催化学报 ›› 2023, Vol. 52: 14-31.DOI: 10.1016/S1872-2067(23)64511-5
收稿日期:
2023-07-11
接受日期:
2023-08-28
出版日期:
2023-09-18
发布日期:
2023-09-25
通讯作者:
*电子信箱: guj6@sustech.edu.cn (顾均).
基金资助:
Received:
2023-07-11
Accepted:
2023-08-28
Online:
2023-09-18
Published:
2023-09-25
Contact:
*E-mail: About author:
Jun Gu (Southern University of Science and Technology) received his B.S. degree in 2011 and Ph.D. degree in 2016 from Peking University. His doctoral thesis is about the synthesis and the catalytic applications of rare earth- and noble metal-based nanomaterials. At the end of 2016, he joined Lab of Inorganic Synthesis and Catalysis at École Polytechnique Fédérale de Lausanne (Switzerland) as a postdoctor. His research was focused on non-noble metal-based catalysts for CO2 electroreduction. At the beginning of 2021, he joined Department of Chemistry of Southern University of Science and Technology. Now he is an associate professor and the principal investigator of the group of electrocatalysis. His research interests mainly focus on catalyst designing and mechanism study for electrocatalytic activation of small molecules.
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摘要:
二氧化碳电还原技术可以将可再生电能与温室气体二氧化碳转化为高价值燃料和化学品. 选择性、能量转化效率、碳利用效率和可持续性是评价二氧化碳电还原技术是否具有工业应用前景的主要指标. 在碱性或中性电解液中进行二氧化碳电还原, 由于部分二氧化碳在阴极转化为碳酸盐, 导致碳利用效率降低. 碱性电解液和中性电解液还分别存在电解液再生过程耗能巨大和溶液电阻较高等问题. 这些因素导致使用碱性和中性电解液的二氧化碳电还原技术能量转化效率低下. 最近, 酸性条件下二氧化碳电还原技术有望提高碳利用效率和能量利用效率, 成为研究热点. 然而, 在酸性条件下提升二氧化碳还原选择性具有挑战. 前期研究已发展了多种策略以抑制酸性条件下的氢离子还原反应并促进二氧化碳还原反应, 但研究者对于酸性条件下的阳离子效应以及局域pH效应等基础科学问题认识尚不一致. 此外, 气体扩散电极内的碳酸氢盐盐析问题仍限制着酸性条件下二氧化碳还原电解系统的可持续性. 因此, 亟需对促进酸性条件下二氧化碳电还原的不同策略及可能机制进行总结, 并探讨进一步提升电解系统可持续性的潜在路径.
本文首先概述了酸性条件下二氧化碳电还原技术的提出及发展历程, 对比了碱性、中性和酸性电解液中进行二氧化碳电还原的优势和劣势. 着重从传质过程和电极反应两方面对已报道的酸性条件下二氧化碳电还原技术进行归纳总结. 探讨了传质过程中二氧化碳还原半反应引起的局域高pH对氢离子还原反应的抑制作用, 碱金属离子对于氢离子电迁移过程的抑制作用, 以及抑制氢离子扩散过程的基本策略. 对于电极反应, 探讨了催化位点本征活性的调控、碱金属离子调控界面电场对于二氧化碳还原动力学的影响, 以及碱金属离子与反应中间体的直接配位作用. 然后, 概述了近期无金属离子酸性电解液中二氧化碳电还原技术的进展, 该技术旨在提升二氧化碳电还原性能的可持续性. 介绍了酸性条件二氧化碳电还原过程的理论模拟方法, 提出了将原子尺度的密度泛函理论模拟与电极微反应动力学模拟及介观、宏观尺度传质过程的有限元分析相结合的研究思路. 最后, 总结了促进酸性条件二氧化碳电还原的不同策略, 展望了电极微环境检测、模拟和调控的可能途径, 以及进一步提升酸性条件二氧化碳电还原稳定性及降低成本的策略.
邹心仪, 顾均. 酸性条件下二氧化碳高效电还原策略[J]. 催化学报, 2023, 52: 14-31.
Xinyi Zou, Jun Gu. Strategies for efficient CO2 electroreduction in acidic conditions[J]. Chinese Journal of Catalysis, 2023, 52: 14-31.
