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An efficiently tuned d-orbital occupation of IrO₂ by doping with Cu for enhancing the oxygen evolution reaction activity.

ABSTRACT: The oxygen evolution reaction (OER) has been regarded as a key half reaction for energy conversion technologies and requires high energy to create O[double bond, length as m-dash]O bonds. Transition metal oxides (TMOs) seem to be a promising and appealing solution to the challenge because of the diversity of their d-orbital states. We chose IrO₂ as a model because it is universally accepted as a current state-of-the-art OER catalyst. In this study, copper-doped IrO₂, particularly Cu_0.3Ir_0.7O _? , is shown to significantly improve the OER activity in acidic, neutral and basic solutions compared to un-doped IrO₂. The substituted amount of Cu in IrO₂ has a limit described by the Cu_0.3Ir_0.7O _? composition. We determined that the performance of Cu_0.3Ir_0.7O _? is due primarily to an increase in the Jahn-Teller effect in the CuO₆ octahedra, and partially to oxygen defects in the lattice induced by the IrO₆ octahedral geometric structure distortions, which enhance the lift degeneracy of the t_2g and e_g orbitals, making the d _z² orbital partially occupied. This phenomenon efficiently reduces the difference between ?G2 and ?G3 in the free energy from the density functional theoretical (DFT) calculations and can yield a lower theoretical overpotential comparable to that of IrO₂. The proposed method of doping with foreign elements to tune the electron occupation between the t_2g and e_g orbital states of Ir creates an opportunity for designing effective OER catalysts using the TMO groups.

SUBMITTER: Sun W

PROVIDER: S-EPMC6088437 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

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An efficiently tuned d-orbital occupation of IrO2 by doping with Cu for enhancing the oxygen evolution reaction activity.

Sun Wei W Song Ya Y Gong Xue-Qing XQ Cao Li-Mei LM Yang Ji J

Chemical science 20150612 8

The oxygen evolution reaction (OER) has been regarded as a key half reaction for energy conversion technologies and requires high energy to create O[double bond, length as m-dash]O bonds. Transition metal oxides (TMOs) seem to be a promising and appealing solution to the challenge because of the diversity of their d-orbital states. We chose IrO2 as a model because it is universally accepted as a current state-of-the-art OER catalyst. In this study, copper-doped IrO2, partic ...[more]

PMID: 30155005

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Project description:Anionic redox reactions attributed to oxygen have attracted much attention as a new approach to overcoming the energy-density limits of cathode materials. Several oxides have been suggested as new cathode materials with high capacities based on anionic (oxygen) redox reactions. Although most still have a large portion of their capacity based on the cationic redox reaction, lithia-based cathodes present high capacities that are purely dependent upon oxygen redox. Contrary to Li-air batteries, other systems using pure oxygen redox reactions, lithia-based cathodes charge and discharge without a phase transition between gas and condensed forms. This leads to a more stable cyclic performance and lower overpotential compared with those of Li-air systems. However, to activate nanolithia and stabilize reaction products such as Li2O2 during cycling, lithia-based cathodes demand efficient catalysts (dopants). In this study, Ir based materials (Ir and Li2IrO3) were introduced as catalysts (dopants) for nanolithia composites. Oxide types (Li2IrO3) were used as source materials of catalyst because ductile metal (Ir) can hardly be pulverized during the milling process. Two types of Li2IrO3 were prepared and used for catalyst-sources. They were named '1-step Li2IrO3' and '2-step Li2IrO3', respectively, since they were prepared by '1-step' or '2-step' heat treatment. The nanocomposites prepared using lithia & 2-step Li2IrO3 presented a higher capacity, more stable cyclic performance, and lower overpotential than those of the nanocomposites prepared using lithia & 1-step Li2IrO3. The voltage profiles of the nanocomposites prepared using lithia & 2-step Li2IrO3 were stable up to a limited capacity of 600 mAh·g-1, and the capacity was maintained during 100 cycles. XPS analysis confirmed that the capacity of our lithia-based compounds is attributable to the oxygen redox reaction, whereas the cationic redox related to the Ir barely contributes to their discharge capacity.

Dataset Information

An efficiently tuned d-orbital occupation of IrO₂ by doping with Cu for enhancing the oxygen evolution reaction activity.

Publications

An efficiently tuned d-orbital occupation of IrO<sub>2</sub> by doping with Cu for enhancing the oxygen evolution reaction activity.

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