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Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Most hydrogen is gray hydrogen made through steam methane reforming. In this process, hydrogen is produced from a chemical reaction between steam and methane, the main component of natural gas. Producing one tonne of hydrogen through this process emits 6.6–9.3 tonnes of carbon dioxide. When carbon capture and storage is used to remove a large fraction of these emissions, the product is known as blue hydrogen.
Green hydrogen is usually understood to be produced from Renewable energy electricity via electrolysis of water. Less frequently, definitions of green hydrogen include hydrogen produced from other low-emission sources such as biomass. Producing green hydrogen is currently more expensive than producing gray hydrogen, and the efficiency of energy conversion is inherently low. Other methods of hydrogen production include biomass gasification, methane pyrolysis, extraction of underground natural hydrogen, and in situ hydrogen synthesis.
As of 2023, less than 1% of dedicated hydrogen production is low-carbon, i.e. blue hydrogen, green hydrogen, and hydrogen produced from biomass.
In 2020, roughly 87 million tons of hydrogen was produced worldwide for various uses, such as Oil refinery, in the production of ammonia through the Haber process, and in the production of methanol through reduction of carbon monoxide. The global hydrogen generation market was fairly valued at US$155 billion in 2022, and expected to grow at a compound annual growth rate of 9.3% from 2023 to 2030.
Manufacturing elemental hydrogen requires the consumption of a hydrogen carrier such as a fossil fuel or water. The former carrier consumes the fossil resource and in the steam methane reforming (SMR) process produces greenhouse gas carbon dioxide. However, in the newer methane pyrolysis process no greenhouse gas carbon dioxide is produced. These processes typically require no further energy input beyond the fossil fuel. Decomposing water, the latter carrier, requires electrical or heat input, generated from some primary energy source (fossil fuel, nuclear power or a renewable energy). Hydrogen produced by electrolysis of water using renewable energy sources such as wind and solar power, referred to as green hydrogen. When derived from natural gas by zero greenhouse emission methane pyrolysis, it is referred to as turquoise hydrogen.
When fossil fuel derived with greenhouse gas emissions, is generally referred to as grey hydrogen. If most of the carbon dioxide emission is captured, it is referred to as blue hydrogen. Hydrogen produced from coal may be referred to as brown or black hydrogen.
| +Colors that refer to method of production ! colspan=2 | Color ! width=350 | Production source ! width=370 | Process / method / chemistry !Greenhouse gas footprint !Notes ! References | ||
| Renewable electricity: wind, solar, hydro, tidal, geothermal. May also include electricity from low-emission sources such as biomass. | Electrolysis of water 2 H2O → 2 H2 + O2 | Minimal | |||
| Fossil hydrocarbons: natural gas, a.k.a. Methane | Methane pyrolysis (thermal splitting) CH4 → C + 2 H2 | Minimal | Solid carbon byproduct | ||
| Fossil hydrocarbons: natural gas | Gas reforming with carbon capture and storage
1st stage: CH4 + H2O → CO + 3 H2
2nd stage: CO + H2O → CO2 + H2 | Low | CCS networks required | ||
| Fossil hydrocarbons: natural gas | Steam reforming of natural gas
1st stage: CH4 + H2O → CO + 3 H2
2nd stage: CO + H2O → CO2 + H2 | High | CO2 produced | ||
| Fossil hydrocarbons: Coal (anthracite) | Coal Carbonization or gasification
1st stage: 3 C (i.e., coal) + O2 + H2O → H2 + 3 CO
2nd stage: CO + H2O → CO2 + H2 C24H12 + 12 O2 → 24 CO + 6 H2 | Very high | CO2 produced | ||
| Fossil hydrocarbons: brown coal (lignite) | Coal carbonisation or gasification as black hydrogen | Very high | CO2 produced | ||
| Nuclear power | Nuclear heat: thermolysis Thermochemical water splitting H2O( l) ⇌ H2( g) + 1/2 O2( g) | Minimal | |||
| Nuclear power | Nuclear electricity plus water: electrolysis 2 H2O → 2 H2 + O2 | Minimal | |||
| Nuclear power | Nuclear heat plus water: Electrolysis and thermolysis 2 H2O → 2 H2 + O2 | Minimal | Also contributing steam to natural gas reforming | ||
| Solar photovoltaics | Electrolysis 2 H2O → 2 H2 + O2 | Minimal | |||
