Research Article www.afm-journal.de Molecular Engineering to Tune the Ligand Environment of Atomically Dispersed Nickel for Efficient Alcohol Electrochemical Oxidation Zhifu Liang, Daochuan Jiang, Xiang Wang, Mohsen Shakouri, Ting Zhang, Zhongjun Li, Pengyi Tang,* Jordi Llorca, Lijia Liu,* Yupeng Yuan, Marc Heggen, Rafal E. Dunin-Borkowski, Joan R. Morante, Andreu Cabot,* and Jordi Arbiol* 1. Introduction Atomically dispersed metals maximize the number of catalytic sites and enhance their activity. However, their challenging synthesis and The electrochemical oxidation of alcohols characterization strongly complicates their optimization. Here, the aim is is at the basis of several strategic chem- to demonstrate that tuning the electronic environment of atomically dis- ical processes and energy technologies, persed metal catalysts through the modification of their edge coordination including electrochemical organic syn- is an effective strategy to maximize their performance. This article focuses thesis, biomass, and organic waste val- orization, and direct alcohol fuel cells on optimizing nickel-based electrocatalysts toward alcohol electrooxidation (DAFC).[1] The electrooxidation of alcohols in alkaline solution. A new organic framework with atomically dispersed offer numerous advantages over com- nickel is first developed. The coordination environment of nickel within peting valorization strategies and energy this framework is modified through the addition of carbonyl (CO) groups. technologies, such as high energy densities The authors then demonstrate that such nickel-based organic frameworks, and energy conversion efficiency, opera- tion/reaction at low working temperature combined with carbon nanotubes, exhibit outstanding catalytic activity and with high selectivity, and low fuel cost durability toward the oxidation of methanol (CH3OH), ethanol (CH3CH2OH), with easy production, transportation, and and benzyl alcohol (C6H5CH2OH); the smaller molecule exhibits higher storage.[1] However, despite their numerous catalytic performance. These outstanding electrocatalytic activities for alcohol advantages, the deployment of electrocata- electrooxidation are attributed to the presence of the carbonyl group in the lytic valorization strategies and DAFCs is ligand chemical environment, which enhances the adsorption for alcohol, as hampered by their low cost-effectiveness in large part associated with the use of mod- revealed by density functional theory calculations. The work not only intro- erately efficient catalysts based on high-cost duces a new atomically dispersed Ni-based catalyst, but also demonstrates and low-abundance elements such as plat- a new strategy for designing and engineering high-performance catalysts inum and palladium.[2,3] Besides, current through the tuning of their chemical environment. alcohol electrooxidation catalysts become rapidly poisoned with carbon monoxide, Z. F. Liang, T. Zhang, J. Arbiol D. Jiang, Y. Yuan Catalan Institute of Nanoscience and Nanotechnology (ICN2) School of Chemistry and Chemical Engineering CSIC and BIST Anhui University Campus UAB, Bellaterra, Barcelona, Catalonia 08193, Spain Heifei Anhui 230601, China E-mail: arbiol@icrea.cat M. Shakouri Z. F. Liang, X. Wang, A. Cabot, J.R. Morante Canadian Light Source Functional Nanomaterials Group Saskatoon S7N 0X4, Canada Catalonia Institute for Energy Research – IREC Z. J. Li Sant Adrià de Besòs, Barcelona Catalonia 08930, Spain School of Physics E-mail: acabot@irec.cat Hefei University of Technology The ORCID identification number(s) for the author(s) of this article Hefei 230009, P. R. China can be found under https://doi.org/10.1002/adfm.202106349. P. Y. Tang State Key Laboratory of Information Functional Materials, 2020 X-Lab © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH Shanghai Institute of Microsystem and Information Technology GmbH. This is an open access article under the terms of the Creative Com- Chinese Academy of Sciences mons Attribution-NonCommercial-NoDerivs License, which permits use Shanghai 200050, China and distribution in any medium, provided the original work is properly cited, E-mail: py.tang@mail.sim.ac.cn the use is non-commercial and no modifications or adaptations are made. DOI: 10.1002/adfm.202106349 Adv. Funct. Mater. 