Thin film solar cells based on microcrystalline silicon–germanium narrow-gap absorbers

We report on the improved performance of p–i–n junction solar cells incorporating hydrogenated microcrystalline silicon–germanium (μc-Si_1?xGe_x:H) absorber i-layers prepared by low-temperature (～200 °C) plasma-enhanced chemical vapor deposition. While the optical absorption increases with Ge content, the photocarrier transport in the solar cells for x>0.2 is dominated by the carrier recombination due to the increased dangling bond defects and the illumination-induced field distortion in the i-layer. In contrast, the solar cells with smaller Ge contents (x～0.2) exhibit better carrier collection characteristics with extended infrared sensitivities even higher than those of double-thickness μc-Si:H solar cells. As a result, we have achieved a 6.3% efficiency using a 1-μm-thick μc-Si_0.8Ge_0.2:H i-layer.     

Efficient method to obtain Platinum–Cobalt supported on graphene oxide and electrocatalyst development

We have prepared a highly efficient and stable platinum–cobalt catalyst supported on graphene oxide by using a one-step synthesis microwave-irradiation process. The structure and composition of two different compositions (Pt:Co(2.5:1)/rGO, Pt:Co(2:1)/rGO) have been investigated by Fourier infrared spectroscopy (FT-IR), X-ray Photoelectron spectroscopy (XPS), specific surface area (BET), Raman spectroscopy. Their electrocatalytic activity was investigated and the electrochemical response from cyclic voltammetry revealed the high efficiency and stability as well as the potential application as cathode electrode. The electrocatalysts exhibited a superior durability comparing with commercial Pt/C catalyst after accelerated stress test, indicating a lower loss of electrochemical surface area in the case of prepared samples. Moreover, this study extends the applicability of this synthesis method for the preparation of other noble or transitional metal nanoparticles decorated on reduced graphene oxide.     

Reliability of hydrogen sensing based on bimetallic Ni–Pd/graphene composites

Graphene-supported nickel–palladium (Ni–Pd) bimetallic nanoparticles (Ni–Pd/Gr) were synthesized using a simple chemical method, followed by a post-thermal annealing process. The characteristics of resistivity-type hydrogen (H₂) sensors composed of Pd–Gr composites (with small amounts of Ni added to the Pd nanoparticles (Pd NPs)) were investigated in detail. Pd NPs with various amounts of Ni embedded into the Pd lattice were synthesized by varying the molar ratios of the Ni/Pd precursors. The results from this work indicate that the addition of Ni not only enhances performance, but also reduces the hysteresis behavior of the Pd–Gr composite based H₂ sensors. H₂ was detectable from 1 to 1000 ppm based on a rapid recovery response with suitable Ni/Pd percentages. At the optimal Ni/Pd percentage of 7% (Ni/Pd ∼7%), sensors showed a small enhancement of sensitivity, fast recovery, and minimum hysteresis effect. From our experiment, the addition of Ni to Pd NPs results in a reduction of the hysteresis effect and reliability on H₂ sensors based on Pd–Gr composites.     

Surfactant-free Pd–Fe nanoparticles supported on reduced graphene oxide as nanocatalyst for formic acid oxidation

Herein, a novel surfactant-free nanocatalyst of Pd–Fe bimetallic nanoparticles (NPs) supported on the reduced graphene oxide (Pd–Fe/RGO) were synthesized using a two-step reduction in aqueous phase. Electrochemical studies demonstrate that the nanocatalyst exhibits superior catalytic activity towards the formic acid oxidation with high stability due to the synergic effect of Pd–Fe and RGO. The optimized Pd–Fe/RGO (Pd:Fe = 1:5) nanocatalyst possess an specific activity of 2.72 mA cm^?2 and an mass activity of 1.0 A mg^?1_(Pd), which are significantly higher than those of Pd/RGO and commercial Pd/C catalysts.     

Platinum–Iron nanoparticles supported on reduced graphene oxide as an improved catalyst for methanol electro oxidation

Platinum–Iron nanoparticles supported on reduced graphene oxide powder are synthesized by chemical reduction method as an anode catalyst for the methanol electro oxidation. The characterization of the catalyst has been investigated using physical and electrochemical methods. Prepared catalyst was characterized by scanning electron microscopy (SEM), TEM (Transmission electron microscopy), FT-IR (Fourier-transform infrared spectroscopy), Raman spectroscopy and, X-ray diffraction (XRD) and energy dispersive analysis of X-ray (EDX). Pt and Pt-Fe nanoparticles are uniformly dispersed on the surface of reduced graphene oxide (rGO) powder nanocomposite support. The catalytic properties of the catalyst for methanol electro-oxidation were thoroughly studied by electrochemical methods that involved in the cyclic voltammetry, linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The Pt-Fe/rGo exhibits high electrocatalytic activity, catalyst tolerance for the CO poisoning and catalyst durability for electro-oxidation of methanol compared to the Pt/rGo and commercial Pt/C catalyst. Therefore, the Pt-Fe/rGo catalyst is a good choice for application in direct methanol fuel cells.     

