MOF衍生碳基电催化剂限域催化O2还原和CO2还原反应

化石燃料的大量消耗和环境的逐渐恶化导致迫切需要开发和探索有效的能源转换和存储技术. 电化学是各种能源转换装置的基础和关键. 设计和合成具有高催化活性的非贵金属基和非金属基催化剂是最好的选择. 金属有机骨架(MOF)衍生的碳基材料具有比表面积大、 孔隙率高的特点, 可以选择性地限制不同类型的金属. 因此, MOF衍生碳作为催化剂载体使用时具有良好的限域效应, 有利于提高催化剂的活性和稳定性. 本文综合评述了MOF衍生材料在催化反应中的限域效应, 并介绍了MOF衍生碳基材料在氧还原反应(ORR)和二氧化碳还原反应(CO₂RR)电催化方面的最新进展, 揭示了MOF碳基材料在电催化反应中的构效关系. 最后, 讨论了MOF衍生的碳基材料在ORR和CO₂RR电催化中的挑战和机遇, 以及未来可能的解决方案.     

CO2电还原用氮掺杂碳基过渡金属单原子催化剂

温和条件下将CO₂电催化还原(CO₂RR)为高能量密度燃料和高附加值碳产品是降低大气中CO₂浓度、储存间歇性可再生能源、实现碳中和的重要途径之一。设计和开发对电催化CO₂RR兼具高活性、高选择性、高稳定性、且对析氢反应(HER)具有显著抑制作用的高性能廉价催化剂是CO₂RR研究的关键。单原子催化剂(SACs)由于其独特的电子结构和几何结构对许多重要化学反应(如CO氧化反应、加氢反应、析氧反应、氧还原反应、析氢反应等)显示出优异的催化活性而广受关注。近年来,N掺杂多孔碳载体过渡金属单原子催化材料(M-N-C)显示出对电化学二氧化碳还原的广阔前景、并有望成为在水相电解质中还原CO₂的贵金属(Au,Ag)催化剂的替代品。本文从单原子催化材料M-N-C的制备、影响电催化性能的因素及MN_x活性基团三个方向介绍了单原子催化剂M-N-C电催化CO₂RR的研究现状和进展。最后,就目前该方向研究中尚待解决的问题进行了总结、并对下一步的研究进行了展望。     

用于氧还原反应的双原子钴-铁催化剂（英文）

金属-空气电池因其高效率和便携性受到广泛关注.然而,氧还原反应(ORR)的高能垒和缓慢的动力学导致其输出功率低.尽管贵金属铂基材料具有较高的ORR活性,但其在工业上的大规模应用受到高成本的制约.因此,迫切需要以储量丰富的非贵金属为原料,开发具有低成本、高性能和耐用性的催化剂.近年来,单原子过渡金属与氮共掺杂碳材料(M-N-C)成为替代贵金属催化剂的理想材料.理论模拟和实验结果均表明,单原子Fe/Co-N-C催化剂具有良好的ORR活性,其中FeN₄和CoN₄构型被认为是主要活性位点.此外,含有相邻金属位点的双金属单原子催化剂具有加速ORR动力学的巨大潜力.通过对ORR中间体的桥式-顺式吸附,双金属位点可以促进O-O键的裂解,从而提高催化活性.除固有活性外,双金属位点可减少ORR过程中含氧中间体对M-N键的攻击,提高M-N-C对ORR的耐久性和工业应用潜力.因此,近年来,研究者开始探索双金属单原子催化剂的合成和电催化性能,发现Fe-Co, Fe-Mn, Fe-Cu, Co-Zn和Co-Pt双位点可以有效催化ORR.为进一步提高ORR活性,需要合理...     

过渡金属单原子电催化剂还原CO2制CO

电催化二氧化碳还原(ECR)技术是实现“碳中和”目标的一种理想途径,而过渡金属单原子催化剂具有电子结构可调、原子利用率高和活性位点均一等特点,在ECR研究中具有显著优势。本文首先介绍了单原子电催化剂在还原CO₂尤其是在选择性生成CO研究中的优势,然后综述了近年来Fe、Co、Ni及其他单原子电催化剂的反应位点调控策略与电催化选择性的调控机制,重点对质子耦合CO₂还原生成CO的中间过程调控进行了归纳总结,并简要展望了发展方向,以期为推动单原子催化剂在ECR中规模化应用提供指导和参考。     

单原子Co位点的CO2还原反应路径:局部配位环境的影响

在CO2还原反应(CO2RR)应中,单原子催化剂被认为是很有前途的电催化剂.Co-N4活性位点因其优异的CO选择性和活性而受到广泛关注.然而,Co位点的局部配位环境与CO2RR途径之间的相关性尚不明确.本文采用密度泛函理论(DFT)计算,研究了含1,10-菲咯啉基底的N4-大环配体(Co-N4-CPY)负载的CoN4位...     

