Investigations on hydrogenation behaviour of CNT admixed Mg2Ni

The aim of the present paper is to report results on hydrogenation behaviour of the new composite material Mg₂Ni: CNT. Admixing of carbon nanotubes (CNT) in storage material Mg₂Ni leads to noticeable enhancement in desorption kinetics as well as storage capacity. We have found that the composite material Mg₂Ni–2 mole% CNT is the optimum material. The Mg₂Ni–CNT composite exhibits hydrogen desorption rate of 5.7 cc/g/min as against 3.0 cc/g/min for Mg₂Ni alone (enhancement of ∼ 90%) and storage capacity of ∼ 4.20 wt% in contrast to ∼3.20 wt% for Mg₂Ni alone (increase of ∼ 31%). Feasible mechanisms for the enhancement of hydrogen desorption kinetics and storage capacity have been put forward.     

Effect of CNT concentration and agitation on surface heat flux during quenching in CNT nanofluids

In this article, the effect of Carbon Nanotube (CNT) concentration and agitation on the heat transfer rate has been studied during immersion quenching in CNT nanofluids. For this purpose, CNT nanofluids were prepared by suspending chemically treated CNTs (TCNT) at four different concentrations in deionized (D.I) water without using any surfactant. Quench probes with a diameter of 20 mm and a length of 50 mm were machined from 304L stainless steel (SS) and quenched in water and CNT nanofluids with the CNT concentration ranging from 0.25 to 1.0 wt.%. The heat flux and temperature at the quenched surface were estimated based on the Inverse Heat Conduction (IHC) method using the temperature data recorded at 2 mm below the probe surface during quenching. The computation results showed that the peak heat flux increased with an increase in the CNT concentration up to 0.50 wt.% and started decreasing with further increase in the CNT concentration. The enhanced heat transfer performance of CNT nanofluids during quenching at lower concentration of CNTs is attributed to their higher effective thermal conductivity. The reduced heat transfer performance of CNT nanofluids having higher concentration of CNTs is due to the increased viscosity of CNT nanofluids. The effect of agitation on heat transfer rate during quenching has also been studied in this work by stirring the CNT nanofluid prepared with 0.50 wt.% of CNTs which recorded the maximum peak heat flux among the four concentrations. The effect of CNT nanofluid agitation was counter-intuitive and resulted in decreased heat transfer rate with the increase in agitation rate.     

Effect of CNT structures on thermal conductivity and stability of nanofluid

Thermal conductivity and stability of carbon nanotube (CNT) structures in water-based nanofluid, as well as their dependence to temperature and time variation are of a great concern. In order to investigate such dependence, five different structures, namely SWNT (single wall CNT), DWNT (double wall CNT), FWNT (few wall CNT) and two different multiwalls were applied in this study. The experiments reveal that the maximum UV–VIS absorbance of the solution corresponds to the dispersion of SWNT in the base fluid. The results from zeta size distribution and thermal conductivity demonstrate that as the number of nanotube wall increase, both stability and thermal conductivity decrease.     

Microwave assisted,facile synthesis of Pt/CNT catalyst for proton exchange membrane fuel cell application

The present study aims at developing a high performing Pt/CNT catalyst for ORR in PEM fuel cell adopting modified chemical reduction route using a mixture of NaBH₄ and ethylene glycol (EG) as reducing agent. In order to select the most suitable reduction conditions to realize high performing catalyst, heating of the reaction mixture is done following two methods, conventional heating (CH) or microwave (MW) irradiation. The synthesized Pt/CNT catalysts were extensively characterized and evaluated in-situ as ORR catalyst in PEM fuel cell. A comparison of their performance with the standard, commercial Pt/C catalyst was also made. The results showed deposition of smaller Pt nanoparticles with uniform distribution and higher SSA for Pt/CNT-MWH compared to Pt/CNT-CH. In-situ electrochemical characterization studies revealed higher ESA, lower charge transfer resistance, lower activation over-potential loss and higher peak power density compared to the cathode with Pt/CNT-CH and Pt/C. This study suggests the viability of MW assisted, metal particle deposition as a simple, yet effective method to prepare high performing Pt/CNT catalyst for ORR in PEM fuel cell.     

