Unique copper and reduced graphene oxide nanocomposite toward the efficient electrochemical reduction of carbon dioxide

A first-principles study of electro-catalytic reduction of CO2 on transition metal-doped stanene

Employing first-principles calculations based on density functional theory, this work examines the activity of 3d transition metal-doped stanene for electro-catalytic CO2 reduction through the first two electron transfer steps to CO. Our results related to CO2 activation, the first and a crucial step of the reduction process revealed that, among the entire 3d transition metal row studied, only Ti- and Fe-doped stanene can bind and significantly activate the CO2 molecule, while the rest of the TM single atoms are inert in activating the molecule. The activation of the CO2 molecule on Ti- and Fe-doped stanene has been observed in the presence of water as well. In addition, the formation of OCHO has been observed to be energetically preferred over COOH formation as a reaction intermediate, indicating the preference for the formate path of the reduction reaction. Furthermore, despite the strong adsorption of H2O on the catalyst surface, the presence of water seems to enhance CO2 adsorption on the catalysts, contrary to what has been observed recently in graphene-based catalysts. Finally, our difference charge density and the Bader charge calculations reveal that the ability of Ti- and Fe-doped stanene in activating the CO2 molecule and their potential catalytic activity for CO2 reduction is to be attributed to the charge transfer between the catalyst and the molecule, providing new insights into the rational design of 2D catalysts beyond graphene.

Al-Sehemi A, Alargarsamy S, Gajendran P, Ramachandran R. Development of Different Kinds of Electrocatalyst for the Electrochemical Reduction of Carbon Dioxide Reactions: An Overview

Significant advancements have been made in the development of CO2 reduction processes for applications such as electrosynthesis, energy storage, and environmental remediation. Several materials have demonstrated great potential in achieving high activity and selectivity for the desired reduction products. Nevertheless, these advancements have primarily been limited to small-scale laboratory settings, and the considerable technical obstacles associated with large-scale CO2 reduction have not received sufficient attention. Many of the researchers have been faced with persistent challenges in the catalytic process, primarily stemming from the low Faraday efficiency, high overpotential, and low limiting current density observed in the production of the desired target product. The highlighted materials possess the capability to transform CO2 into various oxygenates, including ethanol, methanol, and formates, as well as hydrocarbons such as methane and ethane. A comprehensive summary of the recent research progress on these discussed types of electrocatalysts is provided, highlighting the detailed examination of their electrocatalytic activity enhancement strategies. This serves as a valuable reference for the development of highly efficient electrocatalysts with different orientations. This review encompasses the latest developments in catalyst materials and cell designs, presenting the leading materials utilized for the conversion of CO2 into various valuable products. Corresponding designs of cells and reactors are also included to provide a comprehensive overview of the advancements in this field.

Synthesis of 3D Porous Cu Nanostructures on Ag Thin Film Using Dynamic Hydrogen Bubble Template for Electrochemical Conversion of CO2 to Ethanol

Cu-based nanomaterials have been widely considered to be promising electrocatalysts for the direct conversion of CO₂ to high-value hydrocarbons. However, poor selectivity and slow kinetics have hindered the use of Cu-based catalysts for large-scale industrial applications. In this work, we report on a tunable Cu-based synthesis strategy using a dynamic hydrogen bubble template (DHBT) coupled with a sputtered Ag thin film for the electrochemical reduction of CO₂ to ethanol. Remarkably, the introduction of Ag into the base of the three-dimensional (3D) Cu nanostructure induced changes in the CO₂ reduction reaction (CO2RR) pathway, which resulted in the generation of ethanol with high Faradaic Efficiency (FE). This observation was further investigated through Tafel and electrochemical impedance spectroscopic analyses. The rational design of the electrocatalyst was shown to promote the spillover of formed CO intermediates from the Ag sites to the 3D porous Cu nanostructure for further reduction to C₂ products. Finally, challenges toward the development of multi-metallic electrocatalysts for the direct catalysis of CO₂ to hydrocarbons were elucidated, and future perspectives were highlighted.