| Hydrogen | Microbial activity in depleted oil wells, drilling | Low | CCS networks required | ||
| Hydrogen occurring naturally in underground deposits | Drilling, mining | Minimal |
Steam methane reforming (SMR) produces hydrogen from natural gas, mostly methane (CH4), and water. It is the cheapest source of industrial hydrogen, being the source of nearly 50% of the world's hydrogen. The process consists of heating the gas to in the presence of steam over a nickel Catalysis. The resulting endothermic reaction forms carbon monoxide and molecular hydrogen (H2). (2025). 9780471779858, John Wiley & Sons. ISBN 9780471779858
In the water-gas shift reaction, the carbon monoxide reacts with steam to obtain further quantities of H2. The WGSR also requires a catalyst, typically over iron oxide or other . The byproduct is CO2. Depending on the quality of the Raw material (natural gas, naphtha, etc.), one ton of hydrogen produced will also produce 9 to 12 tons of CO2, a greenhouse gas that may be captured.
For this process, high temperature steam (H2O) reacts with methane (CH4) in an endothermic reaction to yield syngas.
In a second stage, additional hydrogen is generated through the lower-temperature, exothermic, water-gas shift reaction, performed at about :
Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.
In parts of the world, steam methane reforming is between $1–3/kg on average excluding hydrogen gas pressurization cost. This makes production of hydrogen via electrolysis cost competitive in many regions already, as outlined by Nel Hydrogen and others, including an article by the IEA examining the conditions which could lead to a competitive advantage for electrolysis.
A small part (2% in 2019) is produced by electrolysis using electricity and water, consuming approximately 50 to 55 kilowatt-hours of electricity per kilogram of hydrogen produced.
Water electrolysis is using electricity to split water into hydrogen and oxygen. As of 2020, less than 0.1% of hydrogen production comes from water electrolysis. Electrolysis of water is 70–80% efficient (a 20–30% conversion loss) while steam reforming of natural gas has a thermal efficiency between 70 and 85%. The electrical efficiency of electrolysis is expected to reach 82–86% before 2030, while also maintaining durability as progress in this area continues apace.
Water electrolysis can operate at , while steam methane reforming requires temperatures at . The difference between the two methods is the primary energy used; either electricity (for electrolysis) or natural gas (for steam methane reforming). Due to their use of water, a readily available resource, electrolysis and similar water-splitting methods have attracted the interest of the scientific community. With the objective of reducing the cost of hydrogen production, renewable sources of energy have been targeted to allow electrolysis.
There are three main types of electrolytic cells, solid oxide electrolyser cells (SOECs), polymer electrolyte membrane cells (PEM) and alkaline electrolysis cells (AECs). Traditionally, alkaline electrolysers are cheaper in terms of investment (they generally use nickel catalysts), but less-efficient; PEM electrolysers, conversely, are more expensive (they generally use expensive platinum group metal catalysts) but are more efficient and can operate at higher Current density, and can therefore be possibly cheaper if the hydrogen production is large enough.
SOECs operate at high temperatures, typically around . At these high temperatures, a significant amount of the energy required can be provided as thermal energy (heat), and as such is termed high-temperature electrolysis. The heat energy can be provided from a number of different sources, including waste industrial heat, nuclear power stations or concentrated solar thermal plants. This has the potential to reduce the overall cost of the hydrogen produced by reducing the amount of electrical energy required for electrolysis.In the laboratory, water electrolysis can be done with a simple apparatus like a Hofmann voltameter:
PEM electrolysis cells typically operate below . These cells have the advantage of being comparatively simple and can be designed to accept widely varying voltage inputs, which makes them ideal for use with renewable sources of energy such as Solar cell. AECs optimally operate at high concentrations of electrolyte (KOH or potassium carbonate) and at high temperatures, often near .
