Cooperative role of cobalt and gallium under the ethanol steam reforming on Co/CeGaOx

The performance of gallium promoted cobalt-ceria catalysts for ethanol steam reforming (ESR) was studied using H₂O/C₂H₅OH = 6/1 mol/mol at 500 °C. The catalysts were synthetized via cerium-gallium co-precipitation and wetness impregnation of cobalt. A detailed characterization by N₂-physisorption, XRD, H₂-TPR and TEM allowed the normalization of contact time and rationalization of the role of each catalysts component for ESR. The gallium promoted catalyst, Co/Ce₉₀Ga₁₀O_x, was more efficient for the ethanol conversion to H₂ and CO₂, and the production of oxygenated by-products (such as, acetaldehyde and acetone) than Co/CeO₂. The catalytic performance is explained assuming that: (i) bare ceria is able to dehydrogenate ethanol to ethylene; (ii) Ce–O–Ga interface catalyzes ethanol reforming; (iii) both Ce–O–Co and Ce–O–Ga interfaces takes part in acetone production; and (iv) cobalt sites further allow C–C scission. It is suggested that a cooperative role between Co and Ce–O–Ga sites enhance the H₂ and CO₂ yields under ESR conditions.     

A boron-11 NMR study of the stability of the alkaline aqueous solution of sodium borohydride that is both an indirect fuel and a direct fuel for low-temperature fuel cells

Alkaline aqueous solution of sodium borohydride NaBH₄ (denoted SB-fuel) is an indirect fuel when it is used to generate H₂ by hydrolysis, with the as-generated H₂ feeding a fuel cell, and it is a direct fuel when it is an anodic fuel of a direct fuel cell. However, SB-fuel suffers from a major drawback: NaBH₄ spontaneously hydrolyzes. Our study falls within this context. We studied the instability, at the NMR scale and over 12 weeks, of a series of SB-fuels (initial NaBH₄ concentration from 3.65 to 31.22 wt%, NaOH concentration from 1 to 16 M, and temperature between ?15 and 60 °C) to find the conditions at which SB-fuel can be stored for weeks in relative safety. We found that SB-fuel with a NaOH concentration of ≥8 M is relatively stable under cold conditions (?15 and 4 °C). In these conditions, NaBH₄ is not prevented from hydrolyzing, but the reaction is significantly mitigated. Otherwise, our study highlights the gaps in our understanding of the SB-fuel, emphasizes SB-fuel is a new concept of fuel (it should not be seen as any current fuel), and points out the challenges for attaining higher technology readiness levels.     

TiI4-doping induced bulk defects passivation in halide perovskites for high efficient photovoltaic devices

Power conversion efficiency (PCE) and stability are two important properties of perovskite solar cells (PSCs). Particularly, defects in the perovskite films could cause the generation of trap states, thereby increasing the nonradiative recombination. To address this issue, suitable dopants can be incorporated to react with non-bonded atoms or surface dangling bonds to passivate the defects. Herein, we introduced TiI₄ into CH₃NH₃PbI₃ (MAPbI₃) film and obtained a dense and uniform morphology with large crystal grains and low defect density. The champion cell based on 0.5% TiI₄-doped MAPbI₃ achieved a PCE as high as 20.55%, which is superior to those based on pristine MAPbI₃ (17.64%). Moreover, the optimal solar cell showed remarkable stability without encapsulation. It retained 88.03% of its initial PCE after 300 h of storage in ambient. This work demonstrates TiI₄ as a new and effective passivator for MAPbI₃ film.     

Challenges and strategies of all-inorganic lead-free halide perovskite solar cells

Hybrid lead halide perovskite solar cells (PSCs) have experienced a rapid development in the past decade and a certified efficiency up to 25.5% has been achieved. However, the presence of toxic lead component and the inherent poor thermal stability of the organic cations in the hybrid lead halide perovskites obstruct the commercial applications of their corresponding photovoltaic devices. Therefore, fabricating high-efficient all-inorganic lead-free PSCs is a promising direction. This review summarizes the related research progress, which mainly focuses on the structural and optoelectronic properties of inorganic lead-free perovskites and devices. In particular, the strategies for improving the properties and stability of Cs–Sn perovskites, as well as enhancing the photovoltaic performance of the corresponding devices are highlighted. An outlook of challenges and future directions regarding to all-inorganic lead-free PSCs are also proposed.     

A matryoshka-like CuS@void@Co3O4 double microcube-locked sulfur as cathode for high-performance lithium-sulfur batteries

Lithium-sulfur battery cathodes still remain a challenge on capacity decay due to the shuttle effect even though a series of strategies have been tried. Here we report a novel matryoshka-like CuS@void@Co₃O₄ architecture of double micro-cubes (μ-cubes) that locks sulfur between the CuS core and the Co₃O₄ shell. Plenty of existing spaces between the μ-cubes suffice a high loading of sulfur and volumetric accommodation. The robust, double closed cubes configuration greatly enhances the confinement of polysulfides. In parallel, the CuS core increases the electronic conductivity and contributes to additional capacity, while the Co₃O₄ shell ensures a better interface activity. A high Li⁺ ion diffusion coefficient is obtained during the sulfur and lithium sulfide transformation. The constructed battery displays an initial capacity up to 1480 mAh g⁻¹, and a Coulombic efficiency (CE) exceeding 99%. A capacity retention higher than 500 mAh g⁻¹ with a CE larger than 99.8% after cycling 400 times at 0.2 C are achieved. In addition, under a temperature of −5 °C, a high capacity of 700 mAh g⁻¹ at 0.2 C after 200 cycles is achieved, indicating a good low-temperature tolerance.     

