How Electrochemistry will Disrupt Energy Storage
Electro-what? I know what you may be thinking. But don’t close this tab just yet. Give it a chance, it’s worth your time.
Electrochemistry may sound intimidating, so let’s take a step back and start with the basics, shall we?
Why is energy storage important for transitioning to renewable energy?
Turn on the lights... go ahead.
Most likely, the light you are seeing is powered by electricity being produced at this instant in an electricity production plant.
Because the electricity being consumed has to be produced at the moment it is being used, supply and demand for electricity have to be equal at any given moment.
This is not an easy task. Energy demand changes at different times of the day. Think about the times of the day in which you consume the most energy. Maybe when you get home in the afternoons or after sunset. Whenever that is, it is likely that most people follow similar patterns.
These charts show a trend on when people consume the most energy:
These show trends in demand and trends in prices follow similar patterns. When more energy is being consumed it becomes more expensive.
Thanks to our energy grid systems, we always have access to energy. Electricity production in energy grids is monitored and controlled to match peak demand. When more electricity is needed, more electricity is produced.
But it’s a different story when talking about renewables.
Usually, the production of renewable energy can’t be changed throughout the day to match demand. There is no way to make the sun brighter or the wind stronger when we need more electricity and the electricity produced using these methods doesn’t match peak demand. So what happens with electricity produced at times of the day when it is not needed? It still has to be consumed, so usually, the energy grid brings it to whoever needs the energy at that given moment.
Key idea: If we produce a certain amount of electricity using solar panels or wind turbines, this energy has to be consumed in the instant when it is produced. Therefore, the world can’t rely on it to produce electricity during the peak hours.
Most likely, if you see a house that has solar panels or wind turbines, the people who live house are not the ones consuming the electricity produced by these sources. This electricity goes to the grid and is taken to people who are using electricity at that time. The house still ends up using electricity from the grid.
Imagine an apple tree harvest. Apples may grow at a certain time of the year. But if the owner of the land doesn’t have any use for the apples at a given moment, they will just have to someone else who needs to consume them. There is no way for the farmer to grow the apples at the moment he needs them, so if when he needs the apples there are none in the trees, he will still have to go to the store and buy some.
Unless… we add energy storage into the equation. This means producing energy, keeping it somewhere, and using it later. Taking the apples from the harvest, freezing them, and using them when they are needed.
How can we do this? There is not a single answer.
Current methods of energy storage and their implications
Pumped hydro
Hydroelectric dams use excess electricity (when demand is low) to pump water from a lower reservoir to a higher one. When needed, the water is released back into the lower reservoir for it to spin a turbine and generate electricity.
- Pros: responds quickly (within 10 minutes you’ll get electricity), doesn’t use fossil fuels, maintenance is low, lasts a long time, low energy losses (around 80% efficient).
- Cons: expensive to build, limited possible locations, not accessible at lower scales.
Batteries
Store energy as chemical energy, which is converted back into electricity. Batteries linked to the grid are controlled by algorithms to release energy when needed. Types include sodium sulfur, metal-air, lead acid, and most importantly: Lithium-ion.
- Pros: scalable, realistic for smaller scales, very low energy losses (around 95% efficiency).
- Cons: last 2–3 years and have to be disposed of, their production requires fossil fuels (such as cobalt), and can become very expensive (eg. lithium prices are rising).
Thermal
Energy is stored as heat in water or molten salt. These are kept and maintained at high temperatures until heat is needed for running a turbine to generate electricity.
- Pros: may be implemented at smaller scales and most of the materials required are abundant.
- Cons: energy transfer isn’t very efficient (around 60% efficiency) and the materials used may create waste or emissions when heated.
Compressed air
Electricity is used to force air into an underground cavern, and then release it to turn a turbine.
- Pros: infrastructure can last more than 30 years, energy can be stored for over 25 days, and cleaner materials.
- Cons: large caverns have to be mined (environmental concerns) and it has large energy losses (40–50% efficiency).
Hydrogen
Energy is used to compress or liquefy hydrogen for it to be used in combustion or fuel cells (imagine a battery fueled by hydrogen).
- Pros: may have high energy for its volume if stored at extremely low temperatures.
- Cons: it is usually produced from fossil fuels, has high energy losses (50–60% efficiency), has to be stored at very low temperatures, and is easily flammable and dangerous.
In summary, energy storage can have these problems:
- Environmental factors.
- Safety.
- Efficiency — some of the methods for energy storage will slowly lose some of the stored energy or waste electricity in the process of storing it.
- Scalability and accessibility — the need for complex infrastructure, rare chemicals, or extreme conditions makes it hard for these to be implemented at larger scales or by different possible users.
