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Physical characterization of N-doped graphene foam. (a) An SEM image showing a representative graphene foam with an open frame structure. (b) High-magnification SEM image of a NG-800 sheet. (c) TEM image of a NG-800 sheet. (d) High-resolution TEM image of NG-800 sheet and inset is the FFT pattern. (e) XPS of N 1s. (f) N content distribution at various doping temperatures.
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The practical recycling of carbon dioxide (CO2) by the electrochemical reduction route requires an active, stable and affordable catalyst system. Although noble metals, such as gold and silver have been demonstrated to reduce CO2 into carbon monoxide (CO) efficiently, they suffer from poor durability and scarcity. Here we report three dimensional (...
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... atomic absorption spectroscopy measurement shows the collected NG is free of Ni contamination. 15 The scanning electron microscopy (SEM) images (Figure 1a,b) show 3D microporous structure of the representative N-doped graphene doped at 800 °C (denoted as NG-800). The transmission electron microscopy (TEM) study of folded edges and two sets of hexagonal diffraction spots in the Fast Fourier transform (FFT) pattern show that the NG sheets are composed of a few atomic layers (Figure 1c,d). ...
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... The scanning electron microscopy (SEM) images (Figure 1a,b) show 3D microporous structure of the representative N-doped graphene doped at 800 °C (denoted as NG-800). The transmission electron microscopy (TEM) study of folded edges and two sets of hexagonal diffraction spots in the Fast Fourier transform (FFT) pattern show that the NG sheets are composed of a few atomic layers (Figure 1c,d). The peak intensity ratio of G to 2D band observed in the Raman spectra varies from 0.75 to 0.87, also suggesting the presence of 2−4 layers in the synthesized NGs (Supporting Information Figure S1). ...
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... transmission electron microscopy (TEM) study of folded edges and two sets of hexagonal diffraction spots in the Fast Fourier transform (FFT) pattern show that the NG sheets are composed of a few atomic layers (Figure 1c,d). The peak intensity ratio of G to 2D band observed in the Raman spectra varies from 0.75 to 0.87, also suggesting the presence of 2−4 layers in the synthesized NGs (Supporting Information Figure S1). 16,17 Furthermore, the hexagonal diffraction pattern reveals that carbon sp 2 structure in graphene is maintained after incorporation of N heteroatoms, which is in agreement with the small value (0.1−0.2) of peak intensity ratio of D to G band (Supporting Information Figure S1). ...
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... peak intensity ratio of G to 2D band observed in the Raman spectra varies from 0.75 to 0.87, also suggesting the presence of 2−4 layers in the synthesized NGs (Supporting Information Figure S1). 16,17 Furthermore, the hexagonal diffraction pattern reveals that carbon sp 2 structure in graphene is maintained after incorporation of N heteroatoms, which is in agreement with the small value (0.1−0.2) of peak intensity ratio of D to G band (Supporting Information Figure S1). ...
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... concentration of nitrogen in the surface layers and its chemical states were analyzed using X-ray photoelectron spectroscopy (XPS, Supporting Information Figure S2). The deconvolution of N 1s peak reveals three different bonding states of N atom at 398.5, 400.1, and 401.2 eV, corresponding to pyridinic, pyrrolic, and graphitic-N, respectively ( Figure 1e). 18,19 NG-800 possesses the highest total N content (∼6.5 atom %) based on N/(N + C) atomic ratio followed by NG-700, NG-900, and NG-1000 ( Figure 1f). ...
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... deconvolution of N 1s peak reveals three different bonding states of N atom at 398.5, 400.1, and 401.2 eV, corresponding to pyridinic, pyrrolic, and graphitic-N, respectively ( Figure 1e). 18,19 NG-800 possesses the highest total N content (∼6.5 atom %) based on N/(N + C) atomic ratio followed by NG-700, NG-900, and NG-1000 ( Figure 1f). The N content decreases owing to the removal of some relatively unstable N defects such as pyridinic and pyrrolic-N as temperature increases, consistent with previous findings. ...
