Controllable preparation of boron nitride microspheres and their epoxy-based thermoconductive composites

How to prepare spherical boron nitride (BN) particle with different size is an extremely challenging work. In this paper, the controllable preparation of spherical BN particle from nanospheres to microsphere was realized by changing the synthesis temperature of trimethyl borate (B(OMe)₃) and ammonia. The spherical precursor (SP) with high oxygen content was obtained first, and then it was heated under flowing ammonia atmosphere to form stable boron nitride microspheres (BNMS). The BNMS exhibits onion-like cavitation structure with a diameter of 0.8–3.4 μm. The effects of the lower reaction temperature (700–825 °C) and gas flow rate on the spherical precursor are discussed. A possible mechanism is proposed to explain the formation of precursors and the appearance of onion-like structure. It is believed that the formation of microsphere is due to the deposition and growth of BO species during the flow process of nanosphere. In addition, the effect of the addition of BNMS on the thermal conductivity of epoxy resin (EP) composites was investigated.     

The synthesis,properties, and potential applications of CoS2 as a transition metal dichalcogenide (TMD)

Cobalt disulfide (CoS₂) is an attractive member of the dichalcogenides family, which has attracted a lot of attention due to its abundance of constituents and its special properties such as semi-metallic conductivity and large surface area. Particularly, the high theoretical capacity of CoS₂ is so beneficial for energy storage systems such as different types of batteries, supercapacitors, and dye-sensitized solar cells (DSSCs). Furthermore, CoS₂ has the lowest chemisorption energy for atomic hydrogen among other pyrite types. In this review, different methods for the synthesis of CoS₂ are discussed and the role of CoS₂ as an active electrode material for various applications such as different kinds of batteries, supercapacitors, DSSCs, an electrocatalyst for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR) reactions, and as a component in the sensor's construction is investigated. Moreover, several solutions to solve the challenges of using CoS₂, such as volume changes during cycling or aggregation of nanoparticles, are presented and discussed. We hope that this information will be beneficial for many researchers around the world and suggest promising paths for future projects.     

Compressor speed control design using PID controller in hydrogen compression and transfer system

Hydrogen is an energy carrier which can be processed by high pressure compressor and they can be transported, stored and converted to electricity for later use. This paper proposes a hydrogen compression model development and modeling of hydrogen transportation between two tanks using MATLAB software version 22. The proposed model provides amount of hydrogen required in volumes (m³) and compressor power required in (KW) for compressor speed of 500 rad/s, 1000 rad/s and 1500 rad/s. This model provides hydrogen volume of 1 m³ and 10 KW compressor power requirement at 500 rad/s compressor speed. For compressor speed of 1000 rad/s, the proposed model provides hydrogen volume of 10 m³and 20 KW compressor power requirements and for 1500 rad/s this model provides volume of 30 m³and 30 KW compressor power requirements which indicates that the increase in compressor speed increases hydrogen volume generated and increase the power requirement also. For maintaining compressor speed at desired value, a PID (Proportional + Integral + Derivative) controller has been designed and the results were compared with Proportional (P), PI (Proportional + Integral), and PD (Proportional + Derivative) controllers. PID controller performance can be measured using the parameters delay time and settling time. Low values of settling time and delay time indicate the better performance of PID controller. P controller achieves the desired compressor speed with delay time of 228 ms; settling time of 1250 s. PI controller achieves the desired compressor speed with delay time of 210 ms, settling time of 1210 s. PD controller achieves the desired compressor speed with delay time of 185 ms, settling time of 1280 s. PID controller provides better speed regulation with low delay time of 110 ms and settling time of 1120 s when compared with P, PI, PD controllers. From the simulation results it is observed that PID controller can be a good option for slow process like hydrogen gas flow through pipeline for effective speed regulation.     

