Theoretical insight into the relevance between the oxidation states of CeO₂ supported Pt^{4+/2+/1+/0/2−} and their HER performance

Abstract

The oxidation states (OSs) of Pt catalysts play a key role in the hydrogen evolution reaction (HER), which has become a focus in recent years. As for Pt/CeO₂ catalysts, we have systematically explored the effect of Pt^{4+/2+/1+/0/2−} OSs on the HER. H atoms could not adsorb on the Pt⁴⁺ and Pt_4c²⁺ sites, and they prefer to locate on the adjacent O atoms (labeled as Pt⁴⁺–O and Pt_4c²⁺–O). As for the other OSs, the adsorption ability of H atoms follows the order Pt⁰ > Pt_3c²⁺ > Pt¹⁺ > Pt²⁻. The electron-enriched Pt²⁻ is the most suitable oxidation state for the HER, no matter the reaction mechanism, which is the Volmer–Heyrovsky or Volmer–Tafel mechanism. The Pt OSs would greatly affect the electronic structures of Pt catalysts, which will further impact their overall catalytic properties. Our study could shed light on the research of Pt-based catalysts for the HER.

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1. Introduction

The development of modern society mainly depends on fossil fuels, which would cause fossil fuel exhaustion and environmental issues. Hydrogen has a very high energy density and the combustion product is only water, thus hydrogen is one of the most promising clean and sustainable energy sources. To date, platinum (Pt) is still the most effective electrocatalyst for the hydrogen evolution reaction (HER), though the scarcity of Pt has severely limited its large-scale applications.^1–3 One of the most straightforward methods to address this issue is to improve the utilization efficiency of Pt atoms, reducing the size of Pt electrocatalysts from nanoparticles (NPs) to nanoclusters (NCs) or even to single atoms (SAs).^4–6 A very recent study found that Pt single-atoms anchored to functional CeO_x nanoglues could remain dispersed in both oxidizing and reducing environments at high temperatures.⁷ As is well known, the catalytic activity of Pt/CeO₂ is affected by multiple factors, such as the size and loading of Pt, and the surface facets and morphology of CeO₂.^8–13 Remarkably, the importance of OSs present in CeO₂ supported Pt catalysts has been gradually discovered in determining the catalytic activity for the HER.¹⁴

The electrons of Pt catalysts are usually taken away by metal–support interactions because of their difference in electronegativity, resulting in electron-deficient Pt (Pt^δ+, 0 < δ < 4).^15–18 Many studies have shown that the HER activity of oxidized Pt^δ+ can be obviously better than that of metal Pt⁰, and Pt–O bonds act as an active site superior to Pt⁰.^19–21 Strikingly, Wei et al. found that the rich oxygen vacancies of porous TiO₂ could reverse the electron transfer from TiO₂ to Pt NCs, leading to the ultrahigh mass activity of Pt^δ− NCs/TiO₂.²² Yan et al. found that Pt^δ− NPs supported on MgO nanosheets with rich oxygen vacancies could create a local acid-like environment in an alkaline medium, which brings about excellent HER performances.²³ Yan et al. found that electron-enriched Pt (Pt^δ−) NCs caused by the size-dependent electron transfer reversal are far more active than electron-deficient Pt single atoms for the HER.²⁴ On the other hand, Shi et al. found that the decrease of single-atom Pt OSs could optimize the HER performance in an acidic environment.²⁵ Similarly, Fang et al. also discovered that the near-free single-atom Pt resembling a free metallic atom is responsible for the superior HER activity.²⁶

The Pt OSs depend on the kind of support and specific synthesis conditions, and various Pt OSs would lead to diverse reaction data.¹⁴ In this article, we have systematically explored the effect of CeO₂ supported Pt^{4+/2+/1+/0/2−} OSs on the HER by density functional theory (DFT) calculations.

