Atomically precise Cu₁₄ and Cu₁₃ nanoclusters for the oxygen evolution reaction: one additional Cu atom matters

Abstract

Atomically precise coinage metal nanoclusters have been widely explored as model catalysts to study structure–performance relationships, yet single atom addition to the metal core to tailor the catalytic properties remains challenging. Herein, we report a pair of atomically precise Cu nanoclusters, namely [Cu₁₄(Fur)₃(PPh₃)₈H₁₀]⁺ and [Cu₁₃(Nap)₃(PPh₃)₇H₁₀]⁰ (hereafter referred to as Cu₁₄ and Cu₁₃; Fur: 2-methyl-3-furanthiolate and Nap: 1-naphthalene thiolate), which exhibit an astonishingly high degree of structural similarity, differing merely by the addition of a single Cu atom, yet possessing drastically different catalytic performance toward the oxygen evolution reaction (OER). Specifically, in 1 M KOH solution, Cu₁₄ has a much lower overpotential than Cu₁₃ (306 mV vs. 382 mV) to afford a current density of 10 mA cm⁻², a smaller Tafel slope and a lower charge transfer resistance. Density functional theory calculations were employed to further identify the catalytically active site, confirming that the additional Cu atom in Cu₁₄ is the key catalytic site, which can significantly lower the energy barrier of the rate-determining step in the OER. This study highlights the crucial role of single-atom addition in modulating the properties and functionalities of atomically precise metal nanoclusters, shedding light on future catalyst design.

---

1. Introduction

Atomically precise coinage metal nanoclusters have been emerging as ideal models and effective catalysts for a variety of catalytic reactions, mainly thanks to their unique attributes.^1–3 Firstly, these metal nanoclusters usually possess ultrasmall sizes with diameters less than 3 nm, and such a high surface-to-volume ratio concomitantly signifies a marked increase in the number of active sites available for catalytic reactions. Secondly, the identified formula, definitive composition, and atomically precise structure of the metal nanocluster provide great opportunities to establish the structure–performance correlation.^4,5 Finally, these metal nanoclusters have molecule-like characteristics and rich chemical reactivity; that is, the metal core or the surface-capping ligands can be precisely modified to tune the composition/structure, thereby opening new avenues to optimize the catalytic performance.⁶ Generally speaking, when using atomically precise metal nanoclusters as catalysts, there are two strategies that are most widely employed to further boost the catalytic performance: ligand engineering and metal core tailoring. The surface ligand not only protects the metal core, but also plays a critical role in determining the catalytic properties.^7–10 For instance, Liu et al. reported that, when using thiolate Au₂₅ nanoclusters as paradigm electrocatalysts, the oxygen evolution reaction (OER) rate-determining step can be switched by rationally choosing ligands with different electron-withdrawing/donating capabilities.¹¹ In electrocatalytic CO₂ reduction, the precise incorporation of two 2-thiouracil-5-carboxylic acid ligands into the cavity of [Au₂₅(p-MBA)₁₈]⁻ clusters (p-MBA = para-mercaptobenzoic acid) caused an enhanced local CO₂ concentration near the active sites, thereby substantially accelerating the reaction kinetics.¹² Our group also discovered that alkynyl-protected Ag₃₂ nanoclusters exhibited higher CO₂ electroreduction activity than their thiolate- and phosphine-co-protected Ag₃₂ counterparts,¹³ and when anchored on NiFe layered double hydroxide (NiFe-LDH), alkynyl-protected Au₂₈ nanoclusters demonstrated superior OER performance compared to their thiolate Au₂₈ counterparts, as the former exhibited more significant charge transfer between the clusters and the NiFe-LDH support.¹⁴ Recently, we discovered that alkynyl-protected Cu₆ nanoclusters also outcompete phosphine-protected Cu nanocluster counterparts toward the OER.¹⁵ The three cases all highlight the ligand effect, where the alkynyl-protected metal nanoclusters were able to lower the energy barrier of the rate-determining step in the electrocatalytic process. Furthermore, different ligands can tune the chemical coordination environment, thereby modulating the catalytic performance. Wu et al. synthesized an atomically defined Cu₆(MBD)₆ (MBD = 2-mercaptobenzimidazole) nanocluster with symmetry-broken CuS₂N₁ active sites, and the Cu₆(MBD)₆ nanocluster showed a faradaic efficiency toward hydrocarbons as high as 65.5%, but the Cu₆ nanocluster with symmetric CuS₃ active sites can only yield the HCOOH product. DFT calculations revealed that the asymmetric binding mode is conducive to generating the key intermediate of *COOH instead of *OCHO, thereby favoring the *CO formation and hindering the HCOOH pathway.¹⁶

