Anomalous Growth of Fe-Ni on Au (111) Chemical Insight from Structural Evidence

Abstract

The electrodeposition of Fe-Ni alloys usually develops a deposit that is more Fe-rich than the electrolyte. The preferential deposition of the less noble element, often encountered among Fe-group alloys, was introduced by A. Brenner as anomalous codeposition [1]. More recently, it was revealed that the transient growth of Fe-Ni develops a deposit that is even more Fe-rich than the steady-state growth, and leads to a composition gradient along the growth direction [2]. This work is focused on the electrodeposition of Fe-Ni on Au (111) substrate in order to leverage the established knowledge of epitaxial growth of Fe on Au (111) [3]. Transmission electron microscopy was used to investigate the Fe-Ni / Au (111) cross section (Figure 1). The work to be presented will demonstrate how chemical insight about the transient growth can be conjectured based on structural evidence, such as the orientation relationship between the substrate and the electrodeposit. Adding onto the existing theories based on the adsorption of the intermediate electroactive species [4], we attempt to provide insight on the mechanism leading to the composition gradient developed during the transient growth of Fe-Ni on Au (111).[1] A. Brenner, Electrodeposition of Alloys, Academic Press, Cambridge, MA (1963).[2] K. Neuróhr, A. Csik, K. Vad, G. Molnár, I. Bakonyi, L. Péter, Electrochimica Acta 103 (2013) 179-187.[3] Q. Lin, E. Hoglund, G. Zangari, Electrochimica Acta 338 (2020) 135876.[4] I. Tabakovic, J. Gong, S. Riemer, M. Kautzky, J. Electrochem. Soc. 162 (3) (2015) D102-D108. Figure 1. Cross section transmission electron microscopy image of an Fe-Ni thin film electrodeposited on Au (111) substrate. Courtesy: the figure was published in Electrochimica Acta 338 (2020) 135876. Figure 1