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Co‐free Ni‐rich layered oxides are considered a promising cathode material for next‐generation Li‐ion batteries due to their cost‐effectiveness and high capacity. However, they still suffer from the practical challenges of low discharge capacity and poor rate capability due to the hysteresis of Li‐ion diffusion kinetics. Herein, based on the regulation of the lattice magnetic frustration, the Li/Ni intermixing defects as the primary origin of kinetic hysteresis are radically addressed via the doping of the nonmagnetic Si element. Meanwhile, by adopting gradient penetration doping, a robust Si−O surface structure with reversible lattice oxygen evolution and low lattice strain is constructed on Co‐free Ni‐rich cathodes to suppress the formation of surface dense barrier layer. With the remarkably enhanced Li‐ion diffusion kinetics in atomic and electrode particle scales, the as‐obtained cathodes (LiNixMn1−xSi0.01O2, 0.6≤x≤0.9) achieve superior performance in discharge capacity, rate capability, and durability. This work highlights the coupling effect of magnetic structure and interfacial chemicals on Li‐ion transport properties, and the concept will inspire more researchers to conduct an intensive study. [ABSTRACT FROM AUTHOR]

[Display omitted] O3 phase layered oxides are highly attractive cathode materials for sodium-ion batteries because of their high capacity and decent initial Coulombic efficiency. However, their rate capability and long cycling life are unsatisfactory due to the narrow Na+ transfer channel and irreversible phase transitions of O3 phase during sodiation/desodiation process. Constructing O3/P2 multiphase structures has been proven to be an effective strategy to overcome these challenges. In this study, we synthesized bi-phasic structured O3/P2 Na(Ni 2/9 Fe 1/3 Cu 1/9 Mn 1/3) 1- x Mn x O 2 (x = 0.01, 0.02, 0.03, 0.04, 0.05) materials through Mn doping during sodiation process. Benefiting from surface P2 phase layer with the enhanced Na+ transfer dynamics and high structural stability, the Na(Ni 2/9 Fe 1/3 Cu 1/9 Mn 1/3) 0.98 Mn 0.02 O 2 (NFCM-M2) cathode delivers a reversible capacity of 139.1 mA h g−1 at 0.1 C, and retains 71.4 % of its original capacity after 300 cycles at 1 C. Our work provides useful guidance for designing multiphase cathodes and offers new insights into the structure-performance correlation for sodium-ion cathode materials. [ABSTRACT FROM AUTHOR]

Constructing an internal electric field (IEF) within the hematite (Fe2O3) photoanode for highly efficient water oxidation performance with facilitated charge transfer and separation remains still a significant challenge. Unlike the conventional approach of creating interfacial electric fields through heterojunction design by introducing another semiconductor, a novel strategy is proposed for engineering localized n‐p homojunctions on the surface of Fe2O3 photoanode using gradient Zn2+ doping strategy. By implementing this approach, the inherent n‐type characteristics of Fe2O3 can be transformed into p‐type, thereby facilitating the formation of an n‐p junction with robust IEF, which enables more efficient charge separation and transfer. Additionally, the gradient Zn2+ doping is accompanied by the generation of oxygen vacancies, which further improves the charge transfer efficiency and accelerates water oxidation kinetics. As expected, the photocurrent density of optimized Fe2O3 photoanode at 1.23 V versus reversible hydrogen electrode is ≈2.6‐fold that of Fe2O3. This work provides a novel perspective on the design of localized n‐p homojunction within photoanodes for achieving high solar energy conversion efficiency. [ABSTRACT FROM AUTHOR]

This work deals with the simulation of a perovskite solar cell with structure, ITO/SnO2/MAPbI 3 − x Clx/Spiro-MeOTAD/Ag using SCAPS-1D software. The optimization of absorber thickness and carriers' lifetime results in PCE = 1 9. 7 0 % ( V oc = 1. 1 4 V, J sc = 2 4. 3 1 mA/cm2 and FF = 7 0. 8 8 %). The same structures are also analyzed without ETL and HTL for making cost-effective solar cell. The efficiencies for both ETL and HTL free structures are found to be 17.42% and 9.98%, respectively. Further, the optimization of gradient doping shows a significant increment in performance parameters i.e. PCE = 2 4. 4 2 % ( V oc = 1. 1 9 V, J sc = 2 3. 9 8 mA/cm2 and FF = 8 4. 8 4 %). Moreover, the analysis of various factors like average doping concentration, number of absorber sublayers, recombination velocities and temperature on the cell performance are performed to examine device stability. Present observations suggest that by considering only two sublayers, one can achieve the highest cell performance by using the gradient doping method. We have also validated the cell performance by comparing it with the experimental results and found a good agreement in both. Our findings may provide an effective route to fabricate highly efficient solar cell devices. [ABSTRACT FROM AUTHOR]

The key to realizing the applications of ceramic based laser lighting devices depends on the heat management capability of color converters. In order to sufficiently absorb the blue light and smoothen the temperature gradient of luminescent ceramics, multistage gradient doping Ce3+:Y 3 Al 5 O 12 (Ce:YAG) transparent ceramics (TCs) with five different concentrations were designed, including 0.01 at%, 0.05 at%, 0.1 at%, 0.2 at% and 0.4 at% Ce. The composite green bodies were prepared by aqueous tape casting and multistage gradient doping Ce:YAG TCs, with concentrations from low to high, were fabricated by vacuum sintering. The in-line transmission values at 800 nm of composite structure Ce:YAG TCs could reach 80.3%. Under 21.13 W/mm2 blue laser excitation, the gradient doping Ce:YAG TC (1.32 mm) realized a high luminous efficacy of 280.3 lm/W, which was 15.8% higher than that of 0.15 at% Ce:YAG TC (240.27 lm/W). Finally, during lighting process, the input-output temperature differences (T in -T out) between excitation surface and light-exit surface of 0.15 at% Ce:YAG TC was 5 ℃, while that in gradient doping TC reduced by 50% (2.5 ℃). The results indicate that the multistage gradient doping Ce:YAG TCs will be an interesting color converter for high-power and energy-saving laser-driven lighting. [ABSTRACT FROM AUTHOR]

The quest for smart electronics with higher energy densities has intensified the development of high‐voltage LiCoO2 (LCO). Despite their potential, LCO materials operating at 4.7 V faces critical challenges, including interface degradation and structural collapse. Herein, we propose a collective surface architecture through precise nanofilm coating and doping that combines an ultra‐thin LiAlO2 coating layer and gradient doping of Al. This architecture not only mitigates side reactions, but also improves the Li+ migration kinetics on the LCO surface. Meanwhile, gradient doping of Al inhibited the severe lattice distortion caused by the irreversible phase transition of O3−H1−3−O1, thereby enhanced the electrochemical stability of LCO during 4.7 V cycling. DFT calculations further revealed that our approach significantly boosts the electronic conductivity. As a result, the modified LCO exhibited an outstanding reversible capacity of 230 mAh g−1 at 4.7 V, which is approximately 28 % higher than the conventional capacity at 4.5 V. To demonstrate their practical application, our cathode structure shows improved stability in full pouch cell configuration under high operating voltage. LCO exhibited an excellent cycling stability, retaining 82.33 % after 1000 cycles at 4.5 V. This multifunctional surface modification strategy offers a viable pathway for the practical application of LCO materials, setting a new standard for the development of high‐energy‐density and long‐lasting electrode materials. [ABSTRACT FROM AUTHOR]

