ZIF-8基复合材料高效、稳定电催化还原CO2

电催化CO₂还原反应(eCO₂RR)受到催化剂本征活性以及传质的限制,导致材料的催化活性低、反应起始电位高等问题。我们以类沸石锌盐咪唑骨架(ZIF-8)材料为研究对象,探究了不同粒径ZIF-8材料的eCO₂RR性能。优选粒径为50 nm的ZIF-8材料,进一步引入碳纳米管(CNT)作为其导电基底材料,通过原位生长,构建了复合材料ZIF-8-50@CNT的多级孔结构和疏水界面。eCO₂RR实验结果表明,CNT的引入提高了催化剂的导电性,优化后的复合材料有效地降低了反应的起始电位。在-1.1 V(相对可逆氢电极(RHE))电位下,CO部分电流密度为15.6 mA·cm^-2,ZIF-8-50@CNT催化剂的比表面活性提升了3.5倍(相比ZIF-8-50),塔菲尔斜率降低到136 mV·dec^-1。并且产物CO的选择性和稳定性得到了提高,在宽电势窗口-0.9～-1.2 V(vs RHE)内,CO的法拉第效率(FE)保持在80%以上。在10 h稳定性测试中,催化剂活...     

Se掺杂WO3·0.5 H2O/g-C3N4光电催化剂的析氢反应性能

以二氰二胺、硒粉和钨酸钠为前驱体,采用一锅法成功制备出Se掺杂WO₃·0.5 H₂O/g-C₃N₄(Se/WCN)催化剂。并采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)和 X 射线光电子能谱(XPS)对样品的物相结构、形貌及化学组成进行表征。与原始的 WO₃和 g-C₃N₄相比,Se/WCN 催化剂的起始电位降到了-0.75 V(vs RHE),电流密度高达 70 mA·cm^-2,表现出更高的电催化活性。而光照后,Se/WCN 的催化性能进一步提升,起始电位从-0.75 V(vs RHE)降至-0.65 V(vs RHE),电荷转移电阻由371.4 Ω减小到310.0 Ω。     

室温快速合成Ag基金属有机骨架材料用于电催化还原CO2

选择具有强给电子能力的1,2,4-三唑为配体,成功合成了银基金属有机骨架材料(Ag-MOF)并用于电催化还原CO₂反应(CO₂RR)。借助粉末X射线衍射、透射电子显微镜、扫描电子显微镜、计时电流法等表征手段对材料的晶体结构、形貌和电催化CO₂RR性能进行了系统的研究。与商品化的纳米Ag颗粒对比,Ag-MOF展现出更优异的电催化CO₂RR产物选择性、催化活性和稳定性,在-0.9 V (vs RHE)时,CO的法拉第效率高达96.1%。当电压为-1.1 V (vs RHE)时,电流密度可达17 mA·cm^-2,且电极可以稳定运行300 min。这说明通过选择合适的配体结构,可以改变催化位点周围的化学环境,从而高效将CO₂转化为目标产物。     

室温快速合成Ag基金属有机骨架材料用于电催化还原CO2

选择具有强给电子能力的1,2,4-三唑为配体,成功合成了银基金属有机骨架材料(Ag-MOF)并用于电催化还原CO₂反应(CO₂RR)。借助粉末X射线衍射、透射电子显微镜、扫描电子显微镜、计时电流法等表征手段对材料的晶体结构、形貌和电催化CO₂RR性能进行了系统的研究。与商品化的纳米Ag颗粒对比,Ag-MOF展现出更优异的电催化CO₂RR产物选择性、催化活性和稳定性,在-0.9 V (vs RHE)时,CO的法拉第效率高达96.1%。当电压为-1.1 V (vs RHE)时,电流密度可达17 mA·cm^-2,且电极可以稳定运行300 min。这说明通过选择合适的配体结构,可以改变催化位点周围的化学环境,从而高效将CO₂转化为目标产物。     

室温快速合成Ag基金属有机骨架材料用于电催化还原CO2

选择具有强给电子能力的1,2,4-三唑为配体,成功合成了银基金属有机骨架材料(Ag-MOF)并用于电催化还原CO₂反应(CO₂RR)。借助粉末X射线衍射、透射电子显微镜、扫描电子显微镜、计时电流法等表征手段对材料的晶体结构、形貌和电催化CO₂RR性能进行了系统的研究。与商品化的纳米Ag颗粒对比,Ag-MOF展现出更优异的电催化CO₂RR产物选择性、催化活性和稳定性,在-0.9 V (vs RHE)时,CO的法拉第效率高达96.1%。当电压为-1.1 V (vs RHE)时,电流密度可达17 mA·cm^-2,且电极可以稳定运行300 min。这说明通过选择合适的配体结构,可以改变催化位点周围的化学环境,从而高效将CO₂转化为目标产物。     

