单原子催化剂在CO2转化中的应用

单原子催化剂(SAC)是由互相隔离分散的原子级活性位点锚定在基底上而形成的一类新兴催化剂材料, 其具有最大化的原子利用率、 可调控的独特电子结构, 因而在热催化、 光催化及电催化等方面展现出良好的应用前景. 通过SAC的热/光/电催化CO₂转化反应(CCR)能将温室气体CO₂转化为燃料或具有附加值的化学品, 为解决严重的全球变暖和能源短缺问题提供了一种有效策略. 本文总结了近年来SAC在CO₂转化领域的研究进展, 讨论了其合成、 调控及催化各类CO₂转化反应的优缺点, 并对其未来的发展进行了展望.     

2020 Roadmap on gas-involved photo-and electro-catalysis

Green reactions not only provide us chemical products without any pollution,but also offer us the viable technology to realize difficult tasks in normal conditions.Photo-,photoelectro-,and electrocatalytic reactions are indeed powerful tools to help us to embrace bright future.Especially,some gas-involved reactions are extremely useful to change our life environments from energy systems to liquid fuels and cost-effective products,such as H2 evolution(H2 production),02 evolution/reduction,CO_2 reduction,N2 reduction(or N_2 fixation) reactions.We can provide fuel cells clean H_2 for electric vehicles from H_2 evolution reaction(HER),at the same time,we also need highly efficient 02 reduction reaction(ORR) in fuel cells for improving the reaction kinetics.Moreover,we can get the clean oxidant O_2 from water through O_2 evolution reaction(OER),and carry out some reactions without posing any pollution to reaction systems.Furthermore,we can translate the greenhouse gas CO_2 into useful liquid fuels through CO_2 reduction reaction(CRR).Last but not the least,we can get ammonia from N_2 reduction reaction(NRR),which can decrease energy input compared to the traditional Hubble process.These reactions,such as HER,ORR,OER,CRR and NRR could be realized through solar-,photoelectro-and electro-assisted ways.For them,the catalysts used play crucial roles in determining the efficiency and kinds of products,so we should consider the efficiency of catalysts.However,the cost,synthetic methods of catalysts should also be considered.Nowadays,significant progress has been achieved,however,many challenges still exist,reaction systems,catalysts underlying mechanisms,and so on.As extremely active fields,we should pay attention to them.Under the background,it has motivated us to contribute with a roadmap on 'GasInvolved Photo-and Electro-Catalysis'.     

基于单原子催化剂的二氧化碳选择性转化

Industrial revolution has led to increased combustion of fossil fuels. Consequently, large amounts of CO₂ are emitted to the atmosphere, throwing the carbon cycle out of balance. Currently, the most effective method to reduce the CO₂ concentration is direct CO₂ capture from the atmosphere and pumping of the captured CO₂ deep underground or into the mid-ocean. The transformation of CO₂ into high-value chemicals is an attractive yet challenging task. In recent years, there has been much interest in the development of CO₂ utilization technologies based on electrochemical CO₂ reduction, photochemical CO₂ reduction, and thermal CO₂ reduction, and CO₂ valorization has emerged as a hot research topic. In electrochemical CO₂ reduction, the cathodic reaction is the reduction of CO₂ to value-added chemicals. The anodic reaction should be the oxygen evolution reaction, and water is the only renewable and scalable source of electrons and protons in this reaction. There is a plethora of research on the use of various metals to catalyze this reaction. Among these, Cu-based materials have been demonstrated to show unique catalytic activity and stability for the electrochemical conversion of CO₂ to valuable fuels and chemicals. Moreover, the solar-driven conversion of CO₂ into value-added chemical fuels has attracted great attention, and much effort is being devoted to develop novel catalysts for the photoreduction of CO₂, especially by mimicking the natural photosynthetic process. The key step in the photocatalytic process is the efficient generation of electron-hole pairs and separation of these charge carriers. The efficient separation of photoinduced charge carriers plays a crucial role in the final catalytic activity. Compared with CO₂ reduction via electrocatalysis and photocatalysis, thermal reduction is more attractive because of its potential large-scale application in the industry. Heterogeneous nanomaterials show excellent activity in the electrocatalytic, photocatalytic, and thermal catalytic conversion of CO₂. However, nanostructured materials have drawbacks on the investigation of the intrinsic activity of the active sites. In recent years, single-site catalysts have become popular because they allow for maximum utilization of the metal centers, show specific catalytic performance, and facilitate easy elucidation of the catalytic mechanism at the molecular level. Accordingly, numerous single-site catalysts were developed for CO₂ reduction to produce value-added chemicals such as CO, CH₄, CH₃OH, formate, and C₂₊ products. Value-added chemicals have also been synthesized with the aid of amines and epoxides. This review summarizes recent state-of-the-art single-site catalysts and their application as heterogeneous catalysts for the electroreduction, photoreduction, and thermal reduction of CO₂. In the discussion, we will highlight the structure-activity relationships for the catalytic conversion of CO₂ with single-site catalysts.     

