Controllable synthesis of trisoctahedral Au@Pd core-shell nanoparticles with tunable Pd shell thickness for enhanced ethanol electrooxidation

Abstract

Efficient palladium-based electrocatalysts are crucial for ethanol oxidation in fuel cells. Here, a series of TOH-Au@Pd_x core-shell nanoparticles with precisely controlled Pd shell thicknesses were successfully synthesized using well-defined trisoctahedral Au seeds (~45 nm). The prepared nanoparticles are uniform, and the Pd shell thickness progressively grows from 0.54 to 1.39 nm. XPS analysis reveals significant electronic interactions between the Au core and Pd shell, with the binding energy shifts of the Au 4f and Pd 3d core levels systematically decreasing as the shell thickness increases. All TOH-Au@Pd_x catalysts surpass commercial Pd/C, with TOH-Au@Pd₄₀ showing the highest activity: an electrochemical surface area of 128.8 m²/g, a mass activity of 13.6 A/mg, and a specific activity of 10.6 mA/cm², corresponding to 5.0-, 68.0-, and 13.3-fold improvements over Pd/C. It also exhibits the smallest Tafel slope and charge transfer resistance, indicating the most favorable reaction kinetics and interfacial charge transfer capability. Moreover, it retains 27.5% of its initial current after 7200 s, far exceeding Pd/C (1.4%). The enhanced performance arises from the synergy between the high-index facets (rich in steps, edges, and kinks) of the trisoctahedral morphology and the optimal electronic interaction between the Au core and the Pd shell. This study not only provides an effective strategy for the controlled synthesis of high-performance core-shell catalysts but also offers fundamental insights into how geometric and electronic effects jointly govern electrocatalytic activity and stability.

Keywords

Au@Pd / Core-shell nanoparticles / Pd shell thickness / High index facet / Electrocatalysis

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement

Li Kong: Writing – review & editing, Writing – original draft, Supervision, Funding acquisition, Data curation.

Acknowledgements

This work was financially supported by the Instrument Improvement Funds of Shandong University (No. ts20250301) and the Laboratory Construction and Management Research Project of Shandong University (No. sy20213206).

References

[1] D. Saritha, N.M. Reddy, G.V. Ramesh, Pt- and Pd-based intermetallic anode catalysts for direct ethanol fuel cell (DEFC): An overview, Mater. Today: Proc. 64 (2022) 357-362, doi: 10.1016/j.matpr.2022.04.705.

[2] A.L. De Bortoli, A two-phase stable model for non-isothermal direct ethanol proton exchange membrane fuel cells, J. Power Sources 659 (2025) 238394-238401, doi: 10.1016/j.jpowsour.2025.238394.

[3] M. Roschger, S. Wolf, A. Billiani, S. Gorgieva, B. Genorio, V. Hacker, Electrode configurations study for alkaline direct ethanol fuel cells, J. Electrochem. Sci. Eng. 13 (2023) 783-793, doi: 10.5599/jese.1623.

[4] J. Kaur, R.K. Gupta, A. Kumar, Electrocatalytic ethanol oxidation reaction: Recent progress, challenges, and future prospects, Discover Nano 19 (2024) 137-155, doi: 10.1186/s11671-024-04067-9.

[5] S.G.M. Carvalho, F.N. Tabuti, E.I. Santiago, R. Abe, R.M. Guimaraes, Y. Miura, Y. Fukuyama, F.C. Fonseca, Advancing direct ethanol metal supported fuel cells with catalytic layer, Mater. Sci. Eng. B 318 (2025) 118259-118302, doi: 10.1016/j.mseb.2025.118259.

[6] J.G. Ruiz-Montoya, L.M.S. Nunes, A.M. Baena-Moncada, G. Tremiliosi-Filho, J.C. Morales-Gomero, Effect of palladium on gold in core-shell catalyst for electrooxidation of ethanol in alkaline medium, Int. J. Hydrogen Energy 46 (2021) 23670-23681, doi: 10.1016/j.ijhydene.2021.04.159.