Electrochemical Reduction of Carbon Dioxide at TiO2/Au Nanocomposites

Herein, we report on the facile synthesis of nanocomposite consisting of TiO₂ and Au nanoparticles (NPs) via a tailored galvanic replacement reaction (GRR). The electrocatalytic activity of the synthesized TiO₂/Au nanocomposites for CO₂ reduction was investigated in an aqueous solution using various electrochemical methods. Our results demonstrated that the TiO₂/Au nanocomposites formed through the GRR process exhibited improved catalytic activities for CO₂ reduction, while generating more hydrocarbon molecules than the typical formation of CO in contrast to polycrystalline Au. GC analysis and NMR spectroscopy revealed that CO and CH₄ were the gas products, whereas HCOO^-, CH₃COO^-, CH₃OH, and CH₃CH₂OH were the liquid products from the CO₂ reduction at different cathodic potentials. This remarkable change was further studied using the density functional theory (DFT) calculations, showing that the TiO₂/Au nanocomposites may increase the binding energy of the formed ^·CO intermediate and reduce the free energy compared to Au, thus favoring the downstream generation of multicarbon products. The TiO₂/Au nanocomposites have high catalytic activity and excellent stability and are easy to fabricate, indicating that the developed catalyst has potential application in the electrochemical reduction of CO₂ to value-added products.

Development of highly efficient magnetically recyclable Cu2+/Cu0 nano-photocatalyst and its enhanced catalytic performance for the degradation of organic contaminations

This work reports the successful functionalization of l-proline on the surface of superparamagnetic iron oxide nanoparticles (SPION) synthesized via a simple, cost-effective hydrothermal method. Moreover, the chemical attachment of Cu²⁺/Cu⁰ nanoparticles on the surface of SPION@l-proline was done by an in-situ deposition method. The developed nano-photocatalyst was characterized in detail by XRD, FT-IR, XPS, FE-SEM, TEM, EDX, BET, TGA, and VSM. XRD of SPION@l-proline-Cu reveals peaks of both SPION and copper nanoparticles which confirms the formation of nanophotocatalyst. TGA demonstrates a major weight loss between 250 and 310 °C due to l-proline which ensures the successful immobilization of SPION on the surface of l-proline. The band energy at 932 eV suggests a complete reduction of Cu²⁺ ion to Cu⁰ metal on the surface of SPION@l-proline nanocomposite as confirmed by the XPS technique. Under UV light irradiation, the photocatalytic reduction performance of the developed Cu²⁺ metal ion-based and Cu⁰ nanoparticle-based magnetic nano-photocatalysts was demonstrated and compared for the first time for the photocatalytic reduction of 4-NP, 4-NA, NB, MO, MB, and CR. The results show that Cu⁰-based magnetic nanophotocatalyst has slightly enhanced catalytic activity. Furthermore, solar-driven photocatalytic degradation of CR azo dye by synthesized nano-photocatalyst was also investigated, with a 95 % degradation efficiency in just 40 min. The developed magnetic nano-photocatalyst can easily be separated by using an external magnet due to the superparamagnetic nature of core material (SPION) at room temperature as confirmed from VSM and can be reused for multiple cycles without losing considerable catalytic activity. Because of its high photocatalytic efficiency, cost-effectiveness, good magnetic separation performance, non-toxicity, and strong thermal and chemical stabilities, Cu²⁺/Cu⁰-based magnetic nano-photocatalyst has potential application in wastewater treatment.