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... N content decreases owing to the removal of some relatively unstable N defects such as pyridinic and pyrrolic-N as temperature increases, consistent with previous findings. 19−21 Pyridinic-N predominates in all NGs, and the highest pyridinic-N reaches 4.1 atom % in NG-800 ( Figure 1f). ...
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In this mini-review we compare two prototypical metal foam electrocatalysts applied to the transformation of CO 2 into value-added products ( e.g. alcohols on Cu foams and formate on Bi foams). A substantial improvement in the catalyst performance is typically achieved through thermal annealing of the as-deposited foam materials, followed by the el...
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... Previous studies have shown that the positively charged carbon atom adjacent to graphitic N is believed to bind to the COOH* intermediate and pyridinic N has the activity for CO 2 RR. 46,47 However, there is no electron aggregation at the pyridinic N site of 1D carbon, which is not conducive to CO 2 RR. Therefore, the active site of CO 2 RR is the positively charged carbon atom adjacent to the graphitic N on 1D carbon. ...
Electrochemical reduction of CO 2 to syngas (CO and H 2 ) offers an efficient way to mitigate carbon emissions and store intermittent renewable energy in chemicals. Herein, the hierarchical one‐dimensional/three‐dimensional nitrogen‐doped porous carbon (1D/3D NPC) is prepared by carbonizing the composite of Zn‐MOF‐74 crystals in situ grown on a commercial melamine sponge (MS), for electrochemical CO 2 reduction reaction (CO 2 RR). The 1D/3D NPC exhibits a high CO/H 2 ratio (5.06) and CO yield (31 mmol g ⁻¹ h ⁻¹ ) at −0.55 V, which are 13.7 times and 21.4 times those of 1D porous carbon (derived from Zn‐MOF‐74) and N‐doped carbon (carbonized by MS), respectively. This is attributed to the unique spatial environment of 1D/3D NPC, which increases the adsorption capacity of CO 2 and promotes electron transfer from the 3D N‐doped carbon framework to 1D carbon, improving the reaction kinetics of CO 2 RR. Experimental results and charge density difference plots indicate that the active site of CO 2 RR is the positively charged carbon atom adjacent to graphitic N on 1D carbon and the active site of HER is the pyridinic N on 1D carbon. The presence of pyridinic N and pyrrolic N reduces the number of electron transfer, decreasing the reaction kinetics and the activity of CO 2 RR. The CO/H 2 ratio is related to the distribution of N species and the specific surface area, which are determined by the degree of spatial confinement effect. The CO/H 2 ratios can be regulated by adjusting the carbonization temperature to adjust the degree of spatial confinement effect. Given the low cost of feedstock and easy strategy, 1D/3D NPC catalysts have great potential for industrial application.
... Although great developments have been made in the CRR, there are still some challenges: the unavoidable competitive reaction, the hydrogen evolution reaction (HER), which forms high-order polycarbonate products with high overpotential and low product selectivity, and CO 2 mass transfer limitations. Three-dimensional graphene with a porous network has been used in an electrocatalytic CRR system as a support to improve the dispersion of catalysts and the CO 2 adsorption capacity, provide more catalytic active sites, and enhance the conductivity and stability of the catalytic system [35][36][37][38]. It has also been reported that the hydrophobicity and porous structures of supports can effectively inhibit the competitive HER [39]. ...
