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Xin Zhao, Wan-Peng Li, Yanhui Cao, Arsenii Portniagin, Bing Tang, Shixun Wang, Qi Liu, [Denis Y. W. Yu](https://orcid.org/0000-0002-5883-7087), Xiaoyan Zhong, Xuerong Zheng, Andrey L. Rogach
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This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, copyright © 2024 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsnano.3c09639[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)
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[Dual-Atom Co/Ni Electrocatalyst Anchored at the Surface-Modified Ti3C2T x MXene Enables Efficient Hydrogen and Oxygen Evolution Reactions](https://mdr.nims.go.jp/datasets/60ab424f-db7b-40e4-b89e-3638edeeb4af)
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Supporting InformationDual-atom Co/Ni Electrocatalyst Anchored at the Surface-Modified Ti3C2Tx MXene Enables Efficient Hydrogen and Oxygen Evolution ReactionsXin Zhao,a Wanpeng Li, a Yanhui Cao, b Arsenii S Portniagin, a Bing Tang, a Shixun Wang, a Qi Liu, a Denis Y. W. Yu,c Xiaoyan Zhong, a Xuerong Zheng, a,b,d * Andrey L. Rogacha *Xin Zhao,a Wanpeng Li, a Yanhui Cao, b Arsenii S Portniagin, a Bing Tang, a Shixun Wang, a Qi Liu, a Denis Y. W. Yu,c Xiaoyan Zhong, a Xuerong Zheng, a,b,d * Andrey L. Rogacha *a Department of Materials Science and Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong S.A.R. 999077, P.R. China b School of Materials Science and Engineering, Tianjin University, Tianjin, 300072 P. R. Chinac Research Center for Energy and Environmental Materials (GREEN), National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki, Japan 305-0044d Key Laboratory of Pico Electron Microscopy of Hainan Province, School of Materials Science and Engineering, Hainan University, Haikou 570228, P.R. China*E-mail: andrey.rogach@cityu.edu.hk; E-mail: xrzh@tju.edu.cnFigure S1. Schematic illustration of the synthesis procedure of Ti3C2Tx MXene.Figure S2. SEM image of Ti3C2Tx MXene.Figure S3. Illustration of the covalent bonding of L-tryptophan at the surface of Try-Ti3C2Tx MXene.Figure S4. FTIR spectrum of tryptophan.Figure S5. High-resolution XPS spectra of a) N 1s, b) C 1s and c) Ti 2p in Try-Ti3C2Tx and Ti3C2Tx.Figure S6. HAADF-STEM image of Try-Ti3C2Tx.Figure S7. Elemental mapping of Ti, Ni, C, O and N in a piece of Ni-Ti3C2Tx composite (TEM image provided at the top left), and its EDS spectrum.Figure S8. Elemental mapping of Ti, Co, N, O and C in a piece of Co-Ti3C2Tx composite (TEM image provided at the top left), and its EDS spectrum. Figure S9. Intensity profiles obtained on adjacent metal atomic pairs, taken from three different sites marked by red rectangles in Figure 2a. Figure S10. Schematics of chelating Co and Ni single atoms through N-bonds at the Try-Ti3C2Tx surface.Figure S11. Schematics of bonding of Co and Ni single atoms to oxygen terminating atoms at the Ti3C2Tx surface.Figure S12. High-resolution XPS spectra of a) C 1s and b) O 2p in CoNi-Ti3C2Tx, Ni-Ti3C2Tx and Co-Ti3C2Tx composites.Figure S13. High-resolution XPS spectra of Ti 2p in a) CoNi-Ti3C2Tx, b) Ni-Ti3C2Tx and c) Co-Ti3C2Tx composites.Figure S14. FTIR spectra of CoNi-Ti3C2Tx, Ni-Ti3C2Tx and Co-Ti3C2Tx composites.Figure S15. Raman spectra of CoNi-Ti3C2Tx, Ni-Ti3C2Tx and Co-Ti3C2Tx