SNF-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 1^st-step solar endothermic dissociation of ZnO and a 2^nd-step non-solar exothermic hydrolysis of Zn :

1^st step dissociation (solar): ZnO → Zn + 0.5 O₂(1)

2^nd step hydrolysis (non-solar): Zn + H₂O → ZnO + H₂(2)

Fig. 1: 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 2^nd 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.

Fig. 2: Schematic of the aerosol reactor concept featuring 3 T-controlled zones for mixing, nanoparticle formation, and hydrolysis reaction.

Key objectives

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.
Design and fabrication of a novel aerosol reactor featuring 3 temperature-controlled zones for the Zn-evaporation, steam-quenching, and Zn/H₂O-reaction.
Experimental demonstration of the combined process of Zn-nanoparticle formation and in-situ hydrolysis; optimization by parametric study.
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