High-stability, high-capacity oxygen carriers: Iron oxide-perovskite composite materials for hydrogen production by chemical looping

Cristina Dueso,Claire Thompson,Ian Metcalfe

doi:10.1016/j.apenergy.2015.05.062

Abstract

Iron oxide has been widely used as an oxygen carrier material (OCM) for hydrogen production by chemical looping due to its favourable thermodynamic properties. In spite of this, iron oxide loses much of its activity after redox cycling mainly due to sintering and agglomeration. Perovskites, such as La0.7Sr0.3FeO3-δ (LSF731), have been suggested as potential candidate OCMs for hydrogen production due to their excellent oxygen transport properties and stability under cycling. However, hydrogen production per cycle for a similar carrier weight is lower than with iron oxide. This work proposes the use of composite OCMs made of iron oxide clusters embedded in an LSF731 matrix. The perovskite matrix facilitates oxygen transport to the iron oxide clusters while preventing agglomeration. Two preparation methods, mechanical mixing and a modified Pechini method, were used to obtain composite materials with different iron oxide weight fractions, 11 and 30wt.%. The reactivity of these OCMs was studied in a thermogravimetric analyser. Hydrogen production and carrier stability were investigated in a microreactor over 25 redox cycles while periodically feeding carbon monoxide and water in order to produce carbon dioxide and hydrogen in separate streams. Hydrogen production was stable over 25 cycles for LSF731 and the composite OCM with 30wt.% iron oxide produced by the modified Pechini method but iron oxide particles alone underwent a decrease in the hydrogen production with cycling. The hydrogen production during the 25th cycle was eight times higher for the composite material than for iron oxide alone and four times higher than for LSF731. The hydrogen production was therefore also higher than that expected from a simple combination of the iron oxide and LSF731 alone, indicating a synergetic effect whereby the LSF731 may have a higher effective oxygen capacity when in the form of the composite material.

Highlights

Chemical looping hydrogen production typically utilises iron oxide as an oxygen carrier as this material has several thermodynamically favourable phase changes that can be exploited [1,2,3,4]
The elemental composition of the oxygen carrier material (OCM) was studied by EDX analyses which proved that the desired composite structure, encapsulating iron oxide in an LSF731 matrix, was obtained using both preparation methods
The behaviour of several OCMs composed of LSF731 and iron oxide for hydrogen production by chemical looping was investigated

Summary

Introduction

Chemical looping hydrogen production typically utilises iron oxide as an oxygen carrier as this material has several thermodynamically favourable phase changes that can be exploited [1,2,3,4]. In this process a carbonaceous fuel, here carbon monoxide, is used. Water is used to re-oxidise the iron and produce hydrogen. This is performed in a cyclic manner.

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Results

Conclusion