Thermomechanical stability and inelastic energy dissipation as durability criteria for fuel cell gas diffusion media with pre-assembly effects

In this article, pre-assembly hot-press pressure and thermal expansion effects in gas-diffusion layers (GDLs) are addressed to explore the practicalities of the constitutive model reported in the companion article. A facile technique is proposed to include deformation history dependent residual strain effects. The model is implemented in the numerical environment and compared with widely followed conventional models such as isotropic and orthotropic material models. With the normal and accelerated thermal expansion effects no significant variation in stresses or strains is reported with the compressible GDL model in contrast to the conventional incompressible form of the GDL model. The present work identifies the critical differences with advanced and extended variants of the model along with conventional GDL material models in terms of planar stress/strain distribution and the membrane response. Finally, the model is simulated for micro-cyclic stress loads of varying amplitudes that imitate the real working conditions of fuel cell. The inelastic energy dissipation in GDLs is predicted using the proposed model, which is utilized further to distinguish the safe (elastic) and unsafe (inelastic shakedown) operating limits. The inelastic collapse of GDLs is shown to be a active function of high amplitude micro-cyclic load with high initial clamping load.     

Microstructures and properties of nickel-titanium carbide composites fabricated by laser cladding

In this work, Ni/TiC composites were synthesized by the laser cladding technique (LCT). A scanning electron microscope (SEM), X-ray diffractometer (XRD), microhardness meter, electrochemical workstation, and friction and wear tester examined the microstructure, surface morphology, phase structure, microhardness, wear, and corrosion resistances of the Ni/TiC composites. These results indicated the Ni/40TiC composite contained finer equiaxed crystals than the Ni and Ni/20TiC composites. In addition, numerous TiC particles in the Ni/40TiC composite impeded growth of the nickel crystals, which resulted in the fine microstructure of the Ni/40TiC composite. The Ni, Ni/20TiC, and Ni/40TiC composites exhibited face-centered cubic (f c c) lattices. The average microhardness values of the Ni/20TiC and Ni/40TiC composites were approximately 748 HV and 851 HV, respectively. The Ni/40TiC composite had the lowest friction coefficient (0.43) among all three coatings, and only some shallow scratches appeared on the surface of the Ni/40TiC composite. The corrosion potential (E) of Ni/40TiC exceeded the Ni/20TiC composite, and both were larger than the Ni composite, which indicated the Ni/40TiC composite had outstanding corrosion resistance and the Ni composite had poor corrosion resistance. The corrosion current densities (i) of Ni, Ni/20TiC, and Ni/40TiC composites were 5.912, 4.405, and 3.248 μA/cm², respectively.     

Catalytic combustion synthesis of CNTs/MgO composite powders and the influences on the thermal shock resistance of low-carbon Al2O3–C refractories

Using MgC₂O₄, Mg powders as raw materials and Ni(NO₃)₂?6H₂O as a catalyst, CNTs/MgO composite powders were prepared by a catalytic combustion synthesis method. The CNTs/MgO composite powders were characterized by XRD, Raman spectroscopy, FESEM/EDS and HRTEM. The effects of catalyst content on the degree of graphitization and aspect ratio of the CNTs in composite powders were investigated. Moreover, the thermal shock resistance of low-carbon Al₂O₃–C refractories after adding the composite powder was investigated. The results indicated that the CNTs prepared with 1 wt% Ni(NO₃)₂?6H₂O addition had a higher degree of graphitization and aspect ratio. In particular, the aspect ratio could reach approximately 200. The growth mechanism of hollow bamboo-like CNTs in the composite powders was proven to be a V-L-S mechanism. The thermal shock resistance of Al₂O₃–C samples could be improved significantly after adding CNTs/MgO composite powders. In particular, compared with CM0, the residual strength ratio of Al₂O₃–C samples with added 2.5 wt% composite powders could be increased 63.9%.     

Density functional theory study of the hydrogen evolution reaction in haeckelite boron nitride quantum dots

To satisfy arising energy needs and to handle the forthcoming worldwide climate transformation, the major research attention has been drawn to environmentally friendly, renewable and abundant energy resources. Hydrogen plays an ideal and significant role is such resources, due to its non-carbon based energy and production through clean energy. In this work, we have explored catalytic activity of a newly predicted haeckelite boron nitride quantum dot (haeck-BNQD), constructed from the infinite BN sheet, for its utilization in hydrogen production. Density functional theory calculations are employed to investigate geometry optimization, electronic and adsorption mechanism of haeck-BNQD using Gaussian16 package, employing the hybrid B3LYP and wB97XD functionals, along with 6–31G(d,p) basis set. A number of physical quantities such as HOMO/LUMO energies, density of states, hydrogen atom adsorption energies, Mulliken populations, Gibbs free energy, work functions, overpotentials, etc., have been computed and analysed in the context of the catalytic performance of haeck-BNQD for the hydrogen-evolution reaction (HER). Based on our calculations, we predict that the best catalytic performance will be obtained for H adsorption on top of the squares or the octagons of haeck-BNQD. We hope that our prediction of most active catalytic sites on haeck-BNQD for HER will be put to test in future experiments.     