2. Computational methods

All DFT calculations were performed using the spin-polarized Kohn–Sham formalism as implemented in the Vienna ab initio simulation package (VASP).²⁷ The exchange–correlation was described by the Perdew–Burke–Ernzerhof (PBE) functional of the generalized gradient approximation (GGA).²⁸ The valence wave functions were expanded in plane-wave basis sets with a cutoff energy of 400 eV, and the Γ point was used for Brillouin zone integration. The convergence criteria of energy and force for structural optimization were set to 1 × 10⁻⁵ eV and 0.02 eV Å⁻¹, respectively. The on-site Coulomb interaction via the Hubbard-like term U was adopted for the highly localized 4f electrons with an effective U of 5.0 eV. AIMD simulations were performed using the canonical (NVT) ensemble for 10 ps with a time step of 2 fs with the Nośe–Hoover thermostats at 300 K and 700 K.

Pt incorporated in or loaded on ceria (CeO₂) has been widely used in various catalytic reactions because of the well-defined structures.^29,30 CeO₂ (111) surface cells were adopted as the support to construct various Pt OSs, and have been always used in many experimental and theoretical studies.^31–35 As for the combustion-synthesized Pt/CeO₂ catalysts, Pt could be incorporated into the CeO₂ lattice, mostly as Pt²⁺/Pt⁴⁺ and rarely as Pt⁰.^36,37 Numerous studies have demonstrated that Pt SAs can be stabilized on CeO₂ (111) steps through different preparation methods.^31–33 The (4 × 4) CeO₂ (111) model contains three O–Ce–O tri-layers separated by a 15 Å vacuum in the normal direction, and the bottom tri-layer was fixed during the geometry optimization.

The Gibbs free energy change (ΔG_H*) in the hydrogen reduction was calculated according to the method developed by Nørskov et al.:³⁸

ΔG = ΔE + ΔE_zpe − TΔS (1)

where ΔE is the energy difference between the products and reactants, and ΔE_zpe and ΔS are the zero-point energy and entropy corrections between the adsorbed state and the gas phase, respectively.

The d-band center (ε_d) was calculated according to the formula:^39,40

where x and ρ(x) are the electronic energy and electronic density of states, respectively.^41–43 The integral domain is from the minimum energy to zero for the d electrons.

3. Results and discussion

3.1. Construction of Pt^{4+/2+/1+/0/2−} OSs

We have first explored the situation of Pt atoms incorporated into the CeO₂ lattice, where one surface Ce cation is substituted by a single Pt atom (Fig. 1a) or two Pt atoms (Fig. 1b).^34,44 There are three possible structures for the latter system, namely Pt_2c + Pt_4c, Pt_3c + Pt_3c, and Pt_3c + Pt_4c (Fig. S1†), and the Pt_3c + Pt_4c structure is the most energetically stable, where the subscripts represent the coordination number of the Pt atoms. Although identifying OSs is a challenge,⁴⁵ the magnetic moment of CeO₂ could well describe the Pt OSs of Pt/CeO₂ single-atom catalysts by counting the number of Ce³⁺ species.⁴⁶ Ce⁴⁺ presents no net magnetic moment, and the magnetic moment of Ce³⁺ is about ∼1μ_B on the 4f orbitals because of electron ejection.¹⁷ The magnetic moment of CeO₂ has almost no significant changes when the surface Ce cation is substituted by one or two Pt atoms, suggesting that the OSs of the Pt single-atom and Pt_3c + Pt_4c should be similar to that of the replaced Ce⁴⁺. As for the situation of Ce⁴⁺ substituted by Pt_3c + Pt_4c, the Bader charge of Pt_3c and Pt_4c is 9.28 and 9.26 e respectively, which means that the valence states of Pt_3c and Pt_4c should be roughly equal, namely Pt_3c²⁺ and Pt_4c²⁺. The coordination number of Ce⁴⁺ is seven, and the number of nearest neighbor O atoms coordinated with Pt⁴⁺ is six. The Pt⁴⁺–O bonds of the upper three O atoms are about 2.16 Å, and the values for the lower three O atoms are about 2.10 Å. As for Pt_4c²⁺–O and Pt_3c²⁺–O, their average Pt²⁺–O bonds are all above 2.00 Å, which are shorter than the Pt⁴⁺–O bonds.

Fig. 1 The optimized structures of (a) Pt⁴⁺/CeO₂ and (b) Pt²⁺/CeO₂. The Ce, O and Pt atoms are denoted by yellow, red and light blue balls, respectively. The silver balls are the nearest O atoms to the Pt atoms.

