Aluminum-silicon hydride clusters for prospective hydrogen storage

The structures and bonding properties of Al₄Si₂H_2n (n = 0–10) clusters are systematically studied by using the evolutionary algorithm combined with ab initio computations. While the H atoms are bond on the terminal sites of the clusters at low H contents, the Al atoms are combined together by double H-bridges and the Al/Si atoms are tetrahedrally coordinated at high H contents. The Al₄Si₂H_2n clusters break into a few fragments for n = 9,10. Analysis on the bonding natures shows that the Al–H bonds are strongly polarized and the Si atoms balance the charge states of the Al/H atoms according to the hydrogen concentrations. The hydrogen storage capacity in Al₄Si₂H₁₆ cluster reaches 8.9 wt%, and the estimated strength of the hydrogen bonding is about −0.55 eV per H₂, which falls in the ideal window for reversible hydrogen storage at ambient temperatures. The high hydrogen capacity and moderate bonding strength suggest that Al–Si hydrides can be promising candidates for hydrogen storage.     

Hydrogen generation from the reaction of Al pretreated in acidic or alkaline solution and water

Al and Al₂O₃ film react with strong acid or alkaline solution, bring the extensive corrosion. To decrease the corrosion, Al is first pretreated with a small amount of HCl, NaOH, NaAlO₂ and a mixture of NaAlO₂+Al(OH)₃ in this work. Al pretreatment allows for the rapid removal of oxide film, shortens the induction time and ensures the initial Al–H₂O reaction rate. Typically, immersion of the pretreated Al by a mixture of NaAlO₂+Al(OH)₃ into water, generates hydrogen rapidly without an induction time, and the average H₂ generation rate reaches 5.5 mL min⁻¹. As the Al–H₂O reaction proceeds, the potential changes, which is similar to hydrogen evolution of pretreated Al in water. Hydrogen generated rapidly with the consecutive addition of Al, and the initial hydrogen generation rate reaches ~37 mL min⁻¹. Therefore, Al pretreatment by a mixed alkaline solution is an effective method to accelerate hydrogen generation for the first cycle. Rapid and consecutive hydrogen generation by the Al–H₂O reaction could provide on-demand and high-purity hydrogen, meet some equipment requirements and promote the competition in renewable-energy sources.     

Cocatalyst free nickel sulphide nanostructure for enhanced photocatalytic hydrogen evolution

Metal chalcogenides are highly active, inexpensive, and earth-abundant materials for photocatalytic hydrogen evolution. This work presents cocatalyst-free Nickel Sulphides (α and β phases) nanostructures for photocatalytic hydrogen generation. NiS nanostructures are synthesized by the solvothermal method by varying the water to ethanol ratio. The synthesized sample has shown an optical bandgap of 1.83 eV, which is favorable for H₂ generation. X-ray diffractometer (XRD) patterns confirm the formation of hexagonal and rhombohedral crystal structures with high phase purity for both NiS-α and NiS-β nanostructures. The multifaceted regular-shaped morphology with 50 nm sized particles was confirmed by high-resolution transmission electron microscopy (HR-TEM). The photocatalytic H₂ generation studies reveal that the NiS-α phase exhibited better H₂ generation activity of 13.413 m mol h^?1g^?1 than the NiS-β phase of 12.713 m mol h^?1g^?1 under UV–Vis light irradiation without any cocatalyst.     

Synergistically modulating the electronic structure of Cr-doped FeNi LDH nanoarrays by O-vacancy and coupling of MXene for enhanced oxygen evolution reaction

Water splitting is an environmentally friendly method of hydrogen generation. However, it is severely limited by the slow anodic oxygen evolution reaction (OER). Iron-nickel layered double hydroxides (FeNi LDH) are promising electrocatalysts for OER, but their intrinsically low electrical conductivity and activity limit the practical applications. Herein, chromium-doped FeNi LDH nanoarrays in situ vertically grown on the surface of the Ti₃C₂T_x MXene (Cr-FeNi LDH/MXene) are successfully synthesized. Remarkably, the robust interaction and electrical coupling between Cr–FeNi LDH and MXene, as well as conspicuous charge transfer and the oxygen vacancies optimizing the adsorption free energy of intermediates, equip the nanocomposites with brilliant catalytic activity and stability toward OER. Thus, the optimized Cr–FeNi LDH/MXene shows a considerable boost in the OER, which affords low overpotential (232 mV at 10 mA cm^?2) and excellent durability. This work offers a new path to designing highly efficient and earth-abundant catalysts for water splitting and beyond.     

