Ni–Fe bimetallic carbon nanotube catalysts derived from a two-dimensional metalloporphyrin Fe-MOF precursor for oxygen reduction and oxygen evolution reactions

Abstract

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical half-reactions in energy conversion devices such as metal–air batteries and reversible fuel cells, and their sluggish kinetics severely limit the overall device performance. Therefore, the development of efficient, stable, and low-cost non-precious metal bifunctional electrocatalysts is of great significance. In this study, a MOF-derived bifunctional electrocatalytic material (NiFe@CNT), featuring NiFe bimetallic alloys uniformly anchored within a carbon nanotube network, was successfully fabricated using a two-dimensional metalloporphyrin-based Fe-MOF precursor via metal site modulation by introducing Ni, combined with a high-temperature pyrolysis strategy. Structural characterization results indicate that NiFe@CNT possesses an intact three-dimensional CNT conductive network, a high degree of graphitization (I_D/I_G = 0.39), and uniformly dispersed NiFe alloy active phases. Electrochemical evaluations reveal that NiFe@CNT functions as a highly active bifunctional catalyst for both ORR and OER in alkaline environments. Regarding its ORR activity, the material exhibits a half-wave potential comparable to that of benchmark Pt/C, with reaction kinetics proceeding through an approximately four-electron transfer mechanism. In terms of OER performance, a current density of 10 mA cm⁻² is attained at a modest overpotential of merely 1.514 V. In alkaline electrolyte, the ORR proceeds predominantly through a four-electron pathway converting O₂ to H₂O (O₂ + 4H⁺ + 4e⁻ → 2H₂O), while the OER involves the reverse four-electron oxidation of hydroxide to produce molecular oxygen (2H₂O → O₂ + 4H⁺ + 4e⁻). Furthermore, durability assessments confirm that NiFe@CNT surpasses commercial noble metal benchmarks in long-term operational stability. This work presents a viable approach for fabricating advanced noble-metal-free oxygen electrocatalysts through two-dimensional MOF-derived engineering.