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Solid Oxide Membrane Electrolyzer for the production of pure hydrogen
and syn-gas from a source of waste and steam

Prof. Uday B. Pal, Prof. Srikanth Gopalan, Dr. Soobhankar Pati and Mr. Michael Galbo

View a PDF presentation about the Clean Energy from Waste

An electrolyzer based on solid-oxygen-ion-conducting membrane serving as the electrolyte is used for generating high-purity hydrogen and syn-gas (mixture of CO(g), CO2(g) and H2(g)) from steam and hydro-carbon waste (such as saw dust, plastics, shredded tires, etc.).

In particular, the device employs one-end-closed yttria-stabilized zirconia (YSZ) tube at temperatures between 1000-1200 C as an oxygen-ion-conducting solid electrolyte. Liquid metal, with high solubility and diffusivity for oxygen, is contained inside the YSZ tube and function as the non-consumable anode. Nickel-yttria stabilized zirconia (Ni-YSZ) porous cermet is applied on the outer surface of the YSZ tube and used as cathode. Steam-rich feed (97% steam and 3% H2) is introduced over the Ni-YSZ cermet cathode. Waste feed containing compounds of C and H along with other impurities injected using a molybdenum alloy tube into the liquid metal anode; the molybdenum alloy tube also serves as an electrical lead for the anode. Similarly, nickel or its alloys is used as an electrical lead for the Ni-YSZ cermet cathode. Electrical potential is applied between the cathode and the anode. The applied electrical potential reduces the steam at the Ni-YSZ cermet cathode producing pure hydrogen and oxygen ions.

The hydrogen gas is collected and stored after condensing the residual steam. The oxygen ions produced at the cathode from steam migrates through the solid YSZ electrolyte tube towards the liquid-metal anode. At the YSZ/liquid metal anode interface, the oxygen ions oxidize (lose electrons) and dissolves in the liquid metal as neutral oxygen atoms ([O]). The dissolved oxygen oxidizes the waste feed (C, N, H, etc.) injected into the liquid metal to produce syn-gas. It is to be noted that the hydrogen produced at the cathode does not mix with the syn-gas produced at the anode. The applied electrical potential between the electrodes depends on the resistive and polarization losses in the electrolyzer, the desired rate of hydrogen production and the corresponding feed rate of waste. It is the objective of this research to pass 1A/cm2 through the electrolyzer cell.

This translates to producing 67 l/m2-min of hydrogen gas. By having the waste feed, the electrical energy needed to produce hydrogen from the steam feed is greatly reduced. Furthermore, the waste feed in the process also gets converted to useful syn-gas.