Formation of Hierarchical FeCoS2–CoS2 Double-Shelled Nanotubes with Enhanced Performance for Photocatalytic Reduction of CO2

Article abstract of DOI:10.1002/anie.202004609

Hierarchical FeCoS₂–CoS₂ double-shelled nanotubes have been rationally designed and constructed for efficient photocatalytic CO₂ reduction under visible light. The synthetic strategy, engaging the two-step cation-exchange reactions, precisely integrates two metal sulfides into a double-shelled tubular heterostructure with both of the shells assembled from ultrathin two-dimensional (2D) nanosheets. Benefiting from the distinctive structure and composition, the FeCoS₂–CoS₂ hybrid can reduce bulk-to-surface diffusion length of photoexcited charge carriers to facilitate their separation. Furthermore, this hybrid structure can expose abundant active sites for enhancing CO₂ adsorption and surface-dependent redox reactions, and harvest incident solar irradiation more efficiently by light scattering in the complex interior. As a result, these hierarchical FeCoS₂–CoS₂ double-shelled nanotubes exhibit superior activity and high stability for photosensitized deoxygenative CO₂ reduction, affording a high CO-generating rate of 28.1 μmol h^?1 (per 0.5 mg of catalyst).

Full text of DOI:10.1002/anie.202004609

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Formation of Hierarchical FeCoS2-CoS2 Double-Shelled
Nanotubes with Enhanced Performance for Photocatalytic
Reduction of CO2
Authors: Xiong-Wen (David) Lou
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202004609
Link to VoR: https://doi.org/10.1002/anie.202004609

10.1002/anie.202004609
Angewandte Chemie International Edition
Formation of Hierarchical FeCoS2-CoS2 Double-Shelled Nanotubes with Enhanced
Performance for Photocatalytic Reduction of CO2
Yan Wang, Sibo Wang, Song Lin Zhang, and Xiong Wen (David) Lou*
[*] Y. Wang, Dr. S. Wang, S. L. Zhang, Prof. X. W. Lou
School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang
Drive, Singapore 637459, Singapore
Email: xwlou@ntu.edu.sg; davidlou88@gmail.com
Webpage: http://www.ntu.edu.sg/home/xwlou/
Abstract
Hierarchical FeCoS2-CoS2 double-shelled nanotubes have been rationally designed and constructed
for efficient photocatalytic CO2 reduction under visible light. The synthetic strategy, engaging the
two-step cation-exchange reactions, precisely integrates two metal sulfides into a double-shelled
tubular heterostructure with both of the shells assembled from ultrathin two-dimensional (2D)
nanosheets. Benefiting from the distinctive structure and composition, the FeCoS2-CoS2 hybrid can
reduce bulk-to-surface diffusion length of photoexcited charge carriers to facilitate their separation.
Furthermore, this hybrid structure can expose abundant active sites for enhancing CO2 adsorption and
surface-dependent redox reactions, and harvest incident solar irradiation more efficiently by light
scattering in the complex interior. As a result, these hierarchical FeCoS2-CoS2 double-shelled
nanotubes exhibit superior activity and high stability for photosensitized deoxygenative CO2
reduction, affording a high CO-generating rate of 28.1 µmol h-1 (per 0.5 mg of catalyst).
Keywords: CO2 reduction; heterostructure; hollow; metal sulfides; photocatalysis
1
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
The fixation of CO2 into energy-rich low-carbon products by photocatalysis is one promising strategy
to mitigate global warming by lowering the greenhouse gas concentration, and simultaneously to
pursue renewable energy alternatives by storing the solar energy into chemical bonds.[1-3] In recent
years, researchers have indeed made some impressive progresses in the studies of exploring catalytic
materials and constructing reaction systems for CO2 conversion powered by the sun.[4-10] Nevertheless,
the current efficiency of photocatalytic CO2 reduction does not meet the criteria for practical
utilization. This is mainly restricted by the great energy barriers of CO2 reduction in both
thermodynamics and kinetics,[3, 11] and the low efficiency of multiple physiochemical processes
during photocatalysis.[1, 12] Therefore, to realize the ultimate objective of CO2 photoreduction for
sustained solar fuel production, it is desirable to develop new catalysts to selectively operate the
reaction with high efficiency.