2021, 31, 2106349 2106349 (1 of 8) © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH www.advancedsciencenews.com www.afm-journal.de which further limits their cost-effectiveness. Thus, the develop- 2,5-hydroxyterephthalaldehyde (HBC) (Scheme S1, Supporting ment of efficient and stable alcohol oxidation electrocatalysts Information) and tetramino-benzoquinone (TABQ) (Scheme S2, based on abundant elements is a topic of major interest. Supporting Information) in N-methyl-2-pyrrolidone (NMP) Several non-precious transition metal catalysts have been (see details in Figure 1a; Scheme S3, Supporting Information). proposed for alcohol electro-oxidation.[4,5] Among them, nickel- The dark-black color of the obtained solid indicated the for- based catalysts are considered the most promising candidates mation of a conjugated polymer, which was washed by water owing to their high catalytic activity, low price, and notable and methanol to remove low molecular mass impurities, and abundance. Numerous Ni-based catalysts, such as Ni0.75Cu0.25,[6] then dried under vacuum. For comparison, a reference nickel- NiSn alloy,[7] Ni93Bi7,[8] NiSe,[9] NiO,[10] and metal–organic frame- based 2D organic framework without carbonyl chemical groups works with Ni(OH)4,[11] and Ni-Co hydroxide[12] have been devel- (Ni–2D–SA) was prepared under the same reaction condition oped and tested for alcohol electrochemical-oxidation. However, but using 1,2,4,5-benzenetetraamine tetrahydrochloride (TAB) the reported onset potentials and stabilities are still not fully instead of TABQ (Scheme S4, Supporting Information).[18] satisfactory, which calls for novel strategies to design and engi- Scanning electron microscopy (SEM) images (Figure S1a,b, neer nickel-based catalysts with improved performance. Supporting Information) show that the Ni–2D–O–SA sample Recently, 2D covalent organic frameworks and metal–organic has a cotton-like morphology. The X-ray diffraction (XRD) pat- frameworks (MOF) with highly tunable pore structure and tern (Figure S3, Supporting Information) of the Ni–2D–O–SA functionality, and high density of active sites, have arisen broad powder was similar to that of graphite, with a diffraction peak interest as electrocatalysts.[13] Optimized electrocatalysts based at 26.29° corresponding to the (001) family planes and which on such 2D structures have demonstrated outstanding perfor- indicated π–π layered stacking.[19] In contrast to the clear crys- mances toward oxygen evolution and reduction,[14,15] and carbon talline and layered structure displayed by Ni–2D–O–SA, the dioxide reduction.[16,17] However, despite their high potential for XRD pattern of Ni–D–SA displayed a much broader and less alcohol electrooxidation, these 2D materials and particularly a intense peak at around 26°. This result indicates that the intro- nickel-containing 2D organic framework have yet to be devel- duction of carbonyl groups enhances the crystallinity of the oped and optimized toward this electrocatalytic reaction. nickel-based 2D organic framework used here. Here, we report the synthesis of an atomically-dispersed Fourier transform infrared (FT-IR) spectroscopy was used to nickel 2D molecular organic framework containing abundant evaluate the chemical structure of the samples (Figure S4, Sup- carbonyl (CO) functional groups within the nickel ion coor- porting Information). Based on the FT-IR spectra, the signal for dination environment. Its atomic structure and how the out- CN appeared at 1642 cm−1 for Ni–2D–SA, and 1648 cm−1 for standing electrocatalytic activities and durabilities obtained for Ni–2D–O–SA. The vibration of the carbonyl bond (CO) in Ni– the electrochemical-oxidation of methanol, ethanol, and benzyl 2D–O–SA negatively shifted below 1600 cm−1 and overlapped with alcohol were analyzed, are related to the alcohol adsorption other vibrations. For Ni–2D–O–SA, the vibration peak for the ability of the carbonyl functional groups and the high unsatu- C(CO)C bond, which is a footprint of TABQ, shifted from rated coordination number of the nickel ions within the new 1140 to 1010 cm−1 due to the coordination effect and the attraction catalyst presented here. between the layers. This result already points out to the successful introduction of the carbonyl groups in the organic framework.