Heat transfer of aqueous suspensions of carbon nanotubes (CNT nanofluids)

This paper is mainly concerned about the heat transfer behaviour of aqueous suspensions of multi-walled carbon nanotubes (CNT nanofluids) flowing through a horizontal tube. Significant enhancement of the convective heat transfer is observed and the enhancement depends on the flow conditions (Reynolds number, Re), CNT concentration and the pH, with the effect of pH smallest. Given other conditions, the enhancement is a function of axial distance from the inlet, increasing first, reaching a maximum, and then decreasing with increasing axial distance. The axial position of the maximum enhancement increases with CNT concentration and Re. Given CNT concentration and the pH level, there appears to be a Re above which a big increase in the convective heat transfer coefficient occurs. Such a big increase seems to correspond to the shear thinning behaviour. For nanofluids containing 0.5 wt.% CNTs, the maximum enhancement reaches over 350% at Re = 800, which could not be attributed purely to the enhanced thermal conduction. Particle re-arrangement, shear induced thermal conduction enhancement, reduction of thermal boundary due to the presence of nanoparticles, as well as the very high aspect ratio of CNTs are proposed to be possible mechanisms.     

Aligned CNT/Polymer nanocomposite membranes for hydrogen separation

CNT/Polymer nanocomposites have been fabricated by dispersing (0.1%) weight fraction of SWNT and MWNT in polycarbonate matrix separately using benzene as a solvent. Alignment has been performed by inducing DC electric field (500 V/cm). X-ray diffraction measurements have been performed to confirmation of SWNT, MWNT and their presence in PC matrix. Gas permeability has been found to be increased in aligned CNT/polymer nanocomposites comparison to random dispersed CNT/polymer nanocomposites. The electrical conductivity in aligned CNT/polymer composite membranes indicates two resistive regions. Experimental results exhibits here that CNT/polymer nanocomposite membranes can be used as good hydrogen separating media. Surface morphology of aligned CNT/polymer nanocomposites was confirmed by optical microscopy.     

Hydrogen supply chain and challenges in large-scale LH2 storage and transportation

Hydrogen is considered to be one of the fuels of future and liquid hydrogen (LH2) technology has great potential to become energy commodity beyond LNG. However, for commercial widespread use and feasibility of hydrogen technology, it is of utmost importance to develop cost-effective and safe technologies for storage and transportation of LH2 for use in stationary applications as well as offshore transportation. This paper reviews various aspects of global hydrogen supply chain starting from several ways of production to storage and delivery to utilization. While each these aspects contribute to the overall success and efficiency of the global supply chain, storage and delivery/transport are the key enablers for establishing global hydrogen technology, especially while current infrastructure and technology are being under development. In addition, while all storage options have their own advantages/disadvantages, the LH2 storage has unique advantages due to the familiarity with well-established LNG technology and existing hydrogen technology in space programs. However, because of extremely low temperature constraints, commercialization of LH2 technology for large-scale storage and transportation faces many challenges, which are discussed in this paper along with the current status and key gaps in the existing technology.     

B 12/ CNT anodic nano catalysis applied on polishing the performance of microbial fuel cells

Microbial fuel cells (MFCs) are a newly emerging technology in bioenergy processing. This research is to replace the use of platinum catalysts. Three types of oxygen reduction catalysts (B12/XC-72, B12/CNT and B12/AC) are analyzed and compared with the other two activated sludge and no catalyst where the performance of activated carbon in MFCs are evaluated. The results show that the catalyst with B12 vitamin as the main body has a higher open-circuit voltage. Among them, the open-circuit voltage of B12/CNT is the highest with 0.667 V, which is about 2 times that of MFCs without catalyst. The highest electrical performance with 0.54 W m^?2 is 3.17 times that of catalyst-free MFCs, which shows that the self-made B12/CNT catalyst MFCs have the best performance in this study. The related research will be helpful for the application of wastewater to energy.     