薄膜铂电阻元件稳定性测试与分析

高端军事应用环境对测温传感器提出了小结构、高精度、良好的长期稳定性等要求,采用溅射方式制备的薄膜铂电阻元件成为了首选。通过分析薄膜铂电阻元件的结构、工艺,探讨影响稳定性的主要因素,包括薄膜缺陷、杂质、电迁移、结构封装应用与温度应力等。选择薄膜铂电阻在水三相点下的电阻值作为稳定性的比较基准,设计了一款不大于3mK的高精度测试系统。通过对薄膜铂电阻元件进行高温电寿命试验和温度冲击试验,评估得出薄膜铂电阻元件长期稳定性达到10mK,满足设计需求。     

Discrete-time setpoint-triggered reset integrator design with guaranteed performance and stability

According to Bode's gain-phase relationship, in linear time-invariant controllers, introducing an integral action to eliminate the steady-state error has an adverse effect of increased phase delay and overshoot, leading to performance deterioration. Moreover, increasing the bandwidth of the closed-loop system to enhance the low-frequency disturbance rejection invariably amplifies the sensitivity to high-frequency disturbances. Hence, the performance of the linear controllers is always limited due to these fundamental frequency- and time-domain limitations. Motivated by the desire to address the fundamental limitations of linear controllers and improve the time-varying closed-loop performance, we put forward a novel setpoint-triggered reset integrator strategy that varies the integrator cut-off frequency based on the setpoint information. Particularly, to tackle the time-varying disturbances and setpoint profiles, the proposed controller consists of a nominal linear controller and a variable-gain reset integrator. We show the global asymptotic stability of the proposed methodology using positive-real lemma along with the LaSalle's invariance principle and experimentally validate using measured frequency response function. Moreover, the efficacy of the proposed technique compared to that of the linear controller is experimentally demonstrated on a benchmark rotary servo system. Experimental results assessed using the tracking error and cumulative power spectral density substantiate that the proposed control strategy can not only improve the low-frequency disturbance rejection but also augment the high-frequency trajectory tracking performance.     

Artificial pancreas under stable pulsatile MPC: Improving the closed-loop performance

This work presents a pulsatile Zone Model Predictive Control (pZMPC) for the control of blood glucose concentration (BGC) in patients with Type 1 Diabetes Mellitus (T1DM). The main novelties of the algorithm – in contrast to other existing strategies – are: (i) it controls the patient glycemia by injecting short duration insulin boluses for both, the basal and bolus infusions, in an unified manner, (ii) it performs the predictions and estimations (critical to anticipate both, hypo and hyperglycemia) based on a physiological individualized long-term model, (iii) it employs disturbance observers to compensate plant-model mismatches, (iv) it ensures, under standard assumptions, closed-loop stability, and (v) it can be used – under minor modifications – as an optimal basal–bolus calculator to emulate conventional therapies. Because of the latter characteristic, a significantly better performance is achieved, not only in terms of classical indexes (time in the normoglycemia zone, avoidance of hypoglycemia in the short term, avoidance of hyperglycemia in the long term) but also in terms of its applicability (use of the pump or injections). Such a performance is tested in a cohort of in-silico patients from the FDA-accepted UVA/Padova simulation platform, considering the most challenging scenarios.     

Optimal supplementary frequency controller design using the wind farm frequency model and controller parameters stability region

In most of the existing studies, the frequency response in the variable speed wind turbines (VSWTs) is simply realized by changing the torque set-point via appropriate inputs such as frequency deviations signal. However, effective dynamics and systematic process design have not been comprehensively discussed yet. Accordingly, this paper proposes a proportional-derivative frequency controller and investigates its performance in a wind farm consisting of several VSWTs. A band-pass filter is deployed before the proposed controller to avoid responding to either steady state frequency deviations or high rate of change of frequency. To design the controller, the frequency model of the wind farm is first characterized. The proposed controller is then designed based on the obtained open loop system. The stability region associated with the controller parameters is analytically determined by decomposing the closed-loop system's characteristic polynomial into the odd and even parts. The performance of the proposed controller is evaluated through extensive simulations in MATLAB/Simulink environment in a power system comprising a high penetration of VSWTs equipped with the proposed controller. Finally, based on the obtained feasible area and appropriate objective function, the optimal values associated with the controller parameters are determined using the genetic algorithm (GA).     

Adding new floors to old timber-framed buildings: An assessment of demolished and preserved courtyard houses in the historic centre of Madrid

The constructive analysis of Madrid's old timber-framed collective courtyard buildings, whether demolished, preserved intact, or enlarged, has achieved the dating of relevant case studies. New parameters established in this study set a chronology based on front sector original projects: old (1737–1788), pre-modern (1788–1847) and modern (1847–1892). The on-site inspection and archival research point to ongoing misleading construction in the historic Southern area. Some modern corralas erected on top of pre-existing buildings confirm the initial hypothesis. First dimensioning rules for new façades and the stability required in old ones before adding new storeys, maintaining the original masonry or double-layered system, are discovered. Undated buildings suggest their possible origin a la malicia and a later transformation into transitional corralas. Finally, an analysis of the demolished courtyards narrows down the dating and points to new conjectures in some preserved by showing their uneven layout, old features, and structural discordances in each sector.