Electrochemistry as a green alternative to power chemical reactions
Since the infamous key and kite experiment completed by Benjamin Franklin, electricity has proven vital to our everyday lives. It has pervaded fields such as energy storage, energy conversion, biology, pharmacy, and industrial synthesis, among many others. Despite its ubiquity and impact, the majority of electricity is generated via the burning of fossil fuels as compared to renewable alternatives. Thus, the fight for green electricity is currently underway.
What is electrochemistry?
Electrochemistry is the study of electricity and its relation to chemical reactions. As opposed to heating, shaking, or pressurizing, in electrochemistry energy is provided in the form of electricity, or moving electrons. As electrons move from one element to another through a circuit, an electrical current is generated (Figure 1).1 This electrical current is a form of energy that can be used to do useful things such as power automobiles, light our houses, or be stored in batteries for later use.
Electricity, in the form of static electricity, was discovered as early as 600 BC by the Ancient Greeks who rubbed fur on tree amber (static charge is one of the simplest forms of generating electricity. It is as easy as rubbing fur on glass!). In the late 18th century, Benjamin Franklin confirmed, with his key and kite experiment, that lightning and electric sparks were the same thing.2 Soon after, Italian physicist Alessandro Volta discovered that some chemical reactions could spontaneously generate a flow of electrical current. In the late 19th century, Michael Faraday created a very early version of an electrical generator which opened the door for American inventors, Thomas Edison and Brit Joseph Swan, to simultaneously develop the incandescent light bulb and ultimately commercialize electricity.2
Today, electricity is essential to our daily life. From the alarm clock that wakes us up every morning to the television screen we fall asleep to at night, electricity pervades all aspects of our day. While we constantly interact with electricity and it is a vital component of how we live our lives, it has only recently been adapted towards aiding synthetic chemistry.
Is electricity a green source of energy?
Electricity is a green source of energy because the movement of electrons produces no byproduct. However, electrons do not move spontaneously, but energy must be supplied to move the electrons and produce electricity. Traditionally, electricity is generated through the burning of carbon-based products such as fossil fuels, natural gas, or oil.4 This leads to carbonaceous products like soot and other hazardous greenhouse gases being emitted into the atmosphere which contribute to the ongoing climate crisis. In 2019, the US Energy Information Administration reported that natural gas and coal together accounted for 61 % of the nationally generated electricity compared with 17 % generated via renewable alternatives (solar, wind, geothermal, hydroelectric, and biomass) (Figure 2).4 This is a significant discrepancy which continues to exacerbate the nation’s carbon footprint.
Recently, in the midst of such a global climate crisis, renewable energy sources such as solar, wind, or geothermal have been increasingly employed while coal has seen a steep decrease in usage in the past 10 years (Figure 3).4 This transition away from a carbon-centered energy economy towards renewable alternatives remains vital. Therefore, current research efforts focus on developing molecules, materials, and other systems that can harness natural phenomena (i.e. sunlight and wind) for electricity generation. This ongoing work has opened the door to realizing energy by environmentally-friendly means in order to create a greener world.
Towards electrochemically-driven chemical reactions
Spontaneous chemical reactions (acids and bases reacting, wood burning, etc.) do not require any additional energy input to convert the starting material(s) into product(s), whereas non-spontaneous reactions (ammonium chloride dissolving in an ice pack, photosynthesis, etc.) necessitate the addition of energy to accomplish such a transformation. Conventionally, scientists employ temperature, pressure, or additional chemicals to move a reaction to completion (turn reactants into products). But, now that we are moving towards green electricity, we can take advantage of this movement of electrons to power many useful chemical reactions sustainably.
With electrochemistry in hand, it can be applied to chemical transformations. For example, the reduction of carbon dioxide, a conversion which can transform carbon dioxide into usable chemicals, lessens its negative effects on the environment, but is a highly energy intensive process.5 Additionally, methane oxidation, a process which can convert methane, the main component of natural gas, into liquid fuels such as methanol is also quite challenging.6 Both carbon dioxide and methane are deleterious to our atmosphere, but are relatively inert molecules and thus require energy to react. While kinetic energy, either in the form of elevated temperature and pressure, are viable options, they have inherent limitations which electricity can overcome.
As opposed to temperature, pressure, or other established energy inputs, electrochemistry can provide a greener alternative to traditional methods and induce new reactivities. As discussed earlier, electricity generation can arise from natural processes, rendering the system environmentally friendly. Additionally, electrochemistry requires less infrastructure and can even increase product selectivity over undesired byproducts.7 Moreover, the electrochemistry user has deft control over the flux of electrons (current) that is applied to the chemical reaction.8 This allows for a high degree of sensitivity and delicate tunability which can be difficult to achieve in conventionally heated systems. Additionally, as electricity is a fundamentally different energy source than temperature or other established methods, new and unknown chemical reactivities and reactions are now possible.8 Thus, electrochemistry has opened the door to chemical transformations that are essential in the environmental, energy, and pharmaceutical sectors that would otherwise be impossible.
