Hydrogen storage mechanism in transition metal decorated graphene oxide: The symbiotic effect of oxygen groups and high layer spacing

Transition metal nanoparticle decoration is widely used to enhance the hydrogen storage properties of carbon materials. However, little efforts have been devoted to unveil structural interaction between nanoparticles and substrate and understand the underlying kinetic mechanism for hydrogen sorption. In this work, a suite of TiO₂ nanoparticles decorated graphene oxide (GO) composites is fabricated and characterized to determine the interactions between material structure and hydrogen storage kinetics. EELS and XPS results show that interactions between nanoparticles and GO cause changes of the chemical states of C–O, CO and C–OH groups; furthermore, reactions of C–OH, HO–CO and C–O–C groups with TiO₂ nanoparticles create C–Ti and Ti–O–C bonding. Decoration of TiO₂ nanoparticles improves the capacity of GO by 2.3×, and 80% of the adsorption is reversible. By means of semi-empirical kinetic analysis, it is determined that hydrogen adsorption is controlled by two-dimensional diffusion regardless of layer spacing; while desorption is controlled by multiple diffusion processes and is sensitive to layer spacing. Collectively, these new findings deepen the understanding of transition metal nanoparticles decorated GO materials in the aspects of nanoparticle incorporation and hydrogen storage kinetic mechanism. In particular, oxygen groups enhance nanoparticle decoration, while high layer spacing improves desorption kinetics and reversibility.     

One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V₂O₅) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V₂O₅, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V₂O₅/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by different electrochemical methods including cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) in 0.5 M Na₂SO₄ solution. Remarkably, V₂O₅/PPy/GO nanocomposite shows a specific capacitance of 750 F g^?1 at a current density of 5 A g^?1, which is far better than PPy (59.5 F g^?1), V₂O₅/PPy (81.5 F g^?1) and PPy/GO (344.5 F g^?1). Furthermore, V₂O₅/PPy/GO maintains 83% of its initial value after 3000 cycles, which demonstrates good electrochemical stability of the electrode during repeated cycling. These results demonstrate that the combination of electrical double layer capacitance of GO and pseudocapacitive behavior of the PPy and V₂O₅ can effectively increase the specific capacitance and cycling stability of the prepared electrode. Also, a symmetric supercapacitor device assembled by V₂O₅/PPy/GO nanocomposite yielded a maximum energy density of 27.6 W h kg^?1 at a power density of 3600 W kg^?1, and a maximum power density of 13680 W kg^?1 at an energy density of 22.8 W h kg^?1.     

Synthesis of manganese ferrite/graphene oxide nanocomposite and investigation of its supercapacitor behaviors

Currently, researchers are struggling with the development of energy storage systems, like high energy density supercapacitors, with cheap cost and high stability. Herein research we present a facile preparation and evaluation of the manganese ferrite/graphene oxide (MnFe₂O₄/GO) nanocomposite electrochemical behavior as active electrode material in supercapacitors. The chemical composition and morphology were specified with different physicochemical characterization techniques. The TEM and FESEM images exhibit MnFe₂O₄ semi-spherical nanoparticles on GO plates. The prepared electrodes performance were proceeded with charge-discharge galvanostatic measurement (GCD), electrochemical impedance (EIS), and cyclic voltammetry (CV). The specific capacity value of MnFe₂O₄/GO new composite determined 298 F g⁻¹ in 1 A/g current density. Also MnFe₂O₄/GO electrodic composite shows acceptable GCD stability, by maintaining its original capacity of 92% at 500 cycles. The EIS analysis also displays low internal resistance of MnFe₂O₄/GO compared to other electrodes in the same conditions. In addition to experimental analysis, density functional theory was also used to get a more accurate understanding of the electrochemical behavior of electrode materials. The theoretical results showed that with the formation of MnFe₂O₄/GO nanocomposite, the electron conductivity is improved (energy gap decreases to 0.019 eV) and leads to an increase in supercapacitor performance, which is in agreement with the experimental results.     

