Xiaopeng Han

Enhancing Electrocatalytic Oxygen Reduction on MnO2 with Vacancies

Oxygen-vacant nanocrystalline MnO(2) has been prepared by the simple process of annealing pristine oxide in Ar or O(2) . Both experimental and computational studies indicate that the catalytic activity of MnO(2) towards oxygen reduction is enhanced by introducing a modest concentration of oxygen vacancies.

Cobalt Sulfide Nanosheet/Graphene/Carbon Nanotube Nanocomposites as Flexible Electrodes for Hydrogen Evolution

Flexible three-dimensional (3D) nanoarchitectures have received tremendous interest recently because of their potential applications in wearable electronics, roll-up displays, and other devices. The design and fabrication of a flexible and robust electrode based on cobalt sulfide/reduced graphene oxide/carbon nanotube (CoS2 /RGO-CNT) nanocomposites are reported. An efficient hydrothermal process combined with vacuum filtration was used to synthesize such composite architecture, which was then embedded in a porous CNT network. This conductive and robust film is evaluated as electrocatalyst for the hydrogen evolution reaction. The synergistic effect of CoS2 , graphene, and CNTs leads to unique CoS2 /RGO-CNT nanoarchitectures, the HER activity of which is among the highest for non-noble metal electrocatalysts, showing 10u2005mAu2009cm(-2) current density at about 142u2005mV overpotentials and a high electrochemical stability.

Phase and composition controllable synthesis of cobalt manganese spinel nanoparticles towards efficient oxygen electrocatalysis

Spinel-type oxides are technologically important in many fields, including electronics, magnetism, catalysis and electrochemical energy storage and conversion. Typically, these materials are prepared by conventional ceramic routes that are energy consuming and offer limited control over shape and size. Moreover, for mixed-metal oxide spinels (for example, CoxMn3−xO4), the crystallographic phase sensitively correlates with the metal ratio, posing great challenges to synthesize active product with simultaneously tuned phase and composition. Here we report a general synthesis of ultrasmall cobalt manganese spinels with tailored structural symmetry and composition through facile solution-based oxidation–precipitation and insertion–crystallization process at modest condition. As an example application, the nanocrystalline spinels catalyse the oxygen reduction/evolution reactions, showing phase and composition co-dependent performance. Furthermore, the mild synthetic strategy allows the formation of homogeneous and strongly coupled spinel/carbon nanocomposites, which exhibit comparable activity but superior durability to Pt/C and serve as efficient catalysts to build rechargeable Zn–air and Li–air batteries.

Unique Cobalt Sulfide/Reduced Graphene Oxide Composite as an Anode for Sodium-Ion Batteries with Superior Rate Capability and Long Cycling Stability

Exploitation of high-performance anode materials is essential but challenging to the development of sodium-ion batteries (SIBs). Among all proposed anode materials for SIBs, sulfides have been proved promising candidates due to their unique chemical and physical properties. In this work, a facile solvothermal method to in situ decorate cobalt sulfide (CoS) nanoplates on reduced graphene oxide (rGO) to build CoS@rGO composite is described. When evaluated as anode for SIBs, an impressive high specific capacity (540 mAh g(-1) at 1 A g(-1) ), excellent rate capability (636 mAh g(-1) at 0.1 A g(-1) and 306 mAh g(-1) at 10 A g(-1)), and extraordinarily cycle stability (420 mAh g(-1) at 1 A g(-1) after 1000 cycles) have been demonstrated by CoS@rGO composite for sodium storage. The synergetic effect between the CoS nanoplates and rGO matrix contributes to the enhanced electrochemical performance of the hybrid composite. The results provide a facile approach to fabricate promising anode materials for high-performance SIBs.

Hydrogenated Uniform Pt Clusters Supported on Porous CaMnO3 as a Bifunctional Electrocatalyst for Enhanced Oxygen Reduction and Evolution

Hydrogenated uniform Pt clusters supported on porous CaMnO3 nanocomposites are synthesized and investigated as a new electrocatalytic material for oxygen reduction and evolution reactions. Due to the synergistic effect of Pt and CaMnO3, the nanocomposites exhibit superior activity and durability to the benchmark Pt/C catalyst.

