Lithium ion batteries have attracted a lot of attention due to their high energy density, but they have relatively lower power density and poorer cyclic stability compared with supercapacitors. Manganese oxide is a promising electrode material for lithium ion batteries due to its low cost, low toxicity, high theoretical capacity, and wide availability. However, it suffers from serious capacity fading which impedes its commercial application. In this work, aligned carbon nanotubes (ACNTs) were grown directly over Al foil as 3D current collectors and then manganese oxide thin film was coated over ACNTs through a spontaneous reduction of potassium permanganate. The obtained 3D manganese oxide/ ACNT coaxial nanotube arrays on Al foils provide remarkable advantages such as the large surface area of the 3D thin manganese oxide layer, the very low electric resistance of the electrode, excellent lithium ion diffusion in the manganese oxide layer and in the channel between the tubes, and excellent elastic properties to tolerate the large volume changes during charge and discharge. As a result, a remarkable improvement of rate capability and stability of the lithium ion batteries was achieved. The 3D thin film electrodes can deliver a capacity of 308 mA h g À1 at 0.1 C which is identical to the theoretical capacity of 95 mA h g À1 at 20 C and maintain a capacity of 133 mA h g À1 after 100 cycles at 1 C. The continuous growth of a solid electrolyte interface (SEI) layer due to trace amounts of water remaining in the manganese oxide layers has been identified as the main cause of the capacity fading. The stability was improved but the initial capacity decreased with increasing annealing temperature in the inert gas.

Nitrogen-doped graphene is synthesized by one-step electrochemical exfoliation of graphite, which exhibits superior catalytic performances towards the oxygen reduction reaction.

Development of cost-effective electrocatalysts as the alternative to platinum for oxygen reduction reaction (ORR) is of great significance for boosting the applications of green energy devices such as fuel cells and metal-air batteries. Here we report a general approach to synthesize a new type of iron, nitrogen and phosphorus tri-doped hierarchically porous carbon composite derived from biomass. This low-cost composite outperforms most of state-of-the-art ORR catalysts in alkaline electrolyte. Aberration-corrected HAADF-STEM, XPS and XAFS measurements reveal the atomically dispersed Fe-N-P-C complex as dominant active sites for ORR. Combining structure characterization by XAFS results with DFT calculations, a new molecule-like structure is proposed where the associated Fe-O-P bond can significantly lower the stability of strongly adsorbed O* and OH* on the catalytically active sites and thus give rise to enhanced ORR performance. Fe is identified as the main active canter and its ORR activity is clearly correlated to the charge of Fe, which is controlled by the local surrounding structure in the active site. It rationalizes the outperformance of Fe-N-P-C than Fe-N-C, and N-C. The insights reported here open a new avenue for constructing highly efficient molecule-like heterogeneous catalysts in electrochemical energy technologies.

Highly efficient, stable and cost-effective electrocatalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) have been pursued for several decades. Herein, by employing density...