PH Micro-Sensor from Modified Pt SECM Microelectrode for Local pH Measurement While Chromium Electrodeposition

Abstract

In this work, it will be presented the chromium electrodeposition mechanisms with the use of a Scanning ElectroChemical Microscopy (SECM) micro-electrode. Among several factors, the pH is key to achieve even a metallic deposit. pH buffers and complexing agents are often used for this purpose [1] but in the vicinity of the electrode, at the electrode/electrolyte interface, strong variations are highly likely to occur. To this respect, since pH is a key parameter, a pH micro-electrode is intended to be developed to scan the pH gradient upon the electrodeposition of chromium. The first part of this work is so devoted to the pH micro-electrode realization from a platinum microelectrode on which iridium oxide is deposited. Iridium oxide has been reported to be suitable for local pH sensing [2-4]. Different parameters have been studied such as IrOx thickness and thermal treatment. The addition of Nafion has been assessed as well to achieve a tradeoff between fast response time, good selectivity and good stability [5]. An optimized IrOx micro-electrode has been obtained and used as SECM micro-electrode to get the evolution of the pH at the electrode/electrolyte interface upon electrodeposition. Different micro-electrode diameters have been used to improve the resolution. These results are promising and will allow going further to the development of chromium electrodeposition electrolyte helping to select the different complexing agents.[1] D. Del Pianta et al. Determination of the chromium(III) reduction mechanism during chromium electroplating. Electrochimica Acta (2018) 234-241.[2] H. A. Elsen et al. Effects of electrodeposition conditions and protocol on the properties of iridium oxide pH sensors electrodes. J. Electrochem Soc. 156 (2009).[3] C. S. Santos et al. Fabrication and use od dual-function iridium oxide coated gold SECM tips. An application to pH monitoring above copper electrode surface during nitrate reduction. Electroanalysis 28 (2016) 1441-1447.[4] Z. Zhu et al. A fabrication of iridium oxide film pH micro-sensor on Pt ultramicroelectrode and its application on in-situ pH distribution of 316 stainless steel corrosion at open circuit potential. Sensors and Actuators B 25 (2018) 1974-1982.[5] I. G. Borislav et al. Thin-film IrOx pH microelectrode for microfluidic-based microsystems. Biosensors and Bioelectronics 21 (2005) 248-256.