Misplaced Pages

#396603

63-425: It is of special interest in the context of the serpentinization , the formation of hydrogen by the action of water on a common mineral. The Schikorr reaction can be viewed as two distinct processes: The global reaction can thus be decomposed in half redox reactions as follows: to give: Adding to this reaction one intact iron(II) ion for each two oxidized iron(II) ions leads to: Electroneutrality requires

126-425: 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

189-479: A layer of hydrothermally altered diabases and pillow basalts , and a layer of deep water sediments containing radiolarian ribbon chert . Seismic wave studies can detect the presence of large bodies of serpentinite in the crust and upper mantle, since serpentinization has a huge impact on shear wave velocity. A higher degree of serpentinization will lead to lower shear wave velocity and higher Poisson's ratio . Seismic measurements confirm that serpentinization

252-420: A range of other emerging electrochemical processes such as high temperature electrolysis or carbon assisted electrolysis. However, current best processes for water electrolysis have an effective electrical efficiency of 70-80%, so that 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. In parts of the world, steam methane reforming

315-467: A rotating electrolyser, where centrifugal force helps separate gas bubbles from water. Such an electrolyser at 15 bar pressure may consume 50 kilowatt-hours per kilogram (180 MJ/kg), and a further 15 kilowatt-hours (54 MJ) if the hydrogen is compressed for use in hydrogen cars. Conventional alkaline electrolysis has an efficiency of about 70%, however advanced alkaline water electrolysers with efficiency of up to 82% are available. Accounting for

378-432: A second stage, additional hydrogen is generated through the lower-temperature, exothermic , water-gas shift reaction, performed at about 360 °C (680 °F): Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO 2 . This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of

441-401: A sizable amount of Hydrogen as a byproduct. In the port of Antwerp a 1MW demonstration fuel cell power plant is powered by such byproduct. This unit has been operational since late 2011. The excess hydrogen is often managed with a hydrogen pinch analysis. Gas generated from coke ovens in steel production is similar to Syngas with 60% hydrogen by volume. The hydrogen can be extracted from

504-405: A temperature of 300 °C (572 °F) and pressure of 500 bars, olivine serpentinizes with release of hydrogen gas. In addition, methane and complex hydrocarbons are formed through reduction of carbon dioxide. The process may be catalyzed by magnetite formed during serpentinization. One reaction pathway is: Lizardite and chrysotile are stable at low temperatures and pressures, while antigorite

567-500: Is a solid solution of forsterite , the magnesium endmember of (Mg , Fe ) 2 SiO 4 , and fayalite , the iron endmember, with forsterite typically making up about 90% of the olivine in ultramafic rocks. Serpentine can form from olivine via several reactions: Reaction 1a tightly binds silica, lowering its chemical activity to the lowest values seen in common rocks of the Earth's crust . Serpentinization then continues through

630-400: Is also relevant for the corrosion of the reinforcement bars ( rebars ) in concrete (Aligizaki et al. , 2000). This deals then with the service life of concrete structures, amongst others the near-surface vaults intended for hosting low-level radioactive waste . The slow but continuous production of hydrogen in deep low-permeability argillaceous formations could represent a problem for

693-584: 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

SECTION 10

#1732872661397

756-910: Is captured, it is referred to as blue hydrogen. Hydrogen produced from coal may be referred to as brown or black hydrogen. Hydrogen is often referred to by various colors to indicate its origin (perhaps because gray symbolizes "dirty hydrogen" ). May also include electricity from low-emission sources such as biomass . 2 H 2 O → 2 H 2 + O 2 CH 4 → C + 2 H 2 1st stage: CH 4 + H 2 O → CO + 3 H 2 2nd stage: CO + H 2 O → CO 2 + H 2 1st stage: CH 4 + H 2 O → CO + 3 H 2 2nd stage: CO + H 2 O → CO 2 + H 2 1st stage: 3 C (i.e., coal) + O 2 + H 2 O → H 2 + 3 CO 2nd stage: CO + H 2 O → CO 2 + H 2 C 24 H 12 + 12 O 2 → 24 CO + 6 H 2 as black hydrogen H 2 O( l ) ⇌ H 2 ( g ) + 1/2 O 2 ( g )   2 H 2 O → 2 H 2 + O 2 2 H 2 O → 2 H 2 + O 2 2 H 2 O → 2 H 2 + O 2 Hydrogen

819-450: 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 , and extraction of underground hydrogen . 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