催化剂中Cu含量对CVD法制备碳纳米管的影响

本文以溶胶-凝胶法制备了以铜为助剂的Ni/MgO催化剂，X-射线衍射(XRD)表明，经400 ℃氢气处理，催化剂中只有部分镍被还原，原因是NiO和MgO间存在强相互作用，形成固溶体。XRD和程序升温还原(TPR)表明，加入铜促进了镍的还原。CO化学吸附得出，随着催化剂中铜含量的增加，还原后催化剂表面镍原子数目增多，因此，催化剂的活性和反应寿命增加，C₂H₄裂解生成碳纳米管(CNT)的产率随之增加；但是，铜含量过高会引起催化剂表面镍颗粒增大，导致产物中纳米碳纤维（CNF）量增多，CNT量减少。对于约50% Ni/MgO催化剂，铜的最佳含量为4%～6%，此时得到的CNT产率最高，达36 g·g^-1，质量较好(纯度高、管径均匀、石墨化程度高)。     

碳纳米管负载的Pd-Ag-Sn催化剂对甲酸的电氧化

采用硼氢化钠还原的方法合成了碳纳米管负载的钯基纳米催化剂（Pd/CNT,Pd₇Ag₃/CNT,Pd₇Sn₂/CNT,Pd₇Ag₁Sn₂/CNT,Pd₇Ag₂Sn₂/CNT和Pd₇Ag₃Sn₂/CNT）。通过XRD,TEM和XPS对其进行了表征,结果表明,相比Pd/CNT和Pd-Ag（或Pd-Sn）催化剂的纳米颗粒,Pd-Ag-Sn催化剂展现出了更小的平均颗粒尺寸（2.3 nm）。此外,还通过循环伏安（CV）和计时电流法（CA）测试了这些催化剂对甲酸氧化的电活性,在酸碱介质中,Pd-Ag-Sn/CNT对甲酸氧化都表现出了更高的电流密度。其中,Pd₇Ag₂Sn₂/CNT催化剂在酸碱介质中的电流密度分别是108.8和211.3 mA·cm^-2,相应的Pd质量电流密度高达1 364和2 640 mA·mg^-1,远远高于商业Pd/C,表明Pd-Ag-Sn/CNT催化剂对甲酸氧化表现出了极好的电催化活性。     

用于高性能超级电容器的金属有机骨架衍生Co(OH)2/C-N@GP纳米复合材料

本文报道一种制备β-Co(OH)₂/氮掺杂碳石墨烯纳米复合材料(Co(OH)₂/C-N@GP)的方法。首先，我们通过在含羧基的聚苯乙烯(PS)乙醇分散体中使Co(NO₃)₂·6H₂O与2-甲基咪唑反应，合成了ZIF-67/聚苯乙烯的复合材料。然后将ZIF-67/聚苯乙烯复合材料高温碳化，同时与硫代乙酰胺和石墨烯反应生成Co(SO₄)₂/C-N@GP。最后，Co(SO₄)₂/C-N@GP在KOH水溶液中浸泡以获得 Co(OH)₂/C-N@GP 纳米复合材料。所制备的 Co(OH)₂/C-N@GP 的扫描电镜图显示尺寸为 10~20 nm 的 Co(OH)₂很好地分散在石墨烯上。电化学分析表明Co(OH)₂/C-N作为超级电容器的电极材料表现出典型的法拉第电荷转移行为，并且当石墨烯存在时，其比电容可显著增强。在2 mol·L^-1 KOH中，Co(OH)₂/C-N@GP在2 A·g^-1下表现出985.4 F·g^-1的高比电容，1 000次循环后的比电容保持率为76.6%。     

