shifted from E F towards higher binding energies and is broader compared to NiO.…”

“…XPS O 1s spectra (not shown) of NiOOH showed presence of an oxide component, which was absent in the Ni(OH) 2 ones (Ref. [3]). Figure 2 also shows that NiOOH was thicker than Ni(OH) 2 , and that the outermost surface of both films was enriched in Ni and depleted in B.…”

“…Since the Si content was rather uniform across the metal/(oxy)hydroxide interface, Fig. 2 indicates that BO 3 3− dissolves easier than SiO 3 2− . XPS depth profiles using Ar + sputtering showed absence of detectable amounts of Si and B in the outermost surface of Ni(OH) 2 and NiOOH.…”

“…According to Pourbaix, [5] in alkaline solutions NiO will hydrate to Ni(OH) 2 , while SiO 2 and B 2 O 3 may dissolve as SiO 3 2− and BO 3 3− , respectively. Figure 1 shows absence of any crystallinity in the polarised Ni 78 Si 8 B 14 sample.…”

“…The relevant electrochemistry and STS characterisation associated with the electrochemical formation of the Ni(OH) 2 and NiOOH films were described in the previous work, [3] and only a brief description is given here. Cyclic voltammograms were acquired by changing the potential between −0.8 and +0.6 V RHE under N 2 -atmosphere and at 25…”