The poor cycling stability resulting from the large volume expansion caused by lithiation is a critical issue for Si‐based anodes. Herein, we report for the first time of a new yolk–shell structured high tap density composite made of a carbon‐coated rigid SiO2 outer shell to confine multiple Si NPs (yolks) and carbon nanotubes (CNTs) with embedded Fe2O3 nanoparticles (NPs). The high tap density achieved and superior conductivity can be attributed to the efficiently utilised inner void containing multiple Si yolks, Fe2O3 NPs, and CNTs Li+ storage materials, and the bridged spaces between the inner Si yolks and outer shell through a conductive CNTs “highway”. Half cells can achieve a high area capacity of 3.6 mAh cm−2 and 95 % reversible capacity retention after 450 cycles. The full cell constructed using a Li‐rich Li2V2O5 cathode can achieve a high reversible capacity of 260 mAh g−1 after 300 cycles.

A flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn-air batteries. A facile two-step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen-rich functional groups and an enhanced surface area, is presented here. Impressively, this two-step activated CC (CC-AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen-doped carbon materials reported to date. Especially, CC-AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm −2 in 1 m KOH, which is among the best performances of metal-free OER electrocatalysts. The practical application of CC-AC is presented via its use as an FAE in a flexible rechargeable Zn-air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm −3 at 77.5 mA cm −3 , good cycling performance with a small chargedischarge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high-performance selfsupported metal-free electrodes.

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The vast majority of the reported hydrogen evolution reaction (HER) electrocatalysts perform poorly under alkaline conditions due to the sluggish water dissociation kinetics. Herein, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS and WS ). A series of ultrathin 2D-hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D-TMD nanosheets. The resultant Ni(OH) and Co(OH) hybridized ultrathin MoS and WS nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The 2D-MoS /Co(OH) hybrid achieves an extremely low overpotential of ≈128 mV at 10 mA cm in 1 m KOH. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides.

Electronic structure engineering lies at the heart of efficient catalyst design. Most previous studies, however, utilize only one technique to modulate the electronic structure, and therefore optimal electronic states are hard to be achieved. In this work, we incorporate both Fe dopants and Co vacancies into atomically thin CoSe 2 nanobelts for /coxygen evolution catalysis, and the resulted CoSe 2-D Fe-V Co exhibits much higher catalytic activity than other defect-activated CoSe 2 and previously reported FeCo compounds. Deep characterizations and theoretical calculations identify the most active center of Co 2 site that is adjacent to the V Co-nearest surface Fe site. Fe doping and Co vacancy synergistically tune the electronic states of Co 2 to a near-optimal value, resulting in greatly decreased binding energy of OH* (ΔE OH) without changing ΔE O , and consequently lowering the catalytic overpotential. The proper combination of multiple defect structures is promising to unlock the catalytic power of different catalysts for various electrochemical reactions.