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. 2023 Dec 29;15(1):70.
doi: 10.3390/mi15010070.

A Comparative Study on the Effect of Substrate Structure on Electrochemical Performance and Stability of Electrodeposited Platinum and Iridium Oxide Coatings for Neural Electrodes

Linze Li  1 , Changqing Jiang  2 , Luming Li  2   3
Affiliations

A Comparative Study on the Effect of Substrate Structure on Electrochemical Performance and Stability of Electrodeposited Platinum and Iridium Oxide Coatings for Neural Electrodes

Linze Li et al. Micromachines (Basel). .

Abstract

Implantable electrodes are crucial for stimulation safety and recording quality of neuronal activity. To enhance their electrochemical performance, electrodeposited nanostructured platinum (nanoPt) and iridium oxide (IrOx) have been proposed due to their advantages of in situ deposition and ease of processing. However, their unstable adhesion has been a challenge in practical applications. This study investigated the electrochemical performance and stability of nanoPt and IrOx coatings on hierarchical platinum-iridium (Pt-Ir) substrates prepared by femtosecond laser, compared with the coatings on smooth Pt-Ir substrates. Ultrasonic testing, agarose gel testing, and cyclic voltammetry (CV) testing were used to evaluate the coatings' stability. Results showed that the hierarchical Pt-Ir substrate significantly enhanced the charge-storage capacity of electrodes with both coatings to more than 330 mC/cm2, which was over 75 times that of the smooth Pt-Ir electrode. The hierarchical substrate could also reduce the cracking of nanoPt coatings after ultrasonic, agarose gel and CV testing. Although some shedding was observed in the IrOx coating on the hierarchical substrate after one hour of sonication, it showed good stability in the agarose gel and CV tests. Stable nanoPt and IrOx coatings may not only improve the electrochemical performance but also benefit the function of neurobiochemical detection.

Keywords: coating stability; femtosecond laser; hierarchical structures; iridium oxide; neural electrodes; platinum.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Study overview. (a) Cross-sectional schematic diagram and (b) surface morphology under scanning electron microscope (SEM) of smooth platinum-iridium (sPt-Ir) and hierarchical platinum-iridium (hPt-Ir) substrates. (c) Electrodeposition of nanoPt and IrOx coatings on sPt-Ir and hPt-Ir substrates. WE, RE, and CE represent working electrode, reference electrode, and counter electrode, respectively. (d) Ultrasonic testing, (e) agarose gel testing, and (f) cyclic voltammetry (CV) testing. EIS: electrochemical impedance spectroscopy. OM: optical microscopy.
Figure 2
Figure 2
Electrochemical performance and surface morphology of electrodeposited nanoPt and IrOx coatings on sPt-Ir and hPt-Ir substrates. The charge-storage capacity of (a) nanoPt and (b) IrOx varied with deposition CV cycles or deposition time. Impedance magnitude and phase before and after adding (c) nanoPt (deposited by 720 CV cycles) and (d) IrOx coatings (deposited by 60 min), (e) surface and cross-sectional morphology of nanoPt (deposited by 720 CV cycles) and IrOx (deposited by 60 min) on sPt-Ir and hPt-Ir substrates. There were 3 samples of each kind of electrode.
Figure 3
Figure 3
Surface morphology and failure summary of nanoPt and IrOx coatings on sPt-Ir and hPt-Ir substrates (a) initially and after (b) ultrasonic, (c) agarose gel, and (d) cyclic voltammetry testing.
Figure 4
Figure 4
Platinum and iridium element proportion on sPt-Ir and hPt-Ir substrates with and without nanoPt and IrOx coatings.
Figure 5
Figure 5
Ultrasonic testing results of electrodeposited nanoPt and IrOx coatings. The charge-storage capacity retention rates of (a) nanoPt and (b) IrOx varied with ultrasonic time. Impedance magnitude and phase of (c) nanoPt and (d) IrOx coatings before and after ultrasonic testing. (e) Surface morphology of nanoPt and IrOx on sPt-Ir and hPt-Ir substrates after 60 min of ultrasonic treatment. The were 3 samples of each kind of electrode.
Figure 6
Figure 6
Agarose gel testing results of electrodeposited nanoPt and IrOx coatings. The charge-storage capacity retention rates of (a) nanoPt and (b) IrOx varied with insertion times. Impedance magnitude and phase of (c) nanoPt and (d) IrOx coatings before and during 3 times of agarose gel testing. (e) Surface morphology of nanoPt and IrOx on sPt-Ir and hPt-Ir substrates after agarose gel testing.
Figure 7
Figure 7
CV testing results of electrodeposited nanoPt and IrOx coatings. The charge-storage capacity retention rates of (a) nanoPt and (b) IrOx after 1500 CV cycles. Impedance magnitude and phase of (c) nanoPt and (d) IrOx coatings before and after 1500 CV cycles. (e) Surface morphology of nanoPt and IrOx coatings on sPt-Ir and hPt-Ir substrates after 1500 CV cycles. There were 3 samples of each kind of electrode.
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