Metal−Organic polymer-derived interconnected Fe−Ni alloy by carbon nanotubes as an advanced design of urea oxidation catalysts

Arindam Modak, Roopathy Mohan, Kalaiyarasi Rajavelu, Rivka Cahan, Tatyana Bendikov, Alex Schechter

Research output: Contribution to journalArticlepeer-review

66 Scopus citations

Abstract

The electrochemical urea oxidation reaction (UOR) is considered as a promising renewable source for harvesting energy from waste. We report a new synthetic design approach to produce an iron−nickel alloy nanocatalyst from a metal−organic polymer (MOP) by a single-step carbonization process at 500 °C, thus forming a core−shell of iron−nickel-coated carbon (C@ FeNi) nanostructures wired by embedded carbon nanotubes (CNTs) (CNT/C@FeNi). Powder X-ray diffraction confirmed the formation of metallic FeNi3 alloy nanoparticles (∼20 to 28 nm). Our experimental results showed that MOP containing CNTs acquired an interconnected hierarchical topology, which prevented the collapse of its microstructure during pyrolysis. Hence, CNT/ C@FeNi shows higher porosity (10 times) than C@FeNi. The electrochemical UOR in alkaline electrolytes on these catalysts was studied using cyclic voltammetry (CV). The result showed a higher anodic current (3.5 mA cm−2) for CNT/C@FeNi than for C@ FeNi (1.1 mA cm−2) at 1.5 V/RHE. CNT/C@FeNi displayed good stability in chronoamperometry experiments and a lower Tafel slope (33 mV dec−1) than C@FeNi (41.1 mV dec−1). In this study, CNT/C@FeNi exhibits higher exchange current density (3.2 μA cm−2) than does C@FeNi (2 μA cm−2). The reaction rate orders of CNT/C@FeNi and C@FeNi at a kinetically controlled potential of 1.4 V/RHE were 0.5 and 0.9, respectively, higher than the 0.26 of β-Ni(OH)2, Ni/Ni(OH)2 electrodes. The electrochemical impedance result showed a lower charge-transfer resistance for CNT/C@FeNi (61 Ω·cm−2) than for C@FeNi (162 Ω·cm−2), due to faster oxidation kinetics associated with the CNT linkage. Moreover, CNT/C@FeNi exhibited a lower Tafel slope and resistance and higher heterogeneity (25.2 × 10−5 cm s−1), as well as relatively high faradic efficiency (68.4%) compared to C@ FeNi (56%). Thus, the carbon-coated FeNi3 core connected by CNT facilitates lower charge-transfer resistance and reduces the UOR overpotential.

Original languageEnglish
Pages (from-to)8461-8473
Number of pages13
JournalACS applied materials & interfaces
Volume13
Issue number7
DOIs
StatePublished - 24 Feb 2021

Keywords

  • CNTs
  • Charge transfer
  • Core−shell
  • Metal−organic polymer
  • Nickel−iron alloy
  • Urea oxidation reaction

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