Lithium‐ion batteries (LIBs) with LiFePO4 (LFP) cathode materials have occupied a significant market share in state‐of‐the‐art power storage systems and electric vehicles, yet the approaching "retiring wave" of these LIBs should be appropriately treated (i.e., recycling of spent LIBs). Current recycling strategies of degraded LFP materials largely direct on leaching of lithium elements, leaving the leached FePO4 residual as a waste. Inspiringly, LiMnxFe1−xPO4 material is considered one of the potential candidates for next‐generation cathode materials because of its high electrochemical performance, extraordinary stability, and low cost. Herein, the direct upcycling of leached FePO4 toward LiMn0.25Fe0.75PO4 (LMFP) cathode material is demonstrated via a green, simple, and scalable mechanochemical pathway. The product features a gradient‐doping of Mn, as well as a uniform carbon coating for LMFP particles. As a result, the LMFP cathode material delivers superior electrochemical performance; the capacity (161.3 mA h g−1 at 0.1 C), rate capability (90.1 mA h g−1 at 5 C), cycling stability (95.6% capacity retention after 800 cycles at 1 C), and energy density (≈15% increase as compared to LFP) are almost comparable with those of fresh materials. The as‐established upcycling protocol offers a favorable reuse method for leached FePO4 materials. [ABSTRACT FROM AUTHOR]

Gradient W-doped Bismuth vanadate (BiVO 4) photoanodes were fabricated to figure out the main factor improving the photoelectrochemical (PEC) performance, achieved by the gradient doping. We found that the film in which the concentration of W in the bulk was higher than that in the surface showed the highest photocurrent density, compared to those of other samples, which could be mainly attributed to the improvement of the charge transfer efficiency. It means that W existing on the surface of BiVO 4 played a crucial role in the enhancement of the water splitting efficiency and the charge separation achieved by the built-in electric field modestly contributed to the improvement of the performance. [Display omitted] • Gradient W-doped BiVO 4 photoanodes were fabricated to figure out the main factor improving the performance. • The enhancement of the performance could be mainly attributed to the improvement of the charge transfer efficiency. • W existing on the surface played a crucial role in the enhancement of the water splitting efficiency. [ABSTRACT FROM AUTHOR]

LiCoO2 (LCO) can deliver ultrahigh discharge capacities as a cathode material for Li-ion batteries when the charging voltage reaches 4.6 V. However, establishing a stable LCO cathode at a high cut-off voltage is a challenge in terms of bulk and surface structural transformation. O2 release, irreversible structural transformation, and interfacial side reactions cause LCO to experience severe capacity degradation and safety problems. To solve these issues, a strategy of gradient Ta doping is proposed to stabilize LCO against structural degradation. Additionally, Ta1-LCO that was tuned with 1.0 mol% Ta doping demonstrated outstanding cycling stability and rate performance. This effect was explained by the strong Ta-O bonds maintaining the lattice oxygen and the increased interlayer spacing enhancing Li+ conductivity. This work offers a practical method for high-energy Li-ion battery cathode material stabilization through the gradient doping of high-valence elements. [ABSTRACT FROM AUTHOR]

The crystalline silicon / amorphous silicon heterojunction (HJT) solar cells have attracted much attention due to their advantages of high open-circuit voltage, high conversion efficiency and low temperature coefficient. As the emitters of cell, boron-doped p-type amorphous silicon (p-a-Si:H) thin films play an important role in achieving high conversion efficiency. By changing the boron doping concentration, the electrical properties of the p-layer can be adjusted, and therefore the conversion efficiencies of solar cells are directly affected. In this article, plasma enhanced chemical vapor deposition (PECVD) device was used to deposite amorphous silicon thin films applied in the crystalline silicon / amorphous silicon HJT solar cells. By changing the doping concentration of B2H6, p-a-Si:H layer in the cells was optimized. As a result, the relative efficiency of HJT cell was improved by 0. 75%. Further, gradient doped double-layer emitter structure was adopted. An improvement of 400 µs and 3 mV could be achieved for the minority carrier lifetime (@ Δn = 5 x 1015 cm-3) and implied Voc (@ 1-Sun) respectively. Eventually benefiting from an obvious boost in FF and Voc, the efficiency of the solar cells was increased by 2. 03% relatively and an optimized p-type emitter process was therefore established. [ABSTRACT FROM AUTHOR]

High entropy materials offer optimal conditions for regulating and modifying new material properties due to their vast composition space. Through traditional solid phase sintering, this article successfully synthesized a series of Sr(Ti 0.2 Zr 0.2 Y 0.2 Sn 0.2 Hf 0.2 Sc 0.2x)O 3-σ high entropy perovskite oxides with varying Sc3+ doping concentrations and comprehensively investigated the microstructure morphology, crystal structure, and electrical conductivity of Sc-doped HEPs as well as their influence on oxygen transfer rate. The results demonstrate the successful incorporation of Sc3+ into the high entropy lattice, resulting in a transformation of the crystal to a positively cubic structure with enhanced reciprocity. While the lattice vibration of BO 6 octahedron is weakened by the introduction of Sc3+, it has no impact on the phase stability of the crystal structure. Moreover, The results of the electrochemical impedance spectroscopy test demonstrate that at a temperature of 750 °C, with a doping amount of Sc3+ at 0.14, the conductivity (σ) of Sc3+ is measured to be 5.74 × 10−3 S/cm, exhibiting an increase of 61.7% compared to non-doped samples. Correspondingly, the activation energy (Ea) is reduced from 0.51 eV to 0.39 eV as well. This doping strategy effectively expands the potential applications of high entropy perovskite oxides in solid oxide fuel cells (SOFCs). These findings serve as a driving force for further investigation into high entropy ceramics of the strontium series that exhibit optimal properties. [ABSTRACT FROM AUTHOR]

The work is aimed at the investigation of the influence of nonlinear active ions concentration profiles in Yb:YAG laser elements on temperature distribution and wavefront distortions during amplification using sub-kilowatt level diode pumping. A mathematical model is presented for the theoretical study of the amplification process in crystals with cubic crystal system. A detailed comparison of Yb:YAG active elements with the same thickness and absorbed pumping power, but with various concentration profiles of Yb3+, ions is carried out. It is shown that the use of active elements with an increasing dopant concentration in the pump beam direction allows one to optimize the temperature profile inside the active element and, thus, reduce the thermal-induced wavefront distortions of the amplified radiation. Modeling is carried out for the experimentally grown crystal with linear concentration gradient profile. It is shown that the linear doping profile with a gradient of 0.65 at.%/mm allows increasing the small-signal gain up to 10% and decreasing the thermal-induced wavefront distortions by ~15%. [ABSTRACT FROM AUTHOR]

