Electrochemistry is a ubiquitous part of modern society, appearing in a wide range of applications. For example, our phones rely on microchips manufactured through the electrodeposition of copper and are powered by electrochemical batteries. This blog post introduces some basic concepts of electrochemistry and how we can assess electrochemical processes.
In electrochemical systems, we study the processes and factors that influence the movement of electrons across the interface between different chemical phases — most commonly between a solid electrode and a liquid electrolyte. This electron transfer is always accompanied by a redox (reduction–oxidation) reaction, Fig. 1. A redox reaction involves the transfer of electrons from one species to another: one substance is oxidized by losing electrons, while another is reduced by gaining them. For example, in a zinc–copper electrochemical cell, zinc metal and copper metal are immersed in their respective ionic solutions, connected via an external circuit but physically separated from each other. At the anode — the electrode where oxidation occurs — zinc metal loses electrons to form zinc ions (Zn²⁺), which dissolve into the solution. These electrons then travel through the external circuit to the cathode — the electrode where reduction takes place — where copper ions (Cu²⁺) in solution gain electrons and are deposited as solid copper.
Figure 1. A galvanic cell showing a redox process. Redrawn with inspiration from [1]
To gauge whether such a process will happen spontaneously or not we can consider the electrical potential U. This potential reflects the tendency of electrons to move from one electrode to another, driving the redox reaction. Knowing whether the process is spontaneous is important because it determines whether a system can generate electrical energy on its own (as in batteries) or if an external energy source is needed to drive the reaction (as in electroplating or electrolysis). Each redox couple (like Zn2+/Zn or Cu2+/Cu) has an associated standard reduction potential that reflects its tendency to gain or lose electrons, which is by definition defined against the standard hydrogen electrode (SHE). The Nernst equation then describes how the potential of an electrode depends on the concentration of the oxidized and reduced species. For our copper vs zinc cell, we can calculate the cell potential as follows under certain assumptions:
Where E°cell is the standard cell potential (E°cathode - E°anode), R is the universal ideal gas constant, T is the temperature in kelvins, n is the number of electrons transferred in the redox reaction and F is Faraday’s constant. As the redox reaction proceeds, there is a flow of electrons from the negative to positive electrode. The rate at which these electrons flow is called the current I and is very useful as we directly relate it to the rate of the redox reaction. Furthermore, as we measure this current over a given time we obtain charge Q and using Faraday’s law we can relate the charge to a number of moles of substance reacted.
By measuring the currents, we can gain quite a lot of insights into our electrochemical system —for instance, whether the rate of the redox reaction is limited by kinetics (how fast electrons can transfer at the electrode surface) or by diffusion (how quickly reactants can reach the surface through the electrolyte). In kinetic control, the current reflects the intrinsic speed of the electron transfer reaction, while in diffusion-limited regimes, the current is limited by how fast species can be replenished at the interface. These parameters are crucial for diagnosing or optimizing electrochemical systems. If the reaction is kinetically limited, improvements can be made by modifying the electrode material, surface structure, or applied potential to enhance electron transfer rates. If diffusion is the limiting factor, then changes to stirring, temperature, or electrolyte composition might be necessary to improve mass transport.
However, we must be careful to distinguish Faradaic currents (those arising from actual redox reactions at the electrode surface) from non-Faradaic contributions arising from charging and discharging the electrical double layer. Faradaic currents involve the transfer of electrons between the electrode and species in the electrolyte, leading to real chemical transformations, such as the deposition or dissolution of a metal. These are the currents that directly reflect the electrochemical reaction rates and are typically the focus of interest when studying electrode processes. In contrast, non-Faradaic (capacitive) currents arise from the rearrangement of ions near the electrode without any electron transfer across the interface; they do not result in any chemical change occurs Failing to separate the two can lead to misinterpretation of data, such as overestimating reaction rates or misidentifying kinetic or diffusion limitations.
In summary, electrochemistry provides a powerful framework for understanding and harnessing redox reactions coupled to electron flow. By measuring current and potential, we can gain insights into the thermodynamics, kinetics, and mass transport characteristics of a system. With this information, we can design more efficient electrochemical processes, troubleshoot performance issues, and tailor experimental conditions to achieve specific outcomes. Whether we’re optimizing battery materials, developing sensors for chemical detection, or interpreting operando measurements, a clear understanding of these principles allows us to connect observed behavior to the underlying mechanisms.
Learn more about the importance of electrochemistry as a method in applications such as batteries and corrosion prevention in the webinar Electrochemical QCM-D - a very short introduction. In this presentation, Viktor introduces some of the basic electrochemical measurement techniques and key methods such as Cyclic Voltammetry, Galvanostatic cycling, and Electrochemical Impedance Spectroscopy, as well as how these can be combined with Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) into so-called EQCM-D.
Viktor Vanoppen, M.Sc., is a guest writer for the blog. When he's not sharing his vast knowledge on electrochemistry and EQCM-D with the blog audience, he spends his time as a PhD candidate at Uppsala University, studying interfacial processes during metal plating for energy storage, combining EQCM-D, automation, machine learning, and advanced modeling techniques like Hydrodynamic Spectroscopy and FreqD-LBM
