Synthesis and reversible oxidation/reduction behavior of delafossite-type CuCr1−x Al x O2

The oxygen storage capacity (OSC) and oxidation–reduction properties of CuCr1−x Al x O2 with the delafossite-type structure were investigated. Solid solutions with the delafossite-type structure were synthesized by a solid-state reaction route at 1100–1150 °C in N2 atmosphere. The substitution of Al3+ for Cr3+ in CuCrO2 suppressed OSC and enhanced its stability to heat treatments under cyclic oxidative/reductive atmosphere. Under 5% H2/He atmosphere, the delafossite phase was reduced to a mixture containing Cu and a corundum-type Cr2O3 solid solution (x = 0–0.3). In the region with x = 0.5–0.9, metallic Cu and delafossite phase coexisted. Following repetitive reduction by H2-pulse injection, a transition alumina phase was detected. The transformation between delafossite- and spinel-type structures can occur without significant diffusion of atoms, and therefore, the cyclic oxidation/reduction of CuCr1−x Al x O2 delafossite is reversible. These results suggested that the reduction of CuCr1−x Al x O2 is the key step in the reversible oxygen storage/release process.