多金属氧酸盐材料在二氧化碳电催化还原领域中的研究进展

随着工业发展和全球人口的持续增长,人类对化石燃料的消耗日益增加,从而导致大气中二氧化碳含量的显著增加以及与之相伴的一系列环境问题.电化学还原二氧化碳制备高附加值的燃料和化学品具有稳定的效率和较高的经济可行性等特点,目前已成为一种有前景的策略来缓解当前全球面临的能源短缺和气候变暖问题.然而,电催化二氧化碳还原过程存在反应...     

Supported molecular catalysts for the heterogeneous CO2 electroreduction

The thorough understanding of homogeneous catalysis has triggered intense research activities on the immobilization of molecular catalysts for the heterogeneous CO₂ electroreduction. Herein, we discuss recent advances in the heterogeneous field with focus on the intrinsic effect coming from the catalyst structure and the extrinsic effect exerted by the catalyst immobilization strategy and support material on the catalytic performance.     

石墨烯基二氧化碳电化学还原催化剂的研究进展

利用电催化技术将CO₂转化为小分子燃料或高值化学品是实现原子经济、构建人工碳循环的绿色能源技术之一。电催化还原CO₂ (ECR)的反应条件温和、产物多样(C₁、C₂和C₂₊),有极大的发展潜力。然而,ECR技术面临一些需要解决的挑战性问题,包括电极过电势高、C₂及C₂₊产物选择性低、伴随析氢反应等。解决这些问题的关键在于创制低成本、高性能电催化剂。近年来,石墨烯基电催化剂的研究成为ECR领域的热点之一,原因包括：1)在电化学环境中稳定性好;2)表面原子、电子结构可调,进而实现材料催化活性的调控;3)维度可调,易暴露较大的比表面积和形成层次孔结构;4)耦合石墨烯的高导电性与特定材料的高活性,可协同提升ECR催化性能。本文评述了石墨烯基材料在ECR中的研究进展,详述了石墨烯基电催化剂的构筑方法,探讨并梳理了石墨烯的点/线缺陷、表面官能团、掺杂原子构型、金属单原子种类、材料表界面性质等与ECR性能之间的本征构效关系。最后展望了石墨烯基催化剂在ECR领域中的挑战和未来发展。     

Theoretical insights into pyridinium-based photoelectrocatalytic reduction of CO2

The role of pyridinium cations in electrochemistry has been believed known for decades, and their radical forms have been proposed as key intermediates in modern photoelectrocatalytic CO(2) reduction processes. Using first-principles density functional theory and continuum solvation models, we have calculated acidity constants for pyridinium cations and their corresponding pyridinyl radicals, as well as their electrochemical redox potentials. Contrary to previous assumptions, our results show that these species can be ruled out as active participants in homogeneous electrochemistry. A comparison of calculated acidities and redox potentials indicates that pyridinium cations behave differently than previously thought, and that the electrode surface plays a critical (but still unknown) role in pyridinium reduction. This work substantially alters the mechanistic view of pyridinium-catalyzed photoelectrochemical CO(2) reduction.     

