Electrocatalytic Epoxidation of Cyclooctene on Surface Modified Ni Foam Using Water as Oxygen Source.

Electrochemical epoxidation of olefins using water as an oxygen atom source is emerging as an alternative approach for an atom economic and sustainable method towards a highly selective synthesis of epoxides. We report an electrochemical procedure for epoxidation of cyclooctene using water as the sole oxygen atom source over a sodium dodecyl sulfonate (SDS) modified nickel hydroxide Ni(OH)2 catalyst directly grown on Ni foam. The SDS modification facilitates the mass transfer of cyclooctene towards the anode, thus achieving a 2.5-fold higher conversion with more than 90 % selectivity towards the corresponding epoxide compared with pure Ni(OH)2 catalyst.

Redox Replacement of Silver on MOF-Derived Cu/C Nanoparticles on Gas Diffusion Electrodes for Electrocatalytic CO2 Reduction.

Bimetallic tandem catalysts have emerged as a promising strategy to locally increase the CO flux during electrochemical CO2 reduction, so as to maximize the rate of conversion to C-C-coupled products. Considering this, a novel Cu/C-Ag nanostructured catalyst has been prepared by a redox replacement process, in which the ratio of the two metals can be tuned by the replacement time. An optimum Cu/Ag composition with similarly sized particles showed the highest CO2 conversion to C2+ products compared to non-Ag-modified gas-diffusion electrodes. Gas chromatography and in-situ Raman measurements in a CO2 gas diffusion cell suggest the formation of top-bound linear adsorbed *CO followed by consumption of CO in the successive cascade steps, as evidenced by the increasingνC-H bands. These findings suggest that two mechanisms operate simultaneously towards the production of HCO2 H and C-C-coupled products on the Cu/Ag bimetallic surface.

B-Cu-Zn Gas Diffusion Electrodes for CO2 Electroreduction to C2+ †Products at High Current Densities.

Electroreduction of CO2 to multi-carbon products has attracted considerable attention as it provides an avenue to high-density renewable energy storage. However, the selectivity and stability under high current densities are rarely reported. Herein, B-doped Cu (B-Cu) and B-Cu-Zn gas diffusion electrodes (GDE) were developed for highly selective and stable CO2 conversion to C2+  products at industrially relevant current densities. The B-Cu GDE exhibited a high Faradaic efficiency of 79 % for C2+  products formation at a current density of -200 mA cm-2 and a potential of -0.45 V vs. RHE. The long-term stability for C2+ formation was substantially improved by incorporating an optimal amount of Zn. Operando Raman spectra confirm the retained Cu+ species under CO2 reduction conditions and the lower overpotential for *OCO formation upon incorporation of Zn, which lead to the excellent conversion of CO2 to C2+ products on B-Cu-Zn GDEs.

A Metal-Organic Framework derived Cux Oy Cz Catalyst for Electrochemical CO2 Reduction and Impact of Local pH Change.

Developing highly efficient and selective electrocatalysts for the CO2 reduction reaction to produce value-added chemicals has been intensively pursued. We report a series of Cux Oy Cz nanostructured electrocatalysts derived from a Cu-based MOF as porous self-sacrificial template. Blending catalysts with polytetrafluoroethylene (PTFE) on gas diffusion electrodes (GDEs) suppressed the competitive hydrogen evolution reaction. 25 to 50 wt % teflonized GDEs exhibited a Faradaic efficiency of ≈54 % for C2+ products at -80 mA cm-2 . The local OH- ions activity of PTFE-modified GDEs was assessed by means of closely positioning a Pt-nanoelectrode. A substantial increase in the OH- /H2 O activity ratio due to the locally generated OH- ions at increasing current densities was determined irrespective of the PTFE amount.

Online Monitoring of Electrochemical Carbon Corrosion in Alkaline Electrolytes by Differential Electrochemical Mass Spectrometry.

Carbon corrosion at high anodic potentials is a major source of instability, especially in acidic electrolytes and impairs the long-term functionality of electrodes. In-depth investigation of carbon corrosion in alkaline environment by means of differential electrochemical mass spectrometry (DEMS) is prevented by the conversion of CO2 into CO3 2- . We report the adaptation of a DEMS system for online CO2 detection as the product of carbon corrosion in alkaline electrolytes. A new cell design allows for in situ acidification of the electrolyte to release initially dissolved CO3 2- as CO2 in front of the DEMS membrane and its subsequent detection by mass spectrometry. DEMS studies of a carbon-supported nickel boride (Nix B/C) catalyst and Vulcan XC 72 at high anodic potentials suggest protection of carbon in the presence of highly active oxygen evolution electrocatalysts. Most importantly, carbon corrosion is decreased in alkaline solution.

