Copper-based Catalysts Research Articles

Hydrothermal Synthesis of CuS Catalysts for Electrochemical CO2 Reduction: Unraveling the Effect of the Sulfur Precursor

Copper-based catalysts have been recognized as promising candidates for electrochemical conversion of CO2 to value-added chemicals and synthetic fuels. Yet, the challenges of high overpotential and low product selectivity have motivated the rational electrode engineering. In the present work, we prepared CuS catalysts using different sulfur precursors, and we aimed to elucidate the precursor-dependent effect on their structure–property–activity relationships for electrochemical CO2 reduction. The different sulfur precursors exhibited varied S release rates in hydrothermal synthesis, which had induced distinct surface morphological features and diverse sulfur vacancy concentrations, and the intrinsic catalytic activity and product selectivity would be affected. The desired CuS-TU catalyst synthesized using thiourea as the sulfur precursor featured a flower-like morphology and had the highest sulfur vacancy concentration. The nanoflower morphology offered expanded space and considerable undercoordinated sites for facilitated interfacial mass transfer in electrochemical CO2 reduction. Density functional theory calculations confirmed that the abundant sulfur vacancy played an important role in strengthening the adsorption of the *COOH intermediates on the surface, which promoted CO production via the *COOH pathway. The CuS-TU catalyst therefore exhibited a relatively higher CO selectivity of 72.67% at −0.51 V vs RHE. These findings will provide more insights into improving the electrochemical CO2 reduction performance of copper-based catalysts by structure engineering.

Unveiling the synergistic effect of multi-valence Cu species to promote formaldehyde oxidation for anodic hydrogen production

•Efficient anodic H2 generation is achieved on a Cu-based catalyst •FOR mechanism of Cu0–Cu+ synergy is clarified •Design guidelines for copper-based catalysts for FOR are proposed •A new strategy for the dual-sides H2 production electrolyzer is provided The ultra-low potential oxidation of aldehydes is a conspicuous replacement for oxygen evolution reaction due to its efficiency in lowering the energy required for hydrogen production and producing H2 on dual sides of the electrolyzer. However, the activity origin of catalysts and the reaction mechanism remains unclear. Herein, a formaldehyde oxidation reaction (FOR) with high current density (165 mA cm−2 at 0.35 VRHE) is realized on partially reduced CuO on Cu foam (Cux[email protected]) electrocatalysts. In situ characterizations and density functional theory calculations identified and investigated the existence of Cu0 and Cu+ and the synergistic effect for FOR and corroborate the reaction pathway. The results reveal that Cu0 can facilitate the reaction energy of HOCH2O∗ + HO∗, and Cu+ is more favorable for C–H bond cleavage. Meanwhile, H atoms in the produced H2 are verified to be entirely from HCHO. This work provides theoretical guidance for designing Cu-based electrocatalysts for FOR. The ultra-low potential oxidation of aldehydes is a conspicuous replacement for oxygen evolution reaction due to its efficiency in lowering the energy required for hydrogen production and producing H2 on dual sides of the electrolyzer. However, the activity origin of catalysts and the reaction mechanism remains unclear. Herein, a formaldehyde oxidation reaction (FOR) with high current density (165 mA cm−2 at 0.35 VRHE) is realized on partially reduced CuO on Cu foam (Cux[email protected]) electrocatalysts. In situ characterizations and density functional theory calculations identified and investigated the existence of Cu0 and Cu+ and the synergistic effect for FOR and corroborate the reaction pathway. The results reveal that Cu0 can facilitate the reaction energy of HOCH2O∗ + HO∗, and Cu+ is more favorable for C–H bond cleavage. Meanwhile, H atoms in the produced H2 are verified to be entirely from HCHO. This work provides theoretical guidance for designing Cu-based electrocatalysts for FOR.

Asymmetric Low-Frequency Pulsed Strategy Enables Ultralong CO2 Reduction Stability and Controllable Product Selectivity.

