Ru Chen

Defect Chemistry of Nonprecious‐Metal Electrocatalysts for Oxygen Reactions

Oxygen electrocatalysis, including the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER), is a critical process for metal-air batteries. Therefore, the development of electrocatalysts for the OER and the ORR is of essential importance. Indeed, various advanced electrocatalysts have been designed for the ORR or the OER; however, the origin of the advanced activity of oxygen electrocatalysts is still somewhat controversial. The enhanced activity is usually attributed to the high surface areas, the unique facet structures, the enhanced conductivities, or even to unclear synergistic effects, but the importance of the defects, especially the intrinsic defects, is often neglected. More recently, the important role of defects in oxygen electrocatalysis has been demonstrated by several groups. To make the defect effect clearer, the recent development of this concept is reviewed here and a novel principle for the design of oxygen electrocatalysts is proposed. An overview of the defects in carbon-based, metal-free electrocatalysts for ORR and various defects in metal oxides/selenides for OER is also provided. The types of defects and controllable strategies to generate defects in electrocatalysts are presented, along with techniques to identify the defects. The defect-activity relationship is also explored by theoretical methods.

Ultrafine nano-sulfur particles anchored on in situ exfoliated graphene for lithium–sulfur batteries

The development of lithium–sulfur is impeded by two main obstacles: the dissolution of lithium polysulfides and the pristine insulation of sulfur. Here, high energy ball-milling with the assistance of dielectric barrier discharge plasma was used in synthesis of ultrafine sulfur particles anchored on in situ exfoliated graphene for Li–S batteries. The ultrafine sulfur particles formed not only afford more sufficient electrical contact towards graphene support, but also alleviate volume expansion compared with bulk sulfur. On the other hand, with robust etching function of dielectric barrier discharge plasma, little oxygen-doping was observed in exfoliated few-layer graphene, offering sufficient capture sites towards lithium polysulfides. The ultrafine sulfur/graphene composite with little oxygen-doping exhibits superior cycling performance and rate capability in contrast to the control samples without the exertion of dielectric barrier discharge plasma. Little capacity degradation rate of 0.07% per cycle was achieved at 0.5C over 500 cycles.

Recent Advances on Black Phosphorus for Energy Storage, Catalysis, and Sensor Applications

As a new type of 2D semiconductor, black phosphorus (BP) possesses high charge-carrier mobility and theoretical capacity, thickness-dependent bandgap, and anisotropic structure, which has attracted tremendous attention since early 2014. To explore its full application in all aspects, studies based on BP nanostructures are swiftly expanding from the electronic field to energy storage and even biochemistry. The mechanism and application of BP in Li-/Na-ion battery anodes, oxygen evolution reaction/hydrogen evolution reaction catalysis, photocatalytic hydrogen production, and selective sensors are summarized. Based on the solid research on this topic, feasible improvements and constructive suggestions regarding these four fields are put forward.