Electrocatalysts For CO2 Reduction Research Articles

NHC-CDI Ligands Boost Multicarbon Production in Electrocatalytic CO2 Reduction by Increasing Accumulated Charged Intermediates and Promoting *CO Dimerization on Cu.

Copper-based materials exhibit significant potential as catalysts for electrochemical CO2 reduction, owing to their capacity to generate multicarbon hydrocarbons. The molecular functionalization of Cu electrodes represents a simple yet powerful strategy for improving the intrinsic activity of these materials by favoring specific reaction pathways through the creation of tailored microenvironments around the surface active sites. However, despite its success, comprehensive mechanistic insights derived from experimental techniques are often limited, leaving the active role of surface modifiers inconclusive. In this work, we show that N-heterocyclic carbene-carbodiimide-functionalized Cu catalysts display a remarkable activity for multicarbon product formation, surpassing bare Cu electrodes by more than an order of magnitude. These hybrid catalysts operate efficiently using an electrolyzer equipped with a gas diffusion electrode, achieving a multicarbon product selectivity of 58% with a partial current density of ca. -80 mA cm-2. We found that the activity for multicarbon product formation is closely linked to the surface charge that accumulates during electrocatalysis, stemming from surface intermediate buildup. Through X-ray photoelectron spectroscopy, we elucidated the role of the molecular additives in altering the electronic structure of the Cu electrodes, promoting the stabilization of surface CO. Additionally, in situ Raman measurements established the identity of the reaction intermediates that accumulate during electrocatalysis, indicating preferential CO binding on Cu step sites, known for facilitating C-C coupling. This study underscores the significant potential of molecular surface modifications in developing efficient electrocatalysts for CO2 reduction, highlighting surface charge as a pivotal descriptor of multicarbon product activity.

Copper/Polyaniline Interfaces Confined CO2 Electroreduction for Selective Hydrocarbon Production.

Polyaniline (PANI) provides an attractive organic platform for CO2 electrochemical reduction due to the ability to adsorb CO2 molecules and in providing means to interact with metal nanostructures. In this work, a novel PANI supported copper catalyst has been developed by coupling the interfacial polymerization of PANI and Cu nanoparticles. The hybrid catalyst demonstrates excellent activity towards production of hydrocarbon products including CH4 and C2H4, compared with the use of bare Cu nanoparticles. A faradaic efficiency of 71.8% and a current density of 16.9 mA/cm2 were achieved at -0.86V vs. RHE, in contrast to only 22.2% and 1.0 mA/cm2 from the counterpart Cu catalysts. The remarkably enhanced catalytic performance of the hybrid PANI/Cu catalyst can be attributed to the synergistic interaction between the PANI underlayer and copper nanoparticles. The PANI favours the adsorption and binding of CO2 molecules via its nitrogen sites to form *CO intermediates, while the Cu/PANI interfaces confine the diffusion or desorption of the *CO intermediates favouring their further hydrogenation or carbon-carbon coupling to form hydrocarbon products. This work provides insights into the formation of hydrocarbon products on PANI-modified Cu catalysts, which may guide the development of conducting polymer-metal catalysts for CO2 electroreduction.

Biomass-based carbon aerogels with interconnected pores and controllable Zn–N sites for CO2 electroreduction

The rational design of renewable, highly active, and selective catalysts has always been the key to the practical application of CO2 electroreduction. In this study, biomass-based Zn/N doped carbon aerogels were fabricated for high-selectivity electrical reduction of CO2 to CO. After in situ Zn/N doping, carbon aerogels exhibited interconnected pores, high surface area, and exposed active sites, and their physicochemical properties are significantly affected by pyrolysis temperature. When the pyrolysis temperature increased to 950 °C, the number of surface active sites and pore structure parameters of carbon aerogels decreased significantly due to the escape of zinc and nitrogen. CAZN-850 exhibited the highest specific surface area of 1317.0 m2/g and abundant Zn–N sites, which results in its high activity and selectivity for electroreduction of CO2 to CO (FECO = 89 % at −1.0V vs. RHE). Moreover, the stability test results for CO2RR showed that the reduction value of FECO for Zn/N doped carbon aerogels was only 5 % under long-time operation. This work provides a new idea for the design of biomass-based catalysts for CO2 electroreduction.