In recent years, inorganic perovskite solar cells (PSCs) based on CsPbI3 have made significant progress in stability compared to hybrid organic–inorganic PSCs by substituting the volatile organic component with Cs cations. However, the cubic perovskite structure of α-CsPbI3 changes to the orthorhombic non-perovskite phase at room temperature resulting in efficiency degradation. The partial substitution of an I ion with Br ion benefits for perovskite phase stability. Unfortunately, the substitution of Br ion would enlarge bandgap reducing the absorption spectrum range. To optimize the balance between band gap and stability, introducing and optimizing the spatial bandgap gradation configuration is an effective method to broaden the light absorption and benefit the perovskite phase stability. As the bandgap of the CsPb(I1–xBrx)3 perovskite layer can be adjusted by I-Br composition engineering, the performance of CsPb(I1–xBrx)3 based PSCs with three different spatial variation Br doping composition profiles were investigated. The effects of uniform doping and gradient doping on the performance of PSCs were investigated. The results show that bandgap (Eg) and electron affinity(χ) attributed to an appropriate energy band offset, have the most important effects on PSCs performance. With a positive conduction band offset (CBO) of 0.2 eV at the electron translate layer (ETL)/perovskite interface, and a positive valence band offset (VBO) of 0.24 eV at the hole translate layer (HTL)/perovskite interface, the highest power conversion efficiency (PCE) of 22.90% with open–circuit voltage (VOC) of 1.39 V, short–circuit current (JSC) of 20.22 mA/cm2 and filling factor (FF) of 81.61% was obtained in uniform doping CsPb(I1–xBrx)3 based PSCs with x = 0.09. By carrying out a further optimization of the uniform doping configuration, the evaluation of a single band gap gradation configuration was investigated. By introducing a back gradation of band gap directed towards the back contact, an optimized band offset (front interface CBO = 0.18 eV, back interface VBO = 0.15 eV) was obtained, increasing the efficiency to 23.03%. Finally, the double gradient doping structure was further evaluated. The highest PCE is 23.18% with VOC close to 1.44 V, JSC changes to 19.37 mA/cm2 and an FF of 83.31% was obtained. [ABSTRACT FROM AUTHOR]

In order to fully pump and smoothen the temperature gradient of the gain medium, multistage gradient doping Yb:YAG laser ceramics were designed. The composite green bodies were fabricated by tape casting, and multistage gradient doping Yb:YAG ceramics with high optical quality were prepared by vacuum sintering and hot isostatic pressing. For samples pre‐sintered at 1740°C for 30 h and then HIP‐ed at 1700°C for 3 h in argon at 200 MPa, the in‐line transmission values at 1100 nm of YAG, 0.6 at.%Yb:YAG, and 1.5 at.%Yb:YAG ceramics were found to be 83.9%, 84.1%, and 83.3%, respectively. Finally, the 940 nm laser diode was used as the pump source to realize the 1030 nm laser output of multistage gradient doping Yb:YAG ceramic slab with a total energy of 3.43 J. The corresponding optical‐to‐optical conversion and slope efficiencies were 30% and 45%. [ABSTRACT FROM AUTHOR]

Band bending modification of metal/semiconductor hybrid nanostructures requires low-cost and effective designs in photoelectrochemical (PEC) water splitting. To this end, it is evinced that gradient doping of Au nanoparticles (NPs) inwards the ZnO nanorods (NRs) through thermal treatment facilitated faster transport of the photo-induced charge carriers. Systematic PEC measurements show that the resulting gradient Au-doped ZnO NRs yielded a photocurrent density of 0.009 mA/cm2 at 1.1 V (vs. NHE), which is 2.5-fold and 8-fold improved compared to those of Au-sensitized ZnO and the as-prepared ZnO NRs, respectively. The IPCE and ABPE efficiency tests confirmed the boosted photoresponse of gradient Au-incorporated ZnO NRs, particularly in the visible spectrum due to the synergistic surface plasmonic effect of Au NPs. A gradient Au dopant profile promoted the separation and transfer of the photo-induced charge carriers at the electrolyte interface via more upward band bending according to the elaborated electrochemical impedance spectroscopy and Kelvin probe force microscopy analyses. Therefore, this research presents an economical and facile strategy for preparing gradient plasmonic noble NP-incorporated semiconductor NRs, which have excellent potential in energy conversion and storage technologies. [ABSTRACT FROM AUTHOR]

Hematite is a promising material for photoelectrochemical (PEC) water oxidation, but its photocurrent is limited by bulk charge recombination and poor oxidation kinetics. In this study, we report a high-performance Fe 2 O 3 photoanode achieved through gradient surface gallium doping, utilizing a Ga 2 O 3 overlayer on FeOOH precursors via atomic layer deposition (ALD) and co-annealing for Ga diffusion. The Ga-doped layer passivates surface states and modifies the band structure, creating a built-in electric field that enhances the charge separation efficiency. Following the electrodeposition of CoFeO x as a cocatalyst, the resulting CoFe-Ga:Fe 2 O 3 photoanode exhibited a notable negative shift in onset potential by approximately 100 mV, a high photocurrent density of 2.6 mA cm -2 at 1.23 V versus RHE, and excellent long-term PEC stability over 40 h. This work presents an effective strategy for enhancing the PEC performance of photoelectrodes through advanced surface coatings.

Bismuth vanadate (BiVO 4 ) is regarded as a promising photoanode candidate for photoelectrochemical (PEC) water splitting, but is limited by low efficiency of charge carrier transport and short carrier diffusion length. In this work, we report a strategy comprised of the gradient doping of W and back-to-back stacking of transparent photoelectrodes, where the 3-2 wt.% W gradient doping enhances charge carrier transport by optimizing the band bending degree and back-to-back stack configuration shortens carrier diffusion length without much sacrifice of photons. As a result, the photocurrent density of 3-2 % W:BiVO 4 photoanode reaches 2.20 mA cm -2 at 1.23 V vs. hydrogen electrode (RHE) with a charge transport efficiency of 76.1 % under AM 1.5 G illumination, and the back-to-back stacked 3-2 % W:BiVO 4 photoanodes achieves a photocurrent of 4.63 mA cm -2 after loading Co-Pi catalyst and anti-reflective coating under AM 1.5 G illumination, with long-term stability of 10 hours., (© 2024 Wiley-VCH GmbH.)

