Oriented nucleation in formamidinium perovskite for photovoltaics.

The black phase of formamidinium lead iodide (FAPbI3) perovskite shows huge promise as an efficient photovoltaic, but it is not favoured energetically at room temperature, meaning that the undesirable yellow phases are always present alongside it during crystallization1-4. This problem has made it difficult to formulate the fast crystallization process of perovskite and develop guidelines governing the formation of black-phase FAPbI3 (refs. 5,6). Here we use in situ monitoring of the perovskite crystallization process to report an oriented nucleation mechanism that can help to avoid the presence of undesirable phases and improve the performance of photovoltaic devices in different film-processing scenarios. The resulting device has a demonstrated power-conversion efficiency of 25.4% (certified 25.0%) and the module, which has an area of 27.83 cm2, has achieved an impressive certified aperture efficiency of 21.4%.

Regulating Cation Interactions for Zero-Strain and High-Voltage P2-type Na2/3 Li1/6 Co1/6 Mn2/3 O2 Layered Oxide Cathodes of Sodium-Ion Batteries.

Deep sodium extraction/insertion of sodium cathodes usually causes undesired Jahn-Teller distortion and phase transition, both of which will reduce structural stability and lead to poor long-cycle reliability. Here we report a zero-strain P2- Na2/3 Li1/6 Co1/6 Mn2/3 O2 cathode, in which the lithium/cobalt substitution contributes to reinforcing the host structure by reducing the Mn3+ /Mn4+ redox, mitigating the Jahn-Teller distortion, and minimizing the lattice change. 94.5 % of Na+ in the unit structure can be reversibly cycled with a charge cut-off voltage of 4.5 V (vs. Na+ /Na). Impressively, a solid-solution reaction without phase transitions is realized upon deep sodium (de)intercalation, which poses a minimal volume deviation of 0.53 %. It attains a high discharge capacity of 178 mAh g-1 , a high energy density of 534 Wh kg-1 , and excellent capacity retention of 95.8 % at 1 C after 250 cycles.

A self-supervised guided knowledge distillation framework for unpaired low-dose CT image denoising.

Low-dose computed tomography (LDCT) can significantly reduce the damage of X-ray to the human body, but the reduction of CT dose will produce images with severe noise and artifacts, which will affect the diagnosis of doctors. Recently, deep learning has attracted more and more attention from researchers. However, most of the denoising networks applied to deep learning-based LDCT imaging are supervised methods, which require paired data for network training. In a realistic imaging scenario, obtaining well-aligned image pairs is challenging due to the error in the table re-positioning and the patient's physiological movement during data acquisition. In contrast, the unpaired learning method can overcome the drawbacks of supervised learning, making it more feasible to collect unpaired training data in most real-world imaging applications. In this study, we develop a novel unpaired learning framework, Self-Supervised Guided Knowledge Distillation (SGKD), which enables the guidance of supervised learning using the results generated by self-supervised learning. The proposed SGKD scheme contains two stages of network training. First, we can achieve the LDCT image quality improvement by the designed self-supervised cycle network. Meanwhile, it can also produce two complementary training datasets from the unpaired LDCT and NDCT images. Second, a knowledge distillation strategy with the above two datasets is exploited to further improve the LDCT image denoising performance. To evaluate the effectiveness and feasibility of the proposed method, extensive experiments were performed on the simulated AAPM challenging and real-world clinical LDCT datasets. The qualitative and quantitative results show that the proposed SGKD achieves better performance in terms of noise suppression and detail preservation compared with some state-of-the-art network models.

Localized Hydrophobicity in Aqueous Zinc Electrolytes Improves Zinc Metal Reversibility.

The rechargeability of aqueous zinc metal batteries is plagued by parasitic reactions of the zinc metal anode and detrimental morphologies such as dendritic or dead zinc. To improve the zinc metal reversibility, hereby we report a new solution structure of aqueous electrolyte with hydroxyl-ion scavengers and hydrophobicity localized in solvent clusters. We show that although hydrophobicity sounds counterintuitive for an aqueous system, hydrophilic pockets may be encapsulated inside a hydrophobic outer layer, and a hydrophobic anode-electrolyte interface can be generated through the addition of a cation-philic, strongly anion-phobic, and OH--reactive diluent. The localized hydrophobicity enables less active water and less absorbed water on the Zn anode surface, which suppresses the parasitic water reduction; while the hydroxyl-ion-scavenging functionality further minimizes undesired passivation layer formation, thus leading to superior reversibility (an average Zn plating/stripping efficiency of 99.72% for 1000 cycles) and lifetime (80.6% capacity retention after 5000 cycles) of zinc batteries.

Engineering Bimetallic NiFe-Based Hydroxides/Selenides Heterostructure Nanosheet Arrays for Highly-Efficient Oxygen Evolution Reaction.

