Facile Photochemical Preparation of Amorphous Iridium Oxide Films for Water Oxidation Catalysis

Abstract

Light-driven decomposition of Ir(acac)3 spin-cast on a conducting glass substrate produces a thin conformal film of amorphous iridium oxide, a-IrO x . The decomposition process, which was carried out under an ambient atmosphere at room temperature and tracked by Fourier transform infrared (FTIR) spectroscopy, appears to proceed by way of a ligand-to-metal charge transfer (LMCT) process. The amorphous nature of the films is based on the lack of any observable Bragg reflections by powder X-ray diffraction techniques; the elemental composition was corroborated by X-ray photoelectron spectroscopy (XPS) measurements. The films are found to be excellent electrocatalysts for mediating the oxygen evolution reaction (OER) in acidic media, as evidenced by the onset of catalysis at 130 mV and a Tafel slope of 34 mV dec–1. These parameters enable current densities of 1 and 10 mA cm–2 to be reached at 190 and 220 mV, respectively. Exposing the films to higher temperatures (500 °C) renders a film of crystalline iridium oxide, c-IrO x , which displays a Tafel slope of 60 mV dec–1, thus requiring an additional 50 mV to reach a current density of 1 mA cm–2. The film of a-IrO x reported here is among the best OER electrocatalysts reported to date.

Selective-leaching method to fabricate an Ir surface-enriched Ir-Ni oxide electrocatalyst for water oxidation

“…The overpotential at the current density of 0.5 mA cm −2 (with respect of the geometric area of GC substrate), which is a convention commonly used in OER literature to evaluate the catalyst performance, is ca. 0.25 V for the leached-Ir 0.7 Ni 0.3 O x and pyrolyzed-Ir 0.7 Ni 0.3 O x , which is close to that of the as-prepared pyrolyzed-IrO x and that recently reported for mesoporous IrO 2 film electrode prepared through electrodeposition [24], but still considerably larger than that exhibited by the amorphous IrO x film fabricated through photochemical deposition [45]. This should be because the present oxide materials have undergone a heat treatment at relatively high temperature (450°C), which can result in increasing crystallinity and thus reducing the electrocatalytic activity of oxide materials toward the OER [46,47].…”

Atomically monodisperse nickel nanoclusters as highly active electrocatalysts for water oxidation

“…9 Recently, many molecular complexes, transition metals oxides and inorganic materials have been explored for water oxidation under electrochemical conditions. [9][10][11][12][13] Owing to the difficulties in the abstraction of four electrons from two water molecules and subsequent formation of an O-O bond, this process poses a great challenge to find a state of the art water splitting system. 14,15 Therefore, there is a continuous effort to develop stable and robust catalytic material for water splitting that could be produced from economical and earth abundant materials, while operating at a modest overpotential and with a high oxygen evolution current density.…”

Facile synthesis of Fe/Ni bimetallic oxide solid-solution nanoparticles with superior electrocatalytic activity for oxygen evolution reaction

“…Because of the slow kinetics, a desirable electrocatalyst is eagerly discovered to increase the rate of the OER. At present, noble metals (e.g., IrO x ) are used in the water-splitting reaction because of their excellent HER or OER activity [9,10]; however, these precious metals have a very rare distribution of elements in the crust. Thus, much effort has been expended searching for earthabundant metals capable of substituting for noble metals.…”

“…Amorphous metal oxides have been recently found to possess much higher activity for OER than crystallized ones, especially precious metal-free Fe/Nibased multicomponent oxides [9,10,20]. Up to now, electrochemical deposition [14,[22][23][24], photochemical metal organic decomposition [10,20,25], the reactive magnetron co-sputtering technique [26], and the solvothermal method [27] have been developed to access amorphous oxides or films for electrochemical OER.…”