Storage with ammonia
Ammonia is used in a similar way to hydrogen, just better. It has more than twice the energy of liquid hydrogen, is easier to transport, and can be more efficiently stored. Ammonia can be stored at -33ºC compared to hydrogen, which has to be stored at -250ºC.
But, what is ammonia?
Ammonia is a compound of 1 nitrogen and 3 hydrogen atoms, usually found as a gas.
It is already used at large scales for the production of fertilizers and cleaning products. This is a huge advantage because the infrastructure for the storage and shipping of ammonia already exists and can be scaled. About 180 million tonnes of Ammonia are already produced yearly.
Ammonia can be combusted to be turned back into electricity and could be used as an alternative to fossil fuels in combustion engines. It behaves like any other liquid fuel⛽️ and doesn’t generate CO2. Check out new ways being discovered to harness energy from ammonia.
It can also be useful for transporting energy long distances.
🌟 Some success stories:
- 1940s: Due to diesel shortages, ammonia was used to power public Buses in Belgium.
- 1960s: Nasa powered their X-15 rocket plane using Ammonia. It set speed and altitude records.
- Marangoni Toyota GT-86 Eco-Explorer: car powered by 100% ammonia.
It sounds pretty good, right? Maybe too good to be true…
Environmental concerns about ammonia production
Haber-Bosch Process
Currently, Ammonia is produced through the Haber-Bosch process.
- Nitrogen and hydrogen are transferred into a reaction vessel at around 450ºC and high pressure (200 atmospheres) with a catalyst made of iron or ruthenium.
- The catalyst helps to bond together the nitrogen and hydrogen atoms to create ammonia. Only around 50% of the hydrogen and nitrogen atoms react.
- The mix of gases is passed through a condenser to cool down and liquefy only Ammonia (thanks to its low boiling point), leaving behind the remaining hydrogen and nitrogen atoms (those that didn’t react).
- Ammonia is extracted and the remaining gases are reused to run the reaction again.
PROBLEMS:
- Getting to the pressure needed for the reaction requires enormous amounts of energy, created through the burning of fossil fuels.
Let me take a step back for a moment… where do nitrogen and hydrogen come from?
Steam reforming
Hydrogen for ammonia is produced through Steam Reforming. This has a low cost and high efficiency.
- Step 1— Steam methane reforming: Methane is purified and used to generate hydrogen and carbon monoxide using very hot steam (700°C–1,000°C). Hydrogen is gathered.
2. Step 2 — Water gas shift reaction: Carbon monoxide and steam (water gas) are then processed using a catalyst into more hydrogen and CO2. Hydrogen is gathered and CO2 and impurities are removed and released 👎.
Cryogenic air separation
Nitrogen is produced, most commonly, through cryogenic air separation, where nitrogen is sourced from the air. Nitrogen makes up 78% of the air so this process is easy compared to steam reforming. Nitrogen is separated from the other gases (CO2, O2, and H2O) by using their differences in boiling points to produce pure gases.
- Air is filtered, compressed, and cooled.
- Because of the low temperatures, water vapor in the air condenses (goes from gas to liquid💦) and can be removed along with CO2.
- The remaining gases are cooled further to the temperature where they become a liquid.
- All gases condense at different temperatures. This property is used to separate the gases.
We have a problem
The production of ammonia and getting the materials to produce it are harming our planet.
Not energy efficient:
- 50% of the energy put in to produce ammonia is lost in the process.
- Haber-Bosch consumes too much energy (around 30 GJ per tonne of ammonia).
- Ammonia consumes around 1–2% of the world’s energy supply.
Too many greenhouse gases:
- For every tonne of hydrogen produced, around 10 tonnes of carbon dioxide equivalent are produced. (CO2 equivalent is used to compare the effect of greenhouse gas emissions)
- Currently, ammonia production creates around 1% of the world’s CO2 emissions.
Green ammonia
Let's not discard ammonia just yet. There are ways around these challenges. Here are 2 alternatives to the current methods of Ammonia production.
Yes, it’s time for electrochemistry.
Electrochemistry is a branch of science that studies how electricity affects chemical reactions.
Some key definitions before we get started:
- Electrodes: metal strips (these are connected to an electric device through a wire).
- Electrolyte: a compound that can carry current.
- Cathode and Anode: Name for the electrodes in the cell. One has a negative charge and the other has a positive charge. There are disagreements on which is the positive and negative electrode. Therefore, we are just going to refer to them as the positive electrode and the negative electrode.
- Electrochemical cell: device that generates energy from chemical reactions (🧪 →⚡️) or uses energy to generate chemical reactions (⚡️→🧪). In simple terms, differences in the charges of each electrode (and solution in the case of galvanic cells) allow the movement of electricity. There are two types: Electrolytic and Galvanic.
- Electrolytic Cell: Requires energy. Its electrodes are placed in the same container. Current is used for starting a chemical reaction (a change in the charge and/or structure of a molecule) in the electrolyte solution.
