potential-pH Response Research Articles

All-solid-state, long term stable, and embedded pH sensor for corrosion monitoring of concrete

The corrosion process of concrete usually accompanies pH changes of the pore solution. Thus, monitoring the pH value of concrete has great significance for the prediction of concrete corrosion. However, the most commonly used methods for measuring the pH value of concrete pore solution are destructive methods, which are very inefficient and cannot provide the pH value for real-time. In this study, an all-solid-state pH sensor constituted with iridium oxide (IrOx) working electrode and manganese/manganese dioxide (Mn/MnO2) reference electrode was developed. The IrOx electrode fabricated with carbonate melt oxidation method and Mn/MnO2 fabricated with powder compaction method exhibited a dense and homogeneous micro structure. The as-prepared pH sensors showed remarkable long-term stability, ideal potential-pH response, low hysteresis, fast pH response time and strong resistance to ionic interference in solutions. Furthermore, the pH sensor was embedded in the mortar samples and used to monitor pH changes during the accelerated carbonation test. The results indicate that the pH sensor can provide accurate pH value variations of the mortar samples during the carbonation process, and it has great potential for non-destructively monitoring the corrosion process of concrete.

A dual-site modulated FRET-based two-photon ratiometric fluorescent probe for tracking lysosomal pH changes in living cells, tissues and zebrafish

Lysosomal pH plays an essential role in mediating various biological processes such as immunization, cell metabolism and enzyme activity. Herein, by utilizing the fluorescence resonance energy transfer (FRET) strategy, a two-photon (TP) ratiometric fluorescent probe (NpLys-pH) has been developed for tracking of lysosomal pH changes in living cells, tissues, and zebrafish. NpLys-pH was constructed by conjugating a pH turn-on TP fluorophore 1 (D-π-A-structured naphthalene derivative) with a pH turn-off naphthalimide fluorophore 2via a non-conjugated linker. Meanwhile, NpLys-pH has two potential pH response sites that modulate the fluorescence signal by ICT and PET, respectively. The FRET process exists between the TP fluorophore 1 and naphthalimide fluorophore 2. In addition, NpLys-pH respond to pH rapidly and reversibly with high selectivity and sensitivity and has been applied for tracking lysosomal pH changes in living cells, tissues and zebrafish. We expect that the new probe present here can prompt the development of a wide variety of TP ratiometric fluorescent probes which can find application in detecting other important analytes in biological systems.

A fabrication of iridium oxide film pH micro-sensor on Pt ultramicroelectrode and its application on in-situ pH distribution of 316L stainless steel corrosion at open circuit potential

An all solid-state pH micro-sensor has been developed using anodic electrodeposition of an iridium oxide (IrOx) film onto a 10μm platinum ultramicroelectrode. The electrochemical growth of the IrOx film was accomplished by 100 potential sweeps at 50mV/s, at different potential ranges of electrochemical deposition, followed by heat treatment at 100°C for 2h. The pH micro-sensor shows quick response to the pH variation, excellent sensitivity, stability and long lifetime in a wide pH range between 1.0 and 13.0. The slope of potential-pH response curve is found to dependent on the Ir(III)/Ir(IV) ratio of in the film, determined by XPS analysis, which is a consequence of scanning potential range during the anodic electrodeposition. The sensor has been employed to explore the localized pH distribution during the corrosion of 316L stainless steel in NaCl solution at open circuit potential and results show that localized anodic and cathodic sites on the 316L stainless steel can be accurately monitored and the pH difference between the cathodic and anodic zones increases from 0.22 to 1.27 with the prolonging of the immersion time.

Cavity microelectrode for studying manganese dioxide powder as pH sensor

The potential–pH response of an electrolytic manganese dioxide is investigated by means of a cavity microelectrode (CME). The potential–pH curves show a complex evolution that could be explained by the disporportionation of MnOOH species, leading to the formation of Mn 2+ ions on the MnO 2 surface. Such a behaviour is not suited for pH sensor application. However when the tip of the electrode is coated by a Nafion membrane, the potential–pH evolution shows a unique slope close to −60 mV pH −1. In addition, the sensor exhibits short time responses to pH variations, a good selectivity, and it can be easily renewed compared to classical sensors.

The diffusivity of mobile hydrogen ion in pH-glass membrane

In this study, a novel method based on potential-pH response drift measurement was used to determine hydrogen ion diffusivity in pH-glass electrode membrane. The diffusivity of hydrogen ion in pH-glass membrane obtained from this method was 1 × 10 −8 cm 2/s. Two pH-sensing mechanisms may be identified for the pH-glass electrode based on the diffusion-site-binding model. These are the charge adsorption mechanism for short time domain and the hydrogen ion diffusion mechanism for long time domain. The hydrogen ion diffusion mechanism may be invoked to explain the observed drift in pH-glass electrode.

A comparison between proton and hydrogen chemical diffusion coefficients of titanium oxide films

Proton and hydrogen diffusion in titanium oxide thin films is of significant interest because of its importance in barrier, sensor, and catalytic coating applications. In this study, a novel method based on potential–pH response measurement was used to determine proton chemical diffusion of titanium oxide thin films. This technique, based on the model of diffusion-controlled proton transport at the oxide surface, measures the potential–pH response drift as a stepwise increase and decrease in pH (i.e., pH = 4, 7, and 10) of buffer is generated in a thermostatic measurement setup. The proton chemical diffusion coefficient for titanium oxide films obtained from this method was 10–17 cm2/s, about two orders smaller than the hydrogen chemical diffusion coefficient (10–15 cm2/s) obtained from the conventional electrochemical permeation technique.

