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Exploitation of hydrogen as an energy carrier requires the development of systems for its storage and delivery. Formic acid has been proposed as valuable hydrogen carrier compound, due to its relatively high hydrogen content (53 g L−1), the latter being easily and cleanly released in catalytic reactions under mild conditions (HCOOH → H2+ CO2). Ionic liquids are interesting solvents for homogeneous catalyzed formic acid decomposition systems as their extremely low volatility avoids solvent contamination of the produced hydrogen stream. In this paper an outstandingly simple, robust and active catalyst system is presented, namely RuCl3dissolved in 1-ethyl-2,3-dimethylimidazolium acetate (RuCl3/[EMMIM][OAc]). This system proved to be fully recyclable over 10 times. Turnover frequencies (TOF) of 150 h−1and 850 h−1were obtained at 80 °C and 120 °C, respectively. [ABSTRACT FROM AUTHOR]

Solar-driven water splitting offers a leading-edge approach to storing abundant and intermittent solar energy and producing hydrogen as a clean and sustainable energy carrier. More importantly, constructing well-designed photocatalysts is a promising approach to develop clean hydrogen energy. In this paper, flower spherical UiO-66-(SCH3)2/ZnIn2S4 (UiOSC/ZIS) photocatalysts are successfully synthesized by a simple two-step hydrothermal method, and they exhibit high hydrogen production activity in light-driven water splitting. The optimized 30-UiOSC/ZIS (the content of UiOSC was 30 mg) composite exhibits optimal hydrogen production activity with a hydrogen production of 3433 μmol g−1 h−1, which is 5 and 235 times higher than that of pure ZIS and UiOSC, respectively. In addition, a long-cycling stability test has shown that the UiOSC/ZIS composite has good stability and recyclability. Experimental and characterization results show the formation of a type-II heterojunction between UiOSC and ZIS. This effectively suppresses the recombination of electrons–holes and promotes the carrier transfer, thus significantly improving the hydrogen production performance. This research further promotes the application of UiO-66-(SCH3)2 in the field of photocatalytic hydrogen production and provides a reference for the rational design of UiO-66-based composite photocatalysts. [ABSTRACT FROM AUTHOR]

In this paper, NiCo2S4 was coated on the surface of WS2 of a 1T/2H mixed phase by a two-step hydrothermal method to form an in situ core–shell structure. The unique S-scheme heterojunction of the NiCo2S4@WS2 core–shell composite photocatalyst improved the easy recombination of carriers caused by the narrow band gap of NiCo2S4 and WS2, and improved the photocatalytic hydrogen production performance. The loading ratio of NiCo2S4@WS2, the addition of Eosin Y, and the pH value of TEOA were optimized. Under the optimal conditions, the hydrogen production rate reached 5.814 mmol g−1 h−1, which is about 8.55 times and 3.35 times the hydrogen evolution rates of NiCo2S4 and WS2, respectively. The composite catalyst exhibits excellent charge separation efficiency in photoelectrochemistry, PL and BET tests, carrier transport rate and large specific surface area that can provide more active sites, which are the main factors for the improvement of the hydrogen evolution performance. This paper demonstrates new design strategies to drive efficient photocatalytic hydrogen production by building in situ core–shell structures and optimizing the carrier transport paths, which will yield new insights. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) is a new type of renewable energy that can meet people's growing energy needs and is environmentally friendly. In order to improve the industrial application prospects and electrochemical performance of hydrogen evolution catalysts, extensive research on transition metal materials has been carried out. Among the many catalytic materials, cobalt is an element with potential for the hydrogen evolution reaction (HER) due to its abundant reserves, low cost, and small energy barrier for H adsorption. This review classifies the latest research on cobalt-based catalysts according to the types of compound, including cobalt-based sulfides, phosphides, carbides, borides, oxides, etc., and summarizes the latest research progress of cobalt-based compound catalysts in acidic and alkaline media. Strategies to tune the properties of cobalt-based compound catalysts for high catalytic activity for HER are focused on, including structural engineering, defect engineering, and doping, etc. The advantages and limitations of each modified approach are reviewed. Not only that, but also the catalytic activity and advantages of the catalyst are evaluated by using density functional theory (DFT) calculation-related descriptors, activity evaluation parameters, etc. Finally, limitations and challenges of cobalt-based materials for HER are presented, as well as prospects for future research. This paper aims to understand the chemical and physical factors that affect cobalt-based catalysts, and to find directions for future research on cobalt-based catalysts. [ABSTRACT FROM AUTHOR]

