Abstract
Iron/carbon-black composite nanoparticles were synthesized by chemically reducing the iron salt mixing with carbon black by adding NaBH 4 in the aqueous solution. Carbon-black particles, with a mean particle size of approximately 40 nm, function as the nucleation cores for iron deposition. Additionally, core-shell iron composite particles are observed to be 30-100 nm with spherical sharp. At the first time discharge, the iron/carbon-black composite nanoparticle discharged 1200 mAh g -1 (Fe) at plateau one and 400 mAh g -1 at plateau two at a high current density of 200 mA g -1 (Fe). The capacity is larger than the theoretical value, which is attributed to the formation of iron hydride (FeH x ) while the iron was reduced by NaBH 4 , followed the hydrogen reaction as an active material while the battery discharge occurs. In further cycles, the iron/carbon-black composite iron electrode shows a good reversibility of about 600 mAh g -1 (Fe) when the nickel-iron battery operated between 1.65 and 0.8 V. XRD analysis results indicate that the carbon black in the core of the iron/carbon-black composite enhances the reduction/oxidation reactions of iron, as achieved by the carbon black forming an enhanced electronic conductive network while iron is discharged as the insulator species such as Fe(OH) 2 and Fe 3 O 4 . SEM images reveal that the iron/carbon-black composite keeps particle sizes smaller than 300 nm during the electrode cycling, indicating that carbon black also acts as the nucleation cores for the dissolution-deposition of iron. © 2009 Elsevier B.V. All rights reserved.