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1.
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.  相似文献   

2.
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.  相似文献   

3.
采用原位阳极氧化-煅烧法制备TiO_2纳米管(TiO_2NTs)电极,运用X射线衍射(XRD)、电场发射扫描电子显微镜(FESEM)、X射线光电子能谱(XPS)、双电位阶跃测试等对制备电极进行表征,考察了其在0.1mol?L~(-1) KHCO_3水溶液中电化学还原CO_2的催化活性。结果表明TiO_2NTs电极上电化学还原CO_2的主产物为CH_3OH,CH_3OH由HCOOH和HCHO进一步还原而来。电极制备的最佳煅烧温度为450℃(TiO_2NTs-450),电解电位-0.56 V(vs RHE(可逆氢电极))时反应120 min后,生成CH_3OH的法拉第效率和分电流密度分别为85.8%和0.2 m A?cm~(-2)。与550和650℃煅烧的电极相比,TiO_2NTs-450电极具有更高的催化活性,归因于电极表面更多的三价钛活性位,有利于CO_2吸附,从而对·CO_2-起到稳定的作用,速率控制步骤转变为·CO_2-的质子化反应。  相似文献   

4.
Conversion of CO2 into valuable molecules is a field of intensive investigation with the aim of developing scalable technologies for making fuels using renewable energy sources. While electrochemical reduction into CO and formate are approaching industrial maturity, a current challenge is obtaining more reduced products like methanol. However, literature on the matter is scarce, and even more for the use of molecular catalysts. Here, we demonstrate that cobalt phthalocyanine, a well‐known catalyst for the electrochemical conversion of CO2 to CO, can also catalyze the reaction from CO2 or CO to methanol in aqueous electrolytes at ambient conditions of temperature and pressure. The studies identify formaldehyde as a key intermediate and an unexpected pH effect on selectivity. This paves the way for establishing a sequential process where CO2 is first converted to CO which is subsequently used as a reactant to produce methanol. Under ideal conditions, the reaction shows a global Faradaic efficiency of 19.5 % and chemical selectivity of 7.5 %.  相似文献   

5.
Utilizing CO2-derived formaldehyde derivatives for fuel additive or polymer synthesis is a promising approach to reduce net carbon dioxide emissions. Existing methodologies involve converting CO2 to methanol by thermal hydrogenation, followed by electrochemical or thermochemical oxidation to produce formaldehyde. Adding to the conventional methanol oxidation pathway, we propose a new electrochemical approach to simultaneously generate formaldehyde derivatives at both electrodes by partial methanol oxidation and the direct reduction of CO2. To achieve this, a method to directly reduce CO2 to formaldehyde at the cathode is required. Still, it has been scarcely reported previously due to the acidity of the formic acid intermediate and the facile over-reduction of formaldehyde to methanol. By enabling the activation and subsequent stabilization of formic acid and formaldehyde respectively in methanol solvent, we were able to implement a strategy where formaldehyde derivatives were generated at the cathode alongside the anode. Further mechanism studies revealed that protons supplied from the anodic reaction contribute to the activation of formic acid and the stabilization of the formaldehyde product. Additionally, it was found that the cathodic formaldehyde derivative Faradaic efficiency can be further increased through prolonged electrolysis time up to 50 % along with a maximum anodic formaldehyde derivative Faradaic efficiency of 90 %.  相似文献   

6.
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.  相似文献   

7.
Fine-tuning electronic structures of single-atom catalysts (SACs) plays a crucial role in harnessing their catalytic activities, yet challenges remain at a molecular scale in a controlled fashion. By tailoring the structure of graphdiyne (GDY) with electron-withdrawing/-donating groups, we show herein the electronic perturbation of Cu single-atom CO2 reduction catalysts in a molecular way. The elaborately introduced functional groups (−F, −H and −OMe) can regulate the valance state of Cuδ+, which is found to be directly scaled with the selectivity of the electrochemical CO2-to-CH4 conversion. An optimum CH4 Faradaic efficiency of 72.3 % was achieved over the Cu SAC on the F-substituted GDY. In situ spectroscopic studies and theoretical calculations revealed that the positive Cuδ+ centers adjusted by the electron-withdrawing group decrease the pKa of adsorbed H2O, promoting the hydrogenation of intermediates toward the CH4 production. Our strategy paves the way for precise electronic perturbation of SACs toward efficient electrocatalysis.  相似文献   

8.
We present herein a Cp*Co(III)‐half‐sandwich catalyst system for electrocatalytic CO2 reduction in aqueous acetonitrile solution. In addition to an electron‐donating Cp* ligand (Cp*=pentamethylcyclopentadienyl), the catalyst featured a proton‐responsive pyridyl‐benzimidazole‐based N,N‐bidentate ligand. Owing to the presence of a relatively electron‐rich Co center, the reduced Co(I)‐state was made prone to activate the electrophilic carbon center of CO2. At the same time, the proton‐responsive benzimidazole scaffold was susceptible to facilitate proton‐transfer during the subsequent reduction of CO2. The above factors rendered the present catalyst active toward producing CO as the major product over the other potential 2e/2H+ reduced product HCOOH, in contrast to the only known similar half‐sandwich CpCo(III)‐based CO2‐reduction catalysts which produced HCOOH selectively. The system exhibited a Faradaic efficiency (FE) of about 70% while the overpotential for CO production was found to be 0.78 V, as determined by controlled‐potential electrolysis.  相似文献   