Influence of Temperature and Electrolyte Concentration on the Structure and Catalytic Oxygen Evolution Activity of Nickel-Iron Layered Double Hydroxide.

NiFe layered double hydroxide (LDH) is inarguably the most active contemporary catalyst for the oxygen evolution reaction under alkaline conditions. However, the ability to sustain unattenuated performance under challenging industrial conditions entailing high corrosivity of the electrolyte (≈30 wt. % KOH), high temperature (>80 °C) and high current densities (>500 mA cm-2 ) is the ultimate criterion for practical viability. This work evaluates the chemical and structural stability of NiFe LDH at conditions akin to practical electrolysis, in 30 % KOH at 80 °C, however, without electrochemical polarization, and the resulting impact on the OER performance of the catalyst. Post-analysis of the catalyst by means of XRD, TEM, FT-IR, and Raman spectroscopy after its immersion into 7.5 m KOH at 80 °C for 60 h revealed a transformation of the structure from NiFe LDH to a mixture of crystalline ß-Ni(OH)2 and discrete predominantly amorphous FeOOH containing minor non-homogeneously distributed crystalline domains. These structural and compositional changes led to a drastic loss of the OER activity. It is therefore recommended to study catalyst stability at industrially relevant conditions.

Evaluation of perovskites as electrocatalysts for the oxygen evolution reaction.

The oxygen evolution reaction (OER) is an enabling process for technologies in the area of energy conversion and storage, but its slow kinetics limits its efficiency. We performed an electrochemical evaluation of 14 different perovskites of variable composition and stoichiometry as OER electrocatalysts in alkaline media. We particularly focused on improved methods for a reliable comparison of catalyst activity. From initial electrochemical results we selected the most active samples for further optimization of electrode preparation and testing. An inverted cell configuration facilitated gas bubble detachment and thus minimized blockage of the active surface area. We describe parameters, such as the presence of specific cations, stoichiometry, and conductivity, that are important for obtaining electroactive perovskites for OER. Conductive additives enhanced the current and decreased the apparent overpotential of OER for one of the most active samples (La(0.58)Sr(0.4)Fe(0.8)Co(0.2)O(3)).

Ag-induced Phase Transition of Bi2 O3 Nanofibers for Enhanced Energy Conversion Efficiency towards Formate in CO2 Electroreduction.

Bi-based electrocatalysts have been widely investigated in the CO2 reduction reaction (CO2 RR) for the formation of formate. However, it remains a challenge to achieve high Faradaic efficiency (FE) and industrial current densities at low overpotentials for obtaining both high formate productivity and energy efficiency (EE). Herein, we report an Ag-Bi2 O3 hybrid nanofiber (Ag-Bi2 O3 ) for highly efficient electrochemical reduction of CO2 to formate. Ag-Bi2 O3 exhibits a formate FE of >90% for current densities from -10 to -250 mA ⋅ cm-2 and attains a yield rate of 11.7 mmol ⋅ s-1 ⋅ m-2 at -250 mA ⋅ cm-2 . Moreover, Ag-Bi2 O3 increased the EE (52.7%) by nearly 10% compared to a Bi2 O3 only counterpart. Structural characterization and in-situ Raman results suggest that the presence of Ag induced the conversion of Bi2 O3 from a monoclinic phase (α-Bi2 O3 ) to a metastable tetragonal phase (ß-Bi2 O3 ) and accelerated the formation of active metallic Bi at low overpotentials (at > -0.3 V), which together contributes to the highly efficient formate formation.

Enhanced Nitrate-to-Ammonia Efficiency over Linear Assemblies of Copper-Cobalt Nanophases Stabilized by Redox Polymers.