One-step solution-induced impregnation synthesis of strongly coupled platinum–molybdenum/silicon carbide quantum dots heterostructures encapsulated on reduced graphene oxide sheet as electrocatalyst for hydrogen evolution reaction

Strongly coupled platinum-based transition-metal oxide/carbon hybrids and the development of quantum-dot structures of hybrid catalysts are cost-effective and maximize accessible active sites. However, a significant obstacle still exists for the rational proposal and simple synthesis of hybrid quantum-dot material catalysts. Herein, novel Pt_xMo_1-xSiC quantum dots encapsulated in reduced graphene oxide (rGO) (Pt_xMo_1-xSiC QDs @rGO) for catalyzing the hydrogen evolution reaction (HER) were fabricated through a simple solution-induced impregnation method. The optimized Pt₅Mo₉₅SiC QDs @rGO catalyst only require overpotentials of 18 mV and 25 mV to deliver current densities of 10 mA cm⁻² and 250 mA cm⁻² in acidic media, respectively. The synergistic effects of the inner Pt_xMo_1-xSiC QDs networks and outer conductive rGO sheets that promote electron transfer are responsible for the outstanding HER performance. This work presents a novel method for producing an extremely effective HER catalyst for applications on large-scale.     

In-situ construction of Mn–Fe mixed oxides nanoparticles on reduced graphene oxide with superior lithium storage property

In this paper, porous Mn₃O₄–Fe₃O₄ nanoparticles with highly uniform composition are in-situ anchored on reduced graphene oxide (rGO) nanosheets by a simple cyanometallic framework template method. Thanks to the synergistic effects between the porous Mn₃O₄–Fe₃O₄ nanoparticles and the well-conductive rGO nanosheets, the Mn₃O₄–Fe₃O₄/rGO composites present superior electrochemical lithium storage performances with a great reversible capacity of 1013 mAh g^?1 after 100 cycles at 0.1 A g^?1, satisfactory rate capability of 510 mAh g^?1 at 3.0 A g^?1, and eminent long-term cycle stability of 804 mAh g^?1 after 500 cycles at 0.5 A g^?1. It is demonstrated that the rGO can not only act as a conducting matrix, but also buffer the volume expansion and avoid the aggregation of the Mn₃O₄–Fe₃O₄ nanoparticles during charging-discharging. The work provides a simple strategy for designing and fabricating advanced multi-component metal oxide-based anodes for high-performance lithium-ion battery.     

A study on the hydrogen storage performance of graphene–Pd(T)–graphene structure

The 1–6 H₂ molecule adsorption energy and electronic properties of sandwich graphene–Pd(T)–Graphene (G–Pd(T)–G) structure were studied by the first-principle analysis. The binding energies, adsorption energies, and adsorption distances of Pd atoms-modified single-layer graphene and bilayer graphene with H₂ molecules at B, H, T adsorption sites were calculated. In bilayer graphene, the adsorption properties at T sites were found to be more stable than those at B and H sites. The binding energy of Pd atoms (4.16 eV) on bilayer graphene was higher than the experimental cohesion energy of Pd atoms (3.89 eV), and this phenomenon eliminated the impact of metal clusters on adsorption properties. It was found that three H₂ molecules were stably adsorbed on the G–Pd(T)–G structure with an average adsorption energy of 0.22 eV. Therefore, it can be speculated that G–Pd(T)–G is an excellent hydrogen storage material.     

Durability study of an intermediate temperature fuel cell based on an oxide–carbonate composite electrolyte

It was reported that ceria–carbonate composites are promising electrolyte materials for intermediate temperature fuel cells. The conductivity stability of composite electrolyte with co-doped ceria and binary carbonate was measured by AC impedance spectroscopy. At 550 °C, the conductivity dropped from 0.26 to 0.21 S cm⁻¹ in air during the measured 135 h. At a constant current density of 1 A cm⁻², the cell performance keeps decreasing at 550 °C, with a maximum power density change from 520 to 300 mW cm⁻². This is due to the increase of both series and electrode polarisation resistances. Obvious morphology change of the electrolyte nearby the cathode/electrolyte interface was observed by SEM. Both XRD and FT-IR investigations indicate that there are some interactions between the doped ceria and carbonates. Thermal analysis indicates that the oxide–carbonate composite is quite stable at 550 °C. The durability of this kind of fuel cell is not good during our experiments. A complete solid oxide-carbonate composite would be better choice for a stable fuel cell performance.     