“Green” path from fossil-based to hydrogen economy: An overview of carbon-neutral technologies

While the dominant role of hydrogen in a sustainable energy future is widely accepted, the strategies for the transition from fossil-based to hydrogen economy are still actively debated. This paper emphasizes the role of carbon-neutral technologies and fuels during the transition period. To satisfy the world's growing appetite for energy and keep our planet healthy, at least 10 TW (or terawatt) of carbon-free power has to be produced by mid-century. Three prominent options discussed in the literature include: decarbonization of fossil energy, nuclear energy and renewable energy sources. These options are analyzed in this paper with a special emphasis on the role of hydrogen as a carbon-free energy carrier. In particular, the authors compare various fossil decarbonization strategies and evaluate the potential of nuclear and renewable energy resources to meet the 10 TW target. An overview of state-of-the-art technologies for production of carbon-free energy carriers and transportation fuels, and the assessment of their commercial potential is provided. It is shown that neither of these three options alone could provide 10 TW of carbon-neutral power without major changes in the existing infrastructure, and/or technological breakthroughs in many areas, and/or a considerable environmental risk. The authors propose a scenario for the transition from current fossil-based to hydrogen economy that includes two key elements: (i) changing the fossil decarbonization strategy from one based on CO₂ sequestration to one that involves sequestration and/or utilization of solid carbon, and (ii) producing carbon-neutral synthetic fuels from bio-carbon and hydrogen generated from water using carbon-free sources (nuclear, solar, wind, geothermal). This strategy would allow taking advantage of the existing fuel infrastructure without an adverse environmental impact, and it would secure a smooth carbon-neutral transition from fossil-based to future hydrogen economy.     

Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy

The generation of energy by clean, efficient and environmental-friendly means is now one of the major challenges for engineers and scientists. Fuel cells convert chemical energy of a fuel gas directly into electrical work, and are efficient and environmentally clean, since no combustion is required. Moreover, fuel cells have the potential for development to a sufficient size for applications for commercial electricity generation. This paper outlines the acute global population growth and the growing need and use of energy and its consequent environmental impacts. The existing or emerging fuel cells’ technologies are comprehensively discussed in this paper. In particular, attention is given to the design and operation of Solid Oxide Fuel Cells (SOFCs), noting the restrictions based on materials’ requirements and fuel specifications. Moreover, advantages of SOFCs with respect to the other fuel cell technologies are identified. This paper also reviews the limitations and the benefits of SOFCs in relationship with energy, environment and sustainable development. Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are discussed.     

Controlled synthesis of MnO2/CNT nanocomposites for supercapacitor applications

Abstract

In this work, manganese oxide (MnO₂)/carbon nanotube (CNT) nanocomposites have been prepared as electrode materials for supercapacitor applications. The materials were synthesised using a traditional and facile chemical deposition method. Effects from CNT amounts, synthesis time, pH value and CNT treatment using nitric acid have been thoroughly investigated. It was found that the sample synthesised for 3 h at pH 5 had achieved the best performance with a specific capacitance of 115 F g^?1 at a discharge rate of 0·5 A g^?1. A capacitance retention of 95% after 1000 cycles has been observed for the sample synthesised in the neutral environment. We believe that findings from this work will pave a road for nanostructured MnO₂/CNT composites with better performance in energy storage applications.     

Effect of Pt loading on the hydrogen production of CNT/Pt composites functionalized with carboxylic groups