- Galvanic Cell: Produces energy. Electrodes are in separate containers. Chemical reactions in the electrolyte solutions and the cathodes create a flow of charged particles (electricity).
Renewable-powered Haber-Bosch and Electrolysis
Powering the Haber-Bosch reaction with renewable energy would lead to 1/3 less CO2 emissions.
But, for an even more “green” alternative, other ways of sourcing hydrogen have to be explored.
Electrolysis uses water to produce very pure hydrogen. It requires fewer steps, is more affordable and scalable, and produces zero greenhouse gases. There are many types of water electrolysis but I will be going through Alkalike Water Electrolysys.
This is done with an electrolytic cell.
The Set-up:
A positive and a negative electrode made of metal, such as nickel, are placed close to each other. We are using an electrolytic cell because for the reaction to happen, we will be adding electricity.
You’ll notice that the picture is different from the ones shown above, but the idea remains the same. The image below shows the setup used at the industrial scale.
A diaphragm separates both electrodes, allowing the movement of some atoms. It is made of a porous, solid material such as Zirfon Perl. Electrodes have to stay separated due to their opposite charges.
The cell contains an alkaline liquid: the electrolyte. It is usually KOH (Potassium hydroxide) and it flows between and through the electrodes.
production” by S. Shiva Kumar and Hankwon Lim)
The Reaction:
At the negative electrode (cathode in the picture), electrons coming from the electrical circuit (aka. electricity) split the water molecules into hydrogen ions and hydroxide ions (made of one hydrogen and one oxygen atom).
This is known as the Hydrogen Evolution Reaction.
After, each individual hydrogen ion bonds with another hydrogen ion and 2 electrons (which come from the electrode). Remember, hydrogen gas is a molecule of 2 hydrogen atoms. Once formed, hydrogen gas is extracted.
The remaining, Hydroxide, then starts moving toward the positive electrode (due to its positive charge).
At the positive electrode (anode in the picture), we have the Oxygen Evolution Reaction. Hydroxide is split with the help of a catalyst. The product is a hydrogen ion, oxygen gas, and some spare electrons (recall that hydroxide had a negative charge, so it had more electrons than it needed).
Oxygen gas is released, the electrons are carried through the wire to the negative electrode as electricity (through the wire) and there are leftover hydrogen ions.
Due to their positive charge, they now move toward the negative electrode and bond with another hydrogen and some electrons to form more hydrogen gas. After, they are released.
The fuel cell operates at temperatures around 30 to 80 ºC and uses around 1.23–1.5 volts of electricity.
UPSIDES: Works with the Haber-Bosh process (for which we already have the infrastructure).
DOWNSIDES: doesn’t solve the energy efficiency issues. Also, reducing 1/3 of emissions is not enough, around 50% efficiency (wasting a lot of energy).
Electrochemical reverse fuel cell
Professor Doug MacFarlane recently developed a method of ammonia production that doesn’t require huge chemical plants. It uses an electrochemical cell that takes air as a source of nitrogen and water as hydrogen. This process removes the need for producing hydrogen independently.
This is also done through an electrolytic cell with a thin membrane separating the anode from the cathode.
The Components: This reaction happens during what we call the 3-phase boundary. Gas, liquid, and solid components take part in the reaction.
- Solids: The electrodes are made of copper (negative) and nickel (positive).
- Gases: water vapor and nitrogen gas are what go into the cell.
- Liquids: The electrolyte of the fuel cell is THF (Tetrahydrofuran) with dissolved Lithium salts. It is between the electrodes and flows through them.
- Lithium is an intermediate compound in the reaction. This means that it transforms into different compounds but it is not used up. It facilitates the reaction but isn’t part of the reactants or the products.
The Set-up:
I’ll use an analogy used by Dr. MacFarlane to explain to me the setup of the cell.
Let’s imagine the cell as a sandwich:
- The two electrodes are the pieces of bread that are put against each other. The electrodes are solid but porous; they are spongy just like a fluffy slice of bread.
- For the filling, there is a slice of cheese separating the two pieces of bread. Remember, one electrode has a positive charge and one has a negative charge so they cannot be in contact with each other. What is a sandwich without cheese? A thin slice of a material, like plastic, stands between the two electrodes. Keep in mind that in the cell, atoms can cross this membrane.
- It’s time for flavor. There are some sauces rubbed in the bread. Most importantly, Lithium salts bond with nitrogen to form Lithium nitride. This is only at the negative electrode.
The Reaction:
- Electricity causes nitrogen and lithium salts to bond, creating Lithium nitride (1 nitrogen and 3 lithium atoms). It stays at the negatively charged electrode.
- Catalysts at the positive electrode split water molecules into oxygen atoms, hydrogen ions (charged particles), and electrons. Oxygen is released as a byproduct, electrons travel through the wire toward the other negative electrode, and hydrogen remains.