A novel system for the production of pure hydrogen from natural gas based on solid oxide fuel cell–solid oxide electrolyzer

In this paper, a novel process for the production of pure hydrogen from natural gas based on the integration of solid oxide fuel cells (SOFCs) and solid oxide electrolyzer cells (SOECs) is presented. In this configuration, the SOFC is fed by natural gas and provides electricity and heat to the SOEC, which carries out the separation of steam into hydrogen and oxygen. Depending on the system layout considered, the oxygen available at the SOEC anode outlet can be either mixed with the SOFC cathode stream in order to improve the SOFC performance or regarded as a co-product. Two configurations of the cell stack are studied. The first consists of a stack with the same number of SOFCs and SOECs working at the same current density. In this case, since in typical operating conditions the voltage delivered by the SOFC is lower than the one required by the SOEC, the required additional power is supplied by means of an electric grid connection. In the second case, the electricity balance is compensated by providing additional SOFCs to the stack, which are fed by a supplementary natural gas feed. Simulations carried out with Aspen Plus show that pure hydrogen can be produced with a natural gas to hydrogen LHV-efficiency that is about twice the value of a typical water electrolyzer and comparable to that of medium-scale reformers.     

Control-oriented thermal management of solid oxide fuel cells based on a modified Takagi–Sugeno fuzzy model

Thermal management for a solid oxide fuel cell (SOFC) is actually temperature control, due to the importance of cell temperature for the performance of an SOFC. An SOFC stack is a nonlinear and multi-variable system which is difficult to model by traditional methods. A modified Takagi–Sugeno (T–S) fuzzy model that is suitable for nonlinear systems is built to model the SOFC stack. The model parameters are initialized by the fuzzy c-means clustering method, and learned using an off-line back-propagation algorithm. In order to obtain the training data to identify the modified T–S model, a SOFC physical model via MATLAB is established. The temperature model is the center of the physical model and is developed by enthalpy-balance equations. It is shown that the modified T–S fuzzy model is sufficiently accurate to follow the temperature response of the stack, and can be conveniently utilized to design temperature control strategies.     

Modeling and simulation of solid oxide fuel cell based on the volume–resistance characteristic modeling technique

Solid oxide fuel cell (SOFC) is a complicated system with heat and mass transfer as well as electrochemical reactions. The real-time dynamic simulation of SOFC is still a challenge up to now. This paper develops a one-dimensional mathematical model for direct internal reforming solid oxide fuel cell (DIR-SOFC). The volume–resistance (V–R) characteristic modeling technique is introduced into the modeling of the SOFC system. Based on the V–R modeling technique and the modular modeling idea, ordinary differential equations meeting the quick simulation are obtained from partial differential equations. This model takes into account the variation of local gas properties. It can not only reflect the distributed parameter characteristics of SOFC, but also meet the requirement of the real-time dynamic simulation. The results indicate that the V–R characteristic modeling technique is valuable and viable in the SOFC system, and the model can be used in the quick dynamic and real-time simulation.     

Study on the hydrogen storage performance of graphene(N)–Sc–graphene(N) structure

The electronic properties of a sandwich graphene(N)–Sc–graphene(N) structure and its average adsorption energies after the adsorption of 1, 3, 5, 7, 10, and 14H₂ molecules were investigated by first principles. The average binding energies and adsorption distances of Sc atoms at different adsorption sites in N-doped bilayer graphene (N–BLG) were calculated. It was found that Sc atoms located at different adsorption sites of BLG generated metal clusters. The binding energy of the Sc atom located at the TT position of N–BLG (5.19 eV) was higher than the experimental cohesion energy (3.90 eV), and eliminated the impact of metal clusters on adsorption properties. It was found that the G(N)–Sc–G(N) system could stably adsorb 10 hydrogen molecules with an average adsorption energy of 0.24 eV. Therefore, it can be speculated that G(N)–Sc–G(N) is an excellent hydrogen storage material.     

