Eliminating Evolved Oxygen through an Electro-flocculation Efficiently Prompts Stability and Catalytic Kinetics of an IrOx·nH2O Colloidal Nanostructured Electrode for Water Oxidation

A facile approach which harnesses dual-potential pulsed amperometric technique to expedite the water oxidation and oxygen reduction reactions intermittently through an electro-flocculation is reported. The new strategy yields discriminated physical morphology and chemical composition of as-prepared IrOx·nH2O, compared with the previous approach, which lead to an alteration of kinetic mechanism and enhancement of stability in alkaline solution (pH 12). By the virtue of the catalyst architecture efficiently producing electroactive Ir sites (Γea = ∼4 × 10−8 mol mol/cm2), η for water oxidation was measured to be 0.22 V (at current density of 1.2 mA/cm2). The tafel slope was estimated to be 29 ± 1 mV per decade, suggesting the recombination of S − Oads as the rate determining step. Contrast to the considerably flocculated structure reported previously, the IrOx·nH2O construction herein was well-defined sphere-like clusters (5-10 nm) and resides separately. Furthermore a XPS examination revealed that the oxygen-containing constituents of the prepared IrOx, regardless of preparation techniques, were hydroxides (dominate) and hydrated water, instead of the lattice oxide ions. IrOx·nH2O formed using the present strategy yielded O-to-Ir ratio to be 2.9, which was substantially lower than 6.4 of a hydroxide-abundant constituent prepared without intermittent elimination of oxygen.