Sustainedly High‐Rate Electroreduction of CO2 to Multi‐Carbon Products on Nickel Oxygenate/Copper Interfacial Catalysts

AbstractCopper (Cu) is the most attractive electrocatalyst for CO2 reduction to multi‐carbon (C2+) products with high economic value in considerable amounts. However, the rational design of a structurally stable Cu‐based catalyst that can achieve high activity and stability towards C2+ products remain a grand challenge. Here, a highly stable nickel oxygenate/Cu electrocatalyst is developed with abundant NiOOH/Cu interfaces by in situ electrochemical reconstruction. The nickel oxygenate/Cu electrocatalyst achieves a superior Faradaic efficiency of 86.3 ± 3.0% and a record partial current density of 2085 A g−1 for C2+ products with long‐term stability. In situ experimental and theoretical studies demonstrates that the exceptional performance in generating C2+ products is attributed to the presence of the NiOOH/Cu interfaces which increase *CO coverage, lower energy barrier for *CO coupling and stabilize *OCCO simultaneously. This work provides new insights into the rational design of electrocatalysts to achieve stable and efficient electrocatalytic CO2 reduction capabilities.

Gray mesoporous SnO2 catalyst for CO2 electroreduction with high partial current density and formate selectivity

The mesoporous metal oxide semiconductors exhibit unique chemical and physical characteristics, making them highly desirable for catalysis, electrochemistry, energy conversion, and energy storage applications. Here, we report the facial fabrication of mesoporous gray SnO2 (MGS) electrocatalysts employing an evaporation-induced co-assembly (EICA) approach, utilizing poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers Pluronic P123 (PEO-PPO-PEO) triblock copolymer as a template for electrochemical CO2 reduction reaction (eCO2RR). By sustaining the co-assembly conditions and utilizing a thermal treatment technique based on carbon, gray mesoporous SnO2 materials with a high density of active sites and oxygen vacancies can be constructed. The MGS materials were employed in eCO2RR in a flow cell type, which exhibits excellent catalytic activity and selectivity toward formate with a high partial current density of -234 mA cm-2 and Faradic efficiency (FE) of 93.60 % at -1.3 V vs. reversible hydrogen electrode (RHE). Interestingly, the mesoporous SnO2 with a 1.5 wt% ratio of Sn precursor to P123 surfactant (MS-1.5@350N-400A) electrode exhibits a high level of Faradaic efficiency (FE) of (98%) at a low overpotential of -0.6 VRHE, which is a seldom recorded performance for similar systems. A stable FE of 96 ± 1% was observed in the range of -0.6 to -1.2 VRHE, which is the result of a large surface area (184 m2 /g) and a high number of active sites and oxygen vacancies within the mesostructured framework.

Efficient Lead Removal by Assembly of Bio-Derived Ellagate Framework, Which Enables Electrocatalytic Reduction of CO2 to Formate.

Lead (Pb) poisoning and CO2-induced global warming represent two exemplary environmental and energy issues threatening humanity. Various biomass-derived materials are reported to take up Pb and convert CO2 electrochemically into low-valent carbon species, but these works address the problems separately rather than settle the issues simultaneously. In this work, cheap, natural ellagic acid (EA) extracted from common plants is adopted to assemble a stable metal-organic framework (MOF), EA-Pb, by effective capture of Pb2+ ions in an aqueous medium (removal rate close to 99%). EA-Pb represents the first structurally well-defined Pb-based MOF showing selective electrocatalytic CO2-to-HCOO- conversion with Faradaic efficiency (FE) of 95.37% at -1.08V versus RHE. The catalytic mechanism is studied by 13CO2 labeling, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and theoretical calculation. The use of EA-Pb as an electrocatalyst for CO2 reduction represents a 2-in-1 solution of converting detrimental wastes (Pb2+) as well as natural resources (EA) into wealth (electrocatalytic EA-Pb) for addressing the global warming issue.

Synergistic Effects of Doping and Strain in Bismuth Catalysts for CO2 Electroreduction.

