One-Step Controlled Electrodeposition Fabrication of Ternary PtNiCo Nanosheets for Electrocatalytic Ammonia–Nitrogen Sensing

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have read the submitted original article entitled “One-step controlled electrodeposition fabrication of ternary PtNiCo nanosheets for electrocatalytic ammonia-nitrogen sensing” by L. Zhang et al in Chemosensors/MDPI. The authors present a one-step electrodeposition technique for fabricating ternary PtNiCo nanosheets, which serve as effective electrocatalytic sensors for ammonia-nitrogen detection. This method enables the simultaneous deposition of platinum, nickel, and cobalt ions onto a conductive substrate, resulting in a self-supporting electrode structure with enhanced sensing capabilities. The sensor demonstrated a high oxidation peak current of 45.27 mA and exhibited excellent long-term stability, retaining 88.09% of its activity after 12 hours of operation. The deposition parameters, including metal ion ratios and deposition time, were systematically optimized. The formation of the PtNiCo alloy was confirmed through electrochemical characterization. The study is well-supported by comprehensive experimental validation and is suitable for publication following some revisions.

 

• The concentration ratio of NH⁴⁺ and NH₃ has been affected by both pH and temperature levels.
• The detection of ammonia-nitrogen can also be detected through fluorometry, colorimetry methods. Then, why use electrochemistry?
• Polymers like polyaniline and polypyrrole have also been reported to show electrochemical responses towards ammonia-nitrogen.
• Lines 50 -54: It could be a good idea to include a recent article, doi.org/10.1002/cnma.202500270 reports on the scalable electrodeposition technique.
• Section 2.1 (lines 75 – 78), all the ratios can be tabulated with appropriate sample labels.
• Section 2.2. E capital in electrochemical.
• Section 3.2.1 title is not clear.
• The redox peaks seen in Figs 2a-c must be well explained, with their minor peak shifts should be well justified.
• What is the role of Ni from 2 to 0?
• The obtained differential pulse voltammetry with a detection limit must be benchmarked with the recently similar article reported in the literature, doi.org/10.1002/admi.202400981.
• Overall, there are lots of typos, and the language must be improved.
• Does the pH influence the DPV analysis?

Author Response

Comments by reviewer (1)

I have read the submitted original article entitled “One-step controlled electrodeposition fabrication of ternary PtNiCo nanosheets for electrocatalytic ammonia-nitrogen sensing” by L. Zhang et al in Chemosensors/MDPI. The authors present a one-step electrodeposition technique for fabricating ternary PtNiCo nanosheets, which serve as effective electrocatalytic sensors for ammonia-nitrogen detection. This method enables the simultaneous deposition of platinum, nickel, and cobalt ions onto a conductive substrate, resulting in a self-supporting electrode structure with enhanced sensing capabilities. The sensor demonstrated a high oxidation peak current of 45.27 mA and exhibited excellent long-term stability, retaining 88.09% of its activity after 12 hours of operation. The deposition parameters, including metal ion ratios and deposition time, were systematically optimized. The formation of the PtNiCo alloy was confirmed through electrochemical characterization. The study is well-supported by comprehensive experimental validation and is suitable for publication following some revisions.

Response: We appreciate the reviewer’s comments and suggestions on our work. We have revised the manuscript based on the reviewer’s suggestions.

Question 1: The concentration ratio of NH₄⁺ and NH₃ has been affected by both pH and temperature levels.

Response: Thanks for this comment.

Ammonia-nitrogen includes two forms: NH₄⁺ and NH₃. The pH and temperature can affect the ratio of NH₄⁺ and NH₃. With the increasing pH value, the ratio of NH₃ increases and the pka is 9.25. In addition, the ratio of NH₃ also increases when the temperature increases.

In this work, we intend to design one PtNiCo alloy for electrochemical detection of ammonia-nitrogen based on the electrochemical catalytic ammonia oxidation reaction. Therefore, NH₄Cl was used as ammonia-nitrogen source. 1 M KOH was used as electrolyte. The measured temperature is about 20 ^oC. Therefore, before starting this work, we have noticed the effects of pH value and temperature for ratio of NH₄⁺ and NH₃ and try to avoid the errors based on pH value and temperature.

Question 2: The detection of ammonia-nitrogen can also be detected through fluorometry, colorimetry methods. Then, why use electrochemistry?

Response: Thanks for this comment.

