Bioinspired trimesic acid anchored electrocatalysts with unique static and dynamic compatibility for enhanced water oxidation

Layered double hydroxides are promising candidates for the electrocatalytic oxygen evolution reaction. Unfortunately, their catalytic kinetics and long-term stabilities are far from satisfactory compared to those of rare metals. Here, we investigate the durability of nickel-iron layered double hydroxides and show that ablation of the lamellar structure due to metal dissolution is the cause of the decreased stability. Inspired by the amino acid residues in photosystem II, we report a strategy using trimesic acid anchors to prepare the subsize nickel-iron layered double hydroxides with kinetics, activity and stability superior to those of commercial catalysts. Fundamental investigations through operando spectroscopy and theoretical calculations reveal that the superaerophobic surface facilitates prompt release of the generated O2 bubbles, and protects the structure of the catalyst. Coupling between the metals and coordinated carboxylates via C‒O‒Fe bonding prevents dissolution of the metal species, which stabilizes the electronic structure by static coordination. In addition, the uncoordinated carboxylates formed by dynamic evolution during oxygen evolution reaction serve as proton ferries to accelerate the oxygen evolution reaction kinetics. This work offers a promising way to achieve breakthroughs in oxygen evolution reaction stability and dynamic performance by introducing functional ligands with static and dynamic compatibilities.

6. Careful examination is needed to avoid typos and other problems (e.g. Figure 13a on page 8).Please double-check.
Reviewer #2 (Remarks to the Author): Actually, the leaching of transition metals always happened in layered double hydroxides upon longterm stability test, which largely limits their activity at high current densities and large-scale commercialization.This manuscript submitted by Lu et al. adopted a static and dynamic compatibility anchor strategy to synthesize a subsize NiFe-LDH nanosheet catalyst (SU-NiFe-LDH(TA)@cp) via modifying with trimesic acid and regulating the type of electrodeposited ions.Benefited from the coordination between ligands and NiFe-LDH by C-O-Fe bonds and the promoted OER kinetic performance, the resulting superhydrophilic and superaerophobic SU-NiFe-LDH(TA)@cp catalyst exhibits enhanced electrocatalytic performance and stability at large current (1500 mA cm-2) for 1300 h.However, the general scope of this paper lacks innovation and is not of interest to a sufficiently broad audience.Over the past decade, LDH -based materials have been well studied in OER and it is not quite clear what is the new science in this work, especially combining the great tunability of enzymatic systems with known oxide-based catalysts to achieve both high activity and stability.Such as Nat.Mater.2022, 21, 673-680; ACS Appl.Mater.Interfaces 2021, 13, 37063-37070.As thus, I would not recommend this manuscript to be published in Nat.Commun.
Other detailed comments: 1.If the authors want to prove that Fe3+ is conducive to the form of smaller nanosheet structure, you should supply the TEM and corresponding HRTEM images about NiFe-LDH(TA)@cp to reveal the structural distinction between SU-NiFe-LDH(TA)@cp and NiFe-LDH(TA)@cp according to the experimental details you mentioned.
2. Ni ion is the dominant part in NiFe-LDH, so why can't we see the C-O-Ni bonds in the spectra of Ni 2p for SU-NiFe-LDH(TA)@cp and NiFe-LDH(TA)@cp?Please give a reasonable explanation for the ligand's binding tendency to metal ions in LDH.Besides, the authors should list the XPS results of the three samples before and after OER test in tables and put them in SI, including the shift of peak position and the content of oxygen defect.