Cd0.5Zn0.5S/Ni2P noble-metal-free photocatalyst for high-efficient photocatalytic hydrogen production: Ni2P boosting separation of photocarriers

Establishing efficient co-catalytic loaded semiconductors for efficient charge separation is a hopeful way for enhance photocatalytic water splitting hydrogen evolution. Herein, we successfully constructed the Cd_0.5Zn_0.5S/Ni₂P (CZS/Ni₂P) nanocomposites via two-step hydrothermal method. The CZS/Ni₂P composites show much improved activity than the origin CZS for photocatalytic H₂ generation. When the content of Ni₂P loaded on the Cd_0.5Zn_0.5S (CZS) is 0.3 mol%, the photocatalyst achieves the highest photocatalytic hydrogen generation rate of 41.26 mmol g⁻¹ h⁻¹ under visible light. The Ni–S bonds on the close contact interface between CZS and Ni₂P can be act as electron-bridge to provide a channel for electron transfer. During the photocatalysis processing, Ni₂P can be used as electron traps to attract electrons from CZS, resulting in the improvement of the photocatalytic performance.     

Photo-assisted electrolysis of urea using Ni-modified WO3/g-C3N4 as a bifunctional catalyst

Urea splitting to produce H₂ is as an energy-saving alternative to water electrolysis. However, efficient catalysts are required for the practical implementation of urea splitting because of the high overpotentials of the urea oxidation reaction and the hydrogen evolution reaction. Herein, a Ni-modified direct Z-scheme photocatalyst for the urea oxidation and hydrogen evolution reactions was synthesized by electroplating a WO₃/g-C₃N₄ nanocomposite on Ni-decorated carbon felt (WO/CN–Ni@CF). The 2D/2D nanostructure of the as-synthesized WO₃/g-C₃N₄ composite was confirmed by SEM and TEM. The WO/CN–Ni@CF catalyst electrode exhibited excellent bifunctional photocatalytic activity for the urea oxidation and hydrogen evolution reactions. Consequently, the potential required to generate 100 mA cm^?2 in an illuminated photoelectrochemical cell using WO/CN–Ni@CF as the anode and the cathode was reduced from 1.80 to 1.50 V. The photoelectrochemical cell exhibited good stability for 18 h with stable H₂ generation.     

Enhanced photocatalytic activity in water splitting for hydrogen generation by using TiO2 coated carbon fiber with high reusability

In this study, TiO₂ coated carbon fiber (TiO₂@CF) was synthesized and used for the improvement of hydrogen (H₂) evolution. Obtained results from scanning electron microscopy (SEM), X-ray diffraction (XRD), gas adsorption analysis (BET), UV–vis diffuse (UV–vis), and X-ray photoelectron spectroscopy (XPS) confirmed that the surface area and light absorption of the material was significantly improved. The synthesized TiO₂@CF photocatalyst exhibited improved photocatalytic performance toward hydrogen generation. The enhancement of photocatalytic H₂ evolution capacity by TiO₂@CF was ascribed to its narrowed bandgap energy (2.76eV) and minimized recombination of photogenerated electron-hole pairs The hydrogen production rate by the TiO₂@CF reached 3.238 mmolg^?1h^?1, which was 4.8 times higher than unmodified TiO₂ (0.674 mmolg^?1h^?1). The synthesized TiO₂@CF was relatively stable with no distinct reduction in photocatalytic activity after five recycling runs. The photoluminescence and photocurrent were employed to support the photocatalytic H₂ production mechanism proposed mechanism.Based on these results, TiO₂@CF with unique properties, easy handle, and high reusability could be suggested as an efficient strategy to develop a high-performance photocatalyst for H₂ production.     

