Cu-based Materials Research Articles

Immiscible tri-phase Cu/Ag/Cu/Nb nanolamellar composite structures generate exceptional strength-conductivity and thermal stability combination in Cu-based composites

It is of significance, but still remains a key challenge, to realize simultaneously high strength, high conductivity and excellent thermal stability in Cu-based materials, as these desirable properties often display a mutually exclusive relationship with each other. Here we propose an effective strategy to overcome this trade-off dilemma by constructing an immiscible tri-phase Cu/Ag/Cu/Nb nanolamellar composite structure in Cu-based materials using accumulative roll bonding (ARB) technique. The resultant immiscible tri-phase Cu/Ag/Cu/Nb nanolamellar structure with an average lamellar spacing of 20 nm produces an exceptional property combination: high tensile strength exceeding 1.0 GPa combined with excellent electrical conductivity above 80% IACS (International Annealed Cu Standard), while maintaining mechanical and thermal stability up to 700 °C for 10h. These desirable properties originate from the synergistic contributions from the unusually high density of immiscible Cu/Ag and Cu/Nb heterophase interfaces, the low density of defects accumulated within the layers and the unique immiscible tri-phase Cu/Ag/Cu/Nb nanolamellar structure. Our results demonstrate the concurrent improvement of several mutually exclusive properties in Cu-based materials including strength-thermal stability, and strength-electrical conductivity, and thus represent a promising route to engineering high performance nanostructured materials.

CuxO nanorod arrays shelled with CoNi layered double hydroxide nanosheets for enhanced oxygen evolution reaction under alkaline conditions

Exploration of highly efficient and cost-effective oxygen evolution reaction (OER) electrocatalysts is of crucial importance for the development of water splitting. In recent years, Cu-based materials have been widely concerned in OER due to their non-toxicity, rich reserves and highest reversibility. Meanwhile, CuxO nanorods is easy to be prepared in industry. Herein, we report a fast preparation method to construct an integrated CuxO@CoNi-LDH electrocatalyst with a unique 1D nanowire-2D nanosheet hierarchical core–shell structure by electrodepositing CoNi-LDH nanosheet arrays directly onto CuxO nanorods (CuxO were in situ-created on the Cu foam) at a large deposition voltage of −3.0 V vs SCE. The unique heterogeneous core–shell nanostructure, large deposition amount of CoNi-LDH and the synergistic effects between CuxO core and CoNi-LDH shell can provide abundant active sites, rich open-channels and reduced charge transfer resistance (Rct) for effective oxygen release and facile electron transport. Consequently, the optimized CuxO@CoNi-LDH/CF exhibits a low overpotential of 207 mV in 1 M KOH solution at the current density of 10 mV cm−2 and a small Tafel slope of 50.1 mV dec−1. After 60 h of long-term stability test, the catalytic performance is only slightly weakened. This work demonstrates a new approach to design the high-performance LDH and Cu-related OER catalysts by constructing a unique hierarchical core–shell nanostructure.

Synthesis of Cu@NC nanocube based on Cu2O for electrocatalytic nitrogen reduction to ammonia

Electrochemical nitrogen reduction reaction is a tremendous potential technology to convert N2 into highly value-added NH3. However, it still faces great challenges due to the difficult activation of nitrogen at room temperature. Herein, Cu@NC nanocubes were synthesized for the electrochemical nitrogen reduction via the calcination of cuprous oxide@PDA. The produced N-doped carbon from the carbonization of the PDA shell not only effectively protects the nanocube structure of the catalyst and enhances N2 adsorption ability but also provides the reduced intermediate to reduce cuprous oxide to Cu0. Cu0 as an effective active site effectively activates N2 and enhances the ammonia synthesis ability. Therefore, Cu@NC nanocubes show an outstanding electrochemical activity with an ammonia yield rate of 35.54 μg/h/mg cat and high Faradaic efficiency of 21.12%. This work provides a way to enhance the electrocatalytic nitrogen reduction reaction performance of Cu-based materials by introducing Cu0.

In Situ Fabrication and Static Contact Resistance of CdMoO4 Reinforced Cu Matrix Composites.