The lateral size of graphene nanosheets plays a critical role in the properties and microstructure of 3D graphene as well as their application as supports of electrocatalysts for CO2 reduction reactions (CRRs). Here, graphene oxide (GO) nanosheets with different lateral sizes (1.5, 5, and 14 µm) were utilized as building blocks for 3D graphene aerogel (GA) to research the size effects of GO on the CRR performances of 3D Au/GA catalysts. It was found that GO-L (14 µm) led to the formation of GA with large pores and a low surface area and that GO-S (1.5 µm) induced the formation of GA with a thicker wall and isolated pores, which were not conducive to the mass transfer of CO2 or its interaction with catalysts. Au/GA constructed with a suitable-sized GO (5 µm) exhibited a hierarchical porous network and the highest surface area and conductivity. As a result, Au/GA-M exhibited the highest Faradaic efficiency (FE) of CO (FECO = 81%) and CO/H2 ratio at −0.82 V (vs. a Reversible Hydrogen Electrode (RHE)). This study indicates that for 3D GA-supported catalysts, there is a balance between the improvement of conductivity, the adsorption capacity of CO2, and the inhibition of the hydrogen evolution reaction (HER) during the CRR, which is related to the lateral size of GO.
... It was discovered that the improved activity of the catalyst is related to the grain boundaries of the oxide-derived Au or Cu nanoparticles [25,28,29]. Many studies also demonstrated that high-index facets and edge sites play key roles in CO 2 RR [30][31][32]. However, noble metals like Au and Ag are not cost-effective, and less expensive alternatives are highly desirable. ...
Environmental problems are among the most pressing issues in the modern world, including the shortage of clean drinking water partially caused by contamination from various industries and the excessive emission of CO2 primarily from the massive use of fossil fuels. Consequently, it is crucial to develop inexpensive, effective, and environmentally friendly methods for wastewater treatment and CO2 reduction, turning them into useful feedstocks. This study explores a unique method that addresses both challenges by utilizing ZnO, which is recognized as one of the most active semiconductors for photocatalysis, as well as a cost-effective electrocatalyst for the CO2 reduction reaction (CO2RR). Specifically, we investigate the influence of the morphology of various ZnO nanostructures synthesized via different low-cost routes on their photocatalytic properties for degrading the rhodamine-B dye (RhB) and on their electrocatalytic performance for the CO2RR. Our results show that the ZnO lamella morphology achieves the best performance compared to the nanorod and nanoparticle structures. This outcome is likely attributed to the lamella’s higher aspect ratio, which plays a critical role in determining the structural, optical, and electrical properties of ZnO.
... Nonetheless, they can be doped with heteroatoms, such as boron, fluorine, nitrogen, and sulfur, to improve their physicochemical and electronic properties. [40][41][42][43][44][45][46][47][48][49][50] In the electrochemical CO 2 RR literature, most of the reported heteroatom-doped carbon materials are doped with nitrogen atoms. Nitrogen doping has been shown to improve the interaction between graphene and CO 2 because nitrogen acts as a Lewis base toward the Lewis acid CO 2 . ...
... Most studies show that pyridinic nitrogen is the most active among all nitrogen functionalities. 40,41,[45][46][47] However, some reports argue that the positively charged adjacent carbon atoms 40 and the graphitic nitrogen 50 are more active compared to pyridinic nitrogen. ...
... This disagreement springs from the fact that there have been many reports about nitrogen-doped carbon materials that efficiently convert CO 2 to CO, hydrocarbons, and even oxygenates. 41,43,45,47 Several atomic configurations could be present when nickel is dispersed as single atoms in a carbon material. Nickel atoms could be coordinated with nitrogen atoms with or without vacancies or coordinated directly with carbon atoms. ...
The electrochemical reduction of carbon dioxide offers a sound and economically viable technology for the electrification and decarbonization of the chemical and fuel industries. In this technology, an electrocatalytic material and renewable energy‐generated electricity drive the conversion of carbon dioxide into high‐value chemicals and carbon‐neutral fuels. Over the past few years, single‐atom catalysts have been intensively studied as they could provide near‐unity atom utilization and unique catalytic performance. Single‐atom catalysts have become one of the state‐of‐the‐art catalyst materials for the electrochemical reduction of carbon dioxide into carbon monoxide. However, it remains a challenge for single‐atom catalysts to facilitate the efficient conversion of carbon dioxide into products beyond carbon monoxide. In this review, we summarize and present important findings and critical insights from studies on the electrochemical carbon dioxide reduction reaction into hydrocarbons and oxygenates using single‐atom catalysts. It is hoped that this review gives a thorough recapitulation and analysis of the science behind the catalysis of carbon dioxide into more reduced products through single‐atom catalysts so that it can be a guide for future research and development on catalysts with industry‐ready performance for the electrochemical reduction of carbon dioxide into high‐value chemicals and carbon‐neutral fuels.
