中空碳球负载铋电极CO₂ 电化学还原产甲酸性能

Preparation of Hollow Nanocarbon Spheres Supported Bismuth and Electrocatalytic Reduction of CO₂ to Formic Acid

摘要

二氧化碳电化学还原（Carbon dioxide electrochemical reduction， CO₂RR）在缓解CO₂引起的环境问题和实现产品增值方面前景突出。甲酸是重要的储氢材料和化工中间体，并且CO₂RR产甲酸可以在温和的条件进行，因而受到了广泛的关注。针对CO₂RR活性低、产甲酸速率低的问题，本文采用模板法制备了中空纳米碳球负载氧化铋催化剂（Bi₂O₃@HCS）用于CO₂RR产甲酸。通过扫描电子显微镜（SEM）、透射电镜（TEM）、X射线衍射仪（XRD）和X射线光电子能谱仪（XPS），对Bi₂O₃@HCS催化剂的表面形貌和结构组成进行了分析；采用线性扫描伏安曲线（LSV）和电化学阻抗谱（EIS）电化学测试方法比较了Bi₂O₃@HCS催化剂的电子转移能力。在“H”形电解槽中，研究了Bi₂O₃@HCS催化剂用于CO₂RR产甲酸性能，考察了Bi负载量、阴极电位、KHCO₃电解液浓度和溶液pH对产甲酸性能的影响。结果表明，尺寸均一的Bi₂O₃@HCS催化剂在Bi负载量为2.0 mmol/L时，Bi₂O₃@HCS-2催化剂具有最佳的电子转移能力；阴极电位为‒1.1 V vs. RHE和电解液浓度为0.1 mol/L KHCO₃的条件下，Bi₂O₃@HCS-2催化剂反应2 h甲酸产率可达1 108.11 μmol/L/h/cm²，其甲酸法拉第效率（F_E）可达50%以上，并且Bi₂O₃@HCS-2催化剂在CO₂RR产甲酸中表现出良好的电极局部pH适应性和稳定性。具有限域作用的中空纳米碳球有效限制了活性组分Bi⁰与Bi₂O₃的团聚，丰富的Bi₂O₃提高了CO₂RR产甲酸的反应动力学，并且Bi⁰与Bi₂O₃之间存在的金属价态转变进一步提高了催化剂的电子转移能力，从而实现了高的CO₂RR产甲酸速率。

