Identification of the Active-Layer Structures for Acidic Oxygen Evolution from 9R-BaIrO₃ Electrocatalyst with Enhanced Iridium Mass Activity

Abstract

Iridium-based perovskites show promising catalytic activity for oxygen evolution reaction (OER) in acid media, but the iridium mass activity remains low and the active-layer structures have not been identified. Here, we report highly active 1 nm IrO x particles anchored on 9R-BaIrO3 (IrO x /9R-BaIrO3) that are directly synthesized by solution calcination followed by strong acid treatment for the first time. The developed IrO x /9R-BaIrO3 catalyst delivers a high iridium mass activity (168 A gIr –1), about 16 times higher than that of the benchmark acidic OER electrocatalyst IrO2 (10 A gIr –1), and only requires a low overpotential of 230 mV to reach a catalytic current density of 10 mA cm–2 geo. Careful scanning transmission electron microscopy, synchrotron radiation-based X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy analyses reveal that, during the electrocatalytic process, the initial 1 nm IrO x nanoparticles/9R-BaIrO3 evolve into amorphous Ir4+O x H y /IrO6 octahedrons and then to amorphous Ir5+O x /IrO6 octahedrons on the surface. Such high relative content of amorphous Ir5+O x species derived from trimers of face-sharing IrO6 octahedrons in 9R-BaIrO3 and the enhanced metallic conductivity of the Ir5+O x /9R-BaIrO3 catalyst are responsible for the excellent acidic OER activity. Our results provide new insights into the surface active-layer structure evolution in perovskite electrocatalysts and demonstrate new approaches for engineering highly active acidic OER nanocatalysts.

Experimental correlation of Mn3+cation defects and electrocatalytic activity of α-MnO2– an X-ray photoelectron spectroscopy study

“…212–219 However, herein we employed 0.0709 mF cm −2 for C s corresponding to the areal capacitance of the bare GC disk electrode, that is, the substrate electrode for the preparation of α-MnO 2 -AB thin-film WEs. 17 On the other hand, according to McCrory et al , 157 for metal oxide catalysts in NaOH and KOH solutions C s values ranging from 0.022 mF cm −2 to 0.130 mF cm −2 are reported, 220–232 thus the C s value based on the bare GC disc electrode, that was used in our work, is well within this range. However, since original (untreated) data to all double-layer capacitance measurements is provided in the ESI† to this manuscript, it will be straightforward for other groups to convert to ECSAs based on other C s values, or the specific capacitance of an atomically flat α-MnO 2 surface, which will possibly be determined in a future study, respectively.…”

“…[212][213][214][215][216][217][218][219] However, herein we employed 0.0709 mF cm À2 for C s corresponding to the areal capacitance of the bare GC disk electrode, that is, the substrate electrode for the preparation of a-MnO 2 -AB thin-lm WEs. 17 On the other hand, according to McCrory et al, 157 for metal oxide catalysts in NaOH and KOH solutions C s values ranging from 0.022 mF cm À2 to 0.130 mF cm À2 are reported, [220][221][222][223][224][225][226][227][228][229][230][231][232] thus the C s value based on the bare GC disc electrode, that was used in our work, is well within this range. However, since original (untreated) data to all This journal is © The Royal Society of Chemistry 2022…”

Enhanced oxygen evolution catalyzed by in situ formed Fe-doped Ni oxyhydroxides in carbon nanotubes

“…[5][6][7][8] The current commercial noble metal based oxides are recognized as state-of-the-art catalysts because of their high activity and selectivity towards the OER, but their high cost and scarcity severely limit large-scale utilization. 9,10 This has led to exploring high-efficiency, cost-effective and robust non-noble metal based OER electrocatalysts to provide the basis for application of water electrolysis toward attaining a cleaner environment.…”

Iridium nanohollows with porous walls for acidic water splitting

“…[11][12][13][14][15][16] However, the scarcity of Ir has posed severe limitations to the widespread application of PEMWEs in terms of both cost and supply constraints, which has motivated considerable research efforts to upgrade Ir-based OER electrocatalysts. [17][18][19][20][21][22] A widely-adopted upgrading strategy is to alloy Ir with other elements. [23][24][25][26][27][28][29] The selection of alloying elements has been mainly guided by an energetic-descriptor-based approach to pursue an optimal adsorption of OER intermediates, with transition metals being the most popular candidates.…”

“…11–16 However, the scarcity of Ir has posed severe limitations to the widespread application of PEMWEs in terms of both cost and supply constraints, which has motivated considerable research efforts to upgrade Ir-based OER electrocatalysts. 17–22…”