O3-type NaNi 0.8 Mn 0.1 Co 0.1 O 2 (NaNMC811) cathode active materials for sodium-ion batteries (SIBs), with a theoretical high specific capacity (∼ 187 mAh g -1 ), are in the preliminary exploration stage. This study comprehensively investigates NaNMC811 from multiple perspectives. For the first time, the phase evolution ( P 3 ¯ m 1 $P\overline{3}m1$ - F m 3 ¯ m $Fm\overline{3}m$ - R 3 ¯ m $R\overline{3}m$ ) during the solid-state synthesis is systemically investigated, which elucidates in-depth the mechanisms of the thermal sodiation process. Furthermore, an Al-gradient doping of NaNMC811 was successfully implemented through Al 2 O 3 coating on the cathode active material (CAM) precursor. The modified Al-NaNi 0.8 Mn 0.1 Co 0.1 O 2 (Al-NaNMC811) exhibits excellent electrochemical dynamics and performance, maintaining a specific capacity above 100 mAh g -1 after 100 cycles at 0.1 C (1.5-4.1 V) while providing a promising capacity retention of 63%. Additionally, the material demonstrates excellent rate capabilities, retaining a specific capacity of 107 mAh g -1 at 5 C. Compared to pristine NaNMC811, the modified Al-NaNMC811 is proven to have improved electrochemical kinetics with a higher Na + diffusion coefficient due to dilated (003) interplanar spacing, and a more stable structure during the electrochemical charge-discharge processes, which is attributed to stronger Al-O bond energy. Understanding phase formations during the synthesis and comprehensive insight in the gradient doping for O3-type NaNMC811 CAMs guides further development of next-generation SIBs materials., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

The work is aimed at the investigation of the influence of nonlinear active ions concentration profiles in Yb:YAG laser elements on temperature distribution and wavefront distortions during amplification using sub-kilowatt level diode pumping. A mathematical model is presented for the theoretical study of the amplification process in crystals with cubic crystal system. A detailed comparison of Yb:YAG active elements with the same thickness and absorbed pumping power, but with various concentration profiles of Yb3+, ions is carried out. It is shown that the use of active elements with an increasing dopant concentration in the pump beam direction allows one to optimize the temperature profile inside the active element and, thus, reduce the thermal-induced wavefront distortions of the amplified radiation. Modeling is carried out for the experimentally grown crystal with linear concentration gradient profile. It is shown that the linear doping profile with a gradient of 0.65 at.%/mm allows increasing the small-signal gain up to 10% and decreasing the thermal-induced wavefront distortions by ~15%.

Doping of oxygen‐deficient binder is an efficient way to alleviate the photo‐bias instability issue of oxide thin‐film transistors (TFTs). However, almost all dopants are working as electron suppressors and degrading mobility. Here we report an effective three‐level O‐anti|O|O‐N (OI|OII|N) gradient doping solution to overcome the adverse mobility‐stability trade‐off in N‐doped InGaZnO (IGZO:N) TFTs. 100 nm‐thick IGZO:OI|IGZO:OII|IGZO:N (IGZO:OI|OII|N) junctionless channel layers are fabricated by varying the partial pressures of oxygen and nitrogen doping gases. Best balance between improved performance and negligible degraded stability is first engineered by reducing the back‐channel IGZO:N depth close to the theoretical diffusion length of photo‐excited holes and forming two‐level graded IGZO:OII|N (40 nm|60 nm) TFTs. Much improved performance and comparable stability are further induced by incorporating ~1.5 nm percolation conduct IGZO:OI at the front‐channel to enhance accumulation. The three‐level graded IGZO:OI|OII|N TFTs exhibit high mobility (34.25 cm2 V−1 s−1) and good photo‐bias stability (∆Vth = −0.85 V@10 000 cd m−2, 3.0 h), which are 2~5‐fold superior to those of the controlled two‐level graded IGZO:OI|N TFTs, IGZO:OII|N TFTs, and homogeneous IGZO:OII TFTs, IGZO:N TFTs. The fabrication of high mobility and photo‐bias stable IGZO TFTs paves the way to future high‐performance oxide electronics. [ABSTRACT FROM AUTHOR]

Herein, it is demonstrated that gradient Ti doping coupled with an overlayer of NiFeOx on hematite can markedly improve the photoelectrochemical (PEC) water‐splitting efficiency of hematite‐based photoanodes, which are prized from sustainability considerations but have met daunting challenges. First, the gradient Ti doping of hematite has effectively lowered the onset potential while maintaining the high efficiency of photo‐generated charge separation and transmission. Second, the NiFeOx layer not only substantially reduces the surface trap states, but also significantly enhances the oxygen evolution kinetics of hematite‐based photoanodes as an oxygen evolution catalyst, resulting in a further improvement of the onset potential. Consequently, with the TiO2 layer and a double electrode stack design, a remarkable photocurrent density of 4.49 mA cm−2 is achieved at 1.23 V versus reversible hydrogen electrode (RHE) for NiFeOx/(Grad Ti)‐Fe2O3/TiO2 photoanode without any hole scavenger, delivering a high applied bias photo‐to‐current efficiency of up to 0.58% at 1 V versus RHE. This multipronged attack for improving PEC water‐splitting efficiency revitalizes the great promise of hematite photoanodes and sheds light on the design and development of the next‐generation photoelectrodes. [ABSTRACT FROM AUTHOR]

Stabilizing Li‐rich layered oxides without capacity/voltage fade upon cycling is a prerequisite for a successful commercialization. Although the inhibition of structural and interfacial changes is identified as an effective strategy, the battery community always seeks for a technologically flexible method to make it really competitive among the cathode. Herein, the gradient W‐doping within Li1.2Mn0.56Ni0.16Co0.08O2 (LLMO) is proposed to relieve crystal disintegration and simultaneously enhance interfacial stability because of the formation of Li2WO4 coating layer on the material surface. This is mainly attributed to the scenario that partial Mn replacement by W can stabilize the LLMO structure and regulate the electrochemical activity of Mn element. The W‐doped LLMO (W@LLMO) possesses improved specific capacity and voltage stability (83.2% capacity retention and voltage retention of 94.9% after 200 cycles at 0.5 C). Besides, a practical pouch cell based on the W@LLMO cathode presents sufficient gravimetric energy density (318 Wh kg−1) and cycling stability (capacity retention of 87.7% after 500 cycles at 1.0 C). This study presents an effective method to design robust Li‐rich layered cathodes for next‐generation Li‐ion batteries. [ABSTRACT FROM AUTHOR]

Optical illusion has always attracted extensive attention, as it provides a superior self‐protection ability for both natural animals and human beings. A decade ago, this motivated the study and application of transformation optics, which provides a universal tool to manipulate light for invisibility cloaking and optical illusion. However, mainstream transformation‐optics‐based optical illusions are inherently hindered by the extreme requirements of metamaterial compositions in practice and unfavorably limited by the very large computational cost caused by their bulky state. To overcome these grand challenges, a novel and intelligent optical illusion supported by form‐free metasurfaces via a deep learning architecture is reported, which can not only render a similar illusion effect but also greatly reduces the parameter space in physics. Illustrative examples of conformal metasurfaces are presented, with a high‐fidelity inverse design from either the near‐ or far‐field in the simulation and experiment. Furthermore, a full set of intelligent systems is developed to benchmark the real‐world optical illusion applicability. The work brings the available illusion strategies closer to a wide range of in situ practical‐oriented applications and lays a foundation for the next generation of intelligent metamaterials. [ABSTRACT FROM AUTHOR]

In the era of big data, the amount of global data is increasing exponentially, and the storage and processing of massive data put forward higher requirements for memory. To deal with this challenge, high-density memory and neuromorphic computing have been widely investigated. Here, a gradient-doped multilayer phase-change memory with two-level states, four-level states, and linear conductance evolution using different pulse operations is proposed. The mechanism of multilevel states is revealed through high-resolution transmission electron microscopy (HRTEM) and finite-element analysis (FEA), which show that the sequential phase change among different sublayers is realized due to the different physical properties of the sublayers with different doping concentrations. Taking advantage of the devices' linear conductance evolution characteristic, a handwritten digit (28 × 28 pixel) recognition task is implemented with a high learning accuracy of 93.46% by building a simulated artificial neural network made up of this gradient-doped multilayer phase-change memory. It is proved that this gradient-doped multilayer phase-change memory is capable of both binary multilevel digital storage and brain-inspired analog in-memory computing in the same device, enabling reconfigurable applications in the future.