Particle-reinforced Cu-based electrical contact materials prepared by traditional powder metallurgical methods suffer the same critical problem, where the agglomeration of the addition phases in the Cu matrix significantly deteriorates the performance of the composites and restricts their application. In this work, CdMoO4/Cu matrix composites were fabricated by an in situ method and followed by a powder metallurgical process. Firstly, CdMoO4/particles formed a nucleus and grew up based on the surfaces of Cu particles, realizing the controllable in situ synthesis of mixed powders with homogeneously dispersed CdMoO4 nanoparticles via a one-step reaction. Secondly, the bulk CdMoO4/Cu composites were fabricated by pressing and sintering and then densified by hot-extrusion and cold rolling processes. The microstructures and properties of the extruded and rolled specimens were characterized, respectively. The results indicated that the rolled CdMoO4/Cu composite exhibited excellent comprehensive properties of electrical conductivity and mechanical properties for electrical contact materials. Moreover, the effects of the contact force on the static contact resistance of the extruded and rolled composites were evaluated in the closed state of the contact materials. It was found that the rolled CdMoO4/Cu contact materials possessed a stable electrical contact characteristic with low and steady contact resistance. This work designed ternary CdMoO4 particles to reinforce Cu-based composites with well-balanced performances by an in situ synthesis method and this strategy can be extended to the design of ternary oxide/metal composites utilized as electrical contact materials.

Hydrogen-Induced Restructuring of a Cu(100) Electrode in Electroreduction Conditions

The rearrangement of Cu surfaces under electrochemical conditions is known to play a key role in the surface activation for major electrocatalytic reactions. Despite the extensive experimental insights into such rearrangements, from surface-sensitive spectroscopy and microscopy, the spatial and temporal resolution of these methods is insufficient to provide an atomistic picture of the electrochemical interface. Theoretical characterization has also been challenged by the diversity of restructuring configurations, surface stoichiometry, adsorbate configurations, and the effect of the electrode potential. Here, atomistic insight into the restructuring of the electrochemical interface is gained from first principles. Cu(100) restructuring under varying applied potentials and adsorbate coverages is studied by grand canonical density functional theory and global optimization techniques, as well as ab initio molecular dynamics and mechanistic calculations. We show that electroreduction conditions cause the formation of a shifted-row reconstruction on Cu(100), induced by hydrogen adsorption. The reconstruction is initiated at 1/6 ML H coverage, when the Cu-H bonding sufficiently weakens the Cu-Cu bonds between the top- and sublayer, and further stabilized at 1/3 ML when H adsorbates fill all the created 3-fold hollow sites. The simulated scanning tunneling microscopy (STM) images of the calculated reconstructed interfaces agree with experimental in situ STM. However, compared to the thermodynamic prediction, the onsets of reconstruction events in the experiment occur at more negative applied voltages. This is attributed to kinetic effects in restructuring, which we describe via different statistical models, to produce the potential- and pH-dependent surface stability diagram. This manuscript provides rich atomistic insight into surface restructuring in electroreduction conditions, which is required for the understanding and design of Cu-based materials for electrocatalytic processes. It also offers the methodology to study the problem of in situ electrode reconstruction.

Electrochemical Synthesis of Ammonia from Nitrate on Preferentially Oriented Cu2 O