Copper-based catalysts are widely explored in electrochemical CO2 reduction (CO2RR) because of their ability to convert CO2 into high-value-added multicarbon products. However, the poor stability and low selectivity limit the practical applications of these catalysts. Here, we proposed a simple and efficient asymmetric low-frequency pulsed strategy (ALPS) to significantly enhance the stability and the selectivity of the Cu-dimethylpyrazole complex Cu3(DMPz)3 catalyst in CO2RR. Under traditional potentiostatic conditions, Cu3(DMPz)3 exhibited poor CO2RR performance with the Faradaic efficiency (FE) of 34.5% for C2H4 and FE of 5.9% for CH4 as well as the low stability for less than 1 h. We optimized two distinguished ALPS methods toward CH4 and C2H4, correspondingly. The high selectivities of catalytic product CH4 (FECH4 = 80.3% and above 76.6% within 24 h) and C2H4 (FEC2H4 = 70.7% and above 66.8% within 24 h) can be obtained, respectively. The ultralong stability for 300 h (FECH4 > 60%) and 145 h (FEC2H4 > 50%) was also recorded with the ALPS method. Microscopy (HRTEM, SAED, and HAADF) measurements revealed that the ALPS method in situ generated and stabilized extremely dispersive and active Cu-based clusters (∼2.7 nm) from Cu3(DMPz)3. Meanwhile, ex situ spectroscopies (XPS, AES, and XANES) and in situ XANES indicated that this ALPS method modulated the Cu oxidation states, such as Cu(0 and I) with C2H4 selectivity and Cu(I and II) with CH4 selectivity. The mechanism under the ALPS methods was explored by in situ ATR-FTIR, in situ Raman, and DFT computation. The ALPS methods provide a new opportunity to boost the selectivity and stability of CO2RR.

A Scientometric Review of CO2 Electroreduction Research from 2005 to 2022

Electrocatalytic CO2 reduction is regarded as a green and promising technology because it can convert carbon dioxide into value-added fuel or chemicals in a flexible and sustainable way. This research aimed to comprehensively analyze the research hotspots and trends in the field of CO2 electroreduction from 2005 to 2022 using bibliometric methods based on the core database of Web of Science. The results showed that 4546 papers on CO2 electroreduction were retrieved from 2005 to 2022, with a clear increasing trend. The research direction was diversified, involving multiple disciplines, and it is a comprehensive research field. ACS Catalysis is the journal with the largest number of articles. China is the country with the largest number of documents and has made significant contributions to the development and progress of this field. Copper-based catalysts are still the research focus in recent years. It is of great practical significance to develop copper-based catalysts with high efficiency, low cost, high stability, and high selectivity for the preparation of C1 products.

3-Bromopyruvate-Loaded Ti3C2 MXene/Cu2O Nanosheets for Photoacoustic Imaging-Guided and Hypoxia-Relieving Enhanced Photothermal/Chemodynamic Therapy

Chemodynamic therapy (CDT) is an innovative and effective treatment that relies on the Fenton or Fenton-like reaction, in which endogenous H2O2 overproduction is converted into cytotoxic hydroxyl radicals (•OH) to suppress tumor growth. Nevertheless, the therapeutic efficiency of CDT is severely restricted by undesirable properties, such as reaction conditions and catalyst performance. Herein, a 2D Ti3C2 MXene/Cu2O nanosheet (MCP NS)-based multifunctional nanoplatform (3-BP@MCG NSs) has been constructed, in which glucose oxidase (GOx) and respiration inhibitor 3-bromopyruvate (3-BP) are sequentially embedded. In this structure, the copper-based catalyst Cu2O releases Cu+ in an acid-triggered manner in the tumor microenvironment (TME), which activates the Fenton-like reaction to catalyze the generation of •OH for CDT. The composite has excellent photothermal properties and a high-resolution photoacoustic imaging (PAI) capability in the near-infrared (NIR) region, and especially under NIR irradiation, the photothermal effect generated by the nanosheets accelerates catalysis. GOx is a natural enzyme catalyst for depleting glucose and oxygen content in cells, upregulating H2O2 levels in situ, and thereby improving the therapeutic effect of CDT. What is more, the supported 3-BP not only reduces oxygen consumption to alleviate hypoxia levels but also inhibits the glycolysis process and lowers ATP levels by suppressing hexokinase activity. As a result, 3-BP@MCG NSs optimize the unique properties of MCP NSs, GOx, and 3-BP via mutual promotion, realizing self-enhanced PTT/CDT synergistic therapy. This work establishes an emerging strategy for highly efficient PAI-guided integrated treatment and provides a proof of concept for the cooperation of hypoxia relief and in situ H2O2 and NIR synergistic enhancement to improve therapeutic efficiency.

Effect of Water Vapor on Oxidation Processes of the Cu(111) Surface and Sublayer.

