Efficient oxygen evolution electrocatalysis in acid by a perovskite with face-sharing IrO6 octahedral dimers

Abstract

The widespread use of proton exchange membrane water electrolysis requires the development of more efficient electrocatalysts containing reduced amounts of expensive iridium for the oxygen evolution reaction (OER). Here we present the identification of 6H-phase SrIrO₃ perovskite (6H-SrIrO₃) as a highly active electrocatalyst with good structural and catalytic stability for OER in acid. 6H-SrIrO₃ contains 27.1 wt% less iridium than IrO₂, but its iridium mass activity is about 7 times higher than IrO₂, a benchmark electrocatalyst for the acidic OER. 6H-SrIrO₃ is the most active catalytic material for OER among the iridium-based oxides reported recently, based on its highest iridium mass activity. Theoretical calculations indicate that the existence of face-sharing octahedral dimers is mainly responsible for the superior activity of 6H-SrIrO₃ thanks to the weakened surface Ir-O binding that facilitates the potential-determining step involved in the OER (i.e., O* + H₂O → HOO* + H⁺ + e_¯).

Fig. 1

Crystal structure and electronic structure of 6H-SrIrO₃. a Crystal structure of 6H-SrIrO₃. b A local connection pattern of IrO₆ octahedra, in which face-sharing IrO₆ octahedral dimers and corner-sharing, isolated IrO₆ octahedron are shown. c Local ball-and-stick model of 6H-SrIrO₃, in which typical Ir–Ir and Ir–O bond lengths are presented. d Plot of electron location function for Ir–Ir bonding in 6H-SrIrO₃. e Density of states of 6H-SrIrO₃, in which the Fermi level is 0 eV

Fig. 2

Structural characterizations of 6H-SrIrO₃. a, XRD pattern with a refinement plot of 6H-SrIrO₃. b, SEM image of 6H-SrIrO₃. Scale bar, 2 µm. c, HRTEM image of 6H-SrIrO₃. Scale bar, 5 nm. Inset: the corresponding fast Fourier transform image

Fig. 3

Electrocatalytic properties for OER of 6H-SrIrO₃. a Polarization curves of 6H-SrIrO₃ and IrO₂ in 0.5 M H₂SO₄ solution with 85% iR-compensations. The current densities are normalized by the geometric area. b Comparison of mass activity, normalized by the mass of iridium at 1.525 V vs. RHE, of 6H-SrIrO₃, IrO₂, 3C-SrIrO₃, and some Ir-containing catalysts reported recently. The error bar represents standard deviation based on five measurements. c Chronopotentiometric curves for OER in the presence of 6H-SrIrO₃ and 3C-SrIrO₃ in 0.5 M H₂SO₄ solution at 10 mA cm⁻²_geo (without iR compensations). d Percentage of total Sr content leached (or deviated from the stoichiometry) in the solution after 30 h-long catalytic stability test in the presence of 6H-SrIrO₃ and 3C-SrIrO₃. e, f HRTEM images for 6H-SrIrO₃ and 3C-SrIrO₃ after 30 h-long catalytic stability test. Scale bars, 5 nm

Fig. 4

Theoretical understanding of electrocatalytic activity for OER of 6H-SrIrO₃. a Side and b top views of the surface-I of 6H-SrIrO₃; c Side and d top views of the surface-II of 6H-SrIrO₃; free-energy diagrams of four elementary reaction steps for the OER on e the surface-I and f surface-II of 6H-SrIrO₃ at the different applied potentials. The optimized structures of HO, O, and HOO adsorptions on the surface-I and surface-II are also shown in e and f