Now that we have shown electrochemistry to be a viable energy alternative with many advantages and possibilities, let’s take a deeper look at where else it has been applied!
The wide breadth of electrochemistry
In the last 50 years, we have seen a surge in research centering around electrochemistry and its numerous applications.9 One thing that differentiates electrochemistry from other branches of chemistry is its ubiquity in application. It has been applied to fields such as chemical industry, pharmacy, metallurgy, medicine, biochemistry, nanochemistry, among many others.
Perhaps one of the most impactful applications of electrochemistry as a green technology is in energy conversion and storage. In addition to the transformations of inert greenhouse gases previously discussed, electrochemistry finds great application in devices such as solar cells. To circumvent generating electricity through combustion of carbon based products, researchers have utilized principles of electrochemistry to pair light absorbing materials to appropriate electronic materials to cleanly convert sunlight into electricity.10
For electricity as a power source, we require immediately adjusable, energy outputs which can be difficult with intermittent power sources like solar and wind. This brings us to energy storage, yet another application of electrochemistry. The 2019 Nobel Prize in Chemistry was awarded for such an application, to the discovery of the lithium ion battery.11 Lithium ion batteries convert the energy stored in chemical bonds into electricity, which allows for on demand energy access. Thus, energy storage in lithium ion batteries has pervaded modern society and found widespread applications (likely including the device you’re using to read this).
Electrochemistry also finds medical and biological applications such as glucose monitoring for diabetes. Companies have taken advantage of electrochemical reactions between glucose and enzymes to use current to continuously monitor glucose levels (Figure 4). The field of biological sensing is evolving around electrochemistry because of the sensitivity and quick response time of electrochemical reactions.9
Though one of the most fundamental applications of electricity to chemical reactions is on the industrial scale in metal corrosion and electrolysis. Elements such as iron that rusts over time (oxidize, lose electrons) in air can feasibly be restored using electrochemistry. In addition, commodity chemicals such as sodium hydroxide are produced on the industrial scale (i.e. million tonnes) as it is used in the manufacture of pulp and paper, textiles, drinking water, and detergents. Electricity is utilized to power many industrial processes, such as sodium hydroxide production, because conditions can be carefully controlled, high purity products are synthesized, and electricity can be generated via renewable sources.
Though significant effort has been put on utilizing electricity in chemical synthesis, there still remains much that needs to be done to generate electricity by green means. The majority of the US’s electricity still comes from burning natural gas and coal (38% and 23%, respectively),4 implying that laboratories where electrochemical synthesis are being developed still rely heavily on environmentally deleterious sources for producing electricity. 17% of electricity is generated from renewable sources, however solar only accounts for roughly 2% of this. Thus, it appears that the next feat limiting the green application of electrochemical synthesis is improving solar harvesting methods to convert solar energy into electricity. This highlights ongoing efforts towards energy storage, as the sun is (un)fortunately only out for half of the day.
1Gregerson, E. Electric Current. Encyclopedia Britannica, 27 May 2020. https://www.britannica.com/science/electric-current
2History of Electricity. Institute for Energy Research. https://www.instituteforenergyresearch.org/history-electricity/
4Electricity in the United States. U.S. Energy Information Administration, 20 March 2020. https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php#:~:text=Most%20electricity%20is%20generated%20with,wind%20turbines%2C%20and%20solar%20photovoltaics
5Artz, J. et al. Sustainable conversion of carbon dioxide: an integrated review of catalysis and life cycle assessment. Chemical Reviews 2018, 118, 434–504
6Caballero, A.; Perez, P. J. Methane as raw material in synthetic chemistry: the final frontier. Chemical Society Reviews 2013, 42, 8809−8820
7Schüth, F. Making more from methane. Science 2019, 363, 1282–1283
8Bard, A. J.; Faulner, L. R. Electrochemical Methods: Fundamentals and Applications. 2nd ed. John Wiley & Sons, Inc., New York, 2001.
9Gulabowski, E. Electrochemistry in the twenty-first century—future trends and perspectives. Journal of Solid State Electrochemistry 2020, 24, 2081
10Photovoltaics and Electricity. U.S. Energy Information Administration, 25 August 2020. https://www.eia.gov/energyexplained/solar/photovoltaics-and-electricity.php#:~:text=Photovoltaic%20cells%20convert%20sunlight%20into,convert%20artificial%20light%20into%20electricity
11The Nobel Prize in Chemistry 2019. Nobel Media AB, 9 October 2019. https://www.nobelprize.org/prizes/chemistry/2019/summary/