In Situ Activation Endows Orthorhombic Fluorite-Type Samarium Iridium Oxide with Enhanced Acidic Water Oxidation

Abstract

Developing electrochemical catalysts for acidic water oxidation with improved activity and stability has been the key to the further popularization of proton exchange membrane electrolyzers. In this work, an orthorhombic fluoritetype samarium iridium oxide (Sm 3 IrO 7 ) catalyst is synthesized by a simple solidstate reaction. After in situ activation, the as-prepared Sm 3 IrO 7 exhibits higher mass activity and durability than that of commercial IrO 2 . The in-depth analyses indicate the formation of amorphous IrO x species on the surface to evolve to a new heterostructure IrO x /Sm 3 IrO 7 , along with Sm leaching during the in situ activation process. More importantly, strong electronic interactions exist between newborn IrO x species and remaining Sm 3 IrO 7 , leading to the compressed Ir−O bonds in IrO x compared to commercial IrO 2 , thus reducing the energy barrier for oxygen evolution reaction (OER) intermediates to improve the OER process. Based on the above-mentioned analyses, it is speculated that the actual active species for enhanced acidic water oxidation should be IrO x /Sm 3 IrO 7 , rather than Sm 3 IrO 7 itself. Theoretical calculations confirm that the optimal energy level path of IrO x /Sm 3 IrO 7 follows the lattice oxygen mechanism, and the energy level of surface Ir 5d orbitals is lower than O 2p orbitals in IrO x /Sm 3 IrO 7 , enabling it a superior OER activity.

Two‐Dimensional Amorphous Iridium Oxide for Acidic Oxygen Evolution Reaction

“…Based on comprehensive consideration, Ir‐based catalysts are still the first choice for acidic OER [22–24] . However, Ir‐based materials are limited by their scarce reserves and high prices [25–27] . Therefore, the design of acidic Ir‐based OER catalysts with high‐performance and high atom utilization has become the main direction to solve this problem [28–30] …”

“…[22][23][24] However, Ir-based materials are limited by their scarce reserves and high prices. [25][26][27] Therefore, the design of acidic Ir-based OER catalysts with high-performance and high atom utilization has become the main direction to solve this problem. [28][29][30] Two-dimensional (2D) catalysts have ultra-high atom utilization and unique catalytic performance due to their special structure, [31,32] which helps alleviate the scarcity and expense of Ir.…”

Unraveling the Most Relevant Features for the Design of Iridium Mixed Oxides with High Activity and Durability for the Oxygen Evolution Reaction in Acidic Media

“…After several OER cycles, such an active framework evolves into an amorphous layer with low conductivity, that is the main cause for the decreased of the OER activity . In Sm 3 IrO 7 , also IrO x is formed at the surface (Figure d) …”

“…116 In Sm 3 IrO 7 , also IrO x is formed at the surface (Figure 8d). 92 Ruddlesden−Popper Sr 2 IrO 4 reconstructs in corner-shared and under-coordinated IrO 6 octahedra, responsible for their high activities. 91 Finally, in oxides such as Ca 4 IrO 6 and Sr 4 IrO 6 , in which the IrO 6 octahedra are completely isolated with no connection between them, a rapid disintegration of the crystal lattice can be anticipated if Ca and Sr leach out in an acid solution.…”

Strategies for the design of ruthenium-based electrocatalysts toward acidic oxygen evolution reaction

“…However, the anodic OER is a complex multi-step reaction and involves four-electron transfer, leading to a much higher energy expenditure to surmount the kinetic barrier than HER. 24,25 To date, substantial OER catalysts, including alloys, metal oxides, pyrochlores, and perovskites, have been developed to improve anodic electrode kinetics and stability. [26][27][28] However, on account of the thermodynamic unsteadiness of non-noble metal elements under harsh acidic OER operation conditions, the most promising acidic OER catalysts are restricted to precious metals at the present stage.…”