The possible OSs of Pt atoms on the Pt/CeO₂ (111) interface with/without an oxygen vacancy were also explored (Fig. 2).^35,47 For the adsorption of Pt on the stoichiometric CeO₂ (111), the OS of the Pt site is zero (Pt⁰) as shown in Fig. 2a.³⁵ The types of oxygen vacancies can be divided into (top) surface and subsurface oxygen vacancies, denoted as SV and SSV, respectively.^48,49 The extraction of an oxygen vacancy would cause the reduction of two Ce⁴⁺ species to Ce³⁺, and the spin moments localized mainly on these two Ce³⁺ ions.⁵⁰ As for the Pt/CeO₂ containing SV/SSV (denoted as Pt + SV and Pt + SSV, respectively), the increase or decrease in the number of Ce³⁺ means the electron transfer between the Pt and CeO₂ caused by the oxygen vacancies (Fig. 2b and c). The number of Ce³⁺ ions on Pt + SSV increases from 2 to 3 which means that one electron transfers from Pt to CeO₂; hence the OS of Pt is +1. As for Pt¹⁺/CeO₂, there are five local spin minima (Fig. S2†), and the lowest energy structure is chosen for further study (Fig. 2b).^51,52 There are no Ce³⁺ ions on Pt + SV suggesting that the CeO₂ donates two electrons to the Pt site; hence the OS of Pt on Pt + SV is −2 (Fig. 2c). The Pt⁰–O bond is 2.14 Å, and that for Pt¹⁺ is 1.98 Å. The distance between Pt²⁻ and Ce⁴⁺ is 2.88 Å, which is larger than that of Pt^δ+–O.

Fig. 2 The optimized structures of (a) Pt⁰/CeO₂, (b) Pt¹⁺/CeO₂ and (c) Pt²⁻/CeO₂. The Ce, O and Pt atoms are denoted by yellow, red and light blue balls, respectively. The black color indicates the reduced Ce³⁺ atoms.

3.2. The electronic structures of Pt^{4+/2+/1+/0/2−} and their HER mechanisms

As is well known, the hydrogen adsorption free energy (ΔG_H*) has been widely used as a useful descriptor for the evaluation of HER activity, and Pt exhibits the optimal level for the Volmer step with a near-zero ΔG_H*, owing to its suitable d-band position.^53,54 The first step of the HER is the Volmer step, in which electron transfer to the electrode surface is coupled to proton adsorption (H⁺ + e⁻ → H*).⁵⁵

H atoms cannot be adsorbed on Pt⁴⁺ and Pt_4c²⁺ sites because of the saturated coordination, and they prefer to adsorb on the O atoms adjacent to Pt⁴⁺ and Pt_4c²⁺ (Fig. S3†), in which the ΔG_H* values for Pt⁴⁺–O and Pt_4c²⁺–O are −0.91 and −0.51 eV, respectively. The adsorption structures of H atoms on Pt_3c²⁺, Pt¹⁺, Pt⁰ and Pt²⁻ sites are displayed in Fig. 3, and their ΔG_H* values are −0.44 eV, −0.23 eV, −0.47 eV and −0.03 eV, respectively. To sum up, the ΔG_H* values are in the following order: (Pt⁴⁺–O) > (Pt_4c²⁺–O) > Pt⁰ > Pt_3c²⁺ > Pt¹⁺ > Pt²⁻. Too negative ΔG_H* values mean the strong adsorption of H*, which will be disadvantageous to the subsequent desorption process. Meanwhile, too positive ΔG_H* values mean the weak adsorption of H*, unfavorable for the subsequent reaction. The Pt¹⁺ is more suitable for the H* adsorption than Pt^4+/2+, and the H* adsorption on Pt⁰ is too strong. All in all, the electron-enriched Pt²⁻ is the most favorable valence state for the Volmer step.

Fig. 3 The optimized structures of (a) Pt_3c²⁺/CeO₂, (b) Pt¹⁺/CeO₂, (c) Pt⁰/CeO₂ and (d) Pt²⁻/CeO₂ with H* adsorption. The Ce, O, Pt and H atoms are denoted by yellow, red, light blue and dark blue balls, respectively. The black color indicates the reduced Ce³⁺ atoms.

