Highly Active Ir/TiO₂Electrodes for the Oxygen Evolution Reaction Using Atomic Layer Deposition on Ordered Porous Substrates

Abstract

Nanostructured Ir/TiO 2 electrodes are investigated toward the oxygen evolution reaction (OER) from water. The electrodes are prepared based on highly ordered TiO 2 nanotubes grown from Ti foils with full geometric control. The tube walls are coated with iridium using atomic layer deposition (ALD), which allows for an accurate tuning of the amount deposited. The electrocatalytic performance of electrodes with different TiO 2 tube lengths and iridium catalyst loadings toward OER is quantified by cyclic voltammetry and steady-state electrolysis. This study enables us to minimize the catalyst loading, and we reach a current density of 31.3 mA cm −2 at an overpotential η = 0.34 V for a tube length of L = 12 μm and a Ir coating thickness of t = 6 nm. The benchmark of 10 mA cm −2 is already achieved at a lower overpotential of η = 0.24 V.

Atomic layer deposition for efficient oxygen evolution reaction at Pt/Ir catalyst layers

“…Energydispersive X-ray analysis confirms the presence of all elements expected (Figure 3d). The metallic nature of the ALD deposits, the lack of any segregation between Pt and Ir, and the metal oxide nature of the surfaces have also been demonstrated in recent publications by X-ray diffraction, selected-area electron diffraction and transmission electron microscopy [22,23]. Herein, we investigate two different catalyst loadings:…”

“…The deposition of platinum and iridium as a binary catalyst can be realized at very low loadings in the range of micrograms per square centimeter [26]. Specifically, the applicability of ALD regarding Ir and bimetallic Pt/Ir catalysts, the homogeneous mixing of both elements in small nanoparticles, the coating of deep pores with them, and the adequacy of anodization with ALD as a surface treatment of Ti felts have all been demonstrated in the recent past [22,23]. Anodization is performed by applying a large positive voltage (+40 V) to the felt in a NH 4 F/glycerol solution for 2 h and results in the formation of a ca.…”

“…In both cases, the composition achieved is near the optimal 1:1 ratio of Pt to Ir. The electrodes based on the thermal decomposition method have been used and characterized in the past [6,21], and the material from the ALD method has been investigated extensively in [22,23]. In particular, we have determined particle sizes by transmission electron microscopy (TEM), investigated the homogeneously mixed nature of the Pt/Ir catalyst by X-ray diffraction (XRD), selected-area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS).…”

Applications of Atomic Layer Deposition in Design of Systems for Energy Conversion

“…The overpotential of OER in 0.1 m H 2 SO 4 was as low as 240 mV versus RHE at current density 10 mA cm −2 and mass activity 200 A g −1 at 340 mV with catalyst loading 160 µg cm −2 . [ 90 ] As an alternative to the porous TiO 2 carrier, porous anodic aluminum oxide (AAO) grown on Al‐plates was used as a template for deposition of the Ir‐catalyst. The overpotentials for OER were as low as 300 mV versus RHE at 10 mA cm −2 in acidic environment, showing the usability of this type of materials (i.e., Ir deposited on a semiconducting porous template) in energy storage systems.…”

Solid state interdigitated Sb2S3 based TiO2 nanotube solar cells

“…2 The geometry of TiO 2 NTs can easily be adjusted by varying the anodization conditions, such as applied potential and electrolyte composition, which enables tailoring the structure exactly to their respective applications. 2 The resulting structures provide a large surface area in combination with short and direct carrier pathways for various electronic applications, such as batteries, 5,6 catalysis, 7 water splitting 8,9 and emerging photovoltaics. 2 In the photovoltaics (PV) eld, TiO 2 NTs have been used to make dye-sensitized solar cells (DSSCs) 10,11 as well as perovskite 12,13 and polymer bulk heterojunction cells, 14 where their quasi-1D structure and the adjustability of their geometry has allowed for a much more thorough ne-tuning than the commonly used mesoporous device architecture.…”