Fig. 2. Schematic illustration of flow cell with KOH solution as electrolyte for CO2RR. Green and brown arrows indicate the flows of CO2 converted to reduction products and consumed by OH-, respectively. Advantages and disadvantages of CO2RR with alkaline electrolyte are shown.
Fig. 3. Schematic illustration of flow cell with near neutral KHCO3 solution as electrolyte for CO2RR. Green and brown arrows indicate the flows of CO2 converted to reduction products and consumed by OH-, respectively. Advantages and disadvantages of CO2RR with alkaline electrolyte are shown.
Fig. 4. Schematic illustration of flow cell with acidic electrolyte for CO2RR. CO2 molecules consumed by OH- are regenerated near the cathode and finally converted to reduction products.
Catalyst | Electrolyte | Type of cell | Major product | FE* (%) | SPCE* (%) | Ref. |
---|---|---|---|---|---|---|
Ag | 0.2 mol L‒1 H2SO4 + 0.01 mol L‒1 Cs2SO4 (anolyte) | MEA with PEM | CO | 80 | 90 | [ |
Au/C | 0.1 mol L‒1 H2SO4 + 0.4 mol L‒1 K2SO4 | flow cell | CO | 91 | — | [ |
Ni3N/CNTs | NaCl + HCl (pH 2.5) | H-cell | CO | 50 | — | [ |
Au | H2SO4 + Cs2SO4 (pH 2) | flow cell | CO | 80 | — | [ |
Ni-N-C | 0.5 mol L‒1 H2SO4 + 0.5 mol L‒1 K2SO4 (anolyte) | MEA with PEM | CO | 95 | 85 | [ |
Ni@N-doped-C | 1 mmol L‒1 H2SO4 + 0.25 mol L‒1 Na2SO4 | flow cell | CO | 84 | — | [ |
Fe/porous C | 0.2 mmol L‒1 H2SO4 + 0.1 mol L‒1 KCl | flow cell | CO | 90 | — | [ |
Ni-N-C | H2SO4 + Cs2SO4 (pH 2) | flow cell | CO | 100 | 76 | [ |
NiPc-OMe/CNTs | 0.05 mol L‒1 H2SO4 + 0.45 mol L‒1 K2SO4 | flow cell | CO | 98 | — | [ |
Ni-N-C | H3PO4 + KH2PO4 + KCl (pH 2) | flow cell | CO | 99 | — | [ |
Bi nanosheets | 0.05 mol L‒1 H2SO4 + 1 mol L‒1 KCl | flow cell | HCOOH | 92 | 27 | [ |
S doped Sn | H2SO4 + K2SO4 (pH 3) | flow cell | HCOOH | 92 | 35 | [ |
SnO2/C | 0.1 mol L‒1 H2SO4 + 0.4 mol L‒1 K2SO4 | flow cell | HCOOH | 88 | — | [ |
SnBi/SiC /PTFE | 0.05 mol L‒1 H2SO4 + 3 mol L‒1 KCl | flow cell | HCOOH | 90 | 65 | [ |
Cs3Bi2Br9/C | 0.05 mol L‒1 H2SO4 + 0.5 mol L‒1 CsBr | flow cell | HCOOH | 92 | 47 | [ |
Bi porous electrode | H2SO4 + Na2SO4 (pH 2.7) | flow cell | HCOOH | 89 | — | [ |
Cu | 1 mol L‒1 H3PO4 + 3 mol L‒1 KCl | flow cell | C2+ | 48 | 77 (50 for C2+) | [ |
Cu/C | 0.1 mol L‒1 H2SO4 + 0.4 mol L‒1 K2SO4 | flow cell | C2+ | 50 | — | [ |
Cu | 0.05 mol L‒1 H2SO4 + 2.5 mol L‒1 KCl | flow cell | C2+ | 90 | 70 for C2+ | [ |
COF:PFSA/Cu | 1 mol L‒1 H3PO4 + 3 mol L‒1 KCl | flow cell | C2+ | 75 | 45 for C2+ | [ |
Cu porous nanosheets | 0.05 mol L‒1 H2SO4 + 3 mol L‒1 KCl | flow cell | C2+ | 84 | 54 for C2+ | [ |
Pd-Cu | H2SO4 + K2SO4 (pH 2) | flow cell | C2+ | 89 | 60 for C2+ | [ |
Modified Cu | H3PO4 + KH2PO4 (pH 2) | flow cell | C2+ | 70 | — | [ |
Ag | 0.1 mol L‒1 H2SO4 | flow cell | CO | 95 | — | [ |
In | 0.1 mol L‒1 H2SO4 | flow cell | HCOOH | 76 | — | [ |
Cu | 0.2 mol L‒1 H2SO4 | flow cell | C2+ | 80 | 90 | [ |
Table 1 Summary of reported CO2RR performances in acidic condition.
