Search

Ti3C2Tx MXene shows great promise as a supercapacitor electrode material owing to its high conductivity and pseudocapacitive nature. Phosphorus doping is an efficient strategy to boost its capacitance due to the synergistic effect of the P–O and P–C species formed. However, the contribution to enhanced capacitance from specific phosphorus doped species in P-doped Ti3C2Tx remains largely unexplored. Herein, phosphorus atoms are selectively grafted onto Ti3C2Tx MXene, introducing only P–O doped species and how this doping configuration contributes to capacitance is unraveled. The results show that 2.1 at% P-doped Ti3C2Tx delivers a capacitance enhancement of 35% (437 F g−1 at 2 mV s−1) in comparison with pristine MXene and outstanding cycling stability. Multiple in situ and ex situ characterization studies along with DFT calculations collectively reveal that the formed P–O bonds are new active sites for a two-proton bonding-debonding process, leading to enhanced charge storage and capacitive performance in MXene. However, higher surface phosphorus doping would destroy crystal integrity of MXene and leads to performance deterioration. [ABSTRACT FROM AUTHOR]

Semicrystalline polymer dielectrics (SPDs) are highly sought‐after state‐of‐the‐art dielectric materials. As the disorder in SPDs degrades their electrical properties, homogeneously ordered SPDs are desired. However, complex crystallization behaviors of polymers make such homogeneity elusive. Polymer lamellar single crystals (PLSCs), the most regularly‐ordered form of SPDs possible under mild crystallizing conditions, are ideal platforms for understanding and developing high‐performance dielectric materials. Here, a typical and widely used SPD, polyethylene (PE) is selected as the model material. We successfully obtained, large, uniform, and high‐quality PE PLSCs and devised a non‐destructive strategy to construct PE PLSC‐based vertical capacitors. These nanometer‐thick capacitors exhibit exceptional dielectric properties, with a high breakdown strength of 6.95 MV/cm and a low dielectric constant of 2.14±0.07, that outperform the properties of any existing neat PE. This work provides novel insights into exploring the performance possibility of ordered SPDs and reveals the PLSCs as potential high‐performance dielectric materials. [ABSTRACT FROM AUTHOR]

Highlights: A simple two-step multi-element co-doping strategy is proposed to fabricate core-shell structured LiCoO2 based on the different diffusivities of dopant ions. The high diffusivity Al3+/Mg2+ ions occupy the core of single-crystal grain while the low diffusivity Ti4+ ions enrich the shell layer. In-situ XRD demonstrates the mitigated structural distortion under a high cut-off voltage of 4.6 V, resulting in a significantly improved cycling stability. Inactive elemental doping is commonly used to improve the structural stability of high-voltage layered transition-metal oxide cathodes. However, the one-step co-doping strategy usually results in small grain size since the low diffusivity ions such as Ti4+ will be concentrated on grain boundaries, which hinders the grain growth. In order to synthesize large single-crystal layered oxide cathodes, considering the different diffusivities of different dopant ions, we propose a simple two-step multi-element co-doping strategy to fabricate core–shell structured LiCoO2 (CS-LCO). In the current work, the high-diffusivity Al3+/Mg2+ ions occupy the core of single-crystal grain while the low diffusivity Ti4+ ions enrich the shell layer. The Ti4+-enriched shell layer (~ 12 nm) with Co/Ti substitution and stronger Ti–O bond gives rise to less oxygen ligand holes. In-situ XRD demonstrates the constrained contraction of c-axis lattice parameter and mitigated structural distortion. Under a high upper cut-off voltage of 4.6 V, the single-crystal CS-LCO maintains a reversible capacity of 159.8 mAh g−1 with a good retention of ~ 89% after 300 cycles, and reaches a high specific capacity of 163.8 mAh g−1 at 5C. The proposed strategy can be extended to other pairs of low- (Zr4+, Ta5+, and W6+, etc.) and high-diffusivity cations (Zn2+, Ni2+, and Fe3+, etc.) for rational design of advanced layered oxide core–shell structured cathodes for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Ruthenium (Ru), benefitting from efficient water dissociation ability, is considered a good candidate for alkaline hydrogen evolution reaction (HER); however, the strong binding of H intermediates over Ru sites leads to a limited desorption behavior and thus an unsatisfactory HER activity. Here, we propose a strategy to fabricate a well-defined hetero-interface via anchoring Ru nanoparticles on Co4N nanorods grown on nickel foam (Ru/Co4N/NF). The as-prepared Ru/Co4N/NF catalyst is demonstrated to effectively catalyze water splitting into hydrogen in an alkaline electrolyte, with an overpotential of 145 mV to reach 100 mA cm−2 and a Tafel slope of 25 mV dec−1, far surpassing bare Ru/NF and Co4N/NF. Experimental observations combined with computational simulations reveal that the charge migration from Ru to Co4N contributes to the formation of electron-deficient Ru sites and shifts the d-band center away from the Fermi level, which is conducive to hydrogen desorption. Meanwhile, the electron coupling effect between Ru and Co4N reduces the H2O adsorption energy and allows more electrons to participate in H2O molecule activation. [ABSTRACT FROM AUTHOR]

The controlled synthesis of hollow structure transition metal compounds has long been a very interesting and significant research topic in the energy storage and conversion fields. Herein, an ultrasound-assisted chemical etching strategy is proposed for fabricating concave Ni(OH)2 nanocubes. The morphology and composition evolution of the concave Ni(OH)2 nanocubes suggest a possible formation mechanism. The as-synthesized Ni(OH)2 nanostructures used as supercapacitor electrode materials exhibit high specific capacitance (1624 F g−1 at 2 A g−1) and excellent cycling stability (77% retention after 4000 cycles) due to their large specific surface area and open pathway. In addition, the corresponding hybrid capacitor (Ni(OH)2//graphene) demonstrates high energy density (42.9 Wh kg−1 at a power density of 800 W kg−1) and long cycle life (78% retention after 4000 cycles at 5 A g−1). This work offers a simple and economic approach for obtaining concave Ni(OH)2 nanocubes for energy storage and conversion. [ABSTRACT FROM AUTHOR]

A Ni-rich cobalt-free layered cathode material (LiNixMn1−xO2) is promising due to its low cost, excellent structural stability, and thermal stability. However, low Li-ion diffusion kinetics, highly reactive Ni4+, and stress-induced intragranular micro-cracking restrict its further application. Here, we report dual-functional boron-modification (doping and coating) on a cobalt-free single-crystal layered cathode (B-LiNi0.75Mn0.25O2) via a simple solid-state method. The boron atoms prefer to occupy the tetrahedral interstices in the Li layer during the sintering process, which enlarges the c-axis for fast Li-ion diffusion kinetics and can also serve as a pillar to achieve an ultra-low (1.62%) c-axis lattice contraction at 80% state of charge (SOC). And boron doping passivates the lattice O, inhibits the irreversible phase transition and provides excellent thermal stability at a high cut-off voltage of 4.5 V. On the other hand, the byproduct LiBO2 can improve Li-ion diffusion and alleviate side reactions at the electrode/electrolyte interface by serving as a Li-ion conductive coating layer. As a result, B–LiNi0.75Mn0.25O2 is almost free of inter- and intragranular micro-cracking with faster Li-ion diffusion kinetics. It delivers 176.6 mA h g−1 at 1C and achieves 82.9% capacity retention after 200 cycles. This work not only provides a low-cost and scalable method to remove Co from conventional Ni-rich layered cathodes, but also reveals the commercial feasibility of highly safe single-crystal layered cathode materials. [ABSTRACT FROM AUTHOR]