Switching between C2+ Products and CH4 in CO2 Electrolysis by Tuning the Composition and Structure of Rare-Earth/Copper Catalysts.

Rational regulation of the reaction pathway to produce the desired products is one of the most significant challenges in the electrochemical CO2 reduction reaction (CO2RR). Herein, we designed a series of rare-earth Cu catalysts with mixed phases. It was found that the products could be switched from C2+ to CH4 by tuning the composition and structure of the catalysts. Particularly at the Cu/Sm atomic ratio of 9/1 (Cu9Sm1-Ox), the Faradaic efficiency (FE) for C2+ products (FEC2+) could reach 81% at 700 mA cm-2 with negligible CH4. However, the FE of CH4 (FECH4) was 65% at 500 mA cm-2 over Cu1Sm9-Ox (Cu/Sm = 1/9), and the FEC2+ was extremely low. Experiments and theoretical studies indicated that the stable CuSm2O4 phase existed in all the catalysts within the Cu/Sm range of 9/1 to 1/9. At a high Cu content, the catalyst was composed of CuSm2O4 and Cu phases. The small amount of Sm could enhance the binding strength of *CO and facilitate C-C coupling. Conversely, at a high Sm content, the catalyst was composed of CuSm2O4 and Sm2O3 phases. Sm could effectively stabilize bivalent Cu and enrich proton donors, lowering the reaction energy of *CO for deep hydrogenation to generate CH4. In both pathways, the stable CuSm2O4 phase could cooperate with the Cu or Sm2O3 phases, which induced the formation of different microenvironments to generate different products. This strategy also had commonality with other Cu-rare-earth (La, Pr, and Eu) catalysts to boost the CO2RR for C2+ or CH4 production.

p-d Orbital Hybridization Induced by p-Block Metal-Doped Cu Promotes the Formation of C2+ Products in Ampere-Level CO2 Electroreduction.

Large-current electrolysis of CO2 to multi-carbon (C2+) products is critical to realize the industrial application of CO2 conversion. However, the poor binding strength of *CO intermediates on the catalyst surface induces multiple competing pathways, which hinder the C2+ production. Herein, we report that p-d orbital hybridization induced by Ga-doped Cu (CuGa) could promote efficient CO2 electrocatalysis to C2+ products at ampere-level current density. It was found that CuGa exhibited the highest C2+ productivity with a remarkable Faradaic efficiency (FE) of 81.5% at a current density of 0.9 A/cm2, and the potential at such a high current density was -1.07 V versus reversible hydrogen electrode. At 1.1 A/cm2, the catalyst still maintained a high C2+ productivity with an FE of 76.9%. Experimental and theoretical studies indicated that the excellent performance of CuGa results from the p-d hybridization of Cu and Ga, which not only enriches reactive sites but also enhances the binding strength of the *CO intermediate and facilitates C-C coupling. The p-d hybridization strategy can be extended to other p-block metal-doped Cu catalysts, such as CuAl and CuGe, to boost CO2 electroreduction for C2+ production. As far as we know, this is the first work to promote electrochemical CO2 reduction reaction to generate the C2+ product by p-d orbital hybridization interaction using a p-block metal-doped Cu catalyst.

Cu2 P7 -CoP Heterostructure Nanosheets Enable High-Performance of 5-Hydroxymethylfurfural Electrooxidation.

Electrooxidation of 5-hydroxymethylfural (HMF) into 2,5-furandicarboxylicacid (FDCA) has been regarded as a promising sustainable approach to achieve value-added chemicals. However, it is still impeded by the unsatisfactory performance of electrocatalysts. Here, Cu2 P7 -CoP heterostructure nanosheets were reported to enable powerful HMF electrooxidation. The Cu2 P7 -CoP heterostructure nanosheets were fabricated by microwave-assisted deep eutectic solvent (DES) approach, along with subsequent phosphiding. The Cu2 P7 -CoP heterostructure nanosheets enabled a superb 100 % HMF conversion at 1.43 V (vs. RHE) with 98.8 % FDCA yield and 98 % Faradaic efficiency (FE), demonstrating its promising application in HMF electrooxidation. X-ray photoelectron spectroscopy (XPS) analysis, open-circuit potential (OCP) approach and density functional theory (DFT) calculation uncovered that the electron transfer and redistribution between Cu2 P7 and CoP improved the adsorption capacity of HMF and modulated the catalytic performance. This study not only offered a powerful electrocatalyst for HMF electrooxidation, but also provided a conceptually new strategy for the heterostructure catalyst design.

