The Influence of Acetone on the Kinetics of Water Electrolysis Examined at Polycrystalline Pt Electrode in Alkaline Solution

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this manuscript, the authors studied the impact of acetone on the electrochemical behaviour of polycrystalline platinum electrode in 0.1 M NaOH solution, with respect to the kinetics of hydrogen and oxygen evolution reactions (HER and OER), and indirectly to underpotential deposition of hydrogen (UPDH). This is a very interesting work, and the findings can have strong implications for improving industrial alkaline water electrolysis process through addition of traces of organic additives into electrolytes. Overall, this work is considered suitable for the journal Catalysts. However, some comments require to be properly addressed to further improve the clarity and quality of the manuscript. Please see below for more details.

1. The authors used coiled Pt wire as the counter electrode. This might be a concern for the assessment of the HER, during which Pt counter electrode might be dissolved and re-deposited on the working electrode. This concern has been raised previously in the HER study (e.g., DOI: 10.1021/acsenergylett.7b00219).

2. To appeal to a broader readership, recent works on water electrolysis and HER/OER can be referenced in the Introduction (e.g., Energy Technology 2022, 10, 2200573; SusMat 2021, 1, 460).

3. There might be a concern about the reduction of acetone during HER, contributing to enhanced overall current density observed. Similarly, there is a concern about the oxidation of acetone during OER, resulting in enhanced overall current density. Is there a way to check the Faradaic efficiency to confirm that the addition of acetone contributes solely to HER or OER instead of other possible side reactions?

4. When evaluating the OER and HER of Pt working electrode in the presence of acetone, did the authors conduct some pre-treatment of the Pt electrode, such as polishing? Did they use the same Pt working electrode? Would there be any contamination and how to avoid this?

 

5. Did the authors fit the EIS data in Figure 9, as they did in Figure 7 and 8? If so, please also include the equivalent circuit for the EIS fitting presented in Figure 9.

Author Response

RESPONSES TO THE REVIEWERS’ COMMENTS

 

Authors:   Aleksandra Adamicka, Tomasz Mikołajczyk, Mateusz Kuczyński and Bogusław Pierożyński

Title: “The influence of acetone on the kinetics of water electrolysis examined at polycrystalline Pt electrode in alkaline solution”

 

Reviewer # 1:

1. We agree upon with the Reviewer that under certain anodic conditions Pt counter electrode could undergo dissolution, which (Pt) would later become cathodically reposited on the working electrode. However, it has to be noticed that in our case such deposition (if any) would take place on polycrystalline Pt electrode, which is identical to that of the counter one. The above is in contrast to the concept described in the paper given under DOI: 10.1021/acsenergylett.7b00219, where Ni-C-based catalyst was used as the working electrode! In the latter case, any Pt surface deposition would immediately increase the HER kinetics of the Ni-C electrode, which in fact is not very catalytic in this process itself…..
2. We agree with the Reviewer. In the revised manuscript, the stated articles have been added to Introduction Section (see Refs. 1 and 2, and page 1 there).
3. The “surface tension” mechanism of acetone influence on the HER (and possibly also OER) was properly described on pages 4-5 (lines 111-120 and Scheme 2) of an original manuscript. It should be stated that overall Pt surface adsorption of acetone is very limited, primarily because acetone molecules have to compete for the Pt adsorption sites with H (also with O/OH species over anodic potentials), which is known to undergo strong chemisorption on the Pt surface, before the HER becomes initiated (the so-called “H UPD” region).

Furthermore, electroreduction of acetone (even when its concentration is as high as 0.5 M) is associated with cathodic current-densities on the order of 130 µA cm^-2 (see Figure 1b in the original manuscript), where at least two orders in magnitude higher Faradaic current-densities are associated with the process of HER at Pt, at the overpotential of 500 mV (see Figures 3 and 4 there).

Finally, having conducted extended electrolysis experiments in the presence of acetone (at 1.0×10^-3 M) in 0.1 M NaOH, further chromatographic analysis showed no evidence of isopropanol presence (at the experimental accuracy), which is a main product of acetone electroreduction. In other words, the side reactions are undeniably insignificant, where their products could later become partly adsorbed on the reaction vessel’s walls, thus depleting their concentration in the solution.

4. Polycrystalline Pt electrode was subjected to flame-annealing procedure, followed by quenching in ultra-pure water before every new experiment/measurement. The latter is a typical procedure to clean platinum surface, employed for high-purity platinum electrochemistry works. In fact, this important information was missing from the manuscript and has now been added to the revised manuscript (see Section Materials and Methods on page 13 there).
5. The impedance results in Figure 7a illustrate the process of UPD of H and were fitted by an equivalent circuit presented in Figure 7b. On the other hand, both the HER and OER impedance results (Figure 8a and Figure 9, correspondingly) were both fitted by an equivalent circuit presented in Figure 8b (CPE-modified Randles circuit; also see a caption to Figure 8 for details).

Reviewer 2 Report

Comments and Suggestions for Authors

The authors study the influence of acetone on the kinetics of polycrystalline Pt electrode for water electrolysis in alkaline solutions. Various electrochemical measurements are conducted to demonstrate the performance origins. However, some important issues must be solved before acceptance.

1.     To highlight the importance of green hydrogen and improve the readability, the authors should combine some data in the introduction part, such as global hydrogen economics and requirement. Please refer to 10.1039/D3EE02695G for this point.

2.     This manuscript lacks necessary investigations on the electrochemical stability. Please refer to 10.1002/adfm.202207618 for this point.

3.     Whether the findings are applicable for other organic chemical added into electrolytes should be further checked.

4.     The authors are suggested to well demonstrate whether the addition of organic chemicals could help improve the practical applications.

 

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Reviewer # 2:

1. In the revised manuscript, additional information on the importance of green hydrogen economy (in reference to a suggested article under DOI: 1039/D3EE02695G) has been incorporated into its Introduction Section (see page 1 and Ref. 3, there).
2. Our work has to be treated as introductory to the problem, which does present a proof that acetone could be regarded (with showing an appropriate reaction mechanism) as the HER and OER kinetics facilitator!

However, we agree upon with the Reviewer on the importance and necessity of electrochemical long-time stability studies. Understandably, such investigation would be required before any conclusion on technical scale could be made! With respect to the above, one should probably decide on whether such study should remind typical laboratory type electrochemistry work or else it should directly be carried-out (e.g. for over at least one month) on a technical-scale alkaline water electrolyser unit. Another question is that such a system should be operated on more “realistic” catalysts and temperature conditions (ca. 40-50^o C) that are relatively close to those of the commercial installations (also see Conclusions Section of the original/revised manuscript).

3/4.  We do agree upon with the importance of studying the influence of various organic molecules (as low concentration additives into alkaline electrolyte) on the kinetics of alkaline water splitting. However, the above is quite a serious matter, as it involves many important aspects, including:

1. chemical stability of such compounds under operational conditions (electrolyte and its temperature) and their safety for the operation of water splitting catalysts (no/low poisoning effect),
2. limited electro-reactivity over operational voltage,
3. environmental safety of such organic molecules, etc……