Designing bifunctional oxygen electrocatalysts with high activity, lasting stability, and low-cost for rechargeable zinc-air batteries (RZABs) is a tough challenge. Herein, an advanced electrocatalyst is prepared by anchoring atomically dispersed Co atoms on N-doped graphene-like hierarchically porous carbon nanosheets (SA-Co-N₄-GCs) and thereby forming Co-N₄-C architecture. Its unique structure with excellent conductivity, large surface area, and three dimensional (3D) interconnected hierarchically porous architecture exposes not only more Co-N₄ active sites to accelerate the kinetics of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), but also provides an efficient charge/mass transport environment to reduce diffusion barrier. Consequently, SA-Co-N₄-GCs exhibits excellent ORR/OER bifunctional activities and durability, surpassing noble-metal catalysts. Liquid RZABs using SA-Co-N₄-GCs cathodes display a high open-circuit voltage of 1.51 V, a remarkable power density of 149.3 mW·cm⁻², as well as excellent stability and rechargeability with faint increase in polarization even at a large depth of charge–discharge cycle with 16 h per cycle over an entire 600 h long-term test. Moreover, flexible quasi-solid-state RZABs with SA-Co-N₄-GCs cathodes also deliver a considerable power density of 124.5 mW·cm⁻², which is even higher than that of liquid batteries using noble-metal catalysts. This work has thrown new insight into development of high-performance and low-cost electrocatalysts for energy conversion and storage.

This paper reports an overpotential-dependent shape evolution of gold nanocrystals (Au NCs) in a choline chloride-urea (ChCl-urea) based deep eutectic solvent (DES). It was found that the growth overpotentials play a key role in tuning the shape of Au NCs. The shape evolution of Au NCs successively from concave rhombic dodecahedra (RD) to concave cubes, octopods, cuboctahedral boxes, and finally, to hollow octahedra (OH) was achieved by carefully controlling the growth overpotentials in the range from –0.50 to –0.95 V (vs. Pt quasi-reference electrode). In addition, the presence of urea was important in the shape evolution of Au NCs. The surface structure of the as-prepared Au NCs was comprehensively characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical studies. It was demonstrated that the electrocatalytic activity of the as-prepared Au NCs for D-glucose electrooxidation was sensitively dependent on their morphologies. The results illustrated that the dehydrogenated glucose adsorbed on concave RD and concave cubic Au NCs was preferentially transformed to gluconolactone at low electrode potentials. Subsequent gluconolactone oxidation occurred favorably on octopods with {111}-truncated arms and hollow OH at high electrode potential. This study opens up a new approach to develop the surface-structurecontrolled growth of Au NCs by combining DES with electrochemical techniques. In addition, it is significant for the tuning of the electrocatalytic properties of NCs.

Sulfur-reduced graphene oxide composite (SGC) materials with uniformly dispersed sulfur on reduced graphene oxide sheets have been prepared by a simple aqueous one-pot synthesis method, in which the formation of the composite is achieved through the simultaneous oxidation of sulfide and reduction of graphene oxide. The synthesis process has been tracked ex situ by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy, which both confirm that the majority of graphene oxide has been reduced during the synthesis reaction. The sulfur contents in the SGC, determined by thermogravimetry and elementary analysis, have been adjusted in the range from 20.9 to 72.5 wt.%. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images reveal that most of the sulfur is uniformly dispersed on the reduced graphene oxide sheets, for which no sulfur in particulate form could be observed. The SGC materials have been tested as the cathode of rechargeable lithium-sulfur (Li-S) batteries, and demonstrated a high reversible capacity and good cycleability. The SGC-63.6%S can deliver a reversible capacity as high as 804 mA·h/g after 80 cycles of charge/discharge at a current density of 312 mA/g (ca. 0.186 C), and 440 mA·h/g after 500 cycles at 1250 mA/g (ca. 0.75 C).