Conventional alkaline electrolysis has an efficiency of about 70%, however advanced alkaline water electrolysers with efficiency of up to 82% are available. Accounting for the use of the higher heat value (because inefficiency via heat can be redirected back into the system to create the steam required by the catalyst), average working efficiencies for PEM electrolysis are around 80%, or 82% using the most modern alkaline electrolysers.
PEM efficiency is expected to increase to approximately 86% before 2030. Theoretical efficiency for PEM electrolysers is predicted up to 94%.
As of 2020, the cost of hydrogen by electrolysis is around $3–8/kg. Considering the industrial production of hydrogen, and using current best processes for water electrolysis (PEM or alkaline electrolysis) which have an effective electrical efficiency of 70–82%, producing 1 kg of hydrogen (which has a specific energy of 143 MJ/kg or about 40 kWh/kg) requires 50–55 kWh of electricity. At an electricity cost of $0.06/kWh, as set out in the Department of Energy hydrogen production targets for 2015, the hydrogen cost is $3/kg.
The US DOE target price for hydrogen in 2020 was $2.30/kg, requiring an electricity cost of $0.037/kWh, which is achievable given recent PPA tenders for wind and solar in many regions. In 2021, the US DOE established the Hydrogen Energy Earthshot (Hydrogen Shot) with a target of $1 (USD) for 1 kg of hydrogen in 1 decade, i.e., $1/kg by 2031 (known as "1 1 1"). This low price was selected to be competitive with the price of hydrogen from natural gas in the United States which is approximately $1.50/kg. In comparison, the cost baseline for hydrogen from electrolysis in 2020 was approximately $5/kg, requiring an 80% cost reduction to meet the Hydrogen Shot goal.
The report by IRENA.ORG is an extensive factual report of present-day industrial hydrogen production consuming about 53 to 70 kWh per kg could go down to about 45 kWh/kg . The thermodynamic energy required for hydrogen by electrolysis translates to 33 kWh/kg, which is higher than steam reforming with carbon capture and higher than methane pyrolysis. One of the advantages of electrolysis over hydrogen from steam methane reforming (SMR) is that the hydrogen can be produced on-site, meaning that the costly process of delivery via truck or pipeline is avoided.
Carbon/hydrocarbon assisted water electrolysis (CAWE) has the potential to offer a less energy intensive, cleaner method of using chemical energy in various sources of carbon, such as low-rank and high sulfur coals, biomass, alcohols and methane (Natural Gas), where pure CO2 produced can be easily sequestered without the need for separation.
Gas generated from coke ovens in steel production is similar to Syngas with 60% hydrogen by volume. The hydrogen can be extracted from the coke oven gas economically.
The partial oxidation reaction occurs when a stoichiometry fuel-air mixture or fuel-oxygen is partially combusted in a reformer or partial oxidation reactor. A distinction is made between thermal partial oxidation (TPOX) and catalytic partial oxidation (CPOX). The chemical reaction takes the general form:
Idealized examples for heating oil and coal, assuming compositions C12H24 and C24H12 respectively, are as follows:
A variation of this process was presented in 2009 using plasma arc waste disposal technology for the production of hydrogen, heat and carbon from methane and natural gas in a plasma converter.
Coke oven gas made from pyrolysis (oxygen free heating) of coal has about 60% hydrogen, the rest being methane, carbon monoxide, carbon dioxide, ammonia, molecular nitrogen, and hydrogen sulfide (H2S). Hydrogen can be separated from other impurities by the pressure swing adsorption process. Japanese steel companies have carried out production of hydrogen by this method.
Bunsen reaction: I2+SO2+2H2O→H2SO4+2HI
HI decomposition: 2HI→H2+I2
Sulfuric acid decomposition: H2SO4→SO2+1/2O2+H2O
The hydrogen production rate of HTGR with IS cycle is approximately 0.68 kg/s, and the capital cost to build a unit of power plant is $100 million.