[20] The survey X-ray photoelectron spectroscopy (XPS) spectra 2. Results and Discussion revealed the sole presence of C, N, Ni, and O in both sam- ples (Figures S5 and S6, Supporting Information).[21] For both The nickel-based 2D organic framework with abundant samples, the high-resolution Ni 2p spectrum showed a unique carbonyl functional groups (Ni–2D–O–SA) was solvother- doublet at binding energies of 856 eV (Ni 2p3/2) and 873.3 eV mally synthesized through a Schiff-based reaction between (Ni 2p1/2), significantly above those of NiO.[22,23] The local environment in Ni–2D–O–SA was further ana- lyzed and compared with that of NiO using X-ray absorption P. Y. Tang, M. Heggen, R. E. Dunin-Borkowski fine structure (XAFS) at the Ni K-edge (Figure 1b–d; Figure S7, Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich GmbH Supporting Information). Comparing the spectral features at 52425 Jülich, Germany the near-edge, that is, the X-ray absorption near-edge structure J. Llorca (XANES), we observe the absorption onset of Ni–2D–O–SA at Institute of Energy Technologies slightly lower energy than that of NiO (Figure 1b). Differences Department of Chemical Engineering and Barcelona are more clearly seen when plotting the first derivative of the Research Center in Multiscale Science and Engineering two spectras (Figure S7a, Supporting Information), as shown Universitat Politècnica de Catalunya EEBE in the inset of Figure 2b. Besides, the main absorption peak of Barcelona Catalonia 08019, Spain Ni–2D–O–SA has a lower intensity than that of NiO. Both fea- L. Liu tures indicate that compared with NiO, where Ni is fully sur- Department of Chemistry rounded by O, within Ni–2D–O–SA, Ni atoms are partially Western University surrounded by a lower electronegativity element, that is, N. 1151 Richmond Street, London ON N6A5B7, Canada E-mail: lijia.liu@uwo.ca A more quantitative picture was obtained by analyzing the A. Cabot, J. Arbiol extended XAFS (EXAFS) features. The fitting of the Fourier trans- ICREA formed EXAFS spectrum suggests that Ni is coordinated with Pg. Lluís Companys 23, Barcelona Catalonia 08010, Spain two N atoms and two O atoms, at a bond length 1.87 and 2.05 Å, Adv. Funct. Mater. 2021, 31, 2106349 2106349 (2 of 8) © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH www.advancedsciencenews.com www.afm-journal.de Figure 1. a) Scheme of the synthesis procedure used to produce Ni–2D–O–SA. b) Ni K-edge XANES spectrum of Ni–2D–O–SA compared with a commercial NiO powder. c) Fourier transformed Ni K-edge EXAFS spectra of Ni–2D–O–SA and NiO plotted in R-space. d) Fitting of the Fourier trans- formed EXAFS spectrum in R-space of Ni–2D–O–SA. respectively (Figure 1c,d).[24] The contribution at longer radial electrocatalysts, they were loaded on multi-wall carbon nano- distances comes from C atoms with a coordination number of tubes (CNT) through the π–π packing interaction. The XRD 6 and a bond length of 2.65 Å. The detailed fitting parameters patterns of the obtained Ni–2D–O–SA–CNT and Ni–2D–SA– can be found in Table S1, Supporting Information. Overall, XAFS CNT composites, showed a unique peak at ≈26° (Figure S10, analysis provided strong evidence of the formation of the NiN2O2 Supporting Information), which was assigned to the overlap salophen structure unit in the Ni–2D–O–SA framework. between the CNT and the organic framework structures. SEM High angle annular dark-field (HAADF) aberration-corrected (Figure S1c,d, Supporting