Spin‐Polarized Surface Capacitance Effects Enable Fe₃O₄ Anode Superior Wide Operation‐Temperature Sodium Storage

Abstract

Fe3O4 is widely investigated as an anode for ambient sodium‐ion batteries (SIBs), but its electrochemical properties in the wide operation‐temperature range have rarely been studied. Herein, the Fe3O4 nanoparticles, which are well encapsulated by carbon nanolayers, are uniformly dispersed on the graphene basal plane (named Fe3O4/C@G) to be used as the anode for SIBs. The existence of graphene can reduce the size of Fe3O4/C nanoparticles from 150 to 80 nm and greatly boost charge transport capability of electrode, resulting in an obvious size decrease of superparamagnetic Fe nanoparticles generated from the conversion reaction from 5 to 2 nm. Importantly, the ultra‐small superparamagnetic Fe nanoparticles (≈2 nm) can induce a strong spin‐polarized surface capacitance effect at operating temperatures ranging from −40 to 60 °C, thus achieving highly efficient Na‐ion transport and storage in a wide operation‐temperature range. Consequently, the Fe3O4/C@G anode shows high capacity, excellent fast‐charging capability, and cycling stability ranging from −40 to 60 °C in half/full cells. This work demonstrates the viability of Fe3O4 as anode for wide operation‐temperature SIBs and reveals that spin‐polarized surface capacitance effects can promote Na‐ion storage over a wide operation temperature range.

Ultrasensitive Paper-Based Photoelectrochemical Biosensor for Acetamiprid Detection Enabled by Spin-State Manipulation and Polarity-Switching

“…The magnetic regulation technique, as a form of noncontact and eco-friendly strategy, can manipulate spin-polarized electrons to promote efficient separation of photoexcited electron–hole pairs, realizing an unprecedented enhancement in photoconversion efficiency. − In fact, influenced by a magnetic field (MF), electron spin polarization is achieved and enhanced, causing the photoexcited electrons in conduction band (CB) to undergo spin-flip (spin-down) due to the hyperfine interaction and spin–orbit coupling. , Whereas, the residual holes (h + ) in the valence band (VB) maintain their original spin-up orientation in the high spin polarization environment. , This effectively hinders the recombination of photoexcited charge carriers to a maximum degree. More excitingly, serving as a persistent driving force, external MF can consistently influence the electron spin state within photoelectrodes, ensuring the continuous separation of photogenerated electron–hole (e – –h + ) pairs and providing more photocarriers for the photon-to-current conversion process. − Herein, inspired by the above principle, we demonstrate for the first time the successful improved sensor sensitivity by regulating the spin-dependent electronic structures and anastrophic switching of electron transport pathways by rational design of the energy band structure.…”