Two-dimensional covalent organic framework films prepared on various substrates through vapor induced conversion

Covalent organic frameworks (COFs) can exhibit high specific surface area and catalytic activity, but traditional solution-based synthesis methods often lead to insoluble and infusible powders or fragile films on solution surface. Herein we report large-area –C=N– linked two-dimensional (2D) COF films with controllable thicknesses via vapor induced conversion in a chemical vapor deposition (CVD) system. The assembly process is achieved by reversible Schiff base polycondensation between PyTTA film and TPA vapor, which results in a uniform organic framework film directly on growth substrate, and is driven by π‐π stacking interactions with the aid of water and acetic acid. Wafer-scale 2D COF films with different structures have been successfully synthesized by adjusting their building blocks, suggesting its generic applicability. The carrier mobility of PyTTA-TPA COF films can reach 1.89 × 10⁻³ cm² V⁻¹ s⁻¹. When employed as catalysts in hydrogen evolution reaction (HER), they show high electrocatalytic activity compared with metal-free COFs or even some metallic catalysts. Our results represent a versatile route for the direct construction of large-area uniform 2D COF films on substrates towards multi-functional applications of 2D π‐conjugated systems.

Solution-based synthesis of covalent organic frameworks (COFs) often leads to insoluble powders or fragile films on solution surfaces. Here, the authors report large-area two-dimensional (2D) COF films with controllable thicknesses via vapour induced conversion.

Promoting Electrocatalytic Reduction of CO2 to C2 H4 Production by Inhibiting C2 H5 OH Desorption from Cu2 O/C Composite

The electrochemical CO₂ reduction reaction (CO₂ RR) has great potential in realizing carbon recycling while storing sustainable electricity as hydrocarbon fuels. However, it is still a challenge to enhance the selectivity of the CO₂ RR to single multi-carbon (C₂₊ ) product, such as C₂ H₄ . Here, an effective method is proposed to improve C₂ H₄ selectivity by inhibiting the production of the other competitive C₂ products, namely C₂ H₅ OH, from Cu₂ O/C composite. Density functional theory indicates that the heterogeneous structure between Cu₂ O and carbon is expected to inhibit C₂ H₅ OH production and promote CC coupling, which facilitates C₂ H₄ production. To prove this, a composite electrode containing octahedral Cu₂ O nanoparticles (NPs) (o-Cu₂ O) with {111} facets and carbon NPs is constructed, which experimentally inhibits C₂ H₅ OH production while strongly enhancing C₂ H₄ selectivity compared with o-Cu₂ O electrode. Furthermore, the surface hydroxylation of carbon can further improve the C₂ H₄ production of o-Cu₂ O/C electrode, exhibiting a high C₂ H₄ Faradaic efficiency of 67% and a high C₂ H₄ current density of 45 mA cm^-2 at -1.1 V in a near-neutral electrolyte. This work provides a new idea to improve C₂₊ selectivity by controlling products desorption.

CO2 and CH2 Adsorption on Copper-Decorated Graphene: Predictions from First Principle Calculations

Single-layer graphene decorated with monodisperse copper nanoparticles can support the size and mass-dependent catalysis of the selective electrochemical reduction of CO2 to ethylene (C2H4). In this study, various active adsorption sites of nanostructured Cu-decorated graphene have been calculated by using density functional theory to provide insight into its catalytic activity toward carbon dioxide electroreduction. Based on the results of our calculations, an enhanced adsorption of the CO2 molecule and CH2 counterpart placed atop of Cu-decorated graphene compared to adsorption at pristine Cu metal surfaces was predicted. This approach explains experimental observations for carbon-based catalysts that were found to be promising for the two-electron reduction reaction of CO2 to CO and, further, to ethylene. Active adsorption sites that lead to a better catalytic activity of Cu-decorated graphene, with respect to general copper catalysts, were identified. The atomic configuration of the most selective CO2 toward the reduction reaction nanostructured catalyst is suggested.