9.
The direct electrochemical conversion of CO2 to multi-carbon products offers a promising pathway for producing value-added chemicals using renewable electricity. However, producing ethanol remains a challenge because of the competitive ethylene formation and hydrogen evolution reactions. Herein, we propose an active hydrogen (*H)-intermediate-mediating strategy for ethanol electroproduction on a layered precursor-derived CuAl2O4/CuO catalyst. The catalyst delivered a Faradaic efficiency of 70 % for multi-carbon products and 41 % for ethanol at current density of 200 mA cm−2 and exhibited a continuous 150 h durability in a flow cell. The intensive spectroscopic studies combined with theoretical calculations revealed that the in situ generated CuAl2O4 could tailor *H intermediate coverage and the elevated *H coverage favors the hydrogenation of the *HCCOH intermediate, accounting for the increased yield of ethanol. This work directs a pathway for enhancing ethanol electroproduction from CO2 reduction by tailoring *H intermediate coverage.  相似文献   

10.
Electrochemical CO2 reduction to value-added chemicals or fuels offers a promising approach to reduce carbon emissions and alleviate energy shortage. Cu-based electrocatalysts have been widely reported as capable of reducing CO2 to produce a variety of multicarbon products (e.g., ethylene and ethanol). In this work, we develop sulfur-doped Cu2O electrocatalysts, which instead can electrochemically reduce CO2 to almost exclusively formate. We show that a dynamic equilibrium of S exists at the Cu2O-electrolyte interface, and S-doped Cu2O undergoes in situ surface reconstruction to generate active S-adsorbed metallic Cu sites during the CO2 reduction reaction (CO2RR). Density functional theory (DFT) calculations together with in situ infrared absorption spectroscopy measurements show that the S-adsorbed metallic Cu surface can not only promote the formation of the *OCHO intermediate but also greatly suppress *H and *COOH adsorption, thus facilitating CO2-to-formate conversion during the electrochemical CO2RR.  相似文献   

11.
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.  相似文献   

12.
甲醇在CeO2担载Pd催化剂上分解机理的研究   总被引:9,自引:0,他引:9  
采用原位红外(in-situFTIR)技术对甲醇在CeO2和Pd/CeO2催化剂上的吸附和反应进行了研究,提出一个新的甲醇分解反应机理模型.甲醇在CeO2上容易吸附并结合其晶格氧生成甲酸盐物种,而甲醇分解的产物氢被Pd活化后,溢流到CeO2上促进了甲酸盐物种的分解.Cl-的存在加强了Pd/CeO2催化剂与氢的相互作用,Pd和CeO2通过对氢和氧物种的作用对甲醇分解反应的过程表现出协同效应.  相似文献   

13.
In response to aggravated fossil resources consuming and greenhouse effect, CO2 reduction has become a globally important scientific issue because this method can be used to produce value-added feedstock for application in alternative energy supply. Photoelectrocatalysis, achieved by combining optical energy and external electrical bias, is a feasible and promising system for CO2 reduction. In particular, applying graphene in tuning photoelectrochemical CO2 reduction has aroused considerable attention because graphene is advantageous for enhancing CO2 adsorption, facilitating electrons transfer, and thus optimizing the performance of graphene-based composite electrodes. In this review, we elaborate the fundamental principle, basic preparation methods, and recent progress in developing a variety of graphene-based composite electrodes for photoelectrochemical reduction of CO2 into solar fuels and chemicals. We also present a perspective on the opportunities and challenges for future research in this booming area and highlight the potential evolution strategies for advancing the research on photoelectrochemical CO2 reduction.  相似文献   

14.
The direct catalytic conversion of atmospheric CO2 to valuable chemicals is a promising solution to avert negative consequences of rising CO2 concentration. However, heterogeneous catalysts efficient at low partial pressures of CO2 still need to be developed. Here, we explore Co/CeO2 as a catalyst for the methanation of diluted CO2 streams. This material displays an excellent performance at reaction temperatures as low as 175 °C and CO2 partial pressures as low as 0.4 mbar (the atmospheric CO2 concentration). To gain mechanistic understanding of this unusual activity, we employed in situ X-ray photoelectron spectroscopy and operando infrared spectroscopy. The higher surface concentration and reactivity of formates and carbonyls—key reaction intermediates—explain the superior activity of Co/CeO2 as compared to a conventional Co/SiO2 catalyst. This work emphasizes the catalytic role of the cobalt-ceria interface and will aid in developing more efficient CO2 hydrogenation catalysts.  相似文献   