ZIF-67/CeO2催化CO2和甲醇直接合成碳酸二甲酯

采用沉淀法将ZIF-67负载到CeO₂上,制备了具有多重活性位点的非均相催化剂ZIF-67/CeO₂,并研究其催化CO₂和甲醇直接反应生成碳酸二甲酯(DMC)的性能。采用 X 射线衍射、N2吸附-脱附、傅里叶变换红外光谱和 X 射线光电子能谱研究了ZIF-67/CeO₂的各种理化性质。结果表明,ZIF-67的引入使ZIF-67/CeO₂催化剂产生更多的氧空位。在考察的ZIF-67/CeO₂系列催化剂中,0.3-ZIF-67/CeO₂(0.3为Co、Ce物质的量之比)在具有高的比表面积的同时还能保持介孔结构,具有丰富的酸碱位点,并且具有较高的CO₂吸附容量,表现出最好的催化性能。在反应温度为140℃、压力为4.5 MPa的条件下反应4 h,DMC收率可达到3.79 mmol_DMC·gcat^-1。     

水热合成二硫化钨/石墨烯复合材料及其氧还原性能

以六氯化钨、硫代乙酰胺、氧化石墨烯为原料,采用一步水热法合成了二维的二硫化钨/石墨烯(WS₂/RGO)复合材料。水热合成的WS₂/RGO具有薄层的二维结构,且由于石墨烯的存在,WS₂以较少的层数形成薄片状生长在石墨烯的表面。尝试将这种非Pt类材料用于电催化氧化原反应,测试结果表明,WS₂在碱性条件下氧还原活性非常低,但是复合RGO形成WS₂/RGO复合材料后,电催化氧化原性能有了极大的提高,其起始电位为-0.17 V(vs SCE),转移电子数为3.7,极限电流密度为2.5 mA·cm^-2,同时其具有较好的抗甲醇性能和循环稳定性。这是因为WS₂/RGO复合材料的二维结构具有更高的电子传输速率,同时硫化钨和石墨烯可以发挥协同催化作用。这种新型的二硫化钨/石墨烯(WS₂/RGO)复合材料作为非贵金属催化剂表现出良好的氧还原性能,在燃料电池上具有较好的应用前景。     

Simultaneous Capture of CO2 Boosting Its Electroreduction in the Micropores of a Metal–organic Framework

Integration of CO₂ capture capability from simulated flue gas and electrochemical CO₂ reduction reaction (eCO₂RR) active sites into a catalyst is a promising cost-effective strategy for carbon neutrality, but is of great difficulty. Herein, combining the mixed gas breakthrough experiments and eCO₂RR tests, we showed that an Ag₁₂ cluster-based metal–organic framework ( 1-NH₂ , aka Ag₁₂bpy-NH₂ ), simultaneously possessing CO₂ capture sites as “CO₂ relays” and eCO₂RR active sites, can not only utilize its micropores to efficiently capture CO₂ from simulated flue gas (CO₂ : N₂=15 : 85, at 298 K), but also catalyze eCO₂RR of the adsorbed CO₂ into CO with an ultra-high CO₂ conversion of 60 %. More importantly, its eCO₂RR performance (a Faradaic efficiency (CO) of 96 % with a commercial current density of 120 mA cm⁻² at a very low cell voltage of −2.3 V for 300 hours and the full-cell energy conversion efficiency of 56 %) under simulated flue gas atmosphere is close to that under 100 % CO₂ atmosphere, and higher than those of all reported catalysts at higher potentials under 100 % CO₂ atmosphere. This work bridges the gap between CO₂ enrichment/capture and eCO₂RR.     

In Situ Reconstruction of a Hierarchical Sn‐Cu/SnOx Core/Shell Catalyst for High‐Performance CO2 Electroreduction

The electrochemical CO₂ reduction reaction (CO₂RR) to give C₁ (formate and CO) products is one of the most techno‐economically achievable strategies for alleviating CO₂ emissions. Now, it is demonstrated that the SnO_x shell in Sn_2.7Cu catalyst with a hierarchical Sn‐Cu core can be reconstructed in situ under cathodic potentials of CO₂RR. The resulting Sn_2.7Cu catalyst achieves a high current density of 406.7±14.4 mA cm^?2 with C₁ Faradaic efficiency of 98.0±0.9 % at ?0.70 V vs. RHE, and remains stable at 243.1±19.2 mA cm^?2 with a C₁ Faradaic efficiency of 99.0±0.5 % for 40 h at ?0.55 V vs. RHE. DFT calculations indicate that the reconstructed Sn/SnO_x interface facilitates formic acid production by optimizing binding of the reaction intermediate HCOO* while promotes Faradaic efficiency of C₁ products by suppressing the competitive hydrogen evolution reaction, resulting in high Faradaic efficiency, current density, and stability of CO₂RR at low overpotentials.     

