Supported Iridium Oxide Films in Aqueous Electrolytes: Charge Injection Dynamics as Monitored by Time-Resolved Differential Reflectance Spectroscopy

Efficient Electro-Oxidation of Water near Its Reversible Potential by a Mesoporous IrOx Nanoparticle Film

“…The work described here uses conductive − films of IrO x nanoparticles (∼2 nm diameter; see the Supporting Information, Figure S-1a,c) prepared by thermal hydrolysis of K 2 IrCl 6 at pH 13 and without addition of stabilizer ligands, producing a clear blue solution (stable to refrigerator storage for >2 months) . Films of nanoparticles were electro-flocculated onto a glassy carbon electrode (GC, 3 mm diameter) at +1.3 V vs Ag/AgCl.…”

“…After 10 min, the current has increased to >15 mA/cm 2 , and is noisy (Figure S-2 of the Supporting Information) owing to the copious O 2 gas evolution. It is well-known 13 that the electrochemical properties of IrO x films can be strongly dependent on the method of film preparation, so it is important to note that forming IrO x films by electro-flocculation is previously unreported.…”

“…These waves are assigned, respectively, to Ir IV /Ir III and Ir V /Ir IV redox steps in the IrO x nanoparticle film, following previous work. 10,11,13 The peak seen on the reverse potential scan at ∼ +0.78 V vs Ag/AgCl (at pH 7) is attributed to reduction of film Ir VI states not yet consumed by water reaction; this peak's potential gives a rough measure of the Ir VI /Ir V potential. The potentials of the Ir IV /Ir III and Ir V /I IV nanoparticle couples, and of the η for O 2 evolution onset, 17 all shift by ∼0.06 V/pH unit (parts A and B of Figure 2, respectively).…”

“…An explanation must consider , how thick films of IrO x nanoparticles can become, throughout, rapidly charged to the Ir VI state and, throughout, react with water (Figure ). First, electron conduction through the IrO x films must be very fast. − Perhaps more importantly, the exceptional electrocatalytic reactivity of the electro-flocculated nanoparticle films may reflect a mesoporous structure, in which the oxidation current density at IrO x /electrolyte interfaces is kept at a reduced value by an extended, accessible internal surface area, irrespective of overall nanoparticle layer depth. That is, the nanoparticle films are mesoporous, with facile water and ion permeation.…”

Investigating the Influence of Amorphous/Crystalline Interfaces on the Stability of IrO2 for the Oxygen Evolution Reaction in Acidic Electrolyte

“…For proton exchange membrane (PEM) electrolysers the main attraction is fast reaction kinetics that generates products which can be separated easily at a low working pressure with the ability to respond rapidly to changes in electrical input [2–5] . To date, iridium oxides are one of the best PEM anode catalysts due to their high catalytic activity for the OER in acidic conditions [5–30] . Several methods have been investigated for the preparation of IrO 2 such as chemical deposition, [31–35] thermal decomposition, [15,36–38] hydrothermal decomposition, [39] magnetron sputtering, [40] modified Adams fusion method, [6,20] electrochemical oxidation of cathodically deposited iridium thin metal films [7,18,41] and direct anodic electrodeposition [12,16,31,36–37,41−45] …”