Facile synthesis and electrochemical hydrogen storage of bentonite/TiO2/Au nanocomposite

In this study, the electrochemical hydrogen storage of bentonite composites containing TiO₂ and Au nanoparticles (NPs) has been investigated by cyclic voltammetry (CV) analysis. TiO₂ NPs were first deposited on the bentonite substrate by reflux technique. Au NPs were then prepared by laser ablation in liquid (LAL) method under different laser irradiation times (6, 12, and 18 min), and utilized in the decoration of bentonite/TiO₂ nanocomposite by physical mixing. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and elemental mapping were carried out in the characterization of the prepared bentonite/TiO₂/Au nanocomposite. The surface and chemical properties of the acquired nanocomposite were analyzed by Brunauer-Emmett-Teller and Fourier transform infrared spectroscopy, respectively. Electrochemical measurement was performed on stainless steel mesh prefabricated electrodes in 1 M KOH electrolyte solution. The B-T/Au nanocomposite prepared under 12 min laser irradiation displayed the highest hydrogen storage capacity (15 Cg^-1).     

Facile synthesis of well dispersed Pd nanoparticles on reduced graphene oxide for electrocatalytic oxidation of formic acid

In present study, we report a facile synthesis of crystalline, small size Pd nanoparticles (NPs) on reduced graphene oxide (RGO) abbreviated as Pd/RGO for electrocatalytic oxidation of formic acid (FA). Here, first graphene oxide (GO) was reduced by the green method using l-ascorbic acid and citric acid and further Pd NPs were decorated on RGO by a facile method without using any reducing agents. The reduction of GO to RGO and synthesis of Pd NPs was confirmed by the X-ray diffraction (XRD) and X-ray photoelectrons (XPS) techniques. Surface morphology of Pd/RGO nanocomposite was evaluated by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The electrocatalytic behavior of Pd/RGO nanocomposite was tested by using of cyclic voltammetric (CV) technique for electro-oxidation of FA in mixed solution of 0.5 M HCOOH + 0.5 H₂SO₄ at RT. Results shows that the higher electrocatalytic activity of Pd/RGO nanocomposite compare to Pd NPs.     

Pd/NiO core/shell nanoparticles on La0.02Na0.98TaO3 catalyst for hydrogen evolution from water and aqueous methanol solution

Novel Pd/NiO core/shell nanoparticles (NPs) have been synthesized by a simple impregnation method with low temperature processing, in a ‘green’, scalable process using nontoxic chemicals. The cocatalyst consisting of a Pd core and a NiO shell formed simultaneously on the surface of La-doped NaTaO₃ photocatalyst. The Pd core both induces migration of photogenerated electrons from the bulk of the La_0.02Na_0.98TaO₃ and transfers electrons to the NiO shell. Without the NiO shell, Pd NPs show negligible H₂ production from water splitting, due to the rapid reaction between hydrogen and oxygen on the surface. On the other hand, the NiO shell allows the permeation of hydrogen and enables hydrogen reduction on Pd. The incorporation of NiO shell onto Pd remarkably enhances the photocatalytic performance of La-doped NaTaO₃ for hydrogen production from pure water. In addition, the core/shell structure can significantly enhance the stability of Pd during the photocatalytic reaction. Similar concepts could be extended to other applications, where the catalytic activity and stability are of concerns. The formation mechanism of the core/shell photocatalyst is proposed based on the high resolution transmission electron microscopy (HRTEM) images and X-ray absorption near-edge structure (XANES) analyses.     

Functionalization of TiO2 nanotubes with palladium nanoparticles for hydrogen sorption and storage

The use of hydrogen as an energy carrier is an attractive solution toward addressing global energy issues and reducing the effects of climate change. Design of new materials with high hydrogen sorption capacity and high stability is critical for hydrogen purification and storage. In this study, titanium dioxide nanotubes (TiO₂NTs) were modified with palladium nanoparticles (PdNPs) utilizing a facile photo-assisted chemical deposition approach. Electrochemical anodization was employed for the direct growth of TiO₂NTs. The PdNP functionalized TiO₂NTs (TiO₂NT/Pd) were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The hydrogen sorption behaviours and stability of the TiO₂NT/Pd nanocomposites were investigated and compared with nanoporous Pd networks that were deposited on a bulk titanium substrate (Ti/Pd) using cyclic voltammetry (CV) and chronoamperometry (CA). Our studies show that the TiO₂NT/Pd nanocomposites possess a much higher hydrogen storage capacity, faster kinetics for hydrogen sorption and desorption, and higher stability than the nanoporous Pd.     

