Highly uniform hierarchical Mo-polydopamine hollow spheres are synthesized for the first time through a liquid-phase reaction under ambient temperature. A self-assembly mechanism of the hollow structure of Mo-polydopamine precursor is discussed in detail, and a determined theory is proposed in a water-in-oil system. Via different annealing process, these precursors can be converted into hierarchical hollow MoO /C and Mo C/C composites without any distortion in shape. Owing to the well-organized structure and nanosize particle embedding, the as-prepared hollow spheres exhibit appealing performance both as the anode material for lithium-ion batteries and as the catalyst for hydrogen evolution reaction (HER). Accordingly, MoO /C delivers a high reversible capacity of 940 mAh g at 0.1 A g and 775 mAh g at 1 A g with good rate capability and long cycle performance. Moreover, Mo C/C also exhibits an enhanced electrocatalytic performance with a low overpotential for HER in both acidic and alkaline conditions, as well as remarkable stability.
Pursuing rechargeable metal-ion batteries with greater energy density is attracting great attention due to increasing demand for energy storage, where alloying anodes can provide very high capacity. [1][2][3][4][5][6][7] This is particularly true since sodium and potassium ion battery technologies offer limited capacity and stability using classic carbon-based anodes compared to lithium ions. [8][9][10][11] However, alloying anodes are notorious for their severe capacity fading, which has hindered their practical applications. The failure mechanism of alloying anodes has always been ascribed to the large volumetric change (~300%) and/or the fragile solid electrolyte interphase (SEI). [12][13][14][15] This interpretation is popular because the pulverization of the alloy-based electrodes can be observed during the reactions. As a result, many strategies have been developed to overcome this issue. These strategies include nano-structural controlling, carbon modification, and improving electrical conductivity. Thus, many nanostructured alloys including particles, 16 fibers/tubes, 5,17 film/membrane, 18,19 and hierarchical material 20,21 are being explored to stabilize alloying anodes. Characteristic, conductive and/or protective materials such as carbon and artificial solid electrolyte interphase (SEI) have been also used to improve alloying anode capacities stabilities. [22][23][24][25] Herein we show that an unprecedented high capacity (>650 mAh g -1 ) and stability (>500 cycles) can be achieved in alloying anodes by simply tuning the electrolyte composition, without the need for nanostructural control, carbon modification, and/or SEI engineering. We confirm that the cation solvation structure (e.g., Na + , K + ), particularly the type and location of the anions present in the metal salt and solvents, plays a critical role in affecting the alloying anode performance. In addition, we present a new anionic model showing that the anion corrosion plays at least an equally important role in alloying anode stability as the volume variation and fragile SEI models. Moreover, we present a new reaction model for alloying anode to make the ASSOCIATED CONTENT Supporting Information. Experimental and simulation section. Figures S1-S17 and Table S1 are included.
The donor:acceptor heterojunction has proved as the most successful approach to split strongly bound excitons in organic solar cells (OSCs). Establishing an ideal architecture with selective carrier transport and suppressed recombination is of great importance to improve the photovoltaic efficiency while remains a challenge. Herein, via tailoring a hybrid planar/bulk structure, highly efficient OSCs with reduced energy losses (Elosss) are fabricated. A p‐type benzodithiophene‐thiophene alternating polymer and an n‐type naphthalene imide are inserted on both sides of a mixed donor:acceptor active layer to construct the hybrid heterojunction, respectively. The tailored structure with the donor near the anode and the acceptor near the cathode is beneficial for obtaining enhanced charge transport, extraction, and suppressed charge recombination. As a result, the photovoltaic characterizations suggest a reduced nonradiative Eloss by 25 meV, and the best OSC records a high efficiency of 18.5% (certified as 18.2%). This study highlights that precisely regulating the structure of donor:acceptor heterojunction has the potential to further improve the efficiencies of OSCs.
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