Abstract

Carbon dioxide electrochemical reduction (CO₂RR) has great prospects in alleviating environmental problems caused by carbon dioxide emissions and achieving value-added products. Among these chemicals, formic acid is suggested to be one of the economically viable products for hydrogen storage material and chemical intermediates. The industrial production of formic acid is an energy-intensive process, so the production of formic acid in CO₂RR under mild conditions has received extensive attention. The production of formic acid in the CO₂RR depends on the development of highly active and selective electrocatalysts. In order to solve the electrocatalysts with low reaction activity, low formic acid formation rate and poor long-term stability in the CO₂RR process, hollow nano-carbon sphere-supported bismuth oxide catalysts (Bi₂O₃@HCS) were prepared by template method. Metallic bismuth (Bi) has preferable HOCO* adsorption energy and hollow nanospheres have a good active component limiting effect. The chemical composition and surface morphology of the Bi₂O₃@HCS catalysts were in detail analyzed by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray powder diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS). These results showed that the active components Bi⁰ and Bi₂O₃ were uniformly dispersed in the hollow carbon nanospheres, and in the Bi₂O₃@HCS-2 catalyst the highest Bi³⁺/Bi⁰ atomic ratio was achived. The sizes of Bi⁰ and Bi₂O₃ particles did not change significantly with increasing Bi loading from 2.0 to 3.0 mmol/L. The result was attributed to the confinement effect of hollow carbon nanospheres in the Bi₂O₃@HCS catalysts. The electrochemical capability of Bi₂O₃@HCS catalysts toward electrochemical CO₂ reduction was investigated by Linear sweep voltammograms (LSV) test in phosphate solution (pH=6.8) saturated with CO₂ or Ar. For Bi₂O₃@HCS-2 catalyst, the current density of CO₂ reduction peak is the largest, which indicated that the higher activity of the Bi₂O₃@HCS-2 catalyst was obtained compared with both Bi₂O₃@HCS-1 and Bi₂O₃@HCS-3 in the CO₂RR. Electrochemical impedance spectroscopy (EIS) was performed to investigate the electron transfer capability of the Bi₂O₃@HCS catalysts. The Bi₂O₃@HCS-2 catalyst exhibited a lower charge-transfer resistance, suggesting a more favorable electron transfer during CO₂RR. The performance of Bi₂O₃@HCS catalysts in CO₂RR for producing formic acid was investigated in a H-shaped electrolyzer. The Bi₂O₃@HCS-2 catalyst, with a Bi loading of 2.0 mmol/L, had the highest formic acid formation rate compared to Bi₂O₃@HCS-1 and Bi₂O₃@HCS-3 catalysts (the Bi loading was 1.0 mmol/L and 3.0 mmol/L, respectively). The effects of the reaction operating conditions (cathode potential, KHCO₃ electrolyte concentration and pH) on the formation of formic acid were optimized in the CO₂RR over the Bi₂O₃@HCS-2 catalyst. The results showed that the Bi₂O₃@HCS-2 catalyst with uniformly-sized particles showed the highest formic acid formation rate (1 108.11 μmol/L/h/cm²), and its Faradaic efficiency (F_E) reached 54.73% in the H-type reactor under the condition of cathode potential of ‒1.1 V vs. RHE and electrolyte concentration of 0.1 mol/L KHCO₃. In order to have an insight into the effects of formic acid formation rate under different pH conditions in the CO₂RR over the Bi₂O₃@HCS-2 catalyst, phosphoric acid buffer solution was used as the electrolyte instead of KHCO₃. The results showed that the Bi₂O₃@HCS-2 catalyst exhibited good adaptability in the CO₂RR in a wide pH range. In addition, the good stability of the Bi₂O₃@HCS-2 catalyst in CO₂RR for synthesis of formic acid was proved through the five successive cycle experiments. Compared with the formic acid formation rate in the literatures, the Bi₂O₃@HCS-2 catalyst showed good performance for the following reasons: 1) the hollow nanocarbon spheres with nanoconfinement effect inhibited the agglomeration of the active components of Bi⁰ and Bi₂O₃ nanoparticles; 2) the abundant Bi₂O₃ particles improved the reaction kinetics for the formic acid formation in the CO₂RR; 3) the transition of the chemical valence state between Bi⁰ and Bi₂O₃ further accelerated the electron transfer capacity. This study on the electrochemical CO₂ reduction for producing formic acid over the Bi₂O₃@HCS-2 catalysts provides a contribution for the synthesis of high-efficiency Bi-based nanocatalysts.

Graphical abstract

关键词

二氧化碳 / 电化学还原 / 甲酸 / 铋基催化剂

Key words

carbon dioxide / electrochemical reduction / formic acid / Bi-based catalyst

本刊网刊

CO₂的过度排放导致全球变暖，加剧了温室效应^[1‒2]。在实现碳减排目标的同时，将CO₂转化为高附加值的化学品，是解决环境问题和能源紧缺问题的一个重要途径，具有环保和经济双重效益^[3]。CO₂电化学还原（CO₂RR）具有能量转化效率较高、选择性可控、反应装置可模块化等优点，且可产生一系列经济效益良好的化学品（如甲酸、甲醇、乙烯、乙醇等），因而受到广泛关注^[4]。其中，甲酸是最适宜规模化生产的化学品^[5]，主要表现在：产甲酸仅为2e^‒转移，能耗较低^[6]；其次，甲酸作为原材料可以被广泛应用（如可作为燃料电池的优良燃料^[7]）；此外，甲酸是一种有前景的储氢介质，可储存质量分数为4.35%的氢^[8]。

CO₂RR产甲酸的性能主要依赖于催化剂^[9]。许多催化剂已被用于CO₂RR产甲酸，包括金属基催化剂^[10]、碳基催化剂^[11]和金属‒有机框架（MOFs）^[12]。在这些催化剂中，Pb、In、Sn等材料由于高氧亲和力和低氢亲和力对产甲酸表现出高选择性^[13]，但毒性高、成本高限制了其应用范围^[14]。