882-691: Is driven largely by hydration and oxidation of olivine and pyroxene to serpentine group minerals (antigorite, lizardite, and chrysotile), brucite ( Mg(OH) 2 ), talc ( Mg 3 Si 4 O 10 (OH) 2 ), and magnetite ( Fe 3 O 4 ). Under the unusual chemical conditions accompanying serpentinization, water is the oxidizing agent, and is itself reduced to hydrogen, H 2 . This leads to further reactions that produce rare iron group native element minerals , such as awaruite ( Ni 3 Fe ) and native iron ; methane and other hydrocarbon compounds; and hydrogen sulfide . During serpentinization, large amounts of water are absorbed into

945-613: Is easily altered under surface weathering conditions. A similar suite of reactions involves pyroxene -group minerals: Reaction 2a quickly comes to a halt as silica becomes unavailable, and Reaction 2b takes over. When olivine is abundant, silica activity drops low enough that talc begins to react with olivine: This reaction requires higher temperatures than those at which brucite forms. The final mineralogy depends both on rock and fluid compositions, temperature, and pressure. Antigorite forms in reactions at temperatures that can exceed 600 °C (1,112 °F) during metamorphism, and it

1008-399: 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. In addition to reduce the voltage required for electrolysis via the increasing of the temperature of

1071-407: Is industrially produced from steam reforming (SMR), which uses natural gas. The energy content of the produced hydrogen is around 74% of the energy content of the original fuel, as some energy is lost as excess heat during production. In general, steam reforming emits carbon dioxide, a greenhouse gas, and is known as gray hydrogen. If the carbon dioxide is captured and stored, the hydrogen produced

1134-473: Is known as blue hydrogen. Steam methane reforming (SMR) produces hydrogen from natural gas, mostly methane (CH 4 ), 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 700–1,100 °C (1,300–2,000 °F) in the presence of steam over a nickel catalyst . The resulting endothermic reaction forms carbon monoxide and molecular hydrogen (H 2 ). In

1197-402: Is measured by energy consumed per standard volume of hydrogen (MJ/m ), assuming standard temperature and pressure of the H 2 . The lower the energy used by a generator, the higher would be its efficiency; a 100%-efficient electrolyser would consume 39.4 kilowatt-hours per kilogram (142 MJ/kg) of hydrogen, 12,749 joules per litre (12.75 MJ/m ). Practical electrolysis typically uses

1260-471: Is particularly important at the sea floor at tectonic plate boundaries. Serpentinization is a form of low-temperature (0 to ~600 °C) metamorphism of ferromagnesian minerals in mafic and ultramafic rocks, such as dunite , harzburgite , or lherzolite . These are rocks low in silica and composed mostly of olivine ( (Mg , Fe ) 2 SiO 4 ), pyroxene ( XY(Si,Al) 2 O 6 ), and chromite (approximately FeCr 2 O 4 ). Serpentinization

1323-400: Is pervasive in forearc mantle. The serpentinization can produce an inverted Moho discontinuity , in which seismic velocity abruptly decreases across the crust-mantle boundary, which is the opposite of the usual behavior. The serpentinite is highly deformable, creating an aseismic zone in the forearc, at which serpentinites slide at stable plate velocity. The presence of serpentinite may limit

SECTION 20

#1732872661397

1386-509: Is possible to write the balanced global reaction: in its final form, known as the Schikorr reaction : The Schikorr reaction can occur in the process of anaerobic corrosion of iron and carbon steel in various conditions. Anaerobic corrosion of metallic iron to give iron(II) hydroxide and hydrogen: followed by the Schikorr reaction: give the following global reaction: At low temperature,

1449-516: Is presently the object of many studies (King, 2008; King and Kolar, 2009; Nagra Technical Reports 2000–2009) in the countries (Belgium, Switzerland, France, Canada) envisaging the option of disposal in clay formation. When nascent hydrogen is produced by anaerobic corrosion of iron by the protons of water, the atomic hydrogen can diffuse into the metal crystal lattice because of the existing concentration gradient. After diffusion , hydrogen atoms can recombine into molecular hydrogen giving rise to

1512-519: Is stable at higher temperatures and pressure. Its presence in a serpentinite indicates either that serpentinization took place at unusually high pressure and temperature or that the rock experienced higher grade metamorphism after serpentinization was complete. Infiltration of CO 2 -bearing fluids into serpentinite causes distinctive talc-carbonate alteration . Brucite rapidly converts to magnesite and serpentine minerals (other than antigorite) are converted to talc. The presence of pseudomorphs of

