Metal–Support Interaction Can Deactivate IrO_x/Sb:SnO₂ OER Catalysts in Polyol Process

Abstract

Only a few materials can remain undissolved under working conditions for the oxygen evolution reaction (OER) in acidic media, which limits the choice of catalysts and supports. One of the practical catalyst/support candidates is IrO x /Sb:SnO2 (Ir/ATO) because both components are thermodynamically stable under low-pH anodic conditions. Moreover, between Ir and ATO, a strong metal–support interaction is present, thereby allowing for long-lasting OER activity unless the support degrades. However, we demonstrate that the strong interaction can paradoxically deactivate Ir/ATO structures when synthesizing them using the polyol process. We reveal that the strong interaction in the presence of polyol at elevated temperatures can cause the reduction of the Sb dopant to zero-valency. Findings show that the varied oxidation state of the dopant decreases the electrical conductivity of the Ir/ATO, impeding the electron transfer through the support, hence deteriorating electrocatalytic activity toward the OER.

IrO2/Ir Composite Nanoparticles (IrO2@Ir) Supported on TiNxOy Coated TiN: Efficient and Robust Oxygen Evolution Reaction Catalyst for Water Electrolysis

“…Hence, the formation of amorphous phase possibly takes place through hydrolysis of intermediate Ir‐hydroxide species (leading to formation of amorphous Ir‐Oxide) followed by reduction of the surface to metallic Ir. Such a formation of lower oxidation state Ir species (e. g. Ir + ) under microwave‐assisted heating to higher temperatures (>140 °C) in presence of ethylene glycol has also been reported previously [43] …”

“…Such a formation of lower oxidation state Ir species (e. g. Ir + ) under microwave-assisted heating to higher temperatures (> 140 °C) in presence of ethylene glycol has also been reported previously. [43] Further, the high-resolution Ti 2p XPS spectra of TiN with/ without Ir loading (Figure 4b) could be deconvoluted into a pair of two the spin-orbital components corresponding to Ti 2p 3/2 and Ti 2p 1/2. Each of the spin-orbital component consists of two sub-components ascribed to the TiÀ N and TiO x N y at the respective binding energies of ~455.7 and ~457.9 eV for the Ti 2p 3/2 component, where for the latter, both N and O are bound to Ti (OÀ TiÀ N), instead of a TiÀ NÀ O or TiÀ OÀ N bonds.…”

Iridium-based catalysts for oxygen evolution reaction in acidic media: Mechanism, catalytic promotion effects and recent progress

“…In addition to the carbon-based materials, metal oxides were also employed as substrate materials in the catalyst construction, and there are also strong charge redistribution and migration of support oxide species to the metal surface between the metal and metal oxide supports [204,205]. The presence of such interactions could also improve the catalytic stability of supported Ir-based materials under OER conditions [206]. For instance, a composite catalyst of IrO x -TiO 2 -Ti (ITOT) was developed by depositing IrO x nanoparticles on the surface of titanium-based nanorods, and good OER activity and long-term stability were observed in acidic conditions due to the presence of a large amount of active OH species and mixed valence of IrO x on its surface.…”

Iridium Stabilizes Ceramic Titanium Oxynitride Support for Oxygen Evolution Reaction

“…Therefore, there is a strong incentive to minimize the amount of currently still irreplaceable iridium in the catalyst layer and enhance its activity and durability. , Following the main concepts of fuel cells and platinum-based catalysts, most approaches for decreasing the loading of iridium are based on synthesizing catalyst core–shell morphologies with minimal Ir content − by alloying iridium with other metals ,− or by mixing iridium nanoparticles with less expensive oxides of earth-abundant elements . Especially effective is dispersing iridium nanoparticles on a high-surface-area support. ,− However, supported OER catalysts represent a multidimensional platform encompassing many unresolved phenomena such as support electroconductivity, metal–support interactions, support morphology, and stability, , to name a few. All of these can potentially influence electrochemical performance.…”

“…14 Especially effective is dispersing iridium nanoparticles on a high-surface-area support. 8,15−24 However, supported OER catalysts represent a multidimensional platform encompassing many unresolved phenomena such as support electroconductivity, metal−support interactions, 25 support morphology, and stability, 26,27 to name a few. All of these can potentially influence electrochemical performance.…”