In this paper, we present a MoP/P–Mn0.5Cd0.5S photocatalytic material (PMOMCS-Px). A novel catalyst can efficiently split water into hydrogen without precious metals. In the sacrificial agent environment, the HER (hydrogen evolution rate) of PMOMCS-P5 was 4368.25 μmol g−1 h−1 which was 11.4 times greater than the HER of Mn0.5Cd0.5S (383.19 μmol g−1 h−1), and its hydrogen production performance was better than that of Pt/Mn0.5Cd0.5S (2.0 wt% Pt). Furthermore, the hydrogen evolution performance of PMOMCS-P5 under pure water conditions was also examined, and the HER of PMOMCS-P5 was 209.76 μmol g−1 h−1, which was 20.4 times that of Mn0.5Cd0.5S (10.29 μmol g−1 h−1). Its characterization proved that the introduction of the co-catalyst MoP and P doping inhibited the recombination of e− and h+, enhanced the reduction capacity, and reduced the hydrogen precipitation reaction overpotential of PMOMCS-Px, thus enhancing the hydrogen production performance of PMOMCS-Px. Therefore, an efficient and economical photocatalyst was prepared. [ABSTRACT FROM AUTHOR]

The development of high-efficiency and low-cost photocatalysts for hydrogen production reactions is very important to solve energy problems. In this paper we study the photocatalytic H2 evolution activity of a CeO2/CoS2 heterojunction catalyst under visible light. Characterization studies such as XRD and XPS proved the successful synthesis of a CeO2/CoS2 catalyst. The composite catalyst with a CeO2 and CoS2 mass ratio of 1 : 20 had the best activity, and the hydrogen evolution rate reached 5172.20 μmol g−1 h−1. BET and UV-Vis DRS characterization showed that the introduction of CeO2 not only increased the specific surface area of the composite catalyst, but also improved the response of the photocatalyst to visible light. In addition, PL and electrochemical experiments showed that the electrons and holes of the CeO2/CoS2 catalyst could be quickly separated and transferred, thereby accelerating the kinetics of the hydrogen evolution reaction. This work provided an experimental basis for designing a composite photocatalyst with high stability and hydrogen production activity. [ABSTRACT FROM AUTHOR]

Metal halide perovskites, such as iodine methylamine lead (MAPbI3), have received extensive attention in the field of photocatalytic decomposition of HI for hydrogen evolution, due to their excellent photoelectric properties. In this paper, a new MAPbI3-based composite, MoC/MAPbI3, was synthesized. The results show that 15 wt% MoC/MAPbI3 has the best hydrogen production performance (38.4 μmol h−1), which is approximately 24-times that of pure MAPbI3 (1.61 μmol h−1). With the extension of the catalytic time, the hydrogen production rate of MoC/MAPbI3 reached 165.3 μmol h−1 after 16 h due to the effective separation and transfer of charge carriers between MoC and MAPbI3, showing excellent hydrogen evolution rate performance under visible light. In addition, the cycling stability of MoC/MAPbI3 did not decrease in multiple 4 h cycle tests. This study used the non-precious metal promoter MoC to modify MAPbI3, and provides a new idea for the synthesis of efficient MAPbI3-based composite catalysts. [ABSTRACT FROM AUTHOR]

A new vision of using carbon dioxide (CO2) catalytic processing of oleic acid into C8–C15 alkanes over a nano-nickel/zeolite catalyst is reported in this paper. The inherent and essential reasons which make this achievable are clearly resolved by using totally new catalytic reaction pathways of oleic acid transformation in a CO2 atmosphere. The yield of C8–C15 ingredients reaches 73.10 mol% in a CO2 atmosphere, which is much higher than the 49.67 mol% yield obtained in a hydrogen (H2) atmosphere. In the absence of an external H2 source, products which are similar to aviation fuel are generated where aromatization of propene (C3H6) oxidative dehydrogenation (ODH) involving CO2 and propane (C3H8) and hydrogen transfer reactions are found to account for hydrogen liberation in oleic acid and achieve its re-arrangement in the final alkane products. The reaction pathway in the CO2 atmosphere is significantly different from that in the H2 atmosphere, as shown by the presence of 8-heptadecene, γ-stearolactone, and 3-heptadecene as reaction intermediates, as well as a CO formation pathway. Because of the highly dispersed Ni metal center on the zeolite support, H2 spillover is observed in the H2 atmosphere, which inhibits the production of short-chain alkanes and reveals the inherent disadvantage of using H2. The CO2 processing of oleic acid described in this paper will significantly contribute to future CO2 utilization chemistry and provide an economical and promising approach for the production of sustainable alkane products which are similar to aviation fuel. [ABSTRACT FROM AUTHOR]