地球上含量丰富的Bi金属因成本低、过电位低、甲酸选择性高且毒性低等优点被电化学还原领域深入研究^[15‒17]。叶片状Bi纳米片^[18]、Bi₂O₃@C纳米棒^[1]和Bi₂O₂CO₃纳米片^[19]催化剂已被用于CO₂RR产甲酸，并表现出较高的甲酸法拉第效率（F_E）和较好的甲酸产率，但这些催化剂的长期稳定性有待提高。此外，研究表明，活性组分Bi的形貌显著影响CO₂RR产甲酸的性能。Miao等^[20]合成了颗粒状的Bi₂O₃（Bi₂O₃-A）和纳米棒状的Bi₂O₃（Bi₂O₃-B）用于CO₂RR产甲酸；其中，Bi₂O₃-A有更小的Tafel斜率，更快的反应速率和更优异的电催化性能。

相比于金属载体，高比表面积、高导电性的碳材料可组装成多种尺寸和结构，能够改善Bi基电极CO₂RR产甲酸性能^[21‒22]。Gong等^[23]制备了以洋葱纳米碳为载体的Bi/MCNOs电极，电化学表面积是Bi电极的3.4倍，表现出比Bi纳米电极更高的电流密度，极大改善了CO₂RR催化活性。

3维中空纳米碳球（hollow carbon nanospheres，HCSs）独特的空心结构可以有效抑制纳米颗粒团聚，纳米级的壳厚度以及高比表面积可以加快电子传输，被认为是金属活性组分的理想载体，在电化学储能、催化和电化学传感等领域受到研究者们的广泛关注^[24‒25]，但尚未见到在CO₂RR产甲酸中使用。

本文制备了中空纳米碳球负载氧化铋催化剂（Bi₂O₃@HCS）用于CO₂RR产甲酸，研究Bi负载量、阴极电位、电解液的浓度及pH对CO₂RR产甲酸性能的影响。研究结果可为合成高效Bi基纳米复合材料CO₂RR产甲酸提供帮助。

1 材料和方法

1.1 材 料

四丙氧基硅烷（TPOS，分析纯）、氨水（分析纯）、间苯二酚（分析纯）、五水合硝酸铋（Bi(NO₃)₂·5H₂O,分析纯）、无水乙醇（分析纯）、甲醛（分析纯）、NaOH（分析纯）均购自麦克林生化科技有限公司。Nafion溶液（质量分数为5%）由上海河森电气有限公司提供。CO₂（纯度为99.999%）和Ar（纯度为99.999%）由德阳东诚气体有限公司提供。

1.2 催化剂制备

1.2.1 Bi₂O₃@HCS催化剂的制备

依次将2.8 mL的 TPOS（纯度为97%）、3.0 mL氨水（浓度为25%~28%）和10.0 mL超纯水加入到70.0 mL无水乙醇中，搅拌15 min后，在混合溶液中加入0.4 g间苯二酚、Bi(NO₃)₂·5H₂O和0.56 mL甲醛溶液（质量分数为37%），继续搅拌24 h。之后分别用无水乙醇和超纯水进行抽滤各3次，得到的棕黄色固体粉末在60 ℃真空干燥箱中烘干。干燥后的固体在Ar气氛中高温煅烧4 h（800 ℃、900 ℃和1 000 ℃），升温速率为5 ℃/min，然后用NaOH溶液（10 mol/L）对煅烧后的样品进行24 h刻蚀，去除SiO₂，最后用无水乙醇和超纯水洗涤并干燥，得到Bi₂O₃@HCS催化剂。Bi(NO₃)₂·5H₂O负载量分别为0、1.0、2.0和3.0 mmol，制备得到的催化剂分别命名为HCS、Bi₂O₃@HCS-1、Bi₂O₃@HCS-2和Bi₂O₃@HCS-3。

1.2.2 碳载Bi₂O₃@HCS工作电极的制备

称取5 mg催化剂依次加入1.7 mL超纯水、0.2 mL Nafion溶液（质量分数为5%）和0.1 mL异丙醇（浓度为99.5%），对混合溶液超声30 min使其分散均匀，将混合溶液均匀涂覆在2.5 cm²碳布表面（1×2.5 cm²，双面滴加）并晾干。工作电极的催化剂负载量为2 mg/cm²。