The sulfur-iodine cycle (S-I cycle) is a thermochemical cycle processes which generates hydrogen from water with an efficiency of approximately 50%. The sulfur and iodine used in the process are recovered and reused, and not consumed by the process. The cycle can be performed with any source of very high temperatures, approximately 950 °C, such as by Concentrating solar power systems (CSP) and is regarded as being well suited to the production of hydrogen by high-temperature nuclear reactors, IEA Energy Technology Essentials – Hydrogen Production & Distribution , April 2007 and as such, is being studied in the High-temperature engineering test reactor in Japan. There are other hybrid cycles that use both high temperatures and some electricity, such as the Copper–chlorine cycle, it is classified as a hybrid thermochemical cycle because it uses an electrochemical reaction in one of the reaction steps, it operates at 530 °C and has an efficiency of 43 percent.Chukwu, C., Naterer, G. F., Rosen, M. A., "Process Simulation of Nuclear-Produced Hydrogen with a Cu-Cl Cycle", 29th Conference of the Canadian Nuclear Society, Toronto, Ontario, Canada, June 1–4, 2008.
Among hydrogen production methods biological routes are potentially less energy intensive. In addition, a wide variety of waste and low-value materials such as agricultural biomass as renewable sources can be utilized to produce hydrogen via biochemical or thermochemical pathways. Nevertheless, at present hydrogen is produced mainly from fossil fuels, in particular, natural gas which are non-renewable sources. Hydrogen is not only the cleanest fuel but also widely used in a number of industries, especially fertilizer, petrochemical and food ones.
Biochemical routes to hydrogen are classified as dark and photo fermentation processes. In dark fermentation, carbohydrates are converted to hydrogen by fermentative microorganisms including strict anaerobe and facultative anaerobic bacteria. A theoretical maximum of 4 mol H2/mol glucose can be produced. Sugars are convertible to volatile fatty acids (VFAs) and alcohols as by-products during this process. Photo fermentative bacteria are able to generate hydrogen from VFAs. Hence, metabolites formed in dark fermentation can be used as feedstock in photo fermentation to enhance the overall yield of hydrogen.
An enzyme-catalyzed process convert the common sugar xylose into hydrogen with nearly 100% of the theoretical yield. The process employs 13 enzymes, including a novel polyphosphate xylulokinase (XK).
Fermentative hydrogen production can be done using direct biophotolysis by green algae, indirect biophotolysis by cyanobacteria, photo-fermentation by anaerobic photosynthetic bacteria and dark fermentation by anaerobic fermentative bacteria. For example, studies on hydrogen production using H. salinarium, an anaerobic photosynthetic bacteria, coupled to a hydrogenase donor like E. coli, are reported in literature. Enterobacter aerogenes is another hydrogen producer.
White hydrogen could be found or produced in the Mid-continental Rift System at scale for a renewable hydrogen economy. Water could be pumped down to hot iron-rich rock to extract the hydrogen.
The industrial quality solid carbon may be sold as manufacturing feedstock, included in asphalt pavement, or landfilled.
Methane pyrolysis technologies are in the early development stages at several companies as of 2023. They have obstacles to overcome before commercialization.
Biological hydrogen can be produced in an algae bioreactor. In the late 1990s it was discovered that if the algae is deprived of sulfur it will switch from the production of oxygen, i.e. normal photosynthesis, to the production of hydrogen. Biological hydrogen can also be produced using feedstocks other than algae, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and excreting hydrogen and CO2.
Hydrogen evolved on the front amorphous silicon surface decorated with various catalysts while oxygen evolved off the back metal substrate. A Nafion membrane above the multijunction cell provided a path for ion transport. Their patent also lists a variety of other semiconductor multijunction materials for the direct water splitting in addition to amorphous silicon and silicon germanium alloys. Research continues towards developing high-efficiency multi-junction cell technology at universities and the photovoltaic industry. If this process is assisted by photocatalysts suspended directly in water instead of using photovoltaic and an electrolytic system, the reaction is in just one step, which can improve efficiency.