Renewable electricity-powered nitrate (NO3 - ) reduction reaction (NO3 RR) offers a net-zero carbon route to the realization of high ammonia (NH3 ) productivity. However, this route suffers from low energy efficiency (EE, with a half-cell EE commonly <36%), since high overpotentials are required to overcome the weak NO3 - binding affinity and sluggish NO3 RR kinetics. To alleviate this, a rational catalyst design strategy that involves the linear assembly of sub-5 nm Cu/Co nanophases into sub-20 nm thick nanoribbons is suggested. The theoretical and experimental studies show that the Cu-Co nanoribbons, similar to enzymes, enable strong NO3 - adsorption and rapid tandem catalysis of NO3 - to NH3 , owing to their richly exposed binary phase boundaries and adjacent Cu-Co sites at sub-5 nm distance. In situ Raman spectroscopy further reveals that at low applied overpotentials, the Cu/Co nanophases are rapidly activated and subsequently stabilized by a specifically designed redox polymer that in situ scavenges intermediately formed highly oxidative nitrogen dioxide (NO2 ). As a result, a stable NO3 RR with a current density of ≈450 mA cm-2 is achieved, a Faradaic efficiency of >97% for the formation of NH3 , and an unprecedented half-cell EE of ≈42%.

Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia.

Electrocatalytic recycling of waste nitrate (NO3-) to valuable ammonia (NH3) at ambient conditions is a green and appealing alternative to the Haber-Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO3--to-NH3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu-Co binary sulfides into potential-dependent core-shell Cu/CuOx and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in-situ Raman spectra reveal that the inner Cu/CuOx phases preferentially catalyze NO3- reduction to NO2-, which is rapidly reduced to NH3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO3--to-NH3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO3- concentrations at pH 13, a high NH3 yield rate of 1.17 mmol cm-2 h-1 in 0.1 M NO3- at -0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports.

Visualization of chlorine evolution at dimensionally stable anodes by means of scanning electrochemical microscopy.

Scanning electrochemical microscopy (SECM) has been used to detect and visualize the local electrocatalytic activity of dimensionally stable anodes (DSA) for Cl(2) evolution from brine. The sample generation-tip collection (SG-TC) mode of SECM shows limitations arising from complications connected with the reduction of Cl(2) at the SECM tip due to the presence of a significant amount of nondissolved Cl(2) gas. Because only dissolved Cl(2) can be electrochemically reduced at the tip, a large amount of the Cl(2) gas which is produced at active spots of the DSA is not detected. Additionally, a decrease of the cathodic current at the tip may occur owing to the adhesion of gas bubbles and blocking of the electrode surface. To overcome this limitation, the redox competition mode of SECM was extended and applied to the local visualization of Cl(2) evolution from highly concentrated brine solutions. High concentrations of Cl(2) produced at the sample can cause inhibition of the same reaction at the tip by accumulation of Cl(2) in the proximity of the SECM tip. In this way the tip current is decreased, which can be used as a measure for the catalytic activity of the sample underneath the tip.

Cytocompatibility Evaluation of a Novel Series of PEG-Functionalized Lactide-Caprolactone Copolymer Biomaterials for Cardiovascular Applications.

Although the use of bioresorbable materials in stent production is thought to improve long-term safety compared to their durable counterparts, a recent FDA report on the 2-year follow-up of the first FDA-approved bioresorbable vascular stent showed an increased occurrence of major adverse cardiac events and thrombosis in comparison to the metallic control. In order to overcome the issues of first generation bioresorbable polymers, a series of polyethylene glycol-functionalized poly-L-lactide-co-ε-caprolactone copolymers with varying lactide-to-caprolactone content is developed using a novel one-step PEG-functionalization and copolymerization strategy. This approach represents a new facile way toward surface enhancement for cellular interaction, which is shown by screening these materials regarding their cyto- and hemocompatibility in terms of cytotoxicity, hemolysis, platelet adhesion, leucocyte activation and endothelial cell adhesion. By varying the lactide-to-caprolactone polymer composition, it is possible to gradually affect endothelial and platelet adhesion which allows fine-tuning of the biological response based on polymer chemistry. All polymers developed were non-cytotoxic, had acceptable leucocyte activation levels and presented non-hemolytic (<2% hemolysis rate) behavior except for PLCL-PEG 55:45 which presented hemolysis rate of 2.5% ± 0.5. Water contact angles were reduced in the polymers containing PEG functionalization (PLLA-PEG: 69.8° ± 2.3, PCL-PEG: 61.2° ± 7.5) versus those without (PLLA: 79.5° ± 3.2, PCL: 76.4° ± 10.2) while the materials PCL-PEG550, PLCL-PEG550 90:10 and PLCL-PEG550 70:30 demonstrated best endothelial cell adhesion. PLLA-PEG550 and PLCL-PEG550 70:30 presented as best candidates for cardiovascular implant use from a cytocompatibility perspective across the spectrum of