Electrochemical Studies of Nickel/H2so4 Oscillating Systems and the Preparation and Testing of Copper Coupled Microelectrode Array Sensors
Authors: Clark David Q. , Wipf David O 
Published: February 2020

Nickel is one of the most important passive metals used for electrodeposition processes in the world (1). Over 150 metric tons of Ni is consumed yearly for electroplating (2). Nickel is well known for its highly lustrous finish and corrosion resistant properties. Although Ni is very resistant to corrosion, it is not completely resistant. Nickel has been known to corrode in acidic medium such as sulfuric acid. The corrosion of Ni in Ni/H2SO4 produce periodic states of oscillations as a potential is applied or a current is passed through the system (3)-(5). Studies on these types of oscillatory states have been performed since 1950.
Traditionally, Ni electrochemical studies on Ni/H2SO4 oscillating systems have been performed by applying external forcing techniques through variations of applied potential or current during the electrodissolution (corrosion) of Ni single wire electrodes in high concentrations of H2SO4 solutions (1 M, 3 M, and 4.5 M). External forcing is the process in which perturbations are applied to a system by an external source and have helped to provide a better understanding of Ni/H2SO4 oscillating systems. However, little attention has been given to performing electrochemical studies on Ni/H2SO4 oscillating systems in low concentrations of H2SO4 solutions (0.3 M - 0.9 M) and no attention has been given to the possibility for the external forcing of these unique systems via concentration change at the Ni electrode surface until now (for example, Figure (1)).
Although electrochemical studies on Ni single wire electrodes provided a significant amount of information about self-organization and periodic oscillations, an in depth analysis of the Ni/H2SO4 oscillating system was not possible because of the lack of adequate technology (6). In order to overcome this issue, coupled microelectrode array sensors (CMAS) have been recently developed. CMAS are integrated devices with multiple electrodes that are connected externally in a circuit, and all of the electrodes on the CMAS have the same amount of potential applied or current passing through them during experiments.
CMAS can be used for studying self-organization and periodic oscillations via external forcing (7)-(8). CMAS have also been used for real-time corrosion monitoring in cooling water systems, simulated seawater, and concrete (9). CMAS are useful devices because they are capable of simulating single wire electrodes of the same size (5)-(6), (9). During the last six decades, many electrochemical studies have been performed by using CMAS; however, there is little published detailed descriptions of CMAS fabrication.
The work demonstrates control of periodic oscillations by changing the concentration of the proton concentration at the Ni electrode surface via external forcing. We present results collected from CV experiments performed on the modified CMAS. In addition, we outline the steps in which the CMAS were fabricated and how the CMAS was modified via electrodeposition of Ni.
Figure 1. (a) changes in oscillations observed with external local forcing a) CVs at 10 mV/s on a 500 μm Ni electrode (WE) in 0.7 M H2SO4 with an 18.5 kΩ series resistor. During the sweeps 8 mA to 10 mA of anodic current is applied to a nearby 300 μm Pt wire, b) Plot of detrended data, (c)Top of the CMAS, (d) Top view of array assembly showing placement of the carbon auxiliary electrodes, (e) Assembled Cu CMAS.
REFERENCES
1. Di Bari, G. A., Electrodeposition of Nickel. In Modern Electroplating, p.79, John Wiley & Sons, Boston (2010).
2. Nickel Institute, Nickel Plating Handbook, p. 80, Nickel Institute, North Carolina, (2013)
3. Zhou, C.; Kurths, J.; Kiss, I. Z.; Hudson, J. L.,. Phys. Rev. Lett., 89, 014101 (2002).
4. Wang, W.; Green, B. J.; Hudson, J. L., J. Phys. Chem. B, 105, 7366 (2001).
5. Kiss, I. Z.; Wang, W.; Hudson, J. L., J. Phys. Chem. B, 103, 11433 (1999).
6. Orlik, M., Self-Organization in Electrochemical Systems I General Principles of Self-Organization. Temporal Instabilities, p 473, Springer, Berlin (2012).
7. Fei, Z.; Kelly, R. G.; Hudson, J. L., J. of Phys. Chem., 100, 18986 (1996).
8. Wickramasinghe, M.; Kiss, I. Z., Physical Review E, 88, 062911 (2013).
9. Yang, L., Techniques for Corrosion Monitoring, p. 187, Woodhead Publishing Limited, Boston (2008).

Figure 1