- Phosphonium salts (big and complex molecules also known as Ylides) carry hydrogen around the cell. They each grab 1 hydrogen ion that was created after splitting water. With the hydrogen, they become positively charged so they flow toward the negative electrode (to where lithium nitride is).
- Phosphonium salts bring the hydrogen ion to the lithium nitrides and release the hydrogen ion. It replaces one of the lithium atoms in Lithium nitride and then diffuses away.
5. After releasing the hydrogen, Phosphonium salts are now neutral compounds that go back to the anode to gather another hydrogen ion. They keep flowing back and forth transporting hydrogen ions and are not used up.
6. Once 3 different Phosphonium salts have delivered 3 hydrogen ions that replaced the 3 lithium atoms in Lithium nitride, it has become ammonia!
Due to the deterioration of the compounds in the cell, this process can run for about 4 days. Scientists are experimenting with different compounds to make the reaction more efficient and more feasible for longer periods of time.
The fuel cell’s efficiency also depends on the types of electrolytes used. Changing the electrolyte to more goopy liquids that contain other components such as fluorine can allow for an increase in efficiency from below 15% to around 60% (around 60% of the energy going into the production is actually stored).
UPSIDE: Could be used for smaller scale and localized production. It completely eliminates the production of hydrogen.
DOWNSIDE: This would require more investment and adaptation.
Impact of Green Ammonia
Let’s go back to the other energy storage methods for a moment. Pumped hydro and compressed air are limited by geographical conditions, (most) batteries use fossil fuels and rare materials, and thermal energy storage can produce greenhouse gas emissions.
Notice a trend? The world hasn’t found the perfect energy storage method.
We are left with ammonia and hydrogen. Even though the production phase of hydrogen is cheaper, ammonia’s price is lower when having to be transported across long distances. This is due to ammonia's low shipping costs.
When transported longer than 2,000 km, one metric tone of ammonia can cost 797–959 USD and one metric tone of hydrogen can cost 1,026– 1,115 USD.
Ammonia is the lowest-cost, non-fossil fuel energy storage option. It is also the solution with the most infrastructure to be transported and scaled.
Why hasn’t this been implemented?
Sustainable Haber-Bosch:
- Electrolysis is less efficient than steam reforming and will only be cheaper when electricity becomes cheaper than natural gas.
- On average, the price for producing hydrogen through steam reforming is 2–4 times lower than electrolysis.
- The normal Haber-Bosch process is still around 73% cheaper (good news- the prices are getting closer every day).
Electrochemical reverse fuel cell:
- Infrastructure is already built around the existing methods for production (Steam Reforming + Haber-Bosch).
- This is a discovery that has been recently made, and getting it to the market will take time.
- Carbon-free processes consume more energy. It is only sustainable if powered by renewables, limiting its accessibility to a few locations.
Clearly, it will take time to change to sustainable ammonia production. But as the world starts moving away from fossil fuels, governments develop emission restrictions, and society moves towards a greener future, green ammonia will be a great medium for energy storage. Good news, it is starting to be.
Progress toward green ammonia
Yara, the leading ammonia producer, has a unit focused on “Clean Ammonia”, headquartered in Olso, Norway. They are actively working towards expanding their green ammonia production. For example, they signed a partnership in July 2022, to make part of a green ammonia plant being built in Oman. Also, in Australia, they are building a facility to produce hydrogen through electrolysis to supply hydrogen to their sustainably powered ammonia plant. They received an AUD 47.5 million grant from the government and the construction is set to start this month and start supplying in 2024. Find out more here.
Japanese company JGC has started working under the NEDO Green Innovation Fund Project to investigate alternative catalysts for the reaction of ammonia and constructed a trial plant at the Fukushima Energy Institute. The plant is meant to operate on Haber-Bosch but uses electrolysis to source hydrogen and is powered by solar panels.
Key takeaways
Thanks for persisting. That was a long read.
I hope you leave with these ideas:
- Energy storage is essential for the transition to renewable energy because sources like wind and sun are neither consistent nor meet the peak demand for electricity.
- We haven’t found the ideal energy storage system. The existing methods have limitations in terms of the environment, energy efficiency, or CO2 emissions.
- Ammonia can be used for energy storage and is currently produced on very large scales. However, not sustainably. This is mainly due to the release of greenhouse gases during hydrogen production and energy waste.
- There are 2 alternatives to traditional ammonia production. First, powering the current production methods with renewable energy coupled with sustainably sourced hydrogen. Second, using a reverse electrochemical cell.
- Ammonia is one of the most promising methods of energy storage for the future, and companies like Yara and JGC are starting to produce it sustainably.
If you are curious and want to learn more about energy storage and other amazing technologies, follow me!
References
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