A hydrothermal route for constructing reduced graphene oxide/TiO2 nanocomposites: Enhanced photocatalytic activity for hydrogen evolution

A series of reduced graphene oxide/TiO₂ (RGO/TiO₂) nanowire microsphere composites were synthesized with a facile one-step hydrothermal method using TiCl₃ and graphene oxide (GO) as the starting materials, during which the formation of TiO₂ and the reduction of GO occur simultaneously. The obtained nanocomposites were characterized with X-ray diffraction, field emission scanning electron microscope, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, respectively. UV–vis absorption spectra showed that the absorption edges of TiO₂ were extended into visible light region with the addition of RGO. The photocatalytic activities of the samples with and without Pt as cocatalysts were evaluated by hydrogen evolution from water photo-splitting under UV–vis light illumination. Enhanced photocatalytic properties were observed for the as-prepared RGO/TiO₂ nanocomposites. The amount of hydrogen evolution from the optimized photocatalyst reached to 43.8 μmol h⁻¹, which was about 1.6 times as high as that of bare TiO₂. The results shown here indicate a convenient and applicable approach to further exploitation of high activity materials for photocatalytic water splitting applications.     

Efficient electrochemical hydrogen evolution reaction and solar activity via bi-functional GO/Co3O4–TiO2 nano hybrid structure

Highly proficient electro and solar catalyst of mixed metal oxides Co₃O₄–TiO₂ modified with graphene oxide (GO) have been synthesized by simple and cost-effective way using sol-gel methodology. This catalyst demonstrated versatile bi-functional features towards the hydrogen evolution reaction (HER) in catalytic water splitting along with solar photo catalytic activity in the degradation of Methyl Orange (MO). XRD profile confirmed that composite presented an anatase and cubic phase for TiO₂ and Co₃O₄, respectively, with the GO network. The morphological structures confirm flaky texture of Co₃O₄ with small irregular spheres of TiO₂ nanoparticles randomly dispersed on the broken sheets of GO. GO and clusters of Co²⁺/Co³⁺ in different regions of host TiO₂ are accountable for decreasing band gap in the composite samples. Co–O–Ti and Co–Ti–C linkages in the composite materials are confirmed by Raman and FTIR studies. In electro catalytic HER in alkaline medium GO/Co₃O₄–TiO₂ catalyst illustrated low onset potential ~343 mV vs. RHE, high current density ~43 mA cm⁻² corresponding small Tafel slope ~97 mV/dec and small R_ct as compared to other catalysts. For HER in GO/Co₃O₄–TiO₂, Co²⁺ sites are more catalytically active than Co³⁺ sites along with Ti⁴⁺ and GO provides the more active surface area by reducing the agglomeration between the mixed metal oxides. GO/Co₃O₄–TiO₂ shows the highest photo catalytic performance over MO as compared to binary and ternary composites. Pining of metal oxides with reactive oxygen functional moieties of GO considerably improve the photo catalytic degradation activity and helpful in the separation of charge carriers for HER.     