Porous calcium–manganese oxide microspheres for electrocatalytic oxygen reduction with high activity

A series of calcium–manganese oxides (Ca–Mn–O) were prepared through thermal decomposition of carbonate solid–solution precursors and investigated as electrocatalysts for oxygen reduction reaction (ORR). The synthesized crystalline Ca–Mn–O compounds, including perovskite-type CaMnO3, layered structured Ca2Mn3O8, post-spinel CaMn2O4 and CaMn3O6, presented similar morphologies of porous microspheres with agglomerated nanoparticles. Electrochemical results, surface analysis, and computational studies revealed that the catalytic activities of Ca–Mn–O oxides, in terms of onset potential, reduction current, and transferred electron number, depended strongly on both the surface Mn oxidation state and the crystallographic structures. Remarkably, the as-synthesized CaMnO3 and CaMn3O6 exhibited considerable activity and enabled an apparent quasi 4-electron oxygen reduction with low yield of peroxide species in alkaline solutions, suggesting their potential applications as cheap and abundant ORR catalysts.

Spherical nano-Sb@C composite as a high-rate and ultra-stable anode material for sodium-ion batteries

An aerosol spray pyrolysis technique is used to synthesize a spherical nano-Sb@C composite. Instrumental analyses reveal that the micro-nanostructured composite with an optimized Sb content of 68.8 wt% is composed of ultra-small Sb nanoparticles (10 nm) uniformly embedded within a spherical porous C matrix (denoted as 10-Sb@C). The content and size of Sb can be controlled by altering the concentration of the precursor. As an anode material of sodium-ion batteries, 10-Sb@C provides a discharge capacity of 435 mAh·g–1 in the second cycle and 385 mAh·g–1 (a capacity retention of 88.5%) after 500 cycles at 100 mAh·g–1. In particular, the electrode exhibits an excellent rate capability (355, 324, and 270 mAh·g–1 at 1,000, 2,000, and 4,000 mA·g–1, respectively). Such a high-rate performance for the Sb-C anode has rarely been reported. The remarkable electrochemical behavior of 10-Sb@C is attributed to the synergetic effects of ultra-small Sb nanoparticles with an uniform distribution and a porous C framework, which can effectively alleviate the stress associated with a large volume change and suppress the agglomeration of the pulverized nanoparticles during prolonged charge-discharge cycling.

ε-MnO2 nanostructures directly grown on Ni foam: a cathode catalyst for rechargeable Li–O2 batteries

A sponge-like ε-MnO2 nanostructure was synthesized by direct growth of ε-MnO2 on Ni foam through a facile electrodeposition route. When applied as a self-supporting, binder-free cathode material for rechargeable nonaqueous lithium-oxygen batteries, the ε-MnO2/Ni electrode exhibits considerable high-rate capability (discharge capacity of ∼6300 mA h g(-1) at a current density of 500 mA g(-1)) and enhanced cyclability (exceeding 120 cycles) without controlling the discharge depth. The superior performance is proposed to be associated with the 3D nanoporous structures and abundant oxygen defects as well as the absence of side reactions related to carbon-based conductive additives and binders.

Spinel LiNi0.5Mn1.5O4 cathode for rechargeable lithiumion batteries: Nano vs micro, ordered phase (P4332) vs disordered phase (Fd\(\bar 3\)m)

Since the high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is one of the most attractive cathode materials for lithium-ion batteries, how to improve the cycling and rate performance simultaneously has become a critical question. Nanosizing is a typical strategy to achieve high rate capability due to drastically shortened Li-ion diffusion distances. However, the high surface area of nanosized particles increases the side reaction with the electrolyte, which leads to poor cycling performance. Spinels with disordered structures could also lead to improved rate capability, but the cyclability is low due to the presence of Mn3+ ions. Herein, we systematically investigated the synergic interaction between particle size and cation ordering. Our results indicated that a microsized disordered phase and a nanosized ordered phase of LNMO materials exhibited the best combination of high rate capability and cycling performance.

Oxygen Bubble-Templated Hierarchical Porous ε-MnO2 as a Superior Catalyst for Rechargeable Li–O2 Batteries

Nickel foam-supported ε-MnO2 is synthesized through an oxygen-bubble template-assisted electrodeposition route and is applied as a new cathode catalyst for Li-O2 batteries. Owing to the 3D macro/micro/nano (multiscale) porous architecture, the prepared electrode exhibits low overpotential, high rate capability, and superior cycling durability.