The authors emphasize that the coordinated carboxylates anchored on LDH by C-O-Fe bonds could
stabilize the metal active sites to improve the OER stability and dynamics performance.So, in this NiFe system, which metal ion is the true catalytic active site or which metal ion dissolution is more detrimental to the stability of the structure?It is suggested that the authors should use XPS, XAS, etc to supply the relevant experimental data to strengthen the study of catalytic mechanism.
4. The authors should specify the electrochemical test conditions, especially the test voltage for electrolyzing water under the large current density (1500 mA cm-2).Secondly, it is suggested that the author supply the test results under industrial conditions to highlight the excellent performance of the catalyst.
5. In fact, only the in situ Raman result of the SU-NiFe-LDH(TA)@cp is not enough to show that the coordinated carboxylates are favorable to stabilize the metal center and the involvement of carboxyl groups in proton transfer of OER intermediates.The authors should supply the in situ Raman data of other two samples (NiFe-LDH(TA)@cp and NiFe-LDH@cp) for comparative analysis.Moreover, It is recommended to supply the in situ infrared test to state the dynamic evolution behavior of carboxyl ligands during OER process.
6.There are many grammar and typo errors in this text.Thus, for a better readability, please check throughout the whole article text and correct all the errors.Reviewer #3 (Remarks to the Author): The work by X. Lin et al. reports a trimesic acid anchored NiFe-LDH with enhanced stability and activity for alkaline water oxidation.The authors argue that C-O-Fe bonds can be formed to stabilize LDH, thus realizing long-term stability as well as accelerated OER kinetics.Although the idea looks fancy, the major conclusions are not raised with solid evidence.Besides, some key characterizations, electrochemical results and DFT calculations seem to be conducted in an improper way.Considering these problems, I cannot suggest publication of this work.Below are some major concerns: 1.A key concern is that the stability tests of NiFe-LDH (Figure 1a) and NiFe-LDH(TA) (Figure S10) seem to be conducted under different potential.Such comparison cannot support the conclusion of enhanced stability.

2.
Another key concern is that the evidence used to support the formation of C-O-Fe bonds is unconvincing.First, the FTIR analysis in Page 6 can only suggest the existence of tremesic acid and NiFe-LDH.The conclusion that 'trimesic acid ligand is successfully embedded in NiFe-LDH' seems to be speculation.Second, the XPS fitting in Figure 3 is far from rational.Taking Figure 3c as an example, the peak fitting seems to be conducted in a very subjective manner.Therefore, conclusions derived from Figure 3 are highly skeptical.S2 seem to be irrelevant to the labelled standard reference of Ni(OH)2.The authors should clarify this point.4.OER normally takes place at the uppermost surface layer of catalyst.However, based on the model in Figure 7a and Figure S21, the adsorption of OER intermediates are placed at the interlayer of LDH.The authors should explain more on this abnormal adsorption.7c cannot tell how the charge redistribute at the interface.I suggest use bader charge analysis.

5.The charge density difference results in Figure
6.Based on the proposed mechanism in Figure 6b, the hydrogen atom in OOH intermediate can interact with two oxygen atoms in trimesic acid.However, the OOH adsorption structure in Figure S20 and S21 cannot identify such a binding configuration.The authors should elucidate this inconsistency.
7.More details of the electrochemical tests should be provided, e.g., the scan rate, potential range and the potential set for stability test.The electrodes in this work were prepared on carbon paper.Therefore, the comparison data should also be those loaded on carbon paper.The authors should specify whether the comparisons in Figure 4c and 4g are those loaded on carbon paper.