PtGd/Gd2O3 alloy/metal oxide composite catalyst for methanol oxidation reaction

Pt-transition metal alloys are frequently used to improve the catalytic activity for methanol oxidation reaction. However, the severe dealloying strongly limits the applications of Pt-based alloy in fuel cells. Recently, Pt-rare earth metal alloys are considered to be the promising catalysts for electrocatalytic application in fuel cells. Metal oxide as the co-catalytic component of composite catalyst, is also applied to regulate the electronic structure and strengthen resistance to CO poisoning. In this work, we utilized hydrogen reduction method to prepare PtGd/Gd₂O₃ composite catalyst. X-ray diffraction result illustrates that both Gd₂O₃ and PtGd alloy co-exist in PtGd/Gd₂O₃ material. X-ray photoelectron spectroscopy data confirms that the main valence states of Pt and Gd are metal form in the PtGd/Gd₂O₃ catalyst and emerges obvious transfer of element binding energy. Transmission electron microscopy data presents that composite PtGd/Gd₂O₃ particles are uniformly dispersed on the carbon power with a typical core-shell structure. And upon the increase of Gd precursor in reduction process, the metal oxide layer becomes more thicker for PtGd/Gd₂O₃ composite material. Because of the synergistic contributions given by the Pt–Gd bimetals and alloy-metal oxide between PtGd alloy and Gd₂O₃ oxide, the PtGd/Gd₂O₃ composite catalysts exhibit superior catalytic performance toward methanol oxidation reaction. Specifically, the mass activity of Pt₁Gd₁/Gd₂O₃ is about 1.9 times that of commercial Pt/C; besides this, the optimal specific activity of Pt₁Gd₂/Gd₂O₃ is almost 4 times that of commercial Pt/C. More importantly, the Pt₁Gd₁/Gd₂O₃ emerged a 20.9% degradation after 8000 cycles test, while commercial Pt/C showed a 61.7% degradation. And this work provides an important insight for rare earth elements investigation on the electrocatalysis application in fuel cells.     

Novel synthesis of graphene oxide/In2S3/TiO2 NRs heterojunction photoanode for enhanced photoelectrochemical (PEC) performance

Novel heterostructure photocatalyst built from titanium dioxide (TiO₂), graphene oxide (GO) and indium sulfide (In₂S₃) has been successfully prepared for photoelectrochemical hydrogen production. The stepwise introduction of three materials on conductive glass substrate has been realized through hydrothermal, electrochimical and spin coating deposition methods, respectively. The structure, morphology, composition, optical and photoelectrochemical properties of the resultant photoanodes were investigated in detail. The presence of GO in the heterostructure film was confirmed by Raman analysis with D and G band intensity. Surface morphology analysis of the GO/In₂S₃/TiO₂ NRs structure reveal the homogenous distribution of graphene oxide on In₂S₃/TiO₂ NRs surface. From UV–Vis analysis, band gap energy of the samples decreases gradually from 3.34 eV (TiO₂ NRs) to 3.12 eV, with In₂S₃ and GO addition. The electrochemical impedance spectroscopy (EIS) further confirmed that GO/In₂S₃/TiO₂NRs heterostructure possessed the lowest charge-transfer resistance, revealing that In₂S₃ and GO could significantly accelerate the electron mobility compared with bare TiO₂. From Mott-Schottky plots, several parameters such as flat-band potential and free carrier concentration were determined. Next, The GO/In₂S₃/TiO₂ NRs electrode achieved remarkably improved current density (0.45 mAcm² at 0.8 V vs Ag/AgCl) compared to pure TiO₂ NRs or In₂S₃/TiO₂ NRs electrodes, which attributes to the uniform structure and excellent electrical conductivity of GO, which could reduce the combination rate of the photo electron-hole pairs. These results reveal that GO/In₂S₃/TiO₂ NRs possesses great potential toward the development of newly synthesizable catalysts in the field of photoelectrochemical water splitting.     

Preparation and characterization of nano‐enhanced myristic acid using metal oxide nanoparticles for thermal energy storage