Nickel doped MoS2 nanoparticles as precious-metal free bifunctional electrocatalysts for glucose assisted electrolytic H2 generation

Hydrogen, as the one of clean energy source, has the advantages of high energy density and carbon-free emission. Water electrolysis is one of the most promising ways to generate hydrogen, but the rather high energy required seriously hinders its widespread applications yet. In this study, we report an alkaline electrolyzer to implement energy-saving H₂ generation by coupling cathodic hydrogen evolution reaction (HER) with anodic glucose oxidation reaction (GOR) other than oxygen evolution reaction, in which nickel-doped MoS₂ nanoparticles (Ni–MoS₂ NPs) has been developed as bifunctional electrocatalyst for HER and GOR. The electrolyzer only requires a cell voltage of 1.67 V to reach an electrolysis current density of 10 mA cm⁻², about 270 mV lower than the corresponding value in the traditional electrolyzer. Electrolytic H₂ generation with the assistance of biomass derived materials may open a new way for the future sustainable development.     

Bimetallic PtNi alloy modified 2D g-C3N4 nanosheets as an efficient cocatalyst for enhancing photocatalytic hydrogen evolution

Platinum-based alloy materials as effective cocatalysts in improving the performance of photocatalytic H₂ production have raised great interest. Herein, a facile strategy of chemical reduction is established to synthesize bimetallic PtNi nanoparticles on 2D g-C₃N₄ nanosheets with excellent photocatalytic activity. The addition of PtNi nanoparticles can provide new H⁺ reduction sites and increase more active sites of the material. The synergistic effect between PtNi alloy nanoparticles and 2D g-C₃N₄ nanosheets can regulate electronic structure, narrow the band, accelerate charge transfer efficiency and inhabit the recombination of photo-induced electron (e⁻) and hole pairs (h⁺), contributing to the improvement of hydrogen evolution activity. The optimal hydrogen evolution rate of Pt_0.6Ni_0.4/CN shows higher hydrogen evolution rate (9528 μmol·g⁻¹·h⁻¹), which is 13.1 times than that of pure g-C₃N₄ nanosheets. Besides, a possible mechanism of photocatalytic hydrogen generation has been brought up according to a series of physical and chemical characterization. This work also provides a potential idea of developing cocatalysts integrating metal alloys with 2D g-C₃N₄ nanosheets for promoting photocatalytic hydrogen evolution.     

Co3O4–C@FeMoP on nickel foam as bifunctional electrocatalytic electrode for high-performance alkaline water splitting

Exploring low-cost, highly efficient, and sustainable non-precious electrocatalysts for electrolytic H₂ generation is driving research for the sustainable green urban development. Herein, we present a simple synthetic approach, through a two-step process, to prepare the bifunctional electrode of Co₃O₄–C@FeMoP hybrid micro rods/nanosheets anchored on nickel foam (NF), in which the Co₃O₄–C microrods grown on NF surface are decorated by FeMoP nanosheet layers, which is directly grown through a simple hydrothermal followed by post-phosphorization processes. The obtained hybrid hierarchical Co₃O₄–C@FeMoP/NF shows a significant enhancement in the electrocatalytic activities of oxygen/hydrogen evolution reactions (OER/HER) in comparison to the individual Co₃O₄–C and FeMoP nanostructures, thanks to more heterointerface active sites provided by FeMoP nanostructures with three-dimensional (3-D) layered architectures. The Co₃O₄–C@FeMoP/NF catalyst exhibits a relatively small overpotential of 200 mV vs. RHE for OER to achieve 20 mA/cm² and 123 mV vs RHE at 10 mA/cm² for HER along with excellent durability in alkaline electrolytes. We demonstrate the bifunctional electrocatalytic electrode as the electrolyzer for the generation of H₂ via water splitting at small applied voltage of 1.61 V to achieve 10 mA/cm² and good stability for 24-h continuous running.     

