Synthesis and characterization of zirconium oxide-based catalysts for the oxygen reduction reaction via the heat treatment of zirconium polyacrylate in an ammonia atmosphere

Abstract

Zirconium oxide-based catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells were synthesized via heat treatment of zirconium polyacrylate in an NH₃ atmosphere. The effects of gas atmosphere and heat treatment temperature on the material structure were systematically examined. The formation of zirconium oxide nanoparticles and carbon residues, which act as electron conduction paths, was observed in all samples. The structure of the material varied significantly depending on the heat treatment conditions. The samples heat-treated in the NH₃ atmosphere showed greater exposure to zirconium oxide nanoparticles and an increase in the specific surface area of the carbon residue caused by NH₃-induced etching. In addition, the conductivity of the carbon residue increased, and its quantity decreased with increasing heat treatment temperature. This trade-off was optimally controlled at 800 °C, which resulted in a high rest potential and a large ORR current density. This study demonstrates that the heat treatment of organometallic complexes in an NH₃ atmosphere is highly effective for exposing metal oxide nanoparticles and increasing the specific surface area of the carbon residue, providing valuable insights into the design of electron conduction paths for metal oxide-based catalysts.

Graphical abstract