To detect ammonia-nitrogen, some methods including fluorometry, colorimetry and electrochemistry have been developed. In contrast to the electrochemical method, fluorometric and colorimetric approaches are not only characterized by complex operations and the need for large quantities of sample solutions but also prove to be time-intensive. Additionally, the phenolic reagent employed in colorimetric methods, along with its by-products, exhibits toxicity. By comparison, the electrochemical method demonstrates several advantages, including fast response speed, high current density, real-time in situ monitoring, excellent spatial resolution, and minimal damage to samples. Based on above reasons, our groups always try to design and fabricate high-performance sensing electrode for ammonia-nitrogen.

[1] G. D. Wang, G. F. Zhou, E. J. Li, et al. In-situ synthesized PtZnCu nanoalloy on carbon cloth for ultrasensitive electrochemical ammonia-nitrogen detection[J]. Journal of Electroanalytical Chemistry, 2025, 991: 119211.

[2] R. M. Qin, Y. H. Zhang, H. G. Xu, et al. Gold nanoparticle-modified electrodes for electrochemical sensing of ammonia nitrogen in water[J]. ACS Applied Nano Materials, 2024, 7(1): 577-593.

[3] Y. F. Ning, P. Yan, Y. P. Chen, et al, Development of a Pt modified microelectrode

aimed for the monitoring of ammonium in solution[J]. International Journal of Environmental Analytical Chemistry, 2017, 97(1): 85-98.

Question 3: Polymers like polyaniline and polypyrrole have also been reported to show electrochemical responses towards ammonia-nitrogen.

Response: Thanks for this comment.

In 1989, G. Gustafsson and his partners published one paper on Synthetic Metals about interaction between ammonia and polypyrrole. They proposed that the ammonia-polymer interaction in p-doped conducting polymers is generally considered to be a compensation effect. Ammonia molecules are electron donating and act as n-type dopants that can decrease the doping level of the polymer chain by compensating the effect of the original dopant. Based on this, polyaniline and polypyrrole and their composites have been reported for ammonia-nitrogen detection [Electrochimica Acta 49 (2004) 3665–3670, Sensors and Actuators B 225 (2016) 510–516, J. Mater. Chem., 2008, 18, 3216–3222, Journal of Electroanalytical Chemistry 669 (2012) 90–94]. Based on these reports, it is easy to find that the sensing performances of conducting polymers showed great enhanced space. Resent years, it is difficult to find the reports about pure conducting polymer. The potential reason is that it is difficult to improve the sensing performances of conducting polymers.

In addition, since 2018, our group try to design conductive polymer-Pt composite for ammonia-nitrogen detection and several articles have been published including polyaniline array-Pt nanosheets, polypyrrole film-Pt nanosphere and poly(methylene blue) file-Pt film and so on [Materials Letters 368 (2024) 136707, Synthetic Metals 259 (2020) 116257, Materials Letters 368 (2024) 136707, Microchemical Journal 199 (2024) 110238]. Compared to pure Pt, conducting polymers showed positive effects on enhancing the electrochemical detection of ammonia-nitrogen: 1) conducting polymers can provide better surface for growth of Pt nanoparticles, 2) conducting polymers can provide the protection for conductive substrate like Ni foam, 3) conducting polymers and Pt nanoparticles may yield typical ohmic contact with low energy barrier.

Therefore, we have noticed the reports about conducting polymer for ammonia-nitrogen detection.

Question 4: Lines 50-54: It could be a good idea to include a recent article, doi.org/10.1002/cnma.202500270 reports on the scalable electrodeposition technique.

Response: Thanks for this comment.

Based on the comment, several articles about electrodeposition technique and replacement reaction have been cited in this revised manuscript.

Question 5: Section 2.1 (lines 75 – 78), all the ratios can be tabulated with appropriate sample labels.

Response: Thanks for this comment.

Based on the comment, a table about all the ratios have been provided in revised supporting information and this table has been named as Table S1.

Question 6: Section 2.2. E capital in electrochemical.

Response: Thanks for this comment.

Based on the comment, “E capital in electrochemical” has been revised in this revised manuscript

Question 7: Section 3.2.1 title is not clear.

Response: Thanks for this comment.

Based on the comment, the titles of 3.2.1 and 3.2.2 have been revised in this revised manuscript:

3.2.1. The effect of the molar ratio (H₂PtCl₆·6H₂O, Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O) for electrocatalytic ammonia oxidation reaction

3.2.2. The effect of electrodeposition time for electrocatalytic ammonia oxidation reaction

Question 8: The redox peaks seen in Figs 2a-c must be well explained, with their minor peak shifts should be well justified.