1575-713: Is the serpentine group mineral stable at the highest temperatures. Lizardite and chrysotile can form at low temperatures very near the Earth's surface. Ultramafic rocks often contain calcium-rich pyroxene ( diopside ), which breaks down according to the reaction: This raises both the pH , often to very high values, and the calcium content of the fluids involved in serpentinization. These fluids are highly reactive and may transport calcium and other elements into surrounding mafic rocks. Fluid reaction with these rocks may create metasomatic reaction zones enriched in calcium and depleted in silica, called rodingites . In most crustal rock,

1638-655: 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 50–80 °C (120–180 °F), while steam methane reforming requires temperatures at 700–1,100 °C (1,300–2,000 °F). The difference between

1701-482: The Kola Superdeep Borehole . It is unclear how much molecular hydrogen is available in natural reservoirs, but at least one company specializes in drilling wells to extract hydrogen. Most hydrogen in the lithosphere is bonded to oxygen in water. 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

1764-449: The Schikorr reaction in the anaerobic conditions of serpentinization: Maximum reducing conditions, and the maximum rate of production of hydrogen, occur when the temperature of serpentinization is between 200 and 315 °C (392 and 599 °F) and when fluids are carbonate undersaturated. If the original ultramafic rock (the protolith ) is peridotite, which is rich in olivine, considerable magnetite and hydrogen are produced. When

1827-481: The copper system. Anaerobic oxidation of iron and steel commonly finds place in oxygen-depleted environments, such as in permanently water-saturated soils , peat bogs or wetlands in which archaeological iron artefacts are often found. Anaerobic oxidation of carbon steel of canisters and overpacks is also expected to occur in deep geological formations in which high-level radioactive waste and spent fuels should be ultimately disposed. Nowadays, in

1890-545: The water-gas shift reaction , the carbon monoxide reacts with steam to obtain further quantities of H 2 . The WGSR also requires a catalyst, typically over iron oxide or other oxides . The byproduct is CO 2 . Depending on the quality of the feedstock (natural gas, naphtha , etc.), one ton of hydrogen produced will also produce 9 to 12 tons of CO 2 , a greenhouse gas that may be captured . For this process, high temperature steam (H 2 O) reacts with methane (CH 4 ) in an endothermic reaction to yield syngas . In

1953-612: The Department of Energy hydrogen production targets for 2015, the hydrogen cost is $ 3/kg. The US DOE target price for hydrogen in 2020 is $ 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. 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 H 2 . The thermodynamic energy required for hydrogen by electrolysis translates to 33 kWh/kg, which

Schikorr reaction - Misplaced Pages Continue

2016-468: The Italian Alps shows a sharp serpentinization front that may be a relict seismic Moho. Serpentinization is an important phenomenon in subduction zones that has a strong control on the water cycle and geodynamics of a subduction zone. Here mantle rock is cooled by the subducting slab to temperatures at which serpentinite is stable, and fluids are released from the subducting slab in great quantities into

2079-629: The anaerobic corrosion of iron can give rise to the formation of "green rust" ( fougerite ) an unstable layered double hydroxide (LDH). In function of the geochemical conditions prevailing in the environment of the corroding steel, iron(II) hydroxide and green rust can progressively transform in iron(II,III) oxide, or if bicarbonate ions are present in solution, they can also evolve towards more stable carbonate phases such as iron carbonate (FeCO 3 ), or iron(II) hydroxycarbonate (Fe 2 (OH) 2 (CO 3 ), chukanovite ) isomorphic to copper(II) hydroxycarbonate (Cu 2 (OH) 2 (CO 3 ), malachite ) in

2142-448: The atmosphere of Mars has been hypothesized to be a possible evidence for life on Mars if methane was produced by bacterial activity. Serpentinization has been proposed as an alternative non-biological source for the observed methane traces. In 2022 it was reported that microscopic examination of the ALH 84001 meteorite, which came from Mars, shows that indeed the organic matter it contains

2205-616: The chemical activity of oxygen is prevented from dropping to very low values by the fayalite-magnetite-quartz (FMQ) buffer . The very low chemical activity of silica during serpentinization eliminates this buffer, allowing serpentinization to produce highly reducing conditions. Under these conditions, water is capable of oxidizing ferrous ( Fe ) ions in fayalite. The process is of interest because it generates hydrogen gas: However, studies of serpentinites suggest that iron minerals are first converted to ferroan brucite, that is, brucite containing Fe(OH) 2 , which then undergoes