Surface overgrowth on gold nanoparticles modulating high-energy facets for efficient electrochemical CO2 reduction

Electrochemical CO₂ reduction reaction (eCO₂RR) has been considered one of the potential technologies to store electricity from renewable energy sources into chemical energy. For this aim, designing catalysts with high surface activities is critical for effective eCO₂RR. In this study, we introduced a surface overgrowth method on stable Au icosahedrons to generate Au nanostars with large bumps. As a catalyst for eCO₂RR, the Au nanostars exhibited a maximum faradaic efficiency (FE) of 98% and a mass activity of 138.9 A g^-1 for CO production, where the latter was one of the highest activities among Au catalysts. Despite the deducted electrochemically active surface area per mass, the high-energy surfaces from overgrowth provided a 3.8-fold larger specific activity than the original Au icosahedral seeds, resulting in superior eCO₂RR performances that outweigh the trade-off of size and shape in nanoparticles. The Au nanostars also represented prolonged stability due to the durability of high-energy facets. The characterization of surface morphology and density functional theory calculations revealed that predominant Au(321) facets on the Au nanostars effectively stabilized *COOH adsorbates, thus lowering the overpotential and improving the FE for CO production. This overgrowth method is simple and universal for various materials, which would be able to extend into a wide range of electrochemical catalysts.

MnO2@Reduced Graphene Oxide Nanocomposite-Based Electrochemical Sensor for the Simultaneous Determination of Trace Cd(II), Zn(II) and Cu(II) in Water Samples

The rapid detection of trace metals is one of the most important aspect in achieving environmental monitoring and protection. Electrochemical sensors remain a key solution for rapid detection of heavy metals in environmental water matrices. This paper reports the fabrication of an electrochemical sensor obtained by the simultaneous electrodeposition of MnO₂ nanoparticles and RGO nanosheets on the surface of a glassy carbon electrode. The successful electrodeposition was confirmed by the enhanced current response on the cyclic voltammograms. The XRD, HR-SEM/EDX, TEM, FTIR, and BET characterization confirmed the successful synthesis of MnO₂ nanoparticles, RGO nanosheets, and MnO₂@RGO nanocomposite. The electrochemical studies results revealed that MnO₂@RGO@GCE nanocomposite considerably improved the current response on the detection of Zn(II), Cd(II) and Cu(II) ions in surface water. These remarkable improvements were due to the interaction between MnO₂ nanomaterials and RGO nanosheets. Moreover, the modified sensor electrode portrayed high sensitivity, reproducibility, and stability on the simultaneous determination of Zn(II), Cd(II), and Cu(II) ions. The detection limits of (S/N = 3) ranged from 0.002–0.015 μg L⁻¹ for the simultaneous detection of Zn(II), Cd(II), and Cu(II) ions. The results show that MnO₂@RGO nanocomposite can be successfully used for the early detection of heavy metals with higher sensitivity in water sample analysis.

Copper/reduced graphene oxide film modified electrode for non-enzymatic glucose sensing application

Numerous studies suggest that modification with functional nanomaterials can enhance the electrode electrocatalytic activity, sensitivity, and selectivity of the electrochemical sensors. Here, a highly sensitive and cost-effective disposable non-enzymatic glucose sensor based on copper(II)/reduced graphene oxide modified screen-printed carbon electrode is demonstrated. Facile fabrication of the developed sensing electrodes is carried out by the adsorption of copper(II) onto graphene oxide modified electrode, then following the electrochemical reduction. The proposed sensor illustrates good electrocatalytic activity toward glucose oxidation with a wide linear detection range from 0.10 mM to 12.5 mM, low detection limit of 65 µM, and high sensitivity of 172 μA mM^–1 cm^–2 along with satisfactory anti-interference ability, reproducibility, stability, and the acceptable recoveries for the detection of glucose in a human serum sample (95.6–106.4%). The copper(II)/reduced graphene oxide based sensor with the superior performances is a great potential for the quantitation of glucose in real samples.

H2-CO2 polymer electrolyte fuel cell that generates power while evolving CH4 at the Pt0.8Ru0.2/C cathode

Generating electric power using CO₂ as a reactant is challenging because the electroreduction of CO₂ usually requires a large overpotential. Herein, we report the design and development of a polymer electrolyte fuel cell driven by feeding H₂ and CO₂ to the anode (Pt/C) and cathode (Pt_0.8Ru_0.2/C), respectively, based on their theoretical electrode potentials. Pt–Ru/C is a promising electrocatalysts for CO₂ reduction at a low overpotential; consequently, CH₄ is continuously produced through CO₂ reduction with an enhanced faradaic efficiency (18.2%) and without an overpotential (at 0.20 V vs. RHE) was achieved when dilute CO₂ is fed at a cell temperature of 40 °C. Significantly, the cell generated electric power (0.14 mW cm⁻²) while simultaneously yielding CH₄ at 86.3 μmol g⁻¹ h⁻¹. These results show that a H₂-CO₂ fuel cell is a promising technology for promoting the carbon capture and utilization (CCU) strategy.