Response: Thanks for this comment.

In this work, the CV curves have been obtained in 1 M KOH with/without 0.1 MNH₄Cl to measure the electrocatalytic performances of all samples. Fig. 2, Fig. 3 and Fig. S3-7 showed the above CV curves. Several redox peaks could be observed based on the CV curve. The redox peaks at the potentials from -1 V to -0.5 V could be attributed to the adsorption and desorption processes of hydrogen. [Y. P. Wang, Y. Ji, C. Li, Advances in platinum-based materials for electrocatalytic ammonia oxidation: Mechanisms and research progress[J]. Chinese Chemical Letters,2025, 36: 110370; X. Lin, X. R. Zhang, Z. Wang, et al. Hyperbranched concave octahedron of PtIrCu nanocrystals with high-index facets for efficiently electrochemical ammonia oxidation reaction[J]. Journal of Colloid and Interface Science, 2021, 601: 1-11]

In addition, minor shifts of ammonia oxidation peaks may be attributed to the samples. Specifically, in this work, we intended to design high-performance sensing electrode based on the their electrocatalytic activities. Fig. 2 and Fig 3 showed the CV curves of obtained samples after controlled ratio of H₂PtCl₆·6H₂O, Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O and deposition time. Owing to different ratio and deposition time, all samples showed different electrocatalytic performances. Onset potential, oxidation peak currents and oxidation peak potentials are the important factors to evaluate the electrocatalytic activity of electrocatalyst. The minor shifts of oxidation peaks indicated that 1) all samples showed different overpotential for ammonia oxidation reaction and 2) the ratio and deposition time showed important effect to electrocatalytic performances.

Based on above discussion, some sentences have been added in this revised manuscript:

The CV curves in 1 M KOH showed several redox peaks. Specifically, redox peaks

at the potential range from -1 V to -0.6 V could be attributed to the adsorption and desorption processes of hydrogen. The slight oxidation peak at about -0.3 V belonged to oxidation process of Pt.

Question 9: What is the role of Ni from 2 to 0?

Response: Thanks for this comment.

To enhance the electrochemical catalytic and analytic activities of Pt, we would like to design and fabricate PtNiCo alloy via one step electrodeposition process. During the electrodeposition process, Pt⁴⁺, Ni²⁺ and Co²⁺ ions have been reduced and achieved PtNiCo alloy. Owing to Ni and Co element, the electrode structure of Pt has been change, the electrochemical catalytic and analytic performances have been enhanced compared to pure Pt. Our precious research indicated the adsorption energy of ammonia on PtNi alloy is low than that of pure Pt, indicating the positive effect of Ni element [Journal of Alloys and Compounds 1010 (2025) 177286].

Question 10: The obtained differential pulse voltammetry with a detection limit must be benchmarked with the recently similar article reported in the literature, doi.org/10.1002/admi.202400981.

Response: Thanks for this comment.

Based on the comment, the article (doi.org/10.1002/admi.202400981) has been read carefully. In this article, cobalt oxide decorated graphene nanocomposite (Gr-Co₃O₄) was prepared and used as sensing materials for electrochemical detection of dopamine and uric acid. Differential pulse voltammetry (DPV) measurements demonstrated a detection limit of 0.09 µM for dopamine, with a linear response range from 1 to 500 µM. For uric acid, the detection limit and linear range were estimated as 0.2 and 100 to 8000 µM. Above results indicated that Gr-Co₃O₄ showed great detection performances for detecting dopamine and uric acid.

Compared to this article, our designed PtNiCo alloy showed a bad sensing performance. However, this article and our work showed the obvious differences including sensing materials, electrolytes, and target analytes. Therefore, it is difficult to directly compare the experimental results of the two studies. Consequently, we did not cite this paper in the revised manuscript.

Question 11: Overall, there are lots of typos, and the language must be improved.

Response: Thanks for this comment.

We have carefully checked and revised manuscript and some sentences have been revised in this revised manuscript.

Question 12: Does the pH influence the DPV analysis?

Response: Thanks for this comment.