High-Rate CO2 Electrolysis to Formic Acid over a Wide Potential Window: An Electrocatalyst Comprised of Indium Nanoparticles on Chitosan-Derived Graphene.

Realizing industrial-scale production of HCOOH from the CO2 reduction reaction (CO2 RR) is very important, but the current density as well as the electrochemical potential window are still limited to date. Herein, we achieved this by integration of chemical adsorption and electrocatalytic capabilities for the CO2 RR via anchoring In nanoparticles (NPs) on biomass-derived substrates to create In/X-C (X=N, P, B) bifunctional active centers. The In NPs/chitosan-derived N-doped defective graphene (In/N-dG) catalyst had outstanding performance for the CO2 RR with a nearly 100 % Faradaic efficiency (FE) of HCOOH across a wide potential window. Particularly, at 1.2 A ⋅ cm-2 high current density, the FE of HCOOH was as high as 96.0 %, and the reduction potential was as low as -1.17 V vs RHE. When using a membrane electrode assembly (MEA), a pure HCOOH solution could be obtained at the cathode without further separation and purification. The FE of HCOOH was still up to 93.3 % at 0.52 A ⋅ cm-2 , and the HCOOH production rate could reach 9.051 mmol ⋅ h-1 ⋅ cm-2 . Our results suggested that the defects and multilayer structure in In/N-dG could not only enhance CO2 chemical adsorption capability, but also trigger the formation of an electron-rich catalytic environment around In sites to promote the generation of HCOOH.

Design and Preparation of Electrocatalysts by Electrodeposition for CO2 Reduction.

With the increasing emission of carbon dioxide (CO2 ), the conversion and utilization of CO2 have become a topic of increasing concern. Electrochemical CO2 reduction reaction (CO2 RR) is an attractive and sustainable approach for solving energy and environmental problems. Design of efficient catalysts is crucial for achieving highly efficient CO2 RR. Different methods to prepare catalysts have been reported and used. Among them, electrodeposition is one of the common approaches, which has some obvious advantages, such as requiring simple equipment, environmentally benign. Especially, it can direct deposit catalysts on different substrates to prepare electrodes for CO2 RR. In this review, we discuss recent advances in design and preparation of the catalysts by electrodeposition and their applications in CO2 RR. Furthermore, the perspective of this promising area is also discussed.

Atomic Indium Catalysts for Switching CO2 Electroreduction Products from Formate to CO.

Electrochemical reduction of CO2 to chemicals and fuels is an interesting and attractive way to mitigate greenhouse gas emissions and energy shortages. In this work, we report the use of atomic In catalysts for CO2 electroreduction to CO. The atomic In catalysts were anchored on N-doped carbon (InA/NC) through pyrolysis of In-based metal-organic frameworks (MOFs) and dicyandiamide. It was discovered that InA/NC had outstanding performance for selective CO production in the mixed electrolyte of ionic liquid/MeCN. It is different from those common In-based materials, in which formate/formic acid is formed as the main product. The faradaic efficiency (FE) of CO and total current density were 97.2% and 39.4 mA cm-2, respectively, with a turnover frequency (TOF) of ∼40 000 h-1. It is one of the highest TOF for CO production to date for all of the catalysts reported. In addition, the catalyst had remarkable stability. Detailed study indicated that InA/NC had higher double-layer capacitance, larger CO2 adsorption capacity, and lower interfacial charge transfer resistance, leading to high activity for CO2 reduction. Control experiments and theoretical calculations showed that the In-N site of InA/NC is not only beneficial for dissociation of COOH* to form CO but also hinders formate formation, leading to high selectivity toward CO instead of formate.

Hollow Metal-Organic-Framework-Mediated In†Situ Architecture of Copper Dendrites for Enhanced CO2 Electroreduction.

