V-O Species-Doped Carbon Frameworks Loaded with Ru Nanoparticles as Highly Efficient and CO-Tolerant Catalysts for Alkaline Hydrogen Oxidation.

Efficient and CO-tolerant catalysts for alkaline hydrogen oxidation (HOR) are vital to the commercial application of anion exchange membrane fuel cells (AEMFCs). Herein, a robust Ru-based catalyst (Ru/VOC) with ultrasmall Ru nanoparticles supported on carbon frameworks with atomically dispersed V-O species is prepared elaborately. The catalyst exhibits a remarkable mass activity of 3.44 mA µgPGM, which is 31.3 times that of Ru/C and even 4.7 times higher than that of Pt/C. Moreover, the Ru/VOC anode can achieve a peak power density (PPD) of 1.194 W cm-2, much superior to that of Ru/C anode and even better than that of Pt/C anode. In addition, the catalyst also exhibits superior stability and exceptional CO tolerance. Experimental results and density functional theory (DFT) calculations demonstrate that V-O species are ideal OH- adsorption sites, which allow Ru to release more sites for hydrogen adsorption. Furthermore, the electron transfer from Ru nanoparticles to the carbon substrate regulates the electronic structure of Ru, reducing the hydrogen binding energy (HBE) and the CO adsorption energy on Ru, thus boosting the alkaline HOR performance and CO tolerance of the catalyst. This is the first report that oxophilic single atoms distributed on carbon frameworks serve as OH- adsorption sites for efficient hydrogen oxidation, opening up new guidance for the elaborate design of high-activity catalysts for the alkaline HOR.

Octahedral/Tetrahedral Vacancies in Fe3 O4 as K-Storage Sites: A Case of Anti-Spinel Structure Material Serving as High-Performance Anodes for PIBs.

Potassium-ion batteries (PIBs) have attracted more and more attention as viable alternatives to lithium-ion batteries (LIBs) due to the deficiency and uneven distribution of lithium resources. However, it is shown that potassium storage in some compounds through reaction or intercalation mechanisms cannot effectively improve the capacity and stability of anodes for PIBs. The unique anti-spinel structure of magnetite (Fe3 O4 ) is densely packed with thirty-two O atoms to form a face-centered cubic (fcc) unit cell with tetrahedral/octahedral vacancies in the O-closed packing structure, which can serve as K+ storage sites according to the density functional theory (DFT) calculation results. In this work, carbon-coated Fe3 O4 @C nanoparticles are prepared as high-performance anodes for PIBs, which exhibit high reversible capacity (638 mAh g-1 at 0.05 A g-1 ) and hyper stable cycling performance at ultrahigh current density (150 mAh g-1 after 9000 cycles at 10 A g-1 ). In situ XRD, ex-situ Fe K-edge XAFS, and DFT calculations confirm the storage of K+ in tetrahedral/octahedral vacancies.

Energetic Metal-Organic Frameworks Derived Highly Nitrogen-Doped Porous Carbon for Superior Potassium Storage.

The carbonaceous materials with low cost and high safety have been considered as promising anodes for potassium-ion batteries (PIBs). However, it is still a challenge to design a carbonaceous material with long cycle life and high rate performance due to the poor K+ reaction kinetics. Herein, this article reports a N-doped porous carbon framework (NPCF) with a high nitrogen content of 13.57 at% within high doping level of the pyrrolic N and pyridinic N, which exhibits a high reversible capacity of 327 mA h g-1 over 100 cycles at a current density of 100 mA g-1 , excellent rate capability (144 and 105 mA h g-1 at 10 and 20 A g-1 , respectively) and great cyclability of 258.9 mA h g-1 after 2000 cycles at 1 A g-1 . Such a high rate performance and excellent cycling stability anode material is seldom reported in PIBs. Density functional theory (DFT) calculations reveal that the pyrrolic and pyridinic N-doping are helpful to enhance the K adsorption ability, thereby increasing the specific capacity.

One-Step Construction of V5S8 Nanoparticles Embedded in Amorphous Carbon Nanorods for High-Capacity and Long-Life Potassium Ion Half/Full Batteries.

