Although numerous studies on oxide catalysts for an efficient oxygen evolution reaction have been carried out to compare their catalytic performance and suggest new compositions, two significant constraints have been overlooked. One is the difference in electronic conduction behavior between catalysts (metallic versus insulating) and the other is the strong crystallographic surface orientation dependence of the catalysis in a crystal. Consequently, unless a comprehensive comparison of the oxygen-evolution catalytic activity between samples is made on a crystallographically identical surface with sufficient electron conduction, misleading interpretations on the catalytic performance and mechanism may be unavoidable. To overcome these limitations, we utilize both metallic (001) LaNiO3 epitaxial thin films together with metal dopants and semiconducting (001) LaCoO3 epitaxial thin films supported with a conductive interlayer. We identify that Fe, Cr, and Al are beneficial to enhance the catalysis in LaNiO3 although their perovskite counterparts, LaFeO3, LaCrO3, and LaAlO3, with a large bandgap are inactive. Furthermore, semiconducting LaCoO3 is found to have more than one order higher activity than metallic LaNiO3, in contrast to previous reports. Showing the importance of facilitating electron conduction, our work highlights the impact of the near-Fermi-level d-orbital states on the oxygen-evolution catalysis performance in perovskite oxides.
As chemical reactions and charge-transfer
simultaneously occur
on the catalyst surface during electrocatalysis, numerous studies
have been carried out to attain an in-depth understanding on the correlation
among the surface structure and composition, the electrical transport,
and the overall catalytic activity. Compared with other catalysis
reactions, a relatively larger activation barrier for oxygen evolution/reduction
reactions (OER/ORR), where multiple electron transfers are involved,
is noted. Many works over the past decade thus have been focused on
the atomic-scale control of the surface structure and the precise
identification of surface composition change in catalyst materials
to achieve better conversion efficiency. In particular, recent advances
in various analytical tools have enabled noteworthy findings of unexpected
catalytic features at atomic resolution, providing significant insights
toward reducing the activation barriers and subsequently improving
the catalytic performance. In addition to summarizing important surface
issues, including lattice defects, related to the OER and ORR in this
Review, we present the current status and discuss future perspectives
of oxide- and alloy-based catalysts in terms of atomic-scale observation
and manipulation.
Control of electronic states is a central issue in electrocatalysis, as it determines the charge transfer behavior for better catalytic reaction efficiency. While a variety of chemical modifications thus have...
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