A study of the alloying behaviour of Ni–B amorphous catalysts using Auger parameter measurements, and primary and secondary features of the XPS spectrum

Abstract

Electrodeposited Ni–B alloys of nominal compositions 30 at.% B and 50 at.% B, which were developed as catalysts for the electrolytic hydrogen production process, were studied using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The Ni–B alloys were found to be amorphous. Changes of Auger parameter (AP) values and information from the primary and secondary structure of the XPS spectrum were employed to probe the electronic changes occurring upon alloying. It is suggested that the main electronic change occurring is hybridisation of the Ni occupied states with the B sp empty states and an apparent increase of the electron density around the Ni sites. The electron affinities of the two elements contradict their electronegativity tendencies. It is suggested that the contradiction may be resolved by considering the increase in the electron density at the Ni sites in the Ni–B alloys to be a result of shortening of the interatomic distances via the formation of hybridized bonds between Ni and B atoms.

Acknowledgements

This work forms part of the project ‘Nanocrystalline Alloys in Hydrogen Processes’ supported financially by the Norwegian Research Council. Discussions on the use of the AP in alloying behaviour studies with Professors J.A.D. Matthew, P. Weightman, J.E.C. Castle, J.F. Watts and P. Tsakiropoulos and Dr. Shao are gratefully acknowledged.