Compared with ligand engineering, the metal core tailoring approach is more straightforward, as the core surface metal atoms might be the catalytically active sites.^17–19 For instance, the Zang and Wang team fabricated bulky carboranealkynyl-protected Cu nanoclusters (NCs) from the monomer Cu₁₃ and the bridged dimer Cu₂₆, where Cu₂₆ demonstrated superior catalytic performance in nitrate electroreduction thanks to the metal core structure.²⁰ In a recent study, Ma et al. reported the synthesis of a [AuCu₂₄(dppp)₆H₂₂]⁺ cluster, which bears exposed Cu₃H₃ units in specific surface cavities. In electrochemical CO₂ reduction, the lattice hydrogen (H⁻) in the Cu₃H₃ active unit was recognized as indispensable for the formation of the C₂H₄ product.²¹ Alloying, especially single-atom doping/substitution, has shown great potential to improve catalytic properties,^22,23 as the physicochemical properties and electronic structure of metal nanoclusters can be significantly tuned,²⁴ and introducing new active sites has also been reported in several cases. In 2017, the Lee and Jiang team prepared PtAu₂₄(SC₆H₁₃)₁₈ nanoclusters by simply doping a Pt atom into Au₂₅(SC₆H₁₃)₁₈, which exhibited significantly higher hydrogen evolution reaction (HER) activity. The doped Pt atom can induce the H atoms to spontaneously move into the sub-surface, where they are directly adsorbed, which mainly contributes to the favorable HER energetics.²⁵ A similar case has also been documented by Li et al., where the Au₂₄Pd nanocluster exhibited improved CO₂ electroreduction selectivity to CO formation compared to that of the Au₂₅ nanocluster.²⁶ Recently, Zhu and his colleagues reported a pair of Au₈M₁ nanoclusters (M = Ag/Cu), which differ only by the metal dopant at the same site. In electrochemical CO₂ reduction, Au₈Cu₁ possessed a much higher faradaic efficiency for CO than Au₈Ag₁.²⁷ It is worth noting that, in the above cases, the main chemical structure and configuration were preserved upon doping or substitution; however, there are rare cases where additional metal atoms, even one single metal atom, have been introduced into an existing nanocluster to achieve improved catalytic activity. The Wu group successfully added two Ag atoms onto an Au₂₅ nanocluster to form an Au₂₅Ag₂ nanocluster, where the latter one demonstrated markedly superior catalytic performance in the hydrolysis of 1, 3-diphenylprop-2-ynyl acetate.²⁸ Dong et al. developed a facile method that was able to transform a [Cu₅₈H₂₀PET₃₆(PPh₃)₄]²⁺ (PET: phenylethane thiolate) nanocluster into a surface-defect analog of the [Cu₅₇H₂₀PET₃₆(PPh₃)₄]⁺ nanocluster, where the one-Cu-atom-deficient Cu₅₇ cluster showed improved catalytic activity in click chemistry, particularly for photoinduced [3 + 2] azide–alkyne cycloaddition.²⁹

Inspired by the above findings, herein, we synthesized a pair of atomically precise Cu nanoclusters, [Cu₁₄(Fur)₃(PPh₃)₈H₁₀]⁺ and [Cu₁₃(Nap)₃(PPh₃)₇H₁₀]⁰ (hereafter referred to as Cu₁₄ and Cu₁₃; Fur: 2-methyl-3-furanthiolate and Nap: 1-naphthalene thiolate). Cu₁₄ exhibits an astonishingly high degree of structural similarity to Cu₁₃, and it can be regarded as Cu₁₃ with one additional Cu atom added to its metal core. However, they exhibit drastically different catalytic performances toward the OER. To reach a current density of 10 mA cm⁻², Cu₁₄ requires an overpotential of 306 mV, much lower than that of Cu₁₃ (382 mV). Density functional theory calculations further confirmed that the additional Cu atom is the key catalytic site that mainly leads to the superior OER performance of Cu₁₄ compared to Cu₁₃. As a note, Shingyouchi et al. reported a ligand-dependent surface effect in electrochemical CO₂ reduction of two [Cu₁₄(SR)₃(PPh₃)₈H₁₀]⁺ nanoclusters, where the [Cu₁₄(PET)₃(PPh₃)₈H₁₀]⁺ cluster possessed a much higher faradaic efficiency of HCO₂H than the [Cu₁₄(CHT)₃(PPh₃)₈H₁₀]⁺ cluster (CHT = cyclohexane thiolate).³⁰

2. Experimental section

The synthetic route to Cu₁₄ is shown in Scheme S1 and all the experimental details are available in the ESI.†