15.
Bio-inspired molecular-engineered systems have been extensively investigated for the half-reactions of H2O oxidation or CO2 reduction with sacrificial electron donors/acceptors. However, there has yet to be reported a device for dye-sensitized molecular photoanodes coupled with molecular photocathodes in an aqueous solution without the use of sacrificial reagents. Herein, we will report the integration of SnIV- or AlIII-tetrapyridylporphyrin (SnTPyP or AlTPyP) decorated tin oxide particles (SnTPyP/SnO2 or AlTPyP/SnO2) photoanode with the dye-sensitized molecular photocathode on nickel oxide particles containing [Ru(diimine)3]2+ as the light-harvesting unit and [Ru(diimine)(CO)2Cl2] as the catalyst unit covalently connected and fixed within poly-pyrrole layer (RuCAT-RuC2-PolyPyr-PRu/NiO). The simultaneous irradiation of the two photoelectrodes with visible light resulted in H2O2 on the anode and CO, HCOOH, and H2 on the cathode with high Faradaic efficiencies in purely aqueous conditions without any applied bias is the first example of artificial photosynthesis with only two-electron redox reactions.  相似文献   

16.
Selective synthesis of specific value-added aromatics from CO2 hydrogenation is of paramount interest for mitigating energy and climate problems caused by CO2 emission. Herein, we report a highly active composite catalyst of ZnZrO and HZSM-5 (ZZO/Z5-SG) for xylene synthesis from CO2 hydrogenation via a coupling reaction in the presence of toluene, achieving a xylene selectivity of 86.5 % with CO2 conversion of 10.5 %. A remarkably high space time yield of xylene could reach 215 mg gcat−1 h−1, surpassing most reported catalysts for CO2 hydrogenation. The enhanced performance of ZZO/Z5-SG could be due to high dispersion and abundant oxygen vacancies of the ZZO component for CO2 adsorption, more feasible hydrogen activation and transfer due to the close interaction between the two components, and enhanced stability of the formate intermediate. The consumption of methoxy and methanol from the deep hydrogenation of formate by introduced toluene also propels an oriented conversion of CO2.  相似文献   

17.
Oxide-derived Cu (OD−Cu) featured with surface located sub-20 nm nanoparticles (NPs) created via surface structure reconstruction was developed for electrochemical CO2 reduction (ECO2RR). With surface adsorbed hydroxyls (OHad) identified during ECO2RR, it is realized that OHad, sterically confined and adsorbed at OD−Cu by surface located sub-20 nm NPs, should be determinative to the multi-carbon (C2) product selectivity. In situ spectral investigations and theoretical calculations reveal that OHad favors the adsorption of low-frequency *CO with weak C≡O bonds and strengthens the *CO binding at OD−Cu surface, promoting *CO dimerization and then selective C2 production. However, excessive OHad would inhibit selective C2 production by occupying active sites and facilitating competitive H2 evolution. In a flow cell, stable C2 production with high selectivity of ∼60 % at −200 mA cm−2 could be achieved over OD−Cu, with adsorption of OHad well steered in the fast flowing electrolyte.  相似文献   

18.
Research on the photoreduction of CO2 often has been dominated by the use of sacrificial reducing agents. A pathway that avoids this problem would be the development of photocathodes for CO2 reduction that could then be coupled to a photoanodic oxygen evolution reaction. Here, we present the use of copper-substituted graphitic carbon nitride (Cu−CN) on a fluorinated tin oxide (FTO) electrode for the photoelectrochemical two-electron reduction of CO2 to CO as a major product (>95 %) and formic acid (<5 %). The results show that at a potential of −2.5 V versus Fc\Fc+ the CO2 reduction activity of Cu−CN on FTO electrode improves by 25 % upon illumination by visible light with a faradaic efficiency of nearly 100 %. Independently, X-ray photoelectron spectroscopy conclusively shows a pronounced increase in the electrical conductivity of the Cu−CN upon white light illumination under vacuum and a contactless measuring configuration. This photo-assisted charge mobility is shown to play a key role in the increased reactivity and faradaic efficiency for the reduction of CO2.  相似文献   

19.
We report a ternary hybrid photocatalyst architecture with tailored interfaces that boost the utilization of solar energy for photochemical CO2 reduction by synergizing electron and heat flows in the photocatalyst. The photocatalyst comprises cobalt phthalocyanine (CoPc) molecules assembled on multiwalled carbon nanotubes (CNTs) that are decorated with nearly monodispersed cadmium sulfide quantum dots (CdS QDs). The CdS QDs absorb visible light and generate electron-hole pairs. The CNTs rapidly transfer the photogenerated electrons from CdS to CoPc. The CoPc molecules then selectively reduce CO2 to CO. The interfacial dynamics and catalytic behavior are clearly revealed by time-resolved and in situ vibrational spectroscopies. In addition to serving as electron highways, the black body property of the CNT component can create local photothermal heating to activate amine-captured CO2, namely carbamates, for direct photochemical conversion without additional energy input.  相似文献   

20.
In the presence of a molecular CoII catalyst, CO2 reduction occurred at much less negative potentials on Si photoelectrodes than on an Au electrode. The addition of 1 % H2O significantly improved the performance of the CoII catalyst. Photovoltages of 580 and 320 mV were obtained on Si nanowires and a planar Si photoelectrode, respectively. This difference likely originated from the fact that the multifaceted Si nanowires are better in light harvesting and charge transfer than the planar Si surface.  相似文献   

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