SrFeO 3-δ perovskite material is considered as a potential substitute for Ni-based fuel electrodes, while the problem of Sr segregation limits the development of material. Herein, different high-valence elements Ti4+, Nb5+and Mo6+ are gradient doped into La 0.5 Sr 0.5 FeO 3-δ (LSF) to solve Sr segregation and study the influence mechanism for high valence elements. After the LSF is doped by high-valence elements, the reduction stability and CO 2 tolerance are found to be obviously improved in a CO 2 :CO = 1:1 atm. Under the premise of stability, lower-valence element doping requires less Fe4+ reduction and lattice oxygen to match the charge, therefore, La 0.5 Sr 0.5 Fe 0.9 Ti 0.1 O 3-δ (LSFTi5591) possesses more oxygen vacancies than La 0.5 Sr 0.5 Fe 0.9 Nb 0.1 O 3-δ (LSFNb5591) and La 0.5 Sr 0.5 Fe 0.9 Mo 0.1 O 3-δ (LSFMo5591). Since Ti ions possess a weaker binding force with O ions, LSFTi5591 more easily loses lattice oxygen and generates oxygen vacancies under high-temperature and reduction conditions, which results in stronger CO 2 adsorption. Using LSCF-GDC as the oxygen electrode of electrolytic cells, the LSFTi5591 cell (1.35 A cm−2) exhibits higher electrochemical performance than LSFNb5591 (1.18 A cm−2) and LSFMo5591 (1.04 A cm−2) cells due to stronger CO 2 adsorption and dissociation in the medium-frequency resistance range. [Display omitted] [ABSTRACT FROM AUTHOR]

The hole‐conductor‐free printable mesoscopic perovskite solar cells based on the inorganic scaffolds of mesoporous titania, mesoporous zirconia, and porous carbon have attracted much attention due to their excellent stability and low manufacturing cost. However, in such hole‐conductor‐free devices, the transport of the photogenerated holes is dominated by the diffusion‐assisted charge carrier movement, while the driving force is insufficient. Reinforcing the built‐in electric field (BEF) is an effective strategy to promote oriented carrier transport. Herein, by using an optimized two‐step deposition method, the BEF is reinforced by creating a work function difference of perovskite (Δµ) in different layers via a gradient self‐doping. The enhanced BEF improves the hole transport and extraction, and significantly reduces the carrier recombination losses in the device. As a result, an average open‐circuit voltage improvement over 60 mV and a power conversion efficiency of 17.68% are achieved without any additives or complex processes. This strategy provides a new approach toward fabricating highly efficient printable mesoscopic perovskite solar cells with reduced carrier recombination losses. [ABSTRACT FROM AUTHOR]

The surficial residual alkali is a key factor that leads to aggravated phase transition and decay in cobalt-free high-nickel cathode. In this paper, we develop a one-step in-situ modification technique to convert the residual alkali on the LiNi 0.9 Mn 0.1 O 2 (NM91) surface into Li 2 MoO 4 coating. As a fast ionic conductor, Li 2 MoO 4 coating not only facilitate Li+ diffusion, but also inhibits the transition from layered to rock salt phase on the cathode surface. Moreover, the multi-aperture architecture formed in the conversion promotes the high-valent Mo enter-into the lattice and realizes the gradient doping of Mo4+ through thermodynamic diffusion. Due to the pillar effect, Mo doping increases c-axis spacing, mitigates cation mixing, and reduces the irreversible H2-H3 phase transition. As a result, both the Li+ diffusion kinetics and thermodynamic stability are improved. Consequently, the as-prepared Mo modified NM91 exhibits an increased capacity retention from original 62.3–75.6 % (100 cycles, 0.2 C) and enhanced rate capability of 131.96 mAh g−1 at 5.0 C. This work provides a facile "reducing alkali" technological process, and lays foundation for the material design and performance optimization of high energy density cathodes in lithium-ion batteries. • Cobalt-free high nickel LiNi 0.9 Mn 0.1 O 2 cathode material was synthesized, and LiNi 0.9 Mn 0.1 O 2 was modified by doping and coating synergistically by one-step method to achieve a discharge capacity of 131.91 mAh g−1 at 5 C rate (LiNi 0.9 Mn 0.1 O 2 is only 77.7 mAh g−1) and a capacity retention rate of up to 75.6 % after 100 cycles at 0.2 C (LiNi 0.9 Mn 0.1 O 2 is only 62.3 %). • The mechanism of synergistic modification on the interfacial side reaction and structural stability of cobalt-free high nickel materials was clarified by characterization and DFT calculation. • The help of in-situ alkali reduction process to improve the stability of cobalt-free high nickel cathode materials was studied in a pioneering way, which laid a foundation for the correlation of interface stability and performance optimization of cobalt-free high nickel cathode materials, and had potential industrial application prospects. [ABSTRACT FROM AUTHOR]

[Display omitted] • A one-step synthesis of bi-element gradient doped TiO 2 with B/N non-uniform distribution. • Boron tends to be surface doped while nitrogen intervenes at deeper positions. • Ti3+/O v defects and positive charge surface in the B/N-TiO 2-x are formed due to Ti-B bonding. • High catalytic performance is reflected in the treatment of g/L level Cr(VI). • The interfacial catalytic properties of the composites are highly Boron dose-dependence. Studying the influence of non-uniform distribution of bi-element doping on the surface structure and photocatalytic performance of TiO 2 in interface photocatalytic processes can be an interesting research topic. Taking B/N bi-element doped TiO 2 as an example, this article reports an extremely simple gradient doping method of TiO 2 and its enhancement mechanism for high concentration wastewater treatment. The surface enrichment and doping of B caused by electrostatic and atomic radius factors changed the charge properties of the complex during the induction of in-situ reduction of Ti4+. The defects in gap N and Ti3+ lead to the formation of intermediate states, resulting in a narrowing of the band gap of the composite to 2.58 eV. The gradient doping of two atoms endows the optimal photocatalyst with a larger specific surface area (114 m2∙g), stronger photocurrent response (0.179 mA·cm−2), suitable Ti3+/O v double defect structure, and surface positive charge properties. These characteristics improve the effective treatment of high-concentration pollutants by the preferred B 2 /N-TiO 2-x [ e.g. , 0.0059 min−1 for 0.5 g·L-1 Cr(VI)] and sustainable treatment (removal efficiency > 90 % within 5 cycles). The synthesis strategy will provide a fast, simple, and safe method for the design and synthesis of new TiO 2 based catalysts in the future. [ABSTRACT FROM AUTHOR]