[7] Z.F. Wu, R.B. Duan, J.L. Cui, C.P. Ye, S.C. Zhang, S.H. Yan, An overview of the Pd based electrocatalysts utilized in direct alcohol fuel cells, Electrocatalysis 16 (2025) 197-223, doi: 10.1007/s12678-024-00920-8.

[8] Y. Zheng, X.J. Wan, X. Cheng, K. Cheng, Z.F. Dai, Z.H. Liu, Advanced catalytic materials for ethanol oxidation in direct ethanol fuel cells, Catalysts 10 (2020) 166-188, doi: 10.3390/catal10020166.

[9] H. Wu, Z.C. Mao, B.Q. Liu, D.Y. Chen, M.Q. Shi, B.S. Lv, Y.H. Xu, L.B. Wang, Ultra-low-loading Pd nanocrystals modified Ni foam electrode for efficient electrochemical hydrodechlorination, Appl. Catal. B 337 (2023) 122978-122988, doi: 10.1016/j.apcatb.2023.122978.

[10] R.M. Zhu, Y.X. Jiang, Y.Z. Song, L.M. Liu, Y.H. Xu, H. Pang, Recent progress in core-shell structural materials towards high performance batteries, Chem. Eng. J. 490 (2024) 151681-151717, doi: 10.1016/j.cej.2024.151681.

[11] W.J. Lu, X.T. Guo, Y.Q. Luo, Q. Li, R.M. Zhu, H. Pang, Core-shell materials for advanced batteries, Chem. Eng. J. 355 (2019) 208-237, doi: 10.1016/j.cej.2018.08.132.

[12] D.P. Chen, Z.Y. Shao, L.R. Yang, Y. Chen, Y.H. Wei, Z.H. Hu, L.Y. Cai, Y.F. Zhang, X. He, A special carbon core@Au/Pd shell structure catalyst: Au-Pd layer on the mesoporous carbon microsphere for enhanced activity of ethanol electro-oxidation, Int. J. Hydrogen Energy 87 (2024) 107-116, doi: 10.1016/j.ijhydene.2024.08.495.

[13] Y.Y. Liang, Q. Wu, F. Liang, Analysis of catalytic activity of Au@Pd core-shell nanodendrites for highly efficient ethanol electrooxidation, Chin. J. Anal. Chem. 49 (2021) E21087-E21095, doi: 10.1016/s1872-2040(21)60103-2.

[14] T.L. Guo, S.T. Bao, J. Guo, W. Chen, L.L. Wen, Bimetallic Au-Pd NPs embedded in MOF ultrathin nanosheets with tuned surface electronic properties for high-performance benzyl alcohol oxidation, Chem. Res. Chin. Univ. 38 (2022) 1344-1348, doi: 10.1007/s40242-022-2210-y.

[15] G.G. Zhang, Y.Y. Ma, X.W. Fu, W.J. Zhao, F. Liu, M.C. Liu, Y.Q. Zheng, Enriching the branching of Au@PdAu core-shell nanocrystals using a syringe pump: Kinetics control meets lattice mismatch, CrystEngComm 23 (2021) 2582-2589, doi: 10.1039/d1ce00107h.

[16] J.F. Hao, B. Liu, M. Takahashi, S. Maenosono, J.H. Yang, Large Au@Pd/PdO_x core-porous shell nanoparticles as efficient ethanol oxidation electrocatalysts , Catal. Sci. Technol. 13 (2023) 4141-4147, doi: 10.1039/d3cy00637a.

[17] P. Gnanaprakasam, A. Gowrisankar, S. Senthilkumar, A. Murugadoss, T. Selvaraju, R.V. Mangalaraja, One pot in situ synthesis of nano Au-Pd core-shells embedded on reduced graphene oxide for the oxygen reduction reaction, Mater. Sci. Eng. B 264 (2021) 114924-114934, doi: 10.1016/j.mseb.2020.114924.

