物理化学学报 >> 2021, Vol. 37 >> Issue (5): 2009023.doi: 10.3866/PKU.WHXB202009023

所属专题: CO2还原

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CeO2担载Cu纳米粒子电催化CO2还原产乙烯:CeO2不同暴露晶面对催化性能的影响

楚森林1, 李欣1, Robertson Alex W.2, 孙振宇1,*()   

  1. 1 北京化工大学化学工程学院,有机-无机复合材料国家重点实验室,北京 100029
    2 牛津大学材料系,牛津OX1 3PH
  • 收稿日期:2020-09-07 录用日期:2020-09-28 发布日期:2020-10-15
  • 通讯作者: 孙振宇 E-mail:sunzy@mail.buct.edu.cn
  • 基金资助:
    国家自然科学基金(21972010);北京自然科学基金(2192039)

Electrocatalytic CO2 Reduction to Ethylene over CeO2-Supported Cu Nanoparticles: Effect of Exposed Facets of CeO2

Senlin Chu1, Xin Li1, Alex W. Robertson2, Zhenyu Sun1,*()   

  1. 1 State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China
    2 Department of Materials, University of Oxford, Oxford, OX1 3PH, UK
  • Received:2020-09-07 Accepted:2020-09-28 Published:2020-10-15
  • Contact: Zhenyu Sun E-mail:sunzy@mail.buct.edu.cn
  • About author:Zhenyu Sun, Email: sunzy@mail.buct.edu.cn. Tel.: +86-13301308339
  • Supported by:
    National Natural Science Foundation of China(21972010);Beijing Natural Science Foundation, China(2192039)

摘要:

化石燃料在未来几十年仍然是主要的能量来源,但是这种不可再生资源的燃烧释放出大量的CO2 (主要的温室气体),空气中CO2的浓度每年仍然持续增加。使用间歇性可再生能源转化的电能驱动电化学CO2还原生成高附加值产品为其减排提供了一种有前景、CO2“零排放”的方法。本文通过利用Cu和不同形状的CeO2纳米晶之间的相互作用,即分别暴露(100)、(110)、(111)晶面的立方体、棒状和八面体CeO2,实现了对电化学CO2还原产乙烯的有效调控。研究发现,电化学CO2还原的选择性和活性与CeO2暴露的晶面密切相关,生成乙烯的法拉第效率和偏电流密度在1.00到1.15 V (相对于可逆氢电极)的施加电势范围内呈现出Cu/CeO2(111) < Cu/CeO2(100) < Cu/CeO2(110)的趋势。在H-型电解池中,以0.1 mol·L-1 KHCO3溶液为电解质,Cu/CeO2(110)电催化CO2还原的法拉第效率为56.7%,这与纯碳纸、CeO2(100)、CeO2(110)、CeO2(111)纳米颗粒上只发生析氢副反应形成了鲜明对比,并且Cu/CeO2(110)可在较温和的过电势下(1.13 V)电催化CO2还原产乙烯,其法拉第效率达到39.1%,和文献报道的很多Cu-基材料的性能相当,而Cu/CeO2(100)与Cu/CeO2(111)产乙烯的法拉第效率分别为31.8%和29.6%。此外,经过6 h的持续电解后,乙烯的法拉第效率基本保持稳定。Cu/CeO2(110)还原CO2产乙烯的活性可能与CeO2(110)表面的亚稳态性质有关,其不仅能有效促进CO2的吸附,还能有效稳定Cu+,从而促进了CO2还原为乙烯。本工作为增强电化学CO2还原提供了晶面工程途径。

关键词: 二氧化碳, 电化学还原, 乙烯, 铜, 二氧化铈, 暴露晶面

Abstract:

Fossil fuels are expected to be the major source of energy for the next few decades. However, combustion of nonrenewable resources leads to the release of large quantities of CO2, the primary greenhouse gas. Notably, the concentration of CO2 in the atmosphere is increasing annually at an astounding rate. Electrochemical CO2 reduction (ECR) to value-added fuels and chemicals using electricity from intermittent renewable energy sources is a carbon-neutral method to alleviate anthropogenic CO2 emissions. Despite the steady progress in the selective generation of C1 products (CO and formic acid), the production of multi-carbon species still suffers from low selectivity and efficiency. As an ECR product, ethylene (C2H4) has a higher energy density than do C1 species and is an important industrial feedstock in high demand. However, the conversion of CO2 to C2H4 is plagued by low productivity and large overpotential, in addition to the severe competing hydrogen evolution reaction (HER) during the ECR. To address these issues, the design and development of advanced electrocatalysts are critical. Here, we demonstrate fine-tuning of ECR to C2H4 by taking advantage of the prominent interaction of Cu with shape-controlled CeO2 nanocrystals, that is, cubes, rods, and octahedra predominantly covered with (100), (110), and (111) surfaces, respectively. We found that the selectivity and activity of the ECR depended strongly on the exposed crystal facets of CeO2. The overall ECR Faradaic efficiency (FE) over Cu/CeO2(110) (FE ≈ 56.7%) surpassed that of both Cu/CeO2(100) (FE ≈ 51.5%) and Cu/CeO2(111) (FE ≈ 48.4%) in 0.1 mol·L-1 KHCO3 solutions with an H-type cell. This was in stark contrast to the exclusive occurrence of the HER over pure carbon paper, CeO2(100), CeO2(110), and CeO2(111). In particular, the FE toward C2H4 formation and the partial current density increased in the sequence Cu/CeO2(111) < Cu/CeO2(100) < Cu/CeO2(110) within applied bias potentials from -1.00 to -1.15 V (vs. the reversible hydrogen electrode), reaching 39.1% over Cu/CeO2(110) at a mild overpotential (1.13 V). The corresponding values for Cu/CeO2(100) and Cu/CeO2(111) were FEC2H4 ≈ 31.8% and FEC2H4 ≈ 29.6%, respectively. The C2H4 selectivity was comparable to that of many reported Cu-based electrocatalysts at similar overpotentials. Furthermore, the FE for C2H4 remained stable even after 6 h of continuous electrolysis. The superior ECR activity of Cu/CeO2(110) to yield C2H4 was attributed to the metastable (110) surface, which not only promoted the effective adsorption of CO2 but also remarkably stabilized Cu+, thereby boosting the ECR to produce C2H4. This work offers an alternative strategy to enhance the ECR efficiency by crystal facet engineering.

Key words: CO2, Electrochemical reduction, Ethylene, Cu, CeO2, Exposed facet

MSC2000: 

  • O646