2268-406: The coke oven gas economically. Hydrogen production from natural gas and heavier hydrocarbons is achieved by partial oxidation. A fuel-air or fuel-oxygen mixture is partially combusted , resulting in a hydrogen- and carbon monoxide-rich syngas. More hydrogen and carbon dioxide are then obtained from carbon monoxide (and water) via the water-gas shift reaction. Carbon dioxide can be co-fed to lower

2331-436: 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

2394-480: The electrolysis cell it is also possible to electrochemically consume the oxygen produced in an electrolyser by introducing a fuel (such as carbon/coal, methanol , ethanol , formic acid , glycerol, etc.) into the oxygen side of the reactor. This reduces the required electrical energy and has the potential to reduce the cost of hydrogen to less than 40~60% with the remaining energy provided in this manner. Carbon/hydrocarbon assisted water electrolysis (CAWE) has

2457-437: The following links: Serpentinization Serpentinization is a hydration and metamorphic transformation of ferromagnesian minerals, such as olivine and pyroxene , in mafic and ultramafic rock to produce serpentinite . Minerals formed by serpentinization include the serpentine group minerals ( antigorite , lizardite , chrysotile ), brucite , talc , Ni-Fe alloys, and magnetite . The mineral alteration

2520-597: The formation of high-pressure micro-bubbles of H 2 in the metallic lattice. The trends to expansion of H 2 bubbles and the resulting tensile stress can generate cracks in the metallic alloys sensitive to this effect also known as hydrogen embrittlement . Several recent studies (Turnbull, 2009; King, 2008; King and Kolar, 2009) address this question in the frame of the radioactive waste disposal in Switzerland and Canada. For detailed reports on iron corrosion issues related to high-level waste disposal, see

2583-417: The frame of the corrosion studies related to HLW disposal, anaerobic corrosion of steel is receiving a renewed and continued attention. Indeed, it is essential to understand this process to guarantee the total containment of HLW waste in an engineered barrier during the first centuries or millennia when the radiotoxicity of the waste is high and when it emits a significant quantity of heat . The question

Schikorr reaction - Misplaced Pages Continue

2646-404: The generation of H 2 , a geochemical source of energy that can support both abiotic and biological synthesis of organic molecules. Serpentinization occurs at mid-ocean ridges , in the forearc mantle of subduction zones, in ophiolite packages, and in ultramafic intrusions. Conditions are highly favorable for serpentinization at slow to ultraslow spreading mid-ocean ridges. Here

2709-405: The hydration of olivine to yield serpentine and brucite (Reaction 1b). The mixture of brucite and serpentine formed by Reaction 1b has the lowest silica activity in the serpentinite , so that the brucite phase is very important in understanding serpentinization. However, the brucite is often blended in with the serpentine such that it is difficult to identify except with X-ray diffraction , and it

2772-469: The hydrogen production is large enough. SOECs operate at high temperatures, typically around 800 °C (1,500 °F). 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

2835-447: The iron cations on both sides of the equation to be counterbalanced by 6 hydroxyl anions (OH): For completing the main reaction, two companion reactions have still to be taken into account: The autoprotolysis of the hydroxyl anions; a proton exchange between two OH, like in a classical acid–base reaction : it is then possible to reorganize the global reaction as: Considering then the formation reaction of iron(II,III) oxide : it

2898-403: The long-term disposal of radioactive waste (Ortiz et al. , 2001; Nagra, 2008; recent Nagra NTB reports). Indeed, a gas pressure build-up could occur if the rate of hydrogen production by the anaerobic corrosion of carbon-steel and by the subsequent transformation of green rust into magnetite should exceed the rate of diffusion of dissolved H 2 in the pore water of the formation. The question

2961-532: 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 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

3024-435: The maximum depth of megathrust earthquakes as they impede rupture into the forearc mantle. Hydrogen production 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 ,

3087-588: The methane. Methods to produce hydrogen without the use of fossil fuels involve the process of water splitting , or splitting the water molecule (H 2 O) into its components oxygen and hydrogen. When the source of energy for water splitting is renewable or low-carbon, the hydrogen produced is sometimes referred to as green hydrogen . The conversion can be accomplished in several ways, but all methods are currently considered more expensive than fossil-fuel based production methods. Hydrogen can be made via high pressure electrolysis , low pressure electrolysis of water, or