Fatty acids have been broadly used as phase change materials (PCMs) for thermal energy storage. However, low thermal conductivity limits their performances. This paper investigates the influence of metal oxide nanoparticle addition on myristic acid (MA) as nano‐enhanced PCM (NEPCM). Stability, chemical, and thermal properties were considered. Four types of nanoaprticles, TiO₂, CuO, Al₂O₃, and ZnO, were dispersed in MA at 0.1, 0.5, 1, and 2 wt%. Stability and dispersion were checked by sediment photograph capturing and scanning electron microscopy/energy‐dispersive spectroscopy. The Fourier‐transformed infrared (FTIR) and X‐ray diffraction analysis confirmed no chemical interaction between the nanoparticles and MA. The results revealed a ratio of thermal conductivity of 1.50, 1.49, 1.45, and 1.37, respectively, for 2 wt% of ZnO, Al₂O₃, CuO, and TiO₂. The T‐history method confirmed this enhancement. The latent heat thermal energy storage (LHTES) properties of the nano‐enhanced MA were evaluated using differential scanning calorimetry. The latent heat capacities of nano‐enhanced MA samples have dropped between 9.64 and 5.01 % compared with pure MA, and phase change temperature range was not affected significantly. The NEPCM was subjected to 500 thermal cycling, it showed a good thermal reliability as LHTES properties remained unchanged, while FTIR analysis showed similar characteristics compared with uncycled samples, indicating a good chemical stability. Based on the results regarding with the LHTES properties, cycling thermal reliability, and higher thermal conductivity improvement, it can be achieved that the MA/Al₂O₃ (2.0 wt%) and MA/ZnO (2.0 wt%) composites could be better PCMs for solar TES applications.     

Enhanced room-temperature hydrogen storage capacity in Pt-loaded graphene oxide/HKUST-1 composites

Series of Pt-loaded graphene oxide (GO)/HKUST-1 composites were synthesized by the reaction between Pt@GO and precursors of HKUST-1. The parent materials and composites have been characterized by powder X-ray diffraction (XRD), Infrared (IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and gas adsorption analyzer. The XRD and IR analysis showed that the incorporation of Pt@GO did not prevent the formation of HKUST-1 units. SEM, TEM and EDS results revealed that Pt nanoparticles were well-dispersive and anchored tightly into composites. Meanwhile, the percentage of Pt@GO has an obvious effect on morphologies, crystallinities and surface areas of composites. More importantly, the significant enhancement of hydrogen storage capacity at ambient temperature for the composite with low Pt@GO content can be ascribed to the hydrogen spillover mechanism in such system.     

Synthesis and characterization of transition metal mixed oxide doped graphene embedded durable electrocatalyst for hydrogen evolution reaction

A promising electrocatalyst containing variable percentage of V₂O₅–TiO₂ mixed oxide in graphene oxide support was prepared by embedding the catalyst on Cu substrate through facile electroless Ni–Co–P plating for hydrogen evolution reaction. The solvothermal decomposition method was opted for tuning the crystalline characteristics of prepared material. The optimized mixed oxide was well characterized, active sites centres were identified and explained by X-ray diffraction, high resolution tunnelling electron microscopy, scanning electron microscopy coupled with energy dispersive X-ray and X-ray photon spectroscopy analysis. The structural and electronic characteristics of material was done by fourier transform infrared spectroscopy and the electrochemical behaviour of the prepared material was evaluated by using Tafel plot, electrochemical impedance analysis, linear sweep voltammetry, open circuit analysis and chronoamperometry measurements. The results show the enhanced catalytic activity of Ni–Co–P than pure Ni–P plate, due to synergic effect. Moreover, the prepared mixed oxide incorporated Ni–Co–P plate has a high activity towards HER with low over potential of 101 mV, low Tafel slope of 36 mVdec^?1, high exchange current density of 9.90 × 10^?2 Acm^?2.     

Enhancement of photoelectrochemical hydrogen production by using a novel ternary Ag2CrO4/GO/MnFe2O4 photocatalyst

Novel Ag₂CrO₄/GO/MnFe₂O₄ photocatalysts synthesized by precipitation method and fabricated on indium tin oxide surface by electrophoretic deposition technique. The obtained Ag₂CrO₄/GO/MnFe₂O₄ composite has been verified by microscopic study, chemical and structural analyses. Also, the ternary composite showed higher photocurrent response and weaker photoluminescence spectrum than MnFe₂O₄, GO, Ag₂CrO₄ and GO/MnFe₂O₄. Photo-cathodes prepared using semiconductor photocatalyst powders were investigated for visible-light-driven photoelectrochemical hydrogen evolution. The best result of the photoelectrochemical hydrogen production in the presence of Ag₂CrO₄/GO/MnFe₂O₄ composite was determined as 446.93 μmol.cm⁻² in 90 min under visible light illumination. So, the enhanced hydrogen producing over the ternary composite was obtained. This study presents the development of stable visible light active photocatalytic materials and the design of efficient for the advancement of hydrogen production via photoelectrochemical water splitting in the future.     

