Designing highly active oxygen reduction reaction (ORR) catalysts is crucial to boost the fuel cell economy. Previous research has mainly focused on Ptbased alloy catalysts in which surface Pt is the solely active site and the activity improvement was challenged by the discovered scaling relationship. Herein we report a new concept of utilizing dual active sites for the ORR and demonstrate its effectiveness by synthesizing a SnO x /Pt− Cu−Ni heterojunctioned catalyst. A maximum of 40% enhancement in the apparent specific activity, which corresponds to 10-fold enhancement on interface sites, is measured compared with pure Pt−Cu−Ni. Detailed investigations suggest an altered dual-site cascade mechanism wherein the first two steps occur on SnO x sites and the remaining steps occur on adjacent Pt sites, allowing a significant decrease in the energy barrier. This study with the suggested dual-site cascade mechanism shows the potential to overcome the ORR energy barrier bottleneck to develop highly active catalysts.

As a typical transition-metal chalcogenide material, molybdenum disulfide (MoS2) has received tremendous attention because of its unique layered structure and versatile chemical, electronic, and optical properties. With the focus of this Perspective on the energy storage area, one of the most important contributions of MoS2 is that it sparked the birth of the rechargeable lithium battery in the early 1980s, which later formed the foundation of commercial lithium batteries. After four decades, admitting that MoS2 is still playing a significant role in the lithium-ion battery field and considerable effort was made to decipher the mechanism through ex situ and in situ studies and by means of MoS2 nanostructure engineering that advances the lithium battery performance, it is also used in beyond lithium-ion batteries, such as sodium, magnesium, calcium, and aluminum energy storage systems. Such alternative battery systems are desirable because of the safety concerns of lithium and the depletion of lithium reserves and corresponding increase in cost. In this Perspective, recent development on the fabrication of novel MoS2 nanostructures was discussed, followed by the scrutinization of their application in beyond lithium-ion batteries and the in situ/operando methods involved in these studies. Finally, a brief summary and outlook that may help with the future advancement of the beyond lithium-ion batteries are presented.

Two‐dimensional (2D) layered transition metal carbides/nitrides, called MXenes, are attractive alternative electrode materials for electrochemical energy storage. Owing to their metallic electrical conductivity and low ion diffusion barrier, MXenes are promising anode materials for sodium‐ion batteries (SIBs). Herein, we report on a new 2D carbonitride MXene, viz., Ti2C0.5N0.5Tx (Tx stands for surface terminations), and the only second carbonitride after Ti3CNTx so far. A new type of in situ HF (HCl/KF) etching condition was employed to synthesize multilayer Ti2C0.5N0.5Tx powders from Ti2AlC0.5N0.5. Spontaneous intercalation of tetramethylammonium followed by sonication in water allowed for large‐scale delamination of this new titanium carbonitride into 2D sheets. Multilayer Ti2C0.5N0.5Tx powders showed higher specific capacities and larger electroactive surface area than those of Ti2CTx powders. Multilayer Ti2C0.5N0.5Tx powders show a specific capacity of 182 mAh g−1 at 20 mA g−1, the highest among all reported MXene electrodes as SIBs with excellent cycling stability.