LED light-induced enhanced photocatalytic hydrogen evolution on Au@TiO2 core–shell modified by nitrogen doping and reduced graphene oxide

This study focused on the large band gap of TiO₂ for its use as a photocatalyst under light emitting diode (LED) light irradiation. The photocatalytic activities of core–shell structured Au@TiO₂ nanoparticles (NPs), nitrogen doped Au@TiO₂ NPs, and Au@TiO₂/rGO nanocomposites (NCs) were investigated under various light intensities and sacrificial reagents. All the materials showed better photocatalytic activity under white LED light irradiation than under blue LED light. The N-doped core–shell structured Au@TiO₂ NPs (Au@N–TiO₂) and Au@TiO₂/rGO NCs showed enhanced photocatalytic activity with an average H₂ evolution rate of 9205 μmol h^?1g^?1 and 9815 μmol h^?1g^?1, respectively. All these materials showed an increasing rate of hydrogen evolution with increasing light intensity and catalyst loading. In addition, methanol was more suitable as a sacrificial reagent than lactic acid. The rate of hydrogen evolution increased with increasing methanol concentration up to 25% in DI water and decreased at higher concentrations. Overall, Au@TiO₂ core–shell-based nanocomposites can be used as an improved photocatalyst in photocatalytic hydrogen production.     

Monodisperse palladium–nickel alloy nanoparticles assembled on graphene oxide with the high catalytic activity and reusability in the dehydrogenation of dimethylamine–borane

Herein, a highly efficient and stable palladium nickel nanoparticles (PdNi NPs) supported on graphene oxide (GO) was synthesized, characterized and applied for the dehydrogenation of dimethyl ammonia borane (DMAB). The monodisperse PdNi NPs has been synthesized via the ultrasonic double solvent reduction method in the presence of oleylamine and GO as support matrices. The structure morphology and properties of PdNi@GO NPs were characterized by using different techniques such as UV–VIS, XPS, TEM, HRTEM and XRD methods. The PdNi@GO NPs was found to be highly effective and stable in the dehydrogenation of DMAB. This catalyst with the turnover frequency of 271.9 h^?1 shows one of the best results among the all prepared catalysts in literature for the dehydrogenation of DMAB. The apparent activation parameters of the catalytic dehydrogenation reaction were also calculated; apparent activation energy (E_a,app) = 38 ± 2 kJ mol^?1, activation enthalpy (ΔH^#_,app) = 35 ± 1 kJ mol^?1 and activation entropy (ΔS^#_,app) = ?102 ± 1 J K^?1 mol^?1.     

Highly selective hydrogen production from propane by Ru–Ni core–shell nanocatalyst deposited on reduced graphene oxide by sequential chemical vapor deposition

A narrow temperature window (160°C-190°C) was identified for the selective deposition of Ru on Ni supported on reduced graphene oxide (rGO) through a sequential chemical vapor deposition (CVD) method. Cyclopentadiene and cyclopentene were identified as decomposition products of nickelocene CVD on rGO, whereas only methane was detected in gaseous products from ruthenocene CVD. Heat treatment converted the selectively deposited Ru on Ni/rGO into Ru–Ni core–shell bimetallic system on the surface of rGO as confirmed by high-resolution transmission electron microscopy. The Ru–Ni/rGO thus prepared produced hydrogen with high selectivity in propane steam reforming performed in the temperature range of 350°C to 850°C. Addition of 3.6% Ru against Ni supported on rGO improved the turnover frequency (TOF) of propane up to 70% to 100% compared to the Ni/rGO catalyst at lower temperatures (350°C-450°C). The presence of Ru lowered the activation energy of propane SR from 65.7 kJ mol⁻¹ for Ni/rGO to 48.7 kJ mol⁻¹ for Ru–Ni/rGO catalyst.     

Hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticles for highly efficient methanol electrooxidation

Exploiting highly efficient electrocatalysts through simple methods is very critical to the development of energy conversion technologies. Herein, we develop a hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticle catalyst (Pt–Cu/RGO) by a facile one-step electrodeposition of graphene oxide in the presence of H₂PtCl₆ and copper ethylenediamine tetraacetate. The nanostructure and composition were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Meanwhile, the electrocatalytic performance was investigated by cyclic voltammetry and chronoamperometry, showing that the Pt–Cu/RGO catalyst not only equips with an outstanding electrocatalytic activity for the methanol oxidation reaction (2.3 times that of commercial Pt/C catalyst), but also shows a robust durability and superior tolerance to CO poisoning. The excellent electrocatalytic performance could be attributed to the three-dimensional hierarchical structure, porous dealloyed nanoparticles and synergistic effect between each component.     