composites, all excited at 532 nm. Figure S16. a) k3-weighted Fourier transform (FT) of the Co K-edge EXAFS of CoNi-Ti3C2Tx, Co3O4 and Co foil. b) k3-weighted Fourier transform (FT) of the Ni K-edge EXAFS of CoNi-Ti3C2Tx, NiO and Ni foil.Figure S17. MWT images of Co K-edge EXAFS for Co foil, CoO and Co3O4.Figure S18. MWT images of Ni K-edge EXAFS for Ni foil, NiO and Ni2O3. Figure S19. OER LSV curves of CoNi-Ti3C2Tx electrodes with the Co/Ni ratio of 1:1, 2:1 and 1:2, at 5 mV s−1. Figure S20. CVs of a) CoNi-Ti3C2Tx, b) Ni-Ti3C2Tx, and c) Co-Ti3C2Tx electrodes, recorded in 1.0 M KOH at different scan rates.Figure S21. a) OER and b) HER chronopotentiometry response of Ni-Ti3C2Tx and Co-Ti3C2Tx electrodes at a current density of 10 mA cm−2. Figure S22. a) HAADF-STEM image of Co@Ti3C2Tx composite where single Co atoms were anchored directly on the MXene substrate. b) Elemental mapping images of Co, Ti, and C in this Co@Ti3C2Tx composite. Schematics of bonding of Co single atoms to oxygen terminating atoms at c) Ti3C2Tx and d) Try-Ti3C2Tx surface and corresponding mass loading (wt%) determined by ICP-OES analyses. e) OER and f) HER LSV curves of Co@Ti3C2Tx and Co-Ti3C2Tx electrodes at 5 mV s−1.Figure S23. The optimized configurations of CoNi-Ti3C2Tx(Ni), CoNi-Ti3C2Tx(Co), Ni-Ti3C2Tx, Co-Ti3C2Tx showing chemisorption of three intermediates in the OER process in an alkaline solution. Table S1. Metal loading in the studied electrocatalysts (wt%) determined by ICP-OES analysis. Ni loading Co loading Total metal loading CoNi-Ti3C2Tx 2.5 3.1 5.6 Ni-Ti3C2Tx 5.4 0 5.4 Co-Ti3C2Tx 0 5.2 5.2Table S2. Comparison of metal loading achieved in this work with other reported MXene-based electrocatalysts. Metal Substrate Metal loading (wt%) Reference CoNi Ti3C2Tx 5.6 This work Ni Ti3C2Tx 5.4 This work Co Ti3C2Tx 5.2 This work Pt Ti3C2Tx 0.2 1 Pt Mo2TiC2Tx 1.2 2 Ru Ti3C2Tx 1.2 3 Pt N, P co-doped Ti3C2TX 2.32 4 Ni Ti3C2Tx 2.9 5 Ir NS-Ti3C2Tx 2.5 6 Fe Mo2TiC2Tx 1.8 7 Cu Ti3C2Tx 1.19 8 Ru N- Ti3C2Tx 1.1 9 Co Ti3C2Tx 1.61 10 Co Ni2CTx 1.63 10 Co V2CTx 1.58 10Table S3. Co K-edge EXAFS analysis for CoNi-Ti3C2Tx and Co-Ti3C2Tx composites Path CN R (Å) σ2 (Å2) ∆E0 (eV) R-factor CoNi-Ti3C2Tx Co-O 2.8 1.91 0.0092 8.902 0.0038 Co-O-Co 11.4 3.38 0.0022 Co-Ti3C2Tx. Co-O 2.9 1.91 0.0089 6.410 0.0090 Co-O-Co 11.2 3.50 0.0054 N, coordination number; R, distance between absorber and backscatter atoms; σ2, Debye–Waller factor to account for both thermal and structural disorders; ΔE0(eV), inner potential correction to account for the difference in the inner potential between the sample and the reference compound; R-factor (%) indicates the goodness of the fit.Table S4. Ni K-edge EXAFS analysis results of the CoNi-Ti3C2Tx and Ni-Ti3C2Tx. Sample Path CN R (Å) σ2 (Å2) ∆E0 (eV) R-factor CoNi-Ti3C2Tx Ni-O 2.7 2.06 0.0000 0.5 0.0074 Ni-O-Ni 11.5 3.07 0.0091 Ni-Ti3C2Tx. Co-O 3.0 2.06 0.0049 0.005 0.0016 Ni-O-Ni 11.8 3.38 0.0042 N, coordination number; R, distance between absorber and backscatter atoms; σ2, Debye–Waller factor to account for both thermal and structural disorders; ΔE0(eV), inner potential correction to account for the difference in the inner potential between the sample and the reference compound; R-factor (%) indicates the goodness of the fit.Table S5. Z-fit equivalent circuit data