铜基串联催化剂电催化CO2还原的研究进展

化石燃料的燃烧和其他人类活动排放了大量的CO₂气体,引发了诸多环境问题。电催化CO₂还原反应(CO₂RR)可以储存间歇可再生能源,实现人为闭合碳循环,被认为是获得高附加值化学品和燃料的有效途径。电催化CO₂RR涉及多个电子-质子转移步骤,其中^*CO通常被认为是关键中间体。铜由于对^*CO具有合适的吸附能,已被广泛证明是唯一能够有效地将CO₂还原为碳氢化合物和含氧化合物的金属催化剂。然而,纯Cu稳定性差、产品选择性低、过电位高,阻碍了工业级多碳产品的生产。构筑Cu基串联催化剂是提高CO₂RR性能的一种有前途的策略。本文首先介绍电催化CO₂RR的反应路线和串联机理。然后,系统地总结铜基串联催化剂对电催化CO₂RR的最新研究进展。最后,提出合理设计和可控合成新型电催化CO₂RR串联催化剂面临的挑战和机遇。     

铜基串联催化剂电催化CO2还原的研究进展

Through the combustion of fossil fuels and other human activities, large amounts of CO₂ gas have been emitted into the atmosphere, causing many environmental problems, such as the greenhouse effect and global warming. Thus, developing and utilizing renewable clean energy is crucial to reduce CO₂ emission and achieve carbon neutrality. The electrochemical CO₂ reduction reaction (CO₂RR) has been considered as an effective approach to obtain high value-added chemicals and fuels, which can store intermittent renewable energy and achieve the artificial carbon cycle. In addition, due to its multiple advantages, such as mild reaction conditions, tunable products, and simple implementation, electrochemical CO₂RR has attracted extensive attention. Electrochemical CO₂RR involves multiple electron–proton transfer steps to obtain multitudinous products, such as C₁ products (CO, HCOOH, CH₄, etc.) and C₂ products (C₂H₄, C₂H₅OH, etc.). The intermediates, among which ^*CO is usually identified as the key intermediate, and reaction pathways of different products intersect, resulting in an extremely complex reaction mechanism. Currently, copper has been widely proven to be the only metal catalyst that can efficiently reduce CO₂ to hydrocarbons and oxygenates due to its suitable adsorption energy for ^*CO. However, the low product selectivity, poor stability, and high overpotential of pure Cu hinder its use for the production of industrial-grade multi-carbon products. Tandem catalysts with multiple types of active sites can sequentially reduce CO₂ molecules into desired products. When loaded onto a co-catalyst that can efficiently convert CO₂ to ^*CO (such as Au and Ag), Cu acts as an electron donor owing to its high electrochemical potential. ^*CO species generated from the substrate can spillover onto the surface of electron-poor Cu due to the stronger adsorption and be further reduced to C₂₊ products. The use of Cu-based tandem catalysts for electrochemical CO₂RR is a promising strategy for improving the performance of CO₂RR and thus, has become a research hotspot in recent years. In this review, we first introduce the reaction routes and tandem mechanisms of electrochemical CO₂RR. Then, we systematically summarize the recent research progress of Cu-based tandem catalysts for electrochemical CO₂RR, including Cu-based metallic materials (alloys, heterojunction, and core-shell structures) as well as Cu-based framework materials, carbon materials, and polymer-modified materials. Importantly, the preparation methods of various Cu-based tandem catalysts and their structure–activity relationship in CO₂RR are discussed and analyzed in detail. Finally, the challenges and opportunities of the rational design and controllable synthesis of advanced tandem catalysts for electrochemical CO₂RR are proposed.     