Facile synthesis of nickel-vanadium bimetallic oxide and its catalytic effects on the hydrogen storage properties of magnesium hydride

To improve the dehydrogenation/hydrogenation performance of magnesium hydride (MgH₂), a nickel-vanadium bimetallic oxide (NiV₂O₆) was prepared by a simple hydrothermal method using ammonium metavanadate and nickel nitrate as raw materials. This oxide was used to improve the hydrogen storage performance of MgH₂. NiV₂O₆ reacted with Mg to form Mg₂Ni and V₂O₅; Mg₂Ni and V₂O₅ played an important role in improving the hydrogen storage properties of MgH₂. The NiV₂O₆-doped MgH₂ had an excellent hydrogen absorption and desorption kinetics performance, and it could absorb 5.59 wt% of hydrogen within 50 min at 150 °C and release about 5.3 wt% of hydrogen within 12 min. The apparent activation energies for the dehydrogenation and hydrogenation of MgH₂-NiV₂O₆ were 92.9 kJ mol^?1 and 24.9 kJ mol^?1, respectively. These were 21.7% and 66.3% lower than those of MgH_2, respectively. The mechanism analysis demonstrated that the improved kinetic properties of MgH₂ resulted from the heterogeneous catalysis of vanadium and nickel.     

Two step synthesis of TiO2–Co3O4 composite for efficient oxygen evolution reaction

For an active hydrogen gas generation through water dissociation, the sluggish oxygen evolution reaction (OER) kinetics due to large overpotential is a main hindrance. Herein, a simple approach is used to produce composite material based on TiO₂/Co₃O₄ for efficient OER and overpotential is linearly reduced with increasing amount of TiO₂. The scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) investigations reveal the wire like morphology of composite materials, formed by the self-assembly of nanoparticles. The titania nanoparticles were homogenously distributed on the larger Co₃O₄ nanoparticles. The powder x-ray diffraction revealed a tetragonal phase of TiO₂ and the cubic phase of Co₃O₄ in the composite materials. Composite samples with increasing TiO₂ content were obtained (18%, 33%, 41% and 65% wt.). Among the composites, cobalt oxide-titanium oxide with the highest TiO₂ content (CT-20) possesses the lowest overpotential for OER with a Tafel slope of 60 mV dec^?1 and an exchange current density of 2.98 × 10^?3A/cm². The CT-20 is highly durable for 45 h at different current densities of 10, 20 and 30 mA/cm². Electrochemical impedance spectroscopy (EIS) confirmed the fast charge transport for the CT-20 sample, which potentially accelerated the OER kinetics. These results based on a two-step methodology for the synthesis of TiO₂/Co₃O₄ material can be useful and interesting for various energy storage and energy conversion systems.     

Improved hydrogen permeation through thin Pd/Al2O3 composite membranes with graphene oxide as intermediate layer

Here we proposed the decreasing in the roughness of asymmetric alumina (Al₂O₃) hollow fibers by the deposition of a thin graphene oxide (GO) layer. GO coated substrates were then used for palladium (Pd) depositions and the composite membranes were evaluated for hydrogen permeation and hydrogen/nitrogen selectivity. Dip coating of alumina substrates for 45, 75 and 120 s under vacuum reduced the surface mean roughness from 112.6 to 94.0, 87.1 and 62.9 nm, respectively. However, the thicker GO layer (deposited for 120 s) caused membrane peel off from the substrate after Pd deposition. A single Pd layer was properly deposited on the GO coated substrates for 45 s with superior hydrogen permeance of 24 × 10⁻⁷ mol s⁻¹m⁻² Pa⁻¹ at 450 °C and infinite hydrogen/nitrogen selectivity. Activation energy for hydrogen permeation through the Al₂O₃/GO/Pd composite membrane was of 43 kJ mol⁻¹, evidencing predominance of surface rate-limiting mechanisms in hydrogen transport through the submicron-thick Pd membrane.     