of CoNi-Ti3C2Tx, Ni-Ti3C2Tx, and Co-Ti3C2Tx composites. Rs CPE Rct CoNi-Ti3C2Tx 3.12 0.81 14.61 Ni-Ti3C2Tx 3.23 0.92 40.54 Co-Ti3C2Tx 3.86 0.87 49.66Table S6. Comparison of overpotentials (at 10 mA cm-2) of the CoNi-Ti3C2Tx electrocatalyst introduced in this work with other reported MXene-based electrocatalysts for OER. Electrocatalyst Electrolyte Overpotential (mV) Ref. Ru-SA/Ti3C2Tx 0.1M HClO4 290 11 LDH/MQD/NG 0.1 M KOH 270 12 Ti3C2Tx-N6 1.0 M KOH 360 13 Ti3C1.6N0.4 1.0 M KOH 450 14 Co-CoO/Ti3C2-MXene/NF 1.0 M KOH 271 15 NiFeCoP/MXene 1.0 M KOH 240 16 FeS2@MXene 1.0 M KOH 240 17 CoNi-ZIF-67@Ti3C2Tx 1.0 M KOH 275 18 FeNi-LDH/Ti3C2Tx 1.0 M KOH 298 19 MWCNT@V2CTx 1.0 M KOH 560 20 Co@V2CTx 1.0 M KOH 242 10 10-Ag/M 0.5 M H2SO4 250 21 MXene/ZIF-67 1.0 M KOH 366 22 MXene@RuCo NPs 1.0 M KOH 253 23 ZnCoCH@Ti3C2Tx 1.0 M KOH 280 24 NiSe–NiO/Ta4C3Tx 1.0 M KOH 255 25 MXene@Ce-MOF 1.0 M KOH 270 26 CoNi-Ti3C2Tx 1.0 M KOH 241 This workTable S7. Comparison of overpotentials (at 10 mA cm-2) of the CoNi-Ti3C2Tx electrocatalyst introduced in this work with other reported MXene-based electrocatalysts for HER. Electrocatalyst Electrolyte Overpotential(mV) Ref. Co-CoO/Ti3C2-MXene/NF 1.0 M KOH 45 15 Ru-SA/Ti3C2Tx 0.1 M HClO4 70 11 Mo2CTx-Co 1.0 M H2SO4 180 27 Mo2TiC2Tx−PtSA 0.5 M H2SO4 30 2 RuSA−N−Ti3C2Tx 0.5 M H2SO4 23 9 RuSA−N−Ti3C2Tx 1.0 M KOH 27 9 RuSA−N−S−Ti3C2Tx 0.5 M H2SO4 76 28 Co3+@3D-Nb2CTx NW 1.0 M KOH 236 29 Fe3+@3D-Nb2CTx NW 1.0 M KOH 302 29 V-Ti4N3Tx 0.5 M H2SO4 330 30 P3-V2CTx 0.5 M H2SO4 74 31 P-Mo2CTx 0.5 M H2SO4 114 32 Mo2CTx/2H-MoS2 0.5 M H2SO4 119 33 MXene@Pt/SWCNTs 0.5 M H2SO4 78 34 Pt SA-PNPM 1.0 M KOH 33 4 Co@V2CTx 1.0 M KOH 35 10 MX@RG 1.0 M KOH 121 35 Ru/Mo2CTx 1.0 M phosphate 73 36 Nb2CTx@Pt3.8 0.5 M HClO4 141 37 Re@Ti3C2Tx 0.5 M H2SO4 298 38 10-Ag/M 0.5 M H2SO4 117 21 LDH(60%)/H-Ti3C2Tx 1.0 M KOH 187 39 CoNi-Ti3C2Tx 1.0 M KOH 31 This workTable S8. Comparison of the two-electrode CoNi-Ti3C2Tx (,) electrolyzer with previous reports. Electrocatalyst Electrolyte Cell voltage at 10 mA cm-2(V) Ref. Ni0.7Fe0.3PS3/Ti3C2Tx 1.0 M KOH 1.65 40 BP QDs/Ti3C2Tx 1.0 M KOH 1.78 41 Ti3C2@mNiCoP 1.0 M KOH 1.61 42 Co-NC@Mo2C 1.0 M KOH 1.68 43 1T/2H MoSe2/ Ti3C2Tx 1.0 M KOH 1.64 44 Ti3C2Tx-N6 1.0 M KOH 1.72 13 CoS2@Ti3C2Tx 1.0 M KOH 1.63 45 FeMC-MXene/GrH 1.0 M KOH 1.60 46 Co@V2CTx 1.0 M KOH 1.60 10 Co@Nb2CTx 1.0 M KOH 1.73 10 Co@Ti3C2Tx 1.0 M KOH 1.80 10 CoNi-Ti3C2Tx 1.0 M KOH 1.58 This workReferences 1. Zhao, D.; Chen, Z.; Yang, W.; Liu, S.; Zhang, X.; Yu, Y.; Cheong, W.-C.; Zheng, L.; Ren, F.; Ying, G.; Cao, X.; Wang, D.; Peng, Q.; Wang, G.; Chen, C. MXene (Ti3C2) Vacancy-Confined Single-Atom Catalyst for Efficient Functionalization of CO2. J. Am. Chem. Soc. 2019, 141 (9), 4086-4093.2. Zhang, J.; Zhao, Y.; Guo, X.; Chen, C.; Dong, C.-L.; Liu, R.-S.; Han, C.-P.; Li, Y.; Gogotsi, Y.; Wang, G. Single platinum atoms immobilized on an MXene as an efficient catalyst for the hydrogen evolution reaction. Nat. Catal. 2018, 1 (12), 985-992.3. 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Mater. 2023, 33 (7), 2210101.21image3.pngimage4.tifimage5.pngimage6.jpegimage7.jpegimage8.jpegimage9.tifimage10.pngimage11.tiffimage12.jpegimage13.jpegimage14.tifimage15.tifimage16.tiffimage17.tiffimage18.jpegimage19.tifimage20.jpegimage21.tifimage22.pngimage23.tiffimage1.jpgimage2.tif