[18] H. Liu, H. Wang, H.C. Ma, B. Liu, J.H. Yang, Au core-porous Pd shell loaded Au nanoparticles superstructures as efficient electrocatalysts for ethanol oxidation reaction, Mater. Res. Bull. 188 (2025) 113406-113413, doi: 10.1016/j.materresbull.2025.113406.

[19] Y. Dai, Z. Xie, Y. Zhang, X. Du, Z. Li, J. Xie, Z. Sun, J. Zhou, Mapping surface and subsurface atomic structures of Au@Pd core-shell nanoparticles in three dimensions, ACS Nano 19 (2025) 9006-9016, doi: 10.1021/acsnano.4c17462.

[20] H.F. Huang, A. Yamamoto, R. Sugiyama, A. Tanaka, H. Kominami, H. Yoshida, Core-shell Au@Pd cocatalyst for efficient and selective photocatalytic synthesis of deuterated alkanes from lauric acid and heavy water, Catal. Today 461 (2026) 115520-115528, doi: 10.1016/j.cattod.2025.115520.

[21] K. Ramesh, G.B. Reddy, C. Raghavender, V. Gopi, M. Noorjahan, Biogenic synthesis of gold-palladium bimetallic nanoparticles using Passiflora edulis fruit peel extract for catalytic reduction of rhodamine B and methyl orange dyes, React. Kinet. Mech. Catal. 138 (2025) 4259-4272, doi: 10.1007/s11144-025-02945-6.

[22] P. Singh, P.K. Gangadharan Sonika, Z. Khan, S. Kurungot, A. Jaiswal, Cubic palladium nanorattles with solid octahedron gold core for catalysis and alkaline membrane fuel cell applications, Chemcatchem 11 (2019) 4383-4392, doi: 10.1002/cctc.201900741.

[23] C. Fernández-Navarro, S. Mejía-Rosales, Stability of Au-Pd core-shell nanoparticles, J. Phys. Chem. C 121 (2017) 21658-21664, doi: 10.1021/acs.jpcc.7b04564.

[24] Z.H. Ye, B. Shen, D.H. Kang, J. Huang, Z. Wang, C.B. Wahl, D. Shin, L.L. Huang, J.H. Shen, C.M. Wolverton, C.A. Mirkin, Using surface composition and energy to control the formation of either tetrahexahedral or hexoctahedral high-index facet nanostructures, J. Am. Chem. Soc. 146 (2024) 13519-13526, doi: 10.1021/jacs.4c03088.

[25] N. Goubet, J.H. Yang, P.A. Albouy, M.P. Pileni, Spontaneous formation of high-index planes in gold single domain nanocrystal superlattices, Nano Lett. 14 (2014) 6632-6638, doi: 10.1021/nl503289a.

[26] B. Shen, L.L. Huang, J.H. Shen, K. He, C.Y. Zheng, V.P. Dravid, C. Wolverton, C.A. Mirkin, Crystal structure engineering in multimetallic high-index facet nanocatalysts, Proc. Natl. Acad. Sci. U.S.A. 118 (2021) e2105722118-e2105722124, doi: 10.1073/pnas.2105722118.

[27] J. Carnis, L. Gao, S. Fernández, G. Chahine, T.U. Schulli, S. Labat, E.J.M. Hensen, O. Thomas, J.P. Hofmann, M.I. Richard, Facet-dependent strain determination in electrochemically synthetized platinum model catalytic nanoparticles, Small 17 (2021) 2007702-2007712, doi: 10.1002/smll.202007702.

[28] K. Huang, R.M. Crooks, Enhanced electrocatalytic activity of Cu-modified, high-index single Pt NPs for formic acid oxidation, Chem. Sci. 13 (2022) 12479-12490, doi: 10.1039/d2sc03433f.

[29] L. Kong, M. Hao, L. Li, Synthesis of small-sized trisoctahedral gold nanoparticles with high catalytic activity for methanol electrooxidation, Chem. Res. Chin. Univ. 41 (2025) 903-909, doi: 10.1007/s40242-025-5003-2.

