Beatrice Lang
Hydrogen is a versatile energy carrier that can be converted into electricity in fuel cells. Hydrogen is abundant on Earth but is rarely found in its pure form, so it must be separated from compounds like water or methane using chemical or electrochemical reactions. Electrolysis is a popular method for producing hydrogen, where electricity is used to split water into hydrogen and oxygen. Hydrogen can be produced from diverse resources, including fossil fuels, biomass, and water, and it has the advantage of being storable for long periods. Hydrogen fuel cells are used in various sectors, including electronics, chemicals, and transportation, and they are known for their efficiency, reliability, and quiet operation. Hydrogen has the potential to play a significant role in decarbonization efforts, and research is ongoing to reduce the costs associated with low-carbon hydrogen production.
| Characteristics | Values |
|---|---|
| Hydrogen production methods | Electrolysis, microbial biomass conversion, thermochemical water splitting, photobiological water splitting, photoelectrochemical water splitting |
| Electrolysis | The process of using electricity to split water into hydrogen and oxygen |
| Electrolyzer | A unit where the reaction of splitting water into hydrogen and oxygen takes place |
| Fuel cells | A clean, efficient, reliable, and quiet source of power |
| Fuel cell composition | Anode, cathode, and an electrolyte membrane |
| Fuel cell working | Hydrogen is passed through the anode of a fuel cell and oxygen through the cathode. At the anode site, a catalyst splits the hydrogen molecules into electrons and protons. The protons pass through the porous electrolyte membrane, while the electrons are forced through a circuit, generating an electric current and excess heat. At the cathode, the protons, electrons, and oxygen combine to produce water molecules |
| Fuel cell types | Proton Exchange Membrane Fuel Cells (PEMFCs), Direct Methanol Fuel Cells (DMFCs), Molten Carbonate Fuel Cells (MCFCs), Alkaline Fuel Cells (AFCs) |
| PEMFCs | Use a polymer membrane for its electrolyte and a precious metal, typically platinum, for its catalyst |
| DMFCs | Use a polymer membrane as an electrolyte and commonly a platinum catalyst; they draw hydrogen from liquid methanol, rather than using direct hydrogen fuel |
| MCFCs | Operate at temperatures upwards of 1200 degrees Fahrenheit, utilizing a molten carbonate-salt mixture suspended in a ceramic matrix as an electrolyte |
| AFCs | One of the most efficient types of fuel cells, with a potential of 60% electrical efficiency, and 80% to 90% in CHP applications; highly sensitive and can fail when exposed to carbon dioxide, primarily used in controlled aerospace and underwater applications |
| Hydrogen uses | Rocket fuel, heat production, transport, or to store energy for later conversion to electricity |
| Hydrogen production | Hydrogen can be produced from natural gas, nuclear power, biogas, renewable power like solar and wind, fossil fuels, biomass, and water |
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What You'll Learn
- Electrolysis: electricity splits water into hydrogen and oxygen
- Hydrogen fuel cells: hydrogen and oxygen produce electricity, heat and water
- Hydrogen from biomass: biomass is converted to sugar-rich feedstocks, then fermented to produce hydrogen
- Hydrogen from natural gas: natural gas is reformed to produce a hydrogen-rich synthesis gas
- Hydrogen for transport: hydrogen can be used as fuel for cars, HGVs and rockets
Electrolysis: electricity splits water into hydrogen and oxygen
Electrolysis is a process that uses electricity to split water into hydrogen and oxygen. This process takes place in a unit called an electrolyzer, which consists of an anode and a cathode separated by an electrolyte. Electrolyzers can vary in size, from small, appliance-sized equipment used for small-scale hydrogen production, to large-scale, central production facilities that can be tied directly to renewable or other non-greenhouse-gas-emitting forms of electricity production.
The water splitting reaction occurs at the anode, where water (H2O) is converted into oxygen (O2), hydrogen ions (H+) and electrons (e-). The hydrogen ions then move across the electrolyte to the cathode, where they combine with the electrons from the anode to form hydrogen gas (H2). This process is known as the cathode reaction.
There are several types of electrolyzers, each with a different electrolyte material and ionic species. For example, polymer electrolyte membrane (PEM) electrolyzers use a solid specialty plastic material as the electrolyte, while alkaline electrolyzers use a liquid alkaline solution of sodium or potassium hydroxide. Solid oxide electrolyzers, on the other hand, use a solid ceramic material that selectively conducts negatively charged oxygen ions at elevated temperatures.