Hydrogen ion diffusion coefficient of a hydrogenated amorphous silicon thin film

Hydrogen ion diffusion in a hydrogenated amorphous silicon thin film is of significant interest because of its importance in semiconductor, sensor and solar cell coating applications. In this study, a novel method based on potential–pH response measurement was used to determine hydrogen ion diffusion in a hydrogenated amorphous silicon thin film. The drift in the potential–pH response is believed to be due to the hydrated layer, which affects hydrogen ion diffusion on to the gate of ion sensitive field effect transistors (ISFETs). The hydrogen ion diffusion coefficient of a hydrogenated amorphous silicon film obtained from this method was 3 × 10−17 cm2 s−1. The unique feature of the potential–pH response method is its relatively simple experimental procedure, which eliminates complications arising from surface related effects and/or presence of hydrogen traps in membranes such as those found in the conventional permeation method.

Determination of the diffusion coefficient of proton in CVD gamma aluminum oxide thin films

Proton diffusion in aluminum oxide thin films is of significant interest because of its importance in barrier, sensor and catalytic coating applications. In this study, a novel method based on potential-pH response measurement was used to determine proton diffusivity in CVD produced gamma aluminum oxide thin films. This technique based on the model of diffusion-controlled transport at the oxide surface, measures the potential-pH response drift as a stepwise increase and decrease in pH (i.e. pH 4 and 7) with a thermostatic measurement set-up. The drift in the potential-pH response is believed to be due to the surface layer, which affects proton diffusion onto the oxide film of the Al 2O 3-gate ion selective field effect transistor. The diffusion coefficient of proton in aluminum oxide thin film using the potential-pH response method was 6.5×10 −18 cm 2/s. The unique feature of this method is its relatively simple experimental procedure, which eliminates complications arising from surface related effects and/or presence of hydrogen traps in the metal, also offers a considerable reduction in test time with the experiment being completed in 10 h as compared to the conventional electrochemical permeation method which takes as long as 5 days.

Hydrogen diffusion coefficient of silicon nitride thin films

Hydrogen concentration and diffusion in silicon nitride thin film is of significant interest because of its importance in barrier, sensor and catalytic coating applications. In this study, a novel method based on potential–pH response measurement was used to determine hydrogen diffusion in silicon nitride thin films. Hydrogen diffusion coefficient of silicon nitride films obtained from this method was 1×10 −19 cm 2/s. The unique feature of the potential–pH response method is its relatively simple experimental procedure, which eliminates complications arising from surface related effects and/or presence of hydrogen traps in the metal. The method also offers a considerable reduction in test time.

Hydrogen ion diffusion coefficient of silicon nitride thin films

Hydrogen ion diffusion in silicon nitride thin film is of significant interest because of its importance in barrier, sensor and catalytic coating applications. In this study, a novel method based on potential–pH response measurement was used to determine hydrogen ion diffusion in silicon nitride thin films. Hydrogen ion diffusion coefficient in silicon nitride films obtained from this method was 1×10 −19 cm 2/s. A potential–pH response drift was observed and is believed to be due to the presence of a hydrated layer affecting the hydrogen ion diffusion onto the nitride film of the Si 3N 4-gate hydrogen ion-sensitive field effect transistors (ISFETs). The unique feature of the potential–pH response method is its relatively simple experimental procedure, which eliminates complications arising from surface-related effects and/or presence of hydrogen traps in membrane, such as those found in the conventional permeation method. The method also offers a considerable test time reduction, with the experiment being completed in 10 h as compared to the conventional electrochemical permeation method which takes as long as 5 days.

A novel method to determine the diffusion coefficient of hydrogen ion in ruthenium oxide films

Hydrogen ion diffusion in ruthenium oxide film is of significant interest because of its importance in capacitor, sensor and catalyst applications. In this study, a method based on potential–pH response measurement was used to determine hydrogen ion diffusion in ruthenium oxide films. The drift in the potential–pH response is believed to be due to the hydrated layer, which affects hydrogen ion diffusion onto the oxide film of the pH sensor. Hydrogen ion diffusion coefficient of ruthenium oxide films obtained from this method was 6×10 −14 cm 2/ s . The unique feature of the potential–pH response method is its relatively simple experimental procedure, which eliminates complications arising from surface related effects and/or presence of hydrogen traps in membrane such as those found in the conventional permeation method.

Electrically free-standing IrO itx thin film electrodes for high temprature, corrosive environment pH sensing

In this paper we show that electrodes prepared by d.c. reactive sputtering of iridum oxide on to alumina substrates have utility for pH sensing in high temperature/corrosive aqueous environments. The electrode potential pH response, resulting from a potential-determining reaction between protons from solution and the film, is also transmitted along the film, the alumina rod being an inactive support. With this structure interferences resulting from electrochemical reaction between ions from solution and a substrate metal are precluded, and film peeling due to corrosive attack of such a support-metal is also reduced. We report results of measurements in concentrated acids at temperatures T‘ 100°C and atmospheric pressure, and in dilute aqueous systems at 100°‘ T ‘ 200°C and high pressure in an autoclave.