Metal sulfide semiconductors have attracted enormous interest in photocatalysis for CO2
reduction, owing to their suitable band structures, rich redox functions and tunable electronic and
optical properties.[13-19] In particular, the coupling of matched metal sulfides forming heterostructures
is deemed as an effective method to strengthen their photocatalytic activity,[16, 20] because the potential
gradient between the interfaces can powerfully boost charge separation and migration. Meanwhile,
metal sulfide hybrids typically possess improved photo-stability and extended optical harvesting
compared with the individual counterparts.[21-22] Apart from designing the composition, delicate
engineering of favorable structures for the materials is also of significant importance to enhance their
photocatalytic performance.
Due to the apparent structural virtues, hierarchical hollow heterostructures composed of 2D
nanosheets are being actively employed as photocatalysts for solar-to-chemical energy conversion,
such as CO2 reduction and water splitting.[17, 23-27] To be specific, hierarchical materials hold readily
accessible and interconnected porous networks, which can promote the transport of guest species to
promote reaction dynamics.[28-29] Besides, hollow scaffolds with interior cavities can work as a trap-
2
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
well to render scattering/reflection of incident light,[30-32] and this photo-trapping effect would be
further reinforced if the hollow structures are multi-shelled.[33] Moreover, the nanosheet-constructed
hierarchical hollow architectures possess shortened diffusion pathway of charges, large surface area
and high content of exposed active sites, which will inhibit recombination of electron-hole pairs,
improve CO2 capture/adsorption, and support kinetics of photoredox reactions.[26, 34-35] Based on the
above considerations, it is motivated to fabricate hierarchical metal sulfide heterostructures with
multi-shells and nanosheet substructures for efficient CO2 photoreduction.
We herein demonstrate a facile metal-organic framework (MOF)-assisted synthesis method to
construct hierarchical FeCoS2-CoS2 double-shelled nanotubes (DSNTs) with both of the shells
assembled from 2D nanosheet subunits. As schematically elucidated in Figure 1, starting with the
Fe-based MOF (MIL-88A, MIL=Materials of Institut Lavoisier) hexagonal prisms, MIL-88A@Fe-
Co hydroxide yolk-shell nanotubes (YSNTs) are produced via the cation-exchange reaction between
MIL-88A and Co2+ ions in a mixture of water and ethanol (step i). Following that, Fe-Co hydroxide
DSNTs are formed by further etching the MOF cores through the second cation-exchange reaction
(step ii). Finally, the Fe-Co hydroxide DSNTs are subjected to a sulfidation treatment by annealing
with sulfur powder at 400°C in N2 atmosphere (step iii), producing the hierarchical FeCoS2-CoS2
DSNTs. Thanks to the unique compositional and structural merits, the FeCoS2-CoS2 hybrid can
effectively enhance CO2 adsorption and surface redox catalysis, promote separation and movement
of photo-formed charges, and increase utilization of incident light irradiation. Consequently, the
FeCoS2-CoS2 hybrid can catalyze the CO2-to-CO conversion reaction with remarkable activity and
high stability in a photosensitized system under visible light irradiation, giving a superior CO
production rate of 28.1 µmol h-1 (per 0.5 mg of catalyst).
Dispersed MIL-88A nanorods with high uniformity are synthesized through a modified
hydrothermal method (Figure S1a, Supporting Information). The field-emission scanning electron
microscopy (FESEM) image and transmission electron microscopy (TEM) image show the smooth
3
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
surface and solid nature of the hexagonal prisms with an average diameter of about 500 nm (Figure
S1b,c, Supporting Information). The X-ray diffraction (XRD) pattern confirms the formation of MIL-
88A (Figure S2a, Supporting Information),[36-37] and energy-dispersive X-ray (EDX) analysis verifies
its chemical composition of C, O and Fe elements (Figure S2b, Supporting Information). After the
first cation-exchange reaction, the produced MIL-88A@Fe-Co hydroxide YSNTs remain the overall
nanorods structure (Figure 2a, and Figure S3a, Supporting Information). The high-magnification
FESEM images show the hierarchical surface of the nanorods with 2D nanosheet subunits on the
surface (Figure S3b,c, Supporting Information). In this process, the MIL-88A prisms are steadily
etched by the protons generated from hydrolysis of Co2+ ions, releasing Fe3+ ions outward to react
with Co2+ ions and OH- ions forming Fe-Co hydroxide nanosheets. Because the dissolution of MIL-
88A is kinetically faster than the formation of the hydroxide nanosheets, a gap between the MOF core
and the hydroxide shell emerges, thus forming the yolk-shell structure for MIL-88A@Fe-Co
hydroxide, which can be clearly discerned from the TEM images (Figure 2b,c). The XRD pattern of
MIL-88A@Fe-Co hydroxide YSNTs gives distinct diffraction signals attributed to that of MIL-88A,
suggesting the MOF core is not etched completely (Figure S4a, Supporting Information). The EDX
spectrum of MIL-88A@Fe-Co hydroxide YSNTs indicates the presence of Fe, Co and O elements
with the Fe to Co atomic ratio of about 1:2.3, reflecting the formation of the Fe-Co hydroxides (Figure
S4b, Supporting Information).