Differential Pulse Voltammetry (DPV) is based on Linear Sweep Voltammetry (LSV). It works by superimposing a series of pulsed voltages with a fixed amplitude, collecting the current before and after each pulse, and finally plotting the "current difference before and after the pulse" against the sweeping voltage. This method can effectively eliminate the interference of background currents (such as charging currents) and highlight the Faraday current, which is precisely generated by the redox reactions (electron transfer processes) occurring on the electrode surface.

In this work, the electrochemical detection of ammonia-nitrogen is based on the electrocatalytic ammonia oxidation reaction. The ratio of ammonia depends on the pH values [International Journal of Environmental Analytical Chemistry, 2017, 97(1): 85-98, Trends in Analytical Chemistry, 2019, 119: 115627, Trends in Analytical Chemistry, 2020, 127: 115890, Trends in Environmental Analytical Chemistry, 2020, 27: e00098]. Therefore, low pH value can decrease the ratio of ammonia and further effect the current charge of DPV. To avoid this effect, 1 M KOH was used as electrolyte in this work to keep high ratio of ammonia.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article reports synthesis of the ternary PtCoNi alloy and its activity in ammonia nitrogen detection and oxidation. a number of new materials is synthesised and characterised, giving a valuable insight into the studied problem. The main text is accompanied by the supplementary information file which provides a lot of data.

I would like to ask why the majority of the text is focused on the characterisation of the Pt₆Ni₂Co₂-2000 material. Why this composition was chosen as the representative of all studied ones?

Tables 1 and 2 are missing in the main body of the manuscript! There are references to them in manuscript, but they are not present there. One can find them in the supplementary material file (SI). This is acceptable but either a clear reference to SI should be given in the text or both tables should be shifted to the main manuscript.

Some studies are done on the real-world water samples. Please provide the country of provenience, not only the name of the city.

Why some of the recoveries exceeded 100%? 

Comments on the Quality of English Language

Some language mistakes and typos are found in the manuscript, such as incomplete phrases (e.g., line 80: "In addition, when the ratio of H2PtCl6·6H2O/Ni(NO3)2·6H2O/Co(NO3)2·6H2O is 6: 2: 2.") or the lack of capital letters in some of the titles.

 

Author Response

Comments by reviewer (2)

The article reports synthesis of the ternary PtCoNi alloy and its activity in ammonia nitrogen detection and oxidation. a number of new materials is synthesised and characterised, giving a valuable insight into the studied problem. The main text is accompanied by the supplementary information file which provides a lot of data.

Response: We appreciate the reviewer’s comments and suggestions on our work. We have revised the manuscript based on the reviewer’s suggestions.

Question 1: I would like to ask why the majority of the text is focused on the characterisation of the Pt₆Ni₂Co₂-2000 material. Why this composition was chosen as the representative of all studied ones?

Response: Thanks for this comment.

In this work, we would like to design and fabricate one PtNiCo alloy via electrochemical deposition technique for electrochemical detection of ammonia-nitrogen based on the great electrocatalytic activity for electrochemical ammonia oxidation reaction. In order to obtain the high-performance PtNiCo alloy, the ratio of H₂PtCl₆·6H₂O, Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O and electrodeposition time have been controlled during the synthesis process. Electrochemical catalytic performance of all obtained samples for ammonia oxidation reaction have been measured via CV technique. Based on the oxidation peak currents, Pt₆Ni₂Co₂-2000 has been obtained under the electrodeposition time of 2000 s and under the ratio of 6:2:2 (H₂PtCl₆·6H₂O : Ni(NO₃)₂·6H₂O : Co(NO₃)₂·6H₂O). In addition, all samples have been used to measure the sensing activities via CV technique with the ammonia-nitrogen concentration from 0.1 mM to 1 mM. Pt₆Ni₂Co₂-2000 showed the biggest sensitivity compared to other samples. Therefore, based on the above results. Pt₆Ni₂Co₂-2000 has been selected to further measure ammonia-nitrogen detection performances including limit of detection, selectivity, stability and so on.

Question 2: Tables 1 and 2 are missing in the main body of the manuscript! There are references to them in manuscript, but they are not present there. One can find them in the supplementary material file (SI). This is acceptable but either a clear reference to SI should be given in the text or both tables should be shifted to the main manuscript.

Response: Thanks for this comment.

Based on the comment, we have carefully checked this part. The sentences about Table 1 and Table 2 have been revised and highlighted Table S2 and Table S3. In addition, the supporting information has also been revised and highlighted in this revised manuscript.

Question 3: Some studies are done on the real-world water samples. Please provide the country of provenience, not only the name of the city.