Doping is a recognized method for enhancing catalytic performance. The introduction of strains is a common consequence of doping, although it is often overlooked. Differentiating the impact of doping and strain on catalytic performance poses a significant challenge. In this study, Cu-doped Bi catalysts with substantial tensile strain are synthesized. The synergistic effects of doping and strain in bismuth result in a remarkable CO2RR performance. Under optimized conditions, Cu1/6-Bi demonstrates exceptional formate Faradaic efficiency (>95%) and maintains over 90% across a wide potential window of 900 mV. Furthermore, it delivers an industrial-relevant partial current density of -317 mA cm-2 at -1.2 VRHE in a flow cell, while maintaining its selectivity. Additionally, it exhibits exceptional long-term stability, surpassing 120 h at -200 mA cm-2. Through experimental and theoretical mechanistic investigations, it has been determined that the introduction of tensile strain facilitates the adsorption of *CO2, thereby enhancing the reaction kinetics. Moreover, the presence of Cu dopants and tensile strain further diminishes the energy barrier for the formation of *OCHO intermediate. This study not only offers valuable insights for the development of effective catalysts for CO2RR through doping, but also establishes correlations between doping, lattice strains, and catalytic properties of bismuth catalysts.

Large language model enhanced corpus of CO2 reduction electrocatalysts and synthesis procedures

CO2 electroreduction has garnered significant attention from both the academic and industrial communities. Extracting crucial information related to catalysts from domain literature can help scientists find new and effective electrocatalysts. Herein, we used various advanced machine learning, natural language processing techniques and large language models (LLMs) approaches to extract relevant information about the CO2 electrocatalytic reduction process from scientific literature. By applying the extraction pipeline, we present an open-source corpus for electrocatalytic CO2 reduction. The database contains two types of corpus: (1) the benchmark corpus, which is a collection of 6,985 records extracted from 1,081 publications by catalysis postgraduates; and (2) the extended corpus, which consists of content extracted from 5,941 documents using traditional NLP techniques and LLMs techniques. The Extended Corpus I and II contain 77,016 and 30,283 records, respectively. Furthermore, several domain literature fine-tuned LLMs were developed. Overall, this work will contribute to the exploration of new and effective electrocatalysts by leveraging information from domain literature using cutting-edge computer techniques.

Recent Progress in Hollow Fiber Gas Diffusion Electrodes for CO2 Electroreduction

CO2 electroreduction (CO2RR) to high‐value chemicals by renewable energy is a promising route for achieving carbon cycling. Traditional two‐dimensional planar electrodes applied in CO2RR are faced with problems of high mass transfer resistance, carbonate precipitation, flooding, and complicated structures, seriously limiting their CO2RR efficiency and application. Three‐dimensional hollow fiber gas diffusion electrodes (HFGDEs) are promising candidates due to their rich specific surface area, low mass transfer resistance, simplified component, and no flooding trouble, which are beneficial for achieving high current density as well as high CO2RR efficiency. In this review, we provide inspirations and positive paradigms for the rational design of HFGDE toward CO2RR by following part: 1. The mechanism of CO2RR. 2. The classification of the typical metal‐based CO2RR catalysts. 3. The preparation process of HFGDEs. 4. Recent advanced HFGDE studies for CO2RR. 5. Challenges at this stage and future development of HFGDEs towards accelerating application of industrial CO2 reduction electrolyzers.

Investigating the interplay between charge transfer and CO2 insertion in the adsorption of a NiFe catalyst for CO2 electroreduction on a graphite support through DFT computational approaches.

This article describes a density functional theory (DFT) study to explore a bio-inspired NiFe complex known for its experimental activity in electro-reducing CO2 to CH4 when adsorbed on graphite. The coordination properties of the complex are investigated in isolated form and when physisorbed on a graphene surface. A comparative analysis of DFT approaches for surface modeling is conducted, utilizing either a finite graphene flake or a periodic carbon surface. Results reveal that the finite model effectively preserves all crucial properties. By examining predicted structures arising from CO2 insertion within the mono-reduced NiFe species, whether isolated or adsorbed on the graphene flake, a potential species for subsequent electro-reduction steps is proposed. Notably, the DFT study highlights two positive effects of complex adsorption: facile electron transfers between graphene and the complex, finely regulated by the complex state, and a lowering of the thermodynamic demand for CO2 insertion.

