Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

Summary

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.

Abstract

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 µm diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

Introduction

Nearly five decades ago, the first observation of surface enhanced Raman spectroscopy (SERS) occurred on electrochemically roughened silver¹. Electrochemical roughening of metal foils is still attractive today because of its simplicity over other roughening methods^2,3 and its usefulness in many applications like improving aptamer sensors⁴, improving neural probes⁵, and improving adhesion to metal substrates⁶. Electrochemical roughening methods exist for many bulk metals^1,

Protocol

​CAUTION: Please consult all relevant safety data sheets (SDS) before use. Several of the chemicals used in this protocol are acutely toxic, carcinogenic, oxidizing and explosive when used at high concentrations. Nanomaterials may have additional hazards compared to their bulk counterpart. Please use all appropriate safety practices when carrying out this protocol including the use of engineering controls (fume hood) and personal protective equipment (safety glasses, gloves, lab coat, full length pants, closed-toe shoes).

1. Cleaning the Pt electrode(s) before initial characterization and surface roughening

1. Chemically clean the ....

Results

A schematic showing the voltage application for roughening both macroelectrodes and microelectrodes is shown in Figure 2. Optical microscopy can be used to visualize the difference in the appearance of a roughened macroelectrode (Figure 3) or microelectrode (Figure 4). In addition, electrochemical characterization of the Pt surface using impedance spectroscopy and cyclic voltammetry can readily show .......

Discussion

The electrochemical roughening of thin-film macroelectrodes and microelectrodes is possible with oxidation-reduction pulsing. This simple approach does require several key elements to nondestructively roughen thin-film electrodes. Unlike foils, roughening of thin metal films may lead to sample destruction if parameters are not properly chosen. Critical parameters of the roughening procedure are pulse amplitude, duration and frequency. Additionally, ensuring electrode cleanliness and perchloric acid purity prior to the pr.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetone	Fisher Scientific, Sigma Aldrich or similar	n/a	Laboratory grade
EC-Lab Software	Bio-Logic Science Instruments	n/a	For instrument control and data analysis
Leakless Silver/Silver Chloride Reference	eDAQ Company, Australia	ET069-1	Free from chloride anion contamination (or other type of chloride free electrode e.g. Mercury sulfate electrode)
Mercury Sulfate & Acid Electrode Kit	Koslow, Scientific Testing Instruments	5100A	glass, 9mm version
Milipore DI water	MilliporeSigma	n/a	Certified resistivity of 18.2 MΩ.cm (at 25°C)
Perchloric acid, 99.9985%	Sigma Aldrich	311421	High Purity
Phosphate-buffered saline	Teknova	P4007	10mM PBS with 100mM NaCl, pH 7 or similar product from elsewhere
Platinum Wire Auxiliary Electrode (7.5 cm)	BASi	MW-1032	Counter electrode
Pt macroelectrodes	Lawrence Livermore National Laboratory	n/a	1.2 mm diameter, 250 nm thick Pt disc electrodes insulated in polyimide. More information in Reference 9.
Pt microelectrode arrays	Lawrence Livermore National Laboratory	n/a	20 µm diameter 250 nM thick Pt disc electrodes insulated in polyimide. More information in Reference 9.
Sulfuric acid, 99.999%	Sigma Aldrich	339741	High Purity
UV & Ozone Dry Stripper	Samco	UV-1	for cleaning electrodes
VersaSTAT 4 Potentiostat	AMETEK, Inc.	n/a	Good time resolution for pulsing tests
VersaStudio Software	AMETEK, Inc.	n/a	For instrument control
VMP-200 Potentiostat	Bio-Logic Science Instruments	n/a	Low current resolution option is preferable for measurements with microelectrodes