An effective and safe route is proposed to prepare supported Mo2C-based catalysts from organic–inorganic hybrids, which exhibit high activity and stability for producing H2from methanol catalytic decomposition. [ABSTRACT FROM AUTHOR]

Non-metallic η²-H2 complexes are extremely rare; moreover in the case of boranes (with the exception of the BH5 molecule) the existence of such structures was only indicated by computational studies. In a recent paper we have demonstrated that external electron donor groups can stabilize the η²-H2 complexes, similar to the backdonation in the case of transition metals. In this paper we present evidence of a new stabilizing effect: electron donation from the B-R bonds to the H2 σ* orbital. The stability and electronic structure of several mono-, di-, and trisubstituted borane-H2 complexes were investigated by ab initio calculations. SiR3 groups were found to facilitate the σ(B-R)σ*(H-H) interaction, increasing the stability of the η² complexes. Furthermore in the case of tris(trimethyl)silylborane, the exceptional stability of a novel neutral pentavalent borane structure is shown. [ABSTRACT FROM AUTHOR]

Methanol is an important H-carrier and C1 chemical feedstock. In this paper, a direct conversion of methanol to n-C4H10 and H2 was achieved for the first time in a dielectric barrier discharge (DBD) non-thermal plasma reactor. The selective formation of n-C4H10 by limiting COx (x = 1 and 2) generation was obtained by optimizing different plasma processing parameters including the methanol inlet concentration, discharge power, and pre-heating temperature. The results showed that a higher methanol inlet concentration and a higher pre-heating temperature favors the formation of n-C4H10, while a higher methanol inlet concentration and a lower discharge power can effectively limit the formation of CO. The optimal selectivity for n-C4H10 (37.5%), H2 (28.9%) and CO (14%) was achieved, with a methanol conversion of 40.0%, at a methanol inlet concentration of 18 mol%, a discharge power of 30 W and a pre-heating temperature of 140 °C using N2 as a carrier gas. Value-added liquid chemicals (e.g., alcohols, acids, and heavy hydrocarbons) were also obtained from this reaction. Emission spectroscopy diagnostics reveals the formation of various reactive species (e.g., CH, C2, CN, H and metastable N2) in the CH3OH/N2 DBD. Possible reaction pathways for the formation of n-C4H10 were proposed and discussed. [ABSTRACT FROM AUTHOR]

The paper reports on the experimental and theoretical investigation of bonding properties of potassium amidoborane, (K[NH2BH3]), which is one of the most promising compounds for hydrogen storage material among metallated derivatives of ammonia borane (NH3BH3). For this purpose, in situ Raman spectroscopy, synchrotron X-ray diffraction measurements and complementary ab initio calculations study have been performed under static pressure conditions in the range from ambient pressure up to 25 GPa. Unusual interplay between strong electrostatic and weak dispersive interactions has been revealed, resulting in experimental observation of pressure induced formation of relatively strong conventional hydrogen bonding between negatively charged molecular ions. This finding provides new insight for tailoring materials with desirable properties for various uses. [ABSTRACT FROM AUTHOR]

The most difficult issue as regards hydrogen (H) analysis using the laser-induced plasma technique is the disturbance of H emission by H2O molecules. This problem is essentially solved in this paper by employing a novel technique that makes use of the specific characteristics of a TEA CO2laser. Thus, a small helium gas plasma was produced by focusing a TEA CO2laser onto a zircaloy surface containing H atoms. High-purity helium (He) gas was passed over the focusing point during the experiment so that the plasma was totally covered by the He gas and the H2O molecules remaining in the surrounding gas could not attack the plasma region. This technique ensures that only hydrogen atoms come out from the melted region of the sample surface, and are excited viametastable He atoms. This method has allowed us to confirm that H alpha (Hα), H beta (Hβ), H gamma (Hγ), and H delta (Hδ) emission can clearly be detected from a hydrogen-containing zircaloy sample with no interference from host emission lines or the H emission arising from H2O. The intensity ratio of Hα, Hβ, and Hγwas compared with that obtained for a low pressure hydrogen discharge lamp. [ABSTRACT FROM AUTHOR]