Novel MoSe2–Ni(OH)2 nanocomposite as an electrocatalyst for high efficient hydrogen evolution reaction

Nowadays, there is a great demand for low-cost and highly active electrocatalyst for the production of clean renewable energy. However, most of the electrocatalysts are noble metal-based which are very costly and unstable. To counter this, electrochemical water splitting in energy storage systems is been widely applied, using non-noble metal-based nanostructured electrocatalysts. In this work, a novel noble metal-free MoSe₂–Ni(OH)₂ nanocomposite electrocatalyst is synthesized using a multi-step hydrothermal technique for efficient hydrogen evolution reaction (HER). The morphology, structural, chemical composition, and functional features of the synthesized nanomaterials were characterized using different techniques that include scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), and Raman analysis. The new developed MoSe₂–Ni(OH)₂ nanocomposite combines a high active surface area with a high chemical stability, generating a novel material with a synergistic effect that enhances water splitting process performance. Thus, an outstanding low Tafel slope of 54 mV dec⁻¹ is accomplished in the hydrogen evolution reaction.     

Hardystonite/palladium nanocomposite as a high performance catalyst for electrochemical hydrogen storage and Cr(VI) reduction

In this work, the catalytic performance of hardystonite/palladium nanocomposite (HT/Pd) for hydrogen evolution reaction (HER) and reduction of organic pollutants in water has been studied. For this purpose, palladium nanoparticles (Pd NPs) were synthesized by laser ablation in liquid (LAL) method in different concentrations and decorated on hardystonite substrate using a simple method. HT/Pd nanocomposite was characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET) analyses. The prepared nanocomposites were coated on a stainless steel mesh and their HER activity was investigated using cyclic voltammetry (CV). The results indicated that HT/Pd catalyst had good HER performance and capability of hydrogen storage. Moreover, HT/Pd nanocomposite with high surface area exhibited excellent catalytic activity in Cr(VI) reduction within 2.5 min.     

Bimetallic Pd–Bi nanocatalysts derived from NaBH4 reduction of BiOCl and Pd2+ and exhibit highly efficient hydrogen production over formaldehyde solution

Using liquid formaldehyde as a carrier to obtain clean hydrogen is a promising method. The development of inexpensive catalysts with high activity and stability is crucial for this reaction. Herein, bimetallic Pd–Bi nanocatalysts with different Pd to Bi ratios were prepared through one step in-situ reduction of BiOCl and Pd²⁺ ions by sodium borohydride (NaBH₄). The effect of Pd/Bi ratios and reaction parameters such as formaldehyde concentration and sodium hydroxide concentration on hydrogen production performance were systematically studied. By optimizing the Pd contents in Pd–Bi nanocatalysts under the optimized reaction conditions, an much higher hydrogen (H₂) production rate of 472.2 mL min^?1g^?1 over Pd/BiOCl-3% under 298.15 K can be achieved, which is 4.01 times that of pure Pd nanoparticles (NPs) and much higher than most reported metal-based catalysts.     

