Improving the cycling stability of LiNi0.8Co0.1Mn0.1O2 by boron doping to inhibit Li/Ni mixing.

Boron doping significantly reduces the Li/Ni cation mixing of LiNi0.8Co0.1Mn0.1O2, decreases the charge transfer resistance, and improves the reversibility of the H2-H3 phase transition at 4.2 V. Among similar materials, the cathode material with 1.0 mol% boron doping shows excellent cycling performance, with capacity retention of 96% after 200 cycles at 50 °C.

"Wane and wax" strategy: Enhanced evolution kinetics of liquid phase Li2S4 to Li2S via mutually embedded CNT sponge/Ni-porous carbon electrocatalysts.

The lithium-sulfur battery (Li-S) has been considered a promising energy storage system, however, in the practical application of Li-S batteries, considerable challenges remain. One challenge is the low kinetics involved in the conversion of Li2S4 to Li2S. Here, we reveal that highly dispersed Ni nanoparticles play a unique role in the reduction of Li2S4. Ni-porous carbon (Ni-PC) decorated in situ on a free-standing carbon nanotube sponge (CNTS/Ni-PC) enriches the current response of liquid phase Li2S4 and Li2S2 around the cathode more than 8.1 and 5.7 times higher than that of the CNTS blank sample, respectively, greatly boosting the kinetics and decreasing the reaction overpotential of Li2S4 reduction (lower Tafel slope and larger current response). Thus, with the same total overpotential, more space is provided for the concentration difference overpotential, allowing the more soluble polysulfide intermediates farther away from the surface of the conductive materials to be reduced based on the "wane and wax" strategy, and significantly improving the sulfur utilization. Consequently, S@CNTS/Ni-PC delivers excellent rate performance (812.4 mAh·g-1 at 2C) and a remarkable areal capacity of 10.1 mAh·cm-2. This work provides a viable strategy for designing a target catalyst to enhance the conversion kinetics in the Li2S4 reduction process.

Electrodeposition of cobalt-iron bimetal phosphide on Ni foam as a bifunctional electrocatalyst for efficient overall water splitting.

To solve environmental pollution and energy crisis, it is essential to design an efficient, economical, and stable bifunctional electrocatalyst for water splitting to produce renewable energy sources H2 and O2. In this study, low-crystallinity and microspherical CoFe-P/NF catalyst synthesized by potentiostat electrodeposition on a foam nickel substrate had an excellent hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and water splitting performance. In 1 M KOH solution, the CoFe-P/NF required the overpotentials of 45 mV for HER and 287 mV for OER in order to create a current density of 10 mA cm-2. Furthermore, the Tafel slope for HER and OER was measured as 35.4 and 43.2 mV dec-1, respectively. Serving as the bifunctional catalysts, the CoFe-P/NF electrode couple displays a low voltage of only 1.58 V at 10 mA cm-2 with an excellent long-term stability. Such remarkably properties of the CoFe-P/NF are attributed to the crystalline-amorphous phase structure, the synergistic effect of Co, Fe and P, and rapid separation of bubbles from the electrode surface. In summary, this study provides a new method for developing cost-effective catalyst towards green hydrogen production via water splitting.

An Integrated Structural Air Electrode Based on Parallel Porous Nitrogen-Doped Carbon Nanotube Arrays for Rechargeable Li-Air Batteries.

The poor discharge and charge capacities, and the cycle performance of current Li-air batteries represent critical obstacles to their practical application. The fabrication of an integrated structural air electrode with stable parallel micropore channels and excellent electrocatalytic activity is an efficient strategy for solving these problems. Herein, a novel approach involving the synthesis of nitrogen-doped carbon nanotube (N-CNT) arrays on a carbon paper substrate with a conductive carbon-black layer for use as the air electrode is presented. This design achieves faster oxygen, lithium ion, and electron transfer, which allows higher oxygen reduction/evolution reaction activities. As a result, the N-CNT arrays (N/C = 1:20) deliver distinctly higher discharge and charge capacities, 2203 and 186 mAh g-1, than those of active carbons with capacities of 497 and 71 mAh g-1 at 0.05 mA cm-2, respectively. A theoretical analysis of the experimental results shows that the parallel micropore channels of the air electrode decrease oxygen diffusion resistance and lithium ion transfer resistance, enhancing the discharge and charge capacities and cycle performance of Li-air batteries. Additionally, the N-CNT arrays with a high pyridinic nitrogen content can decompose the lithium peroxide product and recover the electrode morphology, thereby further improving the discharge-charge performance of Li-air batteries.

An absorption mechanism and polarity-induced viscosity model for CO2 capture using hydroxypyridine-based ionic liquids.

A series of new hydroxypyridine-based ionic liquids (ILs) are synthesized and applied in CO2 capture through chemical absorption, in which one IL, i.e., tetrabutylphosphonium 2-hydroxypyridine ([P4444][2-Op]), shows a viscosity as low as 193 cP with an absorption capacity as high as 1.20 mol CO2 per mol IL. Because the traditional anion-CO2 absorption mechanism cannot provide an explanation for the influences of cations and temperature on CO2 absorption capacity, herein, a novel cation-participating absorption mechanism based on the proton transfer is proposed to explain the high absorption capacity and the existence of a turning point of absorption capacity with the increase of temperature for the capture of CO2 using [P4444][n-Op] (n = 2, 3, 4) ILs. Also, the relationship between the viscosity of ILs and the linear interaction energy is proposed for the first time, which can guide how to design and synthesize ILs with low viscosity. Quantum chemistry calculations, which are based on the comprehensive analysis of dipole moment, cation-anion interaction energy and surface electrostatic potential, indicate that the different viscosities of hydroxypyridine-based ILs and the changes after CO2 absorption mainly resulted from the different distribution of negative charges in the anion.

Nitrogen-doped carbon quantum dots/Ag3PO4 complex photocatalysts with enhanced visible light driven photocatalytic activity and stability.

Novel nitrogen-doped carbon quantum dots/Ag3PO4 (NCQDs/Ag3PO4) complex photocatalysts were synthesized by a facile precipitation method at room temperature. The physical and chemical properties of Ag3PO4 and NCQDs/Ag3PO4 photocatalysts were detected through X-ray powder diffraction, field emission scanning electron microscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and electron spin resonance techniques. The as-prepared 3-NCQDs/Ag3PO4 composite exhibited much higher activity than the pure Ag3PO4 for eliminating methyl orange and bisphenol A solution under visible light (λ>420nm). Moreover, in the cyclic experiments, the 3-NCQDs/Ag3PO4 exhibited an excellent stability for the decolorization of methyl orange at some level. This suggested that NCQDs played an important role in the process of degradation. The function of NCQDs was discussed and a new mechanism was put forward for the degradation of methyl orange. The high activities and stability were attributed to the transfer of photogenerated charges through the vector of Ag3PO4→NCQDs→Ag in the photocatalytic process, leading to effective charge separation of Ag3PO4.