Electrochemistry-based processes to produce ammonia have recently gained widespread interest by the scientific community because they provide a way to reduce the high carbon emissions currently associated with ammonia production. Global NH3 demand is expected to rise since it is included in various energy scenarios as a possible green transportation fuel and storage medium of renewable electricity involving fuel cells.1 Several electrochemical and hybrid electrochemical processes with plasma integration are currently being investigated to produce NH3 via different nitrogen sources, such as N2, NO3 -/NO2 - or NO. The utilization of NO3 - from wastewater sources can be valuable for the environmental and health issues associated with NO3 - contamination. Additionally, NO3 - electroreduction in aqueous media is an attractive approach to investigate the catalysis due to its high solubility and the low dissociation energy needed to break the N=O bond. Cu and Cu-based materials have extensively been studied for NH3 production through NO3 - electroreduction. Earlier studies on Cu single crystals2 in alkaline media showed that Cu (100) performs better than Cu (111) in reducing the NO2 - intermediate to hydroxylamine, which is believed to be the precursor to NH3. On the contrary, recent density functional theory calculations3 showed that a Cu−Cu couple with 2.57 Å distance serves as a catalytic center, leading to the conclusion that Cu (111) is the most active surface termination. In this work, preferentially oriented Cu2O crystals with (111), (100), and (110) terminations were obtained via electrodeposition and evaluated for their performance in NO3 - electroreduction to NH3 (Figure 1). To understand which oxidation state of Cu represents the active phase, the samples were investigated by in-situ Raman spectroscopy. According to a recent study, the active phase was a combination of Cu and Cu+.4 Our results point to the immediate reduction of remaining Cu+ species during application of -0.3V vs. Ag/AgCl and formation of Cu(OH)2 at more negative potentials. The presence of Cu(OH)2 was also apparent from ex-situ XPS and UV-Vis analysis. Moreover, post-reaction XRD analysis showed a retainment of the crystal orientation on the reduced Cu surfaces. All the nanostructured catalysts were active for NO3 - reduction and produced NH3 with faradaic efficiencies above 40%. Cu2O (111) was the most efficient for NH3 synthesis reaching a faradaic efficiency of up to 99%.1 D. Anastasiadou, Electrochem. Sci. Adv.,submitted. 2 E. Pérez-Gallent, Electrochim. Acta, 2017, 227, 77–84.3 T. Hu, ACS Catal., 2021, 11, 14417–14427.4 Y. Wang, Angew. Chemie Int. Ed., 2020, 59, 5350–5354. Figure 1

Aluminum-Doped Mesoporous Copper Oxide Nanofibers Enabling High-Efficiency CO2 Electroreduction to Multicarbon Products

Copper is the most promising catalyst for the electrocatalytic conversion of CO2 into multicarbon (C2+) products but it is often plagued by low selectivity and productivity. Here, we report that aluminum (Al)-doped mesoporous copper oxide nanofibers (Cu-Al MONFs) can exhibit excellent performance in the electrocatalytic reduction of CO2 to C2+ products, with the remarkable C2+ Faradaic efficiency of 76.4% at a high current density of 600 mA cm–2. In sharp contrast, the comparative CuO nanofibers exhibit extremely severe hydrogen evolution (FE up to ∼70%) and limited C2+ products under the same condition. Detailed investigations indicate that the introduction of Al not only induces the formation of a mesoporous structure during the etching process but also adjusts the electronic structure of Cu via doping, which optimize the intermediate binding and C–C coupling on the Cu-Al MONFs. This work provides new inspiration for exploring high-performance Cu-based materials for electrocatalytic reduction of CO2.

Progress in regulating electronic structure strategies on Cu-based bimetallic catalysts for CO2 reduction reaction

To address the ever-increasing CO 2 concentration problem in the atmospheric air arisen by massive consumption of fossil fuels, electrocatalytic technologies that reduce CO 2 to generate high value-added products have been gaining increasing interest. Cu-based CO 2 reduction catalysts have attracted widespread attention owing to their capability of generating C 1 and C 2+ products. However, Cu-based catalysts are highly challenged by their low product selectivity. Recently, Cu-based bimetallic catalysts have been found the unique catalytical activity and selectivity in CO 2 reduction reactions (CO 2 RR). The incorporation of other metals can change the electronic circumstance of Cu-based catalysts, promoting the adsorption ability of the intermediate products and consequently leading to high selectivity. In this minireview, we intend to summarize recent advances of Cu-based bimetallic catalysts in producing C 1 and C 2+ products, involving designing heterostructure, alloy, defects and surface modification engineering. We pay special attention to the regulation of electronic structure of the composite catalysts, as well as insights into the relationship between electronic property and catalytical performance for Cu-based bimetallic catalysts. This article analyzed the influence of the electronic structure of materials on the catalytic performance. Focusing on the application of four methods of Heterostructure Engineering, Alloy Engineering, Defect design Engineering and Surface modification Engineering to Cu-based bimetallic materials, the advantages of electronic regulation of materials and catalyzing CO 2 to generate high-value chemicals.