Catalyst | Electrolyte | Type of cell | Major product | FE* (%) | SPCE* (%) | Ref. |
---|---|---|---|---|---|---|
Ag | 0.2 mol L‒1 H2SO4 + 0.01 mol L‒1 Cs2SO4 (anolyte) | MEA with PEM | CO | 80 | 90 | [ |
Au/C | 0.1 mol L‒1 H2SO4 + 0.4 mol L‒1 K2SO4 | flow cell | CO | 91 | — | [ |
Ni3N/CNTs | NaCl + HCl (pH 2.5) | H-cell | CO | 50 | — | [ |
Au | H2SO4 + Cs2SO4 (pH 2) | flow cell | CO | 80 | — | [ |
Ni-N-C | 0.5 mol L‒1 H2SO4 + 0.5 mol L‒1 K2SO4 (anolyte) | MEA with PEM | CO | 95 | 85 | [ |
Ni@N-doped-C | 1 mmol L‒1 H2SO4 + 0.25 mol L‒1 Na2SO4 | flow cell | CO | 84 | — | [ |
Fe/porous C | 0.2 mmol L‒1 H2SO4 + 0.1 mol L‒1 KCl | flow cell | CO | 90 | — | [ |
Ni-N-C | H2SO4 + Cs2SO4 (pH 2) | flow cell | CO | 100 | 76 | [ |
NiPc-OMe/CNTs | 0.05 mol L‒1 H2SO4 + 0.45 mol L‒1 K2SO4 | flow cell | CO | 98 | — | [ |
Ni-N-C | H3PO4 + KH2PO4 + KCl (pH 2) | flow cell | CO | 99 | — | [ |
Bi nanosheets | 0.05 mol L‒1 H2SO4 + 1 mol L‒1 KCl | flow cell | HCOOH | 92 | 27 | [ |
S doped Sn | H2SO4 + K2SO4 (pH 3) | flow cell | HCOOH | 92 | 35 | [ |
SnO2/C | 0.1 mol L‒1 H2SO4 + 0.4 mol L‒1 K2SO4 | flow cell | HCOOH | 88 | — | [ |
SnBi/SiC /PTFE | 0.05 mol L‒1 H2SO4 + 3 mol L‒1 KCl | flow cell | HCOOH | 90 | 65 | [ |
Cs3Bi2Br9/C | 0.05 mol L‒1 H2SO4 + 0.5 mol L‒1 CsBr | flow cell | HCOOH | 92 | 47 | [ |
Bi porous electrode | H2SO4 + Na2SO4 (pH 2.7) | flow cell | HCOOH | 89 | — | [ |
Cu | 1 mol L‒1 H3PO4 + 3 mol L‒1 KCl | flow cell | C2+ | 48 | 77 (50 for C2+) | [ |
Cu/C | 0.1 mol L‒1 H2SO4 + 0.4 mol L‒1 K2SO4 | flow cell | C2+ | 50 | — | [ |
Cu | 0.05 mol L‒1 H2SO4 + 2.5 mol L‒1 KCl | flow cell | C2+ | 90 | 70 for C2+ | [ |
COF:PFSA/Cu | 1 mol L‒1 H3PO4 + 3 mol L‒1 KCl | flow cell | C2+ | 75 | 45 for C2+ | [ |
Cu porous nanosheets | 0.05 mol L‒1 H2SO4 + 3 mol L‒1 KCl | flow cell | C2+ | 84 | 54 for C2+ | [ |
Pd-Cu | H2SO4 + K2SO4 (pH 2) | flow cell | C2+ | 89 | 60 for C2+ | [ |
Modified Cu | H3PO4 + KH2PO4 (pH 2) | flow cell | C2+ | 70 | — | [ |
Ag | 0.1 mol L‒1 H2SO4 | flow cell | CO | 95 | — | [ |
In | 0.1 mol L‒1 H2SO4 | flow cell | HCOOH | 76 | — | [ |
Cu | 0.2 mol L‒1 H2SO4 | flow cell | C2+ | 80 | 90 | [ |
Fig. 6. Suppression of H+ reduction by cathodic reactions. (a) Schematic of the suppression of H+ reduction by OH- generated from CO2RR. Reprinted with permission from Ref. [68]. Copyright 2020, American Chemical Society. (b) Simulated pH profile at varied cathodic current density in 1 mol L?1 H3PO4 + 3 mol L?1 KCl based on reaction-diffusion model. (c) FE of H2 and methane from CO2RR on sputtered Cu GDE in 1 mol L?1 H3PO4 + 3 mol L?1 KCl at varied current density. Reprinted with permission from Ref. [30]. Copyright 2021, American Association for the Advancement of Science.
