Shiji Hao

Phase transition of hollow-porous α-Fe2O3 microsphere based anodes for lithium ion batteries during high rate cycling

In the present paper, hollow-porous α-Fe2O3 microspheres are prepared via cation etching of zinc citrate microspheres and subsequent thermal treatment. The superior performance of the as-obtained α-Fe2O3 microspheres as an anode material for lithium ion batteries is evaluated. After 1000 cycles, the capacity still remains more than 1100 mA h g−1 at a current rate of 1 A g−1. Meanwhile, the crystal size induced phase transition of Fe2O3 microspheres (α → γ → β) is observed during cycling by the measurements of ex situ XRD and TEM, which is responsible for their abnormal performance fluctuation.

Nanoscale ion intermixing induced activation of Fe2O3/MnO2 composites for application in lithium ion batteries

Herein, we demonstrate a facile method to prepare hollow-structured oxygen-vacancy-rich Fe2O3/MnO2 nanorods. Our results show that oxygen vacancies are induced by nanoscale ion intermixing between Fe and Mn ions during the annealing process. Owing to their unique core–shell hollow nanostructure and the presence of oxygen vacancies, the Fe2O3/MnO2 nanorods show excellent electrochemical performances as an anode material for lithium ion batteries and a reversible capacity higher than 700 mA h g−1 after 2000 cycles.

Evidence of a nanosized copper anodic reaction in an anaerobic sulfide aqueous solution

The present paper reports the use of TEM to investigate the electrochemical behavior of a copper subject to the both free corrosion and polarization in a 0.1 M NaCl + 5 × 10−4 M Na2S aqueous solution at the nano scale. The pure copper is found to be transformed into nano-crystalline Cu2S in the thin region of the copper needle in the solution at open circuit conditions. However, a rough Cu2S layer is formed in the active region of electrochemical polarization, which is then converted to the passive CuS layer with a uniform thickness at higher potentials. Upon the continuous increase of an applied potential, cubic CuS particles with sizes of ∼100 nm are precipitated on the needle surface due to the breakdown of the passive layer. Meanwhile, the growth of a large amount of nanosized CuCl particles is also found, indicating that Cl− ions participate in the electrochemical reaction in the transpassive region. It is worth noting that the present work also provides a simple and cost-effective way for the synthesis of copper sulfides (Cu2S and CuS) through electrochemical processes.

The Electrochemical Response of Single Crystalline Copper Nanowires to Atmospheric Air and Aqueous Solution

In this paper, single crystalline copper nanowires (CuNWs) have been electrochemically grown through anodic aluminum oxide template. The environmental stability of the as-obtained CuNWs in both 40% relative humidity (RH) atmosphere and 0.1 m NaOH aqueous solution has been subsequently studied. In 40% RH atmosphere, a uniform compact Cu2 O layer is formed as a function of exposure time following the logarithmic law and epitaxially covers the CuNW surfaces. It is also found that the oxide layers on CuNWs are sequentially grown when subjected to the cyclic voltammetry measurement in 0.1 m NaOH solution. An epitaxially homogeneous Cu2 O layer is initially formed over the surface of the CuNW substrates by solid-state reaction (SSR). Subsequently, the conversion of Cu2 O into epitaxial CuO based on the SSR takes place with the increase of applied potential. This CuO layer is partially dissolved in the solution forming Cu(OH)2 , which then redeposited on the CuNW surfaces (i.e., dissolution-redeposition (DR) process) giving rise to a mixed polycrystalline CuO/Cu(OH)2 layer. The further increase of applied potential allows the complete oxidation of Cu2 O into CuO to form a dual-layer structure (i.e., CuO inner layer and Cu(OH)2 outer layer) with random orientations through an enhanced DR process.

Electrochemical behaviors of hierarchical copper nano-dendrites in alkaline media

In this study, hierarchical copper nano-dendrites (CuNDs) are fabricated via the electrodeposition method. The electrochemical behaviors of the as-obtained hierarchical CuNDs in 0.1 M NaOH aqueous solution are subsequently studied. The CuNDs experience a non-equilibrium oxidation process when subjected to cyclic voltammetry (CV) measurements. The first oxidation peak O1 in CV is attributed to the formation of an epitaxial Cu2O layer over the surface of the hierarchical CuNDs. However, the second oxidation peak O2 in CV appears unusually broad across a wide potential range. In this region, the reaction process starts with the nucleation and growth of Cu(OH)2 nanoneedles, followed by the oxidation of Cu2O. Upon the increase of potential, Cu2O is gradually transformed to CuO and Cu(OH)2, forming a dual-layer structure with high productivity of Cu(OH)2 nanoneedles.

Nanostructured CuO/C Hollow Shell@3D Copper Dendrites as a Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

Adoption of bare metal oxides as catalytic materials shows inferior electrochemical activity because of their poor electrical conductivity. Although synthetic strategies for the employment of conductive substrates are well-established, the rational design and fabrication of hollow metal oxides nanostructures on the robust matrix with a high surface area and conductivity remains challenging. In the present research work, a strategy that transforms a metal-organic framework thin layer into a nanostructured CuO/C hollow shell to coat on the 3D nano-dendritic Cu foams as an electrode was successfully developed. This electrode is claimed to provide an extraordinary electrocatalysis for oxygen evolution reaction (OER) in alkaline media. The hierarchical complex presents fast electronic transmission networks and rich redox sites, leading to the significant enhancement in electrocatalytic OER efficiency. Furthermore, the spherical porous structure and robust architecture facilitate the high-speed diffusion of O2 bubbles in a long-term operation. The results of this study may serve as a reference for the designing of novel class 3D metal/metal oxide hierarchical structures for gas-involved (i.e., O2, H2, and CO2) electrocatalytic applications and beyond.