Then, the MIL-88A@Fe-Co hydroxide YSNTs are transferred into Fe-Co hydroxide DSNTs
through the second cation-exchange reaction. The FESEM images show the intact structure and
hierarchical surface of Fe-Co hydroxide DSNTs constructed by hydroxide nanosheets with a larger
size than those of MIL-88A@Fe-Co hydroxide YSNTs (Figure 2d-f). The hierarchical double-shelled
configuration of Fe-Co hydroxide DSNTs is clearly revealed by the TEM images (Figure 2g,h). There
is not any solid core remained in Fe-Co hydroxide DSNTs, suggesting the complete removal of the
MIL-88A precursor. This is further supported by the disappearance of strong diffraction peaks of
4
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
MIL-88A in the XRD pattern (Figure S5a, Supporting Information). The high-magnification TEM
image shows that both shells of Fe-Co hydroxide DSNTs are consisted of randomly assembled
nanosheets (Figure 2i). Formation of Fe-Co hydroxide DSNTs is also supported by the EDX spectrum
(Figure S5b, Supporting Information), which shows strong signals of Fe, Co and O elements with an
increased Co/Fe ratio.
The FeCoS2-CoS2 DSNTs are finally obtained by annealing the Fe-Co hydroxide DSNTs with
sulfur powder at 400°C in N2 as indicated by XRD and EDX analyses (Figure S6, Supporting
Information). The FESEM images show the well preserved hierarchical structure of FeCoS2-CoS2
DSNTs without obvious aggregation (Figure 3a,b). The cross-sectional image of an individual
FeCoS2-CoS2 DSNT displays the nanosheet-assembled hierarchical surfaces of both the outer and
inner shells (inset, Figure 3b). The magnified FESEM image shows that the thickness of the metal
sulfide nanosheets is about 20 nm (Figure 3c). The morphological feature of the FeCoS2-CoS2 DSNTs
is also observed from TEM (Figure 3d). The closer TEM analysis discloses the presence of numerous
pores on the metal sulfide nanosheets (Figure 3e). EDX analysis further confirms the gap between
the two shells by delineating the relative elemental compositions of Fe, Co, and S along the line scan
across the longitudinal direction of a single nanotube (Figure 3f). In the high-resolution TEM
(HRTEM) image (Figure S7, Supporting Information), two distinct lattice fringes with d-spacings of
0.28 and 0.25 nm can be clearly discerned, which can be indexed to the (220) and (101) crystal planes
of CoS2 and FeCoS2, respectively. The high-angle annular dark-field scanning transmission electron
microscopy (HAADF-STEM) image and the corresponding elemental mapping images demonstrate
the distribution of Fe, Co and S elements in the FeCoS2-CoS2 DSNTs (Figure 3g). As can be seen, in
the outermost region of the nanotube, the signal intensity of Fe is weaker than that of Co, indicating
that the outer shell should contain a higher content of CoS2 than the inner shell. This can be easily
understood by the relatively insufficient supply of Fe3+ ions in forming Fe-Co hydroxide during the
first-step ion-exchange reaction, leading to the generation of more cobalt hydroxide on the outer
5
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
surface. To study the chemical states of elements in the FeCoS2-CoS2 nanotubes, X-ray photoelectron
spectroscopy (XPS) characterizations are performed and the results further support the successful
formation of the FeCoS2-CoS2 DSNTs (Figure S8, Supporting Information).
To investigate the influence of compositions and structures of metal sulfide hybrids on catalytic
performance, three control samples, namely FeSx-CoS2 nanotubes (Figure S9, Supporting
Information), FeCoS2-CoS1.97 nanotubes (Figure S10, Supporting Information) and FeCoS2-Co9S8
nanotubes (Figure S11, Supporting Information), are also synthesized by annealing the Fe-Co
hydroxide DSNTs at 300, 500 and 600°C, respectively, under otherwise the same conditions. Also,
the FeCoS2 and CoS2 materials are prepared for comparison (Figure S12, Supporting Information).
