Obtaining energy from water – the most common substance on earth – is like spinning hay into gold. Water covers 75% of the Earth’s surface and even makes up 55% of our bodies. Hydrogen is by far the most abundant element in the universe, with oxygen the third most common; together they comprise water.
But actually producing hydrogen from water is no easy task. Hydrogen is a highly sought-after material in many areas of our lives. Most of the hydrogen generated today is used to make ammonia for the production of fertilizers that are essential for modern agriculture. In addition, hydrogen is one of the leading alternative fuel sources, especially in the context of fueling vehicles.
When used for transportation, hydrogen has several advantages over mineral-based fuels – it can be generated from water using green energy such as solar energy, reducing dependence on mineral fuels and dependence on countries rich in oil reserves;
Today, most of the world’s hydrogen is produced from natural gas, but with this process comes the emission of carbon dioxide (CO2), whose environmental damage is well known. An alternative production method is electrolysis – decomposition of water (H2O) for hydrogen (H2) and oxygen (O2). Although the electrolysis process was discovered more than two centuries ago, not many electrolysis technologies have been developed. In recent years, with the vital transition to alternative energies, it has become clear that the electrolysis process needs to be refined to fit these energy sources.
Hydrogen production from water allows the storage of renewable energy such as solar and wind, which are not available all hours of the day;
unlike diesel and gasoline engines that emit large amounts of air pollution, the only byproduct of hydrogen engines is water.
Against this backdrop, the photoelectrochemical process that breaks down the water directly using the sunlight radiation developed. Although here too, there are various technological challenges. For example, the production of hydrogen using the conventional method of electrolysis – the decomposition of water into hydrogen and oxygen in the same production cell – involves risk because the encounter between hydrogen and oxygen leads to an explosion. Moreover, in large-scale solar fields, it is very difficult to produce hydrogen in this configuration.
Now, researchers at the Technion – Israel Institute of Technology in Haifa have developed a prototype system for the efficient and safe production of hydrogen using only solar energy. Published in the journal Joule published by the Cell group under the title “Decoupled Photoelectrochemical Water Splitting System for Centralized Hydrogen Production,” the study was led by doctoral student Avigail Landman of the Grand Technion Energy Program, together with master’s student Rawan Halabi from the Technion’s Faculty of Materials Science and Engineering.
The study was conducted under the joint guidance of Prof. Gideon Grader of the Faculty of Chemical Engineering and Prof. Avner Rothschild of the Faculty of Materials Science and Engineering, in collaboration with Prof. Adélio Mendes and Dr. Paula Dias of the University of Porto in Portugal.
“Photoelectrochemical (PEC) water splitting offers an elegant approach for solar energy conversion into hydrogen fuel,” the team wrote. “Large-scale hydrogen production requires stable and efficient photoelectrodes and scalable PEC cells that are fitted for safe and cost-effective operation. One of the greatest challenges is the collection of hydrogen gas from millions of PEC cells distributed in the solar field.”
The innovative system contains a tandem cell solar device, which enables more efficient utilization of the light spectrum. Some of the sun’s radiation is absorbed in the upper layer, which is made of semi-transparent iron oxide. The radiation that is not absorbed in this layer passes through it and is subsequently absorbed by a photovoltaic cell. Together, the two layers of the system provide the energy needed to decompose the water.
The researchers hope that academics and industry will continue and advance the system into a commercial product.
The development is a continuation of the theoretical breakthrough by the Technion research team, presented in a March 2017 article in the prestigious journal Nature Materials. In that article, the Israeli researchers introduced a paradigmatic shift in hydrogen production. Instead of one production cell in which the water is broken down into hydrogen and oxygen, the researchers developed a system where hydrogen and oxygen are formed in two completely different cells.
Their work is important, in part, because mixing oxygen and hydrogen creates an explosive and dangerous interaction. The researchers presented the proof of feasibility in a lab system operated with a conventional power source.
In the just-published study, the researchers presented the realization of the theory in applied development – a photoelectrochemical prototype system that produces hydrogen and oxygen in two separate cells using only sunlight. As part of the experiment, approximately 80 working hours (10 days of about eight hours) were conducted, showing the efficiency of the system in natural sunlight. The experiment was conducted at the Technion’s Faculty of Chemical Engineering at the Technion.