Fig. 7. Suppressing the migration of H+ by alkali cations. (a) HER polarization curves of Au RDE in 10 mmol L?1 HClO4 + 0?100 mmol L?1 LiClO4. The red dashed line indicates the limiting diffusion current density deduced from Levich equation. (b) GMPNP-simulated migration rate of H+ (in the form of current density) on Au RDE in 10 mmol L?1 HClO4 + 0?100 mmol L?1 LiClO4 at the limiting mass-transport condition. Reprinted with permission from Ref. [35]. Copyright 2022, American Chemical Society. Schematic illustrations of the migration of H+ in acidic solutions with alkali cations (c) and without alkali cations (d). Reprinted with permission from Ref. [34] with permission. Copyright 2022, Springer Nature.
Fig. 8. The distribution of pH value near the cathode under the condition that H+ reduction reaches the plateau current density (limiting mass-transport condition). (a) In acidic electrolyte free of alkali cations. (b) In acidic electrolyte containing alkali cations.
Fig. 9. Approaches to suppress H+ diffusion. (a) Covering the catalyst with organic adlayers. (b) Depositing porous materials onto the catalyst. (c) Constructing nano-catalysts with confinement structure.
Fig. 10. Suppressing H+ diffusion by covering the catalyst with organic adlayer. (a) Organic layer from N-tolyl pyridinium (tolyl-pyr) electrodeposition polymer on Cu electrode. (b) Limiting diffusion current of H+ reduction on bare Cu RDE and organic adlayer modified Cu RDE in HClO4-KClO4 solution (pH = 2.2). The diffusion coefficient of H+ (DH+) decreased by 23% after the modification. Reprinted with permission from Ref. [67]. Copyright 2023, Wiley-VCH GmbH.
Fig. 11. Physical obstacles for the diffusion of H+ towards cathode surface. (a) Simulation of H+ diffusion without and with the coating layers of polystyrene beads. Simulated pH distribution on Cu surface (b) without the coating and (c) with the coating. Reprinted with permission from Ref. [49]. Copyright 2023, Springer Nature.
Fig. 12. Schematic illustration of Ni nanoparticles encapsulated in N-doped carbon nanocage for CO2RR in acidic solution containing alkali cations. Reprinted with permission from Ref. [59]. Copyright 2022, American Chemical Society.
Fig. 13. Proposed reaction pathways of HER and CO2RR to diverse reduction products. The free energy differences of key intermediates determine the selectivity of reduction products are labeled by grey arrows.
Fig. 14. Modulation of kinetics of C?C coupling step. (a) Screening of M-Cu bimetallic (111) facets. The descriptors of C2+ activity (ΔGOCCOH*) and C2+ selectivity (ΔGOCCOH* ? ΔGCHO*) were calculated. Reprinted with permission from Ref. [66]. Copyright 2022, Springer Nature. (b) Free energy diagram of *CO-*CO coupling on Cu (100) facet without *OH and with *OH on the site nearby. In the right panel, red and blue balls indicate the top and sublayer of Cu atoms, respectively, and the numbers indicate the site of *OH adsorption. Reprinted with permission from Ref. [46]. Copyright 2023, Springer Nature.
Fig. 15. Simulated concentration profiles of H+ and alkali cations in acidic electrolyte at varied electrode potential. (a) The concentration profile of H+ in 10 mmol L?1 HClO4. (b) The concentration profile of Li+ in 10 mmol L?1 HClO4 + 10 mmol L?1 LiClO4. The electrode is Au.
