Ampere-hour-scale soft-package potassium-ion hybrid capacitors enabling 6-minute fast-charging

Extreme fast charging of Ampere-hour (Ah)-scale electrochemical energy storage devices targeting charging times of less than 10 minutes are desired to increase widespread adoption. However, this metric is difficult to achieve in conventional Li-ion batteries due to their inherent reaction mechanism and safety hazards at high current densities. In this work, we report 1 Ah soft-package potassium-ion hybrid supercapacitors (PIHCs), which combine the merits of high-energy density of battery-type negative electrodes and high-power density of capacitor-type positive electrodes. The PIHC consists of a defect-rich, high specific surface area N-doped carbon nanotube-based positive electrode, MnO quantum dots inlaid spacing-expanded carbon nanotube-based negative electrode, carbonate-based non-aqueous electrolyte, and a binder- and current collector-free cell design. Through the optimization of the cell configuration, electrodes, and electrolyte, the full cells (1 Ah) exhibit a cell voltage up to 4.8 V, high full-cell level specific energy of 140 Wh kg-1 (based on the whole mass of device) with a full charge of 6 minutes. An 88% capacity retention after 200 cycles at 10 C (10 A) and a voltage retention of 99% at 25 ± 1 °C are also demonstrated

Synthesis, characterization and sintering of Si-C-N nano-powders via sodium reduction in liquid ammonia

Si-C-N-nano-powders with tunable carbon content were synthesized through the reduction of silicon tetrachloride (SiCl4) and trichloromethylsilane (SiCl3CH3) solution by sodium in liquid ammonia. The nano-powders contain two domains of structure, Si-C-N amorphous or continuous random networks (CRNs), and free carbon. The carbon content in Si3+nCnN4 CRNs, is tunable from n = 0 to n = 1. Free carbon will appeared with the increase of the C/Si mole ratio when C/Si is higher than 1/4. The crystallization of amorphous Si-C-N powders occurs at temperatures ranging from 1300 degrees C to 1500 degrees C depending on the carbon content. The additive-free dense Si-C-N ceramics with relatively low porosity were fabricated by Spark Plasma Sintering (SPS)

Enhanced electrodeposition and separation of metallic Cr from soluble K2CrO4 on a liquid Zn cathode

Carbon contamination and the formation of low-valence oxides limit the preparation of refractory metals by molten salt electrolysis. In this paper, a liquid Zn cathode is adopted for the electrochemical reduction of soluble K2CrO4 to metallic Cr in CaCl2-KCl molten salt. It is found that CrO42- can be directly electrochemically reduced to Cr via a six-electron-transfer step and low-valence Cr oxides is hardly produced. The reduction rate is obviously increased from 16.7 mg(Cr) h(-1) cm(-2) on the solid Mo cathode to 58.7 mg(Cr) h(-1) cm(-2) on liquid Zn cathode. The electrodeposited Cr is distributed in liquid Zn cathode. Carbon contamination is effectively avoided due to the negligible solubility of carbon in the liquid Zn cathode. Furthermore, Cr can be effectively separated and enriched to the bottom of liquid Zn under super-gravity field, realizing the efficient acquisition of metallic Cr and recycling of liquid Zn. The method herein provides a promising route for the preparation of refractory metals with high-purity by molten salt electrolysis. (C) 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved

Self-Supporting Porous CoP-Based Films with Phase-Separation Structure for Ultrastable Overall Water Electrolysis at Large Current Density

Stable non-noble metal electrocatalysts are of essential importance for industrial water electrolysis. Powdery electrocatalysts loaded on current collectors by binders are often designed, but easily fall off due to strong attack by bubbles at an industrial large current density (>400 mA cm(-2)). A novel strategy is developed to construct a self-supported dual-phase porous Co2P-Co3O4 film for oxygen evolution reaction (OER) and micro-nanoporous Co2P film for hydrogen evolution reaction (HER) based on the electrodeposition of single-phase porous CoP film on gas-liquid-solid interface, phase separation to Co2P-Co, and selective oxidation/etching of the Co phase. The self-supported dual-phase Co2P-Co3O4 catalyst exhibits good electrocatalytic activity for OER. The overpotentials are 265 and 405 mV at 20 and 200 mA cm(-2), respectively. In addition, the self-supported micro-nanoporous Co2P catalyst shows high catalytic activity for HER due to large active area and good wettability. Both dual-phase Co2P-Co3O4 and micro-nanoporous Co2P possess ultrastability, even at a large current density of 500 mA cm(-2) due to the self-supported structure. The cell voltage of water electrolysis using a self-supported Co2P-Co3O4 parallel to Co2P electrolyzer at 500 mA cm(-2) is only about 3.36 +/- 0.01 V, which is much lower than that (4.31 +/- 0.05 V) of the IrO2-Ta2O5 parallel to Pt electrolyzer