Superior hydrogen generation from sodium borohydride hydrolysis catalyzed by the bimetallic Co–Ru/C nanocomposite

Sodium borohydride has been widely regarded as a promising hydrogen carrier owing to its greatly hydrogen storing capability (10.8 wt%), high weight density and excellent stability in alkaline solutions. Herein, we first design and synthesize a series of bimetallic M-Ru/C nanocomposites (including Fe–Ru/C, Co–Ru/C, Ni–Ru/C and Cu–Ru/C), via simply alloying of commercial Ru/C with nonprecious metal, for superior H₂ evolution from the NaBH₄ hydrolysis. The result exhibits that H₂ generation is synergetically improved by alloying Ru/C with Co or Ni, while it is hindered by alloying Ru/C with Fe or Cu. Indeed, Co–Ru/C presents the highest efficient catalytic activity for H₂ generation, with the TOF of 117.69 mol(H₂)·mol_Ru^?1·min^?1, whereas Ru/C is only 57.08 mol(H₂)·mol_Ru^?1·min^?1. In addition, the TOF of Co–Ru/C reaches to 436.51 mol(H₂)·mol_Ru^?1·min^?1 (96.7 L(H₂)·g_Ru^?1·min^?1) in the presence of NaOH.     

Facile fabrication of silicon nanowires as photocathode for visible-light induced photoelectrochemical water splitting

We report the fabrication of one dimensional Silicon nanowires (Si NWs) using p-Si (100) substrate through facile two step metal assisted chemical etching (MACE) approach. The evolution of structural and optical properties of Si NWs by etching Si substrate was studied as a function of hydrogen peroxide (H₂O₂), a strong oxidation agent. The length of the NWs increased linearly with the H₂O₂ concentrations and reached maximum of 51 μm for etching of 60 min. The merits of metal free Si NWs as photocathode in the photoelectrochemical (PEC) neutral water splitting under the visible light was investigated. The performance of the photocathode highly depends on the morphology of Si nanostructure. A high density and well separated Si NWs fabricated by 0.6 M of H₂O₂ results in maximum photocurrent density of 6 mA cm^?2 with applied bias photocurrent conversion (ABPE) efficiency of 1.1% under visible light illumination.     

Noble-metal-free Co@Co2P/N-doped carbon nanotube polyhedron as an efficient catalyst for hydrogen generation from ammonia borane

Developing an efficient catalyst for hydrogen (H₂) generation from hydrolysis of ammonia borane (AB) to significantly improve the activity for the hydrogen generation from AB is important for its practical application. Herein, we report a novel hybrid nanostructure composed of uniformly dispersed Co@Co₂P core-shell nanoparticles (NPs) embedded in N-doped carbon nanotube polyhedron (Co@Co₂P/N–CNP) through a carbonization-phosphidation strategy derived from ZIF-67. Benefiting from the electronic effect of P doping, high dispersibility and strong interfacial interaction between Co@Co₂P and N-CNTs, the Co@Co₂P/N–CNP catalyst exhibits excellent catalytic performance towards the hydrolysis of AB for hydrogen generation, affording a high TOF value of 18.4 mol H₂ mol metal^?1 min^?1 at the first cycle. This work provides a promising lead for the design of efficient heterogeneous catalysts towards convenient H₂ generation from hydrogen-rich substrates in the close future.     

Fabricating NixCo1−xO@C cocatalysts sensitized by CdS through electrostatic interaction for efficient photocatalytic H2 evolution

Exploiting efficient and stable noble metal-free hydrogen evolution catalysts for water splitting is of great importance. In this work, Ni_xCo_1-xO@C/CdS hybrid is successfully fabricated through an electrostatic interaction of oppositely charged nanoparticles on their surfaces. The resulting Ni_xCo_1-xO@C nanoboxes cocatalysts which were derived from NiCo-LDH@ZIF-67 with Ni–Co layered double hydroxides (LDH) decorated with ZIF-67 precursor exhibited improved hydrogen production rate compared with bare CdS semiconductor from 0.7 mmol g⁻¹ h⁻¹ to 56 mmol g⁻¹ h⁻¹. It is demonstrated that the electrostatic interaction between the two surface charged nanoparticles of Ni_xCo_1-xO@C and CdS play an important role in migrating and separating of photogenerated charge carriers. The synthesized Ni_xCo_1-xO@C as excellent candidates for cost-effective cocatalysts is aimed to substitute for noble metals in photocatalytic H₂ evolution.     

