Tailoring the high-density active sites via metal-coordinated ionic liquid encapsulated trimetallic core-shell MOF-derived catalysts for superior ORR in flexible Al-air batteries

Abstract

The attainment of practicality in flexible Al-air batteries is impeded by the need for efficient air cathodes. To address this challenge, we systematically engineered the trimetallic (ZnCoFe)NC catalyst with a unique morphology of nitrogen-doped carbon nanotubes (NCNTs) on the 3D polyhedral structure (IL-ZnCoFe@CNT/NC) as an effective cathode. The augmented growth of NCNT facilitated by the metal-coordinated ionic liquid enhances both the specific surface area and the electrochemically active surface area (ECSA). As a result, IL-ZnCoFe@CNT/NC material exhibits a higher onset (1.0 V vs RHE) and half-wave potential (E1/2 = 0.89 V vs. RHE) as well as low Tafel slope (61 mV/dec) and surpassed the bare MOF-derived catalysts and Pt/C. E1/2 decreased by only 7 mV after the stability test describes the durability and fast reaction kinetics in the ORR. Upon testing on flexible Al-air with IL-ZnCoFe@CNT/NC cathode catalysts, it exhibited an OCV of 1.49 V and a peak power density of 34.7 mW cm−2 with 1.3 times higher power performance than the commercial Pt/C along with 3 times longevity than bare catalysts. Additionally, the Density-functional theory (DFT) calculations provide rational evidence that the IL-ZnCoFe@CNT/NC catalyst has an upshifted d-band center, which, in turn, enhances the adsorption of reaction intermediates, making the catalyst highly promising towards ORR.