Revisions and replies to the comments of the reviewers (NCOMMS-23-05989) REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author): This paper proposed a strategy to boost the OER performance of NiFe LDH by anchoring trimesic acid into the lamellar structure.The prepared SU-NiFe-LDH(TA) catalyst shows outstanding OER activity (248 mV@100 mA cm -2 ) and ultrastability at large current (1300 h at 1500 mA cm -2 ).Further comments are noted below: Response: Thanks for your positive evaluation of our manuscript.We have revised the manuscript according to your valuable comments and suggestions.
1.In Figure S6, the peaks located at 1384 and 1501 cm -1 should be contributed to vas(COO-) and aromatic CH groups, respectively.The characteristic infrared absorption wavenumbers of the uncoordinated (-COOH) carboxylate groups are normally strong in intensity and found in 1680-1800 cm -1 .Therefore, the FTIR spectrum of SU-NiFe-LDH(TA)@cp samples maybe has no uncoordinated (-COOH) carboxylate groups.Similarly, the coordinated carboxylate group presented a new doublet at ~ 1420 and ~1630 in Raman test, which were associated with the in-and out-of-phase stretching modes of the carboxylate group.Thus, it is difficult to distinguish the uncoordinated (-COOH) and coordinated (-COO-) carboxylate groups by Raman.In-situ FTIR seems more suitable for this work.
Response: Thanks for your valuable suggestion to improve our paper.We have substituted the prior FTIR spectrum with an attenuated total reflection infrared spectrum (Shimadzu IRTracer-100) to facilitate a precise characterization analysis of the material.For an intuitive comparison, the FTIR and Raman spectra of both trimesic acid (named as TA) and 1,3,5-Benzenetricarboxylic acid, sodium salt (named as TANa) are analyzed as well.
Based on the results, the FTIR spectra are reorganized in Figure S8.The spectral signals associated with M-OH bonds can be detected within the range of 400-650 cm -1 in layered double hydroxides.Compared with the results of NiFe-LDH, TA and TANa, the peaks at 1620 and 1433 cm -1 are ascribed to uas(-COO-) and us(-COO-).
And the broad bonds at 769 and 727 cm -1 are related to the vibration of benzene ring in TANa.Significantly, two new peaks at 1160 and 850 cm -1 are observed in the SU-NiFe-LDH(TA) sample, which correspond to the C-O-Fe vibration modes.These results indicate that the trimesic acid ligand is successfully embedded in NiFe-LDH.The Raman spectra of TA and TANa indicate that the in-and out of phase stretching modes of the coordinated carboxylate groups for TANa are found in 1580 cm -1 and 1420 cm -1 , respectively.The broaden stretching modes at ~1330 cm -1 and ~1646 cm -1 are assigned to uncoordinated carboxylate group in TA (Figure S9).
Besides, the in situ FTIR tests are supplemented to unveil the dynamic evolution between uncoordinated (-COOH) and coordinated (-COO-) carboxylate groups for studying the electrochemical mechanism experimentally.The in situ FTIR device is assembled with SU-NiFe-LDH(TA)@nf and steel disc, which serve as the anode and cathode, respectively (denoted as SU-NiFe-LDH(TA)@nf (+) //steel disc (-) ).In order to confirm the potential range, the water splitting performance (Figure S25) is test before the in situ FTIR test.Based on the voltage window (1-3 V), the in situ FTIR spectra of SU-NiFe-LDH(TA)@nf were collected in a voltage range of 1~3 V with an interval of 200 mV.The results were illustrated in Figure 5b.Besides the well-defined peak at 702 cm -1 attributed to the vibrations of M-OH is observed , another two peaks at 1620 cm -     Response: That is a good question.Indeed, the peak of M-OOH (M-O) can be observed at 529.4 eV in O 1s spectra for SU-NiFe-LDH(TA)@cp electrode after OER test (named as p-SU-NiFe-LDH(TA)@cp), which indicates that the surface restructuration of NiFe LDH is unavoidable in our OER process.
To investigate the coordination of trimesic acid ligand after phase restructuration, XRD, FTIR and Raman analyses are conducted on p-SU-NiFe-LDH(TA)@cp.As shown in Figure S15, the XRD pattern of p-SU-NiFe-LDH(TA)@cp is in accordance with that of the fresh SU-NiFe-LDH(TA).In Figure S16    Response: We are appreciated for your helpful comments and we agree well with it.
The part 2.1 has been moved to the Supporting Information.Appropriate changes in the main text have been made correspondingly, which influence little to the content and framework of the revised manuscript.
6. Careful examination is needed to avoid typos and other problems (e.g. Figure 13a on page 8).Please double-check.
Response: We are sorry for the mistakes such as typos.The manuscript has been carefully checked and revised by a native speaker to improve the English.The corresponding revisions have been highlighted in red in the main text.
Reviewer #2 (Remarks to the Author): Actually, the leaching of transition metals always happened in layered double hydroxides upon long-term stability test, which largely limits their activity at high current densities and large-scale commercialization.This manuscript submitted by Lu et al. adopted a static and dynamic compatibility anchor strategy to synthesize a subsize NiFe-LDH nanosheet catalyst (SU-NiFe-LDH(TA)@cp) via modifying with trimesic acid and regulating the type of electrodeposited ions.Benefited from the coordination between ligands and NiFe-LDH by C-O-Fe bonds and the promoted OER kinetic performance, the resulting superhydrophilic and superaerophobic SU-NiFe-LDH(TA)@cp catalyst exhibits enhanced electrocatalytic performance and stability at large current (1500 mA cm -2 ) for 1300 h.However, the general scope of this paper lacks innovation and is not of interest to a sufficiently broad audience.Over the past decade, LDH -based materials have been well studied in OER and it is not quite clear what is the new science in this work, especially combining the great tunability of enzymatic systems with known oxide-based catalysts to achieve both high activity and stability.Such as Nat.Mater.2022, 21, 673-680; ACS Appl.Mater.Interfaces 2021, 13, 37063-37070.As thus, I would not recommend this manuscript to be published in Nat.