Luminescent materials with engineered optical properties have been developed for multiplexed labeling detection, where encoding capacity plays a pivotal role in the efficiency. However, multi‐dimensional optical identities are usually not independent which essentially hinder the practical encoding numbers to access theoretical capacity. In this work, we carefully studied the sensitizer gradient doping structure in near‐infrared (NIR) excitable upconversion nanoparticles (UCNPs) and managed to achieve independent emission intensity and lifetime tuning. With the orthogonally tunability, it breaks the constraint of intensity (k) and lifetime (n) correlation and expands the practical encoding number to theoretical value as (k+1)n−1 in binary encoding. This method can also be combined with previous lifetime engineering as well to realize high level multiplexing. [ABSTRACT FROM AUTHOR]

The conversion efficiency of thermoelectric generators that have to be operated under a temperature difference (ΔT) is mainly determined by material's dimensionless figure of merit (zT). However, maximization of zT at each temperature requires an optimization of carrier concentration (n opt ) which strongly depends on the temperature and band parameters. Commonly utilized strategy of chemical doping usually enables a homogeneous carrier concentration throughout the material, leading the maximal zT to be achievable only within a narrow temperature range. In this work, a gradiently doping is successfully realized in PbTe 1-x I x using a vertical gradient solidification technique, enabling a spatial gradient in carrier concentration that correspondingly optimizes zT at each portion of the material under its operating temperature. Such a gradient doping results in an extraordinary device efficiency of ≈14% at a ΔT of ≈500 K, corresponding to a ≈40% improvement as compared to that of homogeneous doping. Since directional solidification technique commonly enables gradient dopant concentrations in semiconductors, the resultant gradient carrier concentration is illustrated here as an effective approach for advancing thermoelectrics., (© 2024 Wiley‐VCH GmbH.)

• The Carbon-based HTL-free perovskite solar cell with a gradient doping absorber is explored using SCAPS. • The optimal doping gradient and N aver is 300 and 1018 cm−3, respectively. • The optimal interface defect density is 1014 cm−3. • Under optimized conditions, an efficiency of 25.15% is obtained for gradient doping C-PSC. • Dividing the absorber into two layers with a G of 300 can also improve the device performance significantly. The carbon-based perovskite solar cells (C-PSCs) have attracted tremendous attentions due to the low fabrication cost and simple structure by omitting the hole transporting layer (HTL). However, the performance of C-PCSs is still lag behind those of conventional PSCs with HTL. In this work, an innovative C-PSC with a gradient doping absorber is proposed and explored by SCAPS simulation. The effect of different doping gradient, average doping content of gradient doping absorber and interface defect density are analyzed. Through the optimization of the above-mentioned parameters, an efficiency higher than 25% could be realized by using gradient doping of perovskite absorber in C-PSC, which is much higher than the uniformly doped C-PSC, due to the additional electric field introduced by the gradient doping. In addition, dividing the CH 3 NH 3 PbI 3 absorber simply into two layers with a doping gradient of 300 can also enhance the device performance of C-PSC significantly, which greatly simplifies the fabricating process. This research offers theoretical guidance for the design of high-performance C-PSCs for research and industry. [ABSTRACT FROM AUTHOR]

The photovoltaic properties of ferroelectric films have been extensively studied due to their potential applications in the fields of photodetection, energy conversion harvesting and storage. However, the effect of the gradient distribution of oxygen vacancies on the photovoltaic properties remains unclear. Herein, we prepared BiFeO 3 (BFO) and two types of gradient calcium-doped BiFeO 3 (BiFeO 3 /Bi 0.95 Ca 0.05 FeO 2.975 /Bi 0.90 Ca 0.10 FeO 2.950 /Bi 0.85 Ca 0.15 FeO 2.925 : BCFO-1 and Bi 0.85 Ca 0.15 FeO 2.925 /Bi 0.90 Ca 0.10 FeO 2.950 /Bi 0.95 Ca 0.05 FeO 2.975 /BiFeO 3 : BCFO-2) films deposited on fluorine-doped tin oxide glass substrates. Piezoresponse force microscopy studies indicate the upward self-polarization phenomenon in BFO and BCFO-1 films, while the downward self-polarization phenomenon in BCFO-2 films. The J – V characteristic curves show rectifier behaviors for these films due to the configuration of oxygen vacancies. For photovoltaic response, the open circuit voltage of BCFO-1 films is more than 2 times higher than that of BFO films, and the short-circuit photocurrent densities of BCFO-1 and BCFO-2 films are increased by nearly 32 and 6 times, respectively. The direction and magnitude of photovoltaic response are possibly associated with the energy band modulation governed by self-polarization and the gradient distribution of oxygen vacancies. The work demonstrates the merits of gradient doping with lower valence cation towards enhanced photovoltaic properties with high stability for ferroelectric oxides. [ABSTRACT FROM AUTHOR]

The photoelectrochemical performance of the WO3 photoanode is limited by the severe charge recombination in the bulk phase and at the WO3/electrolyte interface. Herein, In2S3 nanosheets are integrated onto the surface of the WO3 nanowall array photoanode, followed by a facile polyvinylpyrrolidone (PVP) solution treatment. The PVP treatment results in sulfur vacancies and a gradient oxygen doping into In2S3 from surface to interior, which induces the formation of a gradient energy band distribution. The gradient band structured In2S3 and type II band alignment at the WO3/In2S3 interface simultaneously create a channel that favors photogenerated electrons to migrate from the surface to the conductive substrate, thereby suppressing bulk carrier recombination. Meanwhile, the sulfur vacancies and oxygen doping contribute to increased charge carrier concentration, prolonged carrier lifetime, more active sites, and small interfacial transfer impedance. As a consequence, the PVP treated WO3/In2S3 heterostructure photoanode exhibits a significantly enhanced photocurrent of 1.61 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE) and negative onset potential of 0.02 V versus RHE. [ABSTRACT FROM AUTHOR]

The investigation of the charge-transport mechanism across disordered conducting and semiconducting materials is of relevance, considering the applications in modern organic and hybrid electronics. The transition from bulk to nm-thick layers may lead to unexpected physical/chemical properties as the device interfaces do influence the overall charge-carrier conduction. Here, we present an investigation of the electrical transport across vertical heterojunctions having disordered nm-thick films (polypyrrole, PPy) as the active material. The PPy structures are prepared by chemical polymerization from the pyrrole vapor phase, resulting in film thicknesses of a few tens of nanometers. The electrical characteristics of the devices are evaluated as a function of voltage and temperature, and the charge transport is found to be strongly influenced by the presence of trap states at the PPy highest occupied molecular orbitalgiving rise to space-charge-limited conduction with exponential distribution of traps. The trapping-state density is calculated, and X-ray photoelectron spectroscopy revealed an increase of disorder and a reduced doping density at the PPy growth interface. As a proof of concept, the PPy films integrated within the as-fabricated vertical heterostructures are applied as photosensitive devices. The observation of photocurrent is correlated to the presence of a gradient in the doping profile (from ca. 27.6 to 17.2% when thickness decreases from 120 to 20 nm). Our findings contribute to the elucidation of the charge-trapping center's origin in the nm-thick PPy films, as well as envision further applications in photoelectrochemistry, solar cells, and water splitting. [ABSTRACT FROM AUTHOR]