Facile one-step fabrication of bimetallic Co–Ni–P hollow nanospheres anchored on reduced graphene oxide as highly efficient electrocatalyst for hydrogen evolution reaction

It is significant but challenging to develop noble-metal-free electrocatalysts exhibiting high activity and long-term stability toward hydrogen evolution reaction (HER) to satisfy the ever-increasing demand for clean and renewable energy. Herein, an environment-friendly and low-temperature electroless deposition method is developed for the synthesis of Co–Ni–P hollow nanospheres anchored on reduced graphene oxide nanosheets (Co–Ni–P/RGO). By optimizing the molar ratio of Ni/Co precursor, composition dependent electrocatalytic performances toward HER of nanostructured Co–Ni–P/RGO electrocatalyst are investigated in 1.0 M KOH solution. The results suggest that when the molar ratio of Ni/Co precursor is 3/7, as-prepared ternary Co–Ni–P/RGO electrocatalyst exhibits a remarkably enhanced HER activity in comparison to binary Ni–P/RGO and Co–P/RGO electrocatalysts, delivering a current density of 10 mA cm⁻² at the overpotential of only 207 mV. The value of Tafel slope for nanostructured Co–Ni–P/RGO electrocatalyst reveals that HER process undergoes Volmer-Heyrovsky mechanism. Besides, nanostructured Co–Ni–P/RGO electrocatalyst features superior stability under alkaline condition. The results suggest that nanostructured composite of Co–Ni–P hollow nanospheres/RGO is a potential candidate for hydrogen production through water splitting.     

Enhanced photodegradation toward graphene–based MgFe2O4–TiO2: Investigation and optimization

In this work, graphene–based MgFe₂O₄–TiO₂ (MFO–TiO₂@rGO) nanocomposite was synthesized and conducted an efficient photo–treatment with p–nitrophenol (PNP) as a well–known pollutant in water. The ternary material was characterized by modern analysis methods including Fourier transform infrared spectroscopy, X–ray diffraction, Raman spectroscopy, Transmission electron microscopy, Energy–dispersive X–ray spectroscopy, Selected area electron diffraction, and UV–vis spectroscopy. The simultaneous effects of the volume of H₂O₂, catalyst dosage, and pH on the photodegradation of p–nitrophenol were also examined by full factorial experimental design according to Box–Behnken designs. As a result, the characterization has confirmed the uniform bounding of MFO and TiO₂ nanosizing from 4 to 6 nm on graphene with a high crystallinity degree. The photocatalysis of this material toward PNP can reach up to ～99.44% in only 60 min reaction under UV control with 1.12 mL H₂O₂ added, 38.15 mg catalyst, and pH 9. Besides, in solar condition (directly under sun), the material also expressed a relatively impressive capability in degrade PNP from water. Furthermore, the ternary nanocomposite can be easily recycled and reused with an inconsiderable change in yield, represented by the elimination yield of recovered MFO–TiO₂@rGO was significantly more than 90% after ten–run cycles. Indeed, the nanocomposite suggests an efficient pathway for treating organic contaminants in wastewater treatment.     

Monodisperse nickel–palladium alloy nanoparticles supported on reduced graphene oxide as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane

Addressed herein is the catalysis of reduced graphene oxide-supported monodisperse NiPd alloy nanoparticles (NPs) (rGO-NiPd) in the hydrolytic dehydrogenation of ammonia borane (AB). This is the first example of the use of NiPd alloy NPs as catalyst in the hydrolytic dehydrogenation of AB. Monodisperse NiPd alloy NPs (3.5 nm) were synthesized by co-reduction of nickel(II) acetate and palladium(II) acetylacetonate in oleylamine (OAm) and borane-tert-butylamine complex (BTB) at 100 °C. The current recipe allowed to control the composition of NiPd alloy NPs and to study the composition-controlled catalysis of rGO-NiPd in the hydrolytic dehydrogenation of AB. Among the all compositions tested, the Ni₃₀Pd₇₀ was the most active one with the turnover frequency of 28.7 min⁻¹. The rGO-Ni₃₀Pd₇₀ were also durable catalysts in the hydrolytic dehydrogenation of AB providing 3650 total turnovers in 35 h and reused at six times without deactivation. The detailed reaction kinetics of hydrolytic dehydrogenation of AB revealed that the reaction proceeds first order with respect to the NiPd concentration and zeroth order with respect to the AB concentration. The apparent activation energy of the catalytic dehydrogenation of AB was also calculated to be E_a^app = 45 ± 2 kJ*mol⁻¹.