... The catalysts produced formic acid only at more cathodic potentials. As the precision in the quantification of formic acid via HPLC is limited, [3,7,12,20,24,38,39] we will mainly focused in the reminder of the paper, on understanding the selectivity towards CO. ...
The electrochemical reduction of CO2 to produce sustainable fuels and chemicals has attracted great attention in recent years. It is shown that surface‐modified carbons catalyze the CO2RR. This study reports a strategy to modify the surface of commercially available carbon materials by adding oxygen and nitrogen surface groups without modifying its graphitic structure. Clear differences in CO2RR activity, selectivity and the turnover frequency between the surface‐modified carbons were observed, and these differences were ascribed to the nature of the surface groups chemistry and the point of zero charge (PZC). The results show that nitrogen‐containing surface groups are highly selective towards the formation of CO from the electroreduction of CO2 in comparison with the oxygen‐containing surface groups, and the carbon without surface groups. This demonstrates that the selectivity of carbon for CO2RR can be rationally tuned by simply altering the surface chemistry via surface functionalization.
... The formation of CO from CO 2 RR is generally believed to follow two proton-coupled electron-transfer steps to form COOH*, and then CO* that is desorbed from the catalyst surface [52][53][54] . In this process, the formation of COOH* usually is a potential-limiting step due to the high activation energy of CO 2 molecule. ...
Nanostructured metal-nitrides have attracted tremendous interest as a new generation of catalysts for electroreduction of CO2, but these structures have limited activity and stability in the reduction condition. Herein, we report a method of fabricating FeN/Fe3N nanoparticles with FeN/Fe3N interface exposed on the NP surface for efficient electrochemical CO2 reduction reaction (CO2RR). The FeN/Fe3N interface is populated with Fe−N4 and Fe−N2 coordination sites respectively that show the desired catalysis synergy to enhance the reduction of CO2 to CO. The CO Faraday efficiency reaches 98% at −0.4 V vs. reversible hydrogen electrode, and the FE stays stable from −0.4 to −0.9 V during the 100 h electrolysis time period. This FeN/Fe3N synergy arises from electron transfer from Fe3N to FeN and the preferred CO2 adsorption and reduction to *COOH on FeN. Our study demonstrates a reliable interface control strategy to improve catalytic efficiency of the Fe–N structure for CO2RR.
... Ajayan et al. also fabricated an N-doped GF ( Figure 12A) as the catalyst for CO 2 RR. 147 Using the methane as a precursor and the Ni foam as a template, the GF was first fabricated by CVD. Then, use a solid precursor of g-C 3 N 4 at the temperature range of 700-1000°C to vary the N atomic concentration. ...
Graphene and boron nitride (BN) foams, as two types of three‐dimensional (3D) nanomaterials consisting of two‐dimensional (2D) nanosheets, can inherit a series of excellent properties of the 2D individuals. The internal 3D network can prevent aggregation or restacking between isolated graphene or BN nanosheets, and provide a highway for phonon/electron transports. Moreover, the interconnected porous structure creates a continual channel for the mass exchange of exotic species. The light‐element graphene and BN foams can thus possess the characteristics of low density, high porosity, high surface area, and excellent mechanical, thermal, and electrical properties. Benefiting from these advantages, they show a wide range of applications. The usual synthesis methods and the recent functional applications of graphene and BN foams are reviewed herein, including their applications as supporting materials, elastic materials, acoustic shielding materials, thermal interface materials, electromagnetic shielding materials, adsorption materials, electrocatalysis and thermal catalyses materials, electrochemical energy storage, and thermal energy storage materials. Current challenges and outlooks are additionally discussed.