Electrolysis is a promising method for producing hydrogen from renewable and nuclear resources in a carbon-free manner. It may also offer opportunities for synergy with dynamic and intermittent power generation from renewable energy technologies such as wind farms. For example, excess electricity produced by wind farms can be used to generate hydrogen through electrolysis, rather than being curtailed. This integration of hydrogen fuel and electric power generation could provide flexibility in matching resource availability with system operational needs and market factors.
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Hydrogen fuel cells: hydrogen and oxygen produce electricity, heat and water
Hydrogen fuel cells are an efficient and clean way to produce electricity, with the only byproducts being heat and water. This is in contrast to natural gas, which produces carbon dioxide as a waste product. Hydrogen can be produced from a variety of resources, including natural gas, nuclear power, biogas, and renewable power like solar and wind.
Electrolysis is a promising method for producing hydrogen from water, and it can be powered by renewable energy sources. This process involves using electricity to split water into hydrogen and oxygen in a unit called an electrolyzer. Electrolyzers can vary in size and can be used for small-scale distributed hydrogen production or large-scale, central production facilities tied directly to renewable energy sources.
The chemical energy of hydrogen fuel is then used in fuel cells to produce electricity, heat, and water. This process involves splitting hydrogen molecules into electrons and protons at the anode. The protons pass through a porous electrolyte membrane to the cathode, while the electrons are forced through a circuit, generating an electric current. At the cathode, the protons, electrons, and oxygen combine to produce water molecules and heat.
Fuel cells have a wide range of applications, from powering heavy goods vehicles to providing electricity for residential buildings. They can also be coupled with a combined heat and power system to utilize the waste heat for heating or cooling applications, further increasing their efficiency. Additionally, fuel cells can be joined together in stacks to form larger systems, making them scalable to meet various power demands.
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Hydrogen from biomass: biomass is converted to sugar-rich feedstocks, then fermented to produce hydrogen
There are several methods for converting hydrogen into electricity. Electrolysis, for example, is the process of using electricity to split water into hydrogen and oxygen. This reaction takes place in a unit called an electrolyzer, which can range in size from small, appliance-size equipment to large-scale production facilities.
One way to produce hydrogen is through biomass gasification, a mature technology pathway that uses heat, steam, and oxygen to convert biomass to hydrogen and other products, without combustion. Biomass is a renewable organic resource that includes agricultural crop residues, forest residues, special energy crops, organic municipal solid waste, and animal wastes.
Biomass can also be converted into sugar-rich feedstocks, which are then fermented to produce hydrogen. Lignocellulosic biomass, agricultural leftovers, bio-wastes, energy crops, and their by-products like biogas, bio-oil, and biochar are some of the fundamental types of biomass materials that may be used as feedstocks to produce low-cost and low-carbon hydrogen. Municipal bio-waste and agricultural leftovers are cost-effective and do not compete with food crops, making them excellent options for hydrogen production.
Thermochemical processes are an effective method for converting a range of wet biomass into a complete biomass-derived fuel to produce hydrogen without any chemical additions. This method has been analysed for its potential in creating sustainable cities.
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Hydrogen from natural gas: natural gas is reformed to produce a hydrogen-rich synthesis gas
Hydrogen can be produced from a variety of resources, such as natural gas, nuclear power, biogas, and renewable power like solar and wind. Natural gas is a popular choice for hydrogen production due to its wide availability, ease of handling, and relatively low cost. It also has a high hydrogen-to-carbon ratio, which minimises the amount of carbon dioxide produced when it is burnt or reformed into hydrogen.
The process of converting natural gas into hydrogen-rich synthesis gas is called natural gas reforming. This process builds upon the existing natural gas pipeline delivery infrastructure. In this process, natural gas, which predominantly consists of methane (CH4), undergoes a reaction with steam at high temperatures of around 700°C to 1,000°C in the presence of a catalyst. This reaction, known as steam-methane reformation, produces hydrogen, carbon monoxide, and a small amount of carbon dioxide. The reaction is endothermic, meaning heat must be supplied for it to proceed.
The carbon monoxide and steam then undergo a second reaction, known as the water-gas shift reaction, where they react using a catalyst to produce additional carbon dioxide and more hydrogen. Finally, in a step called pressure-swing adsorption, the carbon dioxide and other impurities are removed, leaving behind pure hydrogen. This method of producing hydrogen from natural gas is currently the least expensive available in terms of capital cost, but it does have some challenges.
