Structural study of amorphous ZrFeB and ZrFeSi alloys by 57Fe-Mössbauer and magnetization measurements

The short-range order of melt-spun and mechanically alloyed ZrFeB and ZrFeSi amorphous alloys has been studied by means of ⁵⁷Fe-Mössbauer effect and magnetization measurements. It is shown, that the Fe-surrounding for the Fe concentrations up to 40at.% is nearly independent from additional B alloying, whereas significant changes are obtained for Si additions. It is indicated, that B mainly occupies interstial sites with pure Zr surroundings, whereas Si substitutes on Fe sites. The complete determination of the electric field gradient via magnetic distortion leads to the conclusion, that the same well-defined structural unit is present as observed for binary ZrFe glasses for Fe contents up to 33 at.%. Beyond this concentration, evidence is obtained that separation into a paramagnetic and a ferromagnetic amorphous phase takes place. The ferromagnetic component shows strong induced magnetization in high external fields far above the Curie temperature, preventing the complete determination of the electric field gradient tensor.     

Hexagonal CoSe2 nanosheets stabilized by nitrogen-doped reduced graphene oxide for efficient hydrogen evolution reaction

CoSe₂ is considered as a promising candidate among non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) due to its intrinsic metallicity and low Gibbs free energy for hydrogen adsorption. Recently, the hexagonal CoSe₂ becoming increasingly popular owing to its chemically favorable basal plane, which provides more active sites, but remains limited by the poor stability. In this study, we design a small-molecule-amine-assisted hydrothermal method to in situ anchor the hexagonal CoSe₂ nanosheets (NSs) on nitrogen-doped reduced graphene oxides (RGO) as an advanced electrode material for HER. Due to the existence of abundant functional groups and high specific surface area of RGO, the hexagonal CoSe₂ NSs could be stably formed on RGO. As a result, only a small overpotential of 172 mV is needed for the optimized sample to drive a current density of 10 mA cm⁻² in 0.5 M H₂SO₄ and the Tafel slope is 35.2 mV dec⁻¹, which is comparable with the state-of-the-art Pt catalyst (32.3 mV dec⁻¹). Therefore, the facile and low-cost method for synthesizing hexagonal TMDs with robust electrical and chemical coupling developed in this work is promising in promoting the large-scale application of non-precious electrocatalysts.     

Investigation of the influence of fuel type on energy indicators of an electrochemical generator as a PART of a cogeneration unit

The influence of the type of fuel such as hydrogen, methane, motor diesel fuel, ethanol, motor gasoline and methanol on the fuel utilization ratio, the specific consumption per unit of electrical and heat power generated, the efficiency of the catalytic burner, the solid oxide fuel cell battery and the electrochemical generator has been studied. It has been shown that hydrogen is the best fuel in terms of energy indicators, and methanol is the worst one. For hydrogen, the fuel utilization ratio and specific fuel consumption for the production of electrical power and heat power supplied to heat networks are equal to 1; 0.122 kg r.f./kW·h and 34 kg r.f./GJ, respectively, while for methanol these indicators are 0.359; 0.275 kg r.f./kW·h and 83.7 kg r.f./GJ, respectively. For other types of fuels studied the energy indicators lie between the specified values.     

A theoretical research of dihydrogen storage in ScxNy (x+y=4) compounds

The dihydrogen storage capacity of Sc_xN_y (x + y = 4) compounds have been theoretically investigated at different levels. At B3LYP-D3/6-311G(3df,3pd) level, ScN₃ has multiple isomers with similar energies, which is an interference of hydrogen storage research. Sc₂N₂ and Sc₃N has four and three isomers, respectively. For both systems, the lowest-lying isomers are planar Sc₂N₂ 01 and Sc₃N 01, which are energetically much low-lying by at least 20 kcal/mol than the other isomers, respectively. Sc₃N 01 can adsorb 8H₂ with gravimetric uptake capacity of 9.77 wt %. It satisfies the target specified by US DOE, however, some hydrogen molecules will dissociate and bond atomically on scandium atoms. The strong binding energy (0.66 eV/H₂) exceeds the reversible adsorption range (0.1–0.4 eV/H₂), which will cause high operating temperature to desorb hydrogen during the application process. Sc₂N₂ 01 can adsorb 9H₂ in the molecular form. The H₂ gravimetric uptake capacity of Sc₂N₂ 01 (9H₂) (13.33 wt %) exceeds the target set by US Department of Energy, moreover, its average adsorption energy (0.32 eV/H₂) is in the reversible adsorption range. The interaction of Sc₂N₂ 01 with H₂ molecules is considered by means of the bond critical points (bcp) in the quantum theory of atoms in molecules (QTAIM). The Gibbs free energy corrected adsorption energy points that the adsorption of Sc₂N₂ 01(9H₂) is energetically favorable below 240 K. Therefore, in Sc_xN_y (x + y = 4), the planar compound Sc₂N₂ 01 is more suitable to be a dihydrogen adsorption material.     

Fe3C nanoparticles decorated Fe/N codoped graphene-like hierarchically carbon nanosheets for effective oxygen electrocatalysis

Hierarchically porous carbon sheets decorated with transition metal carbides nanoparticles and metal-nitrogen coordinative sites have been proposed as the promising non-precious metal oxygen electrocatalysts. In this work, we demonstrate a facile and low-cost strategy to in situ form Fe/N codoped hierarchically porous graphene-like carbon nanosheets abundant in Fe-N_x sites and Fe₃C nanoparticles (Fe–N/C) from pyrolyzing chestnut shell precursor. The as-prepared Fe–N/C samples with abundant Fe-N_x sites and Fe₃C nanoparticles show superior electrocatalytic activity to oxygen reduction reaction (ORR) in the alkaline medium as well as high stability and methanol tolerance due to the integration of multi-factors: the high content of Fe-N_x active sites, the coexistence of Fe₃C, the unique hierarchically porous structure and high conductivity of carbon matrix. The optimal Fe–N/C-2-900 sample exhibits a more positive half-wave potential (−0.122 V vs. Ag/AgCl (3 M) reference electrode) than commercial 20 wt% Pt/C catalyst. This study provides a facile approach to synthesize Fe₃C nanoparticles decorated Fe/N co-doped hierarchically porous carbon materials for effective oxygen electrocatalyst.     

