High performance and low-cost electrocatalysts for overall water splitting, i.e., catalyzing hydrogen and oxygen evolution reactions with the same material, are of great importance for large-scale, renewable energy conversion processes. Here, we report an ultrafast (~ 7 ms) synthesis technique for transition metal chalcogenide nanoparticles assisted by high temperature treatment. As a proof of concept, we demonstrate that cobalt sulfide (~ 20 nm in diameter)@ few-layer graphene (~ 2 nm in thickness) core-shell nanoparticles embedded in RGO nanosheets exhibit remarkable bifunctional electrocatalytic activity and stability for overall water splitting, which is comparable to commercial 40 wt.% platinum/carbon (Pt/C) electrocatalysts. After 60 h of continuous operation, 10 mA·cm^-2 water splitting current density can still be achieved at a low potential of ~ 1.77 V without any activity decay, which is among the most active for non-noble material based electrocatalysts. The presented study provides prospects in synthesizing highly efficient bifunctional electrocatalysts for large-scale energy conversion application via a simple yet efficient technique.

Rechargeable Li metal batteries using Li metal anodes have attracted worldwide interest because of their high energy density. The critical barriers limiting their commercial application include uncontrolled dendritic Li growth and the unstable Li–electrolyte interface. Considerable efforts have been directed towards solving these problems, e.g., modifying the electrolyte, creating artificial interfacial layers for the Li metal, and constructing three-dimensional structures for the Li metal. However, stabilizing the Li metal interface remains challenging because of the highly reactive nature of the Li metal. In this study, we utilize a Li-ion conducting hybrid film comprising a garnet-type ion conductor and a poly(ethylene oxide)-based polymer electrolyte as a protective layer to stabilize the Li–electrolyte interface and mitigate the growth of Li dendrites. The hybrid ion-conducting layer can block Li dendrites from proliferating and accommodate Li volume expansion because of its robust mechanical properties. Moreover, the ion-conducting layer allows Li deposition only underneath it, rather than on the surface, functioning as a permanent protective layer to ensure the stability of the Li metal over a long cycling life. The dendrite-inhibiting effect of the ion-conducting protective layer is visually evidenced by in situ microscopy using planar batteries. The protective Li metal anode exhibits excellent cycling stability and low voltage hysteresis (~15 mV at 0.2 mA·cm^–2) for a cycle life as long as 1, 000 h. It also shows a high Coulombic efficiency (~99.5%) in a full cell against a LiFePO₄ cathode, exhibiting promise for application in Li metal batteries. Our results imply that the ion-conducting protective layer markedly improves the metal anode, yielding safe, long-life, and high-energy-density batteries.

Lithium metal is considered the ideal anode material for Li-ion-based batteries because it exhibits the highest specific capacity and lowest redox potential for this type of cells. However, growth of Li dendrites, unstable solid electrolyte interphases, low Coulombic efficiencies, and safety hazards have significantly hindered the practical application of metallic Li anodes. Herein, we propose a three-dimensional (3D) carbon nanotube sponge (CNTS) as a Li deposition host. The high specific surface area of the CNTS enables homogenous charge distribution for Li nucleation and minimizes the effective current density to overcome dendrite growth. An additional conformal Al₂O₃ layer on the CNTS coated by atomic layer deposition (ALD) robustly protects the Li metal electrode/electrolyte interface due to the good chemical stability and high mechanical strength of the layer. The Li@ALD-CNTS electrode exhibits stable voltage profiles with a small overpotential ranging from 16 to 30 mV over 100 h of cycling at 1.0 mA·cm^–2. Moreover, the electrodes display a dendrite-free morphology after cycling and a Coulombic efficiency of 92.4% over 80 cycles at 1.0 mA·cm^–2 in an organic carbonate electrolyte, thus demonstrating electrochemical stability superior to that of planar current collectors. Our results provide an important strategy for the rational design of current collectors to obtain stable Li metal anodes.

Spray-coated carbon nanotube films offer a simple and printable solution for fabricating low cost, lightweight, and flexible thin-film electronics. However, current nanotube spray inks require either a disruptive surfactant or destructive surface functionalization to stabilize dispersions at the cost of the electrical properties of the deposited film. We demonstrate that high-purity few-walled carbon nanotubes may be stabilized in isopropanol after surface functionalization and that optimizing the ink stability dramatically enhances the conductivity of subsequent spray-coated thin films. We consequently report a surfactant-free carbon nanotube ink for spray-coated thin films with conductivities reaching 2, 100 S/cm. Zeta-potential measurements, used to quantify the nanotube ink dispersion quality, directly demonstrate a positive correlation with the spraycoated film conductivity, which is the key metric for high-performance printed electronics.

Contemporary nanostructured transparent electrodes for use in solar cells require high transmittance and high conductivity, dictating nanostructures with high aspect ratios. Optical haze is an equally important yet unstudied parameter in transparent electrodes for solar cells that is also determined by the geometry of the nanostructures that compose the electrode. In this work, the effect of the silver nanowire diameter on the optical haze values in the visible spectrum was investigated using films composed of wires with either small diameters (~60 nm) or large diameters (~150 nm). Finite difference time domain (FDTD) simulations and experimental transmittance data confirm that smaller diameter nanowires form higher performing transparent conducting electrode (TCE) films according to the current figure of merit. While maintaining near constant transmittance and conductivity for each film, however, it was observed experimentally that films composed of silver nanowires with larger diameters have a higher haze factor than films with smaller diameters. This confirms the FDTD simulations of the haze factor for single nanowires with similarly large and small diameters. This is the first record of haze properties for Ag NWs that have been simulated or experimentally measured, and also the first evidence that the current figure of merit for TCEs is insufficient to evaluate their performance in solar cell devices.