The role of the Auger parameter in XPS studies of nickel metal, halides and oxides

Abstract

The critical role of the Auger parameter in providing insight into both initial state and final state factors affecting measured XPS binding energies is illustrated by analysis of Ni 2p(3/2) and L(3)M(45)M(45) peaks as well as the Auger parameters of nickel alloys, halides, oxide, hydroxide and oxy-hydroxide. Analyses of the metal and alloys are consistent with other works, showing that final state relaxation shifts, ΔR, are determined predominantly by changes in the d electron population and are insensitive to inter-atomic charge transfer. The nickel halide Auger parameters are dominated by initial state effects, Δε, with increasing positive charge on the core nickel ion induced by increasing electronegativity of the ligands. This effect is much greater than the final state shifts; however, the degree of covalency is reflected in the Wagner plot where the more polarizable iodide and bromide have greater ΔR. The initial state shift for NiO is much smaller than those of Ni(OH)(2) or NiOOH and the effective oxidation state is much less than that inferred from the average electronegativity of the ligand(s). Auger parameter analysis indicates that the bonding in NiO appears to have stronger contributions from initial state charge transfer from the oxygen ligands than that in the hydroxide and oxyhydroxide consistent with the considerable differences in the Ni-O bond lengths in these compounds with some relaxation of this state occurring during final state phenomena. The Auger parameter of NiOOH is, however, shifted positively, like the iodide, indicating greater polarizability of the ligands and covalency in this bonding. There is support for more direct use of relative bond lengths in interpreting differences between related compounds rather than more general electronegativity or similar parameters.

Scalable self-growth of Ni@NiO core-shell electrode with ultrahigh capacitance and super-long cyclic stability for supercapacitors

“…The peaks centered at 852.4 and 869.5 eV correspond to the characteristic Ni 2p 3/2 and Ni 2p 1/2 peaks of Ni 0 , respectively, whereas the peaks located at 856.1 and 873.8 eV represent the characteristic Ni 2p 3/2 and Ni 2p 1/2 peaks of Ni 2 þ , respectively. 31,32 In comparison with the pristine NF sample, the intensities of the characteristic Ni 2 þ peaks of the ANF sample are much higher, indicating that the NF surface was oxidized after activation. Additionally, the substantially lower intensity of the characteristic Ni 0 peaks also confirms the formation of nickel oxide on the ANF surface.…”

An Operando Investigation of (Ni–Fe–Co–Ce)Ox System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

“…The complete conversion of the Ni (II) (OH)2/NiO system into the Ni (III) OOH phase should involve different initial and final state configurations, leading to a different Ni 2p shape (especially the 3/2 spectral contribution), and the importance of the partial conversion to Ni (III) OOH is discussed further below. 74 Co exhibits a progressive evolution from a mixed oxide (Co3O4 or Co (II) O·Co (III) 2O3) in the pristine material to a mainly Co (II) (OH)2 structure 73 at the OCP, as substantiated by the positive BE shift of the overall peak (by about 0.7 eV) and the important increase of the Co(II) shake up satellite at about 786 eV. 75 This partial reductive conversion is usually ascribed to hydroxylation of the outer surface, due to the high concentration of hydroxyls in the electrolyte.…”

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

“…In spite of the vexed question of the origin of two other weak peaks at 855.5 and 859.0 eV, they are typical of metallic nickel as well. Some authors assign these extra peaks to energy loss peaks due to plasmon excitations in metal [32,33], while other authors attribute them to either a final-state shake-up process or an initial-state configuration-mixing effect [34,35]. Simultaneously, three low-intense peaks are observed at 529.4, 531.4, and 533.1 eV in the O1s spectrum.…”