Turin is storing the energy of tomorrow

When we flip a light switch, we expect it to turn on every time. But what happens when the sun sets and solar panels cease to generate energy? Or when the wind dies down and wind turbines generate far less power? The answer to these seemingly simple questions reveals one of the most complex challenges of the energy transition: how to store energy for when we need it.

At Politecnico di Torino, several research groups are tackling this issue from different angles, each focusing on a particular form of storage. Solutions range from pumping water into dams to store kinetic energy (as discussed in the June episode of Orizzonti), to developing batteries and electrolysers for hydrogen production from water, to underground thermal energy storage, and investigating nanomaterials that could transform fuel cells. This diverse approach paints a picture of a dynamic scientific ecosystem dedicated to advancing innovations that will support the successful transition to renewable energy sources.

What does storing energy mean from the perspectives of physics and chemistry? According to Massimo Santarelli, Full Professor of Polygeneration and advanced energy systems at Politecnico's Department of Energy, storing energy means going against spontaneity (while always respecting the laws of physics).

“Every process in physics has a preferred direction,” he explains. “Given a gravitational field, water naturally flows from a higher elevation to a lower one. Similarly, a positive electric charge moves spontaneously from a high potential to a low potential. These are transport phenomena related to the presence of potential gradients.” Energy can be stored in various ways by reversing spontaneous processes: for example, raising water from a low level to a high level, recharging a battery from a lower energy state (Gibbs free energy) to a higher energy state, or splitting water molecules to produce hydrogen.

We can achieve this by using different types of potential function gradients. The gravitational gradient is the most intuitive but also the weakest: for this reason, the energy accumulated by lifting weight is relatively small. In contrast, chemical gradients, which operate at the level of atomic valence electrons, can provide much higher energy densities. If we were able to harness nuclear processes for energy storage, the energy densities could reach even greater magnitudes. However, at that point, electrical storage might no longer be necessary.

There is a crucial issue, however, an inexorable law of physics that governs all these processes: the second law of thermodynamics and the concept of entropy. “Due to entropic phenomena, recharging a system always requires more energy than you can recover when discharging it,” explains Santarelli. "If you obtain 100 units of usable energy from discharge, you will need 120 to recharge it. This principle applies to batteries as well as to hydrogen and other reverse processes." Splitting water molecules to produce hydrogen consumes more energy than can be recovered by recombining hydrogen and oxygen. This energy deficit must be compensated for by a primary energy source, which could be renewable, nuclear, or fossil fuel.

This research aims to minimize costs by focusing on both thermodynamics—such as the temperature and pressure to which materials are subjected—and transport mechanisms. “Transport mechanisms refer to the kinetics of a catalyst, as well as charge transfer or electron transfer. Some tasks are inherently more challenging than others: while electrons are small and therefore easy to transport, ions are larger and difficult to transport efficiently.”

Every choice has benefits and drawbacks, and optimization requires balancing different factors that often point in opposite directions. We are pursuing maximum efficiency.

“We have been relying on extremely inefficient systems for decades,” explains Silvia Bodoardo, Full Professor at Politecnico's Department of Applied Science and Technology, where she coordinates the task force on batteries and teaches Applied Chemistry and Materials Technology. Fossil fuels can achieve efficiencies of 20-30%, while a battery reaches efficiencies of over 99.9% at the single cell level, falling to 85-90% at the vehicle level. This difference has enormous consequences: less starting energy is needed to do the same job, which means fewer solar panels, fewer wind turbines, and less infrastructure.

Efficiency is only part of the equation; the other part involves the sustainability of raw materials. "Lead-acid batteries are a good example," says Bodoardo. "While lead has been removed from nearly all applications due to its toxicity, it is still used in batteries because it comes entirely from recycling. No one mines lead to produce batteries anymore." This illustrates how it's possible to establish completely closed-loop systems, where all the materials in a battery remain accessible even after the battery has reached the end of its life.

In 2017, the European Commission launched the European Battery Alliance (EBA 250), a strategic initiative aimed at capturing a share of a market valued at €250 billion per year. This effort goes beyond simply building factories, known as gigafactories, to produce batteries. It aims to create an entire industrial ecosystem that includes energy suppliers, manufacturers of machinery for cell assembly, developers of materials, and recycling experts.