From CO2 to Value-Added Products: A Review about Carbon-Based Materials for Electro-Chemical CO2 Conversion

The global warming and the dangerous climate change arising from the massive emission of CO2 from the burning of fossil fuels have motivated the search for alternative clean and sustainable energy sources. However, the industrial development and population necessities make the decoupling of economic growth from fossil fuels unimaginable and, consequently, the capture and conversion of CO2 to fuels seems to be, nowadays, one of the most promising and attractive solutions in a world with high energy demand. In this respect, the electrochemical CO2 conversion using renewable electricity provides a promising solution. However, faradaic efficiency of common electro-catalysts is low, and therefore, the design of highly selective, energy-efficient, and cost-effective electrocatalysts is critical. Carbon-based materials present some advantages such as relatively low cost and renewability, excellent electrical conductivity, and tunable textural and chemical surface, which show them as competitive materials for the electro-reduction of CO2. In this review, an overview of the recent progress of carbon-based electro-catalysts in the conversion of CO2 to valuable products is presented, focusing on the role of the different carbon properties, which provides a useful understanding for the materials design progress in this field. Development opportunities and challenges in the field are also summarized.

Copper decorated with nanoporous gold by galvanic displacement acts as an efficient electrocatalyst for the electrochemical reduction of CO2

The reduction of carbon dioxide (CO2) is recognized as a key component in the synthesis of renewable carbon-containing fuels. Herein, we report on nanoporous gold (NPAu) decorated with copper atoms for the efficient electrochemical reduction of CO2. A facile and green galvanic displacement technique was developed to incorporate Cu onto the surface of the nanoporous gold-zinc (NPAuZn) electrode. The effect of zinc on the morphology and electrochemical performance of the formed NPAuCu electrodes for CO2 reduction was systematically investigated. The NPAuCu electrode exhibited 16.9 and 2.86 times higher current density than those of polycrystalline gold and NPAuZn at -0.60 V (vs. RHE) in a 0.1 M CO2-saturated NaHCO3 solution, respectively. A far higher faradaic efficiency was achieved at the NPAuCu electrode for the electrochemical reduction of CO2 to CO, CH4 and HCOOH. The facile synthesis of the NPAuCu electrode demonstrated in the present study can be employed as a promising strategy in the development of high-performance electrocatalysts for energy and environmental applications.

Electrochemical Reduction of CO2 at Coinage Metal Nanodendrites in Aqueous Ethanolamine

Electrocatalytic reduction of CO₂ into usable chemicals is a promising path to address climate change and energy challenges. Herein, we demonstrate the synthesis of unique coinage metal (Cu, Ag, and Au) nanodendrites (NDs) via a facile galvanic replacement reaction (GRR), which can be effective electrocatalysts for the reduction of CO₂ in an ethanolamine (EA) solution. Each metal ND surface was directly grown on glassy-carbon (GC) substrates from a mixture of Zn dust and the respective precursor solution. The electrocatalytic activities of the synthesized ND surfaces were optimized for CO₂ reduction in EA solution by varying their composition. It was determined that a 0.05 mol fraction of EA exhibited the highest catalytic activity for all metal NDs. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques showed that metal-ND electrodes possessed higher current densities, lower onset potentials and lower charge-transfer resistances for CO₂ reduction than their smooth polycrystalline electrode counterparts, indicating improved CO₂ reduction catalytic activity. It was determined, using FTIR and NMR spectroscopy, that formate was produced as a result of the CO₂ reduction.

