Developing highly efficient, low-cost and bifunctional electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) plays a pivotal role in the scalable applications of zinc–air (Zn–air) batteries. Herein, Co–Fe–P–Se nanoparticles supported on two-dimensional nitrogen-doped carbon (Co–Fe–P–Se/NC) to construct a three-dimensional nanostructure were obtained under the assistance of metal–organic frameworks (MOFs). The two-dimensional nanosheet facilitated the electron transfer rate and exposed abundant active sites. The three-dimensional morphology composed of nanosheets was favorable for electrolyte transport and provided abundant channels for gas diffusion during the catalytic process. Moreover, the coexistence of Co and Fe had important effects on promoting the catalytic performances. Lastly, the catalytic performances for OER and ORR could be promoted effectively after the introduction of selenium and phosphorous in the designed electrocatalyst. Benefiting from the above merits, the prepared Co–Fe–P–Se/NC exhibited excellent catalytic performances for OER (overpotential of 0.27 V at 10 mA cm⁻²), ORR (half-wave potential of 0.76 V) and rechargeable batteries (a low voltage gap of 0.719 V, high power density of 104 mW cm⁻² at 200 mA cm⁻² and high energy density of 805 W h Kg_Zn ⁻¹). Moreover, the prepared electrocatalyst possessed more stable long-term stability in all the conducted experiments. This work provides a novel approach to develop and construct high-performance bifunctional nanocatalysts for metal–air batteries.

Highly wrinkled graphene film (HWGF) with high packing density was synthesized by combining an electrostatically self-assembling process, a vacuum filtration-induced film assembling process and capillary compression. Fe₃O₄ nanoparticles were used as a low-cost and environment-friendly hard template. Hierarchical porosity and high packing density were achieved with the aid of capillary compression in the presence of Fe₃O₄ nanoparticles. This strategy enables integration of highly wrinkled graphene sheets to form highly compact carbon electrodes with a continuous ion transport network. The generated HWGF exhibited a high packing density of 1.53 g cm⁻³, a high specific surface area of 383 m² g⁻¹ and a hierarchically porous structure. The HWGF delivered a high capacitance of 242 F g⁻¹ and 370 F cm⁻³ at 0.2 A g⁻¹ in 6 M KOH aqueous electrolyte system with excellent rate capability (202 F g⁻¹ and 309 F cm⁻³ retained at 20 A g⁻¹). The capacity retention rate reached 97% after 10 000 cycles at 1 A g⁻¹. The HWGF-based supercapacitor exhibited a high energy density of 17 W h kg⁻¹ at the power density of 49 W kg⁻¹. Such high capacitive performances could be attributed to the highly dense but porous graphene assemblies composed of highly wrinkled graphene sheets.

Bismuth (Bi) is a promising anode candidate for sodium ion batteries (SIBs) with a high volumetric capacity (3765 mA h cm⁻³) and moderate working potential but suffers from large volume change (ca. 250%) during the sodiation/desodiation process, resulting in pulverization of the electrode, electrical contact loss, excessive accumulation of solid electrolyte interfaces, etc., devastating the cycling stability of the electrode seriously. Addressing this issue significantly relies on rational micro- and nano-structuring. Herein, we prepared a 3D multi-layered composite assembly of Bi/carbon heterojunctions with 0D bismuth nanospheres distributed and anchored on 2D nitrogen-doped carbon nanosheets (NCSs), using a preorganization strategy by taking full advantage of the strong complexation ability of Bi³⁺. The multi-layered composite assembly is periodic and close-packed, with Bi nanospheres <25 nm, carbon nanosheets ∼30 nm, and an average interlayer space of ∼75 nm. Such a specific architecture provides abundant electrochemically active surfaces and ion migration channels as the Bi nanospheres are attached to the 2D nitrogen-doped carbon nanosheets via a point-to-surface pattern. Moreover, the mono-layer Bi nanospheres oriented along the 2D-surface of NCSs are kinetically favorable for the recognition of Na⁺ by the active sites of Bi nanospheres as well as for avoiding the long distance migration of Na⁺ (external diffusion of Na⁺). Furthermore, thermodynamically, the small size and high surface energy of ultrasmall Bi nanospheres could contribute to high ion mobility (internal diffusion of Na⁺) and promote electrochemical reactions as well. The multi-layered composite assembly of Bi@NCSs (ML-Bi@NCSs) not only provides a robust 3D framework guaranteeing the whole structural stability but also ensures direct and full contact of each active nano-building block with electrolyte, thereby forming a high-throughput electron/ion transport system. When evaluated as the anode for SIBs, ML-Bi@NCSs deliver superior high-rate capability up to 30 A g⁻¹ (specific capacity: 288 mA h g⁻¹) and long-term cycling stability (capacity retention: 95.8% after 5000 cycles at 10 A g⁻¹ and 90.6% after 10 000 cycles at 20 A g⁻¹, respectively).

An easy and scalable synthetic route was proposed for synthesis of a high-energy stable anode material composed of carbon-coated Si nanoparticles (NPs, 80 nm) confined in a three-dimensional (3D) network-structured conductive carbon nanotube (CNT) matrix (Si/CNT@C). The Si/CNT@C composite was fabricated via in situ polymerization of resorcinol formaldehyde (RF) resin in the co-existence of Si NPs and CNTs, followed by carbonization at 700 °C. The RF resin-derived carbon shell (~10 nm) was wrapped on the Si NPs and CNTs surface, welding the Si NPs to the sidewall of the interconnected CNTs matrix to avoid Si NP agglomeration. The unique 3D architecture provides a highway for Li⁺ ion diffusion and electron transportation to allow the fast lithiation/delithiation of the Si NPs; buffers the volume fluctuation of Si NPs; and stabilizes solid–electrolyte interphase film. As expected, the obtained Si/CNT@C hybrid exhibited excellent lithium storage performances. An initial discharge capacity of 1925 mAh g⁻¹ was achieved at 0.1 A g⁻¹ and retained as 1106 mAh g⁻¹ after 200 cycles at 0.1 A g⁻¹. The reversible capacity was retained at 827 mAh g⁻¹ when the current density was increased to 1 A g⁻¹. The Si/CNT@C possessed a high Si content of 62.8 wt%, facilitating its commercial application. Accordingly, this work provides a promising exploration of Si-based anode materials for high-energy stable lithium-ion batteries.