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In this paper, we design a smart pH sensor using untreated platinum sheet based on chronopotentiometry. This novel pH sensor is very suitable for applications in the deep sea, highly polluted water, and other harsh environments, where maintenance is difficult. In order to verify the long-term monitoring stability of the pH sensor, 17-day monitoring experiments are conducted in river water. We draw some conclusions for the properties of the pH sensor. First, the pH values obtained from the positive current agreed well with the pH glass electrode, indicating that it is suitable for pH monitoring. Moreover, the deviation derived from hysteresis is small. Second, the pH values obtained from the negative current could not reflect the actual pH of river water in long-term measurement. There may be two reasons for this: the changing conductivity in the river water and the unstable composition of the platinum sheet. Third, the conductivity may have an obvious impact on the potential obtained from the negative current; the electrochemical reaction where Pt is oxidized to PtO may be influenced by the ionic strength of the solution. Therefore, the pH values obtained from the positive current is more suitable for long-term pH monitoring.

Traditional methods for determining the ammonia nitrogen (NH3-N) concentration are the colorimetric method using Nessler’s reagent or salicylate. To prevent secondary pollution, minimise the time required for measurement, and reduce cation interference, new NH3-N measurement methods have been developed including fluorescence, gas phase molecular absorption spectrometry, and ammonia gas sensing electrode methods. However, in these techniques, the addition of a chemical reagent is unavoidable, so the real-time and accurate measurements of NH3-N are achieved hardly. In this study, we used an ammonium ion-selective electrode (ISE) for the real-time measurement of NH3-N with compensation for the ammonium ion (NH4+) component of the total NH3-N concentration. The basic mechanism is that an ammonium ISE can measure NH4+ concentration, and NH4+ ratio in NH3-N can be calculated based on pH and temperature. Experimental results indicate that the ammonium ISE exhibited near-Nernstian behaviour, having a fitted line with a slope of 56.4 mV/pNH4. The compensation effects and reproducibility are good. Furthermore, the difference in the temperature responses at different NH4+ concentrations agrees with the Nernst equation basically. Therefore, the proposed method can provide a real-time and environmentally friendly solution to determine NH3-N concentration.

This study demonstrated the application of a tungsten oxide electrode to the measurement of ultralow liquid flow velocity based on streaming potential, using a pH glass electrode and temperature sensor to compensate for changes in open circuit potential induced by pH and temperature, respectively. A change in flow velocity on the surface of the tungsten oxide electrode caused the expected shift in its open circuit potential. Experimental results showed that the open circuit potential was linear relative to the logarithmic flow velocity, and the flow sensor exhibited excellent reproducibility and a large dynamic range, with the ratio between measurable maximum and minimum flow velocity surpassing 60:1. Moreover, a higher sensitivity was observed in the alkaline solution relative to the acidic solution, indicating that the alkaline solution is more suitable for this type of measurement. In conclusion, the tungsten oxide flow sensor provides a cheap, simple, adaptable, and energy-saving solution for the measurement of ultralow liquid flow velocity.

In this study, a novel solid-state pH sensor based on an untreated platinum sheet was investigated. Chronopotentiometry using positive and negative currents was applied to effect the interconversion of Pt and PtO. To eliminate the influence of concentration polarization, a galvanostatic double-pulse method was applied for pH measurement. The consecutively applied currents were +100, +3, −100, and −3 μA for excitation times of 0.5, 1, 0.5, and 1 s, respectively. Stable potentials under the small currents were obtained which could be used to determine pH. The platinum sheet electrode exhibited near-Nernstian behavior in the pH range 2–12, with fitted lines having slopes of −44.2 and −51.1 mV/pH unit under the positive and negative currents, respectively. Overall, excellent linearity and reproducibility could be achieved. Moreover, the temperature responses for the method in pH 4, 6.86, and 9.18 buffer solutions obeyed the Nernst equation, and further supported the proposed mechanism for pH determination. In conclusion, this new detection method provides a solid-state, long-lived, and adaptable solution for pH measurement.

A novel electrochemical surface plasmon resonance (EC-SPR) sensor has been developed based on the surface plasmon resonance (SPR) combined with a two-electrode electrochemical configuration. The theory of potential-modulated for EC-SPR was described, and several factors which can induce the change of the SPR resonance angle were revealed. Comparing with the conventional three-electrode electrochemical system, the reference electrode has been eliminated in this design, and the active carbon (AC) electrode employed as the counter electrode. Due to the large specific surface area, AC presents considerable double layer capacitance at the interface of electrode and electrolyte, which can provide a constant potential during the electrochemical reactions. Using an angle modulation SPR sensor and the resolution of that is 5x10-6 RIU (refractive index units), a real-time data-smoothing algorithm is adopted to reduce the noise of the data, which can guarantee an accurate result of the resonance angle of SPR. The EC-SPR setup was used for investigating the electropolymerization of polyaniline by applying a potential of cyclic voltammetry, both of the electrochemical current and the resonance angle shift of SPR are recorded to monitor the growth process of the polymer. Comparing with the three-electrode configuration, the novel AC two-electrode system can also obtain detailed information about the polymerization process from the resonance angle shift curves, including the change of thickness and dielectric constant, deposition and transitions between different redox states of the polymer film. Experimental results demonstrated that this two-electrode EC-SPR configuration is suitable for analyzing the electropolymerization process of a conducting polymer.

To obtain detailed information about electrochemistry reactions, a two-electrode electrochemical surface plasmon resonance (EC-SPR) sensor has been proposed. We describe the theory of potential modulation for this novel sensor and determine the factors that can change the SPR resonance angle. The reference electrode in three-electrode configuration was eliminated, and comparing with several other electrode materials, activated carbon (AC) is employed as the suitable counter electrode for its potential stability. Just like three-electrode configuration, the simpler AC two-electrode system can also obtain detailed information about the electrochemical reactions.