Essays on Conceptual Electrochemistry: I. Bridging Open-Circuit Voltage of Electrochemical Cells and Charge Distribution at Electrode-Electrolyte Interfaces

We ponder over how an electrochemical cell conforms itself to the open-circuit voltage (OCV) given by the Nernst equation, where properties of the electrodes play no role. We first show, via a pedagogical derivation of the Nernst equation, how electrode properties are canceled and then take a closer look into the electrode-electrolyte interface at one electrode by linking charge and potential distributions. We obtain an equilibrium Poisson-Nernst equation that shows how the charge distribution across an electrode-electrolyte interface can be dictated by the chemical potentials of redox species. Taking a H-2/O-2 fuel cell as an example, we demystify the formal analysis by showing how the two electrodes delicately regulate their electron tails to abide by the Nernst equation. In this example, we run into a seemingly counterintuitive phenomenon that two electrodes made of the same transition metal display two distinct potentials of zero charge. This example indicates that the double layer at transition metals with chemisorption can display distinct behaviors compared to ideally polarizable double layers at sp metals.

Automated summary

This study investigates how an electrochemical cell conforms to the open-circuit voltage (OCV) given by the Nernst equation, and shows how electrode properties are canceled through a pedagogical derivation. By analyzing the charge and potential distributions at the electrode-electrolyte interface, the authors derive an equilibrium Poisson-Nernst equation that explains how the charge distribution is determined by the chemical potentials of redox species. Using a H-2/O-2 fuel cell as an example, the authors elucidate how the electrodes regulate their electron tails to abide by the Nernst equation. The study also reveals a counterintuitive phenomenon where two electrodes made of the same transition metal display different potentials of zero charge, indicating distinct behaviors of transition metal double layers compared to sp metal double layers.