Gas diffusion electrodes on the electrosynthesis of controllable iron oxide nanoparticles

Abstract

The electrosynthesis of iron oxide nanoparticles offers a green route, with significant energy and environmental advantages. Yet, this is mostly restricted by the oxygen solubility in the electrolyte. Gas-diffusion electrodes (GDEs) can be used to overcome that limitation, but so far they not been explored for nanoparticle synthesis. Here, we develop a fast, environmentally-friendly, room temperature electrosynthesis route for iron oxide nanocrystals, which we term gas-diffusion electrocrystallization (GDEx). A GDE is used to generate oxidants and hydroxide in-situ, enabling the oxidative synthesis of a single iron salt (e.g., FeCl_2) into nanoparticles. Oxygen is reduced to reactive oxygen species, triggering the controlled oxidation of Fe^(2+) to Fe^(3+), forming Fe_(3-x)O_(4-x) (0 <= x <= 1). The stoichiometry and lattice parameter of the resulting oxides can be controlled and predictively modelled, resulting in highly-defective, strain-heavy nanoparticles. The size of the nanocrystals can be tuned from 5 nm to 20 nm, with a large saturation magnetization range (23 to 73 A m^2 kg^(-1)), as well as minimal coercivity (similar to 1 kA m^(-1)). Using only air, NaCl, and FeCl_2, a biocompatible approach is achieved, besides a remarkable level of control over key parameters, with a view on minimizing the addition of chemicals for enhanced production and applications.