铜基电催化剂还原CO2

温室气体CO₂的大量排放给全球气候造成潜在威胁,电化学还原CO₂为有用的化工产品作为一种人为的碳循环的方式,拓展了新的利用CO₂的可能性,并且是一种很有前景的显著改善环境、促进可持续发展的方法。然而,在转化CO₂为有价值的产品过程中,最大的挑战是抑制析氢副反应的同时达不到高效率、高选择性。铜因其在电催化还原CO₂过程中优异的催化性能而得到广泛关注。本文重点介绍了近年来电催化还原CO₂的发展以及电化学转化CO₂的优缺点,介绍了CO₂RR的热力学与动力学研究并概述了Cu电极、Cu MOFs材料电极以及通过氧化、合金化、纳米化和表面修饰等方法修饰的铜电极的进展,但是电催化还原CO₂的反应机理尚不太确定。最后,讨论了未来铜基电极催化剂高效率地选择性转化CO₂会面临的挑战和可能研究的方向。     

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.     

Modulating the Reaction Configuration by Breaking the Structural Symmetry of Active Sites for Efficient Photocatalytic Reduction of Low-concentration CO2

Photocatalytic conversion of low-concentration CO₂ is considered as a promising way to simultaneously mitigate the environmental and energy issues. However, the weak CO₂ adsorption and tough CO₂ activation process seriously compromise the CO production, due to the chemical inertness of CO₂ molecule and the formed fragile metal-C/O bond. Herein, we designed and fabricated oxygen vacancy contained Co₃O₄ hollow nanoparticles on ordered macroporous N-doped carbon framework (Vo−HCo₃O₄/OMNC) towards photoreduction of low-concentration CO₂. In situ spectra and ab initio molecular dynamics simulations reveal that the constructed oxygen vacancy is able to break the local structural symmetry of Co−O−Co sites. The formation of asymmetric active site switches the CO₂ configuration from a single-site linear model to a multiple-sites bending one with a highly stable configuration, enhancing the binding and structural polarization of CO₂ molecules. As a result, Vo−HCo₃O₄/OMNC shows unprecedent activity in the photocatalytic conversion of low-concentration CO₂ (10 % CO₂/Ar) under laboratory light source or even natural sunlight, affording a syngas yield of 337.8 or 95.2 mmol g⁻¹ h⁻¹, respectively, with an apparent quantum yield up to 4.2 %.     

Positive Valent Metal Sites in Electrochemical CO2 Reduction Reaction

The discovery of high-performance catalysts for the electrochemical CO₂ reduction reaction ( CO₂RR) has faced an enormous challenge for years. The lack of cognition about the surface active structures or centers of catalysts in complex conditions limits the development of advanced catalysts for CO₂RR. Recently, the positive valent metal sites (PVMS) are demonstrated as a kind of potential active sites, which can facilitate carbon dioxide (CO₂) activation and conversation but are always unstable under reduction potentials. Many advanced technologies in theory and experiment have been utilized to understand and develop excellent catalysts with PVMS for CO₂RR. Here, we present an introduction of some typical catalysts with PVMS in CO₂RR and give some understanding of the activity and stability for these related catalysts.     

