Heterostructure Engineering in Metal Sulfides for Electrochemical CO2 Reduction: Advancing Performance and Stability

Abstract

Heterostructure engineering in metal sulfides has emerged as a promising strategy for advancing the performance of electrochemical CO₂ reduction reaction (CO₂RR). By leveraging surface functionalization, interface engineering, doping, and vacancy formation, metal sulfide-based heterostructures offer effective strategies to enhance catalytic performance and durability. This review consolidates recent research findings on the application of metal sulfide-based heterostructures in CO₂RR pathways and electron transfer mechanisms, providing insights into the properties and performance of these heterostructured catalysts. First, the key mechanistic descriptors of CO₂RR are outlined, followed by an examination of the electrocatalytic performances of various metal sulfide-based heterostructures, categorized into Cu sulfides, non-Cu transition metal sulfides (TMSs), and post-TMSs. Finally, future research directions for sustainable CO₂ conversion are discussed.

Keywords: CO2RR; carbon neutral; electrocatalysis; heterostructure; metal sulfide.

Figure 1

a) Schematic diagram illustrating the potential reaction pathways of CO₂RR for the various product formations on a homogeneous catalyst structure. Reproduced with permission.^{[ 41 ]} Copyright 2023, American Chemical Society. b) Proposed mechanism for CH₃CH₂OH formation on the SD‐Cu _x Cd _y catalyst involving interactions at the Cu−Cd alloy/Cu₂S/CdS phase boundaries. Reproduced with permission.^{[ 54 ]} Copyright 2021, Wiley. c) Potential‐dependent electrocatalytic mechanism for CO₂ reduction CuS@CuSe heterostructure selectively producing HCOOH and C₂H₅OH. Reproduced with permission.^{[ 56 ]} Copyright 2024, Royal Society of Chemistry. d) In situ Raman spectra and e) ATR‐FTIR spectra on CeO₂/CuS at different potentials. f) Energy profiles of *CO adsorption and g) energy profiles for initial states (ISs), transition states (TSs), and final states (FSs) of C–C coupling on CuS and CeO₂/CuS heterostructures. Reproduced with permission.^{[ 57 ]} Copyright 2023, Wiley. h) n‐Propanol formation on adjacent CuS_x‐DSV involving initial CO–CO dimerization, followed by a CO–OCCO coupling step. Reproduced with permission.^{[ 58 ]} Copyright 2021, Springer Nature.

Figure 2

a) Schematic representation of the fabrication process of Cu₂O/CuS nanocomposites. b) High‐resolution transmission electron microscopy (HRTEM) image obtained from a typical Cu₂O/CuS particle. c,d) Comparison of the faradaic efficiency and partial current density (for formate production) among Cu gauze, CuS, Cu₂O, and Cu₂O/CuS. Comparison of calculated CO₂RR pathways to produce formic acid from e) OCHO* and f) COOH* intermediates on CuS(110) with vacancy species (V_S). Reproduced with permission.^{[ 59 ]} Copyright 2021, American Chemical Society. g) A free energy diagram of three reaction pathways for H₂, CO, and HCOOH formation on the SnO₂/CuS interface. h) Proposed mechanism for CO₂RR to CO on SnO₂/CuS. i) Volume ratio of CO to H₂ (syngas composition) as a function of applied potential for SnO₂/CuS. j) Potential‐dependent FE of syngas (CO and H₂). Reproduced with permission.^{[ 65 ]} Copyright 2020, Royal Society of Chemistry. k) TEM image of Cu‐Cu₂S heterostructure. l) Energy barrier (ΔE_reaction) for C–C coupling from two *CO to *OCCO at Cu^δ+─Cu⁰, Cu^δ+─Cu^δ+, and Cu⁰─Cu⁰ sites in Cu─Cu₂S, as well as on the pristine Cu surface. m) Calculated free energy for each step in the CO₂ conversion pathway to C₂H₅OH on Cu─Cu₂S heterostructure.^{[ 66 ]} Copyright 2023, American Chemical Society.