Developing cost-effective and high-efficiency electrocatalysts toward alkaline oxygen evolution reaction (OER) is crucial for water splitting. Amorphous bimetallic NiFe-based (oxy)hydroxides have excellent OER activity under alkaline media, but their poorly electrical conductivity impedes the further improvement of their catalytic performance. Herein, a bimetallic NiFe-based heterostructure electrocatalyst that is composed of amorphous NiFe(OH)x and crystalline pyrite (Ni, Fe)Se2 nanosheet arrays is designed and constructed. The catalyst exhibits an outstanding OER performance, only requiring low overpotentials of 180, 220, and 230 mV at the current density of 10, 100, and 300 mA cm-2 and a low Tafel slope of 42 mV dec-1 in 1 m KOH, which is among the state-of-the-art OER catalysts. Based on the experimental and theoretical results, the electronic coupling at the interface that leads to the increased electrical conductivity and the optimized adsorption free energies of the oxygen-contained intermediates plays a crucial role in enhancing the OER activities. This work focusing on improving the OER performance via engineering amorphous-crystalline bimetallic heterostructure may provide some inspiration for reasonably designing advanced electrocatalysts.

Study on the Electrochemical Reaction Mechanism of ZnFe2O4 by In Situ Transmission Electron Microscopy.

A family of mixed transition-metal oxides (MTMOs) has great potential for applications as anodes for lithium ion batteries (LIBs). However, the reaction mechanism of MTMOs anodes during lithiation/delithiation is remain unclear. Here, the lithiation/delithiation processes of ZnFe2O4 nanoparticles are observed dynamically using in situ transmission electron microscopy (TEM). Our results suggest that during the first lithiation process the ZnFe2O4 nanoparticles undergo a conversion process and generate a composite structure of 1-3 nm Fe and Zn nanograins within Li2O matrix. During the delithiation process, volume contraction and the conversion of Zn and Fe take place with the disappearance of Li2O, followed by the complete conversion to Fe2O3 and ZnO not the original phase ZnFe2O4. The following cycles are dominated by the full reversible phase conversion between Zn, Fe and ZnO, Fe2O3. The Fe valence evolution during cycles evidenced by electron energy-loss spectroscopy (EELS) techniques also exhibit the reversible conversion between Fe and Fe2O3 after the first lithiation, agreeing well with the in situ TEM results. Such in situ TEM observations provide valuable phenomenological insights into electrochemical reaction of MTMOs, which may help to optimize the composition of anode materials for further improved electrochemical performance.

In Situ Transmission Electron Microscopy Observation of the Lithiation-Delithiation Conversion Behavior of CuO/Graphene Anode.

The electrochemical conversion behavior of metal oxides as well as its influence on the lithium-storage performance remains unclear. In this paper, we studied the dynamic electrochemical conversion process of CuO/graphene as anode by in situ transmission electron microscopy. The microscopic conversion behavior of the electrode was further correlated with its macroscopic lithium-storage properties. During the first lithiation, the porous CuO nanoparticles transformed to numerous Cu nanograins (2-3 nm) embedded in Li2O matrix. The porous spaces were found to be favorable for accommodating the volume expansion during lithium insertion. Two types of irreversible processes were revealed during the lithiation-delithiation cycles. First, the nature of the charge-discharge process of CuO anode is a reversible phase conversion between Cu2O and Cu nanograins. The delithiation reaction cannot recover the electrode to its pristine structure (CuO), which is responsible for about ∼55% of the capacity fading in the first cycle. Second, there is a severe nanograin aggregation during the initial conversion cycles, which leads to low Coulombic efficiency. This finding could also account for the electrochemical behaviors of other transition metal oxide anodes that operate with similar electrochemical conversion mechanism.

[Mental and behavioral abnormalities after arthroplasty and incomplete cerebral fat embolism].

OBJECTIVE: To investigate the relationship between mild consciousness and mental disorders after arthroplasty and incomplete cerebral fat embolism. METHODS: A retrospective analysis of 12 patients with incomplete cerebral fat embolism after arthroplasty was performed from June 2004 to December 2011. There were 5 males and 7 females,ranging in age from 36 to 82 years old,averaged 56.8 years old. Four patients had femoral neck fractures; 3 patients had avascular necrosis of the femoral head; 3 patients had rheumatoid arthritis; 1 patient had ankylosed hip and 1 patient had knee osteoarthritis. The patients had consciousness and mental disorders after arthroplasty (femoral head replacement in 3 cases, total hip replacement in 7 cases, and knee joint surface replacement in 2 cases), changes of vital sign and abnormal brain MRI examination. RESULTS: Twelve patients had mild consciousness and mental disorders,and the NIHSS score was 1.92+/-3.78,which was correlated with incomplete cerebral fat embolism after arthroplasty. The patients recovered conscious within 24 to 72 hours after treatment with expansion of blood volume,dehydrating agent and neuroprotective drugs,improving respiratory and circulatory function, hormone protection and antibiotic application. The patients were followed up with a mean period of 18 months (ranging from 10 to 36 months). The patients had neurological function recovering to normal without sequelae, and the NIHSS score decreased to 0. CONCLUSION: Incomplete cerebral fat embolism after arthroplasty is the main reason causing mild awareness and mental disorders, which is often to be misdiagnosed or ignored because of not typical clinical manifestations.