Exploitation of hydrogen as an energy carrier requires the development of systems for its storage and delivery. Formic acid has been proposed as valuable hydrogen carrier compound, due to its relatively high hydrogen content (53 g L−1), the latter being easily and cleanly released in catalytic reactions under mild conditions (HCOOH → H2 + CO2). Ionic liquids are interesting solvents for homogeneous catalyzed formic acid decomposition systems as their extremely low volatility avoids solvent contamination of the produced hydrogen stream. In this paper an outstandingly simple, robust and active catalyst system is presented, namely RuCl3 dissolved in 1-ethyl-2,3-dimethylimidazolium acetate (RuCl3/[EMMIM][OAc]). This system proved to be fully recyclable over 10 times. Turnover frequencies (TOF) of 150 h−1 and 850 h−1 were obtained at 80 °C and 120 °C, respectively. [ABSTRACT FROM AUTHOR]

Pyrolysis oils are the cheapest liquid fuel derived from lignocellulosic biomass. However, pyrolysis oils are a very poor quality liquid fuel that cannot be used in conventional diesel and internal combustion engines. In this paper we show that hydrogen, alkanes (ranging from C1to C6) and polyols (ethylene glycol, 1,2-propanediol, 1,4-butanediol) can be produced from the aqueous fraction of wood-derived pyrolysis oils (bio-oils). The pyrolysis oil was first phase separated into aqueous and non-aqueous fraction by addition of water. The aqueous phase of bio-oil contained sugars; anhydrosugars; acetic acid; hydroxyacetone; furfural and small amounts of guaiacols. The aqueous fraction was subjected to a low temperature hydrogenation with Ru/C catalyst at 125–175 °C and 68.9 bar. The hydrogenation step converts the various functionalities in the bio-oil (including aldehydes; acids; sugars) to corresponding alcohols. Undesired methane and light gases are also produced in this low-temperature hydrogenation step. Diols (ranging from C2 to C4) and sorbitol are obtained as major products in this step. After the low temperature hydrogenation step either hydrogen or alkanes can be produced by aqueous-phase reforming (APR) or aqueous-phase dehydration/hydrogenation (APD/H) respectively. APR was done with a 1 wt% Pt/Al2O3catalyst at 265 °C and 55.1 bar. Hydrogen selectivities of up to 60% were observed. The hydrogen selectivity was a function of space velocity. A 4 wt% Pt/SiO2-Al2O3catalyst at 260 °C and 51.7 bar was used for alkane production by APD/H. The carbon conversion to gas phase products of 35% with alkane selectivity of 45% was obtained for a WHSV of 0.96 h−1when hydrogen is produced in situfrom bio-oil. Alkane selectivity can be improved by supplying hydrogen externally. Alkane selectivities as high as 97% can be obtained when HCl is added to the aqueous-phase of the bio-oil and hydrogen is supplied externally. Model compounds for further bio-oil conversion studies are suggested. [ABSTRACT FROM AUTHOR]

The growing need for hydrogen-based fuel cells has driven research into hydrogenase (H2ase)—a natural enzyme that catalyses the extraction of electrons from H2 in water under ambient conditions. Unfortunately, the exact mechanism by which H2ase achieves this feat has remained a matter of some controversy until now, with many mechanisms being inconsistent with experimental data. Recently, however, we have been able to produce a successful catalytic mimic of H2ase that replicates key aspects of it. This paper begins with an overview of the research from many groups that preceded this discovery, followed by a detailed analysis of the key points that set our unique functional model apart-that is to say a proton-like ''hydride'' species, a surprisingly low-valent NiIRuI complex and the key insight that two molecules of H2 are required for electron extraction. [ABSTRACT FROM AUTHOR]