Information), STEM images, and scanning transmission electron microscopy (STEM) was used EDX compositional maps (Figure S11, Supporting Information) to analyse the nickel dispersion. As shown in Figure 2a–c; showed the composites morphology and confirmed the homo- Figure S8a–c, Supporting Information, Ni–2D–O–SA contained geneous loading of Ni–2D–O–SA on the CNTs. a high density of isolated and homogeneously distributed nickel Figure 3a exhibits the cyclic voltammograms (CV) of the atoms. The uniform distribution of Ni, C, N, and O was fur- two samples in the range from 0 to 0.65 V in 1.0 m KOH ther confirmed by energy-dispersed X-ray spectroscopy (EDS) electrolyte with a scan rate of 50 mV s−1. The anodic peak at elemental mapping (Figure 2d). 0.50 V versus Hg/HgO measured in the forward scan with The surface area of Ni–2D–O–SA and Ni–2D–SA, evaluated Ni–2D–O–SA–CNT is attributed to Ni2+ oxidation, and the from N2 adsorption–desorption isotherms at 77 K (Figure S9, cathodic peak in the backward scan at 0.38 V corresponds to the Supporting Information) using the Brunauer–Emmett–Teller reduction of Ni3+ species. For Ni–2D–SA–CNT, the anodic peak equation was 21.1 and 83 m2 g−1, respectively. Thus, the intro- shifted to 0.54 V and the cathodic peak to 0.42 V. The current duction of carbonyl functional groups significantly decreased density at the Ni2+ oxidation peak in the Ni–2D–O–SA–CNT the surface area of the material, which we associate with an electrocatalyst was 19 mA cm−2, which is ≈9.5 times higher enhancement of the layer–layer interaction that results in than that of Ni–2D–SA–CNT, 2 mA cm−2. These results indicate slightly more densely packed frameworks. a much higher electrochemical activity of the Ni ions within To improve the electrical conductivity of these nickel- Ni–2D–O–SA–CNT and their easier oxidation to Ni3+. Besides, based organic frameworks, as required to apply them as the ratio between the anodic and the cathodic peak current Adv. Funct. Mater. 2021, 31, 2106349 2106349 (3 of 8) © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH www.advancedsciencenews.com www.afm-journal.de Figure 2. a–c) HAADF–STEM images of Ni–2D–O–SA displaying the presence of atomically dispersed nickel atoms. d) Low magnification HAADF–STEM image and EDS elemental mapping. densities was close to 1 for both catalysts, indicating a reversible slightly improved compared to that of Ni–2D–SA–CNT. How- Ni2+/Ni3+ redox reaction in both materials.[25] ever, the Ni–2D–O–SA–CNT catalysts showed much higher CV of the reduction/oxidation process allowed to estimate the activity toward methanol oxidation reaction (MOR), with cur- surface coverage (Γ) of Ni2+/Ni3+ within Ni–2D–O–SA–CNT to rent densities increasing from 31 to 106 mA cm−2 in the range be 1.32 × 10−7 mol cm−2, two orders of magnitude above that of 0.5–0.6 V versus Hg/HgO, that is, six-fold higher current den- Ni–2D–SA–CNT, 5.17 × 10−9 mol cm−2 (Figure 3a; Equation (S1), sities compared with Ni–2D–SA–CNT. Thus, the introduction Supporting information).[26] Figure 3b; Figure S12, Supporting of the carbonyl group (CO) at the ligand environment of the Information, display CV curves at different scan rates, from dispersed Ni-atoms active sites clearly results in much higher 10 to 100 mV s−1, obtained with these two catalysts in 1.0 m MOR catalytic activities. KOH electrolyte. The variation of the anodic and cathodic peak The charge transfer resistances of these two catalysts were current densities with the square root of the voltage scan rate evaluated through electrochemical impedance spectroscopy was linearly fitted with R2 > 0.99 for both samples (Figure S12, (EIS). The EIS Nyquist plot of Ni–2D–O–SA–CNT (Figure 3e) Supporting Information), demonstrating the Ni2+/Ni3+ redox presents a smaller semicircle than Ni–2D–SA–CNT at reaction to be diffusion limited.[25] From this dependence, an 0.56 V in 1 m KOH + 1 m methanol electrolyte, denoting a apparent diffusion coefficient D′ was evaluated (see Equation S3, lower charge transfer resistance (R3) and thus faster MOR Supporting Information). The D′ obtained with Ni–2D–O–SA–CNT kinetics.