CoPy/C催化氧还原的碱效应及活性位研究

以碳黑(Vulcan XC-72R)为载体, 硫酸钴(CoSO₄ · 7H₂O)和吡啶(Py)作为催化剂前躯体, 经溶剂分散及800℃热处理可制备出高效催化氧还原反应(ORR)的碳载钴吡啶复合催化剂(15%Co25%Py/C, 质量分数). 采用红外光谱(IR)和X射线光电子能谱(XPS)等对催化剂的结构进行表征. 运用旋转圆盘电极(RDE)技术研究了不同浓度的KOH溶液(0.05~12.0 mol/L)对CoPy/C催化氧还原活性的影响. 结果表明, 不同浓度的KOH溶液对CoPy/C催化剂催化氧还原反应(ORR)的性能影响很大, 在0.05和0.1 mol/L KOH溶液中催化剂活性最高. 以其制备的气体扩散电极在0.05 mol/L KOH溶液(O₂气氛)中的半波电位为-0.138 V, 起峰电位为0.10 V, 同时表现出明显的极限扩散电流. 在-0.381 V时电流密度达到最大值(4.39 mA/cm²). 随着KOH溶液浓度的增加(pH值下降), 起始电压沿负方向移动, 同时动力学、 混合动力学和扩散区的电流密度均下降. RDE研究结果表明, 在0.05和0.1 mol/L KOH溶液中, O₂在CoPy/C电极上的还原主要经4e^-过程还原成H₂O. XPS研究结果表明, 吡啶作为小分子富氮源对提高催化剂的活性具有重要作用, 所制备催化剂经800℃高温热处理形成了石墨N, 吡啶N以及部分氧化态的氮结构, 其中石墨N和吡啶N作为催化剂的活性中心, 提供氧还原活性位, 从而使该类催化剂对氧还原表现出很好的电催化性能和选择性.     

Non-Interacting Ni and Fe Dual-Atom Pair Sites in N-Doped Carbon Catalysts for Efficient Concentrating Solar-Driven Photothermal CO2 Reduction

Solar-to-chemical energy conversion under weak solar irradiation is generally difficult to meet the heat demand of CO₂ reduction. Herein, a new concentrated solar-driven photothermal system coupling a dual-metal single-atom catalyst (DSAC) with adjacent Ni−N₄ and Fe−N₄ pair sites is designed for boosting gas-solid CO₂ reduction with H₂O under simulated solar irradiation, even under ambient sunlight. As expected, the (Ni, Fe)−N−C DSAC exhibits a superior photothermal catalytic performance for CO₂ reduction to CO (86.16 μmol g⁻¹ h⁻¹), CH₄ (135.35 μmol g⁻¹ h⁻¹) and CH₃OH (59.81 μmol g⁻¹ h⁻¹), which are equivalent to 1.70-fold, 1.27-fold and 1.23-fold higher than those of the Fe−N−C catalyst, respectively. Based on theoretical simulations, the Fermi level and d-band center of Fe atom is efficiently regulated in non-interacting Ni and Fe dual-atom pair sites with electronic interaction through electron orbital hybridization on (Ni, Fe)−N−C DSAC. Crucially, the distance between adjacent Ni and Fe atoms of the Ni−N−N−Fe configuration means that the additional Ni atom as a new active site contributes to the main *COOH and *HCO₃ dissociation to optimize the corresponding energy barriers in the reaction process, leading to specific dual reaction pathways (COOH and HCO₃ pathways) for solar-driven photothermal CO₂ reduction to initial CO production.     

Oxygen-Bridged Indium-Nickel Atomic Pair as Dual-Metal Active Sites Enabling Synergistic Electrocatalytic CO2 Reduction

Single-atom catalysts offer a promising pathway for electrochemical CO₂ conversion. However, it is still a challenge to optimize the electrochemical performance of dual-atom catalysts. Here, an atomic indium-nickel dual-sites catalyst bridged by an axial oxygen atom (O-In-N₆-Ni moiety) was anchored on nitrogenated carbon (InNi DS/NC). InNi DS/NC exhibits superior CO selectivity with Faradaic efficiency higher than 90 % over a wide potential range from −0.5 to −0.8 V versus reversible hydrogen electrode (vs. RHE). Moreover, an industrial CO partial current density up to 317.2 mA cm⁻² is achieved at −1.0 V vs. RHE in a flow cell. In situ ATR-SEIRAS combined with theory calculations reveal that the synergistic effect of In-Ni dual-sites and O atom bridge not only reduces the reaction barrier for the formation of *COOH, but also retards the undesired hydrogen evolution reaction. This work provides a feasible strategy to construct dual-site catalysts towards energy conversion.     

