Project: Hydrogen Production by In-situ Formation and Hydrolysis of Zn Nanoparticles

Partner: Particle Technology Laboratory
Funding source: ETH-Zurich TH-Project

Background – The production of solar hydrogen via the Zn/ZnO water-splitting thermochemical cycle is considered, consisting of a 1st-step solar endothermic dissociation of ZnO and a 2nd-step non-solar exothermic hydrolysis of Zn :

1st step dissociation (solar): ZnO → Zn + 0.5 O2 (1)
2nd step hydrolysis (non-solar): Zn + H2O → ZnO + H2 (2)
2-step water splitting cycle Scheme of the 2-step water splitting thermochemical cycle based on the ZnO/Zn redox reactions.

This project focuses on a novel combined process for the efficient execution of the 2nd step, Eq. (2), that encompasses the formation of Zn-nanoparticles followed by their in-situ hydrolysis for H2 generation. The advantages of using Zn-nanoparticles are 3-fold: 1) their inherent high specific surface area augments the reaction kinetics, heat transfer, and mass transfer; 2) their large surface to volume ratio favors complete or nearly complete oxidation; and 3) their entrainment in a gas flow allows for simple, continuous, and controllable feeding of reactants and removal of products.

aerosol reactor concept Schematic of the aerosol reactor concept featuring 3 T-controlled zones for mixing, nanoparticle formation, and hydrolysis reaction.
Key objectives
  1. Thermodynamic and kinetic analysis of the combined nanoparticle formation + hydrolysis, for the purpose of determining the constrains for the design and efficient operation of the chemical reactor.
  2. Design and fabrication of a novel aerosol reactor featuring 3 temperature-controlled zones for the Zn-evaporation, steam-quenching, and Zn/H2O-reaction.
  3. Experimental demonstration of the combined process of Zn-nanoparticle formation and in-situ hydrolysis; optimization by parametric study.
  4. Theoretical modeling using coupled state-of-the-art fluid and particle dynamics accounting for nucleation, condensation, coagulation, surface reactions, and sintering; validation using experimental data.

Project-related Publications (click for abstract)

> Mechanism of Zn particle oxidation by H2O and CO2 in the presence of ZnO
Weibel D., Jovanovic Z.R., Gálvez E., Steinfeld A.
Chemistry of Materials, Vol. 26, pp. 6486-6495, 2014.
> Review of the Two-Step H2O/CO2-Splitting Solar Thermochemical Cycle Based on Zn/ZnO Redox Reactions
Loutzenhiser P., Meier A., Steinfeld A.
Materials, Vol. 3, pp. 4922-4938, 2010.
> CO2 splitting in an aerosol flow reactor via the two-step Zn/ZnO solar thermochemical cycle
Loutzenhiser P., Galvez E., Hischier I, Graf A., Steinfeld A.
Chemical Engineering Science, Vol. 65, pp. 1855-1864, 2010.
> Hydrolysis Rate of Submicron Zn Particles for Solar H2 Synthesis
Ernst F., Steinfeld A., Pratsinis S.
International Journal of Hydrogen Energy, Vol. 34, No. 3, pp. 1166-1175, 2009.
> H2 production by steam-quenching of Zn vapor in a hot-wall aerosol flow reactor
Melchior T., Piatkowski N., Steinfeld A.
Chemical Engineering Science, Vol. 64, No. 5, pp. 1095-1101, 2009.
> In-situ formation and hydrolysis of Zn nanoparticles for H2 production by the 2-step ZnO/Zn water-splitting thermochemical cycle
Wegner K., Ly H., Weiss R., Pratsinis S., Steinfeld A.
International Journal of Hydrogen Energy, Vol. 31, No. 1, pp. 55-61, 2006.
> H2 Production by Zn Hydrolysis in a Hot-Wall Aerosol Reactor
Weiss R., Ly H., Wegner K., Pratsinis S., Steinfeld A.
AIChE Journal, Vol. 51, pp. 1966-1970, 2005.
> Solar hydrogen production via a 2-step water-splitting thermochemical cycle based on Zn/ZnO redox reactions
Steinfeld A.
International Journal of Hydrogen Energy, Vol. 27, pp. 611-619, 2002.
> Solar-Processed Metals as Clean Energy Carriers and Water-Splitters
Steinfeld A., Kuhn P., Reller A., Palumbo R., Murray J., Tamaura Y.
International Journal of Hydrogen Energy, Vol. 23, No. 9, pp. 767-774, 1998.