Synthesis of magnetically responsive hyperbranched polyamidoamine based on the graphene oxide: Application as demulsifier for oil‐in‐water emulsions

In this study, a novel, highly efficient, and magnetically responsive demulsifier, namely, Fe₃O₄@hyperbranched polyamidoamine‐graphene oxide (MKh‐GO), was synthesized. First, Fe₃O₄ was synthesized, and Fe₃O₄ was wrapped in hyperbranched polyamidoamine (h‐PAMAM) by γ‐(methacryloyl oxide) propyltrimethoxysilane (kh570), and MKh‐GO was synthesized by condensation reaction. The chemical structures and morphologies of the samples were characterized by Fourier transform‐infrared spectroscopy (FTIR) and transmission electron microscope (TEM). The magnetic response of the sample was tested by vibrating sample magnetometer (VSM). The MKh‐GO was used to separate crude oil in water emulsion; the effects of MKh‐GO dosage, temperature, and pH value on the demulsifying efficiency were investigated. Possible demulsification mechanisms were summarized. The results show that MKh‐GO is successfully synthesized, and MKh‐GO exhibits excellent demulsification performance; MKh‐GO is recycled seven times, and the demulsification efficiency is 97%.     

Growth of iron diselenide nanorods on graphene oxide nanosheets as advanced electrocatalyst for hydrogen evolution reaction

Advanced electrocatalysts for the fabrication of sustainable hydrogen from water splitting are innermost to energy research. Herein, we report the growth of iron diselenide (FeSe₂) nanorods on graphene oxide (GO) sheets using two-step process viz., simple hydrothermal reduction and followed by wet chemical process. The orthorhombic phase of FeSe₂ incorporated GO nanosheet was developed as a low-cost and efficient electrocatalyst for hydrogen evolution reaction (HER) by water splitting. The phase purity, crystalline structure, surface morphology and elemental composition of the synthesized samples have been investigated by UV–visible absorption spectroscopy (UV–vis), fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDS). Voltammetry and Tafel polarization methods have been utilized to assess the performance of various weight ratio of GO nanosheet in FeSe₂ nanorods towards H₂ evolution. Detailed electrochemical investigations revealed that the 30% FeSe₂/GO composite showed a tremendous electrocatalytic HER activity in acidic medium with high cathodic current density of 9.68 mA/cm² at η = 250 mV overpotential and with a Tafel slope of 64 mV/dec. The 30% FeSe₂/GO composite offers a high synergistic effect towards HER activity, which is mainly due to high electrochemical active catalytic sites, low charge-transfer resistance and enhanced electrocatalytic performances of H₂ production. The present analysis revealed the possible application of FeSe₂/GO composite as a promising low-cost alternative to platinum based electrocatalysts for H₂ production.     

Nano cobalt oxides for photocatalytic hydrogen production

Nano structured metal oxides including TiO_2, Co₃O₄ and Fe₃O₄ have been synthesized and evaluated for their photocatalytic activity for hydrogen generation. The photocatalytic activity of nano cobalt oxide was then compared with two other nano structured metal oxides namely TiO₂ and Fe₃O₄. The synthesized nano cobalt oxide was characterized thoroughly with respect to EDX and TEM. The yield of hydrogen was observed to be 900, 2000 and 8275 μmol h⁻¹ g⁻¹ of photocatalyst for TiO₂, Co₃O₄ and Fe₃O₄ respectively under visible light. It was observed that the hydrogen yield in case of nano cobalt oxide was more than twice to that of TiO₂ and the hydrogen yield of nano Fe₃O₄ was nearly four times as compared to nano Co₃O₄. The influence of various operating parameters in hydrogen generation by nano cobalt oxide was then studied in detail.     