钴联吡啶配合物在硅电极表面高效光电催化二氧化碳还原反应（英文）

光驱动二氧化碳还原实现可再生能源转化近年来引起普遍关注.利用小分子金属配合物电催化剂和吸光半导体材料构建的光电催化体系兼具电催化剂的高选择性和光电极的高光电转化效率等优点,在能源催化领域的应用日益广泛.已有将贵金属配合物催化剂用于光电催化二氧化碳还原的研究报道,但催化剂成本较高且制备方法不简便,在规模化实际应用中受到局限.基于早期的研究报道,我们发现非贵金属多联吡啶铁钴镍配合物在乙腈电解质中能高选择性电催化还原二氧化碳.结合半导体材料的特异性电荷分离性能从而将光能高效转化为电能驱动催化反应进行,我们选择廉价且易于制备的多联吡啶钴配合物催化剂,利用半导体硅晶片光电极,实现了均相体系二氧化碳的高效光电催化还原.我们采用电化学循环伏安法和恒电位电解法分别研究了催化剂在干燥和加水电解质环境中的催化还原行为,并且进一步研究了微量质子源的加入对半导体界面催化过程的影响,从而提出一种能改善半导体光电催化体系选择性的新方法.首先我们构建了电化学三电极体系,研究了在暗环境下三联吡啶钴和二联吡啶钴这两种配合物催化还原二氧化碳的电流密度和电解产物分布情况.由循环伏安曲线发现,这两种配合物都有两组催化还原峰,第二个基于吡啶配体还原的峰具有明显的催化特性.少量水的加入能进一步增加催化电流强度,而三联吡啶钴配合物的催化增强效果更加显著.在变扫速条件下将电流密度对扫速平方根进行归一化处理,发现无论在干燥环境还是少量加水环境下,两种催化剂的归一化电流密度均随扫速降低而明显增强,证明了催化剂具有电催化特性.推测水的催化增强作用可能与质子化电催化过程活性中间体有关.恒电位电解结果说明电催化产物以一氧化碳为主.基于上述研究,我们构建了光电化学三电极体系,以单晶硅片为工作电极,研究了在光照环境下这两种配合物催化还原二氧化碳的电流密度和电解产物分布情况.研究发现,催化剂对二氧化碳仍具有催化活性,光电压为400 m V.不同于硅线电极加水导致产氢,改用少量甲醇做质子源后,光电流强度进一步增强,竞争性产氢受到了抑制,从而使一氧化碳的法拉第效率得到显著提高,分别优化为94%和83%,并且光电流在14h内保持稳定.推测甲醇质子源的催化增强作用可能是与改变光电极液接界面传质动力学过程有关.     

Synergistic Porosity and Charge Effects in a Supramolecular Porphyrin Cage Promote Efficient Photocatalytic CO2 Reduction**

We present a supramolecular approach to catalyzing photochemical CO₂ reduction through second-sphere porosity and charge effects. An iron porphyrin box ( PB ) bearing 24 cationic groups, FePB-2(P) , was made via post-synthetic modification of an alkyne-functionalized supramolecular synthon. FePB-2(P) promotes the photochemical CO₂ reduction reaction (CO₂RR) with 97 % selectivity for CO product, achieving turnover numbers (TON) exceeding 7000 and initial turnover frequencies (TOF_max) reaching 1400 min⁻¹. The cooperativity between porosity and charge results in a 41-fold increase in activity relative to the parent Fe tetraphenylporphyrin ( FeTPP ) catalyst, which is far greater than analogs that augment catalysis through porosity ( FePB-3(N ), 4-fold increase) or charge (Fe p-tetramethylanilinium porphyrin ( Fe-p-TMA ), 6-fold increase) alone. This work establishes that synergistic pendants in the secondary coordination sphere can be leveraged as a design element to augment catalysis at primary active sites within confined spaces.     

Advances in the electrochemical catalytic reduction of CO2 with metal complexes

Electrocatalytic CO₂ reduction has emerged as a promising strategy to effectively produce fuels and chemicals sustainably. In this regard, the study of electrochemical catalytic reduction of CO₂ with metal complexes is a powerful tool for both the development of catalysts that operated under desired conditions (low overpotentials, high catalytic rates and selectivity, and extended durability) and the understanding of basic principles in catalysis. To illustrate the state-of-the-art, this revision presents a selection of the most recent and remarkable findings reported in terms of key strategies to improve reaction rates, selectivity and mechanism understanding for the leading families of homogeneous catalysts.     

燃料电池中Pt基催化剂对CO的催化氧化

燃料电池具有燃料多样性、噪声低、对环境污染小等优势,近年来备受研究者关注。然而,电池中的贵金属催化剂极易被少量的CO毒化,成为制约其商业化的一大障碍。因此,设计出高性能的催化剂对于推动燃料电池的发展十分关键。本文综述了燃料电池中铂(Pt)基催化剂对CO催化氧化的研究现状,首先探讨了CO催化氧化机理以及CO在Pt金属表面化学吸附的机理,其次详细介绍了Pt负载型催化剂、双金属催化剂以及助催化剂在催化反应中的不同作用,然后简单分析了影响Pt基催化剂性能的其他因素。最后,对燃料电池中Pt基催化剂的研究方向作了进一步的展望,旨在为燃料电池中CO催化氧化的发展开拓新思路。     

