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Enhancing pseudocapacitance of Ti 3 C 2 T x MXene-based electrode materials induced by sufficient surface terminating groups (such as Ti–O bonding) becomes one promising way for fabricating high energy-density supercapacitors. However, most of terminating group activity cannot be excited well in the multilayer Ti 3 C 2 T x due to the layer stacking feature, which limits its further performance improvement. In this paper, a CQDs@Ti 3 C 2 T x hybrid material is synthesized by modifying few-layer Ti 3 C 2 T x MXene matrix with highly dispersed carbon quantum dots (CQDs). In this unique hybrid model, the Ti 3 C 2 T x MXene matrix with high conductivity and high specific surface area is just like the "paddy field", which not only promotes the charge rapid transfer, but also provides the high double layer capacitance by ion adsorption. More importantly, the CQDs act as "rice seedlings" firmly anchored to the Ti 3 C 2 T x matrix, and greatly stimulate the activity of the termination groups of Ti 3 C 2 T x. As expected, this hybrid achieves a harmonious coexistence of high conductivity and high pseudocapacitance. As a result, the CQDs@Ti 3 C 2 T x electrode delivers high reversible capacitances of 441.3 F g−1 at 1 A g−1 and 310.1 F g−1 at 20 A g−1, and a relatively stable cyclability with almost 100% capacitance retention after 10 000 cycles at 10 A g−1. A CQDs@Ti 3 C 2 T x hybrid is facilely designed, in which the activity of Ti–O bonding is excited well to enhance its pseudocapacitance. Consequently, this resultant CQDs@Ti 3 C 2 T x realizes a comprehensive energy storage ability. This strategy may provide a promising approach to fabricate high-performance MXene based electrode. [Display omitted] [ABSTRACT FROM AUTHOR]

The poor thermal stability of Ni-rich cathode materials, resulting in thermal runaway of the battery, is a major safety threat to the development of lithium-ion batteries. However, the thermal degradation mechanism that determines thermal stability, especially for the promising single-crystal (SC) Ni-rich cathode material, has not been elucidated. More importantly, this is indeed a fundamental issue. Herein, via a series of in-situ/ex-situ probing technologies, the thermal degradation of SC Ni-rich material is elaborately diagnosed from surface to bulk phase and compared with polycrystalline (PC) Ni-rich material. A comprehensive oxygen release kinetic model including oxygen diffusion distance, mechanical stress and temperature is presented. This model reveals that the SC Ni-rich material exhibits a stable depth-dependent gradient oxygen release kinetics, while the PC Ni-rich material exhibits an accelerated oxygen release kinetics by grain boundaries, which reveals the origin of the high-thermal-stability of SC Ni-rich cathodes. This work highlights the importance of suppressing oxygen release kinetics (e.g., increase oxygen diffusion distance, increase mechanical stress) to improve thermal stability, facilitating the development of safer lithium-ion batteries based on Ni-rich cathodes. [Display omitted] • Precise probing the thermal degradation process from surface to bulk phase. • A comprehensive kinetic model of oxygen release is proposed. • Single-crystal cathodes exhibit a stable depth-dependent gradient oxygen release kinetics. • Increasing oxygen diffusion distance and mechanical stress can stabilize lattice oxygen. [ABSTRACT FROM AUTHOR]

The renewed anion exchange membrane fuel cells (AEMFCs) are expected to minimize the cost constraints of fuel cells owing to the advantages of employing economic catalysts. However, high Pt dosage (almost ten times higher than that in acids) caused by the sluggish hydrogen oxidation reaction (HOR) kinetics in alkaline media hampers the development of AEMFCs. Developing alternative Pt-free electrocatalysts is desirable but is limited by the lack of mechanistic understanding and system-wide design guidance. Against this backdrop, this review starts with the alkaline HOR mechanisms about reaction pathways, hydrogen/hydroxyl binding energy theory, and theoretical interpretations on the low HOR kinetics in alkali. Next, recent advances in developing supports, cocatalysts, and active components for Pt-free HOR catalysts are summarized. The synergistic mechanism of supports and cocatalysts with active metals is for the first time systematically introduced. Finally, a brief perspective on the remaining challenges and future directions of Pt-free electrocatalysts for alkaline HOR is also outlined. [Display omitted] • The mechanism of alkaline HOR electrocatalysis is introduced. • Recent advances in developing Pt-free HOR catalysts are summarized. • System-wide design guidelines on supports, cocatalysts, and main metals are proposed. • Future challenges and prospective of designing Pt-free catalysts are presented. [ABSTRACT FROM AUTHOR]

N-doping can endow carbon materials with high electrochemical activity. Besides the widely validated sp 2 -hybridized nitrogen doping, sp -hybridized nitrogen (sp - N) atoms are also expected to be new active sites. However, both sp - N atoms and cyano (CN) groups containing sp - N are rarely produced in carbon materials presently. In this work, the first cyano groups-modified carbon materials are synthesized firstly via an interesting struggle between the chemical etching of KOH and the catalytic graphitization of Co nanoparticles in carbon frameworks. The theoretical calculations and experimental results manifest that the stronger electronegativity of CN groups renders carbon materials a higher electrochemical activity. As K+ storage anodes, the CN−modified carbon materials exhibit an obvious boost in potassium storage performance in both ester- and ether-based electrolytes. Therefore, as a new N doping form, the successful introduction of CN groups into carbon materials opens a door for exploring sp -N doped carbon materials for applications in energy storage and other fields. [Display omitted] • The first cyano-modified carbon materials are prepared. • As K+ storage anodes, the CN-modified carbon exhibits the impressive performance. • The storage mechanism of CN was explored by theoretical calculation and test. [ABSTRACT FROM AUTHOR]

Polythiophene (Pth) is a good candidate cathode material for aluminum ion battery (AIB) because of its lightness, safety, plasticity and flexibility. However, it always manifests inferior stability. Herein, a stable Pth-based cathode is realized through the anchoring effect between Pth and carboxyl. Pth with a thin film morphology is in situ synthesized on the surface of carboxylated carbon nanotubes (CNT-COOH). As a support, CNT-COOH not only alleviates the agglomeration of Pth that provides abundant transport channels for ions and electrons simultaneously, but also enhances the stability of Pth through the anchoring effect. As a result, the prepared Pth/CNT-COOH composite exhibits high discharge capacity (113 mAh g−1 at 1 A g−1), outstanding rate performance (95 mAh g−1 at 5 A g−1) and stable cycle stability (10,000 cycles with 0.001% decay per cycle). This work realizes a promising Pth-based AIBs with high capacity and long lifespan, which paves the way to the applications of organic materials in AIBs. [ABSTRACT FROM AUTHOR]