Response: Thanks for this comment.

In this work, to carry out the recovery measurements of Pt₆Ni₂Co₂-2000 electrode, actual samples including tap water (Bohai university, Jinzhou, China), lake water (Tinglin lake, Bohai university, Jinzhou, China) and sea water (Baisha Bay, Jinzhou, China) have been collected. According to the reviewers' comments, we have added country information of the sample collection locations and highlighted in this revised manuscript.

Question 4: Why some of the recoveries exceeded 100%?

Response: Thanks for this comment.

In this work, recovery measurements have been conducted for three times to reduce the measured errors. However, based on the measurement results, some of the recoveries exceeded 100%. Some potential reasons include: 1) in the experiment, although we strictly controlled the spiking volume and concentration, the cumulative small positive deviations from multiple operations might result in a slight overestimation of the recovery. 2) On the other hand, this may be attributed to the complex composition of real samples, which leaded to errors in the test results when the added amount of ammonia-nitrogen was low. This result also indicated that we should enhance the sensitivity and selectivity of sensing electrode to meet the real requirements in the next work.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. Certain key sections should be incorporated into the main manuscript to enhance clarity and provide sufficient detail for a better understanding of the discussion.
2. The statement in Line 40 requires additional citation support.
3. Ensure that high-quality images (SEM) of the nanosheets are provided. The present one is not accepted as a nanosheet. Importantly, it has no proper scale bars.   
4. EDAX analysis is essential to confirm the elemental composition of the nanosheets.
5. Include the survey scan spectra for the XPS data, as the current Co 2p and Ni 2p results are not acceptable.
6. Provide the JCPDS number for the reference XRD pattern.
7. State the limitations of the present study.

Comments on the Quality of English Language

English editing is essential, and there are plenty of typos in the whole manuscript. 

Author Response

Comments by reviewer (3)

Question 1: Certain key sections should be incorporated into the main manuscript to enhance clarity and provide sufficient detail for a better understanding of the discussion.

Response: Thanks for this comment.

Based on the comment, a new part (3.3. electrochemical active surface areas (ECSA) and stability of Pt₆Ni₂Co₂-2000 electrode) has been added in this revised manuscript.

Question 2: The statement in Line 40 requires additional citation support.

Response: Thanks for this comment.

Based on the comment, related literatures have been added in this revised manuscript.

Question 3: Ensure that high-quality images (SEM) of the nanosheets are provided. The present one is not accepted as a nanosheet. Importantly, it has no proper scale bars

Response: Thanks for this comment.

Based on the comment, A new SEM image has been provided in this revised manuscript as shown in Fig. R1.

Figure. R1 The SEM image of Pt₆Ni₂Co₂-2000 electrode

Question 4: EDAX analysis is essential to confirm the elemental composition of the nanosheets.

Response: Thanks for this comment.

Based on the comment, the EDX mapping image of Pt, Ni and Co elements have been added in this manuscript as shown in Fig. 1b-d.

Question 5: Include the survey scan spectra for the XPS data, as the current Co 2p and Ni 2p results are not acceptable

Response: Thanks for this comment.

In this work, we would like to design and fabricate one PtNiCo alloy via electrochemical deposition technique for electrochemical detection of ammonia-nitrogen based on the great electrocatalytic activity for electrochemical ammonia oxidation reaction. To confirm the formation of the PtNiCo alloy, HRTEM, XRD, XPS, and EDX mapping were employed to characterize. From the HRTEM image of Pt₆Ni₂Co₂-2000, the lattice fringe (111) of Pt₆Ni₂Co₂-2000 was obvious and the distance of lattice fringe has been calculated with the value of 0.217 nm. Smaller than that of pure Pt (0.226 nm). Compared to the XRD pattern of pure Pt (Pt₁Ni₀Co₀-2000), the peak position showed a slight shift based on the XRD pattern of Pt₆Ni₂Co₂-2000.

Based on the XPS pattern of Pt element in Pt₆Ni₂Co₂-2000, an obvious shift of binding energy could be detected compared to and pure Pt (Pt₁Ni₀Co₀-2000). Above results could prove the formation of the Pt₆Ni₂Co₂-2000 alloy. However, no clear signals of Ni and Co elements could be detected based on the XPS pattern (Fig. R2). the potential reason is that the low ratio of Ni and Co elements in the Pt₆Ni₂Co₂-2000 result in no obvious signals.

