The commercial application of aqueous zinc-ion batteries (AZIBs) is hindered by dendrite growth, side reaction of hydrogen evolution reaction (HER), and corrosion passivation of zinc anode. In this work, trace inorganic additive ammonium hydrogen borate (AB) was introduced into 2 M ZnSO₄ electrolyte to construct a water-deficient pH buffer layer with electrostatic shielding effect at anode–solution interface. The buffer layer can effectively reduce the water content at the interface and maintain the interfacial pH stable, thereby suppressing the HER and the corrosion of anode. In addition, the NH₄⁺ in the additive also demonstrates an electrostatic shielding effect, which alleviates the “tip effect” and increases the nucleation overpotential of the zinc anode. As a result, the buffer layer can induce the uniform deposition of zinc and restrict the growth of dendrites, realizing a highly reversible zinc anode. Under this electrolyte system, the zinc symmetric battery can cycle stably for 7266 h at a current density of 5 mA·cm⁻², and the cumulative deposition capacity could reach 18.17 Ah·cm⁻². Even under the condition of a high depth of discharge (DOD) of 78.54%, it still maintained an excellent cycle life of 450 h. The zinc-copper half-cell can stably cycle 1400 times at a current density of 10 mA·cm⁻² and delivers an ultra-high Coulombic efficiency of 99.70%. The Zn||MnO₂ full cell retains a capacity retention rate of 76.68% after 900 cycles at a current density of 1 A·g⁻¹, indicating its promising application potential.

The non-noble metal (Fe, Co, Ni, etc.) catalysts possess promising potential to replace noble metals (e.g., Pt, Ru, Ir, etc.) as catalysts for oxygen electrocatalysis. Up to now, various mono- and dual-single-atom catalysts have been fabricated, though it is still challenging to synthesise ternary single-atom catalysts due to the difference of interaction forces between different metal ions (Fe, Co, Ni, etc.) and ligands. Here, we report a Fe-Co-Ni ternary single-atom catalyst (FeCoNi-N_x) derived from a zeolitic imidazolate frameworks (ZIF) precursor as an efficient oxygen electrocatalyst, and an optimised flexible casting-drying polyvinyl alcohol (CD-PVA) film as a quasi-solid electrolyte host, for high-efficiency solid-state Zn-air batteries. The aberration-corrected HAADF-STEM and EELS spectrum confirm the co-existence of Fe, Co and Ni single atoms in the FeCoNi-N_x catalyst, and the electrochemical, mechanical, and durability tests prove the superiority of the CD-PVA film. As a result, the FeCoNi-N_x-based rechargeable Zn-air battery delivers superior specific capacity (846.8 mAh·g_Zn^–1) and power density (135 mW·cm^–2) in aqueous electrolyte, as well as an over 60 mW·cm^–2 power density in quasi-solid electrolyte. As a result, the quasi-solid-state Zn-air battery with a small area of only 2 cm² is able to charge a mobile phone, which outperforms all the reported devices to date.

The emerging of single-atom catalysts (SACs) offers a great opportunity for the development of advanced energy storage and conversion devices due to their excellent activity and durability, but the actual mass production of high-loading SACs is still challenging. Herein, a facile and green boron acid (H₃BO₃)-assisted pyrolysis strategy is put forward to synthesize SACs by only using chitosan, cobalt salt and H₃BO₃ as precursor, and the effect of H₃BO₃ is deeply investigated. The results show that molten boron oxide derived from H₃BO₃ as ideal high-temperature carbonization media and blocking media play important role in the synthesis process. As a result, the acquired Co/N/B tri-doped porous carbon framework (Co–N–B–C) not only presents hierarchical porous structure, large specific surface area and abundant carbon edges but also possesses high-loading single Co atom (4.2 wt.%), thus giving rise to outstanding oxygen catalytic performance. When employed as a catalyst for air cathode in Zn-air batteries, the resultant Co–N–B–C catalyst shows remarkable power density and long-term stability. Clearly, our work gains deep insight into the role of H₃BO₃ and provides a new avenue to synthesis of high-performance SACs.