The scale of the project requires training approximately 800,000 people all around Europe. “That's equivalent to the entire population of Turin,” Bodoardo points out. “and it represents one of the main bottlenecks in the sector.”

In parallel, two complementary research platforms have been established. Battery 2030+ is a coordination initiative that unites leading European research centers to develop a battery focused not on a specific technology, but on overall performance improvement. Innovations under consideration include sensors embedded within the cells to monitor their health, self-repairing electrodes, digital twins that can predict battery behavior, and robotic acceleration for discovering new materials.

Batteries Europe, in contrast, operates at a more advanced technological level and is to help with transfer innovations from the laboratory to the production line. Both platforms contribute to the strategic agenda of the Battery Partnership (BEPA), which directly collaborates with the European Commission to establish funding priorities. As one of the founding members of Battery 2030+ and an active participant in all these partnerships, Politecnico di Torino is in a unique position to influence European decision-making and secure funding.

At Politecnico, research encompasses the entire value chain, from initial research to production. Bodoardo states, “We share a pilot line with Fabrizio Pirri's group. They produce supercapacitors, while we produce battery cells. We are likely the only Italian university with a fully operational pilot line.”

Research encompasses a wide range of topics, including the development of innovative materials such as lithium-sulfur and lithium-oxygen batteries. These new batteries have the potential to achieve energy densities that are 5 to 10 times higher than current options, although they still face significant technological challenges. Another topic is the engineering aspects of assembling battery packs to ensure they are as lightweight as possible; “otherwise, energy could be wasted not on moving people or goods, but due to the weight of the battery itself”.

The research on potassium batteries, conducted in collaboration with Federico Bella, professor of Chemical Fundamentals of Technologies at Politecnico di Torino, is particularly noteworthy. These batteries serve as an alternative to lithium for stationary applications. Potassium is significantly more abundant than lithium in the Earth's crust and is cheaper, although it has a lower energy density. For domestic or neighborhood energy storage, where weight and volume are less critical compared to automotive applications, potassium batteries could provide a more sustainable and cost-effective solution.

There are many clichés surrounding electric cars, particularly regarding their range. One common question is whether they truly need to achieve 1,000 kilometers on a single charge, especially when comparing European cars with Chinese models. Bodoardo offers a pragmatic response: "Do they really need to go 1,000 kilometers?" She points out "Traveling 1,000 km from Turin would get you to Calabria. What about a stop along the way? Italy already has an extensive charging infrastructure with over 66,000 charging stations, providing broad coverage across the country.”

An emerging technology that could significantly impact energy usage is Vehicle-to-Grid (V2G). This system enables the energy stored in electric vehicles to be used for other domestic purposes. As Bodoardo explains, “Although V2G is not yet feasible for all vehicles, it changes the paradigm entirely. If I have charged my car and know that I will not be using it in the coming days, I can access and utilize the energy stored within it, for example, to run a washing machine.” Not all vehicles currently permit this, but the trend is now clear.

Most manufacturers now use lithium iron phosphate cells. The reason is straightforward: they are inexpensive and extremely safe. Lithium iron phosphate operates at 3.5 volts per cell, a relatively low but stable voltage. Premium vehicles are instead relying on high-voltage chemistries, which reach up to 4.5 volts per cell, to maximize energy density and thus range. The higher the voltage, the higher the overall energy density.

The European GigaGreen project, coordinated by Bodoardo, is focused on developing sustainable battery cells that avoid cobalt, a critical material often linked to ethically questionable conditions. The project employs high-voltage nickel- and manganese-based cathodes along with ultra-high-capacity silicon anodes to deliver outstanding performance while ensuring environmental sustainability.

“Everything that is stored in a battery remains usable even after the battery is depleted,” explains Bodoardo. “The issue in Europe is the lack of chemical industries capable of processing these recycled materials. As a result, we are forced to send everything back to China for processing, which is a significant contradiction that needs to be addressed.”