Promoting electrochemical reduction of CO2 to ethanol by B/N-doped sp3/sp2 nanocarbon electrode

Electrochemical reduction of CO₂ to value-added chemicals holds promise for carbon utilization and renewable electricity storage. However, selective CO₂ reduction to multi-carbon fuels remains a significant challenge. Here, we report that B/N-doped sp³/sp² hybridized nanocarbon (BNHC), consisting of ultra-small nanoparticles with a sp³ carbon core covered by a sp² carbon shell, is an efficient electrocatalyst for electrochemical reduction of CO₂ to ethanol at relatively low overpotentials. CO₂ reduction occurs with a Faradaic efficiency of 58.8%-69.1% for ethanol and acetate production at ?0.5 ～ ?0.6 V (vs. RHE), among which 51.6%-56.0% is for ethanol. The high selectivity for ethanol is due to the integrated effect of sp³/sp² carbon and B/N doping. Both sp³ carbon and B/N doping contribute to enhanced ethanol production with sp² carbon reducing the overpotential for CO₂ reduction to ethanol.     

Co-Dissolved Isostructural Polyoxovanadates to Construct Single-Atom-Site Catalysts for Efficient CO2 Photoreduction

We explored a co-dissolved strategy to embed mono-dispersed Pt center into V₂O₅ support via dissolving [PtV₉O₂₈]⁷⁻ into [V₁₀O₂₈]⁶⁻ aqueous solution. The uniform dispersion of [PtV₉O₂₈]⁷⁻ in [V₁₀O₂₈]⁶⁻ solution allows [PtV₉O₂₈]⁷⁻ to be surrounded by [V₁₀O₂₈]⁶⁻ clusters via a freeze-drying process. The V centers in both [PtV₉O₂₈]⁷⁻ and [V₁₀O₂₈]⁶⁻ were converted into V₂O₅ via a calcination process to stabilize Pt center. These double separations can effectively prevent the Pt center agglomeration during the high-temperature conversion process, and achieve 100 % utilization of Pt in [PtV₉O₂₈]⁷⁻. The resulting Pt-V₂O₅ single-atom-site catalysts exhibit a CH₄ yield of 247.6 μmol g⁻¹ h⁻¹, 25 times higher than that of Pt nanoparticle on the V₂O₅ support, which was accompanied by the lactic acid photooxidation to form pyruvic acid. Systematical investigations on this unambiguous structure demonstrate an important role of Pt−O atomic pair synergy for highly efficient CO₂ photoreduction.     

Active Sites of Cobalt Phthalocyanine in Electrocatalytic CO2 Reduction to Methanol

Many metal coordination compounds catalyze CO₂ electroreduction to CO, but cobalt phthalocyanine hybridized with conductive carbon such as carbon nanotubes is currently the only one that can generate methanol. The underlying structure–reactivity correlation and reaction mechanism desperately demand elucidation. Here we report the first in situ X-ray absorption spectroscopy characterization, combined with ex situ spectroscopic and electrocatalytic measurements, to study CoPc-catalyzed CO₂ reduction to methanol. Molecular dispersion of CoPc on CNT surfaces, as evidenced by the observed electronic interaction between the two, is crucial to fast electron transfer to the active sites and multi-electron CO₂ reduction. CO, the key intermediate in the CO₂-to-methanol pathway, is found to be labile on the active site, which necessitates a high local concentration in the microenvironment to compete with CO₂ for active sites and promote methanol production. A comparison of the electrocatalytic performance of structurally related porphyrins indicates that the bridging aza-N atoms of the Pc macrocycle are critical components of the CoPc active site that produces methanol. In situ X-ray absorption spectroscopy identifies the active site as Co(I) and supports an increasingly non-centrosymmetric Co coordination environment at negative applied potential, likely due to the formation of a Co−CO adduct during the catalysis.     

Recent advances in 1D nanostructured catalysts for photothermal and photocatalytic reduction of CO2

The development of photocatalysts that can efficiently convert CO₂ into other valuable chemicals via photocatalytic and photothermal processes is critical to the current energy and climate change problems. However, low separation of charge carriers, short light absorption, and low activation of CO₂ molecules in photocatalysis limit the catalysts’ performance. Designing 1D heterostructures containing multiple materials can be a viable solution as their unique properties, such as high surface area, short diffusion paths of charge carriers, and enhanced light absorption properties, can potentially promote the reaction rate and product selectivity. In this review, we summarize the general features of heterostructures involving nanotubes, nanowires, nanorods, and nanobelts. Next, the main synthesis strategies are briefly highlighted, followed by the most important findings concerning their catalytic activity in the photothermal and photocatalytic CO₂ reduction processes. The article concludes with some of the current challenges and potential solutions.     