Spinel zinc ferrite (ZnFe 2 O 4) with an appropriate band gap (2.1 eV) is a promising photoanode in the photoelectrocatalysis field, however, the photoelectrochemical (PEC) performance of ZnFe 2 O 4 is confined due to poor charge separation. Hence, improving charge separation efficiency is essential to modify the PEC performance of ZnFe 2 O 4. Herein, the novel Cu-Sn ions doped ZnFe 2 O 4 nanorods are fabricated for the first time. Cu2+ ions are doped into ZnFe 2 O 4 nanorods from surface to inside with a degressive concentration, it is helpful to enhance the charge separation efficiency of ZnFe 2 O 4 nanorods along horizontal direction. Sn4+ ions originated from fluorine-doped tin oxide (FTO) layer are doped into Cu-ZnFe 2 O 4 nanorods with a decreasing concentration from bottom to top, it is conducive to reducing surface trapping states and accelerating charge separation along vertical direction. Therefore, Cu-Sn dual ions gradient doping synergistically boosts the PEC activity of ZnFe 2 O 4. The Cu.Sn-ZnFe 2 O 4 nanorods have an excellent photocurrent density of 0.46 mA⋅cm−2 at 1.23 V vs RHE, which is 4.18 times than that of ZnFe 2 O 4. The bulk charge separation efficiency (η bulk) and surface charge separation efficiency (η surface) of Cu.Sn-ZnFe 2 O 4 are 17.52% and 55.22%, which are 5.84 and 3.78 times than that of ZnFe 2 O 4 , respectively. This work provides inspirations for promoting charge separation efficiency of photoanodes, thus achieving efficient PEC water splitting. [ABSTRACT FROM AUTHOR]

A silicon heterojunction solar cell structure consisting of a gradient doping emitter layer, which possesses a potential to obtain high power conversion efficiency, is explored by the numerical simulation tool automat for simulation of heterostructures. We have demonstrated that the gradient doping solar cell has a higher open-circuit voltage than a uniform doping solar cell, due to the introduction of an additional electric field, which can achieve a better conversion efficiency, whereas their thickness and defect state distribution are identical. A high conversion efficiency of 29.5% is achieved by using a gradient doping for the n-type emitter layer with the same reference as the uniform doping. In addition, through the investigation of the effect of gradient doping, we find that the field-effect passivation can appropriately explain the interesting behaviors that the recombination rate is less sensitive to the defect density state, and that the open-circuit voltage is enhanced when increasing the doping gradient in the n-a-Si emitter layer. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a gradient phosphate polyanion doping strategy is applied to enhance the electrochemical properties of LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode. This strategy synergistically achieves the gradient doping of phosphate polyanion and in-situ coating of Li 3 PO 4 layer. The gradient doping improves the cycling stability and rate performance of LiNi 0.6 Co 0.2 Mn 0.2 O 2. Especially, the capacity retention of P0.02-NCM sample is 92.9% at high cut-off voltage (4.5 V) and high temperature (55 °C), whereas the LiNi 0.6 Co 0.2 Mn 0.2 O 2 sample only shows lower capacity retention of 55.7%. The X-ray powder diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR) results confirm that the large tetrahedral PO 4 3− polyanions are doped into oxygen layer for stabilizing the lattice structure. In addition, scanning transmission electron microscopy (STEM) and inductively coupled plasma (ICP-MS) analysis show that the Li 3 PO 4 layer availably inhibits the dissolution of transition metal ions (Ni, Co, Mn). Interestingly, the Li 3 PO 4 coating layer as a fast ion conductor also optimizes the Li+ diffusion coefficient. Such excellent results indicate that the surface gradient phosphate polyanion doping strategy is very valuable and useful to remarkably enhance the electrochemical properties of LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode at high cut-off voltage (4.5 V) and high temperature (55 °C). [ABSTRACT FROM AUTHOR]

In the article "Direct Upcycling of Leached FePO4 from Spent Lithium-Ion Batteries toward Gradient-Doped LiMnxFe1-xPO4 Cathode Material," Linfeng Fei and colleagues present a green and scalable method for transforming leached FePO4 material from spent lithium-ion batteries into LiMn0.25Fe0.75PO4 cathode material. The resulting particles exhibit gradient-doping of Mn and a uniform carbon coating on their surface, leading to excellent electrochemical performance when used in lithium-ion batteries. This research offers a promising approach for upcycling materials from spent batteries, contributing to the development of sustainable energy technologies. [Extracted from the article]

Herein, a high-entropy layered oxide (HEO) is proposed as an outstanding cathode material for long-life sodium-ion batteries. Based on the self-segregation of elements from surface to bulk phase, a multi-element gradient doped high-entropy cathode material is prepared by doping steel slag with available elements (Mg, Al, Si, Fe, Ca). The surface high-entropy region vastly improves the air stability of materials and reduces surface impurities and side reactions. The Na-O-Mg configuration of near-surface high-entropy region continuously stimulates the anionic redox activity, and the DEMS shows the high-strength Al-O bonding achieves zero oxygen release. Therefore, the LNSM-0.01 reveals a stable capacity of ∼24 mA h g−1 in the range of 4.0–4.5 V. The Ca2+ in bulk phase high-entropy region disrupts the Na+/vacancy ordering transition and enhances the kinetic performance (90 mA h g−1 at 1000 mA g−1), while Fe2+/3+ provides a large amount number of charge compensation. Further, DFT calculations prove that the entropy stability based on synergistic effect immeasurably reinforce the layered oxide configuration, building a more robust structural framework during cycling. This work deepens the understanding on multi-element gradient doping to prepare HEOs, and provides a novel pathway for resource utilization of solid waste. [Display omitted] • Prepare high-entropy oxides by reusing the steel slag. • High-entropy cathode materials exhibit superior electrochemical performance. • Ca+ acts as the "pillar" to disrupt the Na+/vacancy ordering transition. • The Na-O-Mg configuration continuously stimulates the anionic redox activity. [ABSTRACT FROM AUTHOR]

Abstract This work adopts an effective method to stabilize the structure of Ni-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 with yttrium modifying. The results of XRD, EDS, HR-TEM and XPS tests verify that the yttrium modified materials integrate surface nanoscale LiYO 2 coating and inner gradient Y3+ doping. TGA and DSC tests confirm that yttrium modification can promote the thermal stability of LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode material. The results of galvanostatic charge-discharge tests suggest that the 2 mol% yttrium modified sample can exhibit a superior cycling performance with initial discharge capacity of 189.4 mAh g−1 and outstanding capacity retention of 98.4% after 100 cycles at 2.8–4.5 V, which presents obvious enhancement compared with the 83.5% capacity retention of pristine sample. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests indicate that 2 mol % yttrium modifying significantly enhances the diffusion of Li+ ions (D Li +) and notably decreases the electrochemical polarization of electrodes. The surface Li-ion conductor LiYO 2 coating layer as a surface protector inhibits the side reaction and the gradient Y3+ doping supports the crystal structure, which can show synergistic effect in enhancing the electrochemical performance of LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode material. Highlights • Yttrium modification strategy is firstly proposed to modify LiNi 0.8 Co 0.1 Mn 0.1 O 2. • Yttrium modification integrate surface LiYO 2 coating and inner gradient Y3+ doping. • Yttrium modification shows good synergistic effect of LiYO 2 coating-Y3+ doping. • 2 mol% yttrium modified LiNi 0.8 Co 0.1 Mn 0.1 O 2 shows excellent cycling stability. [ABSTRACT FROM AUTHOR]

