Dr. Arsène Chemin

In the interior of a material, atoms exist in a state of predictable, repeating symmetry. But at the surface, that order vanishes. Atoms are left with "dangling bonds," creating a restless environment where materials rearrange, react, and succumb to even the slightest contamination. This inherent instability is what makes surfaces notoriously difficult to model and control, yet so profoundly interesting to investigate.

This "devilish" complexity is exactly where modern technology lives. Whether it is the flow of electrons in a sub-nanometer transistor, the exchange of ions at a battery electrode, the precise chemical signaling of a biosensor, or the electrochemical production of biofuels—the most critical physical processes do not happen within the volume of a material; they happen at the interface.

My research is dedicated to navigating this frontier. By understanding, probing, and engineering these atomic boundaries, I work to transform the unpredictable chaos of the surface into a foundation for more efficient electronics and sustainable energy solutions.

The inherent complexity of interfaces has historically forced a fragmentation of scientific understanding. We are essentially speaking two different languages, physicists describe how electrons behave inside the solid, while chemists focus on the molecular reactions in the liquid. But electrochemistry happens precisely where those two meet. I seek to bridge these silos by introducing a unified theoretical formalism. It integrates four fundamental pillars:

• Solid State Physics: To describe Fermi levels, band structures, and doping effects within the solid bulk.

• Molecular Chemistry: To account for electron affinities and surface reactivity, grounded in the Sabatier principle.

• Chemical Thermodynamics: To model redox potentials and the critical influence of pH within the electrolyte.

• Electrostatics & Transport Dynamics: To couple reaction kinetics with Helmholtz double layers and depletion zones.

By merging these disciplines, I demonstrate that the origin of the Helmholtz electric double layer lies in the equilibrium of charges at the interface, dictated by the chemical potential of electrons in both the solid and the liquid. This equilibrium creates a significant electric potential variation (so called Helmholtz potential) and local electric fields, which have a direct impact on interfacial electrochemistry.

This framework provides a theoretical basis for emerging concepts—such as the entropy of the electrolyte at the interface—which are becoming critical descriptors of electrocatalytic activity. By incorporating this electronic equilibrium directly into the Butler-Volmer formalism, we can finally account for the decisive role of the Helmholtz potential in governing reaction kinetics.

Ultimately, this approach attempts to transform the "devilish" unpredictability of the interface into a predictable, engineered landscape, providing the missing link for truly understanding and mastering electrochemical systems.

A truly sustainable energy transition will only be possible by closing the carbon cycle by recycling CO2 and using it as a raw material for the organic chemistry of tomorrow (pharmaceuticals, fuels, plastics, etc.). To achieve this, our research aims to understand and optimize the (photo)electrocatalysis of CO2 and the production of H2, utilizing the direct conversion of electrical and solar energy into chemical energy.

• Materials Innovation: We develop new generations of electrodes inspired by photovoltaics (thin films, rare-earth-doped semiconductors) and innovative materials such as synthetic diamonds, MXene or high-entropy alloys nanoparticles.

• Understanding Interfaces: We develop new theoretical approaches to decrypt the complexity of solid–liquid interfaces and overcome bottlenecks related to catalytic kinetics and reaction selectivity.

• Multi-scale Characterization: Our work relies on laboratory techniques and advanced synchrotron methods for structural, electronic, and chemical characterization.

Are you curious about combining fundamental research with environmental challenges? Come discover our projects at the laboratory!

Rethinking Electrochemical Interfaces: The role of the Helmholtz potential on electrocatalytic activity

Chemin, A., Godeffroy, L., Amans, D. et al. The role of the Helmholtz potential on electrocatalytic activity. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70980-5  

Hydrogen is at the heart of the transition to carbon neutrality, serving as both an energy carrier and a reactant for green chemistry, and even a pathway to convert CO₂ into fuel. However, the large-scale production via electrolysis requires catalysts that are much more economical and efficient than those currently available. Just like many of the world’s most critical energy technologies, such as next-generation batteries, hydrogen production depends on a single, invisible boundary: the place where a solid electrode meets a liquid. While this interface is the heart of the energy transi-tion, it has remained notoriously difficult to describe, limiting our ability to design truly efficient and affordable materials.

In the study "The role of the Helmholtz potential on electrocatalytic activity" published in Nature Communications, we have introduced a new theoretical framework connecting charge behaviour in solids and liquids, and demonstrate its implications for the production of hydrogen from water. It aims to lay the groundwork for a new physical understanding of electrochemistry — one that any lab or industry can build on to accelerate their own breakthroughs in green technology.