Electrochemistry is a quite old science since its birthday is considered to be in the 18th century but I think that, scientifically-speaking, it is in the best moment of its life. As an electrochemistry I always have on my mind the social relevance of my beloved scientific field but I also understand that this may not be evident for the general public or even for scientists working in other fields. Therefore, in this post, I would like to highlight the relevance of Electrochemistry in many current technologies and, why not say it, the future of humanity 😉
Electrochemistry is a branch of Physical Chemistry that studies exchange of electrons between a conducting material (electrode) and chemical species, which suffer reduction/oxidation (redox) reactions. In an oxidation reaction, the chemical species lose electrons that are transferred to the electrode, and in a reduction reaction, the chemical species gain electrons coming from the electrode. Then, electrons travel by the electric circuit connected to the electrode and to maintain the neutrality, a reaction of opposite charge must be produced in a counter electrode. Most electrochemical systems work in a way where the electrodes are in contact with a liquid solution, and therefore, to close the electrical circuit, charges have to move in the solution. This is achieved by ion transport since electrons cannot travel freely by this medium. This is a very simplistic way to define Electrochemistry and many singularities can be found in particular systems such as solid state devices or 3-electrode configurations to name a few.
When the redox reactions happening at the electrode surfaces are spontaneous, i.e. happen without external energy supply, energy is produced (electric current) and the system is called a battery (also called galvanic or voltaic cell) (Figure 1). If external electricity has to be applied to induce the redox reaction, then we have an electrolysis process. Electrochemistry is rather versatile and can be observed from different point of views: it could be used in basic research to study and understand fundamental processes or it may have an applied approach where the electrochemical reactions are the foundation of many useful technologies.
In this regard, Electrochemistry is essential in many industrial processes and technologies widely employed. In many occasions, the science behind these technologies is practically invisible leading to the low notoriety of Electrochemistry. I would like to introduce the basic foundations of some current and future technologies with special social relevance where Electrochemistry is involved (Figure 2).
We use devices powered by electrochemical reactions every day. Indeed, if you are reading this text with your phone, laptop or tablet, your device is performing electrochemical reactions. The foundations of rechargeable Li-ion batteries are basically oxidation and reduction reactions in combination with lithium transport and intercalation into two electrodes (Figure 3). However, lithium is a scarce material and it may be eventually consumed from the Earth. But, do not worry, electrochemists are currently working on replacing lithium with other earth-abundant metals such as magnesium or sodium. Many other electrochemical energy storage systems such as redox-flow batteries or supercapacitors have special properties being useful in different applications. It is clear the current importance of energy storage systems and the improvement of properties such as capacity, cost, safety or weight will lead to a global diffusion of useful technologies such as home energy storage for cheaper and cleaner energy or safer electrical vehicles with instantaneous charging and longer ranges.
Energy storage is a great way to have energy readily available for our uses. However, we still need to make energy before storing it. Well, we cannot make it, as you well know by the 1st law of Thermodynamics, so we need to convert it from one form to another. And guess what? Electrochemistry is also playing a significant role in energy conversion technologies and will be essential in order to have a carbon-free energy system. The future of the modern society will depend on the availability of clean and sustainable energy sources to avoid bigger consequences coming from the climate change and to eliminate the dependence from non-renewable fossil fuels.
Hydrogen is considered a clean an renewable energy carrier (Figure 4) since it can be generated by water splitting, which is basically the oxidation and reduction of water to generate oxygen and hydrogen. This can be carried out by applying electricity (water electrolysis). Just as interesting is that hydrogen (in combination with oxygen from air) can be used back to generate electricity in a fuel cell system. In this case, the opposite electrochemical reactions happen. These reactions do not generate any subproduct or pollutant making these energy conversion systems very clean to the environment, and with great possibilities to power up different devices such as electrical vehicles. For the hydrogen generation we do need electricity, which ideally would come from clean renewable sources such as solar or wind. Hydrogen can be generated when we have abundant renewable energy available and then stored in H2 or other chemical form to be used when necessary.
Electrochemistry can also play a significant role in converting sunlight into a convenient energy source. On one hand, dye-sensitized solar cells (DSSCs) are able to directly generate electricity from sunlight. These devices use a photosensitizer able to absorb photons to generate a sequence of electron transfer reactions and finally electricity flows through the electrodes. On the other hand, photoelectrochemical cells (PECs) can be used to produce hydrogen by a similar process than water splitting but using direct sunlight as the energy source, making the hydrogen generation totally green and independent from external electricity.