Potassium ion batteries (KIBs) have attracted great attention recently as a promising large-scale energy storage system by virtue of the bountiful K resource and low standard hydrogen potential of K+/K. However, their development is hindered by the limited capacity and inferior cycling stability resulting from the large size of K+. Here, a unique vanadium sulfide@carbon nanorod is designed and synthesized for high-performance KIBs. Thanks to the hybrid structure, abundant active sites, fast ion diffusion, and capacitive-like electrochemical behavior of the electrode, the anode exhibits a large specific capacity (468 mA h g-1 after 100 cycles at 0.1 A g-1), predominant rate performance (205 mA h g-1 at 5 A g-1), and impressive cycling stability (171 mA h g-1 for 4000 cycles at 3 A g-1). Furthermore, the constructed KIB full cell demonstrates 229 mA h g-1 at 0.5 A g-1 and 86% capacity retention over 300 cycles.

Cage-Confinement Pyrolysis Strategy to Synthesize Hollow Carbon Nanocage-Coated Copper Phosphide for Stable and High-Capacity Potassium-Ion Storage.

Metal phosphides with a high theoretical capacity and low redox potential have been proposed as promising anodes for potassium-ion batteries (PIBs). A reasonable configuration design and introduction of a hollow structure with adequate internal void spaces are effective strategies to overcome the volume expansion of metal phosphides in potassium-ion batteries. Herein, we report a cage-confinement pyrolysis strategy to obtain hollow nanocage-structured nitrogen/phosphorus dual-doped carbon-coated copper phosphide (Cu3P/CuP2@NPC), which exhibits a high initial charge capacity (409 mA h g-1 at 100 mA g-1) and an outstanding cycle performance (100 mA h g-1 after 5000 cycles at 1000 mA g-1) as an anode material for PIBs. The novel hollow nanocage structure could prevent volume expansion during cycling and reduce the electron/ion diffusion distance. Besides, the nitrogen/phosphorus dual-doped carbon-coated layer could promote electronic conductivity. In situ X-ray diffraction (XRD) measurements are conducted to study the potassiation/depotassiation mechanism of Cu3P/CuP2@NPC and reveal the structure stability during the cycle process, which further proves that the design ideas of the conductive carbon layer and the hollow structure with adequate internal void spaces are successful.

Boosting Hydrazine Oxidation Reaction on CoP/Co Mott-Schottky Electrocatalyst through Engineering Active Sites.

The hydrazine oxidation reaction (HzOR), as a substitute for the sluggish oxygen evolution reaction (OER), is identified as a promising powerfrugal strategy for hydrogen production through water splitting. However, the HzOR activity of the present electrocatalysts is unsatisfying because the work potential is much higher than the theoretical value. Herein, we design a typical Mott-Schottky electrocatalyst consisting of CoP/Co nanoparticles for the HzOR, which exhibits remarkable HzOR activity with ultralow potentials of -69 and 177 mV at 10 and 100 mA cm-2, respectively. It stands out in a range of cobalt-based materials and is even comparable to some precious-metal-based materials composed of Pt or Ru. A shown by with structural characterization and density functional theory (DFT) calculations, the interfaces between CoP/Co nanoparticles not only provide the active sites of HzOR but also promote the multistep dehydrogenation reaction of N2H4, thus enhancing the HzOR activity.

Tuning the p-Orbital Electron Structure of s-Block Metal Ca Enables a High-Performance Electrocatalyst for Oxygen Reduction.

Most previous efforts are devoted to developing transition metals as electrocatalysts guided by the d-band center model. The metals of the s-block of the periodic table have so far received little attention in the application of oxygen reduction reactions (ORR). Herein, a carbon catalyst with calcium (Ca) single atom coordinated with N and O is reported, which displays exceptional ORR activities in both acidic condition (E1/2  = 0.77 V, 0.1 m HClO4 ) and alkaline condition (E1/2  = 0.90 V, 0.1 m KOH). The CaN, O/C exhibits remarkable performance in zinc-air battery with a maximum power density of 218 mW cm-2 , superior to a series of catalysts reported so far. X-ray absorption near-edge structure (XANES) characterization confirms the formation of N- and O-atom-coordinated Ca in the carbon matrix. Density functional theory (DFT) calculations reveal that the high catalytic activity of main-group Ca is ascribed to the fact that its p-orbital electron structure is regulated by N and O coordination so that the highest peak (EP ) of the projected density of states (PDOS) for the Ca atom is moved close to the Fermi level, thereby facilitating the adsorption of ORR intermediates and electron transfer.