Copper-based catalysts have different catalytic properties depending on the oxidation states of Cu. We report operando observations of the Cu(111) oxidation processes using near-ambient pressure scanning tunneling microscopy (NAP-STM) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The Cu(111) surface was chemically inactive to water vapor, but only physisorption of water molecules was observed by NAP-STM. Under O2 environments, dry oxidation started at the step edges and proceeded to the terraces as a Cu2O phase. Humid oxidation of the H2O/O2 gas mixture was also promoted at the step edges to the terraces. After the Cu2O covered the surface under humid conditions, hydroxides and adsorbed water layers formed. NAP-STM observations showed that Cu2O was generated at lower steps in dry oxidation with independent terrace oxidations, whereas Cu2O was generated at upper steps in humid oxidation. The difference in the oxidation mechanisms was caused by water molecules. When the surface was entirely oxidized, the diffusion of Cu and O atoms with a reconstruction of the Cu2O structures induced additional subsurface oxidation. NAP-XPS measurements showed that the Cu2O thickness in dry oxidation was greater than that in humid oxidation under all pressure conditions.

Dichloro(2,2′-bipyridine)copper/MAO: An Active and Stereospecific Catalyst for 1,3-Diene Polymerization

Dichloro(2,2'-bipyridine)copper was synthesized by reacting copper dichloride with bypyridine, and its behavior, in combination with methylaluminoxane (MAO), in the polymerization of butadiene, isoprene, 2,3-dimethyl-1,3 butadiene, and 3-methyl-1,3-pentadiene was examined. The purpose of this study is to find catalytic systems that are more sustainable than those currently used for the polymerization of butadiene and isoprene (e.g., Co and Ni), but that are comparable in terms of catalytic activity and selectivity. Predominantly, syndiotactic 1,2 polybutadiene, crystalline syndiotactic 3,4 polyisoprene, crystalline syndiotactic 1,2 poly(3-methyl-1,3-pentadiene), and crystalline cis-1,4 poly(2,3-dimethyl-1,3-butadiene) were obtained in a manner similar to that observed with the analogous iron complex. As far as we know, the investigated catalytic system represents the first example of a copper-based catalyst in the field of stereospecific polymerization. Given the great availability of copper, its extremely low toxicity (and therefore high sustainability), and the similarity of its behavior to that of iron, the result obtained seems to us of considerable interest and worthy of further investigation.

Why copper catalyzes electrochemical reduction of nitrate to ammonia.

Electrochemical reduction of nitrate (NO3RR) has drawn significant attention in the scientific community as an attractive route for ammonia synthesis as well as alleviating environmental concerns for nitrate pollution. To improve the efficiency of this process, the development of catalyst materials that exhibit high activity and selectivity is of paramount importance. Copper and copper-based catalysts have been widely investigated as potential catalyst materials for this reaction both computationally and experimentally. However, less attention has been paid to understanding the reasons behind such high activity and selectivity. Herein, we use Density Functional Theory (DFT) to identify reactivity descriptors guiding the identification of active catalysts for the NO3RR, establish trends in activity, and explain why copper is the most active and selective transition metal for the NO3RR to ammonia among ten different transition metals, namely Au, Ag, Cu, Pt, Pd, Ni, Ir, Rh, Ru, and Co. Furthermore, we assess NO3RR selectivity by taking into account the competition between the NO3RR and the hydrogen evolution reaction. Finally, we propose various approaches for developing highly active catalyst materials for the NO3RR.

On the role of C4 and C5 products in electrochemical CO2 reduction via copper-based catalysts

We identify many larger organics as products of electrochemical CO2 reduction in high-current GDEs – most interestingly, C4 and C5 isomers. The analysis of selectivity trends allows for deduction of general hypotheses to build a detailed mechanism.

Enhancing the activity and stability of Cu2O nanorods via coupling with a NaNbO3/SnS2 heterostructure for photoelectrochemical water-splitting

We synthesized a stable copper-based heterostructure catalyst, NaNbO3/SnS2/Cu2O for photoelectrochemical water-splitting applications with improved activity, stability, and inhibited photocorrosion in Cu2O.

Copper-based catalysts for the electrochemical reduction of carbon dioxide: progress and future prospects.

There is an urgent need for the development of high performance electrocatalysts for the CO2 reduction reaction (CO2RR) to address environmental issues such as global warming and achieve carbon neutral energy systems. In recent years, Cu-based electrocatalysts have attracted significant attention in this regard. The present review introduces fundamental aspects of the electrocatalytic CO2RR process together with a systematic examination of recent developments in Cu-based electrocatalysts for the electroreduction of CO2 to various high-value multicarbon products. Current challenges and future trends in the development of advanced Cu-based CO2RR electrocatalysts providing high activity and selectivity are also discussed.

Constructing carbon supported copper-based catalysts for efficient CO2 hydrogenation to methanol.