3. Results and discussion

The Cu₁₄ NC was first synthesized, and yellow single crystals with well-defined shapes were obtained by a solvent diffusion crystal growth method (Fig. S1†). The CCDC number of the Cu₁₄ single crystal is 2417373.† The crystal structure was then analyzed by single-crystal X-ray diffraction (SC-XRD). Cu₁₄ crystallizes in the P1̄ space group, and it is positively charged with BF₄⁻ as the counter-anion. The overall structure is shown in Fig. 1a, and it contains 14 Cu atoms, 3 Fur ligands, 8 PPh₃ ligands, and 10 hydrides. Furthermore, as shown in Fig. S2,† two Cu₁₄ units are packed into one unit cell. The detailed structural parameters are summarized in Table S1.† Subsequently, electrospray ionization mass spectrometry (ESI-MS) in positive-ion mode was employed to further determine the molecular composition of Cu₁₄. As presented in Fig. 1b, the MS spectra exhibit a pronounced peak with m/z at 3336.8368 Da, in good agreement with the composition of [Cu₁₄(Fur)₃(PPh₃)₈H₁₀]⁺ (cal. 3336.8369 Da, deviation: 0.0001 Da). The comparative cluster of Cu₁₃ was also synthesized by following the previously reported approach.³¹ As a comparison, the single-crystal structure of Cu₁₃ can be found in Fig. S3a.† ³¹ Its molecular composition was further confirmed by ESI-MS. The MS spectra in Fig. S3b† show a prominent peak with an m/z of 3474.9011 Da (cal.: 3474.8997 Da, deviation: 0.0014 Da), and the simulated pattern agrees well with the experimental results. In addition, Fig. S4† shows the UV-Vis absorption spectra of Cu₁₄ and Cu₁₃ NCs in CH₂Cl₂. A featureless exponential decay pattern in absorbance is observed for both clusters, which has been known as a common phenomenon for Cu NCs.⁵ Both clusters can be well-dissolved in CH₂Cl₂ exhibiting a yellow solution (inset in Fig. S4†). In addition, the chemical composition and valence state of Cu₁₄ were investigated by X-ray photoelectron spectroscopy (XPS). Fig. S5a† shows the survey scan spectra, which confirmed the presence of P, O, and C elements in the sample. As shown in the high-resolution Cu 2p XPS spectra (Fig. S5b†), the binding energies of the Cu 2p_3/2 and Cu 2p_1/2 electrons were 932.7 and 952.6 eV, respectively, in good agreement with that of Cu(I) species.

Fig. 1 (a) The total structure of Cu₁₄ (blue, Cu; yellow, S; dark purple, P; red, O; grey, C; and white, H). (b) ESI-MS spectra of [Cu₁₄(Fur)₃(PPh₃)₈H₁₀]⁺ in positive ion mode. Inset: isotopic distribution patterns of [Cu₁₄(Fur)₃(PPh₃)₈H₁₀]⁺ – experimental (blue) and simulated (pink).

Subsequently, the metal core configurations of Cu₁₄ and Cu₁₃ are examined in detail. Both Cu₁₄ and Cu₁₃ are constructed by combining two nested trigonal antiprisms to form a Cu₁₂ skeleton (Fig. 2a and e). Next, a Cu atom is attached along the C₃ axis at the top of the skeleton in both clusters, and three thiolates are adhered at the bottom in a μ₂ binding mode (Fig. 2b and f). Notably, Cu₁₄ has an additional Cu atom bound to the three thiolates. This additional Cu atom does not induce a substantial structural change, but indeed results in a slight distortion of the overall structure. A detailed comparison reveals that the Cu₆ trigonal antiprism core of Cu₁₄ (marked in light purple in Fig. 2a) has a more regular and ordered spatial arrangement. The Cu–Cu bond lengths within the Cu₆ core of Cu₁₄ range from 2.461 Å to 3.100 Å, with an average value of 2.770 Å. Meanwhile, the bond lengths in the Cu₆ core of Cu₁₃ range from 2.494 Å to 3.192 Å, with an average value of 2.792 Å. The completely assembled core structures of both clusters are shown in Fig. 2c and g, and both are structurally symmetric along a C₃ axis. Fig. 2d and h depict the coordination of both nanoclusters with PPh₃ and the positions of ten hydrides. Cu₁₃ is coordinated with seven PPh₃ ligands, and the average Cu–P bond length is calculated to be 2.24 Å. Meanwhile, Cu₁₄ is coordinated with eight PPh₃ ligands, seven of which have an identical coordination mode to that of Cu₁₃, and the 8th PPh₃ is bound to an extra Cu atom, with an average Cu–P bond length of 2.23 Å. One may notice that the hydrogen atoms bonded to the Cu atoms associated with the three thiolates are pushed inwards due to the repulsive force exerted by the added Cu atom. Interestingly, despite Cu₁₄ and Cu₁₃ NCs having virtually similar metal core configurations, the introduction of one more Cu atom indeed causes some structural difference, where the most eye-catching part is that three thiolate ligands are more tightly compressed inward due to their coordination with the Cu atom. Consequently, the whole metal core of Cu₁₄ is more compact compared with that of Cu₁₃.