[30] Y. Song, M. Zhang, H. Fang, H. Xia, Shape transformation of gold nanoparticles in aqueous CTAB/CTAC solution to generate high-index facets for electrocatalysis and SERS activity, ChemPhysMater 2 (2023) 97-113, doi: 10.1016/j.chphma.2022.04.006.

[31] Z.W. Quan, Y.X. Wang, J.Y. Fang, High-index faceted noble metal nanocrystals, Acc. Chem. Res. 46 (2013) 191-202, doi: 10.1021/ar200293n.

[32] Y.H. Song, T.T. Miao, P.N. Zhang, C.X. Bi, H.B. Xia, D.Y. Wang, X.T. Tao, {331}-Faceted trisoctahedral gold nanocrystals: Synthesis, superior electrocatalytic performance and highly efficient SERS activity, Nanoscale 7 (2015) 8405-8415, doi: 10.1039/c5nr01049g.

[33] F. Xue, X. Guo, B. Min, Y. Si, H. Huang, J. Shi, M. Liu, Unconventional high-index facet of iridium boosts oxygen evolution reaction: How the facet matters, ACS Catal. 11 (2021) 8239-8246, doi: 10.1021/acscatal.1c01867.

[34] Z. Li, S.F. Ji, Y.W. Liu, X. Cao, S.B. Tian, Y.J. Chen, Z.G. Niu, Y.D. Li, Well-defined materials for heterogeneous catalysis: From nanoparticles to isolated single-atom sites, Chem. Rev. 120 (2020) 623-682, doi: 10.1021/acs.chemrev.9b00311.

[35] Y.H. Song, C.S. Xiang, C.X. Bi, C.S. Wu, H.P. He, W. Du, L.H. Huang, H. Tian, H.B. Xia, PH-dependent growth of atomic Pd layers on trisoctahedral gold nanoparticles to realize enhanced performance in electrocatalysis and chemical catalysis, Nanoscale 10 (2018) 22302-22311, doi: 10.1039/c8nr07224h.

[36] J.T.L. Gamler, A. Leonardi, X.H. Sang, K.M. Koczkur, R.R. Unocic, M. Engel, S.E. Skrabalak, Effect of lattice mismatch and shell thickness on strain in core@shell nanocrystals, Nanoscale Adv. 2 (2020) 1105-1114, doi: 10.1039/d0na00061b.

[37] K.N. da Silva, S. Shetty, S. Sullivan-Allsop, R.S. Cai, S.Q. Wang, J. Quiroz, M. Chundak, H.L.S. dos Santos, I. Abdelsalam, F.E. Oropeza, V.A.D. O’Shea, N. Heikkinen, E. Sitta, T.V. Alves, M. Ritala, W.Y. Huo, T.J.A. Slater, S.J. Haigh, P.H.C. Camargo, Au@AuPd core-alloyed shell nanoparticles for enhanced electrocatalytic activity and selectivity under visible light excitation, ACS Nano 18 (2024) 24391-24403, doi: 10.1021/acsnano.4c07076.

[38] S.D. Ji, Q. Wang, J.P. Huang, R.Y. Guo, Y.N. Li, Y.Z. Zheng, R. Li, Y.H. Zhao, C. Wu, M.S. Jin, Electrochemical CO₂ reduction via strain-engineered AuPd alloy catalysts , Chem. Eng. J. 520 (2025) 166114 16122, doi: 10.1016/j.cej.2025.166114.

[39] S.T. Tanuja, T. Singha, B. Satpati, Tuning the d-band center via strain and ligand effects in core-shell pentatwinned Au@Pd nanoparticles for enhanced ethanol oxidation reaction, Adv. Funct. Mater. 36 (2026) e14936-e14947, doi: 10.1002/adfm.202514936.

[40] A.C. Foucher, H.T. Ngan, T. Shirman, A. Filie, K. Duanmu, M. Aizenberg, R.J. Madix, C.M. Friend, J. Aizenberg, P. Sautet, E.A. Stach, Influence of Pd concentration in Au-Pd nanoparticles for the hydrogenation of alkynes, ACS Appl. Nano Mater. 6 (2023) 22927-22938, doi: 10.1021/acsanm.3c04278.

