Sylvie Willis
Hydrogen fuel cells are an increasingly popular energy source, particularly in the automotive industry, as they are clean and can be used in cars, houses, and for portable power. When hydrogen fuel cells are in operation, they produce electricity, heat, and water. This water is a by-product of the electrochemical reaction that occurs when hydrogen combines with oxygen in the air. The question of whether this water is potable is an interesting one, as it could be used for drinking, gardening, cleaning, and more.
| Characteristics | Values |
|---|---|
| Water quality | Meets nearly all US Environmental Protection Agency (USEPA) and World Health Organization (WHO) drinking water requirements |
| Water produced by an FC supplying average US household electricity demand | 15 L/day |
| Water produced by an FC supplying average US household electricity demand with 85% capture of exhaust water | 16 L |
| Water produced by a Toyota Mirai for every 100km trip | 5-7.5 L |
| Water produced by a Toyota Mirai on a full tank (5.6 kg) | 50 L |
| Water produced for every kg of hydrogen spent | 9 L |
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What You'll Learn
Hydrogen fuel cells produce water as a by-product
The amount of water produced depends on the amount of hydrogen consumed. For instance, a Toyota Mirai car, which runs on a hydrogen-based fuel cell, can travel 1,003 km on 5.6 kg of hydrogen. This amount of hydrogen would produce around 50 litres of water. In another example, a hydrogen fuel cell supplying the average US household's daily electricity demand of 31 kWh would produce approximately 15 litres of water.
The water produced by hydrogen fuel cells is generally considered to be of high purity and quality. In fact, studies have shown that it meets most US Environmental Protection Agency (USEPA) and World Health Organization (WHO) drinking water requirements. This has led to the suggestion that water could be harvested from hydrogen fuel cells as a by-product, particularly in a future hydrogen economy.
However, it is important to note that the water quality from fuel cells may not always be suitable for drinking. While most water quality parameters were found to be below the maximum contaminant levels, there were higher levels of zinc, lead, and antimony, which may be related to plumbing or fuel cell material leaching.
Overall, the production of water as a by-product of hydrogen fuel cells has the potential to provide a valuable source of clean water, especially in regions facing water scarcity.
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Water produced is of drinking quality
Hydrogen fuel cells produce electricity, heat, and water as by-products. The water produced is generally considered to be of drinking quality, meeting most US Environmental Protection Agency (USEPA) and World Health Organization (WHO) drinking water requirements. However, in some cases, the water may contain impurities such as zinc, lead, and antimony, which could be related to plumbing or fuel cell material leaching.
The quality of water produced by fuel cells is an important area of research, especially as fuel cells become more widely used in applications such as transportation and electricity generation. For example, Arizona State University researchers collected water samples from six different fuel cells (FCs) operated at research centers across the US and found that the water quality was generally below the maximum contaminant levels, indicating that it could be suitable for drinking.
The amount of water produced by a hydrogen fuel cell can vary depending on the specific application. For instance, a hydrogen fuel cell car can produce between 5 to 7.5 litres of water for every 100 km trip, or about 50 ml per km. In another example, a fuel cell supplying the average household electricity consumption in the US could produce approximately 15 litres of water per day, although the quality of this water may vary.
The water produced by fuel cells can be used for various purposes besides drinking, such as gardening, cleaning, and even re-use within the fuel cell system for ongoing hydrogen generation. This aspect of fuel cells becomes particularly important in regions facing water scarcity, as they can potentially provide a source of clean drinking water alongside electricity generation.
While the water produced by hydrogen fuel cells is generally considered safe for drinking, further research and testing are needed to ensure that any impurities or contaminants are within safe limits and do not pose any health risks over the long term.
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Water quantity depends on hydrogen spent
Hydrogen fuel cells produce water through an electrochemical reaction between hydrogen and oxygen. This water is a by-product of the fuel cell's energy generation process. The amount of water produced depends on the amount of hydrogen consumed, with a greater quantity of hydrogen resulting in a higher volume of water.
The water output of a hydrogen fuel cell is directly proportional to the amount of hydrogen consumed. For every kilogram of hydrogen spent, approximately nine kilograms of water are generated. This equates to nine litres of water for every kilogram of hydrogen. Therefore, the water yield is directly influenced by the quantity of hydrogen utilised.
The water production rate can be further contextualised by considering the Toyota Mirai, a hydrogen fuel cell vehicle. With a hydrogen tank weighing 5.6 kilograms, the vehicle can travel between 650 and 1,003 kilometres. This range translates to a water production capacity of 50 to 75 millilitres per kilometre, or approximately 5 to 7.5 litres of water for every 100 kilometres travelled. Consequently, a full tank will yield around 50 litres of water.
