Electrolysis of waterElectrolysis of water is using electricity to split water into oxygen (O2) and hydrogen (H2) gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, but must be kept apart from the oxygen as the mixture would be extremely explosive. Separately pressurised into convenient 'tanks' or 'gas bottles', hydrogen can be used for oxyhydrogen welding and other applications, as the hydrogen / oxygen flame can reach circa 2,800°C. Water electrolysis requires a minimum potential difference of 1.
Water splittingWater splitting is the chemical reaction in which water is broken down into oxygen and hydrogen: 2 H2O → 2 H2 + O2 Efficient and economical water splitting would be a technological breakthrough that could underpin a hydrogen economy, based on green hydrogen. A version of water splitting occurs in photosynthesis, but hydrogen is not produced. The reverse of water splitting is the basis of the hydrogen fuel cell. Electrolysis of water Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and hydrogen (H2) due to an electric current being passed through the water.
Photocatalytic water splittingPhotocatalytic water splitting is a process that uses photocatalysis for the dissociation of water (H2O) into hydrogen (H2) and oxygen (O2). Only light energy (photons), water, and a catalyst(s) are needed, since this is what naturally occurs in natural photosynthetic oxygen production and CO2 fixation. Photocatalytic water splitting is done by dispersing photocatalyst particles in water or depositing them on a substrate, unlike Photoelectrochemical cell, which are assembled into a cell with a photoelectrode.
Hydrogen productionHydrogen production is the family of industrial methods for generating hydrogen gas. As of 2020, the majority of hydrogen (~95%) is produced from fossil fuels by steam reforming of natural gas and other light hydrocarbons, partial oxidation of heavier hydrocarbons, and coal gasification. Other methods of hydrogen production include biomass gasification, methane pyrolysis, and electrolysis of water. Methane pyrolysis and water electrolysis can use any source of electricity including solar power.
Solar fuelA solar fuel is a synthetic chemical fuel produced from solar energy. Solar fuels can be produced through photochemical (i.e. activation of certain chemical reactions by photons), photobiological (i.e., artificial photosynthesis), and electrochemical reactions (i.e. using the electricity from solar panels to drive a chemical reaction). Solar fuels can also be produced by thermochemical reactions (i.e., through the use of solar heat supplied by concentrated solar thermal energy to drive a chemical reaction).
Oxygen evolutionOxygen evolution is the process of generating molecular oxygen (O2) by a chemical reaction, usually from water. Oxygen evolution from water is effected by oxygenic photosynthesis, electrolysis of water, and thermal decomposition of various oxides. The biological process supports aerobic life. When relatively pure oxygen is required industrially, it is isolated by distilling liquefied air. Oxygen evolving complex Photosynthetic oxygen evolution is the fundamental process by which oxygen is generated in the earth's biosphere.
Nanomaterial-based catalystNanomaterial-based catalysts are usually heterogeneous catalysts broken up into metal nanoparticles in order to enhance the catalytic process. Metal nanoparticles have high surface area, which can increase catalytic activity. Nanoparticle catalysts can be easily separated and recycled. They are typically used under mild conditions to prevent decomposition of the nanoparticles. Functionalized metal nanoparticles are more stable toward solvents compared to non-functionalized metal nanoparticles.
Artificial photosynthesisArtificial photosynthesis is a chemical process that biomimics the natural process of photosynthesis to convert sunlight, water, and carbon dioxide into carbohydrates and oxygen. The term artificial photosynthesis is commonly used to refer to any scheme for capturing and storing the energy from sunlight in the chemical bonds of a fuel (a solar fuel). Photocatalytic water splitting converts water into hydrogen and oxygen and is a major research topic of artificial photosynthesis.
OxygenOxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. Oxygen is Earth's most abundant element, and after hydrogen and helium, it is the third-most abundant element in the universe. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2.
Solar energySolar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essential source of renewable energy, and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power.
HydrogenHydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, and highly combustible. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all normal matter. Stars such as the Sun are mainly composed of hydrogen in the plasma state. Most of the hydrogen on Earth exists in molecular forms such as water and organic compounds.
Chemical reactionA chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.
BiohydrogenBiohydrogen is H2 that is produced biologically. Interest is high in this technology because H2 is a clean fuel and can be readily produced from certain kinds of biomass, including biological waste. Furthermore some photosynthetic microorganisms are capable to produce H2 directly from water splitting using light as energy source. Besides the promising possibilities of biological hydrogen production, many challenges characterize this technology. First challenges include those intrinsic to H2, such as storage and transportation of an explosive noncondensible gas.
Hydrogen peroxideHydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%–6% by weight) in water for consumer use, and in higher concentrations for industrial use. Concentrated hydrogen peroxide, or "high-test peroxide", decomposes explosively when heated and has been used both as a monopropellant and an oxidizer in rocketry.
Current densityIn electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point. In SI base units, the electric current density is measured in amperes per square metre. Assume that A (SI unit: m2) is a small surface centred at a given point M and orthogonal to the motion of the charges at M.
Stellar evolutionStellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the current age of the universe. The table shows the lifetimes of stars as a function of their masses. All stars are formed from collapsing clouds of gas and dust, often called nebulae or molecular clouds.
Oxygen-18Oxygen-18 (18O, Ω) is a natural, stable isotope of oxygen and one of the environmental isotopes. 18O is an important precursor for the production of fluorodeoxyglucose (FDG) used in positron emission tomography (PET). Generally, in the radiopharmaceutical industry, enriched water (H218O) is bombarded with hydrogen ions in either a cyclotron or linear accelerator, producing fluorine-18. This is then synthesized into FDG and injected into a patient. It can also be used to make an extremely heavy version of water when combined with tritium (hydrogen-3): 3H218O or T218O.
CarbonCarbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes up about 0.025 percent of Earth's crust. Three isotopes occur naturally, ^12C and ^13C being stable, while ^14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.
Solar vehicleA solar vehicle or solar electric vehicle is an electric vehicle powered completely or significantly by direct solar energy. Usually, photovoltaic (PV) cells contained in solar panels convert the sun's energy directly into electric energy. The term "solar vehicle" usually implies that solar energy is used to power all or part of a vehicle's propulsion. Solar power may also be used to provide power for communications or controls or other auxiliary functions.
Heterogeneous gold catalysisHeterogeneous gold catalysis refers to the use of elemental gold as a heterogeneous catalyst. As in most heterogeneous catalysis, the metal is typically supported on metal oxide. Furthermore, as seen in other heterogeneous catalysts, activity increases with a decreasing diameter of supported gold clusters. Several industrially relevant processes are also observed such as H2 activation, Water-gas shift reaction, and hydrogenation. No gold-catalyzed reaction has been commercialized.
