KOH-activated hollow carbon spheres with surface functionalization for high-capacity and long-cycle-life lithium-selenium batteries.

Lithium-selenium (Li-Se) batteries are considered promising alternatives to lithium-ion batteries due to their higher volumetric capacity and energy density. However, they still face limitations in efficiently utilizing the active selenium. Here, we develop surface-functionalized mesoporous hollow carbon nanospheres as the selenium host. By using KOH activation, the surface of the carbon nanospheres is functionalized with hydroxyl groups, which greatly improve the utilization of selenium and facilitate the conversion of lithium selenides, leading to much higher capacities compared to ZnCl2 activation and untreated carbon nanospheres. Theory and experimental evidence suggest that surface hydroxyl groups can enhance the reduction conversion of polyselenides to selenides and facilitate the oxidation reaction of selenides to elemental selenium. In-situ and ex-situ characterization techniques provided additional confirmation of the hydroxyl groups electrochemical durability in catalyzing selenium conversion. The meticulously engineered Se cathode demonstrates a high specific capacity of 594 mA h g-1 at 0.5C, excellent rate capability of 464 mA h g-1 at 2C, and a stable cycling performance of 500 cycles at 2C with a capacity retention of 84.8 %, corresponding to an ultra-low-capacity decay rate of 0.0144 % per cycle, surpassing many reported lithium-selenium battery technologies.

Leveraging an all-fixed transfer framework to predict the interpretable formation energy of MXenes with hybrid terminals.

MXenes have attracted substantial attention for their various applications in energy storage, sensors, and catalysts. Experimental exploration of MXenes with hybrid terminal surfaces offers a unique means of property tailoring that is crucial for expanding the performance space of MXenes, wherein the formation energy of an MXene with mixed surface terminals plays a key role in determining its relative stability and practical applications. However, the challenge of identifying energetically stable MXenes with multifunctional surfaces persists, primarily due to the absence of precise surface modification during experiments and the vast structural space for DFT calculations. Herein, we use an all-fixed transfer (AFT) framework combined with first-principles calculations to predict the formation energies of MXenes terminated by binary elements from groups VIA and VIIA. The trained model exhibits a high average R2 of 0.99, maintaining transferability and accuracy in predicting larger supercells from smaller-sized MXenes and datasets despite the structural imbalance between the training and prediction sets. The underlying interpretation of the high accuracy is revealed through the capture of main attributes and comparison of node features. Additionally, it is important to mention that the factors influencing the average formation energy include the types of element pairs, the ratio of terminal groups, and the distribution of terminations on two surfaces, with the first one being dominant. Finally, we successfully streamline the diverse structural cardinality of a large hybrid terminated MXene space of over 700 million, thereby facilitating the rapid screening of the top 5 stable MXene classes with binary terminal elements (FO, FCl, FBr, FS, and FSe). Besides, in the scenarios of lithium storage, the TL-predicted MXene can enhance its relative stability by increasing the fluorine ratio where the capacity can be optimized by different surface group combinations. All results indicate that the AFT framework has the advantages of screening functional MXenes with a huge structure space from smaller and imbalanced data sets.

Engineering a High-Loading Sub-4 nm Intermetallic Platinum-Cobalt Alloy on Atomically Dispersed Cobalt-Nitrogen-Carbon for Efficient Oxygen Reduction in Fuel Cells.

Developing a high-performance membrane electrode assembly (MEA) poses a formidable challenge for fuel cells, which lies in achieving both high metal loading and efficient catalytic activity concurrently for MEA catalysts. Here, we introduce a porous Co@NC carrier to synthesize sub-4 nm PtCo intermetallic nanocrystals, achieving an impressive Pt loading of 27 wt %. The PtCo-CoNC catalyst demonstrates exceptional catalytic activity and remarkable stability for the oxygen reduction reaction. Advanced characterization techniques and theoretical calculations emphasize the synergistic effect between PtCo alloys and single Co atoms, which enhances the desorption of the OH* intermediate. Furthermore, the PtCo-CoNC-based cathode delivers a high power density of 1.22 W cm-2 in the MEA test owing to the enhanced mass transport, which is verified by the simulation results of the O2 distributions and current density inside the catalyst layer. This study lays the groundwork for the design of efficient catalysts with practical applications in fuel cells.

APbI3-A2AgBiI6 Double-Layer Perovskite Film for a Self-Powered and High-Stability X-ray Detector.

