MoS2 nanoflower supported Pt nanoparticle as an efficient electrocatalyst for ethanol oxidation reaction

Developing highly active and stable ethanol oxidation electrocatalysts is crucial for direct ethanol fuel cells. Herein, platinum/molybdenum disulfide nanoflower (Pt/MoS₂) nanocomposite is synthesized through a facile method and is first applied as catalyst for ethanol oxidation reaction. In situ electrochemical nuclear magnetic resonance is carried out to investigate the electrocatalytic activity of Pt/MoS₂ and the detailed mechanism of ethanol oxidation reaction. Experimental results indicate that in situ electrochemical nuclear magnetic resonance possesses great advantages for real-time investigation of ethanol oxidation reaction, and Pt/MoS₂ is found to exhibit better electrocatalytic performances in terms of higher current density, better stability, and stronger anti-poisoning activity compared to commercial Pt/C and pure Pt catalysts in acid electrolyte, suggesting its potential for application in direct ethanol fuel cells. Density functional theory calculations indicate that MoS₂-supported Pt atom has a smaller energy barrier for the dissociation of ethanol compared to those of Pt and C-supported Pt atom, leading to the enhancement of catalytic activity. This work reveals the importance of the supporting materials for high performance direct ethanol fuel cells catalysts.     

Multiphase Nb–TiCo alloys: The significant impact of surface corrosion on the structural stability and hydrogen permeation behaviour

Multiphase Nb_xTi_(100-x)/2Co_(100-x)/2 (x = 30–60) alloys are a promising material for hydrogen separating membranes. These alloy membranes exhibit a rapid decline in hydrogen permeation flux within ∼12 h when operated at 773 K. To address this issue, a dense oxide (e.g. Nb₂O₅, TiO₂ and CoO) layer was prepared between a Pd coating layer and an Nb–TiCo substrate by surface corrosion for improving their thermal stability, and the corrosion resistance of Nb–TiCo alloys was investigated. An increase in the Nb content (x) lowers the corrosion resistance of these alloys, but makes it easier to form the above oxide layer. Substantial enhancement of hydrogen permeability and thermal stability at 773 K was observed for the alloys (x = 30 and 40) after corrosion, which can be ascribed to an increase in hydrogen diffusivity. This improved permeability and stability are closely related to the formation of the above surface oxide layer that impeded interdiffusion between the Pd film and Nb–TiCo substrates. This study demonstrates that insertion of a diffusion barrier between the Pd and Nb-based substrates by surface corrosion is a viable approach to enhance the high-temperature stability of Pd-coated Nb–TiCo alloys, an aspect not widely explored in Nb-based hydrogen separation and purification membranes.     

Effect of in-situ boron doping on hydrogen adsorption properties of carbon nanotubes

Floating catalyst chemical vapor deposition method was used for the synthesis of boron doped carbon nanotubes (BCNTs) using ethanol, triethyl borate and ferrocene as carbon source, boron source and catalyst precursor, respectively. The synthesized BCNTs were characterized by transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS). The hydrogen adsorption activity was studied for BCNTs along with undoped single walled and multi walled carbon nanotubes. Significant enhancement in the hydrogen storage value was found in doped CNTs as compared to the other undoped CNTs. Hydrogen storage for BCNTs was found to be 2.5 wt% at 10 bar and 77 K. In-situ doped BCNTs gives higher hydrogen adsorption as compared to ex-situ doped BCNTs. The Langmuir adsorption isotherm was found to be suitable for describing the adsorption isotherm as compared with Freundlich isotherm. Maximum adsorption capacity was about 9.8 wt% at 77 K. Pseudo second order kinetics was followed by BCNTs for hydrogen adsorption.     