Synergistic enhancement of photocatalytic H2 production by Ni decorated 2D bubble-like carbon nitride

In this paper, a novel 2D bubble-like g-C₃N₄ (B–CN) with a highly porous and crosslinked structure is successfully synthesized via a cost-effective bottom-up process. The as-prepared B–CN photocatalyst delivers a considerably expanded specific surface area and increased active sites. Moreover, the 2D bubble-like structure can afford shortened diffusion paths for both photogenerated charge carriers and reactants. As a result, the photocatalytic H₂ evolution rate of B–CN reached 268.9 μmol g^?1 h^?1, over 5 times more than that of bulk C₃N₄. The Ni ions were further deposited on B–CN as a cocatalyst to enhance the photocatalytic activity. Benefit from the synergy of 2D bubble-like structure and Ni species cocatalyst, recombination of photoinduced charges was greatly inhibited and the hydrogen evolution reaction (HER) was significantly accelerated. The resulted catalyst achieved a dramatically high H₂ evolution rate of 1291 μmol g^?1 h^?1. This work provides an alternative way to synthesize novel porous carbon nitride together with non-noble metal cocatalysts toward enhanced photocatalytic activity for H₂ production.     

Oxygen vacancy-engaged interfacial charge transfer modulation for upgrade Rh-catalyzed hydrogen and oxygen productions

Developing efficient modulation strategies to upgrade the catalytic activity and reusability of Rh-catalyzed hydrogen evolution from ammonia borane (AB) hydrolysis are definitely profitable but remains a grand challenge. Here, we develop a stepwise activation strategy to produce highly active and reusable Rh/CoFe₂O₄-SB-H₂ with abundant oxygen vacancies and strong electronic metal-support interaction through stepwise reduction of Rh/CoFe₂O₄ precursor using sodium borohydride and H₂ as the reducing agents. Under ultrasonic irradiation, Rh/CoFe₂O₄-SB-H₂ with an ultralow Rh loading of 0.20 wt% can be utilized as an excellent catalyst for hydrogen production from room-temperature AB hydrolysis with a high turnover frequency (TOF) of 1894 min⁻¹. The TOF value could be further promoted to 15,570 min⁻¹ in the alkaline ultrasonic environment. The catalyst has a superior reusability with 75% maintaining activity of initial one in the 10^th cycle. The strong electronic metal-support interaction, rich oxygen vacancies and ultrasound irradiation promote the oxidative cleavage of the O–H bonds in attracted H₂O and thus account for high performance toward hydrogen production from AB. This catalyst can also be utilized as an active catalyst for oxygen generation from H₂O₂ decomposition. The developed strategies can be applied to upgrade the performance of other reducible metal oxides supported metal catalysts toward catalytic applications.     

Ni3Mo3N coupled with nitrogen-rich carbon microspheres as an efficient hydrogen evolution reaction catalyst and electrochemical sensor for H2O2 detection

Hydrogen evolution reaction (HER) and electrochemical analysis are two important fields of electrochemical research at present. We found that both HER and some electrochemical analytical reactions relied on the concentration of hydrogen ions (H⁺) in solution, so we intended to develop an electrode material that is sensitive to H⁺ and can be used for both HER and some electrochemical analyses. In this work, we synthesized Ni₃Mo₃N coupled with nitrogen-rich carbon microspheres (Ni₃Mo₃N@NC MSs) as highly efficient electrode material for HER and detection of Hydrogen peroxide (H₂O₂), which plays an important role in physiological processes. Here the aniline was used as the nitrogen and carbon sources to synthesize Ni₃Mo₃N@NC. The Ni₃Mo₃N@NC MSs showed high performance for HER in 1 M KOH solution with a small overpotential of 51 mV at 10 mA cm^?2 and superior stability. For H₂O₂ detection, a detection limit of 1 μM (S/N = 3), sensitivity of 120.3 μA·mM^?1 cm^?2 and linear range of 5 μM–40 mM can be achieved, respectively. This work will open up a low-cost and easy avenue to synthesize transition metal nitrides coupled with N-doped carbon as bifunctional electrode material for HER and electrochemical detection.     

