Electrocatalytic Enhancement of CO Methanation at the Metal–Electrolyte Interface Studied Using In Situ X-ray Photoelectron Spectroscopy

Round 1

Reviewer 1 Report

The authors reported an experimental study on electrocatalytic CO methanation at the metal-electrolyte interface using in situ X-ray photoelectron spectroscopy. Their synchrotron-based in situ near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) results showed that alloying of Ni/yttria-stabilized-zirconia (YSZ) cermet electrodes with Cu can be used to control the electrochemical accumulation of interfacial carbon, and to optimize its reactivity toward CO2. Overall, this paper is well written and presented and of high quality. I would recommend for the acceptance of this paper after the following concerns are addressed in revision: 

1. In Introduction, there’s little background information on NiCu alloy. I would suggest the authors include some literature to support their finding about the beneficial role of Cu in inhabiting C deposition, e.g., Journal of Power Sources 196 (2011) 4724–4728; J. Chem. Phys. 131, 174702 (2009).

2. In Experimental Methods, there’s no mention about the synthesis of Ni/8-YSZ and Ni80Cu20/8-YSZ working electrodes.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript reported the " Utilization of renewable electricity to produce synthetic methane". The material design is reasonable and the data can explain the conclusion well. This paper introduces SOECs, optimizes the previous research, and puts forward a new detection idea. Some issues should be addressed before possible publication as follows:

1. The linguistic and logical coherence of the introduction needs to be improved. The consistency with the text is not strong, can introduce the difference between the existing detection methods and this paper, highlight the work content.

2. Some related works maybe are useful for support and background, such as such as Chem Eng J 415 (2021) 129014, etc.

3. Standardized and unified icon classes to enhance clarity and illustrative.More specific explanations and explanations for some of the key points.

4. Appropriately increase the reference content.

5. There is no explanation or reasonable speculation on the mechanism of performance difference between Ni/8-YSZ and Ni80Cu20/8-YSZ. The content support is not strong.

6. Refine the language of the conclusion, highlight the content of the work, and part of the explanation can be put into the body.

Moderate editing of English language required.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Summary:

The authors studied the role of elemental carbon as an intermediate within the reaction path of CO methanation. XPS and CV-QMS experiments are conducted to evaluate the performance of Ni/YSZ and Ni₈₀Cu₂₀/YSZ as working electrodes.

Impact:

The authors studied the reaction pathways of CO electrolysis to methane. This manuscript will be of great interest to the readers of C, especially for researchers working on electrocatalysis. However, lots of questions remain unanswered and many issues need to be addressed.

Issues:

1. Regarding the discussions over Fig.1, the authors conclude that C_TPB is more reactive on the Ni₈₀Cu₂₀/YSZ electrode as it vanishes faster. However, this only shows the vanishing speed compared to the starting position and it may not represent the actual speed/amount of carbon on the electrode, which makes this conclusion questionable. Another question I have is why the authors use different CO₂ pressure here? Also, the study of the reaction between C_TPB and CO₂ may not be helpful in studying the actual CO methanation process.

2. In Fig. 2, the results suggest that no C_TPB is formed on Ni/8-YSZ electrode in CO-H₂ gas. Did the authors look into the other products generated?

3. The author mentioned that the Ni/8-YSZ and Ni₈₀Cu₂₀/8-YSZ show indistinguishable CH₄ formation properties from the QMS data. However, from the results in figure 2, only Ni₈₀Cu₂₀/8-YSZ is able to form C_TPB, which is an important intermediate in the CH₄ formation. Does it mean that there could be a different set of reaction pathways?

Author Response

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Round 2

Reviewer 1 Report

The authors have addressed my comments and I recommend for the acceptance of this paper for publication.

Reviewer 2 Report

 Accept in present form

Reviewer 3 Report

All issues have been addressed.