3150-640: The original serpentinite minerals shows that this alteration takes place after serpentinization. Serpentinite may contain chlorite (a phyllosilicate mineral), tremolite (Ca 2 (Mg 5.0-4.5 Fe 0.0-0.5 )Si 8 O 22 (OH) 2 ), and metamorphic olivine and diopside (calcium-rich pyroxene). This indicates that the serpentinite has been subject to more intense metamorphism, reaching the upper greenschist or amphibolite metamorphic facies . Above about 450 °C (842 °F), antigorite begins to break down. Thus serpentinite does not exist at higher metamorphic facies. The presence of traces of methane in

3213-516: 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 CO 2 produced can be easily sequestered without the need for separation. Biomass is converted into syngas by gasification and syngas is further converted into hydrogen by water-gas shift reaction (WGSR). The industrial production of chlorine and caustic soda by electrolysis generates

SECTION 50

#1732872661397

3276-642: The potential to reduce the overall cost of the hydrogen produced by reducing the amount of electrical energy required for electrolysis. PEM electrolysis cells typically operate below 100 °C (212 °F). 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 photovoltaic solar panels . AECs optimally operate at high concentrations of electrolyte (KOH or potassium carbonate ) and at high temperatures, often near 200 °C (392 °F). Efficiency of modern hydrogen generators

3339-531: The protolith is pyroxenite, which contains more pyroxene than olivine, iron-rich talc is produced with no magnetite and only modest hydrogen production. Infiltration of silica-bearing fluids during serpentinization can suppress both the formation of brucite and the subsequent production of hydrogen. Chromite present in the protolith will be altered to chromium-rich magnetite at lower serpentinization temperatures. At higher temperatures, it will be altered to iron-rich chromite (ferrit-chromite). During serpentinization,

3402-433: The rate of crustal extension is high compared with the volume of magmatism, bringing ultramafic mantle rock very close to the surface where fracturing allows seawater to infiltrate the rock. Serpentinization at slow spreading mid-ocean ridges can cause the seismic Moho discontinuity to be placed at the serpentinization front, rather than the base of the crust as defined by normal petrological criteria. The Lanzo Massif of

3465-405: The rock is enriched in chlorine , boron , fluorine , and sulfur. Sulfur will be reduced to hydrogen sulfide and sulfide minerals, though significant quantities are incorporated into serpentine minerals, and some may later be reoxidized to sulfate minerals such as anhydrite . The sulfides produced include nickel-rich sulfides, such as mackinawite . Laboratory experiments have confirmed that at

3528-702: The rock, increasing the volume, reducing the density and destroying the original structure. The density changes from 3.3 to 2.5 g/cm (0.119 to 0.090 lb/cu in) with a concurrent volume increase on the order of 30-40%. The reaction is highly exothermic , releasing up to 40 kilojoules (9.6 kcal) per mole of water reacting with the rock, and rock temperatures can be raised by about 260 °C (500 °F), providing an energy source for formation of non-volcanic hydrothermal vents . The hydrogen, methane, and hydrogen sulfide produced during serpentinization are released at these vents and provide energy sources for deep sea chemotroph microorganisms . Olivine

3591-412: 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

3654-488: The surface, as has taken place with the serpentinite exposed at the Presidio of San Francisco following cessation of subduction. Serpentinized ultramafic rock is found in many ophiolites . Ophiolites are fragments of oceanic lithosphere that has been thrust onto continents, a process called obduction . They typically consist of a layer of serpentinized harzburgite (sometimes called alpine peridotite in older writings),

3717-965: 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 densities , and can therefore be possibly cheaper if

3780-523: The ultramafic mantle rock. Direct evidence that serpentinization is taking place in the Mariana Islands island arc is provided by the activity of serpentinite mud volcanoes . Xenoliths of harzburgite and (less commonly) dunite are occasionally erupted by the mud volcanoes, giving clues to the nature of the protolith. Because serpentinization lowers the density of the original rock, serpentinization may lead to uplift or exhumation of serpentinites to

3843-431: 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,

SECTION 60

#1732872661397

3906-478: Was formed by serpentinization, not by life processes. Using data from the Cassini probe flybys obtained in 2010–12, scientists were able to confirm that Saturn's moon Enceladus likely has a liquid water ocean beneath its frozen surface. A model suggests that the ocean on Enceladus has an alkaline pH of 11–12. The high pH is interpreted to be a key consequence of serpentinization of chondritic rock , that leads to

3969-452: Was produced worldwide for various uses, such as oil refining , 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. Molecular hydrogen was discovered in

#396603