Catalysts For CO2 Reduction Research Articles

Two-dimensional n-type pyrite with tuned hydrogen interstitials as a highly selective CO2 reduction catalyst

Density functional theory (DFT) calculations were employed to elucidate the impact of hydrogen interstitial (Hi) defects on the optical and efficacy of iron pyrite (FeS2) as a selective carbon dioxide reduction catalyst (CO2RR). Three different charge states were considered, namely Hi1, Hi0 or Hi−1. Upon examining the formation energy of the various possible charge states that the Hi can accommodate, it was found that Hi will be incorporated in the structure as an n-type defect in the (+1) state across almost the entire bandgap. However, under heavy n-type growth conditions, it can act as an amphoteric dopant, and can accommodate the 3 states simultaneously. The performance of FeS2-H in CO2RR is compared to the pristine counterpart. The calculations show that the addition of Hi facilitates the methanol pathway by prioritizing the attachment of the COOH* intermediate. Consequently, Hi promotes the formation of C1 compounds with higher performance. This is achieved by inhibiting the competitor hydrogen evolution reaction (HER), leading to a significant improvement in the efficiency.

Escalating the synergism on CdZnS via Ag2S/Cu2S co-catalysts: Boosts hydrogen evolution from water splitting under sunlight

Photocatalytic hydrogen production through water splitting is one of the effective ways to fulfill future energy demands. In current study, Ag and Cu were simultaneously incorporated into CdZnS through hydrothermal reaction to synthesize 1 % Ag2S/Cu2S codoped-CdZnS. The catalysts were characterized via XRD, FT-IR, SEM, EDX, UV–Vis/DRS, XPS, BET, PL and EIS techniques. It has been observed that 1 % Ag2S/Cu2S is optimized amount of dopants that enables CdZnS to produce hydrogen with 9.76 mmol g−1h−1 rate. This amount of H2 is 3 times higher than that of bare CdZnS (2.91 mmol g−1h−1). Photocatalytic activity shown by 1 % Ag2S/Cu2S-CdZnS is due the incorporation of Ag and Cu which exist in the form of Ag2S and Cu2S clusters respectively and causes synergistic effect during photoreaction. During the photoreactions, oxidation half reactions occur at Ag2S, while reduction half reaction at Cu2S (i.e. conversion of H+ ions to H2). On the basis of the results, it can be concluded that Cu2S acts as reduction co-catalyst while Ag2S serves as oxidation co-catalyst in water reduction reaction. This work could offer efficient and low cost photocatalysts for hydrogen production from the water splitting reactions.

Electrical energy input efficiency limitations in CO2‐to‐CO electrolysis and attempts for improvement

AbstractElectrochemical CO2 reduction is a potentially up‐coming technology to convert anthropogenic emitted CO2 into chemical feedstock. Due to alkaline operating conditions of CO2‐electrolyis in gas diffusion electrodes, exothermal hydroxide ion neutralization with the excess of supplied CO2 leads to unavoidable electricity‐to‐heat conversion at the cathode, therefore limiting electrical energy input efficiency. The decomposition reaction of carbonates by protons from water oxidation completes the inherent CO2 transport at the anode. In this work, different production routes to CO are thermodynamically examined and experimentally validated. Using formic acid as an intermediate towards CO the electrical energy input efficiency can rise to 71% on a thermodynamical basis. Additionally, the possibility of altering the mechanism of CO2 reduction under acidic conditions is investigated, which would lead to even larger electrical energy input efficiencies. The concept was investigated by pH series measurements (pH = 0–6) at 50 mA/cm2 where Pb derived from Pb3O4 was used as a CO2 reduction catalyst. The reduction to formic acid under acidic bulk electrolyte pH is stable at FEHCOOH = 70% down to pH ≈ 1, while HER is becoming dominant below. Even under such acidic bulk electrolyte conditions no change in reduction mechanism could be forced, which is reflected in invariant cell voltages in the model experiment.

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 H2 O 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 CH3 OH (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.

New Spectroelectrochemical Insights into Manganese and Rhenium Bipyridine Complexes as Catalysts for the Electrochemical Reduction of Carbon Dioxide.