As for Pt^4+/2+/1+, the magnetic moment of CeO₂ would not change when the H* adsorption occurs, which leads to the formation of (Pt–H)^4+/2+/1+ states. The CeO₂ support of Pt⁰/CeO₂ would accept one electron resulting in Ce³⁺ because of the H* adsorption; thus the adsorption state of Pt⁰ will turn into (Pt–H)¹⁺. As for Pt²⁻/CeO₂, the number of electrons donated from CeO₂ to Pt²⁻ would decrease from two to one during the Volmer step, forming a (Pt–H)¹⁻ state.

The projected density of states (PDOS) was calculated to study the effect of the Pt OSs on electronic structures (Fig. 4 and S4†). Pt⁴⁺, Pt²⁺ and Pt⁰ exhibit semiconductor behavior, and the band gaps for Pt⁴⁺, Pt_4c²⁺, Pt_3c²⁺ and Pt⁰ are 1.22 eV, 0.58 eV, 0.50 eV and 0.50 eV, respectively. It is noteworthy that Pt¹⁺ shows metallic properties, and the PDOS of Pt²⁻ is highly localized. The d-band center has been widely used in revealing the relationship between electronic structures and hydrogen adsorption. Surprisingly, the ε_d is not relevant to the ΔG_H* values (Fig. 5a), in which the ε_d values of Pt⁴⁺ and Pt_4c²⁺ are not considered because H atoms could not adsorb on these metal sites and thus the Pt²⁺ in Fig. 5 refers to Pt_3c²⁺. As is well known, the valence electronic structures of Pt^2+/1+/0/2− vary largely in the electron number, whereas this difference is not considered in the calculation of ε_d. Furthermore, the s–d orbital interaction of Pt^2+/1+/0/2− would also change with the various valence electronic structures.⁵⁶ Considering these facts, the d-band center has been revised as:

ε_d′ = (−ε_d + ε_s) × [(10 − OSs)/10] (3)

where ε_s is the s-band center, and 10 is the number of valence electrons (Pt, 5d⁹6s¹). The R² value of ε_d′ with ΔG_H* had a significant boost to 0.78 from 0.19 for ε_d (Fig. 5b), which fully demonstrates the importance of Pt OSs to the H* adsorption. From the above analysis, we can clearly see that the Pt OSs markedly affect the electronic structures of Pt sites, and further impact their catalytic properties.^57–59

Fig. 4 The PDOS of (a) Pt_3c²⁺, (b) Pt¹⁺, (c) Pt⁰ and (d) Pt²⁻.

Fig. 5 The relationship between d-band centers and ΔG_H* values: (a) ε_d–ΔG_H* and (b) ε_d′–ΔG_H*.

The second step of the HER is the process of H₂ formation, which may occur via two different pathways: the Heyrovsky and Tafel reactions. In the Heyrovsky reaction, the transfer of a second electron to the H* is coupled with another proton adsorption.⁵⁵ The active sites for the Volmer reaction will retain catalytic activity for the Heyrovsky reaction when the overpotential is zero, and their ΔG_H* values have an opposite relationship.^42,60 Through the above analysis, we can clearly see that the Pt⁴⁺ and Pt_4c²⁺ sites are not suitable for the Volmer step; thus these two metal sites are no longer involved in the following research, in which Pt²⁺ below refers to Pt_3c²⁺ for the sake of argument. As can be seen from Fig. 6, Pt²⁻ exhibits the best performance for the Volmer–Heyrovsky reaction, followed by Pt¹⁺, Pt²⁺ and Pt⁰.

Fig. 6 The calculated reaction pathways with the Volmer–Heyrovsky reaction mechanism of Pt^2+/1+/0/2−.

