Kinetic investigation of hydrogen generation from hydrolysis of SnO and Zn solar nanopowders

The hydrolysis reaction of the two-step ZnO/Zn and SnO2/SnO thermochemical cycles was kinetically investigated for solar hydrogen production. Nanoparticles of Zn and SnO were synthesized by solar thermal reduction of the oxides and neutral gas quenching of the vapors. They were then hydrolyzed to quantify and compare the H2 yields and the kinetic rate laws in fixed-bed. The hydrolysis of Zn nanoparticles reached only up to 55% of H2 yield, whereas SnO hydrolysis was almost complete. In contrast, Zn hydrolysis was much faster than SnO hydrolysis, but Zn deactivation occurred suddenly. Models of solid–gas reactions were applied to identify the controlling mechanisms and the associated kinetic parameters. The kinetic models were fitted to both isothermal and non-isothermal (temperature ramp) hydrolysis experimental data. Activation energies and reaction orders were found to be 122 ± 13 kJ/mol and 2.0 ± 0.3 for SnO, and 87 ± 7 kJ/mol and 3.5 ± 0.5 for Zn, respectively. Finally, a shrinking core approach was applied to the case of SnO to account for the reaction-controlling mechanisms.