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Topic Review
Hydrogen Production through Heterojunction Semiconductors for Environmental Remediation
Today, as a result of the advancement of technology and increasing environmental problems, the need for clean energy has considerably increased. In this regard, hydrogen, which is a clean and sustainable energy carrier with high energy density, is among the well-regarded and effective means to deliver and store energy, and can also be used for environmental remediation purposes. Renewable hydrogen energy carriers can successfully substitute fossil fuels and decrease carbon dioxide (CO2) emissions and reduce the rate of global warming. Hydrogen generation from sustainable solar energy and water sources is an environmentally friendly resolution for growing global energy demands. Among various solar hydrogen production routes, semiconductor-based photocatalysis seems a promising scheme that is mainly performed using two kinds of homogeneous and heterogeneous methods, of which the latter is more advantageous. During semiconductor-based heterogeneous photocatalysis, a solid material is stimulated by exposure to light and generates an electron–hole pair that subsequently takes part in redox reactions leading to hydrogen production.
  • 1.3K
  • 07 May 2022
Topic Review
Hydrogen Permeation Test Methods of Polymer Liner Material
Type IV hydrogen storage cylinders comprise a polymer liner and offer advantages such as lightweight construction, high hydrogen storage density, and good fatigue performance. However, they are also characterized by higher hydrogen permeability. Consequently, it is crucial for the polymer liner material to exhibit excellent resistance to hydrogen permeation. International organizations have established relevant standards mandating hydrogen permeation tests for the liner material of type IV on-board hydrogen storage cylinders. 
  • 718
  • 14 Aug 2023
Topic Review
Hydrogen Generation
Hydrogen generation is the process of producing hydrogen gas from various sources, such as fossil fuels, water, or biomass. Hydrogen gas is a clean and versatile energy carrier that can be used in a wide range of applications, including fuel cells, transportation, and industrial processes. Hydrogen generation can be achieved through various methods, including steam methane reforming, electrolysis, and coal gasification. The use of hydrogen as a fuel offers a clean and sustainable alternative to traditional fossil fuels, with applications in transportation, power generation, industrial processes, heating systems, and energy storage. The development of sustainable hydrogen generation technologies is crucial for achieving a low-carbon economy and combating climate change. However, the technology still faces challenges such as high cost and lack of infrastructure. This entry provides an overview of the different methods and applications of hydrogen generation, and discusses the potential benefits and challenges associated with this technology.
  • 727
  • 23 Mar 2023
Topic Review
Hydrogen Evolution Reaction and MXenes
Green hydrogen production via electrocatalytic water splitting paves the way for renewable, clean, and sustainable hydrogen (H2) generation. H2 gas is produced from the cathodic hydrogen evolution reaction (HER), where the reaction is catalyzed primarily from Pt-based catalysts under both acidic and alkaline environments. MXene is a 2D nanomaterial based on transition-metal carbide or nitride, having the general formula of Mn+1XnTx, where M = transition metal, X = C and/or N and Tx = surface termination groups such as F, O, OH and Cl.
  • 770
  • 26 Dec 2022
Topic Review
Hydrogen Evolution Reaction
In recent years, heteroatom doping has been found to be an effective strategy to improve the electrocatalytic hydrogen evolution reaction (HER) performances of nickel-based catalysts in acidic, neutral, and alkaline media. 
  • 2.8K
  • 26 Oct 2020
Topic Review
Hydrogen Economy
Environmental issues make the quest for better and cleaner energy sources a priority. Worldwide, researchers and companies are continuously working on this matter, taking one of two approaches: either finding new energy sources or improving the efficiency of existing ones. Hydrogen is a well-known energy carrier due to its high energy content, but a somewhat elusive one for being a gas with low molecular weight. The so-called "Hydrogen Economy" is based on the use of hydrogen as an energy source. This entry examines the current electrolysis processes for obtaining hydrogen, with an emphasis on alkaline water electrolysis.
  • 2.1K
  • 18 Sep 2021
Topic Review
Hydrogen Bond Energy
Hydrogen bonds (HBs) play a crucial role in many physicochemical and biological processes. Theoretical methods can reliably estimate the intermolecular HB energies. Quantifying an intramolecular hydrogen bond (IHB) strength is not as straightforward as the intermolecular one. The main difficulty lies in isolating the X–H···Y interaction present within a molecule than in a dimer or a complex. However, the procedure discussed (viz. molecular tailoring approach) in this article, allows the generation of fragments so that the atoms/functional groups involved in the HB formation are parts of two different fragments. The energies of these fragments are added or substracted, using the inclusion exclusion principle in set theory, to obtained the energy of HB bond.
  • 1.5K
  • 19 May 2021
Topic Review
Hydrogen Bond
The hydrogen bond may be treated as a local stabilizing interaction that acts between the proton or the electron charge deficient region of hydrogen centre and the electron rich region that is related to one or more centres. This may be named as the two-sites hydrogen bond definition. However in numerous studies the A-H proton donating bond with the positively charged H-atom and the proton acceptor, say B, being the electron rich centre are taken into account. Thus so-called A-H∙∙∙B hydrogen bridges are often considered. In such a way the three-sites hydrogen bond definition may be proposed that the hydrogen bond is the A-H∙∙∙B local stabilizing system with the proton situated between two A and B electron rich sites, most often closer to one of them, forming the A-H covalent bond; both A and B may correspond to one or more atomic centres.
  • 1.4K
  • 07 Sep 2021
Topic Review
Hydrogen Adsorption in Metal–Organic Frameworks
The development of hydrogen technologies and a wider use of hydrogen fuel cell systems require new materials that can store large amounts of hydrogen at relatively low pressures with small volume, low weight, and fast kinetics for recharging. Among the most challenging materials for hydrogen storage are porous coordination polymers, also called metal–organic frameworks (MOFs). MOFs are two- or three-dimensional porous crystalline materials with infinite lattices. As a result of their ultra-high surface area values (more than 2500 m2·g–1 measured by the Brunauer–Emmett–Teller (BET) approach), they were found to be promising gas adsorbers for small gaseous molecules, including CH4, CHCl3, CCl4, C6H6, C6H12, CO2, Ar, N2, and H2. The main benefit of MOFs is their reversible and high-rate hydrogen adsorption process. A reasonable number of H2 molecules inside the body of MOFs may only be obtained at very low temperatures. To date, MOFs have shown significant progress in applications of gas separation, catalysis, and coordination chemistry.
  • 1.3K
  • 09 Aug 2021
Topic Review
Hydrogels via Diels–Alder Crosslinking
The Diels–Alder (DA) reaction is a promising tool for obtaining covalently crosslinked hydrogels due to its reaction bioorthogonality, the absence of by-products, and the application of mild conditions without a catalyst. The resulting hydrogels are in demand for use in various fields of materials science and biomedicine.
  • 571
  • 10 Feb 2023
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