The textural properties of the FeCoS2-CoS2 DSNTs are investigated by N2 sorption
measurements. The result indicates that the material has a high Brunauer-Emmett-Teller (BET)
surface area of 41.8 m2 g-1 (Figure S13, Supporting Information). The hysteresis loop in the N2
sorption isotherm curve demonstrates the existence of mesopores that are mainly stemmed from the
porous walls and nanosheets. The porous structure and high surface area of the FeCoS2-CoS2
nanotubes are favorable for enhancing CO2 capture and concentration, as revealed by CO2 adsorption
tests. The CO2 sorption isotherms show that the FeCoS2-CoS2 nanotubes can afford a CO2 uptake of
about 8 cm3 g-1 at 0°C and 1 atm (Figure S14, Supporting Information). Meanwhile, the room-
temperature steady-state photoluminescence (PL) analysis is performed to estimate the separation-
recombination rate of the photogenerated charges in the CO2 photoreduction system (Figure S15,
Supporting Information). The PL intensity declines dramatically in the presence of the catalyst,
indicating the largely inhibited recombination of photoinduced charges. These characterizations
reveal that the hierarchical FeCoS2-CoS2 DSNTs own the merits of promoting charge separation and
transport. On the other hand, the flat-band potential of the FeCoS2-CoS2 hybrid is calculated to be -
0.67 V (vs. normal hydrogen electrode, NHE, pH = 7.0) derived by the Mott-Schottky plots (Figure
S16, Supporting Information), which is sufficient to drive the CO2-to-CO conversion reaction.
6
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
2+
+
Besides, the redox potential of Ru(bpy)3 / Ru(bpy)3 (i.e., -1.09 V vs. NHE, bpy = 2’2-bipyridine)
is more negative than the flat-band potential of the FeCoS2-CoS2 hybrids. These results indicate that
the FeCoS2-CoS2 catalysts are thermodynamically capable of receiving the photoexcited electrons
from the reduced photosensitizer for reducing the adsorbed CO2 molecules to generate CO.
Based on the above discussions, photocatalytic CO2 conversion performance of the hierarchical
FeCoS2-CoS2 DSNTs is tested in a mixed medium of acetonitrile and H2O under simulated solar
2+
irradiation (λ ≥ 400 nm), with Ru(bpy)3 (abbreviated as Ru) as the photosensitizer and
triethanolamine (TOEA) as the electron donor. As shown in Figure 4a (column 1), the FeCoS2-CoS2
DSNTs exhibit high CO2 photoreduction activity with a CO generation rate of 28.1 µmol h-1. Such
a photocatalytic CO2-to-CO conversion rate is much higher than that of reported works in similar
systems (Table S1, Supporting Information), suggesting the outstanding performance of the FeCoS2-
CoS2 catalyst. Obviously, the FeCoS2-CoS2 DSNTs have a superior performance than the Fe-Co
hydroxide DSNTs (column 2), indicating the virtues of metal sulfides to the reaction. However, the
CO2 reduction reaction is almost stopped, when the FeCoS2-CoS2 DSNTs are absent in the system
(column 3), which highlights that the catalyst is responsible for the exceptional CO2 photoreduction
efficiency achieved. On the other hand, the individuals of FeCoS2 and CoS2 and their physical mixture
manifest much inferior performance compared with the FeCoS2-CoS2 catalyst (column 4-6). This
suggests that the tight interfacial contacts in the hybrids is essential to the reaction for effectively
boosting the separation and transfer of photoinduced charges.
To understand the critical importance of the composition and structure of the FeCoS2-CoS2
DSNTs, other metal sulfide catalysts are also employed to run the CO2 photoreduction reaction for
comparison. As presented in Figure 4b, the FeSx-CoS2 nanotubes show a CO generation rate of 17.7
µmol h-1, much lower than that of the FeCoS2-CoS2 DSNTs, possibly due to the lack of hexagonal
FeCoS2 phase in the former. As expected, the FeCoS2-CoS1.97 and FeCoS2-Co9S8 nanotubes exhibit
poor CO2 reduction performance compared with the FeCoS2-CoS2 DSNTs, which is primarily
7
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
attributed to their damaged double-shelled structure, although they have enhanced crystallinity that
is typically favorable for photocatalysis. Such findings reveal that both chemical composition and
spatial architecture of the FeCoS2-CoS2 DSNTs contribute largely to the superb photocatalytic CO2
performance.