Abstract The large temperature dependence of electro-strain for Bi 0.5 Na 0.5 TiO 3 (BNT)-based ceramics limits their practical applications. In this work, Li-doped BNT-based lead-free multi-layer piezoelectric ceramic actuators are prepared by solid-state reaction synthesis method. The multi-layer actuator structure is fabricated by gradient doping, in which each layer corresponds to different compositions, with enhanced temperature stability compared to the single-layer one. For specific composition, it could achieve maximum electro-strain value at a certain temperature. Therefore, the electro-strain of each layer in this BNT-based multi-layer actuator could compensate each other at different temperatures with improved temperature stability. Consequently, the electro-strain of the five-layer structure varies less than ∼12% when the temperature changes from 50 °C to 130 °C, and a large electro-strain of 600 pm/V could be obtained at 70 °C. This work provides an effective approach by gradient doping to broaden the use temperature range for BNT-based actuators with improved temperature stability. Highlights • The BNT-based gradient doping multi-layer structure actuator is prepared. • The temperature stability of the multi-layer ceramics is greatly improved. • The strain of the five-layer ceramics varies less than ∼12% from 50 °C to 130 °C. • A large electro-strain of 600 pm/V could be obtained for the five-layer ceramics. [ABSTRACT FROM AUTHOR]

Abstract New and improved electrochemical synthetic approaches have been developed to improve the photoelectrochemical performance of ZnO nanorods by homogenous and gradient doping of copper. The ZnO, Cu-doped ZnO, ZnO Cu-doped ZnO homojunction and also Cu gradient doped ZnO photoanodes were electro-synthesized and characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and UV–visible absorption spectroscopy. A comparative study was done between samples and Cu gradient doped ZnO photoanodes exhibit significantly enhanced photocurrent density in photoelectrochemical cell applications as compared to other photoanodes. By comparing the results, it is found out that the homogeneous Cu-incorporated ZnO photoanodes show an enhanced photoelectrochemical response, but not as well as Cu gradient doped ZnO photoanodes. The photoelectrochemical performance improvement by adjusting the copper concentration profile is attributed to an extra charge separation effect. The linear sweep voltammetry, electrochemical impedance spectroscopy and Mott-Schottky analysis were used to confirm the improved charge separation. Graphical abstract Image Highlights • Electrodeposition of Cu gradient doped ZnO and ZnO/Cu-doped/ZnO homojunction photoanodes. • Effective charge separation and low charge recombination rate in Cu gradient doped ZnO. • Visible light performance of Cu gradient doped ZnO. • Enhanced PEC response of homogeneous Cu-incorporated ZnO photoanodes toward water splitting. [ABSTRACT FROM AUTHOR]

One of the crucial challenges to enhance the photoelectrochemical water‐splitting performance of hematite (α‐Fe2O3) is to resolve its very fast charge recombination in bulk. Herein, we describe the design and fabrication of dual‐axial gradient‐doping on 1D Fe2O3 nanorod arrays with Zr doping for x‐axial and Sn doping for y‐axial directions to promote the charge separation. This dual‐axial gradient‐doping structure fulfills the requirements of a greater electron‐carrier concentration for increasing conductivity as well as a higher charge‐separation efficiency across the dual‐axial direction of Fe2O3 nanorods, ultimately showing an excellent photocurrent density of 1.64 mA cm−2 at 1.23 V vs. RHE, which is 26.3 times more than that of the bare Fe2O3. Furthermore, the remarkably improved photocurrent density, when comparing the uniform Zr‐doped Fe2O3 nanorod arrays (1.0 mA cm−2 at 1.23 V vs. RHE) with dual‐axial gradient‐doped (Zr and Sn) Fe2O3 nanorod arrays, highlights the additional charge‐separation effect resulting from gradient codoping of Zr and Sn. Hence, this promising design may provide guidelines for dual‐axial gradient doping into photoelectrodes to realize efficient PEC water splitting. Solar energy: The dual‐axial gradient doping (Zr and Sn) on hematite with Zr doping for x‐axial and Sn doping for y‐axial directions fulfills the requirements of a greater electron‐carrier concentration for increasing conductivity and a higher charge‐separation efficiency across the dual‐axial direction of Fe2O3 nanorods. [ABSTRACT FROM AUTHOR]

High voltage property applied in cells is one of the critical directions for high energy density lithium-ion battery. In this work, cadmium oxides are used as the modifying material on the LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode materials by a facile chemical precipitation method followed by post-calcination. The cadmium oxides not only cover on the LiNi 0.6 Co 0.2 Mn 0.2 O 2 particles surface homogenously, but also diffuse into the crystal lattice of the LiNi 0.6 Co 0.2 Mn 0.2 O 2 with gradient distribution. The formed cadmium oxide and metal fluorides mixed-layer during cycling on the surface makes the interfacial stability significantly improved. Therefore, the side-reactions are suppressed effectively. The gradient doping of the cadmium in the crystal lattice enhances the structural stability of the LiNi 0.6 Co 0.2 Mn 0.2 O 2 and facilitates the Li + and electron transportation in the bulk material. Moreover, the residual lithium components (Li 2 CO 3 /LiOH) also decrease significantly. As a result, the obtained Cd-modified LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathodes rise 16.60 (100 cycles, 3.0–4.6 V) and 13.87 (200 cycles, 3.0–4.5 V) percentage points at 1 C rate, respectively. The initial capacity of cadmium-modified LiNi 0.6 Co 0.2 Mn 0.2 O 2 is 160.8 mAh g −1 at 8 C rate over 3.0–4.5 V. The proposed cadmium oxide modification may be also potentially applied in other active cathode materials, especially for the high voltage performance. [ABSTRACT FROM AUTHOR]

Featured Application: Nanomaterials for Solar Water Splitting Solar-driven water splitting technology is considered to be a promising solution for the global energy challenge as it is capable of generating clean chemical fuel from solar energy. Various strategies and catalytic materials have been explored in order to improve the efficiency of the water splitting reaction. Although significant progress has been made, there are many intriguing fundamental phenomena that need to be understood. Herein, we review recent experimental efforts to demonstrate enhancement strategies for efficient solar water splitting, especially for the light absorption, charge carrier separation, and water oxidation kinetics. We also focus on the state of the art of photoelectrochemical (PEC) device designs such as application of facet engineering and the development of a ferroelectric-coupled PEC device. Based on these experimental achievements, future challenges, and directions in solar water splitting technology will be discussed. [ABSTRACT FROM AUTHOR]