Operando EC-STM reveals atomic-scale surface dynamics under electrochemical control
Understanding how electrode surfaces evolve under electrochemical control is essential to establishing structure–function relationships at electrochemical interfaces. Electrochemical scanning tunneling microscopy (EC-STM) makes this possible by enabling atomic-scale visualization of electrode surfaces operando — directly correlating structural changes with applied potential in real time.
Here, we demonstrate the capabilities of our operando EC-STM platform using the well-established Au(111)/H2SO4 model system. This benchmark highlights how EC-STM provides space- and time-resolved information on dynamic surface restructuring that is simply inaccessible through conventional electrochemical measurements alone.
Why Au(111) in Sulfuric Acid?
The Au(111)/H2SO4 system is one of the most thoroughly characterized electrochemical interfaces in surface science, making it an ideal benchmark for a new platform. Our study focuses on the electrochemical double-layer region, below the onset of gold oxidation, where cyclic voltammetry (CV) shows characteristic features associated with lifting of the surface reconstruction and sulphate adsorption. By combining electrochemical control with high-resolution STM imaging, we connect these voltammetric signatures directly to real-space surface transformations.
Key Results
1. Potential-Dependent Surface Reconstruction
At cathodic potentials following immersion (-0.3 V/Pt), EC-STM images reveal large, well-ordered terraces separated by monoatomic steps — the signature of the reconstructed Au(111) surface. As the electrode potential is stepped in the anodic direction, clear morphological changes emerge: island formation and evolving step edges appear in correspondence with features in the cyclic voltammogram.
Examples of EC-STM images (300 x 300 nm) recorded at different potentials on a Au(111) electrode in 0.1 M H2SO4
The first voltammetric peak (-0.25 V/Pt) correlates with the appearance of sparse gold islands, marking the onset of reconstruction lifting. The second peak (-0.15 V/Pt) is accompanied by further growth of small monoatomic islands that increasingly cover the terraces. At more anodic potentials (-0.05 V/Pt), fewer but significantly larger islands are observed.
These observations are consistent with the well-understood mechanism of reconstruction lifting: the reconstructed Au(111) surface has a higher atomic surface density than its unreconstructed counterpart. When the reconstruction is lifted, the excess gold atoms are displaced onto the surface and reassemble into islands.
Voltammogram of the Au(111) surface in H2SO4, exhibiting peaks attributed to the lifting of the surface reconstruction
2. Time-Resolved Dynamics at Fixed Potential
Time-resolved imaging at constant potential reveals that surface dynamics persist long after the electrochemical current has returned to near-zero. Following a potential step from -0.2 to -0.15 V/Pt, successive EC-STM images show islands nucleating, growing, and dissolving over the course of several minutes under conditions that would appear fully stable from a current measurement alone.
This directly illustrates a key limitation of conventional electrochemistry: current measurements are spatially averaged across the entire electrode and carry no information about local, ongoing structural rearrangements. EC-STM makes these hidden dynamics visible.
Successive EC-STM images (150 x 150 nm) illustrating the dynamic nature of the surface reconstruction after its initiation by stepping the sample potential
What This Demonstrates
Taken together, these results illustrate two core strengths of operando EC-STM as a characterization tool:
- Direct structure–electrochemistry correlation: voltammetric features can be unambiguously assigned to specific surface transformations, rather than inferred from indirect signals.
- Access to hidden dynamics: surface processes that are electrochemically silent — invisible to current or charge measurements — are directly observable in real space and real time.
Platform Capabilities
Beyond this benchmark system, the Leiden Probe Microscopy operando EC-STM platform is being applied to questions in electrocatalysis, energy conversion, and functional electrode materials, where understanding dynamic surface behaviour under realistic conditions is critical.
The platform is built around a customizable liquid cell design that maintains a standard interface to the potentiostat and STM controller while accommodating a wide range of sample geometries, materials, and electrolyte conditions. Key capabilities include:
- Integrated liquid lines for flow experiments and in-situ electrolyte exchange
- Filling and imaging under potential control, preserving surface state from the first moment of contact with the electrolyte
- Protective gas environment for measurements under argon or nitrogen
- Sealed inert transfer shuttle enabling air-free sample transfer directly from a glovebox to the EC-STM
Interested in Collaborating?
A full account of these results will be published in an upcoming application note, which we are happy to share on request. If you are working on electrochemical interfaces and would like to discuss how operando EC-STM can support your research, we’d love to hear from you.