Figure 3

a) Illustration of the ZnS/ZnO heterostructure synthesis process. b) SEM image and corresponding EDX elemental mappings of the ZnS/ZnO heterostructure. CO₂RR stability test of c) ZnO and ZnS and d) ZnS/ZnO heterostructure at −0.56 V_RHE in a flow cell. Reproduced with permission.^{[ 77 ]} Copyright 2022, American Chemical Society. e) FESEM image of ZnIn₂S₄ grown on NDCC f) FE of different CO₂RR products using ZnIn₂S₄/NDCC. g) A free energy diagram for the CO₂RR over ZnIn₂S₄/NDCC. h) Charge density difference and net Bader charge transfer of CO adsorbed on Zn sites for ZnIn₂S₄/NDCC. Reproduced with permission.^{[ 82 ]} Copyright 2023, Elsevier. i) In situ DEMS monitoring of H₂ and H₂S during CO₂RR on CdS‐CNTs heterostructure. j) Schematic for forming V_S on the surface of CdS‐CNTs during CO₂RR. k) Long‐term stability of CdS‐CNTs for CO₂RR at −1.2 V_RHE. Reproduced with permission.^{[ 86 ]} Copyright 2019, Elsevier. l) HRTEM image of SD‐Cu _x Cd _y . Reproduced with permission.^{[ 54 ]} Copyright 2021, Wiley.

Figure 4

a) HRTEM image of N‐MoS₂@NCDs, the blue square representing NCD and the red square representing N‐MoS₂. b) Free energy diagrams for CO₂ reduction to CO on MoS₂ and N‐MoS₂ electrodes. c) Schematic illustration of the CO formation mechanism on the N‐MoS₂ monolayer. Reproduced with permission.^{[ 90 ]} Copyright 2019, Elsevier. d) Filtered HRTEM image of the Nb‐doped MoS₂ with the corresponding FFT image in the inset. e) FE_CO and FE_H2 at different applied potentials for Nb‐doped MoS₂. f) Schematic of Nb‐doped MoS₂ structures with varying dopant positions. g) Free energy diagrams of MoS₂, NbS₂, and Nb‐doped MoS₂ edges for the reaction pathway of CO₂ to CO. h) Trends in formation energies of COOH* and CO desorption energies on the metal edge of various systems. Reproduced with permission.^{[ 92 ]} Copyright 2017, American Chemical Society. i,j) Low and high magnification TEM images of Cu/MoS₂. k) FE of different products over different Cu/MoS₂ samples at −1.4 V_SCE in 0.1 m NaHCO₃ aqueous solution. Reproduced with permission.^{[ 94 ]} Copyright 2017, Royal Society of Chemistry.

Figure 5

a) HRTEM image of Ag/Ag₂S heterostructure. b) DFT‐derived free energy profiles of optimized Ag and Ag/Ag₂S models. c) Adsorption configurations and corresponding free energies of Ag/Ag₂S interacting with *COOH, *CO, and *CHO intermediates. Reproduced with permission.^{[ 95 ]} Copyright 2021, Wiley. d) HRTEM image of Ag₂S/CdS heterostructure. e) long‐term stability test of Ag₂S/CdS heterostructure conducted at −0.9 V_RHE. Reproduced with permission.^{[ 96 ]} Copyright 2021, Wiley. f) Schematic illustration of the CO₂RR mechanism at Ag sites in Ag₂S/N, S‐doped rGO heterostructure. Reproduced with permission.^{[ 97 ]} Copyright 2018, Elsevier. g) FE_CH3OH and FE_H2 as a function of applied potential for the FeS₂/NiS heterostructure. Reproduced with permission.^{[ 98 ]} Copyright 2017, Royal Society of Chemistry. h) EDX elemental mapping of Co₃S₄@Co₃O₄ heterostructure. i) Schematic energy diagram illustrating the CO₂ to HCOO⁻ on Co₃S₄@Co₃O₄ heterostructure. Reproduced with permission.^{[ 99 ]} Copyright 2017, Wiley.