1.3 分析测试仪器

CHI 760E型电化学工作站，上海辰华公司；Supra55型扫描电子显微镜（SEM），德国卡尔蔡司公司；Tecnai F20型透射电镜（TEM），美国FEI公司；D8 Advance X射线衍射仪（XRD），德国布鲁克公司；Thermo Scientific K-Alpha⁺ X射线光电子能谱仪（XPS），赛默飞（中国）科技有限公司；Agilent 5110型电感耦合等离子发射光谱仪（ICP-OES），美国安捷伦科技有限公司。

1.4 电化学测试

在CHI 760E上进行CO₂RR电化学性能测试，采用三电极体系，分别以Pt片为对电极，饱和银/氯化银（Ag/AgCl）为参比电极，涂有催化剂的碳布为工作电极。在Nafion 117质子交换膜分离的“H”形密闭玻璃电解槽中，以KHCO₃作为电解液。测试过程中不断搅拌阴极室中的电解液，并将CO₂持续输送到阴极室中，反应时间为2 h^[26‒28]。线性扫描伏安法（LSV）曲线以5 mV/s的测试扫描速率记录在‒1.0~1.0 V vs. RHE的电位窗口。电化学阻抗谱（EIS）测试条件：测试开路电压为‒0.8 V vs. RHE，频率范围为1~106 Hz，振幅为5 mV。

1.5 产物分析

CO₂RR结束后，用孔径为0.22 μm的滤膜过滤反应溶液；用离子色谱仪（ECO IC，瑞士万通）测定甲酸盐的浓度，流动相为NaCO₃（4.5 mmol/L）和NaHCO₃（0.8 mmol/L）的混合溶液，流速为1.0 mL/min。

甲酸法拉第效率F_{\mathrm{E}}计算如下：

F_{\mathrm{E}}=\frac{\mathrm{2}nF}{Q}（1）

式中：n为产物甲酸的物质的量，mol；F为法拉第常数，取值为96 485 C/mol；Q为通过电极的总电荷，C。

2 实验结果与讨论

2.1 Bi₂O₃@HCS催化剂结构表征

2.1.1 形貌分析

使用SEM和TEM分析催化剂的微观形貌和元素分布。图1为不同催化剂的SEM图。由图1可知，HCS呈现出表面光滑且规则的球形。Bi负载后，Bi₂O₃@HCS催化剂仍保持球形；当Bi负载量继续增加到3.0 mmol时，纳米球形貌发生轻微的变化。图2为Bi₂O₃@HCS-2的元素分布图。由图2可知，C、O和Bi元素均匀分散在催化剂上。图3为不同催化剂的TEM图。由图3可知，所制备的催化剂均呈现纳米空心球形；当Bi的负载量增加到2.0 mmol以上时，催化剂仍然保持球形，但碳层逐渐变薄，活性组分逐渐分散在碳球空腔内部，表明空心纳米碳球的空腔对Bi活性组分表现出良好的限域作用。

2.1.2 XRD分析

为了进一步揭示催化剂的晶体结构，对催化剂样品进行XRD分析，不同催化剂的XRD图谱如图4所示。由图4可知，所制备的催化剂均在衍射角（2θ）为22.5°时出现明显的石墨碳的衍射峰^[29]。在Bi含量低（1.0 mmol）的Bi₂O₃@HCS-1催化剂中，仅出现了微弱的Bi₂O₃峰（JCPDS No.27-0050）；随着Bi负载量的增加，不仅出现了较强的Bi₂O₃衍射峰，还出现了较弱的金属Bi⁰衍射峰（JCPDS No.85-1329）^{[28, 30]}，说明Bi₂O₃@HCS-2和Bi₂O₃@HCS-3催化剂中Bi以Bi₂O₃和Bi⁰晶体形式共存。由Scherrer公式计算得到，活性组分的晶粒尺寸没有明显增大，Bi₂O₃@HCS-2和Bi₂O₃@HCS-3中Bi₂O₃晶粒尺寸约为11 nm，Bi⁰晶粒尺寸约为1 nm。这主要是因为空心纳米碳球良好的限域作用有效抑制了Bi活性组分的团聚，确保了催化剂有较多的活性位点，与TEM结果一致。

