Deliberate Modification of Fe3O4 Anode Surface Chemistry: Impact on Electrochemistry

Fe3O4 nanoparticles (NPs) with an average size of 8-10 nm have been successfully functionalized with various surface-treatment agents to serve as model systems for probing surface chemistry-dependent electrochemistry of the resulting electrodes. The surface-treatment agents used for the functionalization of Fe3O4 anode materials were systematically varied to include aromatic or aliphatic structures: 4-mercaptobenzoic acid, benzoic acid (BA), 3-mercaptopropionic acid, and propionic acid (PA). Both structural and electrochemical characterizations have been used to systematically correlate the electrode functionality with the corresponding surface chemistry. Surface treatment with ligands led to better Fe3O4 dispersion, especially with the aromatic ligands. Electrochemistry was impacted where the PA- and BA-treated Fe3O4 systems without the -SH group demonstrated a higher rate capability than their thiol-containing counterparts and the pristine Fe3O4. Specifically, the PA system delivered the highest capacity and cycling stability among all samples tested. Notably, the aromatic BA system outperformed the aliphatic PA counterpart during extended cycling under high current density, due to the improved charge transfer and ion transport kinetics as well as better dispersion of Fe3O4 NPs, induced by the conjugated system. Our surface engineering of the Fe3O4 electrode presented herein, highlights the importance of modifying the structure and chemistry of surface-treatment agents as a plausible means of enhancing the interfacial charge transfer within metal oxide composite electrodes without hampering the resulting tap density of the resulting electrode.