Electrocatalytic reduction of CO2 by Co-Cu metastable alloy nanoparticles derived from MOFs

The construction of non-noble metal electrodes for the catalytic reduction of CO2 has drawn much attention in recent years. Herein, a facile CoCu@C composite catalyst was synthesized by simply carbonizing CoCu-MOFs, a bimetal MOFs fabricated by integrating Cu2+ ions into the synthesis of ZIF-67. Co-Cu alloy nanoparticles were closely embedded in porous carbon skeleton. Notably, the optimal Co1Cu3@C sample exhibited a total catalytic current of 29.8mA·cm-2 at -0.7V vs RHE, which was 2.56 times of the Co@C catalyst derived from original ZIF-67. Besides, the Co1Cu3@C sample achieved targeted CO:H2 ratios in the CO2 reduction reactions, covering approximately 1:1.7 to 1:4, meeting well with industrial needs. Density Functional Theory (DFT) calculations unveiled an electron migration from Co to Cu within the alloy, indicating the promoted transfer of electrons. Co atoms in Co-Cu alloy was found as the predominant active sites for the reduction of CO2. The study provided a economical CO2 reduction electrocatalyst with cheap feedstock, low operating voltage and specific ratio of syngas. Additionally, this work significantly advances our understanding of Co-Cu alloy electrocatalysts, providing crucial insights for the ongoing evolution of electrocatalyst research in material preparation and theoretical calculations.

Highly efficient electrocatalytic CO2 reduction by a CrIII quaterpyridine complex

Design tactics and mechanistic studies both remain as fundamental challenges during the exploitations of earth-abundant molecular electrocatalysts for CO2 reduction, especially for the rarely studied Cr-based ones. Herein, a quaterpyridyl CrIII catalyst is found to be highly active for CO2 electroreduction to CO with 99.8% Faradaic efficiency in DMF/phenol medium. A nearly one order of magnitude higher turnover frequency (86.6 s-1) over the documented Cr-based catalysts (<10 s-1) can be achieved at an applied overpotential of only 190 mV which is generally 300 mV lower than these precedents. Such a high performance at this low driving force originates from the metal-ligand cooperativity that stabilizes the low-valent intermediates and serves as an efficient electron reservoir. Moreover, a synergy of electrochemistry, spectroelectrochemistry, electron paramagnetic resonance, and quantum chemical calculations allows to characterize the key CrII, CrI, Cr0, and CO-bound Cr0 intermediates as well as to verify the catalytic mechanism.

Theoretical study on the electrocatalytic CO2 reduction mechanisms using carbon-nanotube-supported carbon-based single metal atom catalysts

In this study, five Ni-doped carbon-based single metal atom catalysts supported by carbon nanotubes, which can be used for electrocatalytic CO2 reduction, were constructed. According to their structures, these catalysts include one Ni phthalocyanine (NiPc) molecule, two di- and tri-coordinated Ni-doped carbon nanoribbons, and two di-/tri-coordination Ni-doped graphene, which are denoted as NiPc/CNT, H2(H3)-Ni/CNT, 2(3)-Ni/CNT respectively. We first optimized their structures and studied the adsorption characteristics of CO2 on these catalysts with PBE+D3 method. Additionally, the electronic structure characteristics were then calculated, and the electrocatalytic mechanisms of CO2 reduction to CO, HCOOH, CH3OH and CH4 using these catalysts were studied in detail. It is found that the electrocatalytic activities of these five catalysts for reducing CO2 follow the order of 2-Ni/CNT>3-Ni/CNT>H3-Ni/CNT>H2-Ni/CNT>NiPc/CNT. As can be seen, the di-coordination catalysts perform best, followed by the tri-coordination catalysts, while the four-coordination NiPc-based catalyst performs worst. Moreover, graphene-based materials have stronger catalytic activities than their nanoribbon counterparts. Apart from these facts, these five catalytic materials may exhibit product selectivity at different limiting potentials, and specific reaction products can therefore be synthesized by controlling the potentials. We simultaneously investigated the mechanism of competing hydrogen evolution reactions in the electrocatalytic reduction of CO2 with five catalysts, and in order to inhibit the competing hydrogen evolution reactions and improve the efficiency of CO2 electrocatalytic reduction, the acidity of the solution can be appropriately reduced. We hope that our present work can provide a theoretical foundation for the future design and synthesis of novel carbon-based electrocatalyst for efficient CO2 reduction.