[27] On the other hand, the charge transfer resistance is 2.3 × 10−6 g cm−1 s−1, which is close to an order of magnitude for OER of Ni–2D–O–SA–CNT is similar to that of Ni–2D– higher than with Ni–2D–SA–CNT, 3.3 × 10−7 g cm−1 s−1. SA–CNT at 0.67 V (Figure S13, Supporting Information), The alcohol electrooxidation performance of Ni–2D–O–SA– which is consistent with the similar OER activities of these CNT and Ni–2D–SA–CNT electrocatalysts was analyzed by two catalysts. linear sweep voltammetry (LSV) in 1 m KOH and 1 m KOH + 1 m As shown in the chronopotentiometry (CP) curve (Figure 3f), methanol solutions using a conventional three-electrode setup the Ni–2D–O–SA–CNT electrocatalyst maintained constant (Figure 3c,d). The OER activity of Ni–2D–O–SA–CNT was just current densities of 10 and 30 mA cm−2 for 12 h without a Adv. Funct. Mater. 2021, 31, 2106349 2106349 (4 of 8) © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH www.advancedsciencenews.com www.afm-journal.de Figure 3. a) CV of Ni–2D–O–SA–CNT and Ni–2D–SA–CNT electrocatalysts in 1 m KOH at 50 mV s−1 potential sweep rate. b) CVs of Ni–2D–O–SA–CNT electrocatalysts in 1 m KOH obtained at an increasing potential sweep rate, from 10 to 100 mV s−1. c,d) LSV curves obtained with Ni–2D–SA–CNT, Ni–2D–O–SA–CNT, and reference carbon nanotubes (CNTs) catalysts in 1.0 m KOH (c) and 1 m KOH + 1 m methanol in the potential range 0 to 0.9 V versus Hg/HgO at a scan rate of 5 mV s−1 (d). e) EIS Nyquist plots at 0.56 V in 1 m KOH + 1 m methanol solution. f) CP long-term stability of Ni–2D–O–SA–CNT at 10, 30, and 60 mA cm−2. No iR compensation was applied to the displayed data. significant increase in the required potential. When increasing Ni–2D–O–SA. What is more, upon adsorption, the HOCH3 the current density to 60 mA cm−2, the potential raised ≈4.8% angle in Ni–2D–O–SA increases from 108.25° to 109.04°, while during 12 h, which is attributed to the methanol consumption. the HOCH3 angle in Ni–2D–SA remains almost unchanged After 36 h chronopotentiometry test, LSV curves recorded after optimization. This result indicates that Ni–2D–O–SA can with the used electrocatalysts in a fresh 1 m KOH + 1 m facilitate the activation of the methanol molecule. We also iden- methanol electrolyte (Figure 3d) showed almost no variation tify the O of the CO group as a methanol adsorption site. DFT with respect to those obtained with the fresh electrocatalysts, calculations show that the methanol molecule tends to adsorb what demonstrates the excellent stability of Ni–2D–O–SA–CNT at such O site with the OH group in methanol parallel to the during MOR. After the stability test, the pH value of the solu- surface. The shortest distance between the methanol molecule tion is 14.12, which is not a significant change compared to the and the surface is 1.87 Å, which is much smaller than in the initial solution (pH = 14). Ni–2D–SA surface (2.5 Å). Thus, based on the DFT calcula- The XRD pattern of Ni–2D–O–SA–CNT after MOR tions, it is reasonable to conclude that the addition of carbonyl (Figure S14, Supporting Information) displayed no significant (CO) groups to the organic framework results in more effec- variation with respect to the sample before the electrochem- tive adsorption as well as activation of the methanol molecule, ical tests, which confirmed the excellent structural stability of which explains the higher activity of Ni–2D–O–SA toward MOR the 2D material and the growth of no additional crystalline when compared with Ni–2D–SA. phase of the nickel or nickel oxide nanoparticles during the Beyond MOR, we also examined the electrocatalytic activity reaction, indicating there is no agglomeration of nickel atom of the produced catalysts toward the oxidation of other alcohols. active sites. Compared with Ni–2D–SA–CNT, Ni–2D–O–SA–CNT presented Methanol adsorption is the initial and a limiting step in significantly higher electrocatalytic performance