Sulfur- and Nitrogen-Doped, Ferrocene-Derived Mesoporous Carbons with Efficient Electrochemical Reduction of Oxygen

Development of inexpensive and sustainable cathode catalysts that can efficiently catalyze the oxygen reduction reaction (ORR) is of significance in practical application of fuel cells. Herein we report the synthesis of sulfur and nitrogen dual-doped, ordered mesoporous carbon (SN-OMCs), which shows outstanding ORR electrocatalytic properties. The material was synthesized from a surface-templating process of ferrocene within the channel walls of SBA-15 mesoporous silica by carbonization, followed by in situ heteroatomic doping with sulfur- and nitrogen-containing vapors. After etching away the metal and silica template, the resulting material features distinctive bimodal mesoporous carbon frameworks with high nitrogen Brunauer–Emmett–Teller specific surface area (of up to ∼1100 m²/g) and uniform distribution of sulfur and nitrogen dopants. When employed as a noble-metal-free electrocatalyst for the ORR, such SN-OMC shows a remarkable electrocatalytic activity; improved durability and better resistance toward methanol crossover in oxygen reduction can be observed. More importantly, it performs a low onset voltage and an efficient nearly complete four-electron ORR process very similar to the observations in commercial 20 wt % Pt/C catalyst. In addition, we also found that the textural mesostructure of the catalyst has superseded the chemically bonded dopants to be the key factor in controlling the ORR performance

In Situ AFM Imaging of Solid Electrolyte Interfaces on HOPG with Ethylene Carbonate and Fluoroethylene Carbonate-Based Electrolytes

Chemical and morphological structure of solid electrolyte interphase (SEI) plays a vital role in lithium-ion battery (LIB), especially for its cyclability and safety. To date, research on SEI is quite limited because of the complexity of SEI and lack of effective in situ characterization techniques. Here, we present real-time views of SEI morphological evolution using electrochemical atomic force microscopy (EC-AFM). Complemented by an ex situ XPS analysis, fundamental differences of SEI formation from ethylene carbonate (EC) and fluoroethylene carbonate (FEC)-based electrolytes during first lithiation/delithiation cycle on HOPG electrode surface were revealed

Acyclic Cucurbit[<i>n</i>]uril Molecular Containers Selectively Solubilize Single-Walled Carbon Nanotubes in Water

Making single-walled carbon nanotubes (SWNTs) soluble in water is a challenging first step to use their remarkable electronic and optical properties in a variety of applications. We report that acyclic cucurbit­[<i>n</i>]­uril molecular containers <b>1</b> and <b>2</b> selectively solubilize small-diameter and low chiral angle SWNTs. The selectivity is tunable by increasing the concentration of the molecular containers or by adjusting the ionic strength of the solution. Even at a concentration 1000 times lower than typically required for surfactants, the molecular containers render SWNTs soluble in water. Molecular mechanics simulations suggest that these C-shaped acyclic molecules complex the SWNTs such that a large portion of nanotube sidewalls are exposed to the external environment. These “naked” nanotubes fluoresce upon patching the exposed surface with sodium dodecylbenzene sulfonate

Li₂O‑Reinforced Cu Nanoclusters as Porous Structure for Dendrite-Free and Long-Lifespan Lithium Metal Anode

A nanostructured protective structure, pillared by the copper nanoclusters and in situ filled with lithium oxide in the interspace, is constructed to efficiently improve the cyclic stability and lifetime of lithium metal electrodes. The porous structure of copper nanoclusters enables high specific surface area, locally reduced current density, and dendrite suppressing, while the filled lithium oxide leads to the structural stability and largely extends the electrode lifespan. As a result of the synergetic protection of the proposed structure, lithium metal could be fully discharged with efficiency ∼97% for more than 150 cycles in corrosive alkyl carbonate electrolytes, without dendrite formation. This approach opens a novel route to improve the cycling stability of lithium metal electrodes with the appropriate protective structure

Effect of LiFSI Concentrations To Form Thickness- and Modulus-Controlled SEI Layers on Lithium Metal Anodes

Improving the cyclic stability of lithium metal anodes is of particular importance for developing high-energy-density batteries. In this work, a remarkable finding shows that the control of lithium bis­(fluorosulfonyl)­imide (LiFSI) concentrations in electrolytes significantly alters the thickness and modulus of the related SEI layers, leading to varied cycling performances of Li metal anodes. In an electrolyte containing 2 M LiFSI, an SEI layer of ∼70 nm that is obviously thicker than those obtained in other concentrations is observed through <i>in situ</i> atomic force microscopy (AFM). In addition to the decomposition of FSI^– anions that generates rigid lithium fluoride (LiF) as an SEI component, the modulus of this thick SEI layer with a high LiF content could be significantly strengthened to 10.7 GPa. Such a huge variation in SEI modulus, much higher than the threshold value of Li dendrite penetration, provides excellent performances of Li metal anodes with Coulombic efficiency higher than 99%. Our approach demonstrates that the FSI^– anions with appropriate concentration can significantly alter the SEI quality, establishing a meaningful guideline for designing electrolyte formulation for stable lithium metal batteries