This work reports the morphological and photocatalytic hydrogen generation properties of CNT/Pt composites with and without functionalization by carboxylic/oxygen groups. The composites with and without functionalization were named f-CNT/Pt and CNT/Pt, respectively. Several f-CNT/Pt and CNT/Pt composites with different content of Pt NPs (from 0 to 30 wt%) were synthesized and analyzed by scanning electron microscopy (SEM). Those images revealed that the composites without functionalization presented higher agglomerations of Pt nanoparticles (NPs). Furthermore, the average sizes of the Pt NPs in the named f-CNT/Pt composites (2.3–2.9 nm) were lower than these in the CNT/Pt composites (2.5–3.1 nm). The hydrogen generation rates were also calculated from the decomposition of pure water under UV irradiation (365 nm) and found maximum values of 45.4 and 193.9 μmol·h⁻¹ g⁻¹ for the CNT/Pt and f-CNT/Pt composites (they contained 20 wt% of Pt NPs), respectively. Additional experiments for hydrogen generation were achieved using sodium sulfite as sacrificial agent; in this case, a maximum value of 13850 μmol·h⁻¹ g⁻¹ was obtained for the f-CNT/Pt composite. The f-CNT/Pt composites produced more hydrogen than the CNT/Pt composites because they presented higher content of defects; this was confirmed by the Raman spectra. We also showed that the Pt NPs acted as electron trap centers, which delayed the recombination of the photogenerated electrons and holes, this in turn, enhanced the hydrogen generation rates of the composites (the hydrogen generation was maximized by varying the content of Pt NPs deposited on the CNTs). The CNT/Pt composites presented here were simpler and easier to synthesize than the previous published ternary systems based on TiO₂, CNTs and Pt NPs.     

Crop residues: applications of lignocellulosic biomass in the context of a biorefinery

Interest in lignocellulosic biomass conversion technologies has increased recently because of their potential to reduce the dependency on non-renewable feedstocks. Residues from a variety of crops are the major source of lignocellulose, which is being produced in increasingly large quantities worldwide. The commercial exploitation of crop residues as feedstocks for biorefineries which could be used to produce a variety of goods such as biofuels, biochemicals, bioplastics, and enzymes is an attractive approach not only for adding value to residues but also for providing renewable products required by the expanding bioeconomy market. Moreover, the implementation of biorefineries in different regions has the potential to add value to the specific crop residues produced in the region. In this review, several aspects of crop residue application in biorefineries are discussed, including the role of crop residues in the bioeconomy and circular economy concepts, the main technical aspects of crop residue conversion in biorefineries, the main crop residues generated in different regions of the world and their availability, the potential value-added bioproducts that can be extracted or produced from each crop residue, and the major advantages and challenges associated with crop residue utilization in biorefineries. Despite their potential, most biomass refining technologies are not sufficiently advanced or financially viable. Several technical obstacles, especially with regard to crop residue collection, handling, and pre-treatment, prevent the implementation of biorefineries on a commercial scale. Further research is needed to resolve these scale-up-related challenges. Increased governmental incentives and bioeconomic strategies are expected to boost the biorefinery market and the cost competitiveness of biorefinery products.     

Metal-organic framework derived Co@NC/CNT hybrid as a multifunctional electrocatalyst for hydrogen and oxygen evolution reaction and oxygen reduction reaction

Seeking a multifunctional electrocatalyst composed of earth-abundant elements for highly hydrogen and oxygen evolution reaction and oxygen reduction reaction (HER, OER and ORR) is technically imperative for the electrocatalytic applications. Herein, we report HER, OER and ORR electrocatalytic performances of metal-organic framework (MOF) derived cobalt nanoparticles encapsulated in nitrogen-doped carbon and carbon nanotube (Co@NC/CNT). The optimized Co@NC/CNT hybrid shows superior HER and OER activities with a small overpotential of 137 mV and 302 mV at a current density of 10 mA cm⁻², respectively. Furthermore, the Co@NC/CNT as an air-cathode in secondary Zn-air battery demonstrates a confined potential gap of 0.88 V over 200 h and a maximum power density of 53.4 mW cm⁻², which are much better than those of Pt/C. The outstanding performances are attributed to the synergistic effects from Co, and N embedded into carbon and CNT. More importantly, the unique surface structure contributes to expose many active sites for superior catalytic activity through allowing a large number of electrons. These outcomes not only prove a facile approach for the preparation of metals/carbon hybrid but also disclose its huge possible as a multifunctional electrocatalyst for sustainable energy systems.     