Based on the above discussion, some sentences have been added in this revised manuscript: The XPS pattern of Ni and Co elements in Pt₆Ni₂Co₂-2000 has been given in Fig. S2a and S2b. However, no clear signals of Ni and Co elements could be detected. the low ratio of Ni and Co elements in the Pt₆Ni₂Co₂-2000 may be the main factor to result in above results.

Figure. R2 The XPS spectra of Pt₆Ni₂Co₂-2000 and Pt₁Ni₀Co₀-2000

Question 6: Provide the JCPDS number for the reference XRD pattern.

Response: Thanks for this comment.

Based on the comment, the JCPDS number (04-0802) has been added in this revised manuscript.

Question 7: State the limitations of the present study.

Response: Thanks for this comment.

In this work, one ternary PtNiCo nanosheets have been prepared via one-step electrodeposition technique. The ratio of H₂PtCl₆·6H₂O, Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O and electrodeposition time have been controlled. All PtNiCo electrodes have been measured via electrochemical catalytic performance for ammonia oxidation reaction and ammonia-nitrogen detection. Under optimal conditions, Pt₆Ni₂Co₂-2000 showed outstanding electrocatalytic performance and detection activities. The SEM, TEM, XPS and XRD have been used to analyze the structure. Electrochemical active surface areas, electrocatalytic stability, limit of detection, selectivity, recovery and stability and other measurements have also been measured.

Bases on above discussion, this work should enhance the two parts: 1) the oxidation process of ammonia should be further discussion, 2) the reasons of enhanced performances should be researched. Above parts should be analyzed based on the theoretical calculation. In the future, we will actively seek partners, strengthen cooperation in this regard, and further enhance the depth of research.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The presence of ammonia and ammonium ion in the aquatic environment and other ecological systems is significantly harmful to them. Therefore, their detection and subsequent mitigation measures are urgent tasks for environmental protection. To create such molecular and ion detectors, there are many catalytic systems on the surface of which reactions with the participation of detected molecules are realized. Among such systems, metal alloys with noble metals as key componets are promising. At the same time, to achieve maximum catalytic/detecting efficiency, a certain selection of components of such a metal system, the ratio of their concentrations, morphology and atomic structure of the surface is necessary. Along with this, the key point is to maintain the stability and durability of the functioning of such systems. The fundamental principles underlying the formation of such systems have not been sufficiently established to date. In realtion to this, the present work suggesting the controlled preparation of PtNiCo alloy with a specific morphology and atomic structure for efficient ammonia and ammonium ion detection fills this gap. There are several novel findings making input to this field, such as establishing relationship between sample preparation route and its compositional, structural and morphological state, as well as the interrelation with the catalytic activity and selectivity and the stability of performance. It is shown that it is due to the synergistic effect that addition of certain amounts of Ni and Co makes to Pt, as a result of surface structure and electronic state modification, the key points determining the catalytic efficiency.

There are next comments:

 

• Lines 131, 132: It is indicated in the text “The XPS pattern of Ni and Co elements in Pt6Ni2Co2-2000 has been given in Fig. S2a and S2b”. The spectra do not contain nether Ni, nor Co signals. It seems somewhat unusual, so this needs some clarification in the text. Otherwise, the above notion remains as if by itself, not attached to anything.

 

• In Fig. 4 the observed linear dependence between currents and ammonia-nitrogen concentrations is not a priori obvious, and therefore it is desirable to provide a more detailed physic-chemical justification for such a dependence.

 

• It would be desirable to compare the SEM, TEM images before and after stability tests to see more clearly how the reaction does or does not affect the surface morphology.

 

In general, the manuscript is scientifically sound with the appropriate design to address the issues under consideration. It is clear, easy to follow, relevant for the field and presented in a well-structured manner. The manuscript provides sufficient details that support the conclusions. Referencing is quite comprehensive and up-to-dated. The manuscript is suitable for publication with account of the above minor comments.

