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Stepwise electrocatalysis can remarkably accelerate the kinetics of two consecutive reactions in sulfur electrochemistry. However, the significant difference between the catalysis and diffusion rates of polysulfides results in persistent shuttling in the stepwise electrocatalysts. Here, a stepwise electrocatalytic strategy of catalysis‐immobilization‐deposition is proposed for achieving the consistency of diffusion and catalysis of polysulfides. Accordingly, a sandwich‐like stepwise electrocatalyst is designed, which is composed of Co nanoparticles (Co‐NP), mesoporous SiO2, and iron single atom (Fe‐SA) (denoted as Co‐NP@SiO2@Fe‐SA), serving as catalysis core, immobilization interlayer, and deposition shell, respectively. Benefitting from the dynamic equilibrium between production and consumption of polysulfides achieved by the spatial synergistic effect of the triple sites, the S/Co‐NP@SiO2@Fe‐SA cathode delivers a high reversible capacity of 731 mAh g−1 over 500 cycles at 1 C with a small capacity decay of 0.039% per cycle. Moreover, a high areal capacity of 3.8 mAh cm−2 at a sulfur loading of 4.5 mg cm−2 is achieved with a low electrolyte/sulfur ratio of 5.9. This work sheds light on a new host design concept with high catalytic activity, stability, and selectivity to enable high performance lithium‐sulfur batteries. [ABSTRACT FROM AUTHOR]

Lead halide perovskites with mixed cations/anions often suffer from phase segregation, which is detrimental to device efficiency and their long‐term stability. During perovskite film growth, the gel stage (in between liquid and crystalline) correlates to phase segregation, which has been rarely explored. Herein, cation diffusion kinetics are systematically investigated at the gel stage to develop a diffusion model obeying Fick's second law. Taking 2D layered perovskite as an example, theoretical and experimental results reveal the impact of diffusion coefficient, temperature, and gel duration on the film growth and phase formation. A homogenous 2D perovskite thin film was then fabricated without significant phase segregation. This in‐depth understanding of gel stage and relevant cation diffusion kinetics would further guide the design and processing of halide perovskites with mixed composition to meet requirements for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Numerical simulation was performed to optimize temperature distribution especially at high temperature zones at the rear part of U‐tube bundle electric heaters with unique one‐plus‐two U‐tube layouts. The influences of variable tube lengths and different outlet nozzle orientations on flow and thermal features on axial separation trisection helical baffle schemes in contrast to segmental schemes were investigated. The results show that the variable tube length schemes can effectively ameliorate high temperature zones and obtain more uniform temperature fields. The mean heat transfer coefficient, h.t.c., and tube wall temperature, Tw, of the variable tube length scheme HV15(10)°‐180° are respectively 0.7% higher and 3.1 K lower than those of the normal scheme H15(10)°‐180°. The optimal relative position of the outlet and tube bundle for helical schemes is that the outlet axis is not only tangent to the last straight edge of the baffle but is also on the side near it, while the optimum outlet angle for the segmental scheme is 90° within the research scope. Compared with segmental scheme S200‐90°, the averaged heat transfer coefficients, h.t.c.s, and comprehensive indexes, h · Δp−1/3, of the helical baffle schemes HV15(10)°‐180°/HV15(10)°‐Ax respectively rise by 14.6/11.8% and 16.1/13.8%, while the average Tw declines by 40.7/33.3 K. [ABSTRACT FROM AUTHOR]

Improving device lifetime is one of the critical challenges for the practical use of metal halide perovskite solar cells (PSCs), wherein a reliable encapsulation is indispensable. Herein, based on an in‐depth understanding of the degradation mechanism for the PSCs, a solvent‐free and low‐temperature melting encapsulation technique, by employing low‐cost paraffin as the encapsulant that is compatible with perovskite absorbers, is demonstrated. The encapsulation strategy enables the full encapsulating operations to be undertaken under an ambient environment. It is found that the strategy not only removes residual oxygen and moisture to prevent the perovskite from phase segregation, but also suppresses the species volatilization to impede absorber decomposition, enabling a PSC devices with good thermal and moisture stability. As a result, the as‐encapsulated PSCs achieve a 1000 h operational lifetime for the encapsulated device at continuous maximum power point output under an ambient environment. This work paves the way for scalable and robust encapsulation strategy feasible to hybrid perovskite optoelectronics in an economic manner. [ABSTRACT FROM AUTHOR]

The recessed trapezoidal groove dual‐gate profile is achieved by the low power CF4 plasma etching based on the principle of ion‐scattering. The recessed trapezoidal groove dual‐gate architecture can increase the lateral broadening of depletion width, yielding the Enhancement‐mode operation. This device demonstrates a threshold voltage of 0.43 V, a maximum drain current of 480 mA mm−1 and a trans‐conductance of 308 mS mm−1. The device exhibits a low off‐state leakage current of ≈10−10 A mm−1 and gate induced drain leakage is effectively improved. An extrinsic current gain cut off frequency of 32 GHz and a maximum oscillation frequency of 65 GHz are deduced. The threshold voltage (Vth) stability of the Schottky gate HEMT is investigated. The recessed trapezoidal groove dual‐gate exhibits a small shift of Vth, which is attributed to the lateral extension of depletion region in the trapezoidal groove dual‐gate structure. [ABSTRACT FROM AUTHOR]

The flow and heat transfer characteristics of helical baffle heat exchangers with diverse inclined angles and baffles, but similar baffle pitch and tube layout, were numerically simulated, three using non-continuous trisection baffles, two using non-continuous quadrant baffles, and one using a continuous helical baffle. The results show that, under the same operating conditions, the 20°TCO (trisection circumferential overlap baffles with 20° inclined angle) structure can significantly enhance shell side heat transfer with strong Dean vortex 'secondary flow' and restrained V-notch leakage, because the shapes of trisection baffles are very suitable to equilateral triangle tube layout and there is a row of tubes to dampen the leakage flow in each circumferential overlapped area of adjacent baffles. The shell side Nusselt Number Nuo and comprehensive index ( Nuo/ Euz,o1/3) of 20°TCO structure are 18.31 %, 25.82 %, 5.93 %, 6.36 %, and 15.04 %, and 15.43 %, 18.47 %, 5.30 %, 3.91 %, and 11.10 % higher than those of the 20°TEE (trisection end-to-end baffles with 20° inclined angle), 36.2°TMO (trisection middle overlap baffles with 36.2° inclined angle), 18°QCO (quadrant circumferential overlap baffles with 18° inclined angle), 18°QEE (quadrant end-to-end baffles with 18° inclined angle), and 18.4°CH (continuous helical baffle with 18.4° helical angle) structures, respectively. [ABSTRACT FROM AUTHOR]