In-situ Formation and Hydrolysis of Zn Nanoparticles for H2 Production

Participants:

• ETH (CH)

• PSI (CH)

Duration:

• January 1, 2005 - December 31, 2007

Contact:

• Aldo Steinfeld, aldo.steinfeld@eth.ch
• Sotiris Pratsinis, pratsinis@ivuk.mavt.ethz.ch

Objective

Project aimed at the development of the Zn hydrolysis reactor.  

Background

The production of solar hydrogen with the Zn/ZnO water-splitting thermochemical cycle consists of a 1st-step solar endothermic dissociation of ZnO and a 2nd-step non-solar exothermic hydro-lysis of Zn.

Achievements in 2006

A novel combined process for the efficient execution of the 2nd step of the ZnO/Zn thermochemical cycle encompasses the formation of Zn nanoparticles followed by their in-situ hydrolysis for H2 generation. The reactor, features three temperature-controlled zones: 1) a mixing zone where separate streams of Zn vapor and steam are brought together and efficiently mixed; 2) a nanoparticle formation zone, where Zn vapor is steam-cooled below its satu-ration temperature to form nanodroplets and/or nanoparticles, and 3) a hydrolysis reaction zone, where Zn nanodrop-lets/nanoparticles react with steam to generate H2 and ZnO(s). This combined process is experimentally demonstrated using a tubular aerosol-flow reactor. The reactor was operated conti-nuously at 1 bar and 623-1023 K, yielding up to 90% chemical conversion for a residence time of about 1 second, and pro-ducing nanoparticles with mean crystallite sizes in the 40-100 nm range.

Left: Experimental setup of the aerosol-flow reactor for the co-production of H2 and Zn/ZnO particles by in-situ formation and hydrolysis of Zn aerosol, featuring three temperature-controlled zones for evaporation/mixing, cooling, and chemical reaction. Right: Molar rates of Zn evaporation and H2 production at 973 K, yielding up to 90% chemical conversion.

Publications:

• Weiss R., Ly H., Wegner K., Pratsinis S., Steinfeld A. (2006) H2 Production by Zn Hydrolysis in a Hot-Wall Aerosol Reactor, AIChE Journal 51, 1966-1970.

• Ernst F., Tricoli A., Steinfeld A., Pratsinis S.E. (2006) Co-Synthesis of H2 and ZnO by in-situ Zn Aerosol Formation and Hydrolysis, AIChE Journal 52, 3297-3303.