This study aimed to demonstrate the behavior of different complexes using IR spectroelectrochemistry (SEC), a technique that combines IR spectroscopy with electrochemistry. Four different Mn and Re catalysts for electrochemical CO2 reduction were studied in dry acetonitrile. In the case of Mn(apbpy)(CO)3Br (apbpy = 4(4-aminophenyl)-2,2'-bipyridine), SEC suggested that a very slow catalytic reduction of CO2 also occurs in acetonitrile in the absence of proton donors, but at rather negative potentials. In contrast, the corresponding Re(apbpy)(CO)3Br clearly demonstrated slow catalytic conversion at the first reduction potential. Switching to saturated CO2 solutions in a mixture of acetonitrile and 5% water as a proton donor, the SEC of Mn(apbpy)(CO)3Br displayed a faster catalytic behavior.

Designing single atom catalysts for exceptional electrochemical CO2 reduction

Designing single atom catalysts for exceptional electrochemical CO2 reduction

Fe-Ni bimetallic composite N-doped carbon catalyst for electrocatalytic reduction of CO2 to produce efficient and controlled syngas

The reduction of CO2 to a tunable syngas by electrochemical catalysis for the industrial synthesis of hydrocarbons, alcohols, aldehydes, and other compounds can effectively realize carbon recycling. Herein, in this paper, non-precious metal FeNi precursors were synthesized by solution method, and then a series of FeNi-NC catalysts were obtained by one-step pyrolysis. The results show that on the prepared catalysts, the products of CO2 electroreduction are CO and H2, and the total Faraday efficiency is close to 100 %. Comparison of the prepared catalysts showed that the Fe3Ni7-NC 800 °C had the best selectivity for CO, with a maximum Faraday efficiency of 81.3 % for CO(FECO) generation at a potential of − 0.9 V (vs. RHE), and a current density of − 22.5 mA cm−2 at − 1.2 V. The catalysts had better durability. Moreover, the syngas ratio from 1:1 to 6:1 (CO/H2) can be easily adjusted by controlling the potential applied during the process over a wide potential range, and the resulting syngas in different ratios can be used for the production of chemical raw materials and fuels.

Size Effect of Graphene Oxide on Graphene-Aerogel-Supported Au Catalysts for Electrochemical CO2 Reduction.

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.

Controlled synthesis and photocatalytic hydrogen evolution activities of cobalt carbides with different phase compositions

Cobalt carbides are emerging as promising materials for various magnetic and catalytic applications. However, exploring dedicated cobalt carbides with optimal catalytic properties via adjusting phase compositions remains a significant challenge. Herein, three different cobalt carbides, Co x C (Co2C-Co3C), Co2C-Co, and Co3C, were successfully prepared using a facile one-pot green method. The phase compositions of cobalt carbides could be easily controlled by varying the cobalt-based precursors and carbon sources. More remarkably, three different cobalt carbides could serve as reduction cocatalysts decorated CdS for improved hydrogen production under visible light. Intriguingly, the obtained Co3C/CdS nanocomposite displayed the highest photocatalytic hydrogen evolution activity among the three composites and superior photocatalytic stability. This work provides a fundamental approach to tuning the photocatalytic properties of cobalt carbides for energy conversion fields.

Nickel supported on polymeric graphitic carbon nitride for electrocatalytic in reduction of carbon dioxide

This study explores the potential of carbon-based materials, specifically CN-Ni-doped, as catalysts for CO2 reduction to methanol in a PEM-R. The research investigates the impact of Ni incorporation on CN's structure, resulting in increased interlayer spacing and reduced crystallite size. Additionally, the introduction of Ni modifies the samples' morphology, creating a more compact structure with smaller sheets. The findings indicate that CN-Ni displays promising catalytic activity, achieving a 25% Faradaic Efficiency (FE) with a methanol production rate of approximately 1.1 mol L−1 h−1. The study underscores the significance of optimizing reactor operational parameters to enhance CO2RR. In conclusion, this research contributes to the advancement of efficient and sustainable approaches for CO2 utilization and methanol synthesis.

