A zinc nanoparticles-dispersed multi-scale web of carbon micro-nanofibers for hydrogen production step of ZnO/Zn water splitting thermochemical cycle

Water splitting via the two-step ZnO/Zn thermochemical cycle is a promising and environmentally benign method for producing hydrogen from steam. In this study, we focus on the second step of the cycle, which is the exothermic hydrolysis reaction of Zn nanoparticles with steam. The unique Zn nanoparticle-dispersed carbon micro-nanofibers (Zn-CNFs) were prepared by impregnating carbon microfibers (ACFs) with a sodium dodecyl sulfate (SDS)-mediated mono-dispersed aqueous solution of Zn(II), followed by calcinations and reduction. The surfactant increased the metal (average crystal size similar to 25 nm) loading by approximately two-fold on the ACFs. The CNFs were grown on Zn-ACF at 700 degrees C by catalytic chemical vapor deposition (CCVD) using acetylene as the carbon source. Zn has dual roles in this system, one as a catalyst for CNF growth and the other as a reactant in the hydrolysis reaction. The water-splitting reaction was performed at different steam and N-2 flow rates and reaction temperatures. The production rate and yield of H-2 at a reaction temperature of 600 degrees C were calculated as 1.66 x 10(-6) mol/g s and 80%, respectively, which are comparable to or higher than results reported in the literature. The Zn-CNFs prepared in this study are a potential candidate for the H-2 production step of the ZnO/Zn thermochemical cycle. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.