Li‐based batteries are a hot research topic because they are the most popular energy storage system for high energy‐density devices. As an important component of the battery, the current collectors ...in both cathode and anode should be well designed. Herein, the design of 3D current collectors for Li‐based batteries is considered, including 3D metal‐based and carbon‐based current collectors. The progress in nanotechnology provides appropriate 3D current collectors characterized by highly efficient morphologies and architectures. In particular, 3D current collectors with different morphology are classified. Critical factors of current collectors that affect the electrochemical performance of Li‐based batteries are comprehensively debated. Finally, conclusion and perspectives of the future research in this field are discussed.
Building up a three‐dimensional current collector can simultaneously optimize the conductive network in the electrochemically active layers and mitigate the volume change during cycling, which leads to enhanced energy density, power density, and cycle stability. Inspiration for further exploitation of the current collectors for Li‐based batteries is given and batteries based on other electrochemistry are considered.
Metal‐free elemental photocatalysts for hydrogen (H2) evolution are more advantageous than the traditional metal‐based inorganic photocatalysts since the nonmetal elements are generally cheaper, more ...earth‐abundant, and environmentally friendly. Black phosphorus (BP) has been attracting increasing attention in recent years based on its anisotropic 2D layered structure with tunable bandgap in the range of 0.3–2.0 eV; however, the application of BP for photocatalytic H2 evolution has been scarcely reported experimentally although being theoretically predicted. Herein, for the first time, the visible light photocatalytic H2 evolution of BP nanosheets prepared via a facile solid‐state mechanochemical method by ball‐milling bulk BP is reported. Without using any noble metal cocatalyst, the visible light photocatalytic hydrogen evolution rate of BP nanosheets reaches 512 µmol h−1 g−1, which is ≈18 times higher than that of the bulk BP, and is comparable or even higher than that of graphitic carbon nitrides (g‐C3N4).
Black phosphorus (BP) is discovered as the missing metal‐free elemental photocatalyst. Few‐layer BP nanosheets are prepared via a facile solid‐state mechanochemical method, exhibiting a visible light H2 evolution rate of 512 µmol h−1 g−1 without using any noble metal cocatalyst, which is increased by ≈18 times relative to that of bulk BP. Thus the missing photocatalytic property of BP is discovered.
Exfoliated black phosphorus (BP), as a monolayer or few-layer material, has attracted tremendous attention owing to its unique physical properties for applications ranging from optoelectronics to ...photocatalytic hydrogen production. Approaching intrinsic properties has been, however, challenged by chemical reactions and structure degradation of BP under ambient conditions. Surface passivation by capping agents has been proposed to extend the processing time window, yet contamination or structure damage rise challenges for BP applications. Here, we report experiments combined with first-principle calculations that address the degradation chemistry of BP. Our results show that BP reacts with oxygen in water even without light illumination. The reaction follows a pseudo-first-order parallel reaction kinetics, produces PO2 3–, PO3 3–, and PO4 3– with reaction rate constants of 0.019, 0.034, and 0.023 per day, respectively, and occurs preferentially from the P atoms locating at BP edges, which yields structural decay from the nanoflake edges in water. In addition, a negligible decay ratio (0.9 ± 0.3 mol %) and preserved photocatalytic activity of BP are observed after storage in deoxygenated water for 15 days without surface passivation under ambient light. Our results reveal the chemistry of BP degradation and provide a practical approach for exfoliation, delivery, and application of BP.
A novel carbon‐nanotube–graphene hybrid nanostructure is developed using an aerosol‐assisted assembly approach. After doping with nitrogen and phosphorus, the prepared hybrid nanomaterials exhibit ...excellent electrocatalytic performance for oxygen reduction in both alkaline and acidic media. This research presents a continuous and low‐cost route to prepare high‐performance metal‐free electrocatalysts while replacing Pt‐based materials.
Lithium metal batteries are vital devices for high-energy-density energy storage, but the Li metal anode is highly reactive with electrolyte and forms uncontrolled dendrite that can cause undesirable ...parasitic reactions and, thus, poor cycling stability and raise safety concerns. Despite remarkable progress to partially solve these issues, the Li metal still plates at the electrode/electrolyte interface where the parasitic reactions and dendrite formation invariably occur. Here, we demonstrate the inward-growth plating of Li atoms into a metal foil of thickness of tens of micrometers while avoiding surface deposition, which is driven by the reversible solid–solution-based alloy phase change. Lithiation of the solid–solution alloy phase allows the freshly generated Li atoms at the surface to sink into the metal foil, while the reversible alloy phase change is companied by the dealloying reaction during delithiation, which extracts Li atoms from inside of the metal foil. The yielded dendrite free Li anode produces an enhanced Coulombic efficiency of 99.5 ± 0.2% with a reversible capacity of 1660 mA h g–1 (3.3 mA h cm–2).