A review of hydrogen production processes by photocatalytic water splitting – From atomistic catalysis design to optimal reactor engineering

‘Renewable energy is an essential part of our strategy of decarbonization, decentralization, as well as digitalization of energy.’ – Isabelle Kocher.Current climate, health and economic condition of our globe demands the use of renewable energy and the development of novel materials for the efficient generation, storage and transportation of renewable energy. Hydrogen has been recognised as one of the most prominent carriers and green energy source with challenging storage, enabling decarbonization. Photocatalytic H₂ (green hydrogen) production processes are targeting the intensification of separated solar energy harvesting, storage and electrolysis, conventionally yielding O₂/H₂. While catalysis is being investigated extensively, little is done on bridging the gap, related to reactor unit design, optimisation and scaling, be it that of material or of operation. Herein, metals, oxides, perovskites, nitrides, carbides, sulphides, phosphides, 2D structures and heterojunctions are compared in terms of parameters, allowing for efficiency, thermodynamics or kinetics structure–activity relationships, such as the solar-to-hydrogen (STH). Moreover, prominent pilot systems are presented summarily.     

Engineering biphasic hybrid phosphide nanowires as efficient electrocatalyst for hydrogen evolution reaction: Experimental and theoretical insights

Development of highly efficient and cheap electrocatalysts towards the hydrogen evolution reaction (HER) is of great importance for electrochemical water splitting. Herein, hybrid Cu/NiMo-P nanowires on the copper foam were successfully fabricated via a simple two-step method. The hierarchically structured Cu/NiMo-P exhibits large surface areas and rapid electron transfer ability, leading to enhanced catalytic activity. The as-prepared Cu/NiMo-P electrodes need overpotentials of 34 mV and 130 mV to obtain 10 mA cm^?2 for HER in acidic and alkaline solutions, respectively. Density functional theory (DFT) calculations reveal that the Cu/NiMo-P hybrid has a more thermo-neutral hydrogen adsorption free energy and enhanced charge transfer ability as well.     

Designing optical glasses by machine learning coupled with a genetic algorithm

Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (T_g) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (n_d) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high n_d (1.7 or more) and low T_g (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses.     

Interface regulation effects on mechanical behavior of heterostructure Ti6Al4V/TiAl-based laminated composite sheets

Design of architectured composites with layered-ordered structure can solve the strength-toughness mismatch problem of structural materials. In the present study, heterostructure Ti6Al4V/TiAl laminated composite sheets with different thicknesses of interface layer and TiAl composite layer were successfully produced by hot-pressing technology. The effects of interface regulation and laminated structure on their mechanical properties, crack propagation, and fracture behavior were studied. The results indicated that compressive strength of the sheets increased with the decrease in interface thickness. Compressive strength of TiAl composite sheet with thicker composite layer reached 1481.55 MPa at the arrester orientation with sintering holding time of 40 min, which was 25.96% higher than that of the sheet obtained at 120 min. Analysis indicated that the interface area transferred stress through slip bands and through-interface cracks. Compressive strength at the divider orientation reached 1443.06 MPa, which was 45.78% higher than that of the sheet obtained at 120 min. In this case, the interface area transferred stress through slip bands and along-interface cracks. For TiAl composite sheets with thinner composite layer, compressive strength was further improved to 1631.01 MPa and 1594.66 MPa at the arrester and divider orientations with sintering holding time of 40 min, respectively. The ductile metal layer exerted a significant toughening effect. Both interface regulation and laminated structure transformation could enhance the hetero-deformation induced (HDI) strengthening and improve the comprehensive mechanical properties of the composite sheets.     

Role and prospects of green quantum dots in photoelectrochemical hydrogen generation: A review

Eco-friendly quantum dots (QDs) can be termed green QDs which stand as an attractive choice to modify the properties of known semiconductors in the direction of getting efficient photoelectrodes for solar-induced photoelectrochemical (PEC) splitting of water, due to their peculiar properties. Thus, it is of high significance to analyze their merit/demerit as an effective scaffold in PEC cell. QDs are known for their excellent optical properties however, the coupling of green QDs with semiconductor is not only useful in improving absorption characteristics but also promotes charge transfer. This review has undertaken the critical analysis on the worldwide research going on the green QDs modified photoelectrode with respect to their optical, electrical & photoelectrochemical properties, role, usefulness, efficiency, and finally the success in PEC system for hydrogen production. Various methods on the facile synthesis & sensitization techniques of green QDs available in the literature have also been discussed. Further, recent advances on the development of green QDs based photo-electrode, along with major challenges of using green QDs in this field have also been presented.     

Design of Ti4+-doped Li3V2(PO4)3/C fibers for lithium energy storage

In this work, we propose a facile approach to fabricate Ti⁴⁺-doped Li₃V₂(PO₄)₃/C (abbreviated as C-LVTP) nanofibers using an electrospinning route followed by a high temperature treatment. In this designed nanocomposite, the ultrafine LVTP dots are homogeneously dispersed into one-dimensional carbon nanofibers and the Ti⁴⁺ doping does not destroy the crystal structure of monoclinic Li₃V₂(PO₄)₃. Compared to the undoped Li₃V₂(PO₄)₃/C (abbreviated as C-LVP), the as-fabricated C-LVTP fibers present higher reversible capacity, superior high-rate capability as well as better cyclic property. Especially, the C-LVT_7%P cathode delivers not only high capacities of 187.2 and 160.3 mAh g^?1 at 0.5 and 10 C respectively, but also stable cyclic property with the reversible capacity of 135.8 mAh g^?1 at 20 C following 500-cycle spans. The good battery characteristics of C-LVT_7%P can be mainly ascribed to Ti⁴⁺ doping, which can increase the electrical conductivity and Li⁺ diffusion coefficient.