Emerging hollow artificial photosynthetic system with S-scheme heterojunction sandwiched between layered redox cocatalysts for overall CO2 reduction and H2O oxidation

The development of artificial photosynthesis is challenged by nonstoichiometric photocatalytic reaction of CO2 with H2O. Herein, a delicate hollow multi-shelled nanoreactor with S-scheme heterojunction sandwiched between layered noble-metal-free redox cocatalysts is fabricated, which exhibits excellent photocatalytic performance for overall CO2-to-CO reduction and H2O-to-O2 oxidation with stoichiometric ratio of the evolved reduction and oxidation products. The synergy of the sandwiched heterojunction and spatially separated dual cocatalysts on the inner/outer sides: (i) promotes the separation and transfer of powerful photoexcited charges towards opposite directions; (ii) maneuvers the occurrence of surface redox reactions in different spaces through lowering the thermodynamic barriers, and (iii) hinders the occurrence of side reactions and photocorrosion on the semiconductor surface. Consequently, the charge separation, transfer and consumption are well balanced, and the photocatalytic activity, selectivity and stability are perfectly optimized. It is expected that this novel design can be extended to other semiconductor heterojunctions towards high-efficient photoredox catalysis.

CO2 Electrochemical reduction on the two dimensional transition metal coordinated by 2,3,6,7,10,11-triphenylenehexathiol and 2,3,6,7,10,11-triphenylenehexamine, a computational survey

ABSTRACT Electrochemical CO2 reduction reaction (CO2RR) provides a feasible technology for alleviating global warming, energy crisis and sustainable energy production. In this work, CO2RR reaction mechanism on TM-THTA (TM = Fe, Co, Ni, Ru, Rh, Pd, THTA is composed by two types of building blocks of 2,3,6,7,10,11-triphenylenehexathiol and 2,3,6,7,10,11-triphenylenehexamine) has been studied by using density functional method. Our study showed that the studied catalysts are stable both thermodynamically and electrochemically. Rh-THTA is a good CO2 reduction catalyst in producing CH4. Pd-THTA is a potential CO2 reduction catalyst in producing HCOOH. Solvent effect plays important role in reaction mechanism. The strong hydrogen evolution reaction in Rh-THTA and Pd-THTA can be refrained by adjusting the pH values of electrolyte. We hope this study could provide a useful way to develop 2D-MOF-based CO2RR electrocatalysts.

Bi/2 H-MoS2−x composite for efficient photo-thermal synergistic catalytic CO2 reduction

The high carrier recombination rate and poor photocorrosion resistance of intrinsic MoS2 lead to a poor photocatalytic CO2 reduction activity. Here, the photocatalytic CO2 reduction performance of 2 H-MoS2 was significantly enhanced by constructing Bi/2 H-MoS2−x composite and photo-thermal synergy strategy. Under the optimal conditions of 200 °C and 42 mW·cm-2 of 420 nm irradiation, Bi/2 H-MoS2−x exhibited an excellent photo-thermal synergistic catalytic activity of CO2 reduction with a CO production rate of 34.42 μmol-1·g-1·h-1. Mechanistic studies showed that the introduction of Bi greatly improved the light absorption ability, generated S vacancies as electron capture centers for rapid separation of photocarriers, and promoted the generation of key intermediates. The involvement of heat led to a photo-thermal synergistic effect, which accelerated the charge migration and surface reaction rate. Our work provides new insights into the development of efficient catalysts for CO2 reduction and the mechanism study of photo-thermal synergistic catalysis.

Catalytic Decomposition of an Organic Electrolyte to Methane by a Cu Complex-Derived In Situ CO2 Reduction Catalyst.

Metal complexes are often transformed to metal complex-derived catalysts during electrochemical CO2 reduction, enhancing the catalytic performance of CO2 reduction or changing product selectivity. To date, it has not been investigated whether metal-complex derived catalysts also enhance the decomposition of the solvent/electrolyte components as compared to an uncoated electrode. Here, we tested the electrochemical stability of five organic solvent-based electrolytes with and without a Cu complex-derived catalyst on carbon paper in an inert atmosphere. The amount of methane and hydrogen produced was monitored using gas chromatography. Importantly, the onset potential for methane production was reduced by 300 mV in the presence of a Cu complex-derived catalyst leading to a significant amount of methane (417.7 ppm) produced at -2.17 V vs Fc/Fc+ in acetonitrile. This suggests that the Cu complex-derived catalyst accelerated not only CO2 reduction but also the reduction of the electrolyte components. This means that Faradaic efficiency (FE) measurements under CO2 in acetonitrile may significantly overestimate the amount of CH4. Only 28.8 ppm of methane was produced in dimethylformamide under an inert atmosphere, much lower than that produced under CO2 (506 ppm under CO2) at the same potential, suggesting that dimethylformamide is a more suitable solvent. Measurements in propylene carbonate produced mostly hydrogen gas while in dimethyl sulfoxide and 3-methoxypropionitrile neither methane nor hydrogen was detected. A strong linear correlation between the measured current and the amount of methane produced with and without the Cu complex-derived catalyst confirmed that the origin of methane production is solvent/electrolyte decomposition and not the decomposition of the catalyst itself. The study highlights that in a nonaqueous system, highly active catalyst in situ deposited during electrochemical testing can significantly influence background measurements as compared to uncoated electrodes, therefore the choice of solvent is paramount for reliable testing.