Transition metal nanoparticle catalysts in releasing hydrogen from the methanolysis of ammonia borane

Ammonia borane (H₃N·BH₃, AB) is one of the promising hydrogen storage materials due to high hydrogen storage capacity (19.6% wt), high stability in solid state as well as in solution and nontoxicity. The methanolysis of AB is an alternative way of releasing H₂ due to many advantages over the hydrolysis such as having high stability against self releasing hydrogen gas. Here we review the reports on using various noble or non-noble metal(0) catalysts for H₂ release from the methanolysis of AB. Ni(0), Pd(0), and Ru(0) nanoparticles (NPs), stabilized as colloidal dispersion in methanol, are highly active and long lived catalysts in the methanolysis of AB. The catalytic activity, lifetime and reusability of transition metal(0) NPs show significant improvement when supported on the surface of solid materials. The supported cobalt, nickel, copper, palladium, and ruthenium based catalysts are quite active in H₂ release from the methanolysis of AB. Rh(0) NPs are highly active catalysts in releasing H₂ from the methanolysis of AB when confined within the void spaces of zeolite or supported on oxide nanopowders such as nanosilica, nanohydroxyapatite, nanoalumina or nanoceria. The oxide supported Rh(0) NPs can provide high activity with turnover frequency values as high as 218 min⁻¹ and long lifetime with total turnover values up to 26,000 in generation of H₂ from the methanolysis of AB at 25 °C. When deposited on carbon the bimetallic AgPd alloy nanoparticles have the highest activity in releasing H₂ through the methanolysis of AB.     

Thermal decomposition synthesis,characterization and electrochemical hydrogen storage characteristics of Co3O4–CeO2 porous nanocomposite

Particle-like Co₃O₄–CeO₂ nanocomposite was synthesized via a facile thermal decomposition process in the presence of fructose as a green capping agent and ammonium cerium(IV) nitrate as Ce source. The effect of various parameters such as different cobalt sources, calcination temperature and time were investigated on the size and morphology of products. The transmission electron microscopy observations indicated that the synthesized products have a particle-like shape with an average diameter of 18–35 nm. For the first time, the electrochemical hydrogen storage performance of Co₃O₄–CeO₂ porous nanocomposite was investigated via chronopotentiometry method in aqueous KOH solution in this paper. The electrochemical measurements showed that this product has a good hydrogen storage capacity at room temperature. Its maximum discharge capacity was 5200 mAh/g after 20 cycles. Therefore, Co₃O₄–CeO₂ porous nanocomposite showed that it is a good candidate for electrochemical hydrogen storage.     

Hydrogen generation via the catalytic hydrolysis of morpholine-borane: A new,efficient and cost-effective hydrogen storage medium

Herein, for the first time, we introduce the morpholine-borane complex (MB) as a new, efficient, cost-effective and commercially available chemical hydrogen storage material for mobile applications. In this regard, hydrogen production from the hydrolysis of MB catalyzed by in situ generated water-soluble polymer stabilized Ag(0) and Pd(0) nanoparticles (NPs) is reported for the first time. In situ generated PSMA-stabilized Ag(0) and Pd(0) NPs showed remarkable activity in hydrogen production from the hydrolysis of MB at room temperature, providing initial TOFs of 16.1 min⁻¹ and 37.3 min⁻¹, respectively. A set of kinetic studies on the catalytic hydrolysis of MB were conducted by changing the catalyst/substrate amount and temperature, and the rate law expression and activation parameters were produced by collecting the kinetic data. The apparent activation energies for the in situ generated Ag(0) and Pd(0) NPs catalyzed MB hydrolysis were calculated to be 71.4 and 32.5 kJ mol⁻¹, respectively.     

Study of the synthesis of PMMA-Mg nanocomposite for hydrogen storage application

The nano metallic-based material has received the particular attention of scientists in H₂ storage. Herein, an efficient air-stable nano metallic magnesium (Mg)-Polymethyl methacrylate (PMMA) system, in which methyl magnesium chloride (MeMgCl) as organic Mg precursor is in-situ reduced to metallic Mg particles (Mg NPs) by lithium naphthalene (Li-naphthalene) in soluble PMMA/THF system, exhibits an excellent H₂ storage performance and do not require harsh operation condition. In order to form well-distributed Mg NPs (co. 5 nm) in PMMA gel framework, it is an important procedure to mix Mg ion and Li-naphthalene completely, as well the restriction effect of polymer molecular chain. The synthesized mechanism of nanocomposite and the optimal reaction conditions were ascertained by designing a series of experiments. Notably, PMMA can not confined the size of metallic Mg by blending method, and the mixed β/γ-Mg presents nearly no ability to adsorb hydrogen. Here, the air stable Mg NPs is in-situ reduced in PMMA can be reacted with H₂, and O₂ and H₂O molecules can not be infiltrated into PMMA. The correlation between the size of Mg NPs, the amount of PMMA and hydrogen storage performance for the PMMA-Mg NPs composite (PMC) is studied. We have found that hydrogen storage capacity of PMC could be enhanced as decreasing the size of Mg NPs by adjusting the amount of PMMA. The Mg NPs in PMMA might release the higher amount of H₂ at below 300 °C with a rapid absorption/desorption kinetics than the reported material in literature. The obtained nanocomposite are able to deliver dense hydrogen in demanding environments.     

