Chemistry

Modeling Water/Metal Interface

What happens when a charged metal surface and water interact?

The answer to this question is fundamental to many industrial and biological processes, from energy storage to orthopedics. As surprising as it may seem, researchers had not, until recently, devised an efficient way to tell exactly how molecules behaved at the critical junction between  a charged metal surface and liquids. Jean-Sébastien Filhol¹– now a junior professor at the Université de Montpellier–together with his former post-doctorate supervisor, Matthew Neurock of the University of Virginia, devised a mathematical model that could replicate the forces at work when several sheets of water come in contact with palladium.

Formulated a few decades ago, existing models could only replicate uncharged surfaces: For example, it was impossible to represent a simple 4-volt battery. The model devised by the Neurock-Filhol team gives scientists insight into the energies and configurations of complex electrochemical surfaces like water molecules as they break down into hydrogen and hydroxide (OH-) on the charged surface of palladium.² The construct was then verified against experimental results obtained with the same palladium-water interface. The results, published in Angewandte Chemie International,³ were conclusive: The model and the experiments showed the same molecular behavior.

---

© J.-S. Filhol

Modeling of hydrogen (white) transfer while water molecules dissociate on a palladium (blue) surface. Oxygen is shown in red.

---

The researchers were surprised to find that even at zero potential, the metal surface was charged. In contact with water, two surfaces were created, one negative, the other positive. This finding is important: Even in electrically neutral settings, metals could react in unexpected ways, particularly, notes the researcher, in the case of bio-materials to be inserted in the body as part of orthopedic equipment. “This opens up very exciting possibilities for practical implementation in orthopedic surgery,” enthuses Filhol.

Marianne Niosi