Potential Dependent Reorientation Controlling Activity of a Molecular Electrocatalyst.

The activity of molecular electrocatalysts depends on the interplay of electrolyte composition near the electrode surface, the composition and morphology of the electrode surface, and the electric field at the electrode-electrolyte interface. This interplay is challenging to study and often overlooked when assessing molecular catalyst activity. Here, we use surface specific vibrational sum frequency generation (VSFG) spectroscopy to study the solvent and potential dependent activation of Mo(bpy)(CO)4, a CO2 reduction catalyst, at a polycrystalline Au electrode. We find that the parent complex undergoes potential dependent reorientation at the electrode surface when a small amount of N-methyl-2-pyrrolidone (NMP) is present. This preactivates the complex, resulting in greater yields at less negative potentials, of the active electrocatalyst for CO2 reduction.

Unveiling mechanisms in Cu2O-catalyzed electroreduction of CO2 through theoretical resolution using periodic boundary and saturation cluster models

The imperative need to reduce atmospheric CO2 to mitigate global warming and advance sustainable energy systems has driven extensive research. Copper oxide (Cu2O) has emerged as a promising catalyst for electroreduction of CO2, yet its catalytic mechanism remains debated. This study employs a theoretical approach to delve into the intricate details of CO2 electroreduction catalyzed by Cu2O. Utilizing both periodic boundary and saturation cluster models, we explore various reaction pathways, successfully identifying key transition states and intermediates with each model. A comprehensive analysis and comparison of results from both models are conducted. To enhance understanding, we develop a method simulating the impact of an electric field, employed to probe the ongoing reaction. Additionally, we consider the solid–liquid interface by introducing solvent molecules and buffer ions into our analysis. This comprehensive theoretical investigation aims to elucidate the mechanism governing the electroreduction of CO2 catalyzed by Cu2O and analogous semiconductor oxides, providing valuable insights into this critical process.

Enhanced Microbial Protein Production from CO2 and Air by a MoS2 Catalyzed Bioelectrochemical System.

Carbon dioxide can be relatively easily reduced to organic matter in a bioelectrochemical system (BES). However, due to insufficient reduction force from in-situ hydrogen evolution, it is difficult for nitrogen reduction. In this study, MoS2 was firstly used as an electrocatalyst for the simultaneous reduction of CO2 and N2 to produce microbial protein (MP) in a BES. Cell dry weight (CDW) could reach 0.81±0.04 g/L after 14 d operation at -0.7 V (vs. RHE), which was 108±3 % higher than that from non-catalyst control group (0.39±0.01 g/L). The produced protein had a better amino acid profile in the BES than that in a direct hydrogen system (DHS), particularly for proline (Pro). Besides, MoS2 promoted the growth of bacterial cell on an electrode and improved the biofilm extracellular electron transfer (EET) by microscopic observation and electrochemical characterization of MoS2 biocathode. The composition of the microbial community and the relative abundance of functional enzymes revealed that MoS2 as an electrocatalyst was beneficial for enriching Xanthobacter and enhancing CO2 and N2 reduction by electrical energy. These results demonstrated that an efficient strategy to improve MP production of BES is to use MoS2 as an electrocatalyst to shift amino acid profile and microbial community.

Constructing 2D Phthalocyanine Covalent Organic Framework with Enhanced Stability and Conductivity via Interlayer Hydrogen Bonding as Electrocatalyst for CO2 Reduction.

Fabricating COFs-based electrocatalysts with high stability and conductivity still remains a great challenge. Herein, 2D polyimide-linked phthalocyanine COF (denoted as NiPc-OH-COF) is constructed via solvothermal reaction between tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato nickel(II) and 2,5-diamino-1,4-benzenediol (DB) with other two analogous 2D COFs (denoted as NiPc-OMe-COF and NiPc-H-COF) synthesized for reference. In comparison with NiPc-OMe-COF and NiPc-H-COF, NiPc-OH-COF exhibits enhanced stability, particularly in strong NaOH solvent and high conductivity of 1.5×10-3 Sm-1 due to the incorporation of additional strong interlayer hydrogen bonding interaction between the O-H of DB and the hydroxy "O" atom of DB in adjacent layers. This in turn endows the NiPc-OH-COF electrode with ultrahigh CO2 -to-CO faradaic efficiency (almost 100%) in a wide potential range from -0.7 to -1.1V versus reversible hydrogen electrode (RHE), a large partial CO current density of -39.2mAcm-2 at -1.1V versus RHE, and high turnover number as well as turnover frequency, amounting to 45000 and 0.76S-1 at -0.80V versus RHE during 12h lasting measurement.

