The solid-state pH electrode has the potential possibility to be used in many extreme situations with satisfactory accuracy and low cost. But its performance is affected by the solid electrolyte, preparation process, and the structure of the sensitive membrane, etc. In this work, the relationships between these factors and the characteristic of the prepared electrode were verified by controlling the preparation conditions with a variety of electrochemical methods. Firstly, the solid electrolyte poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) was electrochemically deposited on the screen-printed carbon electrode (SPCE) substrate by a potentiostatic method in an aqueous solution containing 0.01 M 3,4-ethylenedioxythiophene (EDOT) and 0.1 M polystyrene sulfonic (PSS) acid as the supporting electrolyte. The PEDOT films were then characterized by cyclic voltammetry (CV) in the 0.1 M NaNO3 aqueous solution in order to obtain the optimized polymerization potential and charges where the PEDOT film would have a higher redox capacitance. Finally, the pH electrode was prepared by coating the SPCE/PEDOT(PSS) with a plasticized polyvinyl chloride (PVC) membrane containing tridodecylamine as hydrogen ionophore manually, and experiments were carried out to study the effect of the usage of PVC per square millimeter on the response time and stability of the electrode to optimize the PVC film thickness. The potentiometric response of the pH electrode was studied in the buffer solutions with pH ranging from 5.00 to 10.81 by the open-circuit potential (OCP) method. Experimental results show that the sensitivity of the electrode is −55.7 ± 0.5 mV pH−1 (r2 > 0.9980) at room temperature (24 ± 1 °C) with pH ranging from 2.00–10.50, approximating to the theoretical nernstian slope (−59.16 mV pH−1),and the response time was less than 10 s. Moreover, it has low impedance, high accuracy and potential stability as well as some other useful properties such as pressure and heat resistance, hydrofluoric acid resistance, and it is not as fragile as the glass electrode.
A low-cost flexible polyaniline@carbon nanofiber membrane (PANI@CNM) electrode was fabricated by chemical in situ polymerization of aniline monomer for pH detection. The preparation condition, morphology, chemical structure and the electrochemical properties of the PANI@CNM electrode were investigated. The result showed that PANI@CNM electrode with high sensitivity of 76.2 mV/pH was prepared with 0.3 M aniline solution and hydrochloric acid as the doping acid at 0℃ for 6 h. FTIR and Raman analysis suggested that the pH sensibility of PANI is attributed to the super-Nernstian behavior of the PANI in the emerald imine form. The PANI@CNM working electrode performs a stable electrochemical property without interference by the common metal iron and biochemical, and has an outstanding reversible pH response in the pH range of 6.32–8.34 without interference of deformation. It also maintained a stable sensing performance in the temperature range of 25-40℃ for long time use and presented excellent biocompatibility. Generally, the PANI@CNM working electrode exhibits great potential in flexible biomedical and wearable pH detection application.
Yaosheng Liu,Hanmeng Liu,Zhixia Yao,Yongxing Diao,Guangxing Hu,Qifang Zhang,Yujing Sun,Zhuang Li
pH electrodes exhibited wide applications in the fields of food science, environmental science, and bioanalytical analysis. In this work, we demonstrate the facile fabrication of silver-antimony (Ag–Sb) binary alloy electrodes through a one-step melt casting method. XRD, SEM and EDS were used to characterize the alloy electrodes. The response mechanism of the pH electrode was studied by Tafel plots, which clarified the role of metal (Sb) and metal oxide (SbO ads ) in the pH response process. The corrosion resistance of the alloy electrode was researched by electrochemical impedance spectroscopy (EIS), which proved the advantages of the Ag–Sb alloy electrodes. In addition, our Ag–Sb pH electrodes exhibited promising sensing performance with the near-Nernstian response sensitivity is 54.6 mV/pH. The other performances including response time, stability, reversibility, hysteresis, and temperature coefficient, also demonstrated that the Ag–Sb binary alloy electrodes have good pH speciality, and it will potential applications for environmental monitoring in situ. These research results can complement and perfect the theoretical basis of metal/metal oxide pH electrodes, thus guiding the preparation of metal/metal oxide pH electrodes and promoting the exact and extensive application of metal/metal electrodes in more aspects.
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