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Nanoparticles often exhibit size-dependent redox reactivities, with smaller particles being more reactive in some cases, while less reactive in others. Predicting trends between redox reaction rates and particle sizes is often complicated because a particle’s dimensions can simultaneously influence its aggregation state, reactive surface area, and thermodynamic properties. Here, we tested the hypothesis that interfacial redox reaction rates for nanoparticles with different sizes can be described with a single linear free-energy relationship (LFER) if size-dependent reactive surface areas and thermodynamic properties are properly considered. We tested this hypothesis using a well-known interfacial redox reaction: the reduction of nitrobenzene to aniline by iron-oxide-bound Fe2+. We measured the reduction potential (EH) values of nano-particulate hematite suspensions containing aqueous Fe2+ using mediated potentiometry and characterized the size and aggregation states of hematite samples at circumneutral pH values.We used the measured EH values to calculate surface energies and reactive surface areas using thermodynamic relationships. Nitrobenzene reduction rates were lower for smaller particles, despite their larger surface areas, due to their higher surface energies. When differences in surface areas and thermodynamic properties were considered, nitrobenzene reduction kinetics for all particle sizes was described with a LFER. Our results demonstrate that when Fe2+ serves as a reductant, an antagonistic effect exists, with smaller particles having larger reactive surface areas but alsomore positive reduction potentials. When Fe3+ serves as an oxidant, however, these two effects work in concert, which likely explains past discrepancies regarding how iron oxide particle sizes influence redox reaction rates. [ABSTRACT FROM AUTHOR]

LiNi 1/3 Co 1/3 Mn 1/3 O 2 one-dimensional (1D) hierarchical microrods assembled with nanoparticles have been successfully prepared through post-heat treatment of MC 2 O 4 · x H 2 O (M = Ni, Co, Mn) microrod precursor which was obtained via stepwise co-precipitation. The CoC 2 O 4 ·2H 2 O microrod crystallites formed in the first step can effectively template the subsequent formation of manganese, cobalt and nickel oxalates on the initial CoC 2 O 4 ·2H 2 O microrods during the second step co-precipitation, without assistance of any surfactants. The LiNi 1/3 Co 1/3 Mn 1/3 O 2 1D hierarchical microrods with pores and voids as cathode material for lithium ion batteries exhibit superior initial coulombic efficiency, reversible capacity, rate capability and cycling stability to the LiNi 1/3 Co 1/3 Mn 1/3 O 2 microsized particles. They deliver high specific discharge capacities of 163.3 and 104.9 mAh g −1 at rates of 0.1 and 20 C, respectively. At 0.5 C, they achieve a discharge capacity of 152.2 mAh g −1 with a capacity retention of 89.5% after 160 cycles. The excellent electrochemical performance can be attributed to the novel hierarchical microrod structure with much porous and void space, which shortens the diffusion path of electron and lithium ion, and benefits for their transfer. In addition, this unique structure provides not only appropriate contact area between electrode and electrolyte, but also good accommodation for the strain relaxation during charge and discharge. [ABSTRACT FROM AUTHOR]