High Thermoelectric Performance of Cu3SbSe4 Obtained by Synergistic Modulation of Power Factor and Thermal Conductivity

In this work, Cu3–yAgySb1–xGexSe4 (x = 0, 0.04, 0.06, 0.08, 0.10, 0.12; y = 0, 0.1, 0.2, 0.3, 0.4) is fabricated using a high-temperature melting process, and the thermoelectric properties are investigated in the temperature range of 300–700 K. As a result, a remarkable improvement in thermoelectric performance of Cu-based ternary thermoelectric materials is achieved here. Ge doping increases the carrier concentration leading to a decrease in electrical resistivity; Ag alloying can reduce thermal conductivity significantly and enhance the power factor. Consequently, a maximum figure of merit, 0.95, is obtained for Cu2.7Ag0.3Sb0.94Ge0.06Se4 and Cu2.6Ag0.4Sb0.94Ge0.06Se4 at 700 K, which is higher than most reported Cu3SbSe4-based systems.

Urea-modified Cu-based materials: Highly efficient and support-free adsorbents for removal of H2S in an anaerobic and dry environment

In this work, we report a novel urea-modified copper-based material (XUrea@Cu) obtained by directly calcinating a mixture of urea and copper nitrate. This material enables the efficient purification of H2S under dry and anaerobic conditions. The performance test results showed that the H2S capacity of the optimal adsorbent (2Urea@Cu) could reach 364.2 mg(H2S)∙gsorbent-1, which is much superior to those of other adsorbents in the literature. Further study demonstrates that the ultra-desulfurization performance of 2Urea@Cu is mainly attributed to the extensive alkaline site, the high concentrations of active oxygen, and the abundance of oxygen vacancy; which are quite effective for capturing H2S (acidic and strong reducibility). Interestingly, the deactivation adsorbent (De-2Urea@Cu) is mainly composed of high-purity CuS, which means that the Urea@Cu adsorbent can simultaneously achieve efficient purification of H2S and recovery of sulfur resources since CuS is a valuable product. In addition, in-situ FT-IR and theoretical calculation results indicate that H2S molecules dissociate on the CuO(111) surface by stepwise dehydrogenation, while S combines with adjacent Cu to form CuS. The consumption of active components (CuO) and the accumulation of reaction products (CuS) are the primary reasons for the deactivation of adsorbents. Considering the simple preparation process, low cost, and excellent H2S adsorption activity, these urea-modified copper-based materials are very promising H2S adsorbents.

Concentration Optimization of Localized Cu0 and Cu+ on Cu-Based Electrodes for Improving Electrochemical Generation of Ethanol from Carbon Dioxide.

Copper-based electrodes can catalyze electroreduction of CO2 to two-carbon products. However, obtaining a specific product with high efficiency depends on the oxidation state of Cu for the Cu-based materials. In this study, Cu-based electrodes were prepared on fluorinated tin oxide (FTO) using the one-step electrodeposition method. These electrodes were used as efficient electrocatalysts for CO2 reduction to ethanol. The concentration ratio of Cu0 and Cu+ on the electrodes was precisely modulated by adding monoethanolamine (MEA). The results of spectroscopic characterization showed that the concentration ratio of localized Cu+ and Cu0 (Cu+/Cu0) on the Cu-based electrodes was controlled from 1.24/1 to 1.54/1 by regulating the amount of MEA. It was found that the electrode exhibited the best electrochemical efficiency and ethanol production in the CO2 reduction reaction at the optimal concentration ratio Cu+/Cu0 of 1.42/1. The maximum faradaic efficiencies of ethanol and C2 were 48% and 77%, respectively, at the potential of −0.6 V vs. a reversible hydrogen electrode (RHE). Furthermore, the optimal concentration ratio of Cu+/Cu0 achieved the balance between Cu+ and Cu0 with the most favorable free energy for the formation of *CO intermediate. The stable existence of the *CO intermediate significantly contributed to the formation of the C–C bond for ethanol production.

Cu‐Based Organic‐Inorganic Composite Materials for Electrochemical CO2Reduction

Electrochemical CO2 reduction reaction (CO2RR) is an attractive pathway to convert CO2 into value-added chemicals and fuels. Copper (Cu) is the most effective monometallic catalyst for converting CO2 into multi-carbon products, but suffers from high overpotentials and poor selectivity. Therefore, it is essential to design efficient Cu-based catalyst to improve the selectivity of specific products. Due to the combination of advantages of organic and inorganic composite materials, organic-inorganic composites exhibit high catalytic performance towards CO2RR, and have been extensively studied. In this review, the research advances of various Cu-based organic-inorganic composite materials in CO2RR, i.e., organic molecular modified-metal Cu composites, Cu-based molecular catalyst/carbon carrier composites, Cu-based metal organic framework (MOF) composites, and Cu-based covalent organic framework (COF) composites are systematically summarized. Particularly, the synthesis strategies of Cu-based composites, structure-performance relationship, and catalytic mechanisms are discussed. Finally, the opportunities and challenges of Cu-based organic-inorganic composite materials in CO2RR are proposed.