Another two electrochemical technologies with great current research significance are worth to mention since they could be transferred to the society in the next few years. Firstly, artificial photosynthesis, trying to imitate the natural processes happening in plants, deals with the conversion of carbon dioxide to valuable products such as fuels by regular or sunlight-assisted electrolysis. Secondly, ammonia is an inorganic compound extensively used as source of many products or even as an hydrogen carrier. Ammonia is produced using the cost and energy-intensive Haber-Bosch process. Current research is trying to produce the green and cost-effective electrochemical reduction of nitrogen to ammonia to replace the conventional thermochemical process.
Electrolysis is the fundamental technology for the preparation of several inorganic-based materials such as aluminum, zinc, chlorate, chlorine or sodium hydroxide, to name a few. These materials are very valuable for the fabrication of many final products that we use daily or as a source in other chemical industries such as the paper industry. As mentioned before, electrolysis deals with the application of an electric current to carry out an electrochemical reaction. In some cases such as in the chlor-alkali industry, several valuable products such as chlorine, hydrogen and sodium hydroxide are generated simultaneously, making the proccess more economically viable.
Metal corrosion cause numerous economic losses since many infrastructures have been fabricated with metallic materials such as iron or steel. Corrosion leads to the loss of functionality or the total destruction of the material with the consequent economic losses and even safety implications. Therefore, the development of appropriate materials with strong resistance to corrosion is essential in order to reduce the cost of infrastructure maintenance. Since corrosion processes basically involve the oxidation of materials to form a more stable chemical form, electrochemical techniques are very useful to study corrosion initiation processes and evaluate effective coatings. Therefore, Electrochemistry plays an indirect but important role in the development of novel materials that can avoid or minimize corrosion and the consequences associated to this phenomenon.
Electrochemistry is so versatile that can be used indirectly in many other applications. By Faraday’s laws, we know that the current generated during an electrolysis process is proportional to the amount of the reactant. Therefore, it can be exploited from an analytical perspective for quantification purposes such as in electrochemical sensors. Electrochemical output signals could be obtained directly from the chemical species to analyze (heavy metal sensors) or it could be an indirect tool to monitor redox-inactive processes such as biological reactions (electrochemical biosensors). This opens the possibility to detect disease biomarkers such as proteins or nucleic acids and make Electrochemistry an useful tool for medical diagnostics among many other analytical applications. There is still a lot of room for improvement in order to make these technologies commercially successful, but they have already been demonstrated in some cases such as in glucose sensing. Glucometers (Figure 5) are widely employed by diabetic patients to monitor the glucose levels in blood and most of them are based on electrochemical techniques. But, as said, no many commercial cases have been developed with only a few other niche applications such as lactate monitoring, or electrochemiluminescence sensors developed by Roche to detect biological molecules. One interesting research field is wearable electrochemical sensors, which provide the possibility to extract chemical information from our organism or our close environment by integrating small sensors in the body, clothes or accessories. We could see a wide use of chemical wearable sensors in the future to monitor health issues or even safety threats.
Organic synthesis has a tremendous importance in the fabrication of many relevant chemical compounds with a vast amount of different uses. A significant example is the fabrication of pharmaceuticals. To make these products, organic synthesis employs numerous catalysts, reagents and sometimes tough experimental conditions. Some steps of a total organic synthesis are redox reactions (electron transfers), and therefore, Electrochemistry can be employed as a tool to make these reactions happen. Since electrons are the reactants and they can be provided by an electrode, it may be possible to decrease the number of chemical species used making the overall process simpler and greener. Electrochemistry could also present higher reactivity and by selecting an appropriate reaction potential, it could enable the control of the selectivity, increasing the yield of the process.
Calling all electrochemists!
Electrochemistry has great relevance in many current technologies and will be essential to bypass some of the biggest societal challenges such as clean and affordable energy. However, outside of our inner circle, only a few people has heard about it, and even the name could sound scary to them. Everybody has heard about the Higgs boson, which is completely basic research and do not have any technological relevance in our daily life. We use Electrochemistry every day, but the general public has not heard about it.
I believe that we currently live in a great era for popular science, and we should exploit this moment to spread the goodness of our beloved science. It could be informative and it could be entertaining. I believe that even a simple water splitting experiment with a small battery is stunning! I hope to contribute my bit with this blog and in social networks as much as I can.
Let’s make Electrochemistry more visible!