Low Li⁺ Insertion Barrier Carbon for High Energy Efficient Lithium-Ion Capacitor

Lithium-ion capacitor (LIC) is an attractive energy-storage device (ESD) that promises high energy density at moderate power density. However, the key challenge in its design is the low energy efficient negative electrode, which barred the realization of such research system in fulfilling the current ESD technological inadequacy due to its poor overall energy efficiency. Large voltage hysteresis is the main issue behind high energy density alloying/conversion-type materials, which reduces the electrode energy efficiency. Insertion-type material though averted in most research due to the low capacity remains to be highly favorable in commercial application due to its lower voltage hysteresis. To further reduce voltage hysteresis and increase capacity, amorphous carbon with wider interlayer spacing has been demonstrated in the simulation result to significantly reduce Li⁺ insertion barrier. Hence, by employing such amorphous carbon, together with disordered carbon positive electrode, a high energy efficient LIC with round-trip energy efficiency of 84.3% with a maximum energy density of 133 Wh kg^–1 at low power density of 210 W kg^–1 can be achieved

Optimizing Electrolyte Physiochemical Properties toward 2.8 V Aqueous Supercapacitor

Achieving a wide potential window of aqueous supercapacitor has been one of the key research interests to address its poor energy density. However, in this process, water decomposition becomes an increasingly significant issue that has to be tackled in order to attain a reliable aqueous supercapacitor. In order to avoid possible water decomposition at a wide potential, benign interaction between electrolyte and electrode during the cell operation has to be considered. In this work, a water-in-bisalt electrolyte consisting of 21 M lithium bis­(trifluoromethane)­sulfonamide and 1 M lithium sulfate was proposed. To complement the electrolyte, Li⁺ inserted MnO₂ and carbon were selected as electrode materials due to their low oxygen evolution reaction/hydrogen evolution reaction activities. The resultant aqueous supercapacitor was able to operate at 2.8 V which, to the best of our knowledge, is one of the widest potential windows reported for an aqueous supercapacitor system. The cell was able to deliver an energy density of 55.7 Wh kg^–1 at power density of 1 kW kg^–1, while attaining a good cyclic stability of 84.6% retention after 10000 cycles at a current density of 30 A g^–1. Such a strategy may be effective in the design of wide potential aqueous supercapacitors, which is crucial toward future supercapacitor development

Computational Design of Perovskite Ba_<i>x</i>Sr_1–<i>x</i>SnO₃ Alloys as Transparent Conductors and Photocatalysts

Using a first-principles-based multiscale computational approach involving density functional theory and the cluster expansion method, we produced the structural evolution for the perovskite Ba_<i>x</i>Sr_1–<i>x</i>SnO₃ system in relation to its Ba:Sr composition from the formation energies of different alloy configurations and demonstrated their use as tunable alloy transparent conductors and photocatalysts via structural, electronic, and optical studies. The predicted phase diagram revealed the transformation of the structure of Ba_<i>x</i>Sr_1–<i>x</i>SnO₃ from orthorhombic to tetragonal and finally to cubic with increasing <i>x</i>, forming disordered solid solutions for 0 < <i>x</i> < 1 that is entropically stabilized against phase segregation. This trend is similarly observed in the published experiments. A special quasirandom structure approach is used to model the disordered solid solutions of the Ba_<i>x</i>Sr_1–<i>x</i>SnO₃ alloys. Structural analyses have indicated that the decrease in Ba:Sr ratio is associated with the decrease in unit cell volume, and also the increased distortion of the (Ba,Sr)­O₁₂ cuboctahedra, while the SnO₆ octahedra remained relatively undistorted and underwent tilting to accommodate the smaller Sr atoms. Electronic and optical studies have shown the Ba_<i>x</i>Sr_1–<i>x</i>SnO₃ alloys to possess transparent conducting, photocatalytic water splitting and CO₂-reduction capabilities, which can be tailored via compositional engineering. The results should serve as a guide for the investigations of structure–property relationships of perovskite-based alloys

Ruthenium–Tungsten Composite Catalyst for the Efficient and Contamination-Resistant Electrochemical Evolution of Hydrogen

A new catalyst, prepared by a simple physical mixing of ruthenium (Ru) and tungsten (W) powders, has been discovered to interact synergistically to enhance the electrochemical hydrogen evolution reaction (HER). In an aqueous 0.5 M H₂SO₄ electrolyte, this catalyst, which contained a miniscule loading of 2–5 nm sized Ru nanoparticles (5.6 μg Ru per cm² of geometric surface area of the working electrode), required an overpotential of only 85 mV to drive 10 mA/cm² of H₂ evolution. Interestingly, our catalyst also exhibited good immunity against deactivation during HER from ionic contaminants, such as Cu²⁺ (over 24 h). We unravel the mechanism of synergy between W and Ru for catalyzing H₂ evolution using Cu underpotential deposition, photoelectron spectroscopy, and density functional theory (DFT) calculations. We found a decrease in the d-band and an increase in the electron work function of Ru in the mixed composite, which made it bind to H more weakly (more Pt-like). The H-adsorption energy on Ru deposited on W was found, by DFT, to be very close to that of Pt(111), explaining the improved HER activity