toward the MOR. To understand the contribution of CO groups to meth- electrochemical oxidation of both ethanol (EOR) (Figure 5a) anol adsorption, density functional theory (DFT) calculations and benzyl alcohol (BOR) (Figure 5b). Especially for the BOR, were carried out. Selected fragments were shown in Figure S15, the current density at 0.6 V obtained with Ni–2D–O–SA–CNT Supporting Information. Figure 4 shows the optimal methanol was ≈77 mA cm−2, which is ≈eight times higher than that of adsorption configurations on top of a Ni site in both Ni–2D– Ni–2D–SA–CNT (9.7 mA cm−2). SA and Ni–2D–O–SA. The adsorption energy is −0.248 eV and CP measurements were used to test the stability of −0.225 eV in Ni−2D−SA and Ni−2D−O−SA, respectively. The Ni–2D–O–SA–CNT for EOR. As shown in Figure S16, Supporting negative adsorption energies suggest that methanol adsorption Information, Ni–2D–SA–CNT exhibited excellent long-term is thermodynamically favored in both cases. Interestingly, the stability for EOR, similar to that obtained for MOR. For BOR, adsorption distance (d) between the O atom of methanol and chronoamperometric measurements (Figure S17, Supporting Ni in Ni–2D–O–SA is 3.11 Å, which is shorter than in Ni–2D– Information) show the current density decay associated with the SA (3.27 Å). Compared with Ni–2D–SA, the 10% lower adsorp- consumption of benzyl alcohol. Notice in this respect that the tion energy and 5% shorter adsorption distance indicate a more initial concentration of benzyl alcohol was just 0.1 m, since effective adsorption of the methanol molecule on the surface of the steric hindrance of benzene may prevent an efficient Adv. Funct. Mater. 2021, 31, 2106349 2106349 (5 of 8) © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH www.advancedsciencenews.com www.afm-journal.de Figure 4. a,b) Optimal methanol adsorption configurations on top of the Ni site in both Ni–2D–SA (a) and Ni–2D–O–SA (b). c,d) Optimal methanol adsorption configurations on top of the carbonyl site in both Ni–2D–SA (c) and Ni–2D–O–SA (d) (red is oxygen, light blue is nitrogen, grey is nickel, brown is carbon). reaction at higher concentrations. The EIS spectra for EOR and (Figure S20, Supporting Information) of the products from BOR were similar to those obtained for MOR, confirming that benzyl alcohol oxidation showed a chemical shift in the range Ni–2D–O–SA–CNT is also characterized by a highly efficient of ≈7–8 ppm, which is assigned to the characteristic chemical charge transfer and a highly favorable EOR and BOR kinetics shift of the proton in the benzene ring of benzoate. The char- (Figure S18, Supporting Information). acteristic chemical shift belonging to the aldehyde (CHO) Finally, in order to confirm the product of the electrochem- of benzaldehyde was not observed at the range of ≈9–10 ppm, ical oxidation of alcohol, nuclear magnetic resonance (NMR) demonstrating that the final product of the benzyl alcohol tests were conducted to analyze the associated products of oxidation was benzoate (C6H5COO−). The NMR spectra of electrochemical oxidation of alcohol. As shown in Figure S19, the EOR electrolyte did also not display the characteristic Supporting Information, the NMR spectrum after the MOR chemical shift of the aldehyde (CHO). The characteristic stability test displays the characteristic chemical shift of chemical shift of CH3COO− appears at 1.83 ppm (Figure S21, HCOO− at 8.33 ppm, while the characteristic chemical shift Supporting Information). of HCHO in the range of ≈9–10 ppm was not observed, Taking into account the above NMR results, we propose the demo­ nstrating that the final product of methanol oxida- following electrochemical reaction for the alcohol electrochem- tion is formate (HCOO−). Furthermore, the NMR spectrum ical oxidation (Figure 6): Figure 5. a) LSV of Ni–2D–SA–CNT, Ni–2D–O–SA–CNT, and CNT in 1 m KOH+1 m methanol from 0 to 0.9 V versus Hg/HgO at a scan rate of 5 mV s−1. b) LSV of Ni–2D–SA–CNT, Ni–2D–O–SA–CNT, and the CNT in 1 m KOH + 0.1 m benzyl alcohol from 0 to 0.9 V versus Hg/HgO at a scan rate of 5 mV s−1. Adv. Funct. Mater. 