[41] Q.S. Wu, G.G. Zhang, Y.Y. Wang, Y.Q. Jiao, Y.Y. Ma, Y.Q. Zheng, Seeded growth of gold-based nanoscale homojunctions via controlled etching regrowth and their applications for methanol oxidation reaction, Crystengcomm 25 (2023) 660-670, doi: 10.1039/d2ce01573k.

[42] G.G. Zhang, Y.Y. Wang, Y.Y. Ma, Y.Q. Zheng, H.F. Zhang, M.Y. Tang, Y.Q. Dai, Ultrathin samarium-doped palladium nanocrystals with exotic shapes for efficient electrocatalytic ethanol oxidation, Catal. Today 409 (2023) 63-70, doi: 10.1016/j.cattod.2022.03.024.

[43] X.J. Wu, Y.Y. Sun, Y.L. Zeng, X.Y. Li, Mechanistic insights into oxazolone synthesis by bimetallic Au-Pd-catalyzed catalysis and catalyst design: DFT investigations, J. Org. Chem. 88 (2023) 10693-10700, doi: 10.1021/acs.joc.3c00751.

[44] C.S. Wu, H. Li, H.P. He, Y.H. Song, C.X. Bi, W. Du, H.B. Xia, Compressive strain in core-shell Au-Pd nanoparticles introduced by lateral confinement of deformation twinnings to enhance the oxidation reduction reaction performance, ACS Appl. Mater. Interfaces 11 (2019) 46902-46911, doi: 10.1021/acsami.9b16994.

[45] M. Miyazaki, S. Furukawa, T. Komatsu, Correlation between activation energy and the electronic state of Pd-based bimetallic catalysts for H₂-D₂ equilibration obtained by XPS and DFT calculations , Bull. Chem. Soc. Jpn. 93 (2020) 1020-1025, doi: 10.1246/bcsj.20200085.

[46] J.R. Kitchin, J.K. Norskov, M.A. Barteau, J.G. Chen, Modification of the surface electronic and chemical properties of Pt(111) by subsurface 3d transition metals, J. Chem. Phys. 120 (2004) 10240-10246, doi: 10.1063/1.1737365.

[47] S.K. Das, B. Mohanty, S.C. Sahu, T.J. Sruthi, B. Chakraborty, S. Basu, B.K. Jena, The experimental and theoretical insights on the interaction of AuPd bimetallic nanoentities on graphene: A study on electrocatalytic activity towards oxygen reduction reaction, Electrochim. Acta 356 (2020) 136820-136828, doi: 10.1016/j.electacta.2020.136820.

[48] Z.H. Jin, J.M. Ji, Q.G. He, X.K. Yang, Y.J. Zhang, M.L. Xu, The enhanced electrocatalytic performance of Au@Pd nanoparticles self-assembled on fluorine-modified multi-walled carbon nanotubes for methanol oxidation, Catal. Lett. 148 (2018) 3281-3291, doi: 10.1007/s10562-018-2511-4.

[49] M.M. Zhang, X. Zhang, M. Lv, X.R. Yue, Z.K. Zheng, H.B. Xia, Ethanol oxidation via 12-electron pathway on spiky Au@AuPd nanoparticles assisted by near-infrared light, Small 19 (2023) 2205781, doi: 10.1002/smll.202205781.

[50] C. Wu, H. Li, H. He, Y. Song, C. Bi, W. Du, H. Xia, Compressive strain in core-shell Au-Pd nanoparticles introduced by lateral confinement of deformation twinnings to enhance the oxidation reduction reaction performance, ACS Appl. Mater. Interfaces 11 (2019) 46902-46911, doi: 10.1021/acsami.9b16994.

[51] B. Hammer, J.K. Norskov, Why gold is the noblest of all the metals, Nature 376 (1995) 238-240, doi: 10.1038/376238a0.