Commun.
Response: Thanks for your great effort to improve our paper.Based on your valuable advice, we scrutinized our paper and made some changes.We have conducted a (2)The dynamic changes of carboxyl ligands during OER were visually detected by operando Raman and FTIR spectroscopy, which provided key evidence for the enhancement of kinetic.The uncoordinated carboxylates formed by dynamic evolution in OER process act as proton ferries to accelerate the OER kinetics.
The dynamic and static equilibrium of coordination and uncoordination carboxylates in water oxidation process is the key to maintain high activity and stability of catalysts.These new insights not only provide new insights to reveal the interaction between ligands and layered double hydroxide, but also enable the development of highly stable and efficient catalysts.
As such, we believe that our investigation is a good work with scientific meaning on energy storage filed.And I would like to extend my sincere gratitude for your constructive comments once again.We have made extensive modifications to our manuscript and supplemented extra data to make our results convincing.
Other detailed comments: 1.If the authors want to prove that Fe 3+ is conducive to the form of smaller nanosheet structure, you should supply the TEM and corresponding HRTEM images about NiFe-LDH(TA)@cp to reveal the structural distinction between SU-NiFe-LDH(TA)@cp and NiFe-LDH(TA)@cp according to the experimental details you mentioned.
Response: We appreciate your comments and concur that the TEM and corresponding HRTEM images about NiFe-LDH(TA)@cp are necessary to elucidate the structure differences between SU-NiFe-LDH(TA)@cp and NiFe-LDH(TA)@cp.As depicted in Figure S4b, the HRTEM image of NiFe-LDH(TA)@cp reveals a similar interplanar spacing of 0.7 nm.Additionally, TEM images of SU-NiFe-LDH(TA)@cp and NiFe-LDH(TA)@cp are presented in Figure S7.It is evident that SU-NiFe-LDH(TA)@cp consists of smaller nanosheets (~56.68 nm) compared to NiFe-LDH(TA)@cp (~733.67 nm), which is consistent with SEM results.We have carefully read the authors' responses and agree with the most of revisions they have made in response to our previous comments.However, there are still some questions that we think the authors need to further clarify, in particular those concerning comments 2 and 3. Therefore, I recommend publishing this manuscript after revisions.Below is a list of specific comments and questions the authors should address before publication.
1. NiOOH was generated on the catalyst surface according to the Raman results after OER stability testing and in situ Raman test results.However, there are no obvious shift of the peak position before and after OER test of the three samples listed in table S3.Please explain why high-priced nickel species are formed on the surface of the catalyst, but the valence state of the nickel does not change significantly for p-NiFe-LDH(TA)@cp? 2. Although the authors have demonstrated through a series of characterizations that the coupling between ligands and metal sites can significantly improve the stability of the catalyst, the source of the increased catalytic activity in this system has not been clearly explained.In fact, it is not enough to list the references showing that the dissolution of metal ions is the main source of catalyst deactivation.At the same time, the active site in the NiFe system has been controversial.We would like to know which metal or organic molecule is the source of activity in this work.
Reviewer #3 (Remarks to the Author): I am glad that the authors have addressed some of my concerns and revised the manuscript accordingly.The quality of the revised version has been improved.However, before recommended for publication, the following issues need to be solved：

1 (
uas(-COO-)) and 1433 cm -1 (us(-COO-)) can be observed in the pristine SU-NiFe-LDH(TA)@nf at 0 V.With the increasing of voltage, two broaden stretching vibration modes at around 3000 cm -1 assigned to u(-OH) of uncoordinated carboxylate (-COOH) stand out and keep stable during the operation.Meanwhile, a new peak centered at 1608 cm -1 corresponding to the antisymmetric stretching vibration of -COOH (uas(-COOH)) gradually rises.These results further confirm the dynamic evolution of carboxyl ligands during water oxidation.

