Underpotential Deposition Mechanisms in Electrode Systems

Underpotential deposition (UPD) describes the electrodeposition of a metal monolayer onto a foreign metal substrate at potentials more positive than the Nernst equilibrium for bulk deposition. This phenomenon arises from the favourable interaction between adatoms and the substrate surface, which lowers the effective deposition potential. The process is governed by a balance of thermodynamic driving forces—namely substrate–adatom binding energies and interfacial electric fields—and kinetic factors such as ion transport, hydration‐shell removal and co‐adsorption of anions or organic species. Structural transitions during UPD can include reversible sub‐monolayer adsorption, ordered adlayer formation, surface alloying and, in some systems, bilayer growth. Advanced tools such as in situ vibrational spectroscopy, time‐resolved X‐ray diffraction and high‐resolution microscopies have exposed the roles of interfacial electrification, hydration energies and adsorbate coverage in controlling UPD pathways. Beyond fundamental interest, UPD underpins precision synthesis of core–shell and alloy nanoparticles, fine control of electrocatalytic interfaces, sensor design and nanoscale patterning in microelectronics. Its global significance stems from enabling atomically defined surfaces for energy conversion, heterogeneous catalysis and materials engineering.

Research from Nature Portfolio

Recent studies have exploited graphene‐based transparent electrodes to probe UPD in real time by infrared diffraction spectroscopy. This approach achieves sub‐monolayer sensitivity and interface specificity, revealing reversible field‐induced adsorption of organic cetrimonium bromide on graphene gratings and demonstrating the potential for in situ monitoring of charged species at electrified interfaces. Another investigation combined time‐resolved surface X‐ray diffraction with step‐scan infrared spectroscopy to map transitional structures during UPD of various metal cations on gold(111). It identified metastable outer‐Helmholtz-plane residency for highly hydrated ions, followed by stepwise dehydration and surface incorporation, while low‐hydration ions adsorb directly. These insights link cation hydration energy and co‐adsorbed anion interactions to deposition kinetics, offering a mechanistic framework for tailoring UPD processes by electrolyte composition and applied potential.

Underpotential Deposition Mechanisms in Electrode Systems publication trend

The graph below shows the total number of articles in underpotential deposition mechanisms in electrode systems across all publications each year (not limited to Nature Index journals).

Technical terms

Underpotential Deposition (UPD): Electrochemical deposition of a metal monolayer at potentials more positive than the Nernst equilibrium for bulk plating, driven by strong substrate–adatom interactions.

Monolayer (ML): A single atomic or molecular layer of deposit uniformly covering the substrate surface.

Outer Helmholtz Plane: A conceptual plane at the electrode interface where hydrated ions approach before shedding their solvation shell and adsorbing.

Anion Co-adsorption: Concurrent adsorption of negatively charged ions alongside metal adatoms, influencing adlayer stability and deposition kinetics.

Electrocrystallization: The sequence of nucleation, growth and structural evolution of a crystalline deposit under applied potential.

Scanning Tunnelling Microscopy (STM): A surface imaging technique that maps atomic topography by measuring tunnelling current between a sharp tip and the substrate.

Step-Scan Infrared Spectroscopy: A time-resolved IR method capturing transient vibrational changes during electrochemical processes at interfaces.

References

1. Vibrational spectroscopy at electrolyte/electrode interfaces with graphene gratings. Nature Communications (2015).
2. Real–time observation of interfacial ions during electrocrystallization. Scientific Reports (2017).
3. Underpotential deposition of Cu onto Au(111) in the presence of acetate. Electrochimica Acta (2024).
4. Atomic-Scale Friction Study by EC-AFM: Underpotential Deposition (UPD) of Ag on I-Modified Au(111) and Its Tip Penetration. Journal of The Electrochemical Society (2022).
5. Surface Alloying During Pb Underpotential Deposition on Au(111). Journal of The Electrochemical Society (2022).