Tailoring the Co 3d-O 2p Covalency in LaCoO₃ by Fe Substitution To Promote Oxygen Evolution Reaction

Abstract

LaCoO 3 is an active, stable catalyst in alkaline solution for oxygen evolution reaction (OER). With lower cost, it is a potential alternative to precious metal oxides like IrO 2 and RuO 2 in water electrolysis. However, room still remains for improving its activity according to recent understandings of OER on perovskite oxides. In this work, Fe substitution has been introduced in LaCoO 3 to boost its OER performance. Density function theory (DFT) calculation verified that the enhanced performance originates from the enhanced Co 3d-O 2p covalency with 10 at% Fe substitution in LaCoO 3 . Both DFT calculations and Superconducting Quantum Design (SQUID) magnetometer (MPMS-XL) showed a Co 3+ spin state transition from generally low spin state (LS: t 2g 6 e g 0 , S = 0) to a higher spin state with the effect of 10 at% Fe substitution. X-ray absorption near-edge structure (XANES) supports DFT calculations on an insulator to half-metal transition with 10 at% Fe substitution, induced by spin state transition. The half-metallic LaCo 0.9 Fe 0.1 O 3 possesses increased overlap between Co 3d and O 2p states, which results in enhanced covalency and promoted OER performance. This finding enlightens a new way of tuning the metal−oxygen covalency in oxide catalysts for OER.

Exceptional electrocatalytic oxygen evolution via tunable charge transfer interactions in La0.5Sr1.5Ni1−xFexO4±δ Ruddlesden-Popper oxides

“…Chronoamperometry was then performed at potentials 10 mV more anodic than E p to ensure diffusion-limited intercalation. Linear regression was performed as described elsewhere 48,49 to determine the diffusion rate. Particle sizes were estimated using the surface area calculated from BET measurements and densities determined by Rietveld analysis.…”

Shifting Oxygen Charge Towards Octahedral Metal: A Way to Promote Water Oxidation on Cobalt Spinel Oxides

“…In contrast to tetrahedral bonding, the octahedral bonding of Co-O exhibits greater covalent character. [2,17] To test the hypothesis,s pinel Li 0.5 Zn 0.5 Co 2 O 4 (LZCO) and Li 0.5 Zn 0.5 Fe 0.125 Co 1.875 O 4 (LZCFO) were designed. TheC o 3 O 4 oxide shows ac harge deviation of 1.602 for Co Oct and ac harge deviation of 0.966 for O. TheC o ÀOc ovalency, which can be reflected by the charge deviation of O, is positively related to the OER activities.T he correlation well demonstrates the importance of oxygen charge distribution in OER.…”

Smart Control of Composition for Double Perovskite Electrocatalysts toward Enhanced Oxygen Evolution Reaction

“…Therefore, previous reports have focused on strategies such as the introduction of OER‐active elements into the B‐site and tailoring the oxygen defect to increase the catalytic performance. Among the transition‐metal‐based perovskite oxides (such as Mn, Fe, Co and Ni), Co‐based oxides have emerged as promising candidates owing to the outstanding OER performance of the CoO 6 octahedron . Co in a perovskite structure usually has more oxidation states (Co 2+ , Co 3+ , Co 4+ ) and spin states than Ni (Ni 2+ ) and Fe (Fe 3+ ) because the formation of high oxidation states of Ni 3+ and Fe 4+ typically require high pressures or oxidation conditions .…”

“…Among the transitionmetal-based perovskite oxides (such as Mn, Fe, Co and Ni), Cobased oxidesh ave emerged as promising candidates owing to the outstanding OER performance of the CoO 6 octahedron. [11][12][13][14][15] Co in ap erovskite structure usually has more oxidation states (Co 2 + ,C o 3 + ,C o 4 + )a nd spin states than Ni (Ni 2 + ) and Fe (Fe 3 + )b ecause the formation of high oxidation states of Ni 3 + and Fe 4 + typically require high pressures or oxidation conditions. [4,16] Co 3 + and Co 4 + cationsare beneficial for the formationo f*OH and *OOH, respectively,ina lkalinec onditions.…”