碳基非贵金属氧还原电催化剂的活性位结构研究进展

以热解型Fe/N/C为代表的碳基非贵金属材料被认为是当前最具潜力替代铂的非贵金属氧还原催化剂,其综合性能的进一步突破,对于推动质子交换膜燃料电池商业化应用具有重要意义。对热解型Fe/N/C催化剂活性位结构的深入认识是实现催化剂高活性位密度和高稳定性理性设计的关键。本文总结了热解型Fe/N/C活性位的研究进展,重点介绍了非晶态铁氮配位活性中心、氮掺杂和碳缺陷三类活性位构型。由于热解型Fe/N/C是非均相的,结构非常复杂,导致在活性位认识上还存在诸多争议,本文总结阐述了活性位结构的不同观点。最后,我们展望了Fe/N/C催化剂活性位研究的未来方向。     

Photocatalytic Reduction of CO2 to HCOOH and CO by a Phosphine-Bipyridine-Phosphine Ir(III) Catalyst: Photophysics,Nonadiabatic Effects,Mechanism, and Selectivity

Photocatalytic CO₂ reduction is one of the best solutions to solve the global energy crisis and to realize carbon neutralization. The tetradentate phosphine-bipyridine (bpy)-phosphine (PNNP)-type Ir(III) photocatalyst, Mes-IrPCY2, was reported with a high HCOOH selectivity but the photocatalytic mechanism remains elusive. Herein, we employ electronic structure methods in combination with radiative, nonradiative, and electron transfer rate calculations, to explore the entire photocatalytic cycle to either HCOOH or CO, based on which a new mechanistic scenario is proposed. The catalytic reduction reaction starts from the generation of the precursor metal-to-ligand charge transfer (³MLCT) state. Subsequently, the divergence happens from the ³MLCT state, the single electron transfer (SET) and deprotonation process lead to the formation of one-electron-reduced species and Ir(I) species, which initiate the reduction reaction to HCOOH and CO, respectively. Interestingly, the efficient occurrence of proton or electron transfer reduces barriers of critical steps. In addition, nonadiabatic transitions play a nonnegligible role in the cycle. We suggest a lower free-energy barrier in the reaction-limiting step and the very efficient SET in ³MLCT are cooperatively responsible for a high HCOOH selectivity. The gained mechanistic insights could help chemists to understand, regulate, and design photocatalytic CO₂ reduction reaction of similar function-integrated molecular photocatalyst.     

Covalently Grafting Graphene onto Si Photocathode to Expedite Aqueous Photoelectrochemical CO2 Reduction

Silicon semiconductor functionalized with molecular catalysts emerges as a promising cathode for photoelectrochemical (PEC) CO₂ reduction reaction (CO₂RR). However, the limited kinetics and stabilities remains a major hurdle for the development of such composites. We herein report an assembling strategy of silicon photocathodes via chemically grafting a conductive graphene layer onto the surface of n⁺-p Si followed by catalyst immobilization. The covalently-linked graphene layer effectively enhances the photogenerated carriers transfer between the cathode and the reduction catalyst, and improves the operating stability of the electrode. Strikingly, we demonstrate that altering the stacking configuration of the immobilized cobalt tetraphenylporphyrin (CoTPP) catalyst through calcination can further enhance the electron transfer rate and the PEC performance. At the end, the graphene-coated Si cathode immobilized with CoTPP catalyst managed to sustain a stable 1-Sun photocurrent of −1.65 mA cm⁻² over 16 h for CO production in water at a near neutral potential of −0.1 V vs. reversible hydrogen electrode. This represents a remarkable improvement of PEC CO₂RR performance in contrast to the reported photocathodes functionalized with molecular catalysts.     

调控强活性位点的智能光响应CO2吸附剂

光响应CO₂吸附剂能够通过外部光照的方式有效调节其捕获CO₂的能力,在吸附过程中具有可控性好和能源利用效率高的优势.然而目前报道的光响应CO₂吸附剂主要用于对弱吸附位点的调控,对强吸附位点的调控仍然是一项具有挑战性的任务.本工作构筑了一种光响应智能吸附剂,实现了对CO₂强吸附位点的光响应调控.吸附剂的构筑通过将具有顺反异构体的偶氮苯衍生物和含有伯胺的硅烷偶联剂引入介孔氧化硅实现.光照前偶氮苯处于反式构型,导致伯胺的静电势降低,充分暴露活性位;光照后偶氮苯转变为顺式构型,导致伯胺静电势的增加以及活性位点的遮蔽.吸附量在两种状态下的变化率能够达到43%,并且这一调节过程是可逆的.偶氮苯在不同构型下对伯胺的静电势产生了差异化的影响,从而实现了对吸附能力的调控.