... Meanwhile, g-C 3 N 4 is also a common N-polymer material with a structure in which the C and N atoms are sp2-hybridized to form a π-type conjugated system with a highly delocalized domain. Due to its high stability no matter the extreme chemical environment or high temperature, proper pore structure, redox potential, and abundant functional groups on the surface, there are also many studies based on g-C 3 N 4 materials reported for energy and environmental applications [120,121], especially for electrocatalytic CO 2 reduction [122]. Zhao et al. [123] prepared a Au-CDots-C 3 N 4 material for CO 2 RR that can efficiently convert CO 2 to CO. Electrochemical tests showed that 4 wt% Au-CDots-C 3 N 4 has optimal CO 2 electrocatalytic performance, and this material can undergo CO 2 electrocatalytic reactions at −0.5 V and the Faraday efficiency of CO reached a maximum of 79.8%. ...
Efficient capture of CO2 and its conversion into other high value-added compounds by electrochemical methods is an effective way to reduce excess CO2 in the atmosphere. Porous polymeric materials hold great promise for selective adsorption and electrocatalytic reduction of CO2 due to their high specific surface area, tunable porosity, structural diversity, and chemical stability. Here, we review recent research advances in this field, including design of porous organic polymers (POPs), porous coordination polymers (PCPs), covalent organic frameworks (COFs), and functional nitrogen-containing polymers for capture and electrocatalytic reduction of CO2. In addition, key issues and prospects for the optimal design of porous polymers for future development are elucidated. This review is expected to shed new light on the development of advanced porous polymer electrocatalysts for efficient CO2 reduction.
... The main techniques that have been employed to modify intrinsic defects, i.e., point defects and topological defects, include mechanical ball milling [218], chemical oxidation or etching [219], plasma etching [220,221], nitrogen removal [222], and in situ etching [223]. On the other hand, extrinsic defects such as heteroatom doping with varied electronegativity [85,224] and metal-atom dispersed active sites [225][226][227] are primarily implemented using various chemical vapor deposition (CVD) [228][229][230] and pyrolysis [231] methods for heteroatom doping and pyrolysis synthesis [232,233], with defect engineering [234], spatial confinement [235,236] and coordination design [237] used for the metal-atom dispersive site processes. The appropriate synthesis method yields distinctive electrocatalytic materials that can be employed in efficient CO 2 -RRs in unique ways to provide carbon fuels and other value-added products. ...
Climate change, caused by greenhouse gas emissions, is one of the biggest threats to the world. As per the IEA report of 2021, global CO2 emissions amounted to around 31.5 Gt, which increased the atmospheric concentration of CO2 up to 412.5 ppm. Thus, there is an imperative demand for the development of new technologies to convert CO2 into value-added feedstock products such as alcohols, hydrocarbons, carbon monoxide, chemicals, and clean fuels. The in-trinsic properties of the catalytic materials are the main factors influencing the efficiency of elec-trochemical CO2 reduction (CO2-RR) reactions. Additionally, the electroreduction of CO2 is mainly affected by poor selectivity and large overpotential requirements. However, these issues can be overcome by modifying heterogeneous electrocatalysts to control their morphology, size, crystal facets, grain boundaries, and surface defects/vacancies. This article reviews the recent progress in electrochemical CO2 reduction reactions accomplished by surface-defective electrocatalysts and identifies significant research gaps for designing highly efficient electrocatalytic materials.
... N-3D Graphene KHCO 3 (0.1M) CO (85%) -0.58 V vs. SHE 222 [7] (2015) ...
The direct electroreduction of CO2 into syngas with controllable CO/H2 ratios is a promising approach to rebalance the CO2 cycle and storage intermittent renewable energy. However, it is still challenging...