Electrocatalytic reduction of CO2 to a single product at high current densities and efficiencies remains a challenge. However, the conventional electrode preparation methods, such as drop-casting, usually suffer from low intrinsic activity. Herein, we report a synthesis strategy for preparing heterogeneous electrocatalyst composed of 3D hierarchical Cu dendrites that derived from an in situ electrosynthesized hollow copper metal-organic framework (MOF), for which the preparation of the Cu-MOF film took only 5 min. The synthesis strategy preferentially exposes active sites, which favor's the reduction of CO2 to formate. The current density could be as high as 102.1 mA cm-2 with a selectivity of 98.2 % in ionic-liquid-based electrolyte and a commonly used H-type cell.

Aptamer-functionalized magnetic and fluorescent nanospheres for one-step sensitive detection of thrombin.

A one-step sandwich method is described for detecting proteins with magnetic nanospheres (MNs) and fluorescent nanospheres (FNs). Thrombin is selected as a model analyte to validate the method. Two DNA aptamers (Apt 29 and Apt 15 targeting two different exosites of thrombin) are chosen as recognition elements to modify MNs and FNs. The superparamagnetic MN-Apt 29 conjugate is used to separate and concentrate thrombin. The FN-Apt 15 conjugate encapsulates hundreds of fluorescent quantum dots and is used as reporter to provide a stable signal. Magnetic capture and fluorescence identification are performed simultaneously to form a sandwich complex (MN-Apt 29-thrombin-FN-Apt 15) for fluorescence determination (at excitation/emission wavelengths of 380/622 nm). The method is convenient, time saving, and gives a strong signal (compared to the two-step method where capture and identification are performed in two steps). The one-step method presented here is completed within 30 min and has a 3.5 ng·mL-1 (97 pM) detection limit. The method is reproducible, has an intra-assay variability of 1.5%, and an inter-assay variability of 4.9%. Other serum proteins (HSA, CEA, PSA, and AFP) do not interfere. The method was also applied to analyze serum samples. Almost the same fluorescence intensity was measured when analyzing 1% serum samples (compared to buffer samples). Graphical abstract Magnetic nanospheres with excellent superparamagnetic property and fluorescent QD-based nanospheres were prepared and used in a one-step sensitive method for detecting thrombin. The method exhibits good reproducibility, high specificity, and good selectivity.

Ultrafine Co-MoC particles in porous carbon derived from polyoxometalate-based metal organic framework for efficient hydrogen evolution reaction.

Accurately regulating ultrafine molybdenum carbide (MoC)-based catalysts is a significant challenge in the rational design of hydrogen evolution reaction (HER) electrocatalysts. Herein, under the guidance of the first principle calculations, we proposed an in-situ polyoxometalate-confined strategy for creating uniformly distributed ultrafine Co-MoC bimetallic nanoparticles in porous carbon nanostars, with the assistance of precisely designed metal-organic framework (MOF). The Co-MoC@C electrocatalyst has a high specific surface area of 969 m2·g-1 because of the conductive carbon substrate with abundant mesopores, which makes for exposing more active sites of Co-MoC nanocrystals (∼1.5 nm) and facilitating electron/ion transport. Thus, Co-MoC@C electrocatalyst shows the excellent electrochemical activity with overpotentials of 88.4 mV and 66.6 mV at a current density of 10 mA·cm-2 under acidic and alkaline conditions, respectively. The in-situ polyoxometalate-confined strategy will provide a new guideline for the design and preparation of efficient HER electrocatalysts.

Mn-doped Ni2P: nanocrystal-decorated amorphous nanosheets for efficient electrooxidation of 5-hydroxymethylfurfural.

A Mn-doped Ni2P electrocatalyst with a unique microstructure of nanocrystal-decorated amorphous nanosheets was, for the first time, reported for the electrooxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). This electrocatalyst demonstrated superior HMF electrooxidation performance with 100% HMF conversion, 98.0% FDCA yield, and 97.8% Faraday efficiency.

Construction of 3D copper-chitosan-gas diffusion layer electrode for highly efficient CO2 electrolysis to C2+ alcohols.