2.1.3 XPS分析

利用XPS对催化剂表面组成和化合态进行分析，不同催化剂的高分辨率XPS能谱和不同催化剂的Bi含量分别如图5和表1所示。

由图5可知，所制备的Bi₂O₃@HCS催化剂均由Bi、O、C这3种元素组成。在Bi 4f的XPS谱图中，159.9、165.3 eV附近出现的特征峰归属于Bi³⁺，而在158.2、163.4 eV处的特征峰归属于Bi⁰。由图5（a）可知，在Bi₂O₃@HCS-1中仅存在Bi³⁺的特征峰，说明该催化剂仅有Bi₂O₃；在Bi₂O₃@HCS-2和Bi₂O₃@HCS-3中，除了存在Bi³⁺的特征峰外，还出现了归属于Bi⁰的特征峰，表明Bi₂O₃与Bi⁰同时存在，与XRD结果一致。

由表1可知，Bi₂O₃@HCS-2具有最高的Bi³⁺/Bi⁰原子比（1.17），而Bi₂O₃@HCS-3中Bi^3+/Bi⁰原子比（0.92）低于Bi₂O₃@HCS-2，可能是因为随着Bi负载量的增加，更多的Bi₂O₃得到电子转化成Bi⁰。此外，随着Bi负载量的增加，催化剂整体Bi含量呈上升趋势（质量分数从18.22%提高到19.17%），但是Bi晶粒尺寸没有增加，这也说明活性组分Bi生长于空心碳球内部，从而抑制了活性组分的团聚，此结果与其他文献结果一致^[29,31]。O 1s谱图中，在531.8 eV和533.3 eV处有分别归因于C—O键和C\stackrel{}{̿}O键的特征峰，在529.9 eV出现了Bi—O的特征峰。从C 1s谱图中可以发现，3种催化剂均在284.8、285.5和288.5 eV出现了3个特征峰，分别对应C—C、C—O和C—O键^[32]。

2.2 Bi₂O₃@HCS催化剂电化学活性分析

在Ar和CO₂饱和的KHCO₃溶液中使用LSV曲线分析催化剂的CO₂RR电化学活性，结果如图6所示。在CO₂气氛下，与Bi₂O₃@HCS-1相比，Bi₂O₃@HCS-2在‒0.60 V vs. RHE附近出现了明显的CO₂还原峰，并且具有更高的电流密度，表明Bi₂O₃@HCS-2催化剂更容易发生CO₂RR^[33]，即Bi活性组分的增加有利于吸附和激活CO₂分子，从而提高电极活性^[23]。而与Bi₂O₃@HCS-2相比，Bi₂O₃@HCS-3虽然也在‒0.25 V vs. RHE附近出现了CO₂还原峰，但电流密度明显下降，这可能是由于Bi³⁺/Bi⁰原子含量比降低，导致催化剂的电子转移能力减弱。

不同催化剂的EIS曲线如图7所示。图7中，Z'和Z''分别为阻抗实部和虚部。由图7可知，Bi₂O₃@HCS催化剂对应的EIS图均呈现半圆形，Bi₂O₃@HCS-2显示出比其他催化剂更小的半圆弧，表明适当的Bi负载有利于加快电极表面的电子转移^[34‒35]。

2.3 Bi₂O₃@HCS催化剂CO₂RR甲酸产率的研究

2.3.1 Bi负载量对甲酸产率的影响

图8为不同Bi₂O₃@HCS催化剂的CO₂RR甲酸产率。由图8可知，HCS载体表现出有限的甲酸产率，仅为6.09 μmol/L/h/cm²；Bi负载后，甲酸产率明显提高。当Bi负载量从1 mmol增加到2 mmol时，甲酸产率从11.97 μmol/L/h/cm²增加到82.31 μmol/L/h/cm²，但进一步增加Bi负载量时（3 mmol），甲酸产率降低（54.64 μmol/L/h/cm²）。

图8的结果表明，金属Bi是CO₂RR产甲酸的主要活性组分，Bi₂O₃的含量高有利于吸附和活化CO₂，同时Bi⁰和Bi₂O₃在反应过程中可通过金属价态的转变提高电子转移能力，从而获得最高的甲酸产率；但是过量的Bi活性组分会逐渐生长在空心纳米碳球内部，空心纳米碳球的限域作用可以有效抑制活性组分的团聚，但是Bi³⁺/Bi⁰原子比降低，导致电子转移能力下降，故CO₂RR产甲酸速率降低。

