(95h) Perovskite Microtubular Membranes for Hydrogen Production From Water Splitting

Here we present promising results for pure hydrogen production by chemically-driven water splitting using perovskite membranes. Steam is fed to one side of the oxygen ion and electron conducting perovskite membrane at high temperature (900°C). The water molecule dissociates on the membrane surface producing oxygen and hydrogen. The oxygen is transported through the membrane, as oxygen ions via mobile oxygen vacancies, shifting equilibrium in the direction of dissociation. The oxygen ions are then removed on the other side of the membrane using a reducing sweep gas.  The reaction of this reducing gas with water provides the overall driving force for reaction and permeation. This project aims to develop and characterise hollow fibre perovskite membranes (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ) and subsequently test them for hydrogen production by the water splitting reaction using methane as a reducing gas. The overall reaction is the steam reforming of methane.

La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) hollow fibre membranes of 1.5 mm external diameter and 250µm wall thickness were prepared by phase inversion followed by sintering at high temperature (1300°C). Initially, an oxygen permeation experiment was carried out in order to test the oxygen flux through the hollow-fibres; as expected the oxygen permeation rates had a dependence on temperature and sweep gas flow-rates. Membrane-based hydrogen production experiments were carried out after successfully demonstrating that the membranes could permeate oxygen. From the membrane-based hydrogen production experiment, it was found that hydrogen could be produced continuously by membrane-based steam reforming for more than 250 hours, demonstrating high stability of the membranes under reaction conditions. At the same time as hydrogen was produced by water splitting on one side of the membrane, hydrogen, carbon dioxide and carbon monoxide were produced on the other side, as a result of the oxidation of methane, indicating that hydrogen production by water splitting occurs because of oxygen transport across the membrane and not just surface reaction with the perovskite. This is confirmed by performing detailed carbon, hydrogen and oxygen material balances.

Acknowledgements

We wish to acknowledge the support of the EPSRC SUPERGEN programme through grant EP/G01244X/1 and the group of Professor Kang Li of Imperial College London for supplying the membranes.