The 13C-enriched CO2 is used as a feedstock for the reaction and the yielded CO is analyzed by
13
gas chromatography-mass spectrometry (GC-MS) analysis. The results reveal that only CO with
m/z value of 29 is detected (Figure 4c), proving that the CO product originates from the CO2 gas.
Besides, when conducting the CO2 photoreduction reaction in Ar atmosphere, no formation of CO is
observed (Figure 4a, column 7). This result further supports that the CO2 feedstock is the carbon
source of the CO product obtained. To check the stability of the FeCoS2-CoS2 DSNTs, after each
reaction, the catalyst is collected and utilized to re-start the CO2 reduction reaction for five cycles.
No significant drop in the CO/H2 generation rate is observed during the stability tests (Figure 4d),
which reflects the high durability of the catalyst for the photocatalytic CO2 reduction catalysis.
Besides, FESEM and TEM characterizations of the FeCoS2-CoS2 DSNTs sample after the
photocatalytic CO2 reduction also verify the high structural stability of the photocatalyst (Figure S17,
Supporting Information).The long-term performance evaluation indicates that the FeCoS2-CoS2
catalyst exhibits high CO-releasing activity in the first hour but thereafter the CO yield rate gradually
drops (Figure 4e), which is mainly induced by photobleaching of the Ru photosensitizer as reported
in such CO2 reduction systems.[38-40]
The control experiments demonstrate that the FeCoS2-CoS2 catalyst is inactive for producing
any CO or H2 in the absence of TEOA (Figure S18, Supporting Information), indicating the electron
donor is indispensable to the reaction, which is consistent with previous works.[41-42] Besides, the
CO2-to-CO conversion is completely terminated when the reaction is conducted without the
introduction of visible light or Ru, implying photocatalytic nature of the reaction. Moreover, the
activity of the FeCoS2-CoS2 catalyst is also examined under different wavelength illumination (Figure
8
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
4f). The trend of Co/H2 generation is consistent with optical absorption intensity of Ru, not that of
the catalyst (Figure S19, Supporting Information), which confirms that the CO2 reduction reaction is
a photosensitized process.
In summary, hierarchical FeCoS2-CoS2 double-shelled nanotubes are designed and fabricated
for high-efficiency photocatalytic CO2 reduction with visible light. The multistep synthesis route is
beneficial to make the FeCoS2-CoS2 hybrids with tunable architecture and composition to tailor the
catalytic performance. The nanosheet-assembled hierarchical double-shelled hollow structure could
reduce diffusion distance of photoinduced charges, offer profuse catalytically active sites and utilize
incident photoirradiation more efficiently. As a result, the metal sulfide hybrids manifest outstanding
CO2 reduction activity and high stability in a photosensitized tandem system. This work may inspire
further development of metal sulfide semiconductors with desirable spatial nanostructures for
artificial solar fuel production through visible light CO2 reduction.
Acknowledgements
X. W. L. acknowledges the funding support from the National Research Foundation (NRF) of
Singapore via the NRF investigatorship (NRF-NRFI2016-04), and the Ministry of Education of
Singapore through the Academic Research Fund (AcRF) Tier-2 grant (MOE2017-T2-2-003) and
Tier-1 grant (RG116/18).
References
[1] K. Maeda, Adv. Mater. 2019, 31, 1808205.
[2] J. L. White, M. F. Baruch, J. E. Pander III, Y. Hu, I. C. Fortmeyer, J. E. Park, T. Zhang, K.
Liao, J. Gu, Y. Yan, Chem. Rev. 2015, 115, 12888.
[3] K. E. Dalle, J. Warnan, J. J. Leung, B. Reuillard, I. S. Karmel, E. Reisner, Chem. Rev. 2019,
119, 2752.
[4] Y. Jiang, J.-F. Liao, H.-Y. Chen, H.-H. Zhang, J.-Y. Li, X.-D. Wang, D.-B. Kuang, Chem 2020,
6, 766.
9
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
[5] S. Y. Chae, J. Y. Choi, Y. Kim, D. Le Tri Nguyen, O. S. Joo, Angew. Chem. Int. Ed. 2019, 58,
16395.
