Peer review of: Examining the surface evolution of LaTiOxNy an oxynitride solar water splitting photocatalyst (2020)

Reviewers' comments: 
 
Reviewer #1 (Remarks to the Author): 
 
With the described surface sensitive methods (NR and GIXAS) to study the physicochemical processes 
occurring at the SC/liquid interface, it is possible to reveal the alteration of the surface during the PEC 
reaction and also possible to identify the mechanism of photoelectrocatalyst degradation. Thus, I think 
that this study will attract the interest of the scientific community. However, there are two key steps 
which in my opinion would make even a bigger impact: 
1.) To show data on in-situ measurements 
2.) To demonstrate versatility of these combined techniques on other SCs (I understand, that 
perovskite-type oxynitrides are promising materials due to their optimal bandgap and band edge 
positions, however, to put it mildly, their potential is not fully exploited. Also, it is not elegant to show 
photovoltammograms with 1-2 microA/cm-2 photocurrents which is then changing to 5-6 after adding 
a co-catalyst to the system). 
Overall, the authors have addressed all critical comments and the manuscript is suitable for 
publication in Nature Communications 
 
 
 
Reviewer #3 (Remarks to the Author): 
 
The paper of C. Lawley emphasizes, for the first time, by means of neutron reflectometry and grazing 
incidence X-ray diffraction spectroscopy, an oxidation of the La (A) cations at the surface of perovskite 
oxynitride LaTiO2N thin films undergoing water-splitting process, associated to a local disorder of the 
Ti (B) cations. Such processes are cancelled out when films are decorated with a co-catalyst, thus 
leading to a better photoelectrochemical response. 
The study presented here is of quality and the article is well written. Nevertheless, despite novel and 
high quality results, I find that these are not at the level required for the journal Nature 
Communications and, so, I recommend to reject the article. 
Three mains remarks: 
• As the authors write in their response to Reviewers, the signals are tiny. All their hypothesis and 
model are based on these tiny signals both in neutron reflectometry and grazing incidence X-ray 
diffraction. So the question arises on the reproducibility of the results. To the question n°2 of 
Reviewer 2, the authors respond that “we would not think to measure just one sample once”, but no 
details are given on the exact number of LTON films that were measured. 
 
• This leads to my second remark: the authors clearly evidenced that the epitaxial LTON films are no 
longer stoichiometric with regard to the nitrogen content (i.e. O/N = 10.3 – 10.7 and formulation 
La1.02Ti0.98O3.0N0.28 in Supplementary Table 1). I wonder how this composition, surely associated 
with a defected perovskite structure, can itself be responsible to the oxidation of the La cations during 
the water-splitting process. Do stoichiometric LaTiO2N films, even polycrystalline, respond as their 
epitaxial counterparts? This specific study would have been of interest. The additional remark of 
Reviewer 2 is then of great interest: do the cell parameters emphasize a (strong, weak) distortion of 
the perovskite ABO2N cell and how does this influence the behavior of A and B cations during the 
photoelectrochemical test? 
 
• As a third remark, I find that the very interesting parts, that is scientific detailed discussion of the 
results, are located in … the Supplementary part. Readers get the impression that the results are 
presented in the manuscript as accepted, without detailed arguments. On the contrary, experimental 
results are well argued in Supplementary section (see for example “titanium K pre edge peak 
assignements”), but we should read the article without the help of the Supplementary add-ons. 
 
So, as a conclusion, I find this article very interesting and innovative but the article should be rewrite 
deeply saying clearly on how many samples the analysis has been undertaken, what is the structure of 
the under-stoichiometric LTON films and if it influences the photoresponse and associated processes 
on La and Ti cations. A robust and detailed argumentation has to be put inside the article. 



Dear Dr Pergolesi, 
 
Your manuscript entitled "Oxynitride solar water splitting photocatalysts: examining the surface 
evolution of LaTiOxNY" has now been seen by 2 referees. We note that one of the previous referees 
was unable to assess the work again, although we have found an additional referee to examine the 
work. You will see from their comments below that while they find your work of high interest, some 
important points are raised. Both referees have important suggestions we believe will improve the 
manuscript. For instance, we believe Reviewer #3's concerns regarding the reproducibility and the 
structure plus influence of the sub-stoichiometric films, are particularly important to address. We 
are interested in the possibility of publishing your study in Nature Communications, but would like 
to consider your response to these concerns in the form of a revised manuscript before we make a 
final decision on publication. 
 
We therefore invite you to revise and resubmit your manuscript, taking into account all the points 
raised. Please highlight all changes in the manuscript text file. 
 
We are committed to providing a fair and constructive peer-review process. Do not hesitate to 
contact us if you wish to discuss the revision in more detail or if there are specific requests from the 
reviewers that you believe are technically impossible or unlikely to yield a meaningful outcome.