Influence of oxidation state on the pH dependence of hydrous iridium oxide films

Boosting water oxidation layer-by-layer

“…The CV response of the IrO 2 / PDDA-bilayers strongly resembles that previously reported for hydrous iridium oxide films (HIROFs). [38][39][40][41][42][43][44][45][46][47][48] The two reversible redox couples are commonly attributed to the Ir(III)/Ir(IV) and Ir(IV)/Ir(V) transitions, respectively, reflecting the multiple redox states available for the IrO 2 centers. Interestingly, the electrochemical response strikingly contrasts with the one observed in flocculated films where the charge associated to the transformation between Ir(III)/Ir(IV) is higher than the one assigned to Ir(IV)/Ir(V).…”

“…An in-depth mechanistic study on this topic for the LbL-deposited IrO 2 /PDDA films herein is beyond the scope of this article and the reader is referred to recent mechanistic work by Ahlberg and co-workers in this regard. 47,48 A comparison of the OER onset and thermodynamic potentials for O 2 evolution (inset Fig. 5A) highlighted an essentially pH-independent overpotential (Z), varying slightly from 0.22 to 0.28 V moving from acidic to alkaline conditions, for IrO 2 / PDDA-bilayers FTO electrodes.…”

An array of individually addressable micro-needles for mapping pH distributions

“…is is not fully understood, however, there are evidences for involvement of ions in equilibr ia reactions at Ir oxide films. 24,25 These results highlight a slight sensitivity to CaCl2 and MgCl2, however, at worst this is equivalent to an error of pH units of -0.12 ± 0.01 (n=6). Figure 2b provides evidence that sensors are not susceptible to albumin at least for concentrations below 1 gL -1 since the traces of the potential are almost unaffected, i.e., the displacement of the potential is below 1 mV.…”

“…24,2 5 Iridium oxide electrodes exhibit a super-Nernstian response of 65-80 mV/pH unit depending on preparation and discussions over the complex equilibrium interfacial reactions that account for this behaviour can be found elsewhere. 18,[24][25][26] An example of heterogeneous pH variation is the setting of myocardial ischemia due to a switch towards anaerobic metabolism and the development of lactic acidosis. [27][28][29][30][31][32] Reperfusion of ischemic myocardium 33 leads to a rapid restoration of pH to pre-ischemic values, 34,35 which may in part contribute towards reperfusion injury.…”

In situ pH measurements with hydrous iridium oxide in a rotating ring disc configuration

“…These hydrated films can conveniently be prepared by electrodeposition on a variety of substrates, as was first described by Yamanaka [13]. Similar to AIROFs, EIROFs generally exhibit a pH sensitivity in excess of 60 mV, a behaviour that has been discussed by various authors [11,12,14,15].…”