Oxygen storage-release behavior of delafossite-type CuCr sub(1-x )M sub( x )O sub(2) (M = Fe, Ga)

The oxygen storage capacity (OSC) and oxidation-reduction properties of delafossite-type CuCr sub(1-x )M sub( x )O sub(2) (M = Fe and Ga) were investigated. The solid solutions having 3R-type delafossite-type structure were synthesized by a solid-state reaction method at 860-1100 degree C in N sub(2) atmosphere. Substitution of Fe super(3+) and Ga super(3+) into Cr super(3+) site of CuCrO sub(2) improved their OSC and stability under cyclic oxidative/reductive atmosphere. CuCr sub(0.5)Fe sub(0.5)O sub(2) and CuCr sub(0.3)Ga sub(0.7)O sub(2) exhibited the largest OSC for M = Fe and Ga, respectively. The thermogravimetry in an oxidative atmosphere and XRD analyses revealed that CuCr sub(1-x )M sub( x )O sub(2) oxidized to Cu(Cr sub(1-x )M sub( x )) sub(2)O sub(4) spinel and CuO. Under 5 % H sub(2)/He atmosphere, CuCr sub(1-x)Fe sub(x)O sub(2) was reduced to Cu and (Cr, Fe) sub(3)O sub(4) spinel phase, which was eventually reduced to Fe and Cr sub(2)O sub(3). In the M = Ga system, the delafossite phase was reduced to Cu + Cr sub(2)O sub(3) solid solution (x = 0-0.1) or Cu + Ga sub(2)O sub(3) solid solution (x = 0.9-1.0). In the region x = 0.3-0.7, metallic Cu was formed, coexisting with the delafossite phase, without the formation of Cr and Ga oxides. These results suggest that oxygen release behaviors were attributed to reductive decomposition for CuCr sub(1-x )Fe sub( x )O sub(2) and deposition of Cu from the delafossite phase maintaining the structure for CuCr sub(1-x )Ga sub( x )O sub(2) (x = 0.3-0.7).