From Synthesis to Application: Ni3 Fe N As Oxygen Reduction Electrocatalyst in Anion Exchange Membrane Fuel Cells

Abstract

Catalysis has played a crucial role in advancing and commercializing energy conversion technologies. It is essential to identify abundant, active, and stable materials to enable the reliable and cost-efficient use of catalysts in renewable technologies such as fuel cells (FCs) and electrolyzers. Suitable candidates, like nonprecious metals, can be found in the transition metals' first row, where materials like bimetallics, metal oxides, and metal nitrides can be obtained. Recently, these materials have shown high activity toward the Oxygen Reduction Reaction (ORR) and the Oxygen Evolution Reaction (OER) in an alkaline medium, which can be related to good performance in FCs and electrolyzers. However, most of the studies do not go further than half-cell reactions. In this study, we explored the synthesis of a metal nitride, Ni3FeN, and its application as a cathode material in hydrogen fuel Anion Exchange Membrane Fuel Cells (AEMFC). A one-step ammonolysis synthesis was done to obtain Ni3FeN supported on carbon. Various metal loadings were synthesized with nanoparticles sizes of 7 ± 2 nm and 10 ± 4 nm for 40% and 60%, respectively, revealed with Transmission Electron Microscopy (TEM). High-resolution Scanning Transmission Electron Microscopy (STEM) images and Energy Dispersive X-ray (EDX) mapping analysis revealed a metal nitride core and a metal oxide shell of ca. 3 nm. The bulk electronic structure was further evaluated using X-ray Absorption Spectroscopy (XAS), where the EXAFS modeling suggests a bulk nitride electronic structure. Consequently, cyclic voltammetry (CV) was used to investigate the electrochemical properties and ORR performance of the Ni3FeN catalyst in 1 M KOH. The catalyst exhibited a stable electrochemical structure with a slight decrease in E1/2 of 10 mV (from 0.85 V to 0.84 V) during a 100 K ORR accelerated durability test (ADT). In addition, Levich and Rotating Ring Disk Electrode (RRDE) analyses showed that the number of electrons transferred during the ORR was consistent with a 4-electron pathway. Furthermore, the Ni3FeN catalyst was tested as the cathode in an AEMFC, obtaining a power density output of 400 mW/cm2, highlighting its potential for alkaline medium fuel cell applications.