Cu–Fe Incorporated Graphene-Oxide Nanocomposite as Highly Efficient Catalyst in the Degradation of Dichlorodiphenyltrichloroethane (DDT) from Aqueous Solution

Abstract

Fe/graphene oxide and Cu–Fe/graphene oxide nanocomposite were synthesized by the atomic implantation method to study the photocatalytic degradation of dichlorodiphenyltrichloroethane (DDT). The synthesized nanocomposites were characterized by the XRD, N2 isotherms, SEM with EDX, TEM and XPS analysis. Characterization results have reported that oxides of Cu and Fe were uniformly distributed on graphene oxide and exited in the form of Cu+ and Fe2+ ions in Cu–Fe/graphene oxide nanocomposite. The high photocatalytic DDT removal efficiency 99.7% was obtained for Cu–Fe/graphene oxide under the optimal condition of 0.2 g/L catalyst, 15 mg/L H2O2 and pH 5. It was attributed to the reduction of Fe3+ to Fe2+ by Cu+ ions and –OH radicals formation. However, it was dropped to 90.4% in the recycling study by leaching of iron and without a change in phase structure and morphology.

Graphic Abstract

Durable Cathodes and Electrolyzers for the Efficient Aqueous Electrochemical Reduction of CO2

The world emits over 14 gigatons of CO₂ in excess of what can be remediated by natural processes annually, contributing to rising atmospheric CO₂ levels and increasing global temperatures. The electrochemical reduction of CO₂ (CO₂ RR) to value-added chemicals and fuels has been proposed as a method for reusing these excess anthropogenic emissions. While state-of-the-art CO₂ RR systems exhibit high current densities and faradaic efficiencies, research on long-term electrode durability, necessary for this technology to be implemented commercially, is lacking. Previous reviews have focused mainly on the CO₂ electrolyzer performance without considering durability. In this Review, the need for research into high-performing and durable CO₂ RR systems is stressed by summarizing the state-of-the-art with respect to durability. Various failure modes observed are also reported and a protocol for standard durability testing of CO₂ RR systems is proposed.

Electrochemical CO2 Reduction to CO Catalyzed by 2D Nanostructures

Electrochemical CO2 reduction towards value-added chemical feedstocks has been extensively studied in recent years to resolve the energy and environmental problems. The practical application of electrochemical CO2 reduction technology requires a cost-effective, highly efficient, and robust catalyst. To date, vigorous research have been carried out to increase the proficiency of electrocatalysts. In recent years, two-dimensional (2D) graphene and transition metal chalcogenides (TMCs) have displayed excellent activity towards CO2 reduction. This review focuses on the recent progress of 2D graphene and TMCs for selective electrochemical CO2 reduction into CO.

Interface Engineering of Graphene-Supported Cu Nanoparticles Encapsulated by Mesoporous Silica for Size-Dependent Catalytic Oxidative Coupling of Aromatic Amines

In this study, graphene nanosheet-supported ultrafine Cu nanoparticles (NPs) encapsulated with thin mesoporous silica (Cu-GO@m-SiO₂) materials are fabricated with particle sizes ranging from 60 to 7.8 nm and are systematically investigated for the oxidative coupling of amines to produce biologically and pharmaceutically important imine derivatives. Catalytic activity remarkably increased from 76.5% conversion of benzyl amine for 60 nm NPs to 99.3% conversion and exclusive selectivity of N-benzylidene-1-phenylmethanamine for 7.8 nm NPs. The superior catalytic performance along with the outstanding catalyst stability of newly designed catalysts are attributed to the easy diffusion of organic molecules through the porous channel of mesoporous SiO₂ layers, which not only restricts the restacking of the graphene nanosheets but also prevents the sintering and leaching of metal NPs to an extreme extent through the nanoconfinement effect. Density functional theory calculations were performed to shed light on the reaction mechanism and to give insight into the trend of catalytic activity observed. The computed activation barriers of all elementary steps are very high on terrace Cu(111) sites, which dominate the large-sized Cu NPs, but are significantly lower on step sites, which are presented in higher density on smaller-sized Cu NPs and could explain the higher activity of smaller Cu-GO@m-SiO₂ samples. In particular, the activation barrier for the elementary coupling reaction is reduced from 139 kJ/mol on flat terrace Cu(111) sites to the feasible value of 94 kJ/mol at step sites, demonstrating the crucial role of the step site in facilitating the formation of secondary imine products.