Facile preparation of large-area self-supported porous nickel phosphide nanosheets for efficient electrocatalytic hydrogen evolution

Metal phosphide structures have been widely explored for electrocatalytic hydrogen evolution reaction (HER) owing to their high activity and durability, and the phosphidation reaction is very important for the preparation of metal phosphides. In this paper, we reported a facile, effective, and practical phosphidation strategy to prepare nickel phosphide structures by placing a Ni foam above the red phosphorus powder with a distance of 1 cm in a covered crucible. As-prepared self-supported hierarchical Ni₅P₄/NiP₂ biphase porous nanosheets exhibited an excellent HER activity. The overpotential for a current density of 10 mA/cm² and the Tafel slope are as low as 92 mV and 52.8 mV/dec, respectively, both of which are much better than those delivered by the Ni₅P₄ nanosheets prepared by the conventional carry-gas upstream-downstream method. The complete phosphidation reaction, high electrochemically active surface area, and the Ni₅P₄/NiP₂ biphasic synergistic effect account for the outstanding HER performance. Moreover, the porous Ni₅P₄/NiP₂ nanosheets exhibited excellent stability under both accelerated degradation test and long-term durability test. Besides, this method can be employed to prepare large-area self-supported hierarchical porous Ni₅P₄/NiP₂ nanosheets with nearly same HER activities and long-term stability, suggesting a high potential for practical application.     

Exergoeconomic analysis and determination of power cost in MCFC – steam turbine combined cycle

A novel combined molten carbonate fuel cell – steam turbine based system is proposed herein. In this cycle, steam is produced through the recovery of useful heat of an internal reforming MCFC and operates as work fluid in a Rankine cycle. Exergoeconomic analysis was performed, in order to verify the technical feasibility, including which components could be improved for greater efficiencies, as well as the cost of the power generated by the plant. A 10 MW MCFC was initially proposed, when the system reached 54.1% of thermal efficiency, 8.3% higher than MCFC alone, 11.9 MW of net power, 19% higher than MCFC alone, and an energy cost of 0.352 $/kWh. A sensitivity analysis was carried out and the parameters that most influenced on the cost were pointed out. The analysis pointed to the MCFC generation as the most impactful factor. By manipulating these values, it could be noted a significant power cost decrease, reaching satisfactory values to become economically feasible. The concept of economy of scale could be noticed in the proposed system, proving that a large-scale plant could be the focus of investment and public policies.     

Assessment and optimization of an integrated energy system with electrolysis and fuel cells for electricity,cooling and hydrogen production using various optimization techniques

In this research study, a novel integrated solar based combined, cooling, heating and, power (CCHP) is proposed consisting of Parabolic trough solar collectors (PTSC) field, a dual-tank molten salt heat storage, an Organic Rankine Cycle (ORC), a Proton exchange membrane fuel cell (PEMFC), a Proton exchange membrane electrolyzer (PEME), and a single effect Li/Br water absorption chiller. Thermodynamics and economic relations are used to analyze the proposed CCHP system. The mean of Tehran solar radiation as well as each portion of solar radiation during 24 h in winter is obtained from TRNSYS software to be used in PTSC calculations. A dynamic model of the thermal storage unit is assessed for proposed CCHP system under three different conditions (i.e., without thermal energy storage (TES), with TES and with TES + PEMFC). The results demonstrate that PEMFC has the ability to improve the power output by 10% during the night and 3% at sunny hours while by using TES alone, the overnight power generation is 86% of the power generation during the sunny hours. The optimum operating condition is determined via the NSGA-II algorithm with regards to exergy efficiency and total cost rate as objective functions where the optimum values are 0.058 ($/s) and 80%, respectively. The result of single objective optimization is 0.044 ($/s) for the economic objective in which the exergy efficiency is at its lowest value (57.7%). In addition, results indicate that the amount of single objective optimization based on exergetic objective is 88% in which the total cost rate is at its highest value (0.086 $/s). The scattered distribution of design parameters and the decision variables trend are investigated. In the next step, five different evolutionary algorithms namely NSGA-II, GDE3, IBEA, SMPSO, and SPEA2 are applied, and their Pareto frontiers are compared with each other.     

