Electrochemical AFM with Rod-Like Samples: Copper Electrodeposition on a Commercial Rod-Like Platinum Electrode

Table of Contents

Introduction
Electrochemical Reactions
Experiment
Conclusion

Introduction

The Nanosurf electrochemistry stage ECS 204 can handle both rod and flat-like samples for concurrent electrochemical and AFM measurements.

This article demonstrates this unique capability of the ECS 204 stage, using an in situ electrochemical AFM experiment displaying copper electrochemical deposition and stripping on a commercially available rod-like platinum (Pt) electrode.

Electrochemical Reactions

Metals that are electrochemically deposited on conductive supports are a technologically and fundamentally important class of electrochemical reactions.

In this experiment, copper was electrochemically deposited on a commercially available rod-like platinum working electrode (CHI102, CH Instruments, ∅ 2 mm). After integrating the Pt in an insulating Kel-F sheath (∅ 6.35 mm), the Pt electrode was placed in a cylindrical sample holder, which was fastened on the ECS 204 stage.

Figure 1. Rod-like electrode (left) mounted inside a sample holder (center) and fixed in Electrochemistry Stage ECS 204 (right).

Experiment

Commercial Ag/AgCl/3.4 M KCl electrode (ET072, eDAQ) was used as a reference electrode, and a Pt wire was used as a counter electrode. Once this electrode was mounted, the liquid cell was added with 50 mM H2SO4 and 1.5 ml of 1 mM CuSO4 aqueous solution.

Within a liquid-compatible cantilever holder, an AFM probe of type NCSTAuD (Nanosensors) was installed and operated in dynamic imaging mode. During all experiments, the ECS 204 stage was mounted on an active vibration isolation table.

Figure 2 depicts the Pt electrode’s cyclic voltammograms during the EC-AFM experiment.

At E ≈ 0.16 V vs. Ag/AgCl, a positive-going peak is seen on CV determined in potential range -0.2 < E < 0.3 V (black curve), and at E ≈ 0.03V a second anodic peak is seen when the lower return potential was reduced to -0.25 and -0.3 V (indicated as green and red curves in Figure 2).

This second peak is due to the oxidative dissolution of copper deposited on the surface of Pt at E < -0.2 V.

Figure 2. Steady-state cyclic voltammograms of Pt electrode mounted in ECS 204 measured in 1mM CuSO4 + 50mM H2SO4 with the sweep rate 50mV/s. Current density was calculated using geometric area of the electrode.

In order to acquire minute copper clusters on Pt surface, a single potential sweep was carried out at 50 mV/s to the lower limit E = -0.4 V, and this sweep was subsequently stopped at E = -0.05 V during the return scan.

The latter potential matches to a (quasi)equilibrium between Cu2+ ions in solution and Cu clusters on Pt surface; the Cu clusters in the ionic solution do not dissolve or grow further. Figure 3 shows an AFM image of Cu clusters on Pt surface.

Figure 3. In situ AFM image in 1mM CuSO4 + 50mM H2SO4 showing Pt surface covered with electrochemically deposited copper clusters at E = -0.05V (upper part) and bare Pt surface at E = 0.3V (lower part), 3µm × 3µm, vertical range 100nm. The potential scan was performed at the position of the horizontal green line.

Initially, the electrode potential was maintained in equilibrium at E = -0.05 V (upper part of image) while acquiring Figure 3. After capturing the upper half of Figure 3, the potential was scanned to E = 0.3 V with the sweep rate remaining at 50 mV/s at the location of the green horizontal line.

This results in rapid dissolution of Cu clusters. The Pt surface free of Cu clusters is seen in the lower part of Figure 3.

Conclusion

This in situ electrochemical AFM experiment with a commercial Pt electrode can also be applied to other types of rod-like samples. The Nanosurf electrochemistry stage ECS 204 allows concurrent characterization of AFM and electrochemical surfaces under environmental control.

This information has been sourced, reviewed and adapted from materials provided by Nanosurf AG.

For more information on this source, please visit Nanosurf AG.

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