[6] Q.-Y. Meng, T. E. Schirmer, A. L. Berger, K. Donabauer, B. Kꢀnig, J. Am. Chem. Soc. 2019,
141, 11393.
[7] Q. Wang, X. Wang, Z. Yu, X. Jiang, J. Chen, L. Tao, M. Wang, Y. Shen, Nano Energy 2019,
60, 827.
[8] L. Zeng, Z. Wang, Y. Wang, J. Wang, Y. Guo, H. Hu, X. He, C. Wang, W. Lin, J. Am. Chem.
Soc. 2019, 142, 75.
[9] S. N. Talapaneni, G. Singh, I. Y. Kim, K. AlBahily, A. a. H. Al‐Muhtaseb, A. S. Karakoti,
E. Tavakkoli, A. Vinu, Adv. Mater. 2019, 1904635.
[10] H. Takeda, K. Ohashi, A. Sekine, O. Ishitani, J. Am. Chem. Soc. 2016, 138, 4354.
[11] J. Schneider, H. Jia, J. T. Muckerman, E. Fujita, Chem. Soc. Rev. 2012, 41, 2036.
[12] M. Xiao, Z. Wang, M. Lyu, B. Luo, S. Wang, G. Liu, H.-M. Cheng, L. Wang, Adv. Mater.
2019, 31, 1801369.
[13] L. Zheng, F. Teng, X. Ye, H. Zheng, X. Fang, Adv. Energy Mater. 2020, 10, 1902355.
[14] X. Jiao, X. Li, X. Jin, Y. Sun, J. Xu, L. Liang, H. Ju, J. Zhu, Y. Pan, W. Yan, J. Am. Chem.
Soc. 2017, 139, 18044.
[15] L. Cheng, Q. Xiang, Y. Liao, H. Zhang, Energy Environ. Sci. 2018, 11, 1362.
[16] S. Wang, B. Y. Guan, Y. Lu, X. W. Lou, J. Am. Chem. Soc. 2017, 139, 17305.
[17] X. Jiao, Z. Chen, X. Li, Y. Sun, S. Gao, W. Yan, C. Wang, Q. Zhang, Y. Lin, Y. Luo, J. Am.
Chem. Soc. 2017, 139, 7586.
[18] Y. He, H. Rao, K. Song, J. Li, Y. Yu, Y. Lou, C. Li, Y. Han, Z. Shi, S. Feng, Adv. Funct. Mater.
2019, 29, 1905153.
[19] X. Li, Y. Sun, J. Xu, Y. Shao, J. Wu, X. Xu, Y. Pan, H. Ju, J. Zhu, Y. Xie, Nat. Energy 2019,
4, 690.
[20] S. Wang, B. Y. Guan, X. Wang, X. W. Lou, J. Am. Chem. Soc. 2018, 140, 15145.
[21] D. W. Wakerley, M. F. Kuehnel, K. L. Orchard, K. H. Ly, T. E. Rosser, E. Reisner, Nat. Energy
2017, 2, 17021.
[22] A. Iwase, S. Yoshino, T. Takayama, Y. H. Ng, R. Amal, A. Kudo, J. Am. Chem. Soc. 2016,
138, 10260.
[23] Q. Han, X. Bai, Z. Man, H. He, L. Li, J. Hu, A. Alsaedi, T. Hayat, Z. Yu, W. Zhang, J. Am.
Chem. Soc. 2019, 141, 4209.
[24] X. Sun, H. Huang, Q. Zhao, T. Ma, L. Wang, Adv. Funct. Mater. 2020, 1910005.
10
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
[25] S. Wang, B. Y. Guan, X. W. Lou, J. Am. Chem. Soc. 2018, 140, 5037.
[26] S. Wang, Y. Wang, S. L. Zhang, S. Q. Zang, X. W. Lou, Adv. Mater. 2019, 31, 1903404.
[27] Z. Jiang, W. Sun, W. Miao, Z. Yuan, G. Yang, F. Kong, T. Yan, J. Chen, B. Huang, C. An,
Adv. Sci. 2019, 6, 1900289.
[28] X. Li, J. Yu, M. Jaroniec, Chem. Soc. Rev. 2016, 45, 2603.
[29] C. M. Aitchison, R. S. Sprick, A. I. Cooper, J. Mater. Chem. A 2019, 7, 2490.
[30] P. Zhang, S. Wang, B. Y. Guan, X. W. Lou, Energy Environ. Sci. 2019, 12, 164.