2021, 31, 2106349 2106349 (6 of 8) © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH www.advancedsciencenews.com www.afm-journal.de Conflict of interest The authors declare no conflict of interest. Figure 6. Scheme of the electrochemical oxidation reaction of alcohol. Data Availability Statement Research data are not shared. 3. Conclusion In conclusion, we detailed the synthesis of a new nickel-based 2D organic framework and proposed a facile molecular engi- Keywords neering strategy to tune the ligand coordination environments alcohol oxidation, atomically dispersed metals, electrocatalytic oxidation, of nickel ion centers. Through this strategy, carbonyl (CO) nickel, 2D organic frameworks groups were introduced and proved to decisively contribute to an efficient alcohol electro-oxidation in alkaline solution. Received: July 2, 2021 EXAFS and XANES analysis confirmed the Ni salophen unit Revised: August 12, 2021 structure, NiN2O2, within the 2D organic frameworks. The Published online: September 16, 2021 atomically dispersed nickel within a framework containing the carbonyl groups displayed outstanding MOR, EOR, and BOR performance. DFT calculations suggested that the introduc- tion of the CO functional groups favor the absorption and [1] a) E. Antolini, E. R. Gonzalez, J. Power Sources 2010, 195, 3431; activation of methanol molecules, which is at the origin of the b) K. C. Cheung, W. L. Wong, D. L. Ma, T. S. Lai, K. Y. Wong, Coord. Chem. Rev. 2007, 251, 2367; c) D. P. Hickey, M. S. McCammant, improved MOR observed. The present work not only offers F. Giroud, M. S. Sigman, S. D. Minteer, J. Am. Chem. Soc. 2014, 136, novel materials and a promising strategy to design more effi- 15917; d) N. Kakati, J. Maiti, S. H. Lee, B. Viswanathan, Y. S. Yoon, cient atomically dispersed nickel-based catalysts for alcohol Chem. Rev. 2014, 114, 12397; e) R. Ciriminna, G. Palmisano, oxidation, but it could also benefit other research fields related M. 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Zhang, Z.F.L. and D.J. contributed equally to this work. ICN2 is supported by N. Sethi, L. He, Z. Zheng, W. Liu, Angew. Chem., Int. Ed. 2020, 132, the Severo Ochoa program from Spanish MINECO (Grant No. SEV- 13995. 2017-0706) and is funded by the CERCA Programme /Generalitat de [9] B. Zhao, J. Liu, C. Xu, R. Feng, P. Sui, L. Wang, J. Zhang, J. L. Luo, Catalunya. Part of the present work has been performed in the framework X. Z. Fu, Adv. Funct. Mater. 2020, 31, 2008812. of Universitat Autònoma de Barcelona Materials Science Ph.D. program. [10] C. Liu, W. Zhou, J. Zhang, Z. Chen, S. Liu, Y. Zhang, J. Yang, L. Xu, Z.L. acknowledges funding from MINECO SO-FPT Ph.D. grant (SEV- W. Hu, Y. Chen, Y. Deng, Adv. Energy Mater. 2020, 10, 2001397. 2013-0295-17-1). This project has received funding from the European [11] Y. Wu, J. Tian, S. Liu, B. Li, J. Zhao, L. Ma, D. Li, Y. Lan, X. Bu, Union’s Horizon 2020 research and innovation program under grant Angew. Chem., Int. Ed. 2019, 58, 12185. agreement No 823717-ESTEEM3. The present work is supported by the [12] H. Huang, C. Yu, X. Han, H. Huang, Q. Wei, W. Guo, Z. Wang, European Regional Development Fund and by the Spanish MINECO J. Qiu, Energy Environ. Sci. 2020, 13, 4990. through the projects ENE2016-77798-C4-3-R, ENE2017-85087-C3, and [13] X. Zhao, P. Pachfule, A. Thomas, Chem. Soc. Rev. 2021, 50, 6871. project NANOGEN (PID2020-116093RB-C43). X.W. and T.Z. thank [14] J. Du, F. Li, L.-C. Sun, Chem. Soc. Rev. 2021, 50, 2663. the China Scholarship Council for the scholarship support. P. Tang [15] S. Royuela, E. Martinez-Perinan, M. P. Arrieta, J. I. Martinez, M. M. Ramos, acknowledges the Humboldt Research Fellowship. Authors acknowledge F. Zamora, E. Lorenzo, J. L. Segura, Chem. Commun. 2020, 56, 1267. funding from Generalitat de Catalunya 2017SGR327 and 2017SGR1246. [16] H. Zhu, M. Lu, Y. Wang, S. Yao, M. Zhang, Y. Kan, J. Liu, Y. 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