[52] Z.L. Fan, Z.B. Lu, S.H. Zhan, T. Zhang, Sabatier phenomenon in chemoselective gas-sensing reactions induced by Ag cluster coordination, J. Colloid Interface Sci. 674 (2024) 993-1003, doi: 10.1016/j.jcis.2024.06.245.

[53] Y.H. Ma, S.C. Li, X.Q. Yang, Y.W. Li, R.Y. Bian, A. Hameed, X. Chen, X.W. Li, S.J. Liu, K. Wang, P. Chen, P. Li, Entropy-mediated ultrafine PdSnPtAgBi nanoparticles as a high-performance electrocatalyst with enhanced CO tolerance for alcohol oxidation, J. Colloid Interface Sci. 705 (2026) 139515-139524, doi: 10.1016/j.jcis.2025.139515.

[54] S.Y. Xu, L.P. Zhang, Y.Y. Zhang, Y.K. Peng, Z.X. Zang, Y.F. Cao, T.F. Li, L.F. Zhang, C.L. Yan, T. Qian, Alleviating O-intermediates adsorption strength over PdRhCu ternary metallene via ligand effect for enhanced oxygen reduction in practical PEMFCs, J. Phys. Chem. Lett. 16 (2025) 1899-1908, doi: 10.1021/acs.jpclett.4c03536.

[55] X. Zhou, Y. Ma, Y. Ge, S. Zhu, Y. Cui, B. Chen, L. Liao, Q. Yun, Z. He, H. Long, L. Li, B. Huang, Q. Luo, L. Zhai, X. Wang, L. Bai, G. Wang, Z. Guan, Y. Chen, C.S. Lee, J. Wang, C. Ling, M. Shao, Z. Fan, H. Zhang, Preparation of Au@Pd core-shell nanorods with fcc-2H-fcc heterophase for highly efficient electrocatalytic alcohol oxidation, J. Am. Chem. Soc. 144 (2022) 547-555, doi: 10.1021/jacs.1c11313.

[56] N. Tian, Z.Y. Zhou, S.G. Sun, Y. Ding, Z.L. Wang, Synthesis of tetrahexahedral platinum nanocrystals with high-index facets and high electro-oxidation activity, Science 316 (2007) 732-735, doi: 10.1126/science.1140484.

[57] M. Mamatkulov, V.P. Zhdanov, Ostwald ripening of supported metal nanoparticles: Role of dimers and other general trends, Chem. Eng. Sci. 308 (2025), doi: 10.1016/j.ces.2025.121373.

[58] W.P. Xiao, M.A.L. Cordeiro, M.X. Gong, L.L. Han, J. Wang, C. Bian, J. Zhu, H.L. Xin, D.L. Wang, Optimizing the ORR activity of Pd based nanocatalysts by tuning their strain and particle size, J. Mater. Chem. A 5 (2017) 9867-9872, doi: 10.1039/c7ta02479g.

[59] Y. Ning, J.P. Tang, S.Q. Wang, S. Chen, C. Chen, X.F. Wu, H.Q. Fan, Y.Y. Ma, X.Z. Ma, H.Q. Xie, D.H. Lin, S.G. Sun, Enhanced performance of phosphorus-doped graphene-supported Pd electrocatalysts for ethanol oxidation, Int. J. Hydrogen Energy 126 (2025) 326-335, doi: 10.1016/j.ijhydene.2025.04.138.

[60] F.Y. Ding, K. Xiao, P.L. Li, J.F. Song, Y. Shi, G. Jiang, L.S. Zhou, Theoretical insights into electronic structures and durability of single-atom Pd/TiN catalysts, Int. J. Hydrogen Energy 48 (2023) 8954-8964, doi: 10.1016/j.ijhydene.2022.12.088.

[61] N. Goswami, K.T. Chen, X.J. Wang, J.S. Spendelow, R.L. Borup, P.P. Mukherjee, Mechanistic understanding of thermodynamic metastability of core-shell catalysts in the polymer electrolyte fuel cell catalyst layer durability, Chem. Eng. J. 484 (2024) 149672-149678, doi: 10.1016/j.cej.2024.149672.