Author Response

Comments by reviewer (4)

The presence of ammonia and ammonium ion in the aquatic environment and other ecological systems is significantly harmful to them. Therefore, their detection and subsequent mitigation measures are urgent tasks for environmental protection. To create such molecular and ion detectors, there are many catalytic systems on the surface of which reactions with the participation of detected molecules are realized. Among such systems, metal alloys with noble metals as key components are promising. At the same time, to achieve maximum catalytic/detecting efficiency, a certain selection of components of such a metal system, the ratio of their concentrations, morphology and atomic structure of the surface is necessary. Along with this, the key point is to maintain the stability and durability of the functioning of such systems. The fundamental principles underlying the formation of such systems have not been sufficiently established to date. In realtion to this, the present work suggesting the controlled preparation of PtNiCo alloy with a specific morphology and atomic structure for efficient ammonia and ammonium ion detection fills this gap. There are several novel findings making input to this field, such as establishing relationship between sample preparation route and its compositional, structural and morphological state, as well as the interrelation with the catalytic activity and selectivity and the stability of performance. It is shown that it is due to the synergistic effect that addition of certain amounts of Ni and Co makes to Pt, as a result of surface structure and electronic state modification, the key points determining the catalytic efficiency.

Response: We appreciate the reviewer’s comments and suggestions on our work. We have revised the manuscript based on the reviewer’s suggestions.

Question 1: Lines 131, 132: It is indicated in the text “The XPS pattern of Ni and Co elements in Pt₆Ni₂Co₂-2000 has been given in Fig. S2a and S2b”. The spectra do not contain nether Ni, nor Co signals. It seems somewhat unusual, so this needs some clarification in the text. Otherwise, the above notion remains as if by itself, not attached to anything.

Response: Thanks for this comment.

In this work, we would like to design and fabricate one PtNiCo alloy via electrochemical deposition technique for electrochemical detection of ammonia-nitrogen based on the great electrocatalytic activity for electrochemical ammonia oxidation reaction. To confirm the formation of the PtNiCo alloy, HRTEM, XRD, XPS, and EDX mapping were employed to characterize. From the HRTEM image of Pt₆Ni₂Co₂-2000, the lattice fringe (111) of Pt₆Ni₂Co₂-2000 was obvious and the distance of lattice fringe has been calculated with the value of 0.217 nm. Smaller than that of pure Pt (0.226 nm). Compared to the XRD pattern of pure Pt (Pt₁Ni₀Co₀-2000), the peak position showed a slight shift based on the XRD pattern of Pt₆Ni₂Co₂-2000.

Based on the XPS pattern of Pt element in Pt₆Ni₂Co₂-2000, an obvious shift of binding energy could be detected compared to and pure Pt (Pt₁Ni₀Co₀-2000). Above results could prove the formation of the Pt₆Ni₂Co₂-2000 alloy. However, no clear signals of Ni and Co elements could be detected based on the XPS pattern. the potential reason is that the low ratio of Ni and Co elements in the Pt₆Ni₂Co₂-2000 result in no obvious signals.

Based on the above discussion, some sentences have been added in this revised manuscript: The XPS pattern of Ni and Co elements in Pt₆Ni₂Co₂-2000 has been given in Fig. S2a and S2b. However, no clear signals of Ni and Co elements could be detected. the low ratio of Ni and Co elements in the Pt₆Ni₂Co₂-2000 may be the main factor to result in above results.

Question 2: In Fig. 4 the observed linear dependence between currents and ammonia-nitrogen concentrations is not a priori obvious, and therefore it is desirable to provide a more detailed physic-chemical justification for such a dependence.

Response: Thanks for this comment.

In this work, we would like to design one PtNiCo alloy for electrochemical detection of ammonia-nitrogen based on the electrocatalytic ammonia oxidation reaction. Based on some reports, the oxidation processes of ammonia on Pt-based catalysts have been proposed and two reaction mechanisms are potential: Oswin and Salomon proposed a detailed mechanism for the stepwise dehydrogenation of ammonia ^[1]. Gerischer and Mauerer proposed modifications to the initial dehydrogenation steps, suggesting that coupling between ^∗NH_x and ^∗NH_y intermediates occurs, forming an ^∗N₂H_x+y complex ^[2]. Though the intermediates are different based on above potential processes, a large number of electrons are generated during the oxidation process of ammonia. Moreover, in the process of the oxidation reaction, an oxidation peak can be produced and the peak current can be measured. In addition, in this work, CV measurements have first been used to verify that when ammonia-nitrogen with different concentrations were added to the test system, the oxidation peak current varied significantly. Furthermore, as the concentration of ammonia-nitrogen increased, the oxidation peak current increased gradually, and the two show a linear relationship.