Effects of doping with a third element (Pd,Ru, Ta) on the structure and hydrogen permeation properties of V–10Mo solid solutions

Alloying is an effective method for improving the resistance of V metals to hydrogen embrittlement. The effects of the doping with a third element (Pd, Ru, Ta) on the structure and hydrogen permeation properties of V–10Mo solid solutions have been investigated in this study. As-prepared V–5Mo-5TM (TM = Mo, Pd, Ru, Ta) alloy samples composed of V-based solid solution with a bcc structure are hydrogenated into their corresponding solid solutions (α-phase). Structural changes caused by TM-doping have notable effects on the hydrogen permeation properties (particularly the hydrogen solubility) of V–10Mo alloy, and the ability of the doping element in decreasing the hydrogen solubility of the V–10Mo alloy follows the sequence: Pd > Ru > Ta. Their doping causes a slight decrease in the hydrogen diffusion coefficient as well as an increase in the Vickers hardness of the resulting alloys. This work demonstrates that the mechanical property of V–10Mo alloy can be improved via suitable structure control caused by alloying it with an appropriate element. In addition, this approach might be suitable for improving properties of other relevant binary alloys.     

Multi-tube tantalum membrane reactor for HIx processing section of IS thermochemical process

HI_x processing section of Iodine-Sulphur (IS) thermochemical cycle dictates the overall efficiency of the cycle, which poses extremely corrosive HI–H₂O–I₂ environment, coupled with a very low equilibrium conversion (~22%) of HI to hydrogen at 450 °C. Here, we report the fabrication, characterization and operation of a 4-tube packed bed catalytic tantalum (Ta) membrane reactor (MR) for enhanced HI decomposition. Gamma coated clay-alumina tubes were used as supports for fabrication of Ta membranes. Clay-alumina base support was fabricated with 92% alumina (~8 μm particle size) and 8% clay (~10 μm particle size), sintered at a temperature of 1400 °C. An intermediate gamma alumina coating was provided with 4% polyvinyl butyral as binder for a 10% solid loading. Composite alumina tubes were coated with thin films of Ta metal of thickness <1 μm using DC magnetron sputter deposition technique. The 4-tube Ta MR assembly was designed and fabricated with integration of Pt-alumina catalyst for carrying out the HI decomposition studies, which offered >80% single-pass conversion of HI to hydrogen at 450 °C. The hydrogen throughput of the reactor was ~30 LPH at a 2 bar trans-membrane pressure, with >99.95% purity. This is the first time a muti-tube MR is reported for HI_x processing section of IS process.     

Electrodeposition of Ni–Fe–Mn ternary nanosheets as affordable and efficient electrocatalyst for both hydrogen and oxygen evolution reactions

The synthesis of high performance and economical electrocatalysts in the process of overall water splitting is very important for the production of hydrogen energy and has become one of the most important challenges. Here, various Ni, Ni–Fe, Ni–Mn nanosheets and Ni–Fe–Mn ternary nanosheets were created using cost-effective, versatile and binder-free electrochemical deposition methods, and the electrocatalytic activity of various electrodes for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were investigated in an alkaline environment. Due to the high electrochemical active surface area due to the fabrication of nanosheets, the synergistic effect between different elements on the electronic structure, the high wettability due to the formation of nanosheets and the quick detachment of formed gasses from the electrode, the Ni–Fe–Mn nanosheets electrode showed excellent electrocatalytic activity. In order to deliver the 10 mA cm⁻² current density in HER and OER processes, this electrode required values of 64 mV and 230 mV overpotential, respectively. Also, the stability test showed that after 10 h of electrolysis at a current density of 100 mA cm⁻², the overpotential changes was very small (less than 4%), indicating that the electrode was excellent electrostatic stability. Also, when using as a bi-functional electrode in the full water splitting system, it only needed a cell voltage of 1528 V to deliver a current of 10 mA cm⁻². The results of this study indicate a new strategy for the synthesis of active and stable electrocatalysts.     

Duckweed derived nitrogen self-doped porous carbon materials as cost-effective electrocatalysts for oxygen reduction reaction in microbial fuel cells

Cost-effective metal-free electrocatalysts for oxygen reduction reaction were incredible significance of improvement about microbial fuel cells. In this research, a novel nitrogen self-doped porous carbon material is effectively inferred with KOH activation from a natural and renewable biomass, duckweed. Self-doped nitrogen in carbon matrix of nitrogen-doped porous carbon at 800 °C provides abundant active sites for oxygen reduction and improves the oxygen reduction kinetics significantly. Moreover, the porous structure of nitrogen-doped porous carbon at 800 °C encourages the transition of electrolyte and oxygen molecules throughout the oxygen reduction reaction. Oxygen on the three-phase boundary is reduced to water according to a four-electron pathway on nitrogen-doped porous carbon electrocatalyst. The single-chamber microbial fuel cell with nitrogen-doped porous carbon as electrocatalyst achieves comparable power density (625.9 mW m⁻²) and better stability compared to the commercial Pt/C electrocatalyst. This simple and low-cost approach provides a straightforward strategy to prepare excellent nitrogen-doped electrocatalyst derived from natural and renewable biomass directly as a promising alternate to precious platinum-based catalysts in microbial fuel cells.