Charge delocalization regulation of atomically dispersed tungsten sites by axial sulfur atoms for highly active oxygen reactions in low-temperature zinc-air batteries

Abstract

Atomically dispersed tungsten-nitrogen-carbon with W−N₄ sites acts as a highly efficient catalyst for oxygen reactions. However, the symmetrical charge distribution of W−N₄ sites results in strong binding with oxygen-containing intermediates, leading to unsatisfactory catalytic activities. Here, an axially coordinated sulfur (S) atom is integrated into the atomically dispersed W−N₄ site and anchored onto multi-walled carbon nanotubes (S₁−W₁N₄−MWCNTs) for oxygen reduction/oxygen evolution reactions (ORR/OER). The axial S atom, with significantly different electronegativity and outer electronic structure compared to nitrogen atom, induces localized charge redistribution around W−N₄ site. This change optimizes the adsorption/desorption capabilities of oxygen-containing intermediates on W−N₄ site, thereby enhancing the overall oxygen reaction activities. The S₁−W₁N₄−MWCNTs demonstrates excellent ORR/OER activity with the half-wave potential of 0.916 V for ORR and the potential of 1.644 V (at 10 mA cm⁻²) for OER. At −20 °C, S₁−W₁N₄−MWCNTs-based zinc-air batteries demonstrate increased specific capacity and an extended charging-discharging cycle life of 420 h, surpassing performance at room temperature. Regulating the charge distribution of W−N₄ sites with axial S atoms provides an effective strategy to boost the oxygen reaction activities of tungsten-nitrogen-carbon catalysts.