Peer review of: Intermolecular cascaded π-conjugation channels for electron delivery powering CO2 photoreduct (2020)

Reviewers' comments: 
 
Reviewer #1 (Remarks to the Author): 
 
This manuscript developed the construction of intermolecular cascaded π-conjugation channels by 
modifying both intramolecular and intermolecular conjugation to optimize the photogenerated electron 
delivery and improve the performance of CO2 photoreduction. The highest CO evolution activity of 
2247 μmol g-1 h-1 among all reported conjugated polymers has been achieved. These results may be 
interesting and inspire scientists in the field to further improve the performance of CO2 
photoconversion. However, there are some issues on data analyses about structure and properties. 
Therefore, revision on this draft is necessary before acceptance for publication. 
 
1. The discussion of the band structure is too superficial. Please added the detailed investigation in the 
manuscript, such as Mott-Schottky test and UPS spectra. 
 
2. Page 8, the cyclic-voltammetry method and EPR measurement cannot demonstrated that the 
electrons on LUMO of CPs can have the ability to produce Co (I) from Co (II), because of solvent 
effect. The test conditions for EPR measurement should be provided. More convincing evidence for the 
existence of Co (I) should be provided, e.g. in-situ XPS. 
 
3. According to supplementary Table S4, residual palladium (0.661 wt.%) retains in CPs matrix. 
Whether the residual Pd affect the photocatalytic CO2 reduction activity? There is no explanation 
about it in the manuscript. 
 
4. In Fig. 4a, CO2 absorption-desorption isotherms curves were employed to demonstrate that the 
capacity for CO2 adsorption was not the determining factor for the CO2 photoreduction. However, the 
chemisorption of CO2 is a more important factor in CO2 photoreduction. The chemisorption of CO2, 
e.g. CO2-FTIR, should be added. 
 
5. In Fig. 4c and spplementary Table S6, the author tried to highlight the fact that the photoexcited 
electrons can be fast delivered to CO2 from catalyst. Nevertheless, the short lifetime (τ1) was also 
shortened in CO2 atmosphere. The average lifetime and experimental details of TRPL should be 
provided. 
 
6. The decomposition of the CP should be considered on the conversion of CO2 to CO. 
 
7. The photocatalytic stability should be carried out and the mechanism of the apparent degradation of 
the photocatalytic activity should be discussed. 
 
 
 
Reviewer #2 (Remarks to the Author): 
 
I am supportive of this work as this is very topical area of research and a range of interesting 
measurements (such as TRMC and TAS) are used to gain understanding and the observed AQYs are 
high, which is also important in this field. 
Having said this there are a couple of flaws which I believe should be addressed before this can be 
accepted: 
- I strongly disagree with the premise of ‘molecular architecture’ or design. I actually think it makes 
the manuscript weaker as there is a risk that other important factors have not been considered, the 
data set is simply to small to draw strong conclusions, in particular in photocatalysis where many 
different processes are taking place. I am also a little unsure about the notion of improving alkynyl 
materials: As far as I can tell these have not been previously reported and based on what has been 
reported for hydrogen production from water, I would not have expected them to act as particularly 
good photocatalysts for CO2 reduction. I would recommend focusing on reporting these materials and 
dropping the design aspect (including the title), as it is questionable in this field 
- Transient absorption spectroscopy can be very insightful to understand the dynamics in these 
materials. However, it would be much more useful to perform the measurement in the presence of 
scavenger and/or CO2 to understand what is happening under photocatalysis conditions. 
 
A few other more minor comments and questions: 
1) At first I was very excited about these results only to see later that TEOA was used. This is ok at 
this stage, but the manuscript needs to state clearer in the main-text that a scavenger was used. 
2) Net-like materials are usually referred to as conjugated microporous polymers in the materials 
community. 
3) Comparing rates to other reports makes little sense as this ignores the fact that set-ups are very 
different and light sources vary (statement: ‘highest CO evolution efficiency’ and in a few other 
places). It would be much better to compare AQYs, which are already in the manuscript, to other 
reports. 
4) Particle size and dispersion in the photocatalysis mixture are currently not considered. Some 
reports indicate that this might be important and should be measured and added. 
5) Important experimental details are missing: What was the pressure of the photolysis experiment? 
This needs to be added to figure captions and also mentioned in the main-text. How much of the Co 
complex was used? I was a little unsure at times and it needs to be stated clearer. 
6) CO2 absorption of a dry powder can be very different compared to a measurement under wet 
conditions. This has been reported for conjugated microporous polymers and should be measured if it 
is considered to be important. 
7) Selectivity is only briefly discussed in the main-text but omitted from Fig.3. I am a little unsure how 
important it is right now as the area is in its infancy, but it seems to be standard practise in the field 
and should be added. 
8) Were the TR-PL measurements in Fig.4 performed in the presence of a scavenger? 
 
 
Reviewer #3 (Remarks to the Author): 
 
The manuscript of J.H. Ye et al. reports on the original construction of intermolecular cascaded π-
conjugation channels for powering CO2 photoreduction by modifying both intramolecular and 
intermolecular conjugation of conjugated polymers. This study is of great interest and reports a rather 
novel approach. Detailed experimental analysis and theoretical calculations were conducted to verify 
the proposed approach and conclusion. This work might interest those in pursuit of better 
photogenerated electron delivery from the viewpoint of the molecular architecture. Though I inclined 
to recommend the publication with Nat. Commnun., there are also some important revisions need to 
be made: 
1. Could you please give the loading content of the Co (II) bipyridine complexes cocatalyst on the CPs 
as this may be critical for the photocatalytic efficiency? 
2. As the author showed in Table S4, there are some residual palladium and copper metals detected in 
the CPs. Please explain if these metals, especially the Pd, will have any activity in the photocatalytic 
process. 
3. In this study, the LUMO and HOMO were obtained by hybrid density-functional-theory-based first-
principles calculations. The experimental verifications for these values by UPS or Mott-Schottky plot 
should be conducted. 
4. Authors mentioned that “The conductivity transients and calculated charge mobilities for CPs are 
displayed in Fig. 2a, in which the L-CP-A, with a linear structure and alkynyl group, exhibits charge 
mobility (μtot) of 0.32 cm2 V-1 s-1 (φ Σμ= 7.4×10-5 V-1 s-1). As expected, the charge mobility of L-
CP-D in the absence of alkynyl decreased to a much lower value of 0.15 cm2 V-1 s-1(φ Σμ= 3.4×10-5 
V-1 s-1).” (Page 6). However, there is no corresponding results shown in Fig.2a. Please check this 
carefully. 
5. Authors claimed that “Besides, the net-like CPs (N-CP-A and N-CP-D) possess more cocatalyst 
absorption sites of phenyl in the units, thus resulting in enhanced performance of net-like CPs (N-CP-A 
and N-CP-D) than those of linear CPs (L-CP-A and L-CP-D)” (Page 9). As Fig.4a shows, the N-CPs 
exhibited greater CO2 adsorption than the L-CPs. Does the CO2 adsorption have any effects on the 
CO2 photoreduction efficiency except for the cocatalyst absorption sites number? This may be a result 
of multi-factors. 
6. There is a clerical error in SI (page 46). “As shown in Figure S4” should be “As shown in Figure 
S34”. 
 
Then, I would highly suggest these minor revisions to be thoroughly addressed before re-submission.