Lattice Oxygen Exchange in Rutile IrO₂ during the Oxygen Evolution Reaction

Abstract

The development of efficient acidic water electrolyzers relies on understanding dynamic changes of the Ir-based catalytic surfaces during the oxygen evolution reaction (OER). Such changes include degradation, oxidation, and amorphization processes, each of which somehow affects the material’s catalytic performance and durability. Some mechanisms involve the release of oxygen atoms from the oxide’s lattice, the extent of which is determined by the structure of the catalyst. While the stability of hydrous Ir oxides suffers from the active participation of lattice oxygen atoms in the OER, rutile IrO2 is more stable and the lattice oxygen involvement is still under debate due to the insufficient sensitivity of commonly used online electrochemical mass spectrometry. Here, we revisit the case of rutile IrO2 at the atomic scale by a combination of isotope labeling and atom probe tomography and reveal the exchange of oxygen atoms between the oxide lattice and water. Our approach enables direct visualization of the electrochemically active volume of the catalysts and allows for the estimation of an oxygen exchange rate during the OER that is discussed in view of surface restructuring and subsequent degradation. Our work presents an unprecedented opportunity to quantitatively assess the exchange of surface species during an electrochemical reaction, relevant for the optimization of the long-term stability of catalytic systems.

Recent advances in understanding oxygen evolution reaction mechanisms over iridium oxide

“…1d was supported by studies using mass spectroscopy in conjunction with isotope labelling. 65,[71][72][73][74] These results allowed them to analyse the exchanging of lattice O of iridium oxide with O in the solution during the OER at steady state, and thus indicated the participation of lattice oxygen in the OER mechanism as depicted in the orangecolored cycle in Fig. 1d.…”

“…17,58,[67][68][69] (d) The orange-colored cycle involves the lattice oxygen, where the orange and black O represent the lattice oxygen and adsorbed oxygen species, respectively. 63,65,[71][72][73][74] The squares represent the initial state of each cycle, and the dashed lines indicate the dissolution path of iridium species. The (a) red, (b) blue, (c) green, and (d) orange cycles were reported for the H 2 O oxidation, while the (a) red and (c) green cycles were also reported for OH − oxidation as depicted in the figures.…”

Ruthenium Core–Shell Engineering with Nickel Single Atoms for Selective Oxygen Evolution via Nondestructive Mechanism

“…Recognizing the dominant mechanism of a catalyst for OER is a critical step to give valuable insights for designing a highly active and stable catalyst. [ 46 ] The isotope labeling experiment is one of the most accurate methods to determine the mechanism of OER. [ 11 ] In this process the labeled isotope oxygen in the electrolyte or catalyst can be chased through the mass spectrometry analysis.…”

Effect of the Morphology of the High-Surface-Area Support on the Performance of the Oxygen-Evolution Reaction for Iridium Nanoparticles

“…A correlation of the degree of TiO 2 crystallinity and the OER performance indicates that TiO 2 crystallinity could play an important role at higher OER potentials/current densities ( Figure 7 ), which would be in line with the better electrochemical stability of the crystalline TiO 2 in comparison to the amorphous variant. 36 , 70 − 72 If not stabilized properly, the TiO 2 layer can become too thick for efficient electron conductance/tunneling.…”

“… 57 Even though additional dedicated studies are needed to investigate this effect further, it is reasonable to expect that the crystallinity of TiO 2 would play an important role, based on studies of oxide analogues. 36 , 70 − 72 …”