Effects of rolling and annealing on hydrogen permeability and crystal orientation in Nb-TiNi two-phase alloys

The Nb₁₉Ti₄₀Ni₄₁ alloy has a lamellar structure with bcc-Nb and B2-TiNi phases. It is known that a granule Nb phase forms in the TiNi matrix after thermal annealing and that the hydrogen permeability of unrolled annealed alloy is higher than that of rolled annealed alloy, even though the two alloys have granule Nb phase. Although the “cube-on-cube” relationship of crystal orientation for these phases has been observed in unrolled annealed alloy, no specific crystal orientation relationship has been seen in rolled annealed alloy. This indicates that the crystal orientation between the two phases strongly affects hydrogen permeability in Nb-TiNi two-phase alloys.     

Electrospun iron and nitrogen co-containing porous carbon nanofibers as high-efficiency electrocatalysts for oxygen reduction reaction

One-dimensional carbon nanofibers hold great promise to be potential candidates as high-efficiency electrocatalysts for oxygen reduction reaction (ORR). However, the catalysts in powder form always aggregate when preparing catalyst layer, which significantly hinders the extensive application. Herein, we report the facile synthesis of iron and nitrogen co-containing porous carbon nanofibers derived from PAN nanofibers existing as a flexible film via the electrospinning method, which could avoid aggregation when fabricating catalyst layer of fuel cells. The Fe–N/N–C NFs exhibit onset potential of 0.95 V and the half-wave potential of 0.78 V in 0.1 M KOH solution, suggesting superior electro-catalytic activity for ORR. Meantime, for Fe–N/N–C NFs catalyst, it shows a nearly four electron transferring process and the current density only decreases by 14.2% after 40,000 s. This easy and facile method provides a new idea for synthesis of oxygen reduction reaction with high-activity and good-stability.     

Signal analysis and processing method of transmission optical fiber hydrogen sensors with multi-layer Pd–Y alloy films

To detect hydrogen leakage as soon as possible, researchers try their best to improve the sensitivity and response speed of the hydrogen sensor. However, the sensitivity and response speed are two contradictive parameters. It is hard to improve them simultaneously. The transmission optical fiber sensor with multi-layer films is the only structure which can increase the response speed and enhance sensibility simultaneously. However, because of its special structure, the output signal of the sensor often drifts. This paper designed an in-situ observation system to study the reason why the sensor drifts. The in-situ observation system found a periodic oscillation pattern for the transmission spectrum which depends on the wavelength of the light source. The transmission spectrum patterns of the sensor with multi-layer Palladium–Yttrium (Pd–Y) alloy films under different hydrogen concentrations were analyzed. The source of drift error induced by the wavelength shift of the light source was confirmed. By using a moving average algorithm, the error characteristics of the sensor were analyzed and simulated. The results show that the increased sweep width of the laser can effectively restrain the signal drift of sensors. Particularly, when the sweep width of the laser just is the integer multiples of the period of the transmission spectrum, the suppression of the oscillation was optimal. A sensor with a wavelength-swept laser was implemented. For the sweep width of 1.1 nm, the maximum wavelength sensitivity of the sensor is only 0.046 mv/pm. The wavelength drift error is significantly less than that without signal processing. The sensor has achieved a detection limit of 0.05% which is identical to the sensor with the frequency-stabilized laser. Finally, a design principle was proposed to optimize the light source parameters and structure parameters of the probe for the high stability of the optical fiber hydrogen sensor.     

Investigation on the oxygen reduction reaction mechanism of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ@La2NiO4+δ core-shell structure cathode for solid oxide fuel cells

Excellent electrochemical performance is achieved by PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_5+δ@La₂NiO_4+δ (PBSCF@LN) core-shell structure cathode, LN coating's existence enhances the cathode catalytic activity by promoting the oxygen reduction reaction (ORR) surface process. Besides the LN's excellent oxygen adsorption-desorption property, roughness surface of LN coating provides more ORR active sites compared to pristine PBSCF cathode. Thorough investigation is carried out based on the PBSCF and LN oxide's oxygen diffusion mechanism and corresponding ORR process elementary steps are constructed. Combine the theoretical derivations with experimental results, rate-determining step of PBSCF and PBSCF@LN cathode can be ascertained. With LN coating's introduction, PBSCF cathode's rate-determining step transfers from surface oxygen exchange to oxygen species' crossing LN coating, reducing thickness of LN coating can further improve PBSCF@LN cathode’ performance.