Actually, it is difficult to directly predict in advance whether there is a linear relationship between ammonia-nitrogen concentrations and currents. Therefore, in this work, we obtained the linear relationship between ammonia-nitrogen concentrations and currents based on the catalytic performance of platinum-based catalysts for the electrochemical oxidation of ammonia, relevant literatures on the oxidation process of ammonia, as well as the results of CV tests, DPV tests, etc. conducted with the designed Pt₆Ni₂Co₂-2000 electrode.

[1] H. G. Oswin, M. Salomon, The anodic oxidation of ammonia at platinum black electrodes in aqueous KOH electrolyte[J]. Canadian Journal of Chemistry, 1963, 41(7): 1686-1694.

[2] H. Gerischer, A. Mauerer, Untersuchungen zur anodischen oxidation von ammoniak an platin-elektroden[J]. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1970, 25(3): 421-433.

Question 3: It would be desirable to compare the SEM, TEM images before and after stability tests to see more clearly how the reaction does or does not affect the surface morphology.

Response: Thanks for this comment.

Comparing the morphology before and after the stability tests is a very effective strategy to evaluate whether the reaction has an impact on the morphology. Specifically, due to the summer vacation, the Experiment & Equipment Administrate Center in Bohai university cannot provide TEM testing. Therefore, in response to the reviewers' comments, the Pt₆Ni₂Co₂-2000 after the stability test has been characterized by SEM. Fig. R1a shows the SEM image before the stability test, and the sample exhibits a sheet-like morphology. Fig. R1b presents the SEM image after the stability test. It is easy to observe that the sample also has a sheet-like morphology. Thus, by comparing the SEM images before and after the test, it can be concluded that the reaction has little effect on the morphology.

Based on above discussion, some sentences have been added in this revised manuscript: Fig. S10b showed the SEM image of the Pt₆Ni₂Co₂-2000 after the stability test. Based on the SEM image, the sheet-like morphology could be found and no obvious change could be found compared to SEM image before the stability test (Fig. S10b)

Figure R1. The SEM image of Pt₆Ni₂Co₂-2000 (a) before and (b) after stability test for 12 h.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revised version is suitable for publication.

Author Response

Comments by reviewer (1)

The revised version is suitable for publication.

Response: We appreciate the reviewer’s comments and thank for suggesting publication.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper got improved after the review round. 

Comments on the Quality of English Language

I would only recommend language editing, e.g. line 128 reads ". the low ratio" while it should read ". The low ratio".

Author Response

Comments by reviewer (2)

The paper got improved after the review round.

Response: We appreciate the reviewer’s comments and suggestions on our work. We have revised the manuscript based on the reviewer’s suggestions.

Question 1: I would only recommend language editing, e.g. line 128 reads ". the low ratio" while it should read ". The low ratio".

Response: Thanks for this comment.

Based on the comment, “the low ratio” has been revised in this revised manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors’ responses are somewhat satisfactory. However, Comment 5 has not been adequately addressed. This point is crucial to the present work. If the prepared material contains a low ratio of Ni and Co elements, it is recommended to determine the ratio using XRD data and include the results in the manuscript.

Based on the XPS analysis, the ratio of Ni and Co appears negligible and therefore unacceptable. However, the elemental mapping results clearly demonstrate a uniform distribution of Ni and Co.

Author Response

Comments by reviewer (3)

Question 1: The authors’ responses are somewhat satisfactory. However, Comment 5 has not been adequately addressed. This point is crucial to the present work. If the prepared material contains a low ratio of Ni and Co elements, it is recommended to determine the ratio using XRD data and include the results in the manuscript.

Response: Thanks for this comment.

The determination of element ratios in materials (especially the phase ratios composed of different elements in multiphase systems) using X-ray Diffraction (XRD) data is mainly based on the principle of phase quantitative analysis. It involves deriving the content of each phase through the intensity relationship of characteristic diffraction peaks, and then converting this content into element ratios. However, in this work, the ratios of Ni and Co elements in PtNiCo alloy are low and are difficult to calculate the element ratios using XRD. To further analyze the element ratios of Pt, Ni, and Co, we employed Inductively Coupled Plasma (ICP) to analyze the sample, and obtained the following results:the molar ratios of Pt, Ni, and Co elements were 122:3:1. These results confirm that the ratio of Ni and Co elements are indeed very low. In addition, the above-mentioned results have been added to the revised manuscript: This viewpoint can be verified by the results of ICP analysis and the molar ratios of Pt, Ni, and Co elements were 122:3:1.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

The revised version is now recommended for publication.