Experimental study and optimization of flow field structures in proton exchange membrane fuel cell under different anode modes

As one of the critical components in the proton exchange membrane fuel cell (PEMFC), the flow field is crucial to the improvement of cell performance. However, the current research on flow field structure lacks consideration of the influence of different anode modes, which makes the existing flow field structure rules have limitations in the practical application of PEMFC. In this paper, the PEMFC characteristics of parallel flow field, S-shaped flow field, multi-serpentine flow field and single-serpentine flow field at the cathode side are compared experimentally in the dead-end anode (DEA) mode and hydrogen circulation anode (HCA) mode, respectively. Especially, the spatial current density distribution and parasitic power of different flow field structures are measured. The results show that the performance trends of different flow field structures change with the DEA and HCA anode modes. In DEA mode, the PEMFC is prone to flooding, and the flow field with high gas velocity in the channel has better drainage ability, which can obtain higher cell performance. The HCA mode is helpful for the discharge of water in the PEMFC, which effectively alleviates the adverse impact of water accumulation on the overall performance, and the mass transport ability of the flow field structure plays a leading role in the cell performance improvement. In addition, although the high gas flow velocity has better drainage ability in the flow field, it may lead to a decrease in the current density distribution uniformity and PEMFC net output power density. Based on the comprehensive consideration of the experimental results, the multi-serpentine flow field is more suitable for DEA mode, and the S-shaped flow field is more suitable for HCA mode.     

Performance-emission optimization in a single cylinder CI-engine with diesel hydrogen dual fuel: A spherical fuzzy MARCOS MCGDM based Type-3 fuzzy logic approach

This paper presents a novel approach to optimize the performance and emission characteristics of a single cylinder compression ignition engine using diesel-hydrogen dual fuel. A TMI (timed manifold injection) system was designed employing an ECU (electronic control unit) for hydrogen induction into the engine manifold. The results showed a significant enhancement in BTHE (12.44% Max. enhancement at 85% full load condition under DH4 strategy) compared to base-diesel operation. The NOx emissions were enhanced to a maximum of 10.33 g/kw-hr at full load under the DH4 strategy. The emissions of UHC were found to be higher at lower loads and get significantly reduced to a maximum of 3.98 g/kw-hr at full load under the DH2 strategy. In comparison, soot emissions decrease substantially and are reduced to a maximum of 0.02 g/kw-hr at 85% full load condition under the DH5 strategy. The proposed method utilizes a Spherical Fuzzy MARCOS MCGDM-based Type-3 Fuzzy Logic approach, which integrates several criteria and uncertain inputs to improve decision-making. The paper outlines the theoretical framework of the approach and the experimental setup used for validation. The results demonstrate that the proposed method significantly reduces emissions while simultaneously improving the engine's performance. Overall, this study offers an innovative and effective solution for optimizing the performance and emissions of diesel-hydrogen dual fuel engines.     

The CdS/CaTiO3 cubic core-shell composite towards enhanced photocatalytic hydrogen evolution and photodegradation

The CdS/CaTiO₃ cubic core-shell composite is synthesized via a hydrothermal-chemical method. The CdS/CaTiO₃ cubic core-shell composite (CdS/CTO-2) exhibits remarkable photocatalytic HER activity (∼1025.27 μmol·g⁻¹ h⁻¹) and photodegradation enhancement than that of single CaTiO₃ (∼21 folds of HER, ∼19 folds of photodegradation) and single CdS (∼15 folds of HER, ∼15 folds of photodegradation), and a decent stability. There, CdS/CaTiO₃ composite with appropriate potential gradient and CdS with better visible light response can improve carrier efficiency, including increasing carrier transportation, prolonging lifetime and decreasing recombination. Additionally, cubic core-shell microstructure can increase active sites, while maintaining photocatalytic stability.     

Dynamic hydrogen bubble template electrodeposition of Ru on amorphous Co support for electrochemical hydrogen evolution

Electrolyzing water is an environmentally friendly and renewable way to obtain high purity hydrogen. Ruthenium has strong water dissociation ability and suitable hydrogen adsorption energy, so it is considered as one of the candidates of excellent electrocatalysts for hydrogen evolution in alkaline solution. The dynamic hydrogen bubble template (DHBT) is a good electrodeposition technology, which can obtain the 3D metal foams. However, as far as we know, there is no report on the preparation of Ru electrocatalyst by the DBHT method. In this work, the trumpet-shaped Ru on amorphous cobalt support (T-Ru/a-Co) is prepared by the DHBT electrodeposition for the first time. The defect locations are uniformly distributed on the surface of amorphous cobalt (a-Co), which can effectively lead to the formation of nano-bubble template in the DHBT process. However, this special morphology cannot be obtained on the surface of crystalline Co (c-Co). In addition, the electronic structure of T-Ru/a-Co has also been obviously modified, in which the proportion of Ru⁴⁺/Ru⁰ in T-Ru/a-Co has increased, accompanied by the change of binding energy of Ru. It only needs an overpotential of 49 mV to obtain a current density of 10 mA cm⁻² for the T-Ru/a-Co. The specific activity (SA), turnover frequency (TOF) and mass activity (MA) of T-Ru/a-Co are 0.23 mA cm⁻², 0.48 s⁻¹ and 0.24 A mg⁻¹, which are both higher than those of Pt/C, the disk-shaped Ru on the c-Co support (D-Ru/c-Co) and Ru/C, respectively.     