High catalytic kinetic performance of amorphous CoPt NPs induced on CeOx for H2 generation from hydrous hydrazine

CeO_x-induced amorphization of CoPt nanoparticles (NPs) is achieved by a facile co-reduction method using sodium borohydride (NaBH₄) as the reducing agent at room temperature (298 K) under ambient atmosphere. The investigation results indicate that CeO_x plays a critical role in transferring the crystalline CoPt nanoalloy into the amorphous one. To our surprise, the resultant Co_0.65Pt_0.30(CeO_x)_0.05 NPs exhibit high catalytic kinetic performance with 72.1% hydrogen (H₂) selectivity for the H₂ generation from hydrous hydrazine (N₂H₄) within only a few minute at 298 K. Although complete conversion is not achieved, but the initial turnover frequency value of 194.8 h⁻¹ for the present amorphous catalyst is much higher than that of crystalline one. Moreover, such a highly rapid catalyst may greatly encourage the practical application of hydrous N₂H₄ as a hydrogen storage material.     

Efficient interfacial charge transfer of 2D/2D CoP/CdS heterojunction for extremely boosted photocatalytic H2 evolution performance

Constructing 2D/2D heterojunction photocatalysts has attracted great attentions due to their inherent advantages such as larger interfacial contact areas, short transfer distance of charges and abundant reaction active sites. Herein, 2D/2D CoP/CdS heterojunctions were successfully fabricated and employed in photocatalytic H₂ evolution using lactic acid as sacrificial reagents. The multiple characteristic techniques were adopted to investigate the crystalline phases, morphologies, optical properties and textual structures of heterojunctions. It was found that integrating 2D CoP nanosheets as cocatalysts with 2D CdS nanosheets by Co–S chemical bonds would significantly boost the photocatalytic H₂ evolution performances, and the 7 wt% 2D/2D CoP/CdS heterojunction possessed the maximal H₂ evolution rate of 92.54 mmol g^?1 h^?1, approximately 31 times higher than that of bare 2D CdS nanosheets. Photoelectrochemical, steady photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements indicated that there existed an effective charge separation and migration over 2D/2D CoP/CdS heterojunction, which then markedly lengthened the photoinduced electrons average lifetimes, retarded the recombination of charge carriers, and caused the dramatically boosted photocatalytic H₂ evolution activity. Moreover, the density functional theory (DFT) calculation further corroborated that the efficient charge transfer occurred at the interfaces of CoP/CdS heterojunction. This present research puts forward a promising strategy to engineer the 2D/2D heterojunction photocatalysts endowed with an appealing photocatalytic H₂ evolution performance.     

Facile synthesis of CeO2/g-C3N4 nanocomposites with significantly improved visible-light photocatalytic activity for hydrogen evolution

Ceria dioxide supported on graphitic carbon nitride (CeO₂/g-C₃N₄) composites were facilely synthesized to be application for photocatalytic hydrogen (H₂) generation in this present work. The physical and chemical properties of CeO₂/g-C₃N₄ nanocomposites were determined via a series of characterizations. The CeO₂/g-C₃N₄ composites prepared by facile thermal annealing and rotation-evaporation method exhibit excellent photocatalytic H₂ evolution with visible-light illumination. The best hydrogen generation rate of CeO₂/g-C₃N₄ composite with 1.5 wt% Pt is 0.83 mmol h⁻¹ g⁻¹, which is almost same as that of composite with 3 wt% Pt prepared by simple physical mixing method. The significantly developed photocatalytic activity of CeO₂/g-C₃N₄ composite is majorly ascribed to the stronger interfacial effects with the more visible-light absorbance and faster electron transfer. This work reveals that construction of the CeO₂/g-C₃N₄ composite with high disperse and close knit by the facile thermal annealing and rotation-evaporation method could be an effective method to achieve excellent photocatalytic hydrogen evolution performance.