It has been nearly 80 years since David C. Grahame’s review article (Chemical Reviews 41, 441–501, 1947) on the electrical double layer (EDL). This seminal work (with more than 5000 citations) continues to garner substantial interest and serves as an important pedagogical piece for students learning the fundamentals of electrochemistry. At a recent ESC Meeting I had the privilege to listen to yet another talk on the EDL; and so when asked for a topic for a special issue of Interface, I suggested that it be centered around the EDL. Hence, this special issue coedited with Yue Qi highlights important progress in understanding this fundamental subject along with provocation for pursuing remaining questions.
Although the electrical double layer (EDL) is central to electrochemistry, its behavior is far from universal. The transition from metallic to semiconductor electrodes introduces complexities that challenge conventional models and demand new theoretical approaches. This perspective article traces the historical trajectory of these two distinct interfaces, contrasting the electronic and ionic distributions that define their behavior. By examining recent breakthroughs in modeling these disparate systems, we provide a critical outlook on how a deeper understanding of the metal-vssemiconductor dichotomy can propel the design of more efficient electrochemical energy systems.
The electrical double layer (EDL) is central to electrochemistry and has long been defined by charged species, with charge-neutral solvents treated as passive dielectric media in macroscopic models. Decades of advancements in molecular simulations and characterizations have revealed that solvent molecules are structurally and functionally active components of the EDL. Water, in particular, exhibits layering, potential-dependent orientation, and strong coupling with ions. Together, they determine ion distributions, interfacial potential drop, and capacitance. In organic electrolytes, mixed chargeneutral species further introduce complex and tunable interfacial environments that govern electrochemical reactivity and selectivity. Here, we highlight the evolving understanding of charge-neutral species in the EDL and discuss emerging opportunities to design the interfacial structures for energy storage and electrosynthesis.
From the age of the mercury electrode to the era of sustainable development, the landscape of electrochemistry has transformed. Eighty years after David C. Grahame’s monumental review of the electrical double layer, electrochemical devices are no longer adequately modeled by simple planar interfaces, but by nanoporous electrodes and complex electrolytes. This feature article explores the frontier of this evolution, redefining our fundamental understanding of interfacial thermodynamics, reaction kinetics, and ion transport through experimental advances and multiscale modeling. As we look beyond Grahame’s idealized models, the synthesis of theory and experiment offers a new paradigm for engineering the next generation of electrochemical systems for energy storage and chemical transformation.
The correct thermodynamic potential to use for an ensemble depends on the constraints, the quantities that are kept constant. In electrochemical systems the electrode potential is usually kept constant, so the surface tension is the correct potential. However, whether a particular process occurs at constant potential depends on its speed. A single electrochemical reaction step occurs at a timescale of picoseconds, while double-layer relaxation, which would keep the potential at the reaction site constant, takes much longer. Therefore recent attempts to simulate electrochemical reactions at constant potentials do not correspond to the physical reality.