Hydrogen storage performance of lithium borohydride decorated activated hexagonal boron nitride nanocomposite for fuel cell applications

A safe and cost effective material for hydrogen storage is indispensable for developing hydrogen fuel cell technology to reach its greater heights. The present work deals with hydrogen storage performance of lithium borohydride decorated activated hexagonal boron nitride (LiBH₄@Ah-BN) nanocomposite. where a facile chemical impregnation method was adopted for the preparation of LiBH₄@Ah-BN nanocomposite. The prepared nanocomposite was subjected to various characterization techniques such as X-ray Diffraction (XRD), Micro-Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDX), Brunauer–Emmett–Teller (BET) Studies, CHNS-Elemental Analysis and Thermo Gravimetric Analysis (TGA). From BET studies, it is confirmed that, there is an enhancement in the specific surface area of LiBH₄@Ah-BN nanocomposite (122 m²/g) compared to Ah-BN (70 m²/g). The hydrogen storage ability was examined using a Sieverts-like hydrogenation setup. An excellent hydrogen storage capacity of 2.3 wt% at 100 °C was noticed for LiBH₄@Ah-BN nanocomposite. The TGA study indicates the dehydrogenation profile of stored hydrogen in the range of 110–150 °C. The binding energy of stored hydrogen (0.31 eV) lies in recommended range of US-DOE 2020 targets for fuel cell applications. The present investigation demonstrates the preparation of LiBH₄@Ah-BN nanocomposite based hydrogen storage medium which has remarkable cycling stability and hydrogen storage capacity. Hence these desirable traits make LiBH₄@Ah-BN nanocomposite as a potential hydrogen storage candidate for fuel cell applications in near future.     

Nano-structured palladium impregnate graphitic carbon nitride composite for efficient hydrogen gas sensing

Nanoparticles of palladium (Pd) were incorporated into graphitic carbon nitride (g-C₃N₄) matrix with a view to improving hydrogen sensing efficiency of g-C₃N₄, by a fairly new chemical process that uses ammonium tetrachloropalladate as a Pd metal nanoparticle source along with an appropriate reducing agent. Researchers have explored g-C₃N₄ for various applications such as a catalyst for water splitting, photoluminescence, storage because of its relatively low cost, easy synthesis, and ready availability. For the synthesis of g-C₃N₄, urea was used as a precursor at 550 °C and at atmospheric pressure under a muffle furnace without add-on support. The final solution of the Pd/g-C₃N₄ nanocomposite was then centrifuged and dried for use as a hydrogen-sensing material. g-C₃N₄ and Pd/g-C₃N₄ were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV-VIS-NIR spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and energy dispersive X-ray spectroscopy (EDS). Pd-dispersed graphitic carbon nitride film was deposited on an inter digited carbon electrode by using a screen printing technique. From the qualitative analysis by I–V measurement, a significant change in the resistance was observed during the presence and absence of the hydrogen gas. The results show Pd/g-C₃N₄ nanocomposite as an efficient hydrogen sensing material.     

