Citation: Vali ¯ unien ˙ e, A.; Virbickas, P.; Gabriunaite, I.; Margarian, Z.; Levinas, R.; Janarauskiene, D.; Valincius, G. Titanium–Platinum Thin Films as a Tool for the Electrooxidation of Cyanide. Coatings 2023, 13, 1821. https://doi.org/ 10.3390/coatings13111821 Academic Editor: Alberto Palmero Received: 3 September 2023 Revised: 17 October 2023 Accepted: 20 October 2023 Published: 24 October 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). coatings Article Titanium–Platinum Thin Films as a Tool for the Electrooxidation of Cyanide Aušra Vali¯ unien˙ e 1,2, * , Povilas Virbickas 1 , Inga Gabriunaite 1 , Zana Margarian 3 , Ram ¯ unas Levinas 1 , Dagne Janarauskiene 1 and Gintaras Valincius 3 1 Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Naugarduko Str. 24, LT-03225 Vilnius, Lithuania; povilas.virbickas@chgf.vu.lt (P.V.); inga.gabriunaite@chf.vu.lt (I.G.); ramunas.levinas@chgf.vu.lt (R.L.); dagne.janarauskiene@gmail.com (D.J.) 2 State Research Institute Center for Physical Sciences and Technology, Sauletekio Ave. 3, LT-10257 Vilnius, Lithuania 3 Institute of Biochemistry, Life Sciences Center, Vilnius University, Sauletekio 7, LT-10257 Vilnius, Lithuania; zana.margarian@gmc.vu.lt (Z.M.); gintaras.valincius@gmc.vu.lt (G.V.) * Correspondence: ausra.valiuniene@chf.vu.lt; Tel.: +370-5-219-3179 Abstract: This paper presents a detailed study of a titanium–platinum thin film-based electrode preparation and its practical application in the electrooxidation of cyanides to help protect our environment. The novel electrochemical deposition process of Pt on nearly atomically smooth magnetron-sputtered Ti film has been used to prepare a highly effective glass|Ti|Pt composite electrode with high catalytic activity for the electrooxidation of cyanide ions. The composite electrode exhibits over a 90% electrical current efficiency in the cyanide electrooxidation process and can be used for the decontamination of highly concentrated KCN solutions (up to 0.1 M) without any chemical additives. A high current efficiency (70%) of Pt thin film deposition on a glass|Ti electrode was achieved using a potentiostatic double-pulse method. Fast Fourier transform electrochemical impedance spectroscopy revealed the oxidation kinetics for cyanide ions at the electrode. The glass|Ti electrode was prepared using the magnetron sputtering technique, which allows us to fabricate electrodes of any shape suitable for any electrochemical cell or electroplating bath. Meanwhile, electrochemical deposition of Pt on the glass|Ti electrode is an efficient and environmentally friendly method, since various salts of Pt and/or Pt-containing wastes can be used for electrodeposition instead of pure Pt, which is more expensive. Keywords: sputtering; titanium; platinum; thin films; cyanide electrooxidation; fast Fourier transform electrochemical impedance spectroscopy; spectroscopic ellipsometry 1. Introduction Cyanides are widely used in the mining industry, particularly in the refining of noble metals from ores, where they form water-soluble metal–cyanide complexes. This type of leaching is very efficient [1], as it allows refining of low-grade ores. However, in order to extract most of the metal from the lower quality ore, larger amounts of cyanide must be used [2]. This causes ecological problems as cyanide ions are harmful and toxic to all animals and nature [3]. New Zealand, where gold mining contributes significantly to the local economy, suggested new exposure limits of cyanide, based on an 8 h workday, as 1 mg m −3 at a workplace [4]. The decision was based on The Scientific Committee on Occupational Exposure Limits review [5] and German Research Foundation statement [6] that evaluated cyanide effects on thyroid and neurological damage. Cyanide can also be found in drinking water, potentially affecting people every day, which is why the United States Environmental Protection Agency has set 0.2 mg L −1 limit of cyanide in drinking water [7]. Coatings 2023, 13, 1821. https://doi.org/10.3390/coatings13111821 https://www.mdpi.com/journal/coatings