Silicon is a promising anode material for lithium‐ion batteries because of its high gravimetric/volumetric capacities and low lithiation/delithiation voltages. However, it suffers from poor cycling stability due to drastic volume expansion (>300%) when it alloys with lithium, leading to structural disintegration upon lithium removal. Here, it is demonstrated that titanium atoms inside the silicon matrix can act as an atomic binding agent to hold the silicon atoms together during lithiation and mend the structure after delithiation. Direct evidence from in situ dilatometry of cosputtered silicon–titanium thin films reveals significantly smaller electrode thickness change during lithiation, compared to a pure silicon thin film. In addition, the thickness change is fully reversible with lithium extraction, and ex situ post‐mortem microscopy shows that film cracking is suppressed. Furthermore, Raman spectroscopy measurements indicate that the Si–Ti interaction remains intact after cycling. Optimized Si–Ti thin films can deliver a stable capacity of 1000 mAh g−1 at a current of 2000 mA g−1 for more than 300 cycles, demonstrating the effectiveness of titanium in stabilizing the material structure. A full cell with a Si–Ti anode and LiFePO4 cathode is demonstrated, which further validates the readiness of the technology.
COMMUNICATION (1 of 8)composed of Co, Ni, and Fe have recently shown potentials with excellent catalytic properties, and great structural stabilities toward electrocatalytic OER and HER. [9][10][11][12][13] Active site availability and electronic conductivity are the key factors for electrocatalysts, which are determined by the surface species, morphology, and composition. Thus, tremendous effort has been put into the rational design of Co-, Ni-, and Fe-based catalysts and material interface to promote the reaction kinetics and improve the catalytic efficiency. [14,15] Recently, metal-organic frameworks (MOFs) have attracted great attention due to their flexible, porous structures, and tunable properties. [16,17] Direct exposure of metal nodes in the porous bulk structure to reaction environments makes MOFs a suitable catalyst candidate. Studies show that MOFs possess excellent electrocatalytic activities with high stability against chemical corrosion and bubbles' attack. [17][18][19][20][21] In addition, MOFs can serve as a template of porous carbon-metal structures with good structural stability. [22][23][24][25][26][27] Nevertheless, most MOF-based electrocatalysts show limited efficiencies due to low mass permeability and poor electrical conductivity. In a bulk MOF, the majority of active sites are located inside pores or channels, where the organic linkers may interfere and thus limit the accessibility. [28,29] To circumvent such shortcomings, thin 2D MOFs have been suggested to achieve much larger specific surface area with more active metal sites directly exposed to electrolytes. [30][31][32][33][34][35][36][37][38] Zhao et al. [31] reported that the unsaturated metal atoms on the ultrathin MOF surface could serve as the dominating active centers for OER. They also pointed out that the coupling between metal nodes significantly alters the catalytic activity. More recently, 2D MOFs were prepared by a dissolution-crystallization mechanism on the substrates [30] or selective removal of pillar organics from a 3D pillared-layer MOF. [38] Despite the huge potential, the synthesis of catalytically active 2D MOF with precise control of structure is still challenging, and the real active surface information remain unclear. Thus, the structure-activity relationships among morphology, electronic configuration, and catalytic performance of 2D MOFs still need more explorations.In this work, we report 2D CoNi bimetallic organic frameworks (CoNi-MOFs) directly grown as nanoplate array on a copper foil under hydrothermal conditions. Such CoNi-MOFs (Co:Ni = 1:1) demonstrate highly active OER catalysis, as manifested by a small overpotential of 265 mV at 10 mA cm −2 and Efficient electrocatalysts composed of non-precious elements are central to the development of overall water-splitting system. Herein, it is demonstrated that 2D CoNi-metal-organic framework (CoNi-MOF) array grown directly on a Cu substrate is a highly efficient and stable electrocatalyst for oxygen evolution reaction with a low overpotential (265 mV at 10 m...
Limitations of capacitive deionization (CDI) and future commercialization efforts are intrinsically bound to electrode stability. In this work, thermal treatments are explored to understand their ability to regenerate aged CDI electrodes. We demonstrate that a relatively low thermal treatment temperature of ∼500 °C can sufficiently recover the lost salt adsorption capacity of degraded electrodes. Furthermore, a systematic study of electrode replacement clarifies that the desalination ability loss and regeneration for a CDI cell are isolated to the aged anode, as expected. Characterizations of surface functionalities support that the acidic oxygen-containing functional groups formed in situ during cycling undergo thermal decomposition during treatment. The modified Donnan model quantitatively confirms that the surface charges originate from the formation/decomposition of functional groups. Accordingly, the lost pore volume and the increased resistance are recovered during thermal treatments, while the surface morphologies and pore structure of the electrodes are well-preserved. Therefore, thermal treatment can be applied practically to extend the lifetime of aged electrodes. This study also offers insights into strategies for minimizing electrode degradation or in situ regeneration such that the technology gains momentum for future commercialization.
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