Hybrid oxide coatings generate stable Cu catalysts for CO2 electroreduction

Hybrid organic/inorganic materials have contributed to solve important challenges in different areas of science. One of the biggest challenges for a more sustainable society is to have active and stable catalysts that enable the transition from fossil fuel to renewable feedstocks, reduce energy consumption and minimize the environmental footprint. Here we synthesize novel hybrid materials where an amorphous oxide coating with embedded organic ligands surrounds metallic nanocrystals. We demonstrate that the hybrid coating is a powerful means to create electrocatalysts stable against structural reconstruction during the CO2 electroreduction. These electrocatalysts consist of copper nanocrystals encapsulated in a hybrid organic/inorganic alumina shell. This shell locks a fraction of the copper surface into a reduction-resistant Cu2+ state, which inhibits those redox processes responsible for the structural reconstruction of copper. The electrocatalyst activity is preserved, which would not be possible with a conventional dense alumina coating. Varying the shell thickness and the coating morphology yields fundamental insights into the stabilization mechanism and emphasizes the importance of the Lewis acidity of the shell in relation to the retention of catalyst structure. The synthetic tunability of the chemistry developed herein opens new avenues for the design of stable electrocatalysts and beyond.

Metal–N4 model single‐atom catalyst with electroneutral quadri‐pyridine macrocyclic ligand for CO2 electroreduction

AbstractMetal–N–C single‐atom catalysts, mostly prepared from pyrolysis of metal‐organic precursors, are widely used in heterogeneous electrocatalysis. Since metal sites with diverse local structures coexist in this type of material and it is challenging to characterize the local structure, a reliable structure–property relationship is difficult to establish. Conjugated macrocyclic complexes adsorbed on carbon support are well‐defined models to mimic the single‐atom catalysts. Metal–N4 site with four electroneutral pyridine‐type ligands embedded in a graphene layer is the most commonly proposed structure of the active site of single‐atom catalysts, but its molecular counterpart has not been reported. In this work, we synthesized the conjugated macrocyclic complexes with a metal center (Co, Fe, or Ni) coordinated with four electroneutral pyridinic ligands as model catalysts for CO2 electroreduction. For comparison, the complexes with anionic quadri‐pyridine macrocyclic ligand were also prepared. The Co complex with the electroneutral ligand expressed a turnover frequency of CO formation more than an order of magnitude higher than that of the Co complex with the anionic ligand. Constrained ab initio molecular dynamics simulations based on the well‐defined structures of the model catalysts indicate that the Co complex with the electroneutral ligand possesses a stronger ability to mediate electron transfer from carbon to CO2.

Revealing the Lattice Carbonate Mediated Mechanism in Cu2(OH)2CO3 for Electrocatalytic Reduction of CO2 to C2H4.

Understanding the CO2 transformation mechanism on materials is essential for the design of efficient electrocatalysts for CO2 reduction. In aconventional adsorbate evolution mechanism (AEM), the catalysts encounter multiple high-energy barrier steps, especially CO2 activation, limiting the activity and selectivity. Here, lattice carbonate from Cu2(OH)2CO3 is revealed to be a mediator between CO2 molecules and catalyst during CO2 electroreduction by a 13C isotope labeling method, which can bypass the high energy barrier of CO2 activation and strongly enhance the performance. With the lattice carbonate mediated mechanism (LCMM), the Cu2(OH)2CO3 electrode exhibited ten-fold faradaic efficiency and 15-fold current density for ethylene production than the Cu2O electrode with AEM at a low overpotential. Theoretical calculations and in situ Raman spectroscopy results show that symmetric vibration of carbonate is precisely enhanced on the catalyst surface with LCMM, leading to faster electron transfer, and lower energy barriers of CO2 activation and carbon-carbon coupling. This work provides a route to develop efficient electrocatalysts for CO2 reduction based on lattice-mediated mechanism.