Molten salt induced formation of chitosan based carbon nanosheets decorated with CoNx for boosting rechargeable Zn-air batteries

NaCl-Assisted electrospinning of bifunctional carbon fibers for High-Performance flexible zinc-air batteries

With the increasing demand for flexible, rechargeable zinc-air batteries (ZABs), developing efficient oxygen electrocatalysts is challenging. A large specific surface area and porous structure are critical for electrochemical performance but can compromise mechanical strength and flexibility. Herein, a novel strategy with NaCl-assisted electrospinning and pyrolysis has been proposed to fabricate self-supported carbon fibers with a solid core and mesoporous shell as bifunctional oxygen electrocatalysts for flexible ZABs. The fibers incorporate NaCl and ZnCo-ZIFs via coaxial electrospinning. NaCl enhances both the electrospinning process and ZIF carbonization, creating a porous surface on robust carbon fibers that balances surface exposure with structural stability. Experimental data and density functional theory calculations confirm that cobalt atoms anchored on the carbon surface are the primary active sites, boosting electrocatalytic performance. Zinc facilitates the formation of structural defects and porosity during volatilization at high temperatures, promoting NaCl molten salt infiltration, ZIF decomposition, and large pore formation. The resulting cross-linked porous structure increases active site exposure, enhancing catalytic efficiency. The synthesized ZN3-CNFs-900 exhibit remarkable catalytic activity, achieving an oxygen reduction reaction half-wave potential of 0.834 V and an oxygen evolution reaction overpotential of 1.695 V at 10 mA cm-2. ZABs assembled with these carbon fibers demonstrate an open-circuit voltage of 1.43 V, a peak power density of 111 mW cm-2, and cycling stability beyond 400 h. The carbon fiber-based solid-state ZABs show a high open circuit voltage of 1.39 V, a power density of 81.7 mW cm-2 and a cycle life of 33 h.

PtCo nanoalloy embedded nitrogen-doped carbon nanotube for rechargeable Zn-air batteries

The large-scale application of metal-air batteries strongly depends on the development of cost-effective, highly efficient, and durable bifunctional oxygen catalysts. In this work, a facile approach for preparing the monodisperse PtCo nanoalloy anchored the nitrogen-doped carbon nanotubes (PtCo/NCNT) for zinc-air batteries is reported. The nitrogen-doped carbon shell prevents PtCo nanoalloy from exfoliation, dissolution, and aggregation and enables the accessibility of electrolytes to the alloy surface and the electron transfer. Besides, the strong interaction between PtCo nanoalloy and nitrogen-doped carbon can efficiently modulate the electronic structure of the formed active sites. When used as a cathode catalyst, the constructed rechargeable zinc-air battery presents higher power density (268 mW cm-2), specific capacity (840 mAh g-1), and excellent stability. More importantly, the PtCo/NCNT catalyst allows the all-solid-state cell to exhibit remarkable flexibility and high round-trip efficiency at various bending states, demonstrating a potential possibility to replace the conventional Pt/C and RuO2 catalysts.

Biomass-Derived Catalytically Active Carbon Materials for the Air Electrode of Zn-Air Batteries

Given the growing environmental and energy problems, developing clean, renewable electrochemical energy storage devices is of great interest. Zn-air batteries (ZABs) have broad prospects in energy storage because of their high specific capacity and environmental friendliness. The unavailability of cheap air electrode materials and effective and stable oxygen electrocatalysts to catalyze air electrodes are main barriers to large-scale implementation of ZABs. Due to the abundant biomass resources, self-doped heteroatoms, and unique pore structure, biomass-derived catalytically active carbon materials (CACs) have great potential to prepare carbon-based catalysts and porous electrodes with excellent performance for ZABs. This paper reviews the research progress of biomass-derived CACs applied to ZABs air electrodes. Specifically, the principle of ZABs and the source and preparation method of biomass-derived CACs are introduced. To prepare efficient biomass-based oxygen electrocatalysts, heteroatom doping and metal modification were introduced to improve the efficiency and stability of carbon materials. Finally, the effects of electron transfer number and H2O2 yield in ORR on the performance of ZABs were evaluated. This review aims to deepen the understanding of the advantages and challenges of biomass-derived CACs in the air electrodes of ZABs, promote more comprehensive research on biomass resources, and accelerate the commercial application of ZABs.

A carboxylate linker strategy mediated densely accessible Fe-N4 sites for enhancing oxygen electroreduction in Zn-air batteries

Iron-nitrogen-carbon single-atom catalysts derived from zeolitic-imidazolate-framework-8 (ZIF-8) have presented its great potential for the oxygen reduction reaction (ORR) in Zn-air batteries (ZABs). However, due to insufficient active Fe-N sites, its ORR activity is inferior to Pt-based catalysts. Herein, a carboxylate (OAc) linker strategy is proposed to design a ZIF-8-derived FeNCOAc catalyst with abundant accessible Fe-N4 single-atom sites. Except that imidazole groups can coordinate with Fe ions, the OAc linker on the unsaturated coordination Zn nodes can anchor and coordinate with more Fe ions, resulting in a significant increase in Fe-N4 site density. Meanwhile, the corrosion of carbon skeleton by OAc oxidation during heat-treatment leads to improved porosity of catalyst. Benefitting from the highly dense Fe-N4 sites and hierarchical pores, the FeNCOAc endows superior performance in alkaline medium (E1/2 = 0.906 V), which is confirmed by density functional theory calculation results. Meanwhile, the assembled liquid ZAB delivers a favorable peak power density of 173.9 mW cm-2, and a high specific capacity of 770.9 mAh g-1 as well as outstanding durability. Besides, the solid-state ZAB also shows outstanding discharge performance.