Yildiz Technical University (YTU), Department of Chemical Engineering, Istanbul, Turkey
Centre for Research & Technology Hellas/Chemical Process & Energy Resources Institute (CERTH), Thessaloniki, Greece
Hydrogen production from H2S decomposition in micro-structured proton-conducting solid oxide membrane reactors
Hydrogen has the potential to become the future energy “currency”. H2S that is abundantly found in Black Sea waters can be considered as an important H2 source. Black Sea is unique because 90% of its water is anaerobic and contains H2S. Apart from the harmful effects to human health and ecosystems, the H2S in the Black Sea may serve as a future energy source.
Hydrogen production from Black Sea consists of the following steps: a) pumping of sea water at ~1000m depth, b) extraction of concentrated H2S/H2O mixtures, c) decomposition of H2S to H2 and S. The decomposition of H2S to H2 can be achieved using various technologies, amongst other s by electrochemical methods, this process operates at intermediate temperatures (700-1000 K).
The H2S-PROTON project addressed the priority “Hydrogen production from H2S rich Black Sea Water”, aiming to develop a micro-structured proton conducting electrochemical membrane reactor to enable the efficient exploitation of Black Sea’s water for H2 production. This approach has the potential to deliver substantial quantities of H2 to regional countries, helping them to take part in the forthcoming “H2 economy”
The Concept: Stable ceramic H+ conductors that operate between 700-1000 K are widely investigated at present, because they can be used in electrochemical reactors and fuel cells. Both types of cells consist of a dense solid electrolyte membrane and two porous electrodes. The anode is exposed to a H2 containing gas. The cathode is exposed to either an inert gas or to air. In the proposed process the anode is exposed to the concentrated H2S/H2O mixture (0.1-1% H2S) and catalyze the decomposition of H2S to H+ and S.
Protons are transferred through the membrane to the cathode, where they are converted either to H2 (pumping mode) or to H2O generating power (fuel cell mode). The generated sulphur will react with excess H2O to SO2/SO3 and further to H2SO4. The present concept with H+ conducting membranes is new. Its advantage is based on its poly-generation approach in a single micro-structured device.
In the project several materials for anodes, cathodes and electrolyte membrane, building the electrochemical cell on a porous support, were developed. Stable anode layers based on Co-CeO2 showed high activity in H2S decomposition while having a high electrical conductivity. As cathode material the perovskite LSCF was selected. The material for the electrolyte membrane was Yttrium-doped Barium zirconate (BZY), several parameters like grain size distribution, composition of the paste for coating had to be optimized. As construction material for the design of the microstructured cell and the porous support Nicrofer 3220 was selected. To enhance the corrosion resistance in sulphurous atmosphere protective coatings of Al2O2, SiO2 and ZrO2-Y2O3 (YSZ) were deposited by Magnetron-Sputtering and Plasma Enhanced Chemical Vapor Deposition (PECVD). At the end of the project a complete electrochemical cell was successfully built by sequential coating and sintering.
D.Ipsakis, Tz.Kraia, G.E.Marnellos, M.Ouzounidou, S.Voutetakis, R.Dittmeyer, A.Dubbe, K.HaasSanto, M.Konsolakis, H.E.Figen, N.O.Guldal, S.Z.Baykara, An Electrocatalytic Membrane-assisted Process for Hydrogen Production from H2S in Black Sea: Preliminary Results, International Journal of Hydrogen Energy Volume 40, Issue 24, p.7530-7538 (2015)