Unveiling the promotion effect of Zr species on SBA-15 supported nickel catalysts for CO2 methanation

Introducing promoters on Ni-based catalysts for CO₂ methanation have been proved to be positive for enhancing their performance. And the correlation of the promotion mechanism and the reaction pathway is significant for designing efficient catalysts. In this contribution, series of Zr species promoted SBA-15 supported Ni catalysts were prepared by citric acid complexation method under a range of Zr/Ni atomic ratios from 0 to 2.5. In situ and ex situ characterizations were carried out. It was found that the addition of citric acid was conductive to improve CH₄ selectivity due to the higher concentrations of Ni⁰ confined in SBA-15, harvesting sufficient H atoms for CH₄ formation following formate pathway via a formyl intermediate. Furthermore, a coverage layer of Zr species was found on the support at Zr/Ni = 1.7, which interacted with the Ni particles, providing higher concentrations of medium basic sites for CO₂ activation. Accordingly, the optimum catalytic performance was obtained on ZrNi-1.7(CI), achieving CO₂ conversion as high as 78.1% and nearly 100% CH₄ selectivity at 400 °C, following the formate hydrogenation pathway. In addition, the ZrNi-1.7(CI) showed good stability owing to the confinement effect of SBA-15 and the Ni–Zr interaction, no carbon deposits were detected after 50 h test.     

Deciphering the Superior Electronic Transmission Induced by the Li–N Ligand Pairs Boosted Photocatalytic Hydrogen Evolution

Atomic level decoration route is designated as one of the attractive methods to regulate both the charge density and band structure of photocatalysts. Moreover, to enable more efficient separation and transport of photocarriers, the construction of novel active sites can enhance both the reactivity and electrical conductivity of the crystal. Herein, an Li–N ligand is constructed via co-doping lithium and nitrogen atoms into ZnIn₂S₄ lattice, which achieves a promoted photocatalytic H₂ evolution at 9737 µmol g⁻¹ h⁻¹. The existence of Li–N ligand pairs and the behaviors of photocarriers on L₄₀N₅ZIS are determined systematically, which also provides a unique insight into the mechanism of the improved photocarrier migration rate. With the introduction of Li–N dual sites, the vacancy form of ZnIn₂S₄ has changed and the photocatalytic stability is significantly improved. Interestingly, the change of charge density around Li–N ligand in ZnIn₂S₄ is determined by theoretical simulations, as well as the regulated energy barrier of photocatalytic water splitting caused by Li–N dual sites, which act as both adsorption site for H₂O and stronger reactive sites. This work helps to extend the understanding of ZnIn₂S₄ and offers a fresh perspective for the creation of a Li–N co-doped photocatalyst.     

Enhancing dehydrogenation performance of MgH2/graphene heterojunctions via noble metal intercalation

Graphene has been identified as a promising catalyst for improving the dehydrogenation performance of MgH₂, however, an in-depth understanding of the mechanism is still lacking. Therefore, we constructed MgH₂/graphene heterojunctions to deeply investigate the effect of graphene on the dehydrogenation performance of MgH₂, and introduced noble metals (Pd and Pt) for further dehydrogenation performance enhancement. Our findings showed that graphene experienced difficulty in directly affecting the interaction on the MgH₂ (110) surface, and the enhanced dehydrogenation of MgH₂/graphene heterojunction resulted from the weakened Mg–H interaction via the special charge distribution in the interaction region and narrowing of the band gap due to graphene introduction. In addition, Pd and Pt intercalation enhanced the structural stability and comprehensively improved the dehydrogenation performance indicators. In particular, the altered interfacial properties of intercalated heterojunctions induced a two-step dehydrogenation reaction, resulting in Pd- and Pt-intercalated MgH₂/graphene heterojunctions with a superior dehydrogenation performance.