In 2015, it was reported that Panasonic Corp. has developed a Photocatalysis based on niobium nitride that can absorb 57% of sunlight to support the decomposition of water to produce hydrogen gas. The company plans to achieve commercial application "as early as possible", not before 2020.
None of the thermochemical hydrogen production processes have been demonstrated at production levels, although several have been demonstrated in laboratories.
, hydrogen is mainly used as an industrial feedstock, primarily for the production of [[ammonia]] and [[methanol]], and in petroleum refining. Although initially hydrogen gas was thought not to occur naturally in convenient reservoirs, it is now demonstrated that this is not the case; a hydrogen system is currently being exploited near Bourakebougou, [[Koulikoro Region]] in Mali, producing electricity for the surrounding villages. More discoveries of naturally occurring hydrogen in continental, on-shore geological environments have been made in recent years and open the way to the novel field of natural or native hydrogen, supporting energy transition efforts.White hydrogen could be found or produced in the Mid-continental Rift System at scale for a renewable hydrogen economy. Water could be pumped down to hot iron-rich rock to produce hydrogen and the hydrogen could be extracted.
The use of autothermal reformers (ATR) with integrated capture of carbon dioxide allows higher capture rates at satisfactory energy efficiencies and life cycle assessments have shown lower greenhouse gas emissions for such plants compared to SMRs with carbon dioxide capture. Application of ATR technology with integrated capture of carbon dioxide in Europe has been assessed to have a lower greenhouse gas footprint than burning natural gas, e.g. for the H21 project with a reported reduction of 68% due to a reduced carbon dioxide intensity of natural gas combined with a more suitable reactor type for capture of carbon dioxide. "Facts on low-carbon hydrogen – A European perspective", ZEP Oct 2021. Confirmed 2023-12-12.
Hydrogen produced from renewable energy sources is often referred to as green hydrogen. Two ways of producing hydrogen from renewable energy sources are claimed to be practical. One is to use power to gas, in which electric power is used to produce hydrogen from electrolysis of water, and the other is to use landfill gas to produce hydrogen in a steam reformer. Hydrogen fuel, when produced by renewable sources of energy like wind or solar power, is a renewable fuel.Dvorak, Phred, "WSJ News Exclusive: Green Hydrogen Gets a Boost in the U.S. With $4 Billion Plant: The planned factory, a joint venture by Air Products and AES Corporation ...", Wall Street Journal, December 8, 2022. Retrieved 2023-11-14. Hydrogen produced from nuclear power via electrolysis is sometimes viewed as a subset of green hydrogen, but can also be referred to as pink hydrogen. The Oskarshamn Nuclear Power Plant made an agreement in January 2022 to supply commercial pink hydrogen in the order of kilograms per day.
, estimated costs of production are $1–1.80/kg for grey hydrogen and blue hydrogen, and $2.50–6.80 for green hydrogen.
94 million tonnes of grey hydrogen are produced globally using fossil fuels as of 2022, primarily natural gas, and are therefore a significant source of greenhouse gas emissions.
Hydrogen may be used in fuel cells for local electricity generation or potentially as a transportation fuel.
Hydrogen is produced as a by-product of industrial chlorine production by electrolysis. Although requiring expensive technologies, hydrogen can be cooled, compressed and purified for use in other processes on site or sold to a customer via pipeline, cylinders or trucks. The discovery and development of less expensive methods of production of bulk hydrogen is relevant to the establishment of a hydrogen economy.
Hydrogen uses
Hydrogen is used for the conversion of heavy petroleum fractions into lighter ones via hydrocracking. It is also used in other processes including the aromatization process, hydrodesulfurization and the production of ammonia via the Haber process, the primary industrial method for the production of synthetic nitrogen fertilizer for growing 47 percent of food worldwide.
(2025). 9783527306732 ISBN 9783527306732
See also
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Further reading
(2025). 9780128148532 ISBN 9780128148532
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