An activated carbon-supported Cu/ZnO catalyst (CCZ-AE-ox) was successfully obtained by the ammonia evaporation method for the hydrogenation of carbon dioxide to methanol, and the surface properties of the catalyst post-calcination and reduction were investigated. Activated carbon facilitated the increased dispersion of the loaded metals, which promote the CO2 space-time yield (STY) of methanol and turnover frequency (TOF) on the active sites. Furthermore, the factors affecting the catalyst in the hydrogenation of CO2 to methanol were in-depth investigated. The larger surface area and higher CO2 adsorption capacity are found to make possible the main attributions of the superior activity of the CCZ-AE-ox catalyst.

Copper-based catalysts for CO2 hydrogenation: a perspective on active sites

This Perspective reviews the understanding of active sites on various Cu-based materials for the CO2 hydrogenation to high-value products from theoretical and experimental advances.

Copper‐Based Catalysts for Electrochemical Reduction of Carbon Dioxide to Ethylene

Electrochemical reduction of CO2 into high energy density multi-carbon chemicals or fuels (e. g., ethylene) via new renewable energy storage has extraordinary implications for carbon neutrality. Copper (Cu)-based catalysts have been recognized as the most promising catalysts for the electrochemical reduction of CO2 to ethylene (C2 H4 ) due to their moderate CO adsorption energy and moderate hydrogen precipitation potential. However, the poor selectivity, low current density and high overpotential of the CO2 RR into C2 H4 greatly limit its industrial applications. Meanwhile, the complex reaction mechanism is still unclear, which leads to blindness in the design of catalysts. Herein, we systematically summarized the latest research, proposed possible conversion mechanisms and categorized the general strategies to adjust of the structure and composition for CO2 RR, such as tip effect, defect engineering, crystal plane catalysis, synergistic effect, nanoconfinement effect and so on. Eventually, we provided a prospect of the future challenges for further development and progress in CO2 RR. Previous reviews have summarized catalyst designs for the reduction of CO2 to multi-carbon products, while lacking in targeting C2 H4 alone, an important industrial feedstock. This Review mainly aims to provide a comprehensive understanding for the design strategies and challenges of electrocatalytic CO2 reduction to C2 H4 through recent researches and further propose some guidelines for the future design of copper-based catalysts for electroreduction of CO2 to C2 H4 .

Mixed Nanocomposites of Cu2O and Mn3O4 to Activate Peroxydisulfate for Efficient Degradation of Tetracycline via Cu(III) Species

Copper-based catalysts have attracted increasing interest in wastewater treatment via peroxydisulfate (PDS) activation. However, little attention has been paid to developing cuprous oxide (Cu2O)-based catalysts. In this study, Cu2O–Mn3O4 nanocomposites were synthesized by a high-temperature coprecipitation method and served as PDS activators. The Cu2O–Mn3O4/PDS system exhibited extremely high removal efficiency of tetracycline hydrochloride, with initial rate constants 16 and 43 times that of the Cu2O/PDS system and Mn3O4/PDS system, respectively. The results from X-ray powder diffraction, X-ray photoelectron spectroscopy, linear sweep voltammetry, and H2 temperature-programmed reduction confirmed the transformation of CuO into Cu2O with the presence of Mn3O4 in the composite, and the strong Cu–Mn interaction facilitated high electron density for Cu2O, which made it was easy to donate electrons to PDS. Additionally, chemical quenching tests, Cu(III)–periodate complex identification, and Raman spectra were conducted to illustrate that Cu(III) was formed as the main species to attack the pollutants via two electrons transferring from Cu(I) to PDS. The study developed an effective Cu2O–Mn3O4 catalyst based on the strong interaction of two nanomaterials and provided new mechanistic insights for Cu(I)-triggered PDS activation.

Effects of ligand tuning and core doping of atomically precise copper nanoclusters on CO2 electroreduction selectivity

Atomically precise nanoclusters (NCs) provide opportunities for correlating the structure and electrocatalytic properties at atomic level. Herein, we report the single-atom doping effect and ligand effect on CO2 electroreduction (eCO2RR) by comparing monogold-doped Au1Cu24 and homocopper Cu25 NCs protected by triphenylphosphine or/and tris(4-fluorophenyl)phosphine. Catalytic results revealed that the electronic distribution of Cu25 NCs is enormously contracted by doping Au atoms, entitling it to exhibit the unique inhibition of hydrogen evolution reaction. And the inductive effect of ligand strongly favors the formation of formate in eCO2RR. Overall, this work will provide guidance for the rational design of the copper-based catalysts in the eCO2RR.