Cu-Doped SrTiO3 Nanostructured Catalysts for CO2 Conversion into Solar Fuels Using Localised Surface Plasmon Resonance

Carbon dioxide valorisation is one of the most discussed topics amongst researchers; indeed, finding a way to significantly reduce CO2 concentration in the atmosphere is crucial in order to mitigate climate change effects in the next decades. In this study, SrTiO3-supported Cu nanoparticles are exploited as Localised Surface Plasmon Resonance (LSPR)-mediated catalysts for CO2 reduction. The materials were prepared via sol–gel citrate route methodology, inserting Cu as a dopant in the perovskite structure; reducing treatments at different temperatures were performed to promote copper atom exsolution, thus forming nanostructures upon the surface. The perovskitic structure was confirmed via ex situ and operando XRD analysis, while compositional analysis was carried out through XPS and EDS; SEM and TEM images revealed morphological changes with different reducing treatments, and bulk reducibility was analysed with H2-TPR, revealing different Cu species in the material. Band gap analysis via DRS showed the successful incorporation of copper in the perovskite, affecting the light absorption properties. Finally, catalytic tests showed that copper nanoparticles play a role in CO2 activation with sunlight, proving that LSPR could be exploited for catalytic means.

Comparative analysis of CO2 reduction by soluble Escherichia coli formate dehydrogenase H and its selenocysteine-to-cysteine substitution variant

Metal-dependent formate dehydrogenases (Me-FDHs) are highly active CO2-reducing enzymes operating at low redox potentials and employ either molybdenum or tungsten to reduce the bound substrate. This makes them suitable for electrochemical applications such as fossil-free production of commodity chemicals utilizing renewable energy. Electrocatalytic CO2 reduction by cathode-immobilized Me-FDHs has been recently demonstrated and rational protein engineering can be used to optimize Me-FDHs for various carbon reduction reactions. In the present study, CO2 reduction by soluble monomeric Escherichia coli formate dehydrogenase H (EcFDH-H) was demonstrated and the function of its nucleophilic selenocysteine residue as a transient ligand of a centrally bound molybdenum atom was investigated. Kinetic analysis of the wildtype enzyme revealed maximum CO2 reduction rates of 44 ± 6 s−1 at pH 5.8 that was decreased to 19% and 0% in the case of selenocysteine substitution with the structural homologues cysteine and serine, respectively. Further selenocysteine-to-cysteine substitution effects included an increased acid tolerance as well as stronger inhibition by nitrate and azide indicating a shift of the Mo oxidation state from IV to VI. Conversely, a destabilizing effect on the oxidized Mo(VI) center could be assigned to the native selenocysteine residue that may facilitate the observed efficient CO2 reduction by rapid transition between Mo oxidation states. Taken together, the performed characterization of EcFDH-H as a catalyst for CO2 reduction and the selenocysteine substitution analysis furthers the understanding of the active-site structure of Me-FDHs and thereby supports the development of more efficient biocatalysts for CO2 reduction.

