If renewable energy were a football match, green hydrogen would be the holding midfielder. It isn't necessarily the player scoring the screamers or the goalkeeper making spectacular saves, but it is the vital playmaker who defines the game—stepping up to assist in attack or dropping back to anchor the defence. This clean energy source holds immense potential due to its sheer versatility: it can generate and store electricity, power fuel cells, or serve as a high-grade heat source for industrial processes. In technical terms, it is what is known as an energy carrier.
Rafael d’Amore, a professor at the Technical University of Madrid and a member of the Fuel Cell, Hydrogen Technology and Alternative Engines Research Group (PiCoHiMA), explains the concept and why it is so crucial: “Renewable generation is variable by its very nature, and demand doesn't always align with production. In these instances, energy carriers like hydrogen come into their own as a way to decouple supply and demand—allowing us to store energy when there is a surplus and deploy it exactly when it’s needed.”
Turning to current production methods, he adds: “Currently, the most established option is water electrolysis powered by renewable electricity, mainly solar or wind. This is the most mature technology, already available on a commercial scale, and it offers the greatest certainty in the short to medium term. For these reasons, it is set to be the backbone of the initial green hydrogen rollout.”
However, for hydrogen to truly rival the success of wind or solar power, production processes must become more efficient. This is where technological innovation has a significant role to play in driving down costs and ensuring the fuel is competitive.
Advances in this field are coming thick and fast, from the development of novel materials to circular economy projects that repurpose agricultural waste. As d’Amore notes, “alternatives with significant long-term potential are starting to emerge. Direct solar technologies, such as photoelectrolysis or photocatalysis, are particularly noteworthy. These aim to produce hydrogen directly from solar radiation without needing to generate electricity first. In theory, by cutting out intermediate steps, they could achieve much higher overall efficiency.” One of the most recent breakthroughs is a solar battery that converts photovoltaic energy into green hydrogen, but there are several other promising avenues currently being explored.
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The storage potential of green hydrogen is perfectly captured by a prototype developed in the labs of the University of Ulm in Germany, recently featured in the journal Nature Communications. The scientific team has built a system that successfully converts solar energy into chemical energy, which can then be released as hydrogen several days later.
The system is based on a water-soluble copolymer capable of triggering redox reactions. While we have previously covered redox batteries—liquid energy storage systems with almost limitless charge/discharge cycles—this new approach is different. By using an acid and a hydrogen catalyst, electrons from photovoltaic energy stored in the polymer combine with protons to generate hydrogen on demand with an efficiency of 72%. Crucially, this final step does not require sunlight and, because the solution can be neutralised by adjusting its pH, it can be recharged repeatedly.
Orange peel has already proven to be a remarkably versatile waste product, as we explored in our article on its use for extracting valuable compounds from spent batteries. It is little wonder, then, that the University of Seville—located in the world’s orange capital—has devised a way to extract green hydrogen from the citrus waste generated across the region.
Supercritical water gasification produces a hydrogen-rich gas that can then be stored in ammonia for later use.
The proposal from the university’s Department of Chemical and Environmental Engineering involves supercritical water gasification—a process where water is subjected to extreme temperatures and pressures. By using this method, there is no need to dehydrate the biomass beforehand. The result is a hydrogen-rich gas that can be stored in ammonia for future use. According to the researchers' estimates, 10 tonnes of biomass could produce the energy equivalent of 28 standard 12kg butane cylinders. While the system is currently theoretical, it is expected to move into experimental testing shortly.
“The real value here is the circularity; it turns a waste product into an energy resource. However, its potential is naturally limited by the availability of the raw material. Furthermore, the resulting hydrogen often requires extra purification for high-spec applications like fuel cells,” d’Amore points out.
If orange rinds are versatile, eggshells are giving them a run for their money. We previously highlighted the applications of this humble waste product, from battery development to biodiesel production, thanks to its high calcium carbonate content. Now, green hydrogen is being added to that list.
In 2024, the Korea Institute of Science and Technology announced a new electrolysis system that utilises the membrane of eggshells. The study found that the porous structure and natural calcium of the shells can be repurposed into a low-cost catalyst for splitting water molecules. The material’s high porosity allows it to be coated with nickel and ruthenium nanoparticles, which dramatically increases the catalyst's surface area and optimises the electrolysis process.
Using renewable energy to simultaneously desalinate water and generate green hydrogen is the ambitious goal of researchers at Cornell University. Their device, which is already in the experimental phase, uses a system known as Heat-integrated Solar Distillation and Water Electrolysis (HSD-WE). It currently produces 200 millilitres of green hydrogen per hour with an energy efficiency of 12.6% using nothing but seawater and sunlight.
Waste heat is harnessed to evaporate the water, which—once purified via distillation—undergoes electrolysis powered by photovoltaic energy to produce hydrogen.
Typically, producing green hydrogen requires deionised water, as the molecules must be high-purity to be split into hydrogen and oxygen. This requirement adds a significant cost to the process. However, this prototype uses solar energy to generate both electricity and heat. The waste heat evaporates the seawater, which is purified via distillation and then fed into the electrolysis unit powered by photovoltaic energy. The researchers believe this approach could slash the production cost of green hydrogen to just one dollar per kilo by the end of the 2030s.
Using microbial fauna in industrial processes is well-established, whether for treating wastewater via anaerobic bacteria—as seen in ACCIONA’s Life Celsius project—or for generating bioelectricity. One of the latest frontiers for these bacteria is the microbial electrolysis cell (MEC).
A 150-litre MEC system has successfully produced green hydrogen over an 80-day period while simultaneously treating wastewater.
The University of Barcelona is currently working on this technology to perform electrolysis across two liquids: wastewater and an electrolyte. The electrode in contact with the wastewater (the anode) captures energy from electroactive microorganisms that oxidise organic matter. At the other electrode (the cathode), the resulting electrons produce green hydrogen. In a recent trial, a 150-litre MEC system ran for 80 days, producing high levels of hydrogen while simultaneously purifying the wastewater.
As these examples show, there are many promising routes to future green hydrogen production. “Ultimately, the future of the industry won't rely on a single technology, but on a blend of several. Electrolysis will lead the initial charge, while other complementary methods will gain traction as they mature and as specific local needs dictate,” the researcher concludes.
In the here and now, large-scale electrolysis is best seen in projects like the Valle H2V Navarra, a joint venture between ACCIONA and Plug Power. This upcoming plant will produce 3,880 tonnes of green hydrogen annually using 50MW of hybrid renewable energy, split equally between wind and solar power.
While we haven't touched upon the use of green hydrogen as a raw material—a topic that deserves a article in its own right—it is another area where d’Amore sees huge potential: “Today, the main use for hydrogen isn't energy, but industry. The biggest consumers are the chemical industry (particularly for ammonia and fertiliser production) and oil refining. On top of that, the steel industry is increasingly looking to hydrogen as an alternative to coal for reducing iron ore and producing low-emission steel.”
If you want to learn more about green hydrogen production, as well as the differences with grey and blue hydrogen, check out this article on the Power to Green Hydrogen Mallorca project. It is undoubtedly a topic set to dominate the energy conversation for years to come, and one we will continue to explore in future features.
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David is a journalist specializing in innovation. From his early days as a mobile technology analyst to his latest role as Country Manager at Terraview, an AI-driven startup focused on viticulture, he has always been closely linked to innovation and emerging technologies.
He contributes to El Confidencial and cultural outlets such as Frontera D and El Estado Mental, driven by the belief that the human and the technological can—and should—go hand in hand.