Fuel cells are key devices for converting hydrogen into electrical energy. Unlike batteries, fuel cells draw hydrogen and oxygen from outside sources and make them react to produce electricity, with water as the only waste product. The basic principle is relatively simple: hydrogen reaches the cell's anode, where it is separated into protons and electrons. The electrons travel through an external circuit, generating an electric current, while the protons move through a special membrane to reach the cathode. At the cathode, protons and electrons recombine with oxygen from the air, to form water.

"Fuel cells are electrochemical devices that enable a conversion reaction between hydrogen and oxygen to produce water,” explains Bodoardo. “One of the main challenges is that this reaction occurs at a very slow rate." To optimize this reaction, high-quality catalysts made from platinum or palladium are necessary, which significantly increases costs. Additionally, breaking down water molecules through electrolysis requires a considerable amount of energy, and when hydrogen and oxygen recombine in the fuel cell, the energy recovered is much lower.

The overall efficiency of the complete cycle is a concern, as approximately 60% of the initial energy is lost. The average roundtrip efficiency is around 40%. For this reason, batteries remain the preferred option for light mobility. The automotive market is decisively shifting toward battery technology. Fuel cells, on the other hand, are utilized in about 20% of those sectors that are difficult to decarbonize: steel industries, cement factories, aircraft, large ships, and possibly heavy road transport. In these cases, where energy density is critical and batteries would become too heavy, hydrogen can be a viable solution.

Choosing between using batteries and hydrogen is not ideological but pragmatic, and depends on scale and practical constraints. “Batteries are clearly the best choice for an apartment, with loads of a few kilowatts,” adds Santarelli. At the building scale, batteries are still the optimal solution, simply scaled up. The key turning point occurs at the neighborhood or village scale, where it becomes cost-effective to transition to chemical storage systems that use substances like hydrogen, rather than relying on valuable materials inside electrochemical cells.

Hydrogen applications in transport follows a similar logic to its storage. For motorcycles and cars, batteries are more efficient, easier to use, and better supported by existing infrastructure. In contrast, large ships and aircraft face limitations with hydrogen due to its low energy density, which makes them reliant on e-fuels. For instance, when electrolytic hydrogen is combined with CO2, it produces methanol, while combining it with nitrogen results in ammonia. Ammonia is particularly promising for shipping, although its toxicity presents challenges that require specific safety precautions. As Santarelli confirms, “Ammonia is the most interesting fuel for ships, albeit with toxicity limitations.”

Hydrogen has an Achilles’ heel: its energy density is very low. Being the lightest element in the universe, it requires sophisticated storage solutions. Physical methods include compression to 700 bar—an extremely high pressure that requires resistant and heavy tanks—or liquefaction at -250°C (21 Kelvin), which significantly increases density compared to compressed gas, but requires energy for the liquefaction process and causes continuous evaporation concerns. “It’s expensive to liquefy, and it has an unpleasant tendency to return to gas, so as soon as it receives a little heat, it evaporates,” explains Santarelli.

Chemical methods present intriguing yet complex alternatives. Metal hydrides and Metal-Organic Frameworks (MOFs) act as molecular libraries, where hydrogen atoms are confined in small spaces, allowing for higher densities than in free liquid form. “It’s like a library,” explains Santarelli. “The smaller the compartments, the smaller objects I can fit inside. Hydrogen atoms are very small, so in this library, they are compelled to be closer together than when they exist in the liquid phase.” However, a significant drawback is that these structures tend to be quite heavy, making them less suitable for mobility applications, though they work well for stationary uses.

The most advanced research by Santarelli's group focuses on direct electrochemical synthesis, a revolutionary approach that eliminates intermediate steps. “Instead of first producing hydrogen and then chemically combining it with CO₂, we use electrochemical cells that directly produce methanol or ethylene from water, CO₂, and electricity,” he explains.

The ultimate goal of this research is to develop artificial photosynthesis systems that mimic and even improve the natural processes of plants by using photons instead of electricity. In parallel, Federico Bella is tackling an equally ambitious challenge: the direct electrochemical synthesis of ammonia from water and nitrogen. Successfully achieving this process could revolutionize the chemical industry, which currently relies on the highly energy-intensive Haber-Bosch process to produce ammonia.