Fig. 2 Analysis of the crystal structures of Cu₁₄ and Cu₁₃ NCs. The structural disassembly of (a)–(c) Cu₁₄S₃ and (e)–(g) Cu₁₃S₃. Two triangular antiprisms are combined to form a Cu₁₂ skeleton to which two CuPPh₃ or one CuPPh₃ is added, respectively. The distribution of PPh₃ ligands and ten hydrides in (d) Cu₁₄ and (h) Cu₁₃ (blue/light purple/pink, Cu; yellow, S; dark purple, P; and light grey, H).

Next, the OER was chosen as the model reaction to examine the catalytic effect of single-atom addition/introduction between the Cu₁₄ and Cu₁₃ clusters. The OER has been well recognized as the bottleneck reaction in electrochemical water splitting to produce H₂, a high-energy-density and pollution-free green energy carrier.^32,33 The OER is also the primary half-cell reaction occurring at the cathode of rechargeable metal–air batteries, and hence, it significantly determines the energy conversion efficiency.³⁴ The OER performance of the Cu₁₃ NC and the Cu₁(PPh₃)₂(OH) compound was also investigated for comparison. As a note, Cu₁(PPh₃)₂(OH) is the product obtained during the synthetic trials aimed at preparing a Cu nanocluster protected only by PPh₃. The CCDC number of Cu₁(PPh₃)₂(OH) is 2417860.† Its structural details can be found in Fig. S6.† Carbon black was used as a support to improve the electrical conductivity of the catalyst, and all the tests were conducted in 1 M KOH solution. Particular care was taken to ensure an equivalent Cu loading across all the samples.

Fig. 3a illustrates the OER polarization curves of the samples. At an applied voltage of 1.536 V, the Cu₁₄ NC achieves a current density of 10 mA cm⁻², outperforming the benchmark OER catalyst RuO₂, as well as the Cu₁₃ NC and Cu₁(PPh₃)₂(OH). A direct comparison of the overpotentials of the four samples at a current density of 10 mA cm⁻² is shown in Fig. 3b. The overpotential of the Cu₁₄ NC at 10 mA cm⁻² is 306 mV, which is significantly lower than that of the other samples. The improved catalytic performance of the Cu₁₄ NC compared to the Cu₁₃ NC is probably attributed to the incorporation of the 14th Cu atom, which modulates the geometric and electronic structures, hence facilitating the OER process. Conversely, the poor performance of Cu₁(PPh₃)₂(OH) can be ascribed to the limited accessibility of its active sites, mainly due to the steric hindrance imposed by the bulky PPh₃ ligands. The Tafel plots were recorded (Fig. S7†) to reveal the reaction kinetics, where the Tafel slopes can be calculated. The Tafel slope of the Cu₁₄ NC is lower than those of the other samples, indicating that the Cu₁₄ NC has the most favourable reaction kinetics.

Fig. 3 The OER performance of Cu₁₄, Cu₁₃, RuO₂ and Cu₁(PPh₃)₂(OH) in 1 M KOH. (a) The LSV polarization curves. (b) Overpotential comparison at 10 mA cm⁻² current density. (c) The electrochemical impedance spectra. (d) Linear regression of cathodic charging currents versus scan rate. (e) ECSA comparison. (f) The i–t curve of Cu₁₄ in 30 h.

To further evaluate the intrinsic catalytic activity of the samples, electrochemical impedance spectroscopy (EIS) measurements were performed and the experimental data were fitted using an equivalent circuit model. As shown in Fig. 3c, the Cu₁₄ NC has the smallest semicircle in the Nyquist plot, corresponding to a small charge transfer resistance (R_ct) value of 15.94 Ω. In contrast, the R_ct values of the Cu₁₃ NC and Cu₁(PPh₃)₂(OH) were determined to be 41.54 Ω and 65.19 Ω, respectively. The significantly lower R_ct value of the Cu₁₄ NC indicates a much more facile electron transfer process during the OER, contributing to its enhanced catalytic activity. Furthermore, cyclic voltammetry (CV) measurements were performed in the potential range from 1.1 V to 1.2 V at scan rates varying from 10 mV s⁻¹ to 60 mV s⁻¹ (Fig. S8a–c†). From these measurements, the double-layer capacitance (C_dl) values of the Cu₁₄ NC, the Cu₁₃ NC and Cu₁(PPh₃)₂(OH) were calculated to be 20.07 mF cm⁻², 13.03 mF cm⁻² and 11.52 mF cm⁻², respectively (Fig. 3d). A higher C_dl value indicates a larger electrochemically active surface area (ECSA), as illustrated in Fig. 3e. Finally, the long-term durability of the Cu₁₄ NC catalyst for the OER was evaluated. As shown in Fig. 3f, after 30 hours of continuous chronoamperometry (i–t) testing at a constant potential of 1.536 V, the current density of the Cu₁₄ NC catalyst exhibits only a negligible current decrease of ∼4%, demonstrating remarkably robust long-term stability for the OER. In contrast, the Cu₁₃ NC exhibits a current decay of ∼8%, slightly inferior to that of Cu₁₄ NC. The superior long-term stability of the Cu₁₄ NC is probably attributed to its more symmetric and compact metal core structure.