As for the Tafel reaction on Pt single-atoms, two H* species would combine to form H₂, with the formation of two-hydrogen complexes (H–Pt–H).⁶¹ The optimized structures of Pt^2+/1+/0/2−/CeO₂ with two-H* adsorption are displayed in Fig. 7. The two-H* adsorption on Pt^2+/0/2− will not cause the electron transfer between Pt^2+/0/2− and CeO₂, with the formation of (H–Pt–H)^2+/0/2− states. Significantly, the Ce³⁺ number of Pt¹⁺/CeO₂ is 2 when the process of two-H* adsorption occurs, which means that the adsorption state of Pt¹⁺ will turn into (H–Pt–H)⁰. The number of Ce³⁺ ions with their magnetic moment are marked in Table S1.† The adsorption of the second H atom on Pt^2+/1+/0/2− is an energy decreasing process, and the ΔG_H* of Pt²⁺, Pt¹⁺, Pt⁰ and Pt²⁻ for this step is −0.55, −1.24, −0.88 and −0.29 eV, respectively (Fig. 8). The potential-determining steps of Volmer–Tafel reactions on the Pt^2+/1+/0/2− sites are all the desorption of H₂, and the reaction barriers of Pt²⁺, Pt¹⁺, Pt⁰ and Pt²⁻ for H₂ desorption are 0.99, 1.47, 1.35 and 0.32 eV, respectively. The large values of raised free energy, implying high reaction barriers, will cause a low turnover frequency and reduce the hydrogen production rate.^42,62 Hence, the Volmer–Tafel reaction is more likely to take place on Pt²⁻ than on Pt^2+/1+/0. It is worth noting that Pt²⁻ has considerable stability during 10 ps AIMD simulations at 300 K and 700 K (ESI† Movies S1 and S2).

Fig. 7 The optimized structures of (a) Pt²⁺/CeO₂, (b) Pt¹⁺/CeO₂, (c) Pt⁰/CeO₂ and (d) Pt²⁻/CeO₂ with two-H* adsorption. The Ce, O, Pt and H atoms are denoted by yellow, red, light blue and dark blue balls, respectively. The black color indicates the reduced Ce³⁺ atoms.

Fig. 8 The calculated reaction pathways with the Volmer–Tafel reaction mechanism of Pt^2+/1+/0/2−.

4. Conclusions

We have performed systematically investigations on the structures, electronic features and HER catalysis of Pt^{4+/2+/1+/0/2−}/CeO₂ by using the density functional theory method. The Pt OSs of Pt/CeO₂ are evaluated from the magnetic moment variation of the CeO₂ support. Pt^4+/2+ sites are constructed by Pt doping into the CeO₂ lattice, and Pt⁰ and Pt^1+/2− sites could be obtained by Pt adsorption on stoichiometric and defective CeO₂ (111). As for the Volmer step of the HER, the ΔG_H* values are in the following order: (Pt⁴⁺–O) > (Pt_4c²⁺–O) > Pt⁰ > Pt_3c²⁺ > Pt¹⁺ > Pt²⁻, and the electron-enriched Pt²⁻ is the most suitable for this step. Significantly, Pt²⁻ is still the most suitable valence state for the subsequent process of H₂ formation, no matter the reaction mechanism, which is the Heyrovsky or Tafel mechanism. The d-band center has been revised considering the effect of Pt OSs in this study, in which the revised d-band center could further demonstrate the importance of Pt OSs to the H* adsorption. The OSs would greatly affect the electronic structures of Pt catalysts, which will further impact their overall catalytic properties.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was funded by National Natural Science Foundation of China (No. 11874005 and No. 52202214), Sichuan Natural Science Foundation (No. 23NSFSC3565), China National Postdoctoral Program for Innovative Talents (No. BX2021053) and China Postdoctoral Science Foundation (No. 2021M700680), Youth Science Foundation of Guizhou Province Education Ministry (QJHKY[2019] 106), Science and Technology Foundation Project of Guizhou Province (QKHJC [2019] 1323) and Key field Project of Guizhou Provincial Department of Education (QKHKY[2020]048). This work was also supported by Academic Training Project of Zunyi Normal University (Grant Number: 5727-03) and Doctor Foundation of Zunyi Normal University (ZSBS[2018]10).