Figure 6

a) Schematic representation of the synthesis of 2D In₂S₃‐rGO. b) TEM image of 2D In₂S₃–rGO. c) FE_HCOO− on 2D In₂S₃–rGO, bulk In₂S₃–rGO, and bulk In₂S₃. d) ECSA‐normalized current density of formate. Reproduced with permission.^{[ 104 ]} Copyright 2022, American Chemical Society. e) Schematic representation of the synthetic procedure of Mn‐doped In₂S₃ nanosheets. f) TEM and g) HAADF‐STEM and STEM‐EDX elemental mapping images of Mn‐doped In₂S₃. Optimized adsorption patterns of HCOO* intermediate on the h) In₂S₃ surface and i) Mn‐doped In₂S₃ surface. j) PDOS of the d orbitals of In atoms and p orbitals of O atoms on the In₂S₃ slab. k) PDOS of the d orbitals of In atoms, d orbitals of Mn atoms, and p orbitals of O atoms on the Mn‐doped In₂S₃ slab. l) Calculated reaction energy profiles for CO₂RR to form formate on In₂S₃ and Mn‐doped In₂S₃ slabs. The * represents an adsorption site. Reproduced with permission.^{[ 107 ]} Copyright 2019, American Chemical Society.

Figure 7

a) HAADF‐STEM and corresponding elemental mapping images of an individual Ag‐SnS₂ heterostructure. b) Partial current densities and corresponding syngas proportions at −1.0 V_RHE for Ag‐SnS₂ heterostructure. c) Geometrical current density and FE for formate and CO with time on Ag‐SnS₂ heterostructure at a constant potential of −1.0 V_RHE. d) Nyquist plots and the corresponding equivalent circuit of the different SnS₂‐based catalysts e) Top view of the model showing pristine SnS₂ alongside defective SnS₂. f) The calculated free energy variation (ΔG) for the formate production over pristine SnS₂ and defective SnS₂ slab. Reproduced with permission.^{[ 111 ]} Copyright 2019, Wiley. g) Potential‐dependent FEs of formate, CO, and H₂ over 3 at% Cu–SnS₂. Free‐energy diagrams of CO₂ reduction to h) HCOOH and i) CO on Sn metal, S‐doped Sn and S‐doped Cu/Sn alloy. Reproduced with permission.^{[ 112 ]} Copyright 2021, Wiley. j) Charge density distribution at the defect level of Ni‐doped SnS₂ slab. k) Calculated DOS of SnS₂ and Ni‐doped SnS₂ slabs. Reproduced with permission.^{[ 113 ]} Copyright 2018, Wiley. l) Free‐energy diagram of formate formation over SnS/C and In‐SnS/C. Reproduced with permission.^{[ 114 ]} Copyright 2022, American Chemical Society.

Figure 8

a–e) TEM and corresponding elemental analysis. f) FE for formate formation at different potential values. g) Free‐energy diagram for formate formation on Bi₂S₃–PPy heterostructure and pristine Bi₂S₃. Reproduced with permission.^{[ 117 ]} Copyright 2023, Royal Society of Chemistry. h) Schematic representation of the synthesis process of Bi₂S₃‐Bi₂O₃ heterostructure. i) SEM and j) TEM images of Bi₂S₃‐Bi₂O₃ heterostructure. k) XPS spectra of Bi 4f in Bi₂O₃ and Bi₂S₃‐Bi₂O₃ heterostructure. l) Schematic of the reaction mechanism over Bi₂S₃‐Bi₂O₃ heterostructure for CO₂RR. Reproduced with permission.^{[ 118 ]} Copyright 2022, Wiley.