2.3.2 阴极电位的影响

以Bi₂O₃@HCS-2工作电极为阴极，研究不同阴极电位条件下甲酸产率和F_E，结果如图9所示。当阴极电位从‒0.8 V vs. RHE降低至‒1.1 V vs. RHE时，甲酸产率从82.31 μmol/L/h/cm²提高到1 108.11 μmol/L/h/cm²，F_E可达54.74%，表明Bi₂O₃@HCS-2在较低电位下CO₂RR反应速率良好。当进一步降低阴极电位，甲酸产率逐渐降低，这是因为析氢反应与CO₂RR发生电子竞争，并且析氢反应产生的H₂阻碍了CO₂的传质^[36]。

2.3.3 KHCO₃电解液浓度的影响

图10为不同KHCO₃电解质浓度下Bi₂O₃@HCS-2催化剂CO₂RR的甲酸产率和F_E。由图10可知，KHCO₃浓度对CO₂RR产甲酸速率有很大影响。KHCO₃浓度为0.1 mol/L时，甲酸产率达到最大值（1 108.11 μmol/L/h/cm²），同时实现最高F_E（57.77%）；当KHCO₃浓度较低（＜0.1 mol/L）时，溶液中导电离子数减少，使得CO₂还原的甲酸产率和F_E降低；而当KHCO₃浓度较高（>0.1 mol/L）时，会导致电解液黏度增大，阻碍CO₂的扩散，并且过多的HCO₃^‒离子吸附在电极表面，导致活性位点损失，从而限制了CO₂电化学还原的进行，降低了甲酸产率和F_E^[37‒38]。

2.3.4 pH对甲酸产率的影响

CO₂RR产甲酸关键中间体的形成和转化受到电极/电解质界面处电解质性质的影响^[39‒40]。在反应过程中由于H⁺不断被消耗，电极附近会出现高浓度的OH^‒，可能会促使CO₂转化为惰性碳酸盐。虽然KHCO₃具有一定的缓冲能力，但在反应中电极局部pH仍明显不同于本体电解质的pH^[41]。因此，选用pH缓冲溶液研究CO₂RR反应中pH值对甲酸产率的影响。

图11为不同pH缓冲溶液（5.0～8.0）中Bi₂O₃@HCS-2催化剂CO₂RR的甲酸产率和F_E。由图11可知，在较宽的pH范围内甲酸产率和F_E并无很大变化。当pH从5.0升高至8.0时，产率仅从9.82 μmol/L/h/cm²提高到40.40 μmol/L/h/cm²，F_E仅从0.81%提高到4.91%，这表明制备的Bi₂O₃@HCS-2催化剂在CO₂RR产甲酸中具有较宽的pH工作范围^[42]。

2.4 稳定性分析

图12比较了本文Bi₂O₃@HCS-2催化剂与其他文献中催化剂CO₂RR的甲酸产率。由图12可知，本文Bi₂O₃@HCS-2催化剂的甲酸产率高于文献报道的相关催化剂^[43‒47]。

为了考察Bi₂O₃@HCS-2催化剂CO₂RR产甲酸的稳定性，进行恒电位电解实验，循环反应中甲酸产率如图13所示。结果表明，Bi₂O₃@HCS-2电极经过5次循环甲酸产率仍高达1 090.01 μmol/L/h/cm²，表现出良好的稳定性。

3 结　论

本文将中空纳米球状Bi₂O₃@HCS催化剂用于CO₂RR产甲酸，关键结论如下：

1）具有良好限域作用的中空纳米碳球抑制了Bi晶粒尺寸的增加，丰富的Bi₂O₃活性位点促进了CO₂活化，同时Bi⁰与Bi₂O₃通过价态转变提高了电子转移能力，并且具有最高Bi³⁺/Bi⁰原子比的Bi₂O₃@HCS-2催化剂表现出最好的CO₂RR产甲酸性能。

2）阴极电位、电解液浓度和pH均影响CO₂电化学还原产甲酸性能。实验结果表明：“H”形反应器中，KHCO₃电解液浓度为0.1 mol/L、反应点位为‒1.1 V vs. RHE和pH=6.8的条件下，Bi₂O₃@HCS-2催化剂CO₂RR的甲酸产率达到1 108.11 μmol/L/h/cm²，F_E为54.73%；经过5次循环，其甲酸产率仍高达1 090.01 μmol/L/h/cm²，证明Bi₂O₃@HCS-2催化剂具有良好的CO₂电化学还原产甲酸性能。

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基金资助

国家自然科学基金项目(52030003)