References

1. M. S. Faber and S. Jin, Energy Environ. Sci., 2014, 7, 3519–3542.
2. S. Ye, F. Luo, Q. Zhang, P. Zhang, T. Xu, Q. Wang, D. He, L. Guo, Y. Zhang, C. He, X. Ouyang, M. Gu, J. Liu and X. Sun, Energy Environ. Sci., 2019, 12, 1000–1007.
3. J. Zhang, E. Wang, S. Cui, S. Yang, X. Zou and Y. Gong, Nano Lett., 2022, 22, 1398–1405.
4. B. Qiao, A. Wang, X. Yang, L. F. Allard, Z. Jiang, Y. Cui, J. Liu, J. Li and T. Zhang, Nat. Chem., 2011, 3, 634–641.
5. H. Zhang, P. An, W. Zhou, Y. Guan Bu, P. Zhang, J. Dong and W. Lou Xiong, Sci. Adv., 2018, 4(1), eaao6657.
6. J. Zhang, Y. Zhao, X. Guo, C. Chen, C.-L. Dong, R.-S. Liu, C.-P. Han, Y. Li, Y. Gogotsi and G. Wang, Nat. Catal., 2018, 1, 985–992.
7. X. Li, X. I. Pereira-Hernández, Y. Chen, J. Xu, J. Zhao, C.-W. Pao, C.-Y. Fang, J. Zeng, Y. Wang, B. C. Gates and J. Liu, Nature, 2022, 611, 284–288.
8. S. Yoon, H. Ha, J. Kim, E. Nam, M. Yoo, B. Jeong, H. Y. Kim and K. An, J. Mater. Chem. A, 2021, 9, 26381–26390.
9. A. I. Boronin, E. M. Slavinskaya, A. Figueroba, A. I. Stadnichenko, T. Y. Kardash, O. A. Stonkus, E. A. Fedorova, V. V. Muravev, V. A. Svetlichnyi, A. Bruix and K. M. Neyman, Appl. Catal., A, 2021, 286, 119931.
10. K. Yuan, Y. Guo, Q.-L. Lin, L. Huang, J.-T. Ren, H.-C. Liu, C.-H. Yan and Y.-W. Zhang, J. Catal., 2021, 394, 121–130.
11. B. Song, S. Si, A. Soleymani, Y. Xin and H. E. Hagelin-Weaver, Nano Res., 2022, 15, 5922–5932.
12. Y. Gao, W. Wang, S. Chang and W. Huang, ChemCatChem, 2013, 5, 3610–3620.
13. M. Kourtelesis, T. S. Moraes, L. V. Mattos, D. K. Niakolas, F. B. Noronha and X. Verykios, Appl. Catal., A, 2021, 284, 119757.
14. H. Jeong, D. Shin, B.-S. Kim, J. Bae, S. Shin, C. Choe, J. W. Han and H. Lee, Angew. Chem., Int. Ed., 2020, 59, 20691–20696.
15. Y. Qu, B. Chen, Z. Li, X. Duan, L. Wang, Y. Lin, T. Yuan, F. Zhou, Y. Hu, Z. Yang, C. Zhao, J. Wang, C. Zhao, Y. Hu, G. Wu, Q. Zhang, Q. Xu, B. Liu, P. Gao, R. You, W. Huang, L. Zheng, L. Gu, Y. Wu and Y. Li, J. Am. Chem. Soc., 2019, 141, 4505–4509.
16. L. Liu and A. Corma, Chem. Rev., 2018, 118, 4981–5079.
17. Y. Lykhach, S. M. Kozlov, T. Skála, A. Tovt, V. Stetsovych, N. Tsud, F. Dvořák, V. Johánek, A. Neitzel, J. Mysliveček, S. Fabris, V. Matolín, K. M. Neyman and J. Libuda, Nat. Mater., 2016, 15, 284–288.
18. S. Yang, Y. J. Tak, J. Kim, A. Soon and H. Lee, ACS Catal., 2017, 7, 1301–1307.
19. F.-Y. Yu, Z.-L. Lang, L.-Y. Yin, K. Feng, Y.-J. Xia, H.-Q. Tan, H.-T. Zhu, J. Zhong, Z.-H. Kang and Y.-G. Li, Nat. Commun., 2020, 11, 490.
20. X. Cheng, Y. Li, L. Zheng, Y. Yan, Y. Zhang, G. Chen, S. Sun and J. Zhang, Energy Environ. Sci., 2017, 10, 2450–2458.
