CNT-confined W2N and NiCo nanodomains for bifunctional ORR/OER air cathodes in rechargeable Zn-air batteries

초록

Rechargeable Zn-air batteries require bifunctional catalysts that drive the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, achieving in-tube localization of multiple active phases within carbon nanotube (CNT) hosts remains challenging. Here, we demonstrate a stepwise, sequence-controlled inner-cavity loading strategy that introduces W and Ni/Co precursors into tip-opened CNTs, yielding spatially separated W2N and NiCo nanodomains confined within the CNT cavity (W2N/NiCo@CNT), with minimal deposition on the outer walls. In 1.0 M KOH, the W2N/NiCo@CNT catalyst exhibits an OER overpotential of 190 mV at 10 mA cm-2 and a Tafel slope of 52.8 mV dec-1, alongside an ORR half-wave potential of 0.87 V and a Tafel slope of 87.5 mV dec-1. The catalyst retains 90% of its initial current over 24 hand shows minimal polarization change after 1000 cycles. In rechargeable Zn-air batteries, the catalyst delivers an open-circuit voltage of 1.45 V, a peak power density of 123 mW cm-2, and stable cycling performance, with a modest increase in the charge-discharge voltage gap over 100 h. Simplified density functional theory (DFT)-based electronic structure calculations suggest charge redistribution and electronic modulation among the CNT-confined nanodomains, providing qualitative insight and highlighting CNT inner-cavity engineering as an air-cathode design strategy.

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