Heterostructured Electrocatalysts: from Fundamental Microkinetic Model to Electron Configuration and Interfacial Reactive Microenvironment

Abstract

Electrocatalysts can efficiently convert earth-abundant simple molecules into high-value-added products. In this context, heterostructures, which are largely determined by the interface, have emerged as a pivotal architecture for enhancing the activity of electrocatalysts. In this review, the atomistic understanding of heterostructured electrocatalysts is considered, focusing on the reaction kinetic rate and electron configuration, gained from both empirical studies and theoretical models. We start from the fundamentals of the microkinetic model, adsorption energy theory, and electric double layer model. The importance of heterostructures to accelerate electrochemical processes via modulating electron configuration and interfacial reactive microenvironment is highlighted, by considering rectification, space charge region, built-in electric field, synergistic interactions, lattice strain, and geometric effect. We conclude this review by summarizing the challenges and perspectives in the field of heterostructured electrocatalysts, such as the determination of transition state energy, their dynamic evolution, refinement of the theoretical approaches, and the use of machine learning.

Keywords: adsorption energy theory; electronic state; heterostructured electrocatalyst; interfacial reactive microenvironment; microkinetic model.

Figure 1

a) Schematic illustration of the change in the local electronic structure at a hydrogen atom upon its adsorption on transition metal surfaces. b) Upshift of the d band or p band center of atoms with decreasing atomic number in the same period, and the relative binding strength. c) Coordination number – energy relations for atomic oxygen and oxygenates; Reproduced with permission.^{[ 33 ]} Copyright 2015, Springer Nature. d) Schematic illustration of the OER mechanism in alkaline solution; e) Equilibrium potentials of the elementary reactions versus free binding energy of oxygen on metal oxides ΔG(O_ads); Reproduced with permission.^{[ 34 ]} Copyright 2011, Elsevier. f) Linear correlations between the adsorption energies of various adsorbates, arranged by their HOMO energies; Reproduced with permission.^{[ 35 ]} Copyright 2014, American Chemical Society. g) Illustration of the double electric layer under positive bias. h) Schematic diagram of the water network in a non‐aqueous [BMIM][BF₄] ionic liquid. Reproduced with permission.^{[ 36 ]} Copyright 2023, American Chemical Society.

Figure 2

a) Energy diagrams of heterostructures formed by metal and n‐type semiconductor, metal and p‐type semiconductor, and p‐type semiconductor and n‐type semiconductor. b) Contact and sheet resistance for vertical Ti/MoS₂ and lateral Mo₂C/MoS₂ heterostructures. Reproduced with permission.^{[ 75 ]} Copyright 2018, American Chemical Society. Potential profiles at the interface of c) metal and n‐type semiconductor, d) p‐type semiconductor and n‐type semiconductor after applying bias. e) Rectification effects of p‐type FePc on GaS, H‐MoS₂, 2H‐MoSe₂, 2H‐WS_2, and p‐type GaS. Reproduced with permission.^{[ 76 ]} Copyright 2022, Wiley‐VCH. f) n‐n type heterojunction of Cu₃(HITP)₂@h‐BN and its performance in the NH₃ reduction compared with bare Cu₃(HITP)₂ and h‐BN. Reproduced with permission.^{[ 77 ]} Copyright 2023, Wiley‐VCH.

Figure 3

a) Differential charge density of trigonal MoS₂, van der Waals heterostructure of MoS₂ and graphene, and the effective length relative to ligand effect and space charge region. b) Adsorption energies of H₂ and O₂ versus d band center on different Pt‐M‐Pt sandwich structures, and the effect of sandwiching a guest metal layer as the first subsurface layer under Pt surface. Reproduced with permission.^{[ 89 ]} Copyright 2004, American Institute of Physics. c) Mechanism of the electrocatalytic urea synthesis employing the Bi‐BiVO₄ Mott‐Schottky heterostructure.^{[ 90 ]} Copyright 2021, Wiley‐VCH. d) Schematic illustration of the hydrogen spillover for RuS_x/NbS₂ electrocatalyst owing to strong BIEF.^{[ 91 ]} Reproduced with permission. Copyright 2024, Wiley‐VCH. e) Illustration of dual deprotonation enhanced OER for the MoS₂/NiPS₃ system based on internal polarization field. Reproduced with permission.^{[ 92 ]} Copyright 2022, Wiley‐VCH. f) Distribution of anions along the z‐axis electrode distance for CuCl_BEF and CuCl in KNO₃ solution based on molecular dynamics simulation. Reproduced with permission.^{[ 93 ]} Copyright 2021, Wiley‐VCH.

Figure 4

Strategies for breaking the limitation of scaling relation for OER process via synergistic interaction of heterostructured catalysts: a) Schematic illustration of the dynamic 3D adsorption of oxygenates within OER pathway at the interface of NiO/NiFe LDH. Reproduced with permission.^{[ 114 ]} Copyright 2019, Wiley‐VCH. b) Adsorbate evolution mechanism following the O─O coupling mechanism based on the suitable Co–Co distance at the intersection of Zr‐doped Co₉S₈/Co₃O₄ heterostructure. Reproduced with permission.^{[ 116 ]} Copyright 2023, Wiley‐VCH. c) Schematic of a dual‐metal‐site lattice oxygen mechanism for oxygen reduction reaction; d) Schematics of the bifunctional AEM and LOM coupling pathways for γ‐FeOOH‐NiOOH. Reproduced with permission.^{[ 117 ]} Copyright 2020, Wiley‐VCH.

Figure 5

a) Lattice strain is induced by the lattice mismatch of the heterostructure, as well as the curvature and thickness of the constituting components. Reproduced with permission.^{[ 123 ]} Copyright 2019, American Association for the Advancement of Science. b) Shift of the d band center of the early and late transition metals under tensile and compressive strain. c) Confocal Raman measurements provide a mapping of the strain distribution on the 1L‐MoS₂/ZnO heterostructure. Reproduced with permission.^{[ 124 ]} Copyright 2019, American Chemical Society. d) Aberration‐corrected HRTEM image of de‐alloyed Pt‐Fe nanoparticle and the mappings of the lattice strain relative to the bulk Pt lattice. Reproduced with permission.^{[ 125 ]} Copyright 2012, American Chemical Society. e) HAADF‐STEM projection image of an Au nanodecahedron, 3D visualization of its reconstructed nanoparticle, and 3D strain analysis of the slice through $\epsilon$ _xx and $\epsilon$ _zz volume. Reproduced with permission.^{[ 126 ]} Copyright 2015, American Chemical Society.