Directional spatial charge separation in well-designed S-scheme In2S3–ZnIn2S4/Au heterojunction toward highly efficient photocatalytic hydrogen evolution

Constructing efficient and stable photocatalysts are quite crucial for solar-to-hydrogen energy conversion, which remains a great challenge. Nowadays, many photocatalysts still suffer from low solar energy conversion efficiency due to the rapid recombination of photoirradiated carriers mainly caused by their random flow. Regulating charge separation and transport is essential to improve the catalytic activity of photocatalysts toward highly efficient photocatalytic hydrogen production. Herein, a S-scheme In2S3–ZnIn2S4/Au heterojunction with coherent interfaces were constructed. Particularly, as a reduction cocatalyst, the plasmonic metallic Au nanoparticles were loading on the outer surface of S-scheme In2S3–ZnIn2S4 heterojunction. The coordination of S-scheme heterojunction and reductive cocatalyst can produce a directional spatial charge separation and transfer in In2S3–ZnIn2S4/Au heterojunction, leading to a highly efficient photocatalytic hydrogen production. As expected, the well-designed S-scheme In2S3–ZnIn2S4/Au heterojunction presents a remarkable H2 production rate of 12,369 μmol h−1 g−1. This charge transfer modulation mechanism may be applied to design other remarkable photocatalytic materials for efficient solar energy conversion.

Mechanistic investigation on Ag-Cu2O in electrocatalytic CO2 to CH4 by in situ/operando spectroscopic and theoretical analysis

Silver-copper electrocatalysts have demonstrated effectively catalytic performance in electroreduction CO2 toward CH4, yet a revealing insight into the reaction pathway and mechanism has remained elusive. Herein, we construct chemically bonded Ag-Cu2O boundaries, in which the complete reduction of Cu2O to Cu has been strongly impeded owing to the presence of surface Ag shell. The interfacial confinement effect helps to maintain Cu+ sites at the Ag-Cu2O boundaries. Using in situ/operando spectroscopy and theoretical simulations, it is revealed that CO2 is enriched at the Ag-Cu2O boundaries due to the enhanced physisorption and chemisorption to CO2, activating CO2 to form the stable intermediate *CO. The boundaries between Ag shell and the Cu2O mediate local *CO coverage and promote *CHO intermediate formation, consequently facilitating CO2-to-CH4 conversion. This work not only reveals the structure-activity relationships but also offers insights into the reaction mechanism on Ag-Cu catalysts for efficient electrocatalytic CO2 reduction.

Boron-induced growth of highly textured Ag (1 1 1) films with nano-tentacle structures for the electrochemical reduction of CO2 to CO

Ag is a cost-effective alternative to Au as a catalyst for the electrochemical reduction of CO2 into CO, but a reduction in the accompanying overpotential is required to make Ag viable. In this study we use B to modulate the catalytic performance of Ag towards the electrochemical reduction of CO2 to CO. Initial DFT simulations discloses a deviation from the linear scaling relations with the inclusion of B that stabilizes the *COOH intermediate while weakening the binding strength of *CO. A magnetron co-sputtering process is used to develop a catalyst based on B-induced crystal growth of highly textured Ag (111) films. Incorporation of B facilitates the formation of Ag (111) coherent twin boundaries, which gives rise to unique nano-tentacle structures. The Ag-B catalyst achieves a faradaic efficiency of CO production of 97.9% at −0.9 V vs RHE with a partial current density that is four times higher compared to pristine Ag. Thus, the inclusion of B into Ag offers a facile approach for circumventing the linear scaling relations, allowing for the design of electrocatalysts with high faradaic efficiencies and current densities.

Self-Photosensitizing Dinuclear Ruthenium Catalyst for CO2 Reduction to CO.

The promise of artificial photosynthesis to solve environmental and energy issues such as global warming and the depletion of fossil fuels has inspired intensive research into photocatalytic systems for CO2 reduction to produce value-added chemicals such as CO and CH3OH. Among the photocatalytic systems for CO2 reduction, self-photosensitizing catalysts, bearing the functions of both photosensitization and catalysis, have attracted considerable attention recently, as such catalysts do not depend on the efficiency of electron transfer from the photosensitizer to the catalyst. Here, we have synthesized and characterized a dinuclear RuII complex bearing two molecules of a tripodal hexadentate ligand as chelating and linking ligands by X-ray crystallography to establish the structure explicitly and have used various spectroscopic and electrochemical methods to elucidate the photoredox characteristics. The dinuclear complex has been revealed to act as a self-photosensitizing catalyst, which acts not only as a photosensitizer but also as a catalyst for CO2 reduction. The dinuclear RuII complex is highly durable and performs efficient and selective CO2 reduction to produce CO with a turnover number of 2400 for 26 h. The quantum yield of the CO formation is also very high─19.7%─and the catalysis is efficient, even at a low concentration (∼1.5%) of CO2.