The water production capacity of hydrogen fuel cells is also evident in their application as home energy sources. A hydrogen fuel cell capable of meeting the average daily electricity demand of a typical American household, estimated at 31 kilowatt-hours, would produce approximately 15 litres of water per day. This volume is significant, considering that it exceeds the average daily internal human water consumption.
The direct correlation between hydrogen consumption and water production underscores the importance of efficient hydrogen utilisation in maximising water output. This relationship between hydrogen input and water output provides a clear understanding of the water quantity dependence on hydrogen expenditure in hydrogen fuel cells.
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Water can be reused to generate hydrogen
There are different types of electrolyzers, including alkaline electrolyzers, PEM electrolyzers, and solid oxide electrolyzers. Alkaline electrolyzers use a liquid alkaline solution of sodium or potassium hydroxide as the electrolyte and have been commercially available for many years. PEM electrolyzers operate at lower temperatures, typically between 70°-90°C, while solid oxide electrolyzers require higher temperatures of about 700°-800°C for their solid oxide membranes to function properly. Solid oxide electrolyzers can use heat from various sources, such as nuclear energy, to reduce the amount of electrical energy needed to produce hydrogen from water.
In addition to electrolysis, there are other methods to produce hydrogen from water. One example is the water-gas shift reaction, where carbon monoxide reacts with steam to produce hydrogen and carbon dioxide. Another method is the sulfur-iodine cycle, a thermochemical process that uses very high temperatures to generate hydrogen from water with an efficiency of approximately 50%. The sulfur and iodine used in this process can be recovered and reused.
The water produced by hydrogen fuel cells is a valuable by-product. It has been suggested that this water could be harvested and used as drinking water, potentially providing a solution in regions facing water scarcity. Research has indicated that the water quality produced by modern fuel cells may even be higher than typical tap water and complies with US Environmental Protection Agency (USEPA) regulations.
In conclusion, water can indeed be reused to generate hydrogen through various methods, with electrolysis being a prominent example. The water produced by hydrogen fuel cells is not only safe but also potentially of higher quality than regular drinking water, making it a valuable resource.
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Water production methods vary
Natural Gas Reforming
This is a thermal process that involves steam reforming, where high temperatures are used to react steam with a hydrocarbon fuel, such as natural gas, diesel, renewable liquid fuels, gasified coal, or biomass, to produce hydrogen. This is currently the most common method, with about 95% of all hydrogen produced through steam reforming of natural gas.
Electrolysis
Electrolysis is a process where water is separated into oxygen and hydrogen using an electrolyzer, which functions similarly to a fuel cell but in reverse. It creates hydrogen from water molecules using electricity. Electrolysis can also be combined with solar energy to produce hydrogen through a process called solar-driven electrolysis.
Solar-Driven Processes
Solar-driven processes use light as the agent for hydrogen production. Some examples include photobiological, photoelectrochemical, and solar thermochemical processes. Photobiological processes utilize the natural photosynthetic activity of bacteria and green algae to produce hydrogen, while photoelectrochemical processes use specialized semiconductors to separate water into hydrogen and oxygen. Solar thermochemical hydrogen production employs concentrated solar power to drive water-splitting reactions, often in combination with other materials such as metal oxides.
Biological Processes
Biological processes harness the power of microbes, such as bacteria and microalgae, to produce hydrogen through biological reactions. In microbial biomass conversion, microbes break down organic matter like biomass or wastewater to generate hydrogen. Photobiological processes, on the other hand, use sunlight as an energy source to produce hydrogen.
Water Production in Fuel Cells
When hydrogen fuel cells are in operation, they produce electricity, heat, and water as a by-product. The amount of water produced depends on the amount of hydrogen consumed. For example, a Toyota Mirai hydrogen-based fuel cell car can produce between 5 to 7.5 litres of water for every 100 km trip, or approximately 50 litres of water per full tank (5.6 kg of hydrogen). In another example, a hydrogen fuel cell meeting the daily electricity consumption of a typical US household would produce about 15 litres of water per day.
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Frequently asked questions
A hydrogen fuel cell produces 9kg of water for every kg of hydrogen spent, or 9 litres.
A hydrogen fuel cell car will produce between 5 and 7.5 litres of water per 100km trip, or 50-75ml per km.
The water produced is clean and drinkable, and complies with US Environmental Protection Agency (USEPA) regulations.
The water can be used for any number of things around the house, such as gardening or cleaning.
