Water splitting
Water splitting is a process that separates the hydrogen and oxygen found in water, typically represented by the chemical formula H₂O, where two hydrogen atoms bond with one oxygen atom. This process can be achieved through various methods, including electrolysis, photoelectrolysis, and photobiological hydrogen production. Electrolysis involves running an electrical current through water, resulting in hydrogen gas collecting at the cathode and oxygen at the anode. However, this method usually requires additional energy, making it costly and potentially polluting.
Photoelectrolysis harnesses solar energy to generate electricity, which can then split water, while photobiological processes utilize organisms, such as algae, that naturally produce hydrogen through their metabolic functions. Other techniques for water splitting include thermal decomposition and nuclear methods, but these are often experimental and less economically viable. The successful implementation of water splitting could lead to a clean hydrogen economy, providing accessible energy solutions—especially in regions lacking reliable electricity. Recent advancements in research have focused on developing cost-effective and environmentally friendly methods, such as using specific catalysts, to increase the efficiency of hydrogen production from water. Such innovations hold promise for improving energy access and supporting sustainable development globally.
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Water splitting
Water splitting refers to any one of several processes for separating the hydrogen and oxygen found in water. There are multiple ways to accomplish this task, but most are expensive and can even be dangerous because of the energy released during the splitting process. However, scientists continue to look for ways to accomplish water splitting in a safe and economical way because this would enable the use of hydrogen as a clean alternative fuel.
Background
Water is composed of two elements: hydrogen and oxygen. Both of these elements are gases at standard room temperature, but when properly combined, they form the common liquid known as water. Water's chemical formula is H2O, which means each molecule of water has two hydrogen atoms and one oxygen atom. In order to make water, hydrogen and oxygen are chemically combined in a reaction called an exothermic reaction because it releases energy. In fact, the reaction can be so strong that the resulting release of energy can be difficult to control.
Reversing the process and splitting water into hydrogen and oxygen requires an opposite reaction called an endothermic reaction because it requires the expenditure of energy. Scientists have identified a number of ways to accomplish this. If they were able to do this in a controlled, predictable, and cost-effective way, it could provide large amounts of clean energy that would be almost universally available. However, none of the known methods has proven easy or cost-effective enough to free up the quantity of hydrogen needed for these uses. By 2023, however, scientists were working on two-step chemical cycles that might solve this problem.
Overview
There are a number of known ways to split water into its separate components of hydrogen and oxygen. Electrolysis—running an electrical current through the water—is one of the main techniques used. Others include photoelectrolysis and photobiology. There are also several variations of each of these techniques.
In electrolysis, an electrical current is introduced to the water through a negative terminal (or cathode), travels through the water, and exits through a positive terminal known as an anode. Hydrogen collects at the negative terminal and oxygen at the positive terminal. This method produces a relatively pure form of hydrogen suitable for use in food, pharmaceutical, and electronics industries. However, it relies on another form of energy to produce the electricity needed for the electrolysis process. This makes it relatively expensive and creates pollution as fuels are burned to generate the electricity.
In photoelectrolysis, energy from the sun is used to release the hydrogen. Semiconductors, an electrolyzer, and other elements are combined to form a device known as a photoelectrolyzer. This device is capable of generating electricity. It is placed in the water, and, when exposed to sunlight, generates a charge that separates the hydrogen from the oxygen, allowing it to be collected.
Scientists are also experimenting with photobiological hydrogen production. They have identified more than four hundred types of algae, bacteria, and other organisms that live in water and extract hydrogen from the water as part of their normal life functions. It has also been determined that by altering the living conditions of at least one form of these algae, they can force the algae to produce additional hydrogen.
Water can also be split into its components through thermal decomposition—the use of high levels of heat to break the bonds—as well as through nuclear radiological means. Several chemical compounds have also been shown to have the capability to serve as catalysts to initiate the chemical reaction necessary to break water into its components. However, many of these methods are either more expensive or more dangerous than the other methods, and they are generally used in experimental and specialized conditions.
The ability to split water easily and cleanly is a highly sought-after scientific accomplishment. Being able to use hydrogen as an energy source would provide vast amounts of energy with no significant pollution. Clean, inexpensive hydrogen would create a hydrogen economy in much the same way that the world has had a petroleum-based economy. In addition, this fuel source would be more widely available than most other sources.
For instance, it is estimated that as many as 1.5 billion people in the world do not have regular access to electricity. This is usually because the fuels needed to generate it are either not available, too expensive, or need to be transported too far for their use to be practical. Being able to split water into hydrogen to provide fuel would be a boon to these individuals, many of whom are poor and unable to improve their circumstances because they lack advantages such as the communications technology, education, and health care services that are facilitated by electricity.
In 2017, researchers at the California Institute of Technology developed a method for heat-driven water splitting that used as a catalyst manganese oxide with the sodium ions alternately added and removed to extract hydrogen from water. The technique is more cost-effective than other methods and does not generate any known harmful by-products, researchers have said, though more testing is needed to determine if the production of large amounts of hydrogen is feasible with this technique. Researchers at the University of Houston have also developed a method that uses nickel and ferrous metaphosphate in combination with an electric current to perform the water splitting. The new process can work with solar power to produce clean hydrogen. Research into both techniques and others is ongoing.
Other efforts to generate electricity from the hydrogen and oxygen in water have been attempted over the years. For instance, chemist Daniel Nocera created a device dubbed an artificial or bionic leaf in 2011. The device, which had materials that created a positive terminal on one side and a negative terminal on the other and used a nickel-based alloy, would be dropped into water and exposed to the sun. It would then generate small bubbles of oxygen and hydrogen; this would generate enough energy to power a home in a developing country for a day. It is hoped that individual water splitting devices like this could be developed that would not only be useful in developing countries but also help in times of power outages or in "off the grid" living situations.
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