Fig. 16. Effect of cations on the interfacial electric field strength. (a) Schematic illustration of the Gaussian surface to deduce the value of EStern. ρ is the spatial charge density in the diffuse layer, ε0 is the vacuum permittivity, εr is the relative permittivity, F is the Faradaic constant, zi is the number of charge of species i (i = H+, M+, ClO4-). (b) Schematic illustrations of hydrated Li+ and Cs+ accumulated at OHP. Reprinted with permission from Ref. [78]. Copyright 2020, Royal Society of Chemistry. (c) Simulated plots of electric field strength in Stern layer depending on electrode potential in acidic electrolyte with and without alkali cations. Reprinted with permission from Ref. [35]. Copyright 2022, American Chemical Society.
Fig. 17. Correlation between electric field strength and the kinetics of CO2RR. (a) Illustration of the Frumkin correction. The blue curve indicates the potential profile in the EDL. CO2 molecule located at the OHP is regarded as the acceptor of electron. (b) Schematic illustration of the interaction between the dipole moment of *CO2 intermediate and the electric field in Stern layer.
Fig. 18. Interaction between alkali cations and intermediates of CO2RR. (a) Schematic of the interaction between partially dehydrated Cs+ and *CO2 in the CO2-to-CO process. Reprinted with permission from Ref. [33]. Copyright 2021, Springer Nature. (b) Schematic of the proposed CO-to-C2H4 pathways with the coordination of alkali cations. *OCCO, *OCCOH, and *HOCCOH were identified to be coordinated by alkali cations. (c) Coordination with alkali cations stabilize *CO2 on Ag (111) facet and *OCCO on Cu (100) facet and promotes the electron transfer from the metal surface to the adsorbed intermediates. Isosurface shows the charge difference between the cation-coordinated case and the cation-uncoordinated case (isosurface value is 0.0006 e·a0?3). Yellow and cyan colors indicate charge accumulation and depletion, respectively. Reprinted with permission from Ref. [83]. Copyright 2022, Springer Nature.
Fig. 19. Strategies to accumulate alkali cations near the catalyst. (a) Schematic of Cu cathode decorated by perfluorosulfonic acid ionomer as cation-augmenting layer (CAL). Reprinted with permission from Ref. [30]. Copyright 2021, American Association for the Advancement of Science. (b) Simulated surface K+ density and current density distribution on the surface of Au needle with the tip radius of 5 nm. Reprinted with permission from Ref. [84]. Copyright 2016, Springer Nature. Simulated K+ distribution on (c) porous Cu nanosheet and (d) flat Cu nanosheet. Reprinted with permission from Ref. [65]. Copyright 2022, Springer Nature.
Fig. 20. CO2RR in metal cation-free acidic conditions. (a) Sustainability issues of CO2RR in alkali cation-containing acidic electrolyte. Schematic illustrations of the process of bicarbonate precipitation and alkali cation permeation through the PEM. (b) Schematic illustration of cathode decorated by c-PDDA in metal cation-free acidic electrolyte. The layer of c-PDDA suppresses H+ migration and enhances the interfacial electric field. (c) FE of CO from CO2RR with c-PDDA decorated Ag catalyst in 0.1 mol L?1 H2SO4 (orange) and bare Ag catalyst in 0.1 mol L?1 H2SO4 + 0.4 mol L?1 K2SO4 (blue). Reprinted with permission from Ref. [32]. This work is licensed under a CC BY 4.0 License.
Fig. 21. CO2RR with quaternary ammonium salts as supporting electrolyte. (a) Partial current density of ethylene from CO2RR on bare Cu foil (blue) and QAPPT decorated Cu foil (orange) in PipCl solution as the electrolyte. Modified from Ref. [91] with permission. Copyright 2023, Elsevier. (b) Partial current density of CO from CO2RR on Au/PTFE electrode (blue) and Ag/PTFE electrode (orange) at about ?0.95 V vs. RHE in solution with different bicarbonate salts as supporting electrolyte. Modified from Ref. [92] with permission. Copyright 2023, American Chemical Society.
Fig. 22. Schematic illustration of the combination of atomic-level DFT simulation, micro-kinetics of electrode reactions and finite element analysis of mass transport and homogeneous reactions in diffuse and diffusion layers for the simulation of CO2RR process in acidic condition.
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