Significant enhancement of the electrochemical hydrogen uptake of reduced graphene oxide via boron-doping and decoration with Pd nanoparticles

Development of advanced hydrogen storage materials with high capacity and stability is vital to achieve an envisaged hydrogen economy. Here, we report a uniformly dispersed Pd nanoparticles on the boron-doped reduced graphene oxide (Pd/B-rGO) as a novel nanocomposite for efficient hydrogen storage. The effects of the incorporation of Pd NPs and the substitution of boron atoms into the graphene-based nanomaterial matrix on the electrochemical hydrogen up-taking and releasing were comparatively studied using electrochemical techniques, and duly supported by density functional theory (DFT) calculations. The discharge capacities of the Pd-rGO and Pd/B-rGO nanocomposites were determined to be over 45 and 128 times higher than that of the Pd NPs, respectively, showing that the B doping and the rGO support played significant roles in the enhancement of the hydrogen storage capability. Moreover, the galvanostatic charging and discharging cycling tests demonstrated a high stability and efficient kinetics of the Pd/B-rGO nanocomposite in the H₂SO₄ electrolyte for hydrogen up-taking and release.     

Phase transition of doped LaFeO3 anode in reducing atmosphere and their power generation property in intermediate temperature solid oxide fuel cell

In general, transition metal-doped La_0.6Sr_0.4FeO₃ (LSF) has been used as a cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) because of its high mixed electronic−ionic conductivity and catalytic properties. Recently, some research groups have been investigating the doped LSF as an anode material. In this study, we evaluated the influence of dopant in LSF on anodic properties of LSF in SOFCs. Whereas Mn-doped LSF showed typical perovskite oxide structure even after reduction in hydrogen at high temperature, the LSF and Co-doped LSF exhibited phase transition partially to LaSrFeO₄ and exsolution of metal particles after reduction. The phase transition and metal exsolution occurred at temperature higher than 1008 K in a reducing atmosphere. Despite the partial phase transition, the cell using Co-doped LSF anode exhibited fairly high power density of 1.33 W/cm² at 1173 K with the lowest polarization resistance. These results may originate from the high oxygen-ion conductivity of LaSrFeO₄–La(Sr)Fe(Co)O₃ and the high hydrogen oxidation property of the Co–Fe particles on ceramic anode surface.     

Ruthenium stabilized on transition metal-on-transition metal oxide nanoparticles for naphthalene hydrogenation

The multi-metallic nanocatalysts of ruthenium nanoclusters-on-transition metal/transition metal oxide nanoparticles (TM/TMO NPs) then supported on carbon (Ru/Ni/NiO/C or Ru/Co/Co₃O₄/C) were designed and synthesized. The Ni/NiO or Co/Co₃O₄ NPs strongly stabalized the ruthenium nanoclusters by the interfacial interaction among them. These catalysts exhibited high catalytic activity and 100% selectivity to decalin for naphthalene hydrogenation due to the synergy effect of multiple catalytic sites, where naphthalene was absorbed and activated at the TMO sites (NiO or Co₃O₄), H₂ was activated at the Ru sites and it produced the activated H* species, H* was transferred to the surface of NiO or Co₃O₄ by the hydrogen spillover effect of TM (Ni or Co), reacting with the activated naphthalene and forming decalin. The nanostructures and synergetic effect of the Ru/Ni/NiO/C and Ru/Co/Co₃O₄/C catalysts were revealed by a series of techniques, such as high-resolution transmission electron microscope (HRTEM), temperature-programmed reduction (TPR), scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) mapping, high-sensitivity low-energy ion scattering (HS-LEIS) and X-ray absorption spectroscopy (XAS). It is promising that the hydrogen storage can proceed at room temperature via catalyzing naphthalene hydrogenation over the Ru/Ni/NiO/C or Ru/Co/Co₃O₄/C catalyst.