Solvent Coordination Effect on Copper-Based Molecular Catalysts for Controlled Radical Polymerization

The equilibrium of copper-catalyzed atom transfer radical polymerization was investigated in silico with the aim of finding an explanation for the experimentally observed solvent effect. Various combinations of alkyl halide initiators and copper complexes in acetonitrile (MeCN) and dimethyl sulfoxide (DMSO) were taken into consideration. A continuum model for solvation, which does not account for the explicit interactions between the solvent and metal complex, is not adequate and does not allow the reproduction of the experimental trend. However, when the solvent molecules are included in the coordination sphere of the copper(I,II) species and the continuum description of the medium is still used, a solvent dependence of process thermodynamics emerges, in fair agreement with experimental trends.

Ultrasound-assisted synthesis of copper-based catalysts for the electrocatalytic CO2 reduction: Effect of ultrasound irradiation, precursor concentration and calcination temperature

The reduction of high CO2 concentrations in the atmosphere is an imperative task to reduce the consequences of the greenhouse effect on our planet. Developing active and selective materials for electrochemical CO2 reduction towards value-added products is mandatory to bring this technology to a practical application. This work studied the effect of assisting Cu and Zn oxides co-precipitation with sonochemistry. Different factors were investigated: the ultrasounds (US) amplitude, the effect of US irradiation time during either precipitation or ageing processes, the precursor concentration and calcination temperature. The synthesised catalysts were tested for the electrocatalytic CO2 reduction reaction in a Rotating Disk Electrode (RDE) system. Faradaic efficiencies >14% towards alcohols were obtained using US-assisted synthesised Cu-based catalysts. Instead, with the US-prepared Cupper-Zinc-based catalysts, the selectivity towards H2 and C1 products (CO and formate) was improved, and the syngas productivity was increased by > ⁓1.4-fold compared to the non-sonicated one. The alcohols production of the best Cu-catalyst was also confirmed on scalable electrodes. Controlling the synthesis conditions allowed to tune the physicochemical properties of the nanoparticles, including specific surface area, porosity, crystallite size and phases. Mesoporous materials with a mean pores size of around 25 nm were found to induce a better CO2 diffusion and CO retention time in the porous network, improving the *CO intermediate adsorption at active sites, promoting its dimerisation and thus enhancing the selectivity towards C2+ alcohols. The here reported results open the way for new electrocatalysts designs with properly tuned porosity for the selective CO2 conversion to different valuable products.

Facile preparation of efficient Cu-SiO2 catalysts using a polyhydroxy molecular template to regulate surface copper species for dimethyl oxalate hydrogenation

β-cyclodextrin (β-CD) was used to prepare remarkable and stable copper-based catalysts for hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). The DMO conversion (95.6% vs. 99.9%), EG selectivity (53.6% vs. 97.4%) and lifetime (25 h vs. 200 h) were significantly increased on the 0.2CD-Cu-SiO2 sample compared with Cu-SiO2 at 190 °C. The prominent catalytic property was due to the significant roles of β-cyclodextrin to regulate surface dispersion of copper species along with their particle sizes, namely improved copper phyllosilicate morphology, increased BET surface area, improved Cu dispersion, and enhanced surface ratio of Cu+/(Cu+ + Cu0).

A highly hydrothermal stable copper-based catalyst for catalytic wet air oxidation of m-cresol in coal chemical wastewater

Catalytic wet air oxidation (CWAO) can degrade some refractory pollutants at a low cost to improve the biodegradability of wastewater. However, in the presence of high temperature and high pressure and strong oxidizing free radicals, the stability of catalysts is often insufficient, which has become a bottleneck in the application of CWAO. In this paper, a copper-based catalyst with excellent hydrothermal stability was designed and prepared. TiO2 with excellent stability was used as the carrier to ensure the long-term anchoring of copper and reduce the leaching of the catalyst. The one pot sol–gel method was used to ensure the super dispersion and uniform distribution of copper nanoparticles on the carrier, so as to ensure that more active centers could be retained in a longer period. Experiments show that the catalyst prepared by this method has good stability and catalytic activity, and the catalytic effect is not significantly reduced after 10 cycles of use. The oxidation degradation experiment of m-cresol with the strongest biological toxicity and the most difficult to degrade in coal chemical wastewater was carried out with this catalyst. The results showed that under the conditions of 140 °C, 2 MPa and 2 h, m-cresol with a concentration of up to 1000 mg·L−1 could be completely degraded, and the COD removal rate could reach 79.15%. The biological toxicity of wastewater was significantly reduced. The development of the catalyst system has greatly improved the feasibility of CWAO in the treatment of refractory wastewater such as coal chemical wastewater.