Development of Screen-Printable Nafion Dispersion for Electrochemical Sensor

Round 1

Reviewer 1 Report

                The manuscript reports development of Nafion-ink for screen printed electrodes and there by electrochemical sensing of metal ions. The prepared nafion ink was systematically characterized using various techniques XRD, XPS, viscosity etc. Finally, the ink was used to fabricate a screen printed electrode and used for differential pulse voltammetric sensing of Pb(II). The manuscript is well designed and can be accepted for the publication. 

Author Response

Thank you very much for the comments!

Reviewer 2 Report

Nice and well-conceived manuscript. One suggestion for the authors. Carefully read your manuscript from the line 256 to the line 277, there is a discrepancy in the text with what is given in Figure 4. According to that part of the manuscript, it remains unclear why 55°C was chosen as the curing temperature of modified Nafion.

Author Response

Thank you very much for the comments. There was a small mistake of the legend in Figure 4, which the red curve should be “Nafion 55°C Cured”, instead of 60°C. We have updated Figure 4 in the revised manuscript with the correct label.

As stated in the line 254 to line 255, Nafion membrane with relatively low crystallinity is preferred for electrochemical detection. And the line 277 to line 280 explained why 55°C was selected as the curing temperature of modified Nafion. We found that modified Nafion cured at 55 °C has the lowest degree of crystallinity (D = 32.3) while obtained films have good quality, and bubble issues were observed for membranes cured at 90 °C and 120°C.

Reviewer 3 Report

Recommendation: Minor Revision

Comments:

1.     The mechanical properties of the modified membrane should be reported.

2.     The morphological feature of the prepared samples should be explained.

 

3.     How did the author control the thickness of the Nafion membrane?

Author Response

Thank you very much for the comments and suggestions. Please find our response to the questions in below:

1. The mechanical properties of the modified membrane should be reported.

Response: Thanks for the comment. We have added some discussions on the mechanical strength of the membrane prepared by modified Nafion inks, which are in the revised manuscript from the line 373 to line 375:

No delamination was found in those tested sensors and the Nafion membrane retained its integrity and functionality after 1 months of soaking in the buffer solutions.

Please note that no further characterization was performed in this work for mechanical properties of the Nafion membrane. The main application of the modified Nafion membrane in this paper is as a cation-exchange membrane of electrochemical sensor for environmental monitoring. The membrane is printed on sensor substrates and applied in aqueous samples while no stretching, bending, or scratching are anticipated. Also the operating temperature should be much lower than the transition temperature of the Nafion. We think that characterization of mechanical properties will be very useful in the case of application in the fuel cells and will consider doing in-depth studies in our future works.

 

2. The morphological feature of the prepared samples should be explained.

Response: Thank you for the comment. We have added some discussions and information regarding to the morphological feature of the cured Nafion membranes. They are from the line 170 to line 172, line 280 to line 282, line 329 to line 335 and Table 2. From the XRD data, the low degree of crystallinity indicates that the cured membrane is mainly amorphous with small regions of crystal clusters. The amorphous morphology can also be confirmed from the roughness data provided in Table 2 (added in the revised manuscript), where the cured Nafion film has high degree of roughness (20% of film thickness).

We have also considered using other techniques to characterize film morphology of the Nafion membrane such as small-angle X-ray scattering (SAXS) or TEM. During the exploration we realized that the morphology is highly dependent on many parameters such as chemical modification, selection of solvent system and curing procedure, which should be investigated as a separate work.                                

 

3. How did the author control the thickness of the Nafion membrane?

Response: Very good question. There are several parameters that can play an important role for controlling the thickness of the Nafion membrane:

• The viscosity and percent solid of the Nafion ink. Inks with higher solid content and higher viscosity would form membranes with higher thickness.
• The pressure and the print speed of the squeegee bar. For screen-printing process, the film thickness will decrease with the increase of squeegee bar pressure or print speed.
• Thickness of the stencil. For stencil coating, the thickness of the deposited film is largely dependent on the thickness of the stencil.

In our work, we control and monitor each of the above parameters to control the thickness of the Nafion membrane. The Nafion ink has solid content of 25wt% and viscosity of ~27000 cPs at 10Hz^-1 shear rate (line 135 and Figure 1). For screen-printing process, the squeegee bar pressure was set to 5-bar with print speed of 150 mm/s (line 141 to line 142). For stencil coating the thickness of the stencil is 175 µm (line 146). The thickness of Nafion membranes were measured by laser scanning confocal microscope and we have added results in the revised manuscript as Table 2.