Elucidating intrinsic contribution of d-orbital states to oxygen evolution electrocatalysis in oxides

Abstract

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.

Mechanistic insight into the active centers of single/dual-atom Ni/Fe-based oxygen electrocatalysts

“…5c ), in which the catalysts containing paramagnetic Fe species (NiFe-CNG) show quite different DOS structures. Their spin-up and spin-down components around the Fermi level are strongly fluctuant after connecting with the bridging oxygen atoms, leading to remarkable electronic perturbation 69 . The above discussion implies that the synergistic effect of Ni and Fe through the presence of Fe-O-Ni bonds in NiFe-CNG is a key prerequisite for high OER activity 70 , 71 .…”

The electronic structure of transition metal oxides for oxygen evolution reaction

“…Yun and co-workers recently found that semiconducting LaCoO 3 has an intrinsic OER activity more than one order of magnitude higher than that of metallic LaNiO 3 , in contrast to previous reports. 154 The group of authors showed that misleading interpretations could be avoided by using very thin lms of the catalyst on conducting interlayer as samples.…”

Comparison of Fe-enhanced oxygen evolution electrocatalysis in amorphous and crystalline nickel oxides to evaluate the structural contribution

“…As all the thin films in this work were fabricated by a sol–gel process, 19 both amorphous and perovskite-type crystalline nickelates could be easily acquired by optimal control of annealing temperature. Fig.…”

“…6–11 One of the major directions to achieve better OER electrocatalysis in these oxide-based materials is searching for new transition-metal compositional combinations. 12–19 Since the initial milestone report in 1987 by Corrigan, 20 who demonstrated that Fe impurities dramatically boost the OER activity in Ni, a significant number of studies have been carried out in Ni- and Co-based oxides and hydroxides to elucidate the role of Fe and its neighboring atoms as active sites. 13,14,19,21–30 As specifically shown in layered (oxy)hydroxides, 21,22,25 notable examples reveal remarkable enhancement of more than an order of magnitude in OER activity via Fe addition.…”