Mo-chelate strategy for synthesizing ultrasmall Mo2C nanoparticles embedded in carbon nanosheets for efficient hydrogen evolution

Production of hydrogen from electrochemical water splitting has been regarded as one of the most economic and sustainable techniques for green fuel production. It is significant and challengeable to develop highly efficient and low cost noble metal-free electrocatalysts. Presently, molybdenum-based electrocatalysts were regarded as potential alternatives for the hydrogen evolution reaction (HER). Here, the well-dispersed and ultrasmall Mo₂C nanoparticles (NPs) anchored on 2D carbon nanosheets were synthesized by designing chelate precursor and following pyrolysis, which was proved to be an effective approach for preparing carbon-loaded Mo₂C NPs. The as-obtained Mo₂C/C material exhibits an outstanding activity and stability in hydrogen evolution reaction (HER). It needs an overpotential of 147 mV to drive 10 mA cm⁻² and Tafel slope is 64.2 mV dec⁻¹ in alkaline medium, implying that Mo₂C/C material will be a potential noble metal-free electrocatalyst for HER. The design of Mo-chelate precursor is a feasible route to synthesize ultrafine Mo₂C and it can provide a reference for synthesizing other nanoparticles and hindering particle coalescence at high preparation temperature.     

Electrocatalytic performances of oxygen-deficient titanium dioxide nanosheet coupled palladium nanoparticles for oxygen reduction and hydrogen evolution reactions

The development of multifunctional electrocatalysts is crucial for enhancing the efficiency of electrochemical conversion in energy devices. Here we have synthesized TiO_2-x nanosheets (NSs) supported metallic Pd nanoparticles (Pd/TiO_2-x NSs) as an electrocatalyst using a simple impregnation process. High electrochemical surface areas (ECSAs) and strong metal support interactions (SMSI) of the electrocatalyst showed improved ORR performance throughout a wide pH range under ambient conditions. The outstanding durability of the catalyst was proven by the square-wave potential cycling experiment at 60 °C. Additionally, it was shown that Pd/TiO_2-x NSs showed improved HER activity and stability in 0.5 M H₂SO₄. The catalyst had an overpotential of 19.5 mV for the 10 mA cm⁻² and a low Tafel slope of 41 mV dec⁻¹. The catalyst also showed higher stability for about 30 h in HER performance. This work will help in rationally building nanostructured electrocatalysts loaded on carbon-free support for efficient electrochemical energy storage devices.     

Recoverable Ni2Al3 nanoparticles and their catalytic effects on Mg-based nanocomposite during hydrogen absorption and desorption cycling

The Mg-3.9 wt% Ni₂Al₃ nanocomposite is produced by hydrogen plasma-metal reaction method. The particle size of Mg is in range of 40–160 nm with an average size of 90 nm. The Ni₂Al₃ nanoparticles (NPs) of about 9 nm uniformly disperse on the surface of Mg NPs and in situ transform to Mg₂NiH_0.3 and Al after hydrogen absorption process. Surprisingly, the Mg₂NiH_0.3 and Al can recover to the initial state of Ni₂Al₃ after hydrogenation/dehydrogenation cycle. The Mg-Ni₂Al₃ nanocomposite shows enhanced hydrogen sorption rate and storage capacity. It can quickly uptake 6.4 wt% H₂ within only 10 min at 573 K, and release 6.1 wt% H₂ within 10 min at 623 K. The apparent activation energies for hydrogenation and dehydrogenation are calculated to be 55.4 and 115.7 kJ mol^?1 H₂. The enhanced hydrogen storage performances of the Mg-Ni₂Al₃ nanocomposite are attributed to both the nanostructure of Mg and the catalytic effects of Ni₂Al₃ NPs.     

Preparation and study of electrocatalytic activity of Ni-Pd(OH)2/C nanocomposite for hydrogen evolution reaction in alkaline solution