Energy system based on hydrodynamic power in Yakushima Island

Yakushima Island was used as a model area where material recycling and indigenous energy systems would be realized based on the zero-emission concept in the near future. We evaluated the renewable energy resources to propose a regional energy system on this island. In this paper, the present energy demand and supply structure was quantitatively specified, and the water potential was evaluated. The energy system in Yakushima is unique, with hydroelectric power supplying about 30% of the total energy consumption mainly by commercial and residential sectors. However, petroleum remains the main source of primary energy for transportation, heating, and cooking. The hydroelectric power yielded on the island is sufficient to cover all the energy demands on the island. We found that fossil fuel energy in Yakushima could be substituted with hydroelectric energy without causing an impact on the environment.     

Natural resource limitations to terawatt-scale solar cells

The predicted energy demand will reach 28 TW by 2050 and 46 TW by 2100. The deployment of solar cells as a source of electricity will have to expand to a scale of tens of peak terawatts in order to become a noticeable source of energy in the future. Of the current commercial and developmental solar cell technologies, the majority have natural resource limitations that prevent them from reaching a terawatt scale. These limitations include high energy input for crystalline-Si cells, limited material production for GaAs cells, and material scarcity for CdTe, CIGS, dye-sensitized, crystalline-Si, and thin-film Si cells. In this paper, we examine these limitations under the best scenarios for CdTe, CIGS, GaAs, dye-sensitized, and crystalline-Si solar cells. Without significant technological breakthroughs, these technologies combined would meet only a few percentage points (∼2%) of our energy demand in 2100.     

The environmental impact of decentralised generation in an overall system context

Decentralised-generation technologies are very likely to play an important role in our future energy supply. The operational behaviour of several decentralised-generation technologies, as well as their interaction with the central power system, are being discussed and reviewed. The outcome of this analysis is then used to make correct judgements on the global environmental performance of the concept of embedded generation. In order to assess the environmental impact of a massive installation of decentralised-generation units, simulations are being performed using the code PROMIX, a very accurate model of the generation units presently existing (and anticipating those planned in the future) in Belgium. Finally, the simulation results are being discussed and some important conclusions about the environmental impact of decentralised generation can be drawn.     

A novel Central Composite Design based response surface methodology optimization study for the synthesis of Pd/CNT direct formic acid fuel cell anode catalyst

At present, carbon nanotube supported Pd catalysts are synthesized via NaBH₄ reduction method to investigate their electro catalytic activity thorough formic acid electro oxidation. In order to optimize the synthesis conditions such as %Pd amount (X₁), NaBH₄ amount (times, X₂), water amount (ml, X₃), and time (min., X₄), Central Composite Design (CCD) experiments are designed and determined by the Design-Expert program to determine the maximum observed current (mA/mgPd). Formic acid electro oxidation current density of the catalyst is computed by the model as 974.80 mA/mg Pd for the catalyst prepared at optimum operating conditions (41.14 for %Pd amount, 280.23 NaBH₄ amount, 26.80 ml water amount, and 167.14 min time) obtained with numerical optimization method in CCD. This computed value is very close to the experimentally measured value as 920 mA/mg Pd. Finally, formic acid fuel cell measurements were performed on the Pd/CNT catalyst prepared at optimum operating conditions and compared with the commercial Pd black and Pt black catalysts. As a result, Pd/CNT exhibits better performance compared to Pd black, revealing that Pd/CNT is a promising catalyst for the direct formic acid fuel cell measurements.     

Graphene nanosheet–CNT hybrid nanostructure electrode for a proton exchange membrane fuel cell

This work demonstrates two-step growth of graphene nanosheets (GNS), in which carbon nanotubes (CNTs) are grown directly on a carbon cloth. GNS are subsequently constructed on the CNT surface, revealing the stand-up structure of the GNS–CNT hybrid nanostructure. The GNS–CNT hybrid nanostructure shows Nernstian and fast electron-transfer kinetics for electrochemical reactions of Fe(CN)₆^3−/4−. A 0.1 mg cm⁻² Pt/GNS–CNT is used in the cathode of a proton membrane exchange fuel cell, in which the maximum power density is 1072 mW cm⁻² at 80 °C under H₂/O₂. In addition to a low-resistance electron-transfer pathway, the GNS–CNT hybrid nanostructure also provides numerous edge planes with strong electrochemical activity, ultimately enhancing electrochemical activity and fuel cell performance.