[31] J. Di, C. Zhu, M. Ji, M. Duan, R. Long, C. Yan, K. Gu, J. Xiong, Y. She, J. Xia, Angew. Chem.
Int. Ed. 2018, 57, 14847.
[32] Y. Wang, S. Wang, X. W. Lou, Angew. Chem. Int. Ed. 2019, 58, 17236.
[33] S. Wang, Y. Wang, S. Q. Zang, X. W. Lou, Small Methods 2020, 4, 1900586.
[34] J. Xu, X. Li, Z. Ju, Y. Sun, X. Jiao, J. Wu, C. Wang, W. Yan, H. Ju, J. Zhu, Angew. Chem. Int.
Ed. 2019, 58, 3032.
[35] Y. Zhao, G. Chen, T. Bian, C. Zhou, G. I. Waterhouse, L. Z. Wu, C. H. Tung, L. J. Smith, D.
O'Hare, T. Zhang, Adv. Mater. 2015, 27, 7824.
[36] L. Wang, Y. Zhang, X. Li, Y. Xie, J. He, J. Yu, Y. Song, Sci. Rep. 2015, 5, 14341.
[37] (a) J. Zhang, Z. Li, Y. Chen, S. Gao, X. W. Lou, Angew. Chem. Int. Ed. 2018, 57, 10944. (b)
J. Zhang, L. Yu, Y. Chen, X. F. Lu, S. Y. Gao, X. W. Lou, Adv. Mater. 2020, 32, 1906432.
[38] T. Ouyang, H.-H. Huang, J.-W. Wang, D.-C. Zhong, T.-B. Lu, Angew. Chem. Int. Ed. 2017,
56, 738.
[39] S. Wang, W. Yao, J. Lin, Z. Ding, X. Wang, Angew. Chem. Int. Ed. 2014, 53, 1034.
[40] Y. Wang, N.-Y. Huang, J.-Q. Shen, P.-Q. Liao, X.-M. Chen, J.-P. Zhang, J. Am. Chem. Soc.
2018, 140, 38.
[41] B. Han, X. Ou, Z. Deng, Y. Song, C. Tian, H. Deng, Y. J. Xu, Z. Lin, Angew. Chem. Int. Ed.
2018, 57, 16811.
[42] S. Wang, B. Y. Guan, X. W. Lou, Energy Environ. Sci. 2018, 11, 306.
11
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
Figures and Captions
Figure 1. Illustration of the synthetic process of hierarchical FeCoS2-CoS2 DSNTs. (i): ion-exchange
reaction to form MIL-88A@Fe-Co hydroxide YSNTs, (ii): conversion to Fe-Co hydroxide DSNTs
through a second ion-exchange reaction, and (iii): sulfidation reaction and thermal annealing in N2.
12
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
Figure 2. (a) FESEM images and (b,c) TEM images of MIL-88A@Fe-Co hydroxide YSNTs; (d-f)
FESEM images and (g-i) TEM images of Fe-Co hydroxide DSNTs.
13
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
Figure 3. (a-c) FESEM images, (d,e) TEM images and (f) line scan spectrum of one FeCoS2-CoS2
DSNT. (g) HAADF-STEM and elemental mapping images of one FeCoS2-CoS2 DSNT. (Inset in b
shows the cross-sectional FESEM image of one FeCoS2-CoS2 DSNT).
14
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
Figure 4. (a) Photoreduction of CO2 under various reaction conditions. (b) CO2 photoreduction
13
performance of different samples. (c) Results of GC-MS analysis for CO generated from the CO2
isotope experiment. (d) Stability tests of the FeCoS2-CoS2 DSNTs catalyst for five cycles. (e) Time-
yield plots of the products. (f) Wavelength-dependent CO/H2 generation and the light absorption
spectrum of Ru (blue line).
15
This article is protected by copyright. All rights reserved.

10.1002/anie.202004609
Angewandte Chemie International Edition
TOC image
Hierarchical FeCoS2-CoS2 double-shelled nanotubes are constructed by ultrathin nanosheets for
efficient CO2 photoreduction. The unique structure can sufficiently inhibit recombination of electrons
and holes by shortening diffusion length, exploit incident visible light by enhancing scattering in the
cavity, and expose abundant active sites for redox reactions. Benefiting from these advantages, the
obtained FeCoS2-CoS2 hybrid exhibits outstanding performance for CO2-to-CO conversion powered
by solar light.
16
This article is protected by copyright. All rights reserved.