High-rate electrolysis of CO2 to C2+ alcohols is of particular interest, but the performance remains far from the desired values to be economically feasible. Coupling gas diffusion electrode (GDE) and 3D nanostructured catalysts may improve the efficiency in a flow cell of CO2 electrolysis. Herein, we propose a route to prepare 3D Cu-chitosan (CS)-GDL electrode. The CS acts as a "transition layer" between Cu catalyst and the GDL. The highly interconnected network induces growth of 3D Cu film, and the as-prepared integrated structure facilitates rapid electrons transport and mitigates mass diffusion limitations in the electrolysis. At optimum conditions, the C2+ Faradaic efficiency (FE) can reach 88.2% with a current density (geometrically normalized) as high as 900 mA cm-2 at the potential of -0.87 V vs. reversible hydrogen electrode (RHE), of which the C2+ alcohols selectivity is 51.4% with a partial current density of 462.6 mA cm-2, which is very efficient for C2+ alcohols production. Experimental and theoretical study indicates that CS induces growth of 3D hexagonal prismatic Cu microrods with abundant Cu (111)/Cu (200) crystal faces, which are favorable for the alcohol pathway. Our work represents a novel example to design efficient GDEs for electrocatalytic CO2 reduction (CO2RR).

A crystal growth kinetics guided Cu aerogel for highly efficient CO2 electrolysis to C2+ alcohols.

To realize commercial CO2 electrochemical reduction to C2+ alcohols, the selectivity and production rate should be further improved. Establishing controllable surface sites with a favorable local environment is an interesting route to guide the C2+ pathway. Herein, we report a room-temperature one-step synthetic strategy to fabricate a highly stable Cu aerogel as an efficient CO2 reduction electrocatalyst. Controlling crystal growth kinetics using different reductants is an efficient strategy to modulate the nucleation and growth rate of Cu aerogels, enabling the creation of efficient surface sites for the C2+ pathway. Over the Cu aerogel obtained by reducing Cu2+ using a weak reductant (NH3·BH3), the faradaic efficiency of C2+ products could reach 85.8% with the current density of 800 mA cm-2 at the potential of -0.91 V vs. reversible hydrogen electrode, and the C2+ alcohol selectivity was 49.7% with a partial current density of 397.6 mA cm-2, while the Cu aerogel prepared using a strong reductant (NaBH4) was favorable to generating CO. Experimental and theoretical studies showed that the selectivity of the reaction depended strongly on the desorption and dimerization of *CO intermediates on the catalysts. The strong reductant induced a defective Cu surface that could facilitate the desorption of the *CO intermediate, subsequently producing CO, whereas the low defect Cu produced using a weak reductant could significantly enhance the selectivity for the C2+ product by improving *CO adsorption and the C-C coupling on the catalyst. This work opens a new way for constructing efficient electrocatalysts for CO2 electroreduction to C2+ alcohols.

Phosphorus vacancy-engineered Ce-doped CoP nanosheets for the electrocatalytic oxidation of 5-hydroxymethylfurfural.

The electrooxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furanedioic acid (FDCA) has received increasing attention. To achieve satisfactory electrooxidation of HMF, the development of an efficient electrocatalyst is particularly critical. Herein, porous Ce-CoP nanosheets integrating Ce doping and P vacancies are designed through a deep eutectic solvent approach, and they allow the excellent electrocatalytic oxidation of HMF to FDCA in 1 M KOH electrolyte with 100% HMF conversion, 98% FDCA yield, and a faradaic efficiency of 96.4% at low potential.

In situ dual doping for constructing efficient CO2-to-methanol electrocatalysts.

Methanol is a highly desirable product of CO2 electroreduction due to its wide array of industrial applications. However, the development of CO2-to-methanol electrocatalysts with high performance is still challenging. Here we report an operationally simple in situ dual doping strategy to construct efficient CO2-to-methanol electrocatalysts. In particular, when using Ag,S-Cu2O/Cu as electrocatalyst, the methanol Faradaic efficiency (FE) could reach 67.4% with a current density as high as 122.7 mA cm-2 in an H-type cell using 1-butyl-3-methylimidazolium tetrafluoroborate/H2O as the electrolyte, while the current density was below 50 mA cm-2 when the FE was greater than 50% over the reported catalysts. Experimental and theoretical studies suggest that the anion S can effectively adjust the electronic structure and morphology of the catalysts in favor of the methanol pathway, whereas the cation Ag suppresses the hydrogen evolution reaction. Their synergistic interactions with host material enhance the selectivity and current density for methanol formation. This work opens a way for designing efficient catalysts for CO2 electroreduction to methanol.

Engineering an Fe2O3/FeS hybrid catalyst from a deep eutectic solvent for highly efficient electrocatalytic N2 fixation.