A new catalyst (Ni-Pd(OH)₂/C) for hydrogen evolution reaction (HER) was prepared by coelectrodeposition of Pd(OH)₂/C nanoparticles and Ni on a Cu substrate in two steps. Furthermore, the effect of Mo ions in alkaline solution (1 M NaOH) on the electrocatalytic activity of Ni-Pd(OH)₂/C nanocomposite was studied as an in-situ activator for the HER. The various electrochemical methods were employed to study the HER activity of the investigated new catalyst, including linear sweep voltammetry (LSV), the steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The electrochemical measurements showed that the Ni-Pd(OH)₂/C nanocomposite as a catalyst for the HER has an excellent catalytic activity with good stability in alkaline solution. Furthermore, the rate constants of the forward and backward reactions of Volmer and Heyrovský steps were estimated using Tafel-impedance data and revealed that the proton discharge electrosorption or Volmer reaction (k₁= (6.8 ± 0.7) × 10⁻⁸ mol cm⁻² s⁻¹) was the rate determining step (RDS) of the HER on the surface of Ni-Pd(OH)₂/C nanocomposite. Also, it was observed that the presence of Mo ions in alkaline solution could significantly increase the HER activity of Ni-Pd(OH)₂/C nanocomposite. The comparison of RDS rate constant value with surface roughness (R_f) of Ni-Pd(OH)₂/C catalyst showed that its high activity toward the HER originated from both increase in the surface roughness (∼20%) and increase in synergistic effect (∼80%).     

Improving hydrogen production from the hydrolysis of ammonia borane by using multifunctional catalysts

A novel multifunctional catalytic system has been developed for efficient hydrogen generation through the hydrolysis of ammonia borane. This system combines Pd NPs with acid sites and amines, which are both task-specific functionalities able to destabilize the N → B dative bond. The acidity of the support (zeolites of different structure and SiO₂/Al₂O₃ ratio) used to disperse the Pd NPs causes an increase in the hydrogen production rate. However, the positive effect of incorporating p-phenylenediamine in the catalyst is much more pronounced, causing a two-fold increase in the activity of the catalyst. The combined effect of the different functionalities yields excellent performance in the hydrolysis of ammonia borane, greatly enhancing the activity of the metal-based catalyst and reducing the activation energy of the catalyzed reaction.     

Boosting activity and stability by coupling Pt–Ni nanoparticles with La-modified flexible carbon nanofibers for hydrogen evolution reaction

Platinum (Pt) is considered as the most efficient catalyst for hydrogen evolution reaction (HER) with a nearly zero overpotential, but it is limited by the high cost and poor stability. Herein, we report an efficient electrocatalyst of Pt–Ni alloy nanoparticles (NPs) supported on the La-modified flexible carbon nanocomposite fibers (PtNi@La-CNFs) for HER. The rare earth metal oxide in the catalyst has a structure-effect relationship with the carbon fibers to form a flexible fiber membrane. Experimental results show that the macroscopic and microscopic properties of carbon nanocomposite fibers can be optimized by doping La₂O₃, and the Pt–Ni NPs can be anchored effectively. The Pt₁Ni₁@La-CNFs electrocatalyst exhibits a small overpotential of 32 mV to achieve current density of 10 mA cm^?2 with a low Tafel slope of 51 mV dec^?1 in alkaline medium, outperforming that of Pt@La-CNFs and the commercial Pt/C catalyst. This study reveals that the multiple coupling effect of rare earth compound, precious metal, and transition metal in composite catalyst can tailor its the electronic configuration, and results in an enhanced HER performance. This work opens up a novel approach to design high active and low cost Pt-based HER catalysts.     

Oxidation co-catalyst modified In2S3 with efficient interfacial charge transfer for boosting photocatalytic H2 evolution

Constructing an efficient co-catalyst/photocatalyst system for charge separation boosting photocatalytic hydrogen generation is a vital challenge. Herein, highly-dispersed PdS nanoparticles (NPs) acting as an efficient hole co-catalyst has been decorated on the ultrathin In₂S₃ nanosheets. The strong interactions between PdS and In₂S₃ via Pd–S–In bonds enable an intimate interface junction. Due to the high capacity of PdS for the hole capture with the assistance of internal electric field, the photogenerated charge carriers are not only separated effectively, the semiconductor photocatalyst In₂S₃ is also protected from the photo-oxidation. As expected, a remarkable H₂ production rate of 142.27 μmol/h has been achieved for 3PdS/In₂S₃ nanocomposite, which is 149.8 times higher than that of the pristine In₂S₃ nanosheets, and 13.3 times superior to the In₂S₃ decorated with a reductive co-catalyst Pt. This work provides a new insight into the co-catalyst modification engineering for an efficient photocatalytic energy conversion.