One challenge is that the reforming reaction occurs at high temperatures, making it slow to start up and requiring costly high-temperature materials. Additionally, sulfur compounds present in the fuel can poison certain catalysts, and coking can cause catalyst deactivation during steam reforming. However, new technologies have emerged to address these issues, such as the development of sulfur-tolerant catalysts and methods to prevent coking.
While natural gas reforming is a mature and widely used process for hydrogen production, there is a focus on exploring alternative methods to produce hydrogen from renewable resources. For example, hydrogen can be produced through electrolysis, a process that uses electricity to split water into hydrogen and oxygen. This method offers opportunities for synergy with renewable energy power generation, such as wind farms, where excess electricity can be used to produce hydrogen through electrolysis.
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Hydrogen for transport: hydrogen can be used as fuel for cars, HGVs and rockets
Hydrogen has been used for many years in the space sector as rocket fuel, and it also has promising applications in the transport sector. Hydrogen can be used as fuel for cars, trucks, HGVs, trains, ships, and rockets. Hydrogen fuel cells produce electricity by combining hydrogen and oxygen atoms, in a process that emits no greenhouse gases, only heat and water. This makes hydrogen an attractive option for powering zero-emissions vehicles. Hydrogen can be produced from a variety of resources, including natural gas, nuclear power, biomass, and renewable power like solar and wind.
Hydrogen is an energy carrier that can be used to store, move, and deliver energy produced from other sources. It can be converted into electricity through fuel cells, which combine hydrogen with oxygen to generate an electric current. This electricity can then be used to power electric vehicles. Hydrogen can also be liquefied by cooling it to extremely low temperatures, enabling more efficient transportation over longer distances. However, the liquefaction process is energy-intensive and expensive.
The use of hydrogen fuel cells in vehicles offers several advantages. Hydrogen fuel is more energy-dense than electric power, and it offers quicker refuelling times. Hydrogen can also act as a storage medium for excess electricity generated from renewable sources, such as wind power. This stored hydrogen can then be used to generate electricity when there is a requirement for additional power. For example, during peak periods of generation by renewables, electricity can be converted to hydrogen and transported or stored for later use.
Currently, hydrogen is distributed through pipelines, high-pressure tube trailers, and liquefied hydrogen tankers. However, the infrastructure for distributing hydrogen to a nationwide network of fueling stations for fuel cell electric vehicles still needs development. Hydrogen refueling stations are already available in several countries, including Japan, Germany, and the United States. Hydrogen is classified as an alternative vehicle fuel under the Energy Policy Act of 1992, and it has the potential to play a significant role in decarbonizing the transport sector.
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Frequently asked questions
There are several methods to convert hydrogen into electricity. One way is through fuel cells, which pass hydrogen through the anode of a fuel cell and oxygen through the cathode. The hydrogen molecules are then split into electrons and protons. The protons pass through the porous electrolyte membrane, while the electrons are forced through a circuit, generating an electric current and excess heat. At the cathode, the protons, electrons, and oxygen combine to produce water molecules.
There are many types of fuel cells, including Proton Exchange Membrane Fuel Cells (PEMFCs), Direct Methanol Fuel Cells (DMFCs), Molten Carbonate Fuel Cells (MCFCs), and Alkaline Fuel Cells (AFCs). PEMFCs use a polymer membrane for its electrolyte and a precious metal, typically platinum, as its catalyst. DMFCs also use a polymer membrane as an electrolyte but draw hydrogen from liquid methanol. MCFCs operate at temperatures upwards of 1200 degrees Fahrenheit and use a molten carbonate-salt mixture suspended in a ceramic matrix as an electrolyte. AFCs are highly efficient, with a potential of 60% electrical efficiency, and are best known for their roles in the NASA Apollo mission.
Hydrogen is a promising fuel source for several reasons. It can be used to store electricity and deal with the over-production of renewable electricity from sources such as solar and wind power. Hydrogen can also be produced from a variety of resources, including natural gas, nuclear power, biogas, and renewable power. When burned, hydrogen's only byproduct is water vapour, making it a cleaner alternative to fossil fuels.
One challenge with hydrogen is the cost of production, as the technologies used to produce it can be expensive. Additionally, the infrastructure for distributing hydrogen to a nationwide network of fueling stations for fuel cell electric vehicles is still under development.