Marzia Quaglio, Associate Professor at Politecnico's Department of Applied Science and Technology, where she teaches Technical Physics, and Sergio Bocchini, from the same department and collaborating with the Italian Institute of Technology on “Sustainable Materials for the Future”, lead research on nanomaterials applied to energy conversion systems. Their work focuses on electrolysers and fuel cells.

“The main focus is on developing alternative catalysts to replace traditional materials,” explains Quaglio. “Platinum and rare metals are expensive and raise sustainability concerns. Carbon nanomaterials represent the most promising frontier.”

One of the most significant innovations is laser-induced graphene, which enables the creation of flexible electrodes for fuel cells. “Laser writing allows us to diversify electrical, catalytic, and mechanical properties during the design phase,” explains Quaglio. “This opens the door to fuel cells with unconventional shapes.”

Bocchini's work centers on intrinsically microporous polymers, which have transformed the field of gas separation. “Imagine filling a container with pasta,” Bocchini explains. “There are empty spaces between each piece that's where gases can enter and be separated by size.”

The most promising application involves membranes for electrolyzers and fuel cells. Microporous polymers allow ions to move much faster than traditional membranes, reducing internal resistance. This advancement also has a significant environmental impact. Current membranes contain PFAS, which are problematic at every stage of their life cycle. “From production, which emits PFAS, to use, where they degrade and release toxic compounds, to disposal,” explains Bocchini. Microporous polymers provide a sustainable alternative.

 

Supercapacitors represent a fundamentally different type of energy storage from batteries, both in how they work and in their performance. While batteries store energy through reversible chemical reactions that change electrode materials, supercapacitors store energy physically, separating electric charges across very large surface areas without major chemical change.

This physical storage mechanism allows them to charge and discharge much faster than batteries. “Supercapacitors don’t replace today’s batteries, but they complement them,” explains Andrea Lamberti, full professor at Politecnico di Torino. “They can store a large amount of power in a short time, compensating for batteries’ main shortcoming: a lack of sprint.”

The key differences are characteristic times and power density. A battery can take tens of minutes to several hours to fully charge and delivers energy steadily over time with relatively high energy density. A supercapacitor charges in seconds and can release its energy almost instantly, providing exceptionally high power peaks. Energy density is lower than that of batteries, but power density –the speed at which energy can be delivered –is much higher.

In the automotive sector, this trait can be used smartly in hybrid systems that combine batteries and supercapacitors. When the car is not drawing heavily on the battery, the supercapacitor recharges, and it supplies the intense burst of power needed during rapid acceleration. This synergy improves both overall system performance and cost efficiency. The design challenge is to create complementary solutions like these.

Research excellence in Turin is also echoed in projects with international credit. The CO2CAP project, developed by Andrea Lamberti, together with Bocchini and other Politecnico’s researchers, received prestigious funding from the European Research Council. This project demonstrated, for the first time, the possibility of harvesting energy directly from CO₂ emissions using an electrochemical capacitor based on ionic liquids. The mechanism is completely new and could lead to a new generation of electrochemical devices that operate directly on industrial emission streams, turning an environmental problem – CO₂ emissions – into an opportunity for energy production.

Despite significant progress, challenges remain. The first concerns the sustainability of the battery value chain. “Europe’s main problem is the lack of chemical industry capacity to process materials recycled from batteries”, Bodoardo points out. Building European capacity for refining and recycling is essential not only for environmental reasons but also for supply security and strategic autonomy.

The second challenge is training a specialized workforce. The 800,000 people needed to work in Europe’s battery ecosystem cannot be trained overnight. Dedicated educational programs are needed that combine chemistry, materials science, electrical and mechanical engineering, well-equipped labs with modern technologies, and structured collaborations between universities and industry to ensure that the skills developed meet real market needs.

A recurring theme emerging from the interviews is the crucial importance of interdisciplinary collaboration. “There is no longer a single Leonardo da Vinci who masters every field,” Santarelli observes. “We need teams of experts in mathematics, physics, chemistry, engineering, and socio-economic sciences working together to tackle problems no one could solve alone”. Unity is strength, therefore energy.