Partially Oxidized Palladium Nanodots for Enhanced Electrocatalytic Carbon Dioxide Reduction

Here we report a partially oxidized palladium nanodot (Pd/PdO_x) catalyst with a diameter of around 4.5 nm. In aqueous CO₂‐saturated 0.5 m KHCO₃, the catalyst displays a Faradaic efficiency (FE) of 90 % at −0.55 V vs. reversible hydrogen electrode (RHE) for carbon monoxide (CO) production, and the activity can be retained for at least 24 h. The improved catalytic activity can be attributed to the strong adsorption of CO₂^.− intermediate on the Pd/PdO_x electrode, wherein the presence of Pd²⁺ during the electroreduction reaction of CO₂ may play an important role in accelerating the carbon dioxide reduction reaction (CO₂RR). This study explores the catalytic mechanism of a partially oxidized nanostructured Pd electrocatalyst and provides new opportunities for improving the CO₂RR performance of metal systems.     

Ultra-small Size ZIF-8 Materials for Efficient and Selective Electrocatalytic Reduction of CO2 to CO

Zeolitic Imidazolate Frameworks (ZIFs) are considered as a novel porous material combining high stability in inorganic zeolites with high porosity and organic functionality of MOFs. The cage-like structure selectively and efficiently traps CO₂, which is an indispensable and critical step for Electrocatalytic CO₂ Reduction Reaction (CO₂RR). In this work, ultrasmall ZIF-8 nanomaterials are synthesized by tuning the molar ratio of the feedstock and used as electrocatalysts for the selective reduction of CO₂ to CO. The catalytic activity of the ultra-small size ZIF-8 material for the electrocatalytic reduction of CO₂ can reach satisfactory results with a Faraday efficiency of 91 % for CO and a stability of 12.5 h at a high applied potential of −1.8 V vs. RHE. The investigation can provide a new idea to explore for the design and improvement of catalysts for CO₂RR.     

Self-Accelerating Effect in a Covalent–Organic Framework with Imidazole Groups Boosts Electroreduction of CO2 to CO

Solvent effect plays an important role in catalytic reaction, but there is little research and attention on it in electrochemical CO₂ reduction reaction (eCO₂RR). Herein, we report a stable covalent-organic framework (denoted as PcNi-im ) with imidazole groups as a new electrocatalyst for eCO₂RR to CO. Interestingly, compared with neutral conditions, PcNi-im not only showed high Faraday efficiency of CO product (≈100 %) under acidic conditions (pH ≈ 1), but also the partial current density was increased from 258 to 320 mA cm⁻². No obvious degradation was observed over 10 hours of continuous operation at the current density of 250 mA cm⁻². The mechanism study shows that the imidazole group on the framework can be protonated to form an imidazole cation in acidic media, hence reducing the surface work function and charge density of the active metal center. As a result, CO poisoning effect is weakened and the key intermediate *COOH is also stabilized, thus accelerating the catalytic reaction rate.     

Surface and Interface Engineering for the Catalysts of Electrocatalytic CO2 Reduction

The massive use of fossil fuels releases a great amount of CO₂, which substantially contributes to the global warming. For the global goal of putting CO₂ emission under control, effective utilization of CO₂ is particularly meaningful. Electrocatalytic CO₂ reduction reaction (eCO₂RR) has great potential in CO₂ utilization, because it can convert CO₂ into valuable carbon-containing chemicals and feedstock using renewable electricity. The catalyst design for eCO₂RR is a key challenge to achieving efficient conversion of CO₂ to fuels and useful chemicals. For a typical heterogeneous catalyst, surface and interface engineering is an effective approach to enhance reaction activity. Herein, the development and research progress in CO₂ catalysts with focus on surface and interface engineering are reviewed. First, the fundaments of eCO₂RR is briefly discussed from the reaction mechanism to performance evaluation methods, introducing the role of the surface and interface engineering of electrocatalyst in eCO₂RR. Then, several routes to optimize the surface and interface of CO₂ electrocatalysts, including morphology, dopants, atomic vacancies, grain boundaries, surface modification, etc., are reviewed and representative examples are given. At the end of this review, we share our personal views in future research of eCO₂RR.