The experimental results demonstrate that the Cu₁₄ NC exhibits superior electrocatalytic performance for the OER compared to the Cu₁₃ NC. In order to gain deeper insights, DFT calculations were employed to systematically compare the OER activity of Cu₁₄ and Cu₁₃ NCs, with a particular focus on evaluating the rate-determining step (RDS) and identifying the active sites. We primarily consider the OER activity of the NCs following the removal of a single ligand.^35–39 Specifically, we first examined the removal of a single –PPh₃ ligand in detail. Based on the distinct coordination environments of –PPh₃ ligands in Cu₁₄ and Cu₁₃ NCs, we classified the –PPh₃ ligands in Cu₁₄ as P¹Ph₃, P²Ph₃, P³Ph₃, and P⁴Ph₃ (as shown in Fig. S9a†) and the –PPh₃ ligands in Cu₁₃ as P¹Ph₃, P²Ph₃, and P³Ph₃ (as shown in Fig. S9b†) for differentiation. We found that, compared to the removal of other –PPh₃ ligands, Cu₁₄ with the –P⁴Ph₃ ligand removed exhibits a more stable structure (Fig. S9c†), while exposing a Cu active site coordinated with three thiolate ligands. Therefore, we selected Cu₁₄ with the –P⁴Ph₃ ligand removed as the catalyst for the electrocatalytic OER. The computational results indicate that at an equilibrium potential of U = 1.23 V, the conversion from *OH to *O is the RDS, with a corresponding free energy barrier of 0.96 eV. Furthermore, throughout the entire OER process, all key reaction intermediates preferentially adsorb onto the Cu active site at a top site (Fig. 4a). For the Cu₁₃ NC, the removal of the –P¹Ph₃ ligand instead of –P²Ph₃ or –P³Ph₃ leads to superior stability of the catalyst. During the electrocatalytic OER process, the transformation of *O to *OOH is identified as the RDS, exhibiting a relatively high free energy barrier of 1.11 eV. Analysis of the adsorption configurations of the intermediates reveals that *OH and *O preferentially adsorb on the Cu atom via top-site and hollow-site adsorption, while *OOH tends to adopt a bridging adsorption mode.

Fig. 4 The free energy diagrams (ΔG) for O₂ evolution and corresponding absorption structures of (a) Cu₁₄ and (b) Cu₁₃ NCs after the removal of a –PPh₃ ligand at U = 0 V and U = 1.23 V. Colour legend: Cu, dark orange; C, grey; S, blue; P, purple; H, white; and O, red.

Meanwhile, we also investigated the catalytic behaviour of Cu₁₄ and Cu₁₃ NCs after the removal of a single thiolate ligand. As shown in Fig. S10,† for the Cu₁₄ NC with the thiolate ligand removed, the key reaction intermediates preferentially adsorb at the Cu active sites in a hollow-site configuration during the catalytic process. In contrast, for the Cu₁₃ NC after thiolate ligand removal, the reaction intermediates tend to adopt a bridge-site adsorption configuration. This difference in adsorption modes may originate from variations in the surface atomic coordination environment. Further reaction energy barrier calculations reveal that, for both Cu₁₄ and Cu₁₃ NCs, the conversion of *OOH to O₂ is the RDS, with relatively high free energy barriers of 1.61 eV and 1.49 eV, respectively.

The aforementioned DFT calculations indicate that, in Cu₁₄ and Cu₁₃ NCs, the catalytically active sites are most likely the exposed Cu atoms resulting from the removal of a –PPh₃ ligand. Notably, despite the high structural similarity of the metal cores in Cu₁₄ and Cu₁₃ NCs, the additional Cu atom in Cu₁₄ not only induces local structural alterations but also significantly influences the catalytic properties of the NCs. Specifically, the additional Cu atom serves as the key catalytic site in the Cu₁₄ NC. Compared to Cu₁₃, Cu₁₄ exhibits superior catalytic performance in the OER, highlighting the significance of atomic-level structural modifications in optimizing catalytic performance.

