Anomalous Increases in H2O2 Production by Strained Ni(III) Centers during Electrocatalytic Oxygen Reduction on LaCr1–xNixO3

The electrochemical oxygen reduction reaction (ORR) plays a critical role in energy storage and conversion technologies and may provide a viable method for sustainable generation of H₂O₂ for industrial use, but our understanding of the ways in which the catalyst structure alters reaction selectivity remains incomplete. Analysis of LaCr_1–xNi_xO₃ by X-ray diffraction and X-ray absorption spectroscopy reveals three stages of structural evolution across the composition series. The first stage is characterized by a blend of Ni(II) and Ni(III) residing within a distinct LaCrO₃ lattice, with an increasing proportion of Ni(III) as Ni content increases. Continued increases in Ni content induce substantial structural rearrangement that culminates in a phase transition from a Pnma lattice to R3̅c, all of which occur with negligible changes in the average Ni-oxidation state. Following the phase transition, the Ni(III) content continues to increase as the lattice compresses. Diverging reaction selectivity trends for Ni-rich and Cr-rich samples establish a narrow composition range of maximal H₂O₂ selectivity, with highly strained Ni(III) sites present within a LaCrO₃ lattice found to be particularly selective for H₂O₂ production during the ORR. We attribute the selectivity enhancements in Cr-rich samples to strain-induced alteration of the crystal field splitting for Ni(III) centers.