Two-Dimensional Materials on the Rocks: Positive and Negative Role of Dopants and Impurities in Electrochemistry

Two-dimensional (2D) materials, such as graphene and transition-metal chalcogenides, were shown in many works as very potent catalysts for industrially important electrochemical reactions, such as oxygen reduction, hydrogen and oxygen evolution, and carbon dioxide reduction. We critically discuss here the development in the field, showing that not only dopants but also impurities can have dramatic effects on catalysis. Note here that the difference between dopant and impurity is merely semantic-dopant is an impurity deliberately added to the material. We contest the general belief that all doping has a positive effect on electrocatalysis. We show that in many cases, dopants actually inhibit the electrochemistry of 2D materials. This review provides a balanced view of the field of 2D materials electrocatalysis.

Reduced graphene oxide supported C3N4 nanoflakes and quantum dots as metal-free catalysts for visible light assisted CO2 reduction

The visible light photocatalytic reduction of CO₂ to fuel is crucial for the sustainable development of energy resources. In our present work, we report the synthesis of novel reduced graphene oxide (rGO)-supported C₃N₄ nanoflake (NF) and quantum dot (QD) hybrid materials (GCN) for visible light induced reduction of CO₂. The C₃N₄ NFs and QDs are prepared by acid treatment of C₃N₄ nanosheets followed by ultrasonication and hydrothermal heating at 130-190 °C for 5-20 h. It is observed that hydrothermal exposure of acid-treated graphitic carbon nitride (g-C₃N₄) nanosheets at low temperature generated larger NFs, whereas QDs are formed at higher temperatures. The formation of GCN hybrid materials was confirmed by powder X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy (TEM), and UV-vis spectroscopy. High-resolution TEM images clearly show that C₃N₄ QDs (average diameter of 2-3 nm) and NFs (≈20-45 nm) are distributed on the rGO surface within the GCN hybrid material. Among the as-prepared GCN hybrid materials, GCN-5 QDs exhibit excellent CO₂ reductive activity for the generation of formaldehyde, HCHO (10.3 mmol h^-1 g^-1). Therefore, utilization of metal-free carbon-based GCN hybrid materials could be very promising for CO₂ photoreduction because of their excellent activity and environmental sustainability.

From CO2methanation to ambitious long-chain hydrocarbons: alternative fuels paving the path to sustainability

Comprehensive insight into the thermochemical, photochemical and electrochemical reduction of CO₂to methane and long-chain hydrocarbons as alternative fuels.

Electrodeposition of tin on Nafion-bonded carbon black as an active catalyst layer for efficient electroreduction of CO2 to formic acid

Electroreduction of CO₂ to formic acid (ERCF) based on gas diffusion electrodes (GDEs) has been considered as a promising method to convert CO₂ into value-added chemicals. However, current GDEs for ERCF suffer from low efficiency of electron transfer. In this work, a novel Sn-based gas diffusion electrode (ESGDE) is prepared by electrodepositing Sn on Nafion-bonded carbon black as catalyst layer to enhance electron transfer and thus the efficiency of ERCF. The highest Faraday efficiency (73.01 ± 3.42%), current density (34.21 ± 1.14 mA cm^-2) and production rate (1772.81 ± 59.08 μmol m^-2 s^-1) of formic acid are obtained by using the ESGDE with electrodeposition time of 90 s in 0.5 M KHCO₃ solution, which are one of the highest values obtained from Sn-based gas diffusion electrodes under similar conditions. The notable efficiency of ERCF achieved here should be attributed to the enhancement in the reactants transfer as well as the three-dimensional reaction zone. This work will be helpful for the industrial application of GDEs in EFCF.