Dextran stabilised hematite: a sustainable anode in aqueous electrolytes†

Abstract

During the last decades, the use of innovative hybrid materials in energy storage devices has led to notable advances in the field. However, further enhancement of their electrochemical performance faces significant challenges nowadays, imposed by the materials used in the electrodes and the electrolyte. Such problems include the high solubility of both the organic and the inorganic anode components in the electrolyte as well as the limited intrinsic electronic conductivity and substantial volume variation of the materials during cycling. The present work focuses on the fabrication of novel and sustainable anode electrodes for use in energy storage devices, utilizing cross-linked oxidized dextran (Ox-Dex) as the binder and hematite (α-Fe₂O₃) cubes as the active component. The ion diffusion mechanism within the anode electrode materials, as well as their cycling stability, were studied via cyclic voltammetry measurements, using Li⁺, Zn²⁺ and Al³⁺ aqueous electrolytes. The hybrid iron oxide electrodes exhibited the highest electrochemical performance in the Al₂(SO₄)₃ electrolyte (3000 mA g⁻¹), followed by ZnSO₄ (2000 mA g⁻¹) and Li₂SO₄ (800 mA g⁻¹)_. The differences in the performance of the anodes for the three investigated electrolytes were attributed to the ionic radii of Li⁺, Zn²⁺ and Al³⁺, which affect the rate of ion diffusion within the material lattice exhibiting the highest diffusion coefficient of 4.64 × 10⁻⁹ cm² s⁻¹ in Al³⁺. Notably, the hybrid anodes demonstrated superior cycling performance (with the lowest variance percentage of 1.3% for hybrid compared to 38.1% for the bare in the presence of Zn²⁺), underlining the pivotal role of the natural binder. This was attributed to hydrogen bonding interactions, which increase the contact points between the inorganic and polymeric components, resulting in a more uniform network structure. Additionally, the cross-linking of Ox-Dex promotes stability and tolerance to the volume expansion of the electrodes. These results underscore the immense potential of the proposed hybrid electrodes in the field of energy storage.