21. Y. Zhan, Y. Li, Z. Yang, X. Wu, M. Ge, X. Zhou, J. Hou, X. Zheng, Y. Lai, R. Pang, H. Duan, X. A. Chen, H. Nie and S. Huang, Adv. Sci., 2019, 6, 1801663.
22. Z.-W. Wei, H.-J. Wang, C. Zhang, K. Xu, X.-L. Lu and T.-B. Lu, Angew. Chem., Int. Ed., 2021, 60, 16622–16627.
23. H. Tan, B. Tang, Y. Lu, Q. Ji, L. Lv, H. Duan, N. Li, Y. Wang, S. Feng, Z. Li, C. Wang, F. Hu, Z. Sun and W. Yan, Nat. Commun., 2022, 13, 2024.
24. Q. Q. Yan, D. X. Wu, S. Q. Chu, Z. Q. Chen, Y. Lin, M. X. Chen, J. Zhang, X. J. Wu and H. W. Liang, Nat. Commun., 2019, 10, 4977.
25. Y. Shi, Z.-R. Ma, Y.-Y. Xiao, Y.-C. Yin, W.-M. Huang, Z.-C. Huang, Y.-Z. Zheng, F.-Y. Mu, R. Huang, G.-Y. Shi, Y.-Y. Sun, X.-H. Xia and W. Chen, Nat. Commun., 2021, 12, 3021.
26. S. Fang, X. Zhu, X. Liu, J. Gu, W. Liu, D. Wang, W. Zhang, Y. Lin, J. Lu, S. Wei, Y. Li and T. Yao, Nat. Commun., 2020, 11, 1029.
27. G. Kresse and J. Furthmüller, Phys. Rev. B: Condens. Matter Mater. Phys., 1996, 54, 11169–11186.
28. J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett., 1996, 77, 3865–3868.
29. A. Bruix, J. A. Rodriguez, P. J. Ramírez, S. D. Senanayake, J. Evans, J. B. Park, D. Stacchiola, P. Liu, J. Hrbek and F. Illas, J. Am. Chem. Soc., 2012, 134, 8968–8974.
30. Y. Xuxu, W. Hengwei, L. Yue, L. Xinyu, C. Lina, G. Jian and L. Junling, Nano Res., 2019, 12, 1401–1409.
31. F. Dvořák, M. Farnesi Camellone, A. Tovt, N.-D. Tran, F. R. Negreiros, M. Vorokhta, T. Skála, I. Matolínová, J. Mysliveček, V. Matolín and S. Fabris, Nat. Commun., 2016, 7, 10801.
32. Y. Lu, S. Zhou, C.-T. Kuo, D. Kunwar, C. Thompson, A. S. Hoffman, A. Boubnov, S. Lin, A. K. Datye, H. Guo and A. M. Karim, ACS Catal., 2021, 11, 8701–8715.
33. D. Kunwar, S. Zhou, A. DeLaRiva, E. J. Peterson, H. Xiong, X. I. Pereira-Hernández, S. C. Purdy, R. ter Veen, H. H. Brongersma, J. T. Miller, H. Hashiguchi, L. Kovarik, S. Lin, H. Guo, Y. Wang and A. K. Datye, ACS Catal., 2019, 9, 3978–3990.
34. Y. Tang, Y.-G. Wang and J. Li, J. Phys. Chem. C, 2017, 121, 11281–11289.
35. Z. Yang, Z. Lu and G. Luo, Phys. Rev. B: Condens. Matter Mater. Phys., 2007, 76, 075421.
36. P. Bera, K. R. Priolkar, A. Gayen, P. R. Sarode, M. S. Hegde, S. Emura, R. Kumashiro, V. Jayaram and G. N. Subbanna, Chem. Mater., 2003, 15, 2049–2060.
37. P. Bera, A. Gayen, M. S. Hegde, N. P. Lalla, L. Spadaro, F. Frusteri and F. Arena, J. Phys. Chem. B, 2003, 107, 6122–6130.
38. J. K. Nørskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J. R. Kitchin, T. Bligaard and H. Jónsson, J. Phys. Chem. B, 2004, 108, 17886–17892.
39. A. Nilsson, L. G. M. Pettersson, B. Hammer, T. Bligaard, C. H. Christensen and J. K. Nørskov, Catal. Lett., 2005, 100, 111–114.