Mechanistic Elucidations of Highly Dispersed Metalloporphyrin Metal-Organic Framework Catalysts for CO2 Electroreduction

Immobilization of porphyrin complexes into crystalline metal–organic frameworks (MOFs) enables high exposure of porphyrin active sites for CO₂ electroreduction. Herein, well-dispersed iron-porphyrin-based MOF (PCN-222(Fe)) on carbon-based electrodes revealed optimal turnover frequencies for CO₂ electroreduction to CO at 1 wt.% catalyst loading, beyond which the intrinsic catalyst activity declined due to CO₂ mass transport limitations. In situ Raman suggested that PCN-222(Fe) maintained its structure under electrochemical bias, permitting mechanistic investigations. These revealed a stepwise electron transfer-proton transfer mechanism for CO₂ electroreduction on PCN-222(Fe) electrodes, which followed a shift from a rate-limiting electron transfer to CO₂ mass transfer as the potential increased from −0.6 V to −1.0 V vs. RHE. Our results demonstrate how intrinsic catalytic investigations and in situ spectroscopy are needed to elucidate CO₂ electroreduction mechanisms on PCN-222(Fe) MOFs.     

Inorganic semiconductors-graphene composites in photo(electro)catalysis: Synthetic strategies,interaction mechanisms and applications

The remarkable physicochemical properties of graphene (GR) and derivatives can be leveraged in the photocatalytic activity of GR-semiconductor photocatalysts. The hitherto state of knowledge on the role of GR in these composite materials is insufficient and leaves many questions unanswered, thus it is imperative to fully understand the interaction mechanisms between GR and inorganic semiconductors. Detailed study and optimization of the features related to the interface are still very much sought to efficiently design photocatalysts targeting their eventual commercialization. This review shows that photocatalytic activity of such composites depends not only on high GR electron mobility and charge transfer, but also on the properties of the interface (such as interface morphology, size, crystal phases and facet, dimensionality of composites, etc.). Focusing on the last advancements in this field, this review analyses the challenges involved in the synthetic strategies of GR-semiconductor photo(electro)catalysts in various applications including pollutant degradation, organic synthesis, hydrogen evolution and photoreduction of carbon dioxide (CO₂). Mechanism of interaction between GR and semiconductors are thoroughly discussed by examining the proposed mechanism in the diverse areas where the composite materials are employed in photo(electro)catalytic processes. In addition, various synthetic and characterization technique available hitherto are presented, since they are pivotal to the understanding of the composites properties (such as morphology, crystal phases and exposed facets, degree of crystallinity, dimensionality etc.), and even to shed more light on interaction mechanisms of the photocatalyst constituents. As a future outlook, it is envisaged that research will not only focus on optimizing GR electrical and chemical properties, yet in the synthesis of GR-semiconductor photocatalysts attention needs also be placed on the properties of the resulting composites, using suitable synthetic methods and proper characterizations to assess their performance.     

Organic molecules involved in Cu-based electrocatalysts for selective CO2 reduction to C2+ products

Electrocatalytic carbon dioxide (CO₂) reduction reaction (CO₂RR) is a promising process to mitigate the environmental issues caused by CO₂, as well as to produce valuable multicarbon (C₂₊) products. Significant progresses have been made to explore highly efficient Cu-based electrocatalysts for CO₂RR in recent years. Adding organic molecules into electrocatalytic systems can tune the CO₂ interaction with the electrocatalysts for CO₂RR, therefore, the final C₂₊ products, which are not solely achieved by inorganic modification. In this review, we will summarize the recent progress of the organic molecules participation in CO₂ electroreduction to C₂₊ products on Cu-based electrocatalysts. The applied organic molecules are reviewed based on the heteroatoms (N and S), with the emphasis on their roles in activity and selectivity toward C₂₊ products. A perspective on the application of organic molecules for efficient and selective CO₂RR has been provided.