On the selective desulphurization of biomass derivatives in supercritical water

The nature of organosulphur compounds formed during the reductive supercritical water treatment of sewage sludge, miscanthus and Spirulina was investigated by gas chromatography coupled to a sulphur chemiluminescence detector (GC-SCD). Methanethiol was found to be the dominating species after hydrothermal liquefaction and gasification of all process waters, along with its derivatives dimethyl disulphide and dimethyl trisulphide, likely formed upon quenching and/or after sampling. Various alkylthiophenes, short-chain sulphides and their corresponding disulphides were also found in varying amounts strongly depending on the biomass used. Various commercial sulphur absorbing materials and pure oxide nanoparticles were tested under supercritical water conditions to selectively desulphurize the various mixtures. Cu-based materials were found to be the most active in desulphurizing the organic mixture in hydrothermal conditions as well as absorbing sulphur. ZnO, MoO2, MnO and CeO2 were found to have an intermediate activity in decreasing organosulphur compounds concentration but had a good sulphur absorption capacity. Surprisingly, only Zn and Mn materials led to the formation of crystalline sulphide phases. Iron oxide showed intermediate desulphurization but surprisingly no sulphide absorption capabilities. All of these materials suffered various extents of sintering/coarsening under such harsh conditions, with cerium oxide showing very good structural and crystalline stability. All these results orientate further development of absorbing materials and/or catalysts for selective desulphurization of biomass under hydrothermal conditions.

First-Principles Study of Cu-Based Inorganic Hole Transport Materials for Solar Cell Applications.

Perovskite solar cells (PSCs) and dye-sensitized solar cells (DSCs) both represent promising strategies for the sustainable conversion of sunlight into electricity and fuels. However, a few flaws of current devices hinder the large-scale establishment of such technologies. On one hand, PSCs suffer from instabilities and undesired phenomena mostly linked to the perovskite/hole transport layer (HTL) interface. Most of the currently employed organic HTL (e.g., Spiro-OMeTAD) are supposed to contribute to the perovskite decomposition and to be responsible for charge recombination processes and polarization barriers. On the other hand, power conversion efficiencies (PCEs) of DSCs are still too low to compete with other conversion technologies. Tandem cells are built by assembling p-type and n-type DSCs in a cascade architecture and, since each dye absorbs on a different portion of the solar spectrum, the harvesting window is increased and the theoretical efficiency limit for a single chromophore (i.e., the Shockley–Queisser limit) is overcome. However, such a strategy is hindered by the lack of a p-type semiconductor with optimal photocathode features. Nickel oxide has been, by far, the first-choice inorganic p-type semiconductor for both PV technologies, but its toxicity and non-optimal features (e.g., too low open circuit voltage and the presence of trap states) call for alternatives. Herein, we study of three p-type semiconductors as possible alternative to NiO, namely CuI, CuSCN and Cu2O. To this aim, we compare the structural and electronic features of the three materials by means of a unified theoretical approach based on the state-of-the art density functional theory (DFT). We focus on the calculation of their valence band edge energies and compare such values with those of two widely employed photo-absorbers, i.e., methylammonium lead iodide (MAPI) and the triple cation MAFACsPbBrI in PSCs and P1 and Y123 dyes in DSCs, given that the band alignment and the energy offset are crucial for the charge transport at the interfaces and have direct implications on the final efficiency. We dissect the effect a copper vacancy (i.e., intrinsic p-type doping) on the alignment pattern and rationalize it from both a structural and an electronic perspective. Our data show how defects can represent a crucial degree of freedom to control the driving force for hole injection in these devices.

Facile Synthesis of Micro-Mesoporous Copper Phyllosilicate Supported on a Commercial Carrier and Its Application for Catalytic Hydrogenation of Nitro-Group in Trinitrobenzene.