To develop an efficient material for the cathode of the lithium–oxygen (Li–O2) secondary battery, the oxygen reduction and evolution reactions (ORR and OER) on a well-defined graphene electrode have ...been investigated in a typical organic solvent, dimethyl sulfoxide (DMSO). The adsorption and desorption behaviors of the solvents on the graphene electrode surface were evaluated by an intrinsically surface-selective vibrational spectroscopy of sum frequency generation (SFG) during the ORR and OER. After the initial ORR depositing lithium peroxide (Li2O2) on the graphene electrode surface in a LiClO4/DMSO solution, the SFG spectroscopy revealed that the subsequent OER oxidizing the Li2O2 preferentially proceeds at the interface between the Li2O2 and graphene rather than that between the Li2O2 and bulk solution. Therefore, the OER tends to reduce the electric conductivity between the Li2O2 and graphene by decreasing their contact area before a large part of the deposited Li2O2 was oxidized, which elucidates the origin of the high overpotential for the OER.
At a very low solid concentration of 0.45±0.09 vol %, the room-temperature thermal conductivity (κGF) of freestanding graphene-based foams (GF), comprised of few-layer graphene (FLG) and ultrathin ...graphite (UG) synthesized through the use of methane chemical vapor deposition on reticulated nickel foams, was increased from 0.26 to 1.7 W m–1 K–1 after the etchant for the sacrificial nickel support was changed from an aggressive hydrochloric acid solution to a slow ammonium persulfate etchant. In addition, κGF showed a quadratic dependence on temperature between 11 and 75 K and peaked at about 150 K, where the solid thermal conductivity (κG) of the FLG and UG constituents reached about 1600 W m–1 K–1, revealing the benefit of eliminating internal contact thermal resistance in the continuous GF structure.
Nanoporous nickel hydroxide (Ni(OH)2) thin film was grown on the surface of ultrathin-graphite foam (UGF) via a hydrothermal reaction. The resulting free-standing Ni(OH)2/UGF composite was used as ...the electrode in a supercapacitor without the need for addition of either binder or metal-based current collector. The highly conductive 3D UGF network facilitates electron transport and the porous Ni(OH)2 thin film structure shortens ion diffusion paths and facilitates the rapid migration of electrolyte ions. An asymmetric supercapacitor was also made and studied with Ni(OH)2/UGF as the positive electrode and activated microwave exfoliated graphite oxide (‘a-MEGO’) as the negative electrode. The highest power density of the fully packaged asymmetric cell (44.0 kW/kg) was much higher (2–27 times higher), while the energy density was comparable to or higher, than high-end commercially available supercapacitors. This asymmetric supercapacitor had a capacitance retention of 63.2% after 10 000 cycles.
Lithium metal is an attractive anode material for rechargeable batteries because of its high theoretical specific capacity of 3860 mA h g−1 and the lowest negative electrochemical potential of −3.040 ...V versus standard hydrogen electrode. Despite extensive research efforts on tackling the safety concern raised by Li dendrites, inhibited Li dendrite growth is accompanied with decreased areal capacity and Li utilization, which are still lower than expectation for practical use. A scaffold made of covalently connected graphite microtubes is reported, which provides a firm and conductive framework with moderate specific surface area to accommodate Li metal for anodes of Li batteries. The anode presents an areal capacity of 10 mA h cm−2 (practical gravimetric capacity of 913 mA h g−1) at a current density of 10 mA cm−2, with Li utilization of 91%, Coulombic efficiencies of ≈97%, and long lifespan of up to 3000 h. The analysis of structure evolution during charge/discharge shows inhibited lithium dendrite growth and a reversible electrode volume change of ≈9%. It is suggested that an optimized microstructure with moderate electrode/electrolyte interface area is critical to accommodate volume change and inhibit the risks of irreversible Li consumption by side reactions and Li dendrite growth for high‐performance Li‐metal anodes.
A scaffold made of covalently connected graphite microtubes provides a firm and conductive framework with moderate specific surface area to accommodate Li metal, yielding an anode for Li batteries capable of delivering an areal capacity of 10 mA h cm−2 at a current density of 10 mA cm−2, with Coulombic efficiencies of ≈97%, Li utilization of 91%, and long lifespan of up to 3000 h.
A properly strained graphene monolayer or bilayer is expected to harbour periodic pseudo-magnetic fields with high symmetry, yet to date, a convincing demonstration of such pseudo-magnetic fields has ...been lacking, especially for bilayer graphene. Here, we report a definitive experimental proof for the existence of large-area, periodic pseudo-magnetic fields, as manifested by vortex lattices in commensurability with the moiré patterns of low-angle twisted bilayer graphene. The pseudo-magnetic fields are strong enough to confine the massive Dirac electrons into circularly localized pseudo-Landau levels, as observed by scanning tunneling microscopy/spectroscopy, and also corroborated by tight-binding calculations. We further demonstrate that the geometry, amplitude, and periodicity of the pseudo-magnetic fields can be fine-tuned by both the rotation angle and heterostrain. Collectively, the present study substantially enriches twisted bilayer graphene as a powerful enabling platform for exploration of new and exotic physical phenomena, including quantum valley Hall effects and quantum anomalous Hall effects.
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