The development of lead halide perovskite X-ray detectors has promising applications in medical imaging and security inspection but is hindered by poor long-term stability and drift of the dark current and photocurrent. Herein, we design a (Cs0.05MA0.65FA0.3)PbI3-(Cs0.1MA1.3FA0.6)AgBiI6 double-layer perovskite film to assemble a self-powered flat-panel X-ray detector. The demonstrated X-ray detector achieves an outstanding self-powered sensitivity of 80 µC Gyair-1 cm-2 under a 0 V bias. More importantly, owing to the inhibition of the phase transition process and ion migration of (Cs0.05MA0.65FA0.3)PbI3 by the (Cs0.1MA1.3FA0.6)AgBiI6 layer, the device exhibits excellent continuous operating stability with a retention rate of 99% dark current and photocurrent over X-ray pulses of up to 4000 s and excellent long-term stability without a loss of the original response current after 150 days in an air environment. The strategy of double-layer perovskites improves the stability and sensitivity of devices, which paves a path for the industrial application of lead halide perovskite X-ray detectors.

Dual-salt strategy tuning the solvation structure to achieve high cycling stability for FeS2 cathodes.

Pyrite FeS2, as a promising conversion-type cathode material, faces rapid capacity degradation due to challenges such as polysulfide shuttle and massive volume changes. Herein, a localized high-concentration electrolyte (LHCE) based on dual-salt lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) is designed to address the challenges. By the dual-salt strategy, we tailor a more desirable solvation structure than that in the single-salt system. Specifically, the solvation structure involving FSI- and TFSI- enables milder electrolyte decomposition, which reduces initial capacity loss. Meanwhile, it facilitates the formation of a stable and flexible cathode/electrolyte interphase (CEI), effectively mitigating side effects and accommodating volume changes. Consequently, the micro-sized FeS2 realizes a capacity of 641 mAh g-1 after 600 cycles with a retention rate of 90%, significantly improving the cycling stability of the FeS2 cathode. This work underscores the pivotal role of solvation structure in modulating electrochemical performances and provides a simple and effective electrolyte design concept for conversion-type cathodes.

Enhancement of multilayer lithium storage in a ß12-borophene/graphene heterostructure with built-in dipoles.

The combination of borophene with a supporting metallic layer is beneficial in stabilizing its structure and promoting its application in energy storage. Here, through first-principles calculations, we screen a ß12-borophene/graphene (ß12-B/G) heterostructure with superior structural integrity, strong interlayer binding, and high thermodynamic stability among different B/G heterostructures. Besides, it is noteworthy that ß12-B/G has been recently synthesized, further opening the possibility of expanding its use in energy storage. Then the selected target is systematically investigated as an anode material for lithium-ion batteries (LIBs). Compared with each monolayer component, multiple lithium-ion adsorption is achieved in the ß12-B/G heterostructure, resulting in an ultra-high theoretical specific capacity of 2267 mA h g-1. In addition, a lower diffusion energy barrier indicates faster electron transport and lithium-ion diffusion in the ß12-B/G heterostructure. Notably, the multilayer lithium adsorption avoids the formation of dendritic deposits, as evidenced by complete ionization of the cationic layers. Moreover, the disparity in the work functions of the individual layers gives rise to a built-in dipole in ß12-B/G, further enhancing the multilayer lithium storage and ion migration. All these results suggest that the construction of borophene-based heterostructures with built-in dipoles is a feasible way to design high-performance LIB anode materials.

A weakened Fermi level pinning induced adsorption energy non-charge-transfer mechanism during O2 adsorption in silicene/graphene heterojunctions.

Understanding the mechanisms of gas adsorption on a solid surface and making this process tunable are of great significance in fundamental science and industrial applications. Bond creation and charge transfer are often used to explain the origin of adsorption energy (Ead). However, in this study, a new mechanism is observed in O2 adsorption on pure silicene (PS) and silicene/graphene heterojunction (SGH) surfaces, in which the charge distribution remains almost unchanged, but Ead still has a significant change in the order of 0.3 eV. The weakened Fermi level pinning effect is found to be responsible for this interesting behavior and the variation of Ead is approximately equal to the change of work function. Furthermore, this effect is independent of the twist angles in the van der Waals SGH. Our results are consistent with experimental observations in overcoming the degradation of silicene in air.