Issue 4, 2023

Highly active ZIF-8@CNT composite catalysts as cathode materials for anion exchange membrane fuel cells

Abstract

Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media is important for fuel cell applications. Herein, we report a simple and effective synthesis of transition-metal-doped zeolitic imidazolate framework-8 (ZIF-8) and carbon nanotube (CNT) composite catalysts (ZIF-8@CNT) prepared via high-temperature pyrolysis at 900 °C. The catalysts were characterized using different physicochemical techniques and employed as cathode materials in anion exchange membrane fuel cells (AEMFC). The prepared metal-free (ZNT-900), single-metal-doped (Fe-ZNT-900, Co-ZNT-900) and binary-metal-doped (Fe1Co1-ZNT-900, Fe1Co2-ZNT-900) catalysts had a sufficient amount of N-doping with the presence of FeCo moieties in the carbon skeleton of the latter two materials. N2 adsorption–desorption isotherms showed that all the prepared catalysts possess a sufficient Brunauer–Emmett–Teller surface area with more micropores present in ZNT-900, while a combined micro–mesoporous structure was obtained for transition-metal-doped catalysts. Binary-metal-doped catalysts showed the highest number of ORR-active sites (pyridinic-N, pyrrolic-N, graphitic-N, M–Nx) and exhibited a half-wave potential (E1/2) of 0.846 and 0.847 V vs. RHE for Fe1Co1-ZNT-900 and Fe1Co2-ZNT-900, respectively, which surpassed that of the commercial Pt/C catalyst (E1/2 = 0.834 V). In H2–O2 AEMFCs, the Fe1Co2-ZNT-900 catalyst delivered a maximum power density (Pmax) of 0.171 W cm−2 and current density at 0.5 V (j0.5) of 0.326 A cm−2, which is very close to that of the Pt/C catalyst (Pmax = 0.215 W cm−2 and j0.5 = 0.359 A cm−2). The prepared ZIF-8@CNT catalysts showed remarkable electrocatalytic ORR activity in 0.1 M KOH solution and fuel cell performance comparable to that of the benchmark Pt/C catalyst.

Keywords: Rotating disk electrode; Anion exchange membrane fuel cell; Zeolitic imidazolate framework; Non-precious metal catalyst; Oxygen reduction reaction.

Graphical abstract: Highly active ZIF-8@CNT composite catalysts as cathode materials for anion exchange membrane fuel cells

Supplementary files

Article information

Article type
Paper
Submitted
24 Jul. 2023
Accepted
04 Sep. 2023
First published
06 Sep. 2023
This article is Open Access
Creative Commons BY-NC license

Ind. Chem. Mater., 2023,1, 526-541

Highly active ZIF-8@CNT composite catalysts as cathode materials for anion exchange membrane fuel cells

R. Kumar, M. Mooste, Z. Ahmed, S. Akula, I. Zekker, M. Marandi, M. Käärik, J. Leis, A. Kikas, A. Treshchalov, M. Otsus, J. Aruväli, V. Kisand, A. Tamm and K. Tammeveski, Ind. Chem. Mater., 2023, 1, 526 DOI: 10.1039/D3IM00081H

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