40. B. Hammer and J. K. Nørskov, in Advances in Catalysis, Academic Press, 2000, vol. 45, pp. 71–129.
41. S. Zhou, X. Yang, W. Pei, N. Liu and J. Zhao, Nanoscale, 2018, 10, 10876–10883.
42. Y. Ouyang, C. Ling, Q. Chen, Z. Wang, L. Shi and J. Wang, Chem. Mater., 2016, 28, 4390–4396.
43. M. Qiu, Z. Fang, Y. Li, J. Zhu, X. Huang, K. Ding, W. Chen and Y. Zhang, Appl. Surf. Sci., 2015, 353, 902–912.
44. Y.-Q. Su, J.-X. Liu, I. A. W. Filot, L. Zhang and E. J. M. Hensen, ACS Catal., 2018, 8, 6552–6559.
45. A. Walsh, A. A. Sokol, J. Buckeridge, D. O. Scanlon and C. R. A. Catlow, Nat. Mater., 2018, 17, 958–964.
46. N. Daelman, M. Capdevila-Cortada and N. López, Nat. Mater., 2019, 18, 1215–1221.
47. X. Wang, J. A. van Bokhoven and D. Palagin, Phys. Chem. Chem. Phys., 2017, 19, 30513–30519.
48. X.-P. Wu and X.-Q. Gong, Phys. Rev. Lett., 2016, 116, 086102.
49. P. G. Lustemberg, Y. Pan, B. J. Shaw, D. Grinter, C. Pang, G. Thornton, R. Pérez, M. V. Ganduglia-Pirovano and N. Nilius, Phys. Rev. Lett., 2016, 116, 236101.
50. M. Nolan, S. C. Parker and G. W. Watson, Surf. Sci., 2005, 595, 223–232.
51. H.-Y. Li, H.-F. Wang, X.-Q. Gong, Y.-L. Guo, Y. Guo, G. Lu and P. Hu, Phys. Rev. B: Condens. Matter Mater. Phys., 2009, 79, 193401.
52. W.-J. Zhu, J. Zhang, X.-Q. Gong and G. Lu, Catal. Today, 2011, 165, 19–24.
53. J. K. Nørskov, T. Bligaard, A. Logadottir, J. R. Kitchin, J. G. Chen, S. Pandelov and U. Stimming, J. Electrochem. Soc., 2005, 152, J23.
54. J. Mahmood, F. Li, S. M. Jung, M. S. Okyay, I. Ahmad, S. J. Kim, N. Park, H. Y. Jeong and J. B. Baek, Nat. Nanotechnol., 2017, 12, 441–446.
55. C. G. Morales-Guio, L.-A. Stern and X. Hu, Chem. Soc. Rev., 2014, 43, 6555–6569.
56. H. Häkkinen, M. Moseler, O. Kostko, N. Morgner, M. A. Hoffmann and B. V. Issendorff, Phys. Rev. Lett., 2004, 93, 093401.
57. N. J. O'Connor, A. S. M. Jonayat, M. J. Janik and T. P. Senftle, Nat. Catal., 2018, 1, 531–539.
58. P. Kuang, Y. Wang, B. Zhu, F. Xia, C.-W. Tung, J. Wu, H. M. Chen and J. Yu, Adv. Mater., 2021, 33, 2008599.
59. H. Li, L. Wang, Y. Dai, Z. Pu, Z. Lao, Y. Chen, M. Wang, X. Zheng, J. Zhu, W. Zhang, R. Si, C. Ma and J. Zeng, Nat. Nanotechnol., 2018, 13, 411–417.
60. B. Hinnemann, P. G. Moses, J. Bonde, K. P. Jørgensen, J. H. Nielsen, S. Horch, I. Chorkendorff and J. K. Nørskov, J. Am. Chem. Soc., 2005, 127, 5308–5309.
61. G. Di Liberto, L. A. Cipriano and G. Pacchioni, J. Am. Chem. Soc., 2021, 143, 20431–20441.
62. T. Wu, M. M. Melander and K. Honkala, ACS Catal., 2022, 12, 2505–2512.

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d2ce01246d

‡ These authors contributed equally to this work.

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