Effects of Structures on the Sensing Properties of Long-Term Stable IrO_x pH Electrodes

Abstract

Iridium oxide electrodes made by melted Li 2 CO 3 + Na 2 O 2 in a semi-closed/closed reactor exhibited fast response and high stability. A slight periodic fluctuation of potential change with standard deviation < 0.65 mV in 48 h and < 2.30 mV (0.04 pH) over 139 h were observed. The composition, structure, and sensing mechanism of the pH sensitive substance was examined. The XRD pattern and XPS results suggested the newly produced material H y-x Li x [LiIr 2 ]O 6 was a mixture of H 5-x Li x [LiIr 2 ]O 6 and H 3-x Li x [LiIr 2 ]O 6 with a HCrO 2 structure. Approximately 95% of Li + was replaced by H + after acid treatment. The pH sensing process was found to be an irreversible redox reaction between the tetravalent and trivalent iridium oxides according to the CV and XPS results. The presence of lithium ion in the lattice combined with well-crystallized small crystals corresponded to the fast response during the pH sensing process. The crystal structure may help to protect iridium from the interference of weak oxides, and thus may maintain stability with a relatively acceptable potential drift in the natural redox condition. The large portion of OH − existing in the oxide lattice detected by XPS confirmed the well-hydrated structure, which may also help the electrode to maintain high stability.

Advanced Wound Dressing for Real-Time pH Monitoring

“…The pH transducing ability of Ir oxides has been thoroughly documented in the literature and has long been exploited to build potentiometric pH sensors. − The electrochemical behavior of the PEDOT:PSS/IrOx Ps film was investigated in response to pH variations of the electrolyte solution and is shown in Figure . Potentiometric measurements were carried out by recording the zero-current electrochemical potential (open-circuit potential, OCP) of the film during base additions to a Universal Buffer solution (U.…”

“…Furthermore, robustness and stability of the calibration are essential to enable real-time monitoring over time and avoid unnecessary dressing changes for sensor maintenance. Alternative to the fragile and bulky glass membrane electrodes, solid-state pH sensors based on transition-metal oxides (MOx) have experienced rapid development thanks to their unique electrical and electrochemical properties, inherent stability to harsh experimental conditions, and biocompatibility. , Among them, IrOx finds application in several research fields, including electrocatalysis for water oxidation , and neural probes engineering, − and it is recognized as one of the most promising materials for pH sensing with superior sensitivity, wide detection range, and long-term stability. − Electrochemical methods, sputtering deposition, and sol–gel process are only a few examples among the variety of preparative routes leading to IrOx films with different stoichiometries that strongly affect the final electrochemical properties . Overall, the redox equilibrium involving Ir III /Ir IV species and H + ions is the generally accepted mechanism governing the potentiometric response of the metal oxide anhydrous and hydrous forms, the latter comprising oxyhydroxides that are typically obtained after electrochemical growth and regarded as responsible for the often reported super-Nernstian sensitivity. ,, IrOx films have been utilized for the in vitro monitoring of cells and tissues pH, − the fabrication of transistor-based pH sensors , and, more recently, the development of wearable pH sensors for sweat monitoring on plastic substrates − and conductive fabrics .…”

Recent developments in ionophore-based potentiometric electrochemical sensors for oceanic carbonate detection

“…206 Storing the device in a dry environment and avoiding strong redox active species could also be a good way to slow down the potential decrease and prolong the working life. 206 Throughout the literature, lifetimes have been reported from three days to two and a half months for carbonate sensors (Table 1). 140,148 On average, the lifetime of ISEs, including those not involved in ocean acidification research, is from 4 to 10 weeks.…”

“…Moreover, based on previous investigations by Sun and co-workers, proper activation of the membrane (i.e., aging) in a buffer solution is necessary for a newly prepared electrode to reach a relatively slow potential drift rate and respond effectively to target ions over time. 206 Storing the device in a dry environment and avoiding strong redox active species could also be a good way to slow down the potential decrease and prolong the working life. 206 Throughout the literature, lifetimes have been reported from three days to two and a half months for carbonate sensors (Table 1).…”

In Vivo Molecular Insights into Syntrophic Geobacter Aggregates

“…Among the above-mentioned methods for preparing iridium electrode, the traditional electrodeposition method requires complex deposition solution with strict ratio. 32,33 Thermal oxidation and thermal sputtering require high-temperature oxidation instruments, 34,35 which are generally expensive, further limiting the application of iridium-based electrodes. In this study, the bulk iridium electrode using simple self-electrodeposition approach was prepared by cyclic voltammetry (CV) technology, which has the advantages of cost effectiveness, simple preparation, and good response performance.…”