Figure 5 .
Figure 5.The in situ dynamic evolution of carboxyl ligand.a) In situ Raman spectroscopy measurements on SU-NiFe-LDH(TA)@cp sample at different applied potentials (V vs. Ag/AgCl).b) In situ FTIR pectroscopy measurements on SU-NiFe-LDH(TA)@cp sample at different applied potentials.c) Proposed OER pathways with intermediates for NiFe-LDH and SU-NiFe-LDH(TA).
, the Raman characteristic peaks of p-SU-NiFe-LDH(TA)@cp shift to 474 and 544 cm -1 , respectively, which are associated with the vibration mode of Ni-O in NiOOH.Besides, the Raman vibrations of coordinated and uncoordinated carboxylate are observed in p-SU-NiFe-LDH(TA)@cp, indicating that the trimesic acid ligand can be anchor to the NiFe-LDH stably during OER stability test.This perspective is further validated by the FTIR spectra of p-SU-NiFe-LDH(TA)@cp.As seen in Figure S17, the newly observed peak at 573 cm -1 can be attributed to the vibration of M-O.The signals associated with coordinated carboxylate can be detected at 1373, 769 and 727 cm -1 .Those corresponding to the uncoordinated carboxylate can be detected at 1608, 1454, 1404, 1276, 1246, 744 and 688 cm -1 .Besides, the vibration peaks of Fe-O-C are observed at 1160 and 850 cm -1 in the p-SU-NiFe-LDH(TA)@cp sample, which further qualifies the excellent structural stability.
meticulous comparison and analysis of the articles you referenced.The innovations in the design of the hybrid electrocatalyst, the interaction mechanism and the catalystic effects are completely different.Yuan et al. reported a series of metal hydroxide-organic frameworks (MHOFs) combining the advantages of molecular catalysts and metal oxides through solvothermal reactions.The stability of MHOFs was governed by πstacking interactions between linkers connecting adjacent hydroxide layers and the stability lasts for 20 h in 0.1 M KOH.(Nat.Mater.2022, 21, 673-680) Yang et al. reported a NiFe layered double hydroxide intercalating a conductive polymer of polypyrrole by anion exchange in salt-acid mixed solution, which improved the stability of the catalyst (20 mA cm -2 for 50 h) through the heightened electrostatic attraction.(ACS Appl.Mater.Interfaces 2021, 13, 37063-37070) Their research work and highlights have been discussed and cited in our manuscript.However, the synergy between the anchoring carboxylic molecules and the multi-metal active sites has never been fully understood in case of heterogeneous catalysis.The issues of phase segregation and active site reduction caused by metal dissolution in layered double hydroxides remain unresolved.The stability in the previous researches is far from reaching the industrial application standard as well.And, there is no direct evidence to uncover the mechanism of the stabilization and evolution of carboxylate ligands in catalysts.Therefore, our work differs from the previous work on the following points: (1)Our work synthesized the subsize NiFe-LDH anchored with trimesic acid using electro-deposition method.Control experiments and theoretical calculations have revealed that the coordination between ligands and NiFe-LDH via C-O-Fe bonds optimizes the electronic structure, thereby inhibiting the dissolution of the bimetal active sites.The catalyst shows excellent stability under industrial conditions.

Figure S7 .
Figure S7.TEM image and the particle size distribution of a) SU-NiFe-LDH(TA)@cp and b) NiFe-LDH(TA)@cp.The TEM and HRTEM images of NiFe-LDH(TA) have been supplemented in FigureS4band FigureS7a, respectively.