Development of novel Cu-based catalysts has become one of the frontiers in the catalytic production of platform chemicals and in environment protection. However, the known methods of their synthesis are too complicated and result in materials that cannot be used instantly as commercial catalysts. In the present work, a novel material has been synthesized by the facile method of deposition–precipitation using thermal hydrolysis of urea. The conditions for Cu phyllosilicate formation have been revealed (molar ratio urea:copper = 10, 92 °C, 8–11 h). The prepared Cu-based materials were studied by TG–DTA, SEM, TEM, XRD, N2 adsorption and TPR-H2 methods, and it was found that the material involves nanoparticles of micro-mesoporous copper phyllosilicate phase with a chrysocolla-like structure inside the pores of a commercial meso-macroporous silica carrier. The chrysocolla-like phase is first shown to be catalytically active in the selective reduction of the nitro-group in trinitrobenzene to an amino-group with molecular hydrogen. Complete conversion of trinitrobenzene with a high yield of amines has been achieved in short time under relatively mild conditions (170 °C, 1.3 MPa) of nitroarene hydrogenation over a copper catalyst.

Effects of Metal Matrix Composition on the Pre-Sintering Process of Cu-Based Metallic Friction Materials

This study investigates the effect of the metal matrix composition of the friction material on the pre-sintering process through a simulation experiment on the Sprinkle sintering process. No segregation in the pre-sintered microstructure of the free-deposited friction material powder and no cracks are observed at the interface with the steel plate. In the case of a brass composition containing Zn and trace elements having relatively high vapor pressure, expansion occurs due to the volatilization of the composition elements during pre-sintering. On the contrary, in the case of bronze-based powder, the effect is insignificant. Therefore, when the friction material is manufactured using the sprinkle sintering method, the matrix composition must be selected in consideration of the volatilization effect of the metal matrix element.

Deactivation characteristics of Ce-modified Cu-based carbon materials for catalytic wet air oxidation of phenol wastewater

In this paper, Ce-modified Cu-based carbon materials (Cu-Ce/AC) were prepared by impregnation method using walnut shell as the carbon precursor, Cu-ammonia solution as Cu source and Ce as modifier. The catalytic wet air oxidation (CWAO) degradation of phenol wastewater was carried out in a self-assembled fixed-bed reactor. The stability of Cu-Ce/AC catalyst under different pH conditions was studied. This study combines XRD, BET, FT-IR, ICP-OES and XPS characterization techniques to study the main reasons for the deactivation of Cu-Ce/AC catalysts. The reaction mechanism of Cu-Ce/AC catalytic wet air oxidation degradation of phenol was clarified. The result indicates that although phenol was completely converted in the CWAO process, the acidic intermediate product produced were difficult to completely degraded. Therefore, the pH of the solution gradually decreased. In acidic environment, the interaction between active component Cu and carbon carrier is weak, resulting in a large amount of metal leaching into the solution. As a result, the COD conversion gradually decreases. The alkaline environment can effectively slow down the leaching of catalyst Cu while maintaining its high catalytic activity. In addition, the incompletely degraded intermediate products are easy to accumulate and deposit on the Cu-Ce/AC surface, block the micropores and cover the surface-active sites, which reduces the catalyst activity. The study also found that there is a redox cycle between Cu+, Cu2+ Ce3+ and Ce4+ during phenol degradation, which enables Cu and Ce to form a strong interaction. The redox cycle can also promote the formation of oxygen vacancy (h+), O2−·, and HO·, making the degradation of phenol more thorough. At the same time, the mutual conversion between metal lattice oxygen and surface chemisorbed oxygen can generate high concentration of oxygen defect sites, which can improve the oxygen storage capacity of Cu-Ce/AC. These oxygen vacancies also provide more reactive sites to further promote adsorption and catalytic oxidation degradation of phenol and intermediate products.

(Invited) Effect of Nanostructure and Surface Chemistry on Activity and Selectivity of Cu-Based Electrocatalysts for Carbon Dioxide Reduction

Electrochemical conversion of carbon dioxide (CO2) to value-added chemicals using electricity from renewable sources represents a promising path to carbon-neutral fuel cycle and enhanced economic benefits.1 To date, copper (Cu) has been the leading metal electrocatalyst for the electroreduction of CO2 to high-value chemicals: fuels and chemical feedstocks. Although there has been a significant progress in CO2 reduction reaction (CO2RR), the overall CO2RR performance of Cu-based electrocatalysts is still limited by poor selectivity, resulting in a variety of products, such as hydrogen, carbon monoxide, formic acid, methane, and ethylene.2 Enhancing the CO2RR rate relative to the competing hydrogen evolution reaction (HER) and achieving high selectivity for multi-carbon products thus represent the major scientific challenges.In this presentation, we will summarize our study of innovative Cu-based catalysts aimed at producing high energy-density chemicals, enhancing the understanding of reaction mechanism, and bringing CO2RR closer to practical application. The study has focused on the relationship between the composition and structure of Cu-based electrocatalysts, especially the nanostructure and oxidation states (Cu0, Cu+, and Cu2+), on CO2RR activity. By using a novel approach in the catalyst synthesis we have been able to obtain Cu-based materials with controlled nanostructure, e.g., pore-size distribution, higher surface area, and correlate the catalyst morphology with the selectivity for multi-carbon products. We have associated the formation of CO2RR products with the presence of different active sites on the catalyst surface, a necessary step towards achieving desirable selectivity.We will also recap the results of a study on the effect of adding a secondary transition metal, e.g., Zn, Ni, and Ag, on electrocatalytic properties of Cu-based catalysts. The rationale behind this approach has been to tune electrocatalytic activity and selectivity via changing the binding strength of the key intermediates, such as *OCHO, *CO, *COOH, *CHO, and *COH. References G. Kibria, J. P. Edwards, C. M. Gabardo, C.-T. Dinh, A. Seifitokaldani, D. Sinton, and E. H. Sargent, Adv. Mater. 2019, 31, 1807166.S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramillo, and I. Chorkendorff, Chem. Rev. 2019, 119, 7610−7672.

Magnetoresistive behaviour of ternary Cu-based materials processed by high-pressure torsion

Severe plastic deformation using high-pressure torsion of ternary Cu-based materials (CuFeCo and CuFeNi) was used to fabricate bulk samples with a nanocrystalline microstructure. The goal was to produce materials featuring the granular giant magnetoresistance effect, requiring interfaces between ferro- and nonmagnetic materials. This magnetic effect was found for both ternary systems; adequate subsequent annealing had a positive influence. The as-deformed states, as well as microstructural changes upon thermal treatments, were studied using scanning electron microscopy and X-ray diffraction measurements. Deducing from electron microscopy, a single-phase structure was observed for all as-deformed samples, indicating the formation of a supersaturated solid solution. However, judging from the presence of the granular giant-magnetoresistive effect, small ferromagnetic particles have to be present. The highest drop in room temperature resistivity (2.45% at 1790 kA/m) was found in Cu62Fe19Ni19 after annealing for 1 h at 400 °C. Combining the results of classical microstructural studies and magnetic measurements, insights into the evolution of ferromagnetic particles are accessible.

How to Change the Reaction Chemistry on Nonprecious Metal Oxide Nanostructure Materials for Electrocatalytic Oxidation of Biomass-Derived Glycerol to Renewable Chemicals.

Au and Pt are well-known catalysts for electrocatalytic oxidation of biomass-derived glycerol. Although some nonprecious-metal-based materials to replace the costly Au and Pt are used for this reaction, the fundamental question of how the nonprecious catalysts affect the reaction chemistry and mechanism compared to Au and Pt catalysts is still unanswered. In this work, both experimental and computational methods are used to understand how and why the reaction performance and chemistry for the electrocatalytic glycerol oxidation reaction (EGOR) change with electrochemically-synthesized CuCo-oxide, Cu-oxide, and Co-oxide catalysts compared to conventional Au and Pt catalysts. The Au and Pt catalysts generate major glyceric acid and glycolic acid products from the EGOR. Interestingly, the prepared Cu-based oxides produce glycolic acid and formic acid with high selectivity of about 90.0%. This different reaction chemistry is related to the enhanced ability of CC bond cleavage on the Cu-based oxide materials. The density functional theory calculations demonstrate that the formic acids are mainly formed on the Cu-based oxide surfaces rather than in the process of glycolic acid formation in the free energy diagram. This study provides critical scientific insights into developing future nonprecious-based materials for electrochemical biomass conversions.