A hybrid catalyst of crystalline Fe2O3 with amorphous FeS was designed by a deep eutectic solvent approach with a subsequent annealing process, offering a high-efficiency electrocatalyst for N2 fixation with an NH3 yield of 34.31 µg h-1 mgcat.-1 and faradaic efficiency of 18.06% at -0.25 V versus a reversible hydrogen electrode.

Regeneration of porous Fe3O4 nanosheets from deep eutectic solvent for high-performance electrocatalytic nitrogen reduction.

The production of ammonia through electrocatalytic nitrogen reduction reaction (NRR) is environmentally friendly and energy-saving, but it still suffers from the low NH3 yield rate and poor selectivity. Herein, enlightened by the unique solubility of Fe3O4 in deep eutectic solvent (DES), we, for the first time, reported a DES-based regeneration strategy to fabricate porous Fe3O4 nanosheets utilizing commercial Fe3O4 powder as raw materials. The as-regenerated porous Fe3O4 nanosheets exhibited satisfactory electrocatalytic performance toward NRR, affording a NH3 yield rate of 12.09 µg h-1 mg-1cat along with an outstanding Faradaic efficiency (FE) of 34.38% at -0.1 V versus reversible hydrogen electrode (RHE), in the 0.1 M Na2SO4 electrolyte. The superior electrocatalytic activity of the as-regenerated Fe3O4 nanosheets mainly resulted from their unique sheet-like morphology with large active surface area, high porosity, and abundant oxygen vacancies. Our proposed DES-based regeneration strategy opens a new avenue for the construction of high-performance electrocatalyst from commercial raw materials, holding great promise in NRR.

Selenium modulates cadmium-induced ultrastructural and metabolic changes in cucumber seedlings.

Intensive insight into the potential mechanisms of Se-induced Cd tolerance in cucumber seedlings is essential for further improvement of vegetable crop cultivation and breeding to obtain high yields and quality in Cd-contaminated soil. To reveal the ultrastructural and metabolic differences in Se-induced Cd tolerance, we examined the ultrastructures of chloroplasts and root cells and characterised 155 differentially expressed metabolites under Cd and/or Se stress using gas chromatography-mass spectrometry (GC-MS)-based metabolomics. Exogenous Se greatly relieved Cd-caused injuries to the ultrastructures of cucumber leaves and roots; for example, the shapes of chloroplasts treated with Cd + Se improved or even began to return to normal, the nuclei of root cells began to regenerate better and the chromatin was well-distributed compared with plants treated with Cd alone. Metabolite profiling revealed several intermediates of glycolysis and the tricarboxylic acid (TCA) cycle; also, some amino acids were up-accumulated in Cd + Se-treated cucumber seedlings and down-accumulated in Cd-treated cucumber seedlings, such as pyruvic acid, galactose, lactose, glutaric acid and alanine in leaves, glucose-6-phosphate and serine in roots, and lactic acid and glycine in both leaves and roots. These metabolites may play dominant roles in developing Se-mediated Cd tolerance. Moreover, a high level of sugars and polyols, amino acids and organic acids were up-accumulated in Cd-treated plants. Meanwhile, our data suggest that high accumulation of fructose, α-ketoglutaric acid, shikimic acid, fumaric acid and succinic acid in roots is a Cd-specific response, indicating that these metabolites are vital for cucumbers to develop Cd resistance. This study extends the current understanding of the mechanisms of Se in abating Cd contamination in cucumber and demonstrates that metabolomics profiling provides a more comprehensive view of the response of plants to heavy metals.

A lead-porphyrin metal-organic framework: gas adsorption properties and electrocatalytic activity for water oxidation.

A 3D non-interpenetrating porous metal-organic framework [Pb2(H2TCPP)]·4DMF·H2O (Pb-TCPP) (H6TCPP = 5,10,15,20-tetra(carboxyphenyl)porphyrin) was synthesized by employment of a robust porphyrin ligand. Pb-TCPP exhibits a one-dimensional channel possessing fairly good capability of gas sorption for N2, H2, Ar, and CO2 gases, and also features selectivity for CO2 over CH4 at 298 K. Furthermore, Pb-TCPP shows electrocatalytic activity for water oxidation in alkaline solution. It is the first 3D porous Pb-MOF that exhibits both gas adsorption properties and electrocatalytic activity for an oxygen evolution reaction (OER).