Copper-doped ceria catalysts feature in a variety of catalytic reactions. One important application is selective hydrogen combustion viaoxygen exchange, which forms the basis of cyclic oxidative dehydrogenation. This paper describes the synthesis of monophasic (doped) and biphasic (supported) Cu–ceria catalysts, that are then characterized using a combination of temperature programmed reduction (TPR) and X-ray diffraction (XRD) methods. The catalysts are analyzed both as fresh samples and after redox cycling at 550–800 °C. TPR and XRD characterization clarify the role of the active sites on the catalyst surface and the copper–ceria interactions. Depending on the catalyst type, reduction occurs at ∼110 °C, ∼150 °C, or ∼190 °C. The reduction at 110 °C is ascribed to highly dispersed copper species doped in the ceria lattice, and that at 190 °C to CuO crystallites supported on ceria. Remarkably, both types converge to the 150 °C feature after redox cycling. The reduction temperature of the doped catalyst increases after redox cycling, indicating that stable Cu clusters form at the surface. Conversely, the reduction temperature of the “supported” catalyst decreases after redox cycling, and the CuO crystallites disappear. With this knowledge, a copper-doped ceria catalyst is analyzed after application in selective hydrogen combustion (16 consecutive redox cycles at 550 °C). No CuO crystallites are observed, and the sample reduces at ∼110 °C. This suggests that copper-doped ceria is the active oxygen exchange phase in selective hydrogen combustion. [ABSTRACT FROM AUTHOR]

It is now well known that traces of molecular gases such as hydrogen or nitrogen can affect significantly the electrical characteristics, sputtering rates and relative intensities of emission lines in glow discharge optical emission spectrometry (GD-OES). These changes, caused by the molecular gases which are very often present in the discharge for various reasons, have a serious impact on the accuracy of analytical results. Therefore, it is important to describe these effects in detail and to try to understand the processes involved. The results presented in this paper focus on the effects of hydrogen and nitrogen on intensities of atomic emission lines of iron and titanium. In the case of hydrogen, when intensity ratios (intensities measured in argon–hydrogen relative to those measured in pure argon) are plotted against the excitation energies of the lines, these intensity ratios increase with the excitation energy between approx. 3 and 5 eV for both elements studied. Furthermore, in the case of iron, several emission lines with the excitation energy between 5.3 and 5.6 eV are strongly enhanced in the presence of hydrogen. It has been also observed that this effect is more pronounced at lower currents. On the other hand, it has been found that nitrogen does not have any similar effect: the gradient of the intensity ratios of both elements is negligible or even negative and no emission lines are enhanced in the presence of nitrogen. A comparison was also made between direct current and radiofrequency powered glow discharges and very similar trends have been obtained. [ABSTRACT FROM AUTHOR]

NiFe hydrogenases are unique enzymes that catalyze the H+/H2 interconversion with remarkable efficiency. The determination of the tridimensional structure of their active site (a sulfur-rich dinuclear nickel–iron cluster with diatomic cyanide and carbonyl ligands) has stimulated the synthesis of a variety of nickel-based complexes as potential electrocatalysts for hydrogen production. These catalysts may provide an adequate alternative to platinum. This paper gives an historical perspective of this biomimetic structural approach and then focusses on recently reported bio-inspired functional mimics displaying electrocatalytic activity for hydrogen production. [ABSTRACT FROM AUTHOR]

For the hydrogen transfer of phenalene, a bimolecular ene-like mechanism is proposed, which is preferable over the hypothesized unimolecular rearrangement in the literature. Unique SOMO–SOMO π-bonding of phenalenyl reduces the barriers of pericyclic reactions significantly. π-bonding between radicals is being recognized as a novel type of bonding interaction. This paper adds to the use of this interaction by pointing out its effect on reaction barriers. [ABSTRACT FROM AUTHOR]

The 1-methylallyl radical loses a hydrogen atom following photoexcitation to its lowest valence electronically excited state and displays statistical behavior in decomposition, implying that the presence of methyl rotors cannot be depended upon as an indicator for non-statistical dissociation dynamics in hydrocarbon radicals. [ABSTRACT FROM AUTHOR]

We demonstrate a lamellar NiMoCo@CuS catalyst, showing not only an excellent catalyst performance (η100@72 mV and a Tafel slope of 47 mV dec−1), but also a good stability (20 mA cm−2@30 hours), outperforming the NiMo system and noble Pt. [ABSTRACT FROM AUTHOR]

Correction for 'Mo-Doped/Ni-supported ZnIn2S4-wrapped NiMoO4 S-scheme heterojunction photocatalytic reforming of lignin into hydrogen' by Hang Su et al., Green Chem., 2022, DOI: 10.1039/d1gc04397h. [ABSTRACT FROM AUTHOR]