4. Conclusions

In summary, a pair of atomically precise Cu nanoclusters [Cu₁₄(Fur)₃(PPh₃)₈H₁₀]⁺ and [Cu₁₃(Nap)₃(PPh₃)₇H₁₀]⁰ were successfully synthesized and examined as model catalysts for the OER. They exhibit a high degree of structural similarity, but one additional Cu atom in Cu₁₄ induces some local structural shrinking, and more importantly, when used as catalysts for the OER in 1 M KOH, Cu₁₄ demonstrated markedly superior catalytic performance compared to Cu₁₃, manifested by a lower overpotential at 10 mA cm⁻², smaller charge transfer resistance, and a larger electrochemically active surface area. DFT calculations further validated that the additional Cu atom is the key catalytic site, which is able to significantly lower the energy barrier of the rate-determining step in the OER process. This study highlights the great advantages of employing atomically precise metal nanoclusters as model catalysts, and such atomic-level modification to tune catalytic performance can shed light on future catalyst design.

Data availability

All the data supporting the findings of this study are available within the paper and its ESI.†

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

Z. T. acknowledges funding from the Guangdong Natural Science Funds (No. 2023A0505050107). Q. T. acknowledges the National Natural Science Foundation of China (No. 22473017) and the Chongqing Science and Technology Commission (CSTB2024NSCQMSX0250).

References

1. R. Jin, G. Li, S. Sharma, Y. Li and X. Du, Toward Active-Site Tailoring in Heterogeneous Catalysis by Atomically Precise Metal Nanoclusters with Crystallographic Structures, Chem. Rev., 2021, 121, 567–648.
2. Y. Du, H. Sheng, D. Astruc and M. Zhu, Atomically Precise Noble Metal Nanoclusters as Efficient Catalysts: A Bridge between Structure and Properties, Chem. Rev., 2020, 120, 526–622.
3. W. Jing, H. Shen, R. Qin, Q. Wu, K. Liu and N. Zheng, Surface and Interface Coordination Chemistry Learned from Model Heterogeneous Metal Nanocatalysts: From Atomically Dispersed Catalysts to Atomically Precise Clusters, Chem. Rev., 2023, 123, 5948–6002.
4. Z. Liu, X. Liu, L. Qin, H. Chen, R. Li and Z. Tang, Alkynyl ligand for preparing atomically precise metal nanoclusters: Structure enrichment, property regulation, and functionality enhancement, Chin. J. Struct. Chem., 2024, 43, 100405.
5. M. Chen, C. Guo, L. Qin, L. Wang, L. Qiao, K. Chi and Z. Tang, Atomically Precise Cu Nanoclusters: Recent Advances, Challenges, and Perspectives in Synthesis and Catalytic Applications, Nano-Micro Lett., 2025, 17, 83.
6. S. Li, N.-N. Li, X.-Y. Dong, S.-Q. Zang and T. C. W. Mak, Chemical Flexibility of Atomically Precise Metal Clusters, Chem. Rev., 2024, 124, 7262–7378.
7. Z. Guan and Q.-M. Wang, Ligand Engineering in Metal Nanoclusters: from Structural Control to Functional Modulation, Chin. J. Struct. Chem., 2020, 39, 1194–1200.
8. Z.-J. Guan, R.-L. He, S.-F. Yuan, J.-J. Li, F. Hu, C.-Y. Liu and Q.-M. Wang, Ligand Engineering toward the Trade-Off between Stability and Activity in Cluster Catalysis, Angew. Chem., Int. Ed., 2022, 61, e202116965.
9. J. Wang, F. Xu, Z.-Y. Wang, S.-Q. Zang and T. C. W. Mak, Ligand-Shell Engineering of a Au₂₈ Nanocluster Boosts Electrocatalytic CO₂ Reduction, Angew. Chem., Int. Ed., 2022, 61, e202207492.
10. S. Yoo, S. Yoo, G. Deng, F. Sun, K. Lee, H. Jang, C. W. Lee, X. Liu, J. Jang, Q. Tang, Y. J. Hwang, T. Hyeon and M. S. Bootharaju, Nanocluster Surface Microenvironment Modulates Electrocatalytic CO₂ Reduction, Adv. Mater., 2024, 36, 2313032.
11. Z. Liu, H. Tan, B. Li, Z. Hu, D.-E. Jiang, Q. Yao, L. Wang and J. Xie, Ligand effect on switching the rate-determining step of water oxidation in atomically precise metal nanoclusters, Nat. Commun., 2023, 14, 3374.
12. Z. Liu, J. Chen, B. Li, D.-E. Jiang, L. Wang, Q. Yao and J. Xie, Enzyme-Inspired Ligand Engineering of Gold Nanoclusters for Electrocatalytic Microenvironment Manipulation, J. Am. Chem. Soc., 2024, 146, 11773–11781.
13. L. Chen, F. Sun, Q. Shen, L. Qin, Y. Liu, L. Qiao, Q. Tang, L. Wang and Z. Tang, Homoleptic alkynyl-protected Ag₃₂ nanocluster with atomic precision: Probing the ligand effect toward CO₂ electroreduction and 4-nitrophenol reduction, Nano Res., 2022, 15, 8908–8913.
14. Q.-L. Shen, L.-Y. Shen, L.-Y. Chen, L.-B. Qin, Y.-G. Liu, N. M. Bedford, F. Ciucci and Z.-H. Tang, Heterointerface of all-alkynyl-protected Au₂₈ nanoclusters anchored on NiFe-LDHs boosts oxygen evolution reaction: a case to unravel ligand effect, Rare Met., 2023, 42, 4029–4038.
15. M.-Y. Chen, L.-Y. Shen, L.-B. Qin, F. Ciucci and Z.-H. Tang, Atomically precise Cu₆ nanoclusters for oxygen evolution catalysis: a combined experimental and theoretical study, Rare Met., 2025, 44, 2428–2437.
16. Q.-J. Wu, D.-H. Si, P.-P. Sun, Y.-L. Dong, S. Zheng, Q. Chen, S.-H. Ye, D. Sun, R. Cao and Y.-B. Huang, Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO₂ towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site, Angew. Chem., Int. Ed., 2023, 62, e202306822.
17. S. Wang, Q. Li, X. Kang and M. Zhu, Customizing the Structure, Composition, and Properties of Alloy Nanoclusters by Metal Exchange, Acc. Chem. Res., 2018, 51, 2784–2792.
18. A. Ghosh, O. F. Mohammed and O. M. Bakr, Atomic-Level Doping of Metal Clusters, Acc. Chem. Res., 2018, 51, 3094–3103.
19. X. Liu, X. Cai and Y. Zhu, Catalysis Synergism by Atomically Precise Bimetallic Nanoclusters Doped with Heteroatoms, Acc. Chem. Res., 2023, 56, 1528–1538.
20. J. Wang, J. Cai, K.-X. Ren, L. Liu, S.-J. Zheng, Z.-Y. Wang and S.-Q. Zang, Stepwise structural evolution toward robust carboranealkynyl-protected copper nanocluster catalysts for nitrate electroreduction, Sci. Adv., 2024, 10, eadn7556.
21. X. Ma, C. Fang, M. Ding, Y. Zuo, X. Sun and S. Wang, Atomic-Level Elucidation of Lattice-Hydrogens in Copper Catalysts for Selective CO₂ Electrochemical Conversion toward C₂ Products, Angew. Chem., Int. Ed., 2025, e202500191.
22. J. Yang, R. Pang, D. Song and M.-B. Li, Tailoring silver nanoclusters via doping: advances and opportunities, Nanoscale Adv., 2021, 3, 2411–2422.
23. S. Masuda, K. Sakamoto and T. Tsukuda, Atomically precise Au and Ag nanoclusters doped with a single atom as model alloy catalysts, Nanoscale, 2024, 16, 4514–4528.
24. H. Fakhouri, E. Salmon, X. Wei, S. Joly, C. Moulin, I. Russier-Antoine, P.-F. Brevet, X. Kang, M. Zhu and R. Antoine, Effects of Single Platinum Atom Doping on Stability and Nonlinear Optical Properties of Ag₂₉ Nanoclusters, J. Phys. Chem. C, 2022, 126, 21094–21100.
25. K. Kwak, W. Choi, Q. Tang, M. Kim, Y. Lee, D.-e. Jiang and D. Lee, A Molecule-like PtAu₂₄(SC₆H₁₃)₁₈ Nanocluster as An Electrocatalyst For Hydrogen Production, Nat. Commun., 2017, 8, 14723.
26. S. Li, D. Alfonso, A. V. Nagarajan, S. D. House, J. C. Yang, D. R. Kauffman, G. Mpourmpakis and R. Jin, Mono-Palladium Substitution in Gold Nanoclusters Enhances CO₂ Electroreduction Activity and Selectivity, ACS Catal., 2020, 10, 12011–12016.
27. S. Su, Y. Zhou, L. Xiong, S. Jin, Y. Du and M. Zhu, Structure-Activity Relationships of the Structural Analogs Au₈Cu₁ and Au₈Ag₁ in the Electrocatalytic CO₂ Reduction Reaction, Angew. Chem., Int. Ed., 2024, 63, e202404629.
28. C. Yao, J. Chen, M.-B. Li, L. Liu, J. Yang and Z. Wu, Adding Two Active Silver Atoms on Au₂₅ Nanoparticle, Nano Lett., 2015, 15, 1281–1287.
29. C. Dong, R.-W. Huang, A. Sagadevan, P. Yuan, L. Gutiérrez-Arzaluz, A. Ghosh, S. Nematulloev, B. Alamer, O. F. Mohammed, I. Hussain, M. Rueping and O. M. Bakr, Isostructural Nanocluster Manipulation Reveals Pivotal Role of One Surface Atom in Click Chemistry, Angew. Chem., Int. Ed., 2023, 62, e202307140.
30. Y. Shingyouchi, M. Ogami, S. Biswas, T. Tanaka, M. Kamiyama, K. Ikeda, S. Hossain, Y. Yoshigoe, D. J. Osborn, G. F. Metha, T. Kawawaki and Y. Negishi, Ligand-Dependent Intracluster Interactions in Electrochemical CO₂ Reduction Using Cu₁₄ Nanoclusters, Small, 2024, 2409910.
31. M. Bodiuzzaman, K. Murugesan, P. Yuan, B. Maity, A. Sagadevan, N. H. Malenahalli, S. Wang, P. Maity, M. F. Alotaibi, D.-E. Jiang, M. Abulikemu, O. F. Mohammed, L. Cavallo, M. Rueping and O. M. Bakr, Modulating Decarboxylative Oxidation Photocatalysis by Ligand Engineering of Atomically Precise Copper Nanoclusters, J. Am. Chem. Soc., 2024, 146, 26994–27005.
32. Y. Zhang, B. Wang, C. Hu, M. Humayun, Y. Huang, Y. Cao, M. Negem, Y. Ding and C. Wang, Fe–Ni–F electrocatalyst for enhancing reaction kinetics of water oxidation, Chin. J. Struct. Chem., 2024, 43, 100243.
33. L. Qi, Z. Chen, X. Luan, Z. Zheng, Y. Xue and Y. Li, Atomically dispersed Mn enhanced catalytic performance for overall water splitting on graphdiyne-coated copper hydroxide nanowire, Chin. J. Struct. Chem., 2024, 43, 100197.
34. S. Ding, H. Wang, X. Dai, Y. Lv, X. Niu, R. Yin, F. Wu, W. Shi, W. Liu and X. Cao, Mn-modulated Co–N–C oxygen electrocatalysts for robust and temperature-adaptative zinc-air batteries, Chin. J. Struct. Chem., 2024, 43, 100302.
35. L. Qin, F. Sun, X. Ma, G. Ma, Y. Tang, L. Wang, Q. Tang, R. Jin and Z. Tang, Homoleptic Alkynyl-Protected Ag₁₅ Nanocluster with Atomic Precision: Structural Analysis and Electrocatalytic Performance toward CO₂ Reduction, Angew. Chem., Int. Ed, 2021, 60, 26136–26141.
36. L. Qin, F. Sun, Z. Gong, G. Ma, Y. Chen, Q. Tang, L. Qiao, R. Wang, Z.-Q. Liu and Z. Tang, Electrochemical NO₃⁻ Reduction Catalyzed by Atomically Precise Ag₃₀Pd₄ Bimetallic Nanocluster: Synergistic Catalysis or Tandem Catalysis?, ACS Nano, 2023, 17, 12747–12758.
37. L. Qin, F. Sun, M. Li, H. Fan, L. Wang, Q. Tang, C. Wang and Z. Tang, Atomically precise (AgPd)₂₇ nanoclusters for nitrate electroreduction to NH₃: Modulating the metal core by a ligand induced strategy, Acta Phys.-Chim. Sin., 2025, 41, 100008.
38. G. Deng, H. Yun, M. S. Bootharaju, F. Sun, K. Lee, X. Liu, S. Yoo, Q. Tang, Y. J. Hwang and T. Hyeon, Copper Doping Boosts Electrocatalytic CO₂ Reduction of Atomically Precise Gold Nanoclusters, J. Am. Chem. Soc., 2023, 145, 27407–27414.
39. G. Deng, H. Yun, Y. Chen, S. Yoo, K. Lee, J. Jang, X. Liu, C. W. Lee, Q. Tang, M. S. Bootharaju, Y. J. Hwang and T. Hyeon, Ferrocene-Functionalized Atomically Precise Metal Clusters Exhibit Synergistically Enhanced Performance for CO₂ Electroreduction, Angew. Chem., Int. Ed., 2025, 64, e202418264.

---

Footnotes

† Electronic supplementary information (ESI) available: experimental details, supporting figures and tables, and more calculation results. CCDC 2417373 and 2417860. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5qi00735f

‡ These authors contributed equally.

---