Plasma‐Induced S‐Vacancy and Mn‐Doping Synergistically Boost the Catalytic Activity of NiCo 2 S 4 @Co 2 N Heterostructure for Rechargeable Zinc‐Air Batteries and Alkaline Methanol Fuel Cells

Abstract Here, we introduce a plasma‐assisted sulfurization strategy to synthesize Mn‐doped NiCo 2 S 4 @Co 2 N heterostructures enriched with sulfur‐vacancies (V S ). These heterostructures are incorporated into a 3D network of nitrogen‐doped carbon‐nanotubes (NCNTs) supported by carbon‐cloth, resulting in the p‐Mn‐NiCo 2 S 4 @Co 2 N/NCNTs. It demonstrates excellent bifunctional catalytic activity, with a potential difference (ΔE = E OER,50 ‐E ORR,1/2 ) as low as 0.695 V. The half‐wave potential of oxygen‐reduction reaction (ORR) is 0.828 V, and the overpotential for oxygen‐evolution reaction (OER) to achieve 50 mA cm⁻ 2 is only 293 mV. Density‐Functional‐Theory (DFT) calculations confirm that the exceptional catalytic activity originates from the V S and Mn‐doping structure. The assembled liquid zinc‐air battery (ZAB) has an open‐circuit voltage (OCV) of 1.54 V, a peak power‐density of 139.9 mW cm −2 , and can undergo stable charge/discharge cycles for 1500 cycles at 10 mA cm −2 . The assembled flexible all‐solid‐state ZAB also features a stable OCV of 1.486 V and exhibits a peak power‐density superior to that of commercial 20 wt.% Pt/C+RuO 2 , accompanied by stable charging/discharging cycles of up to 700 cycles. The performance remains stable across various bending angles, demonstrating good flexibility and durability. The maximum power‐density exhibited by alkaline direct methanol fuel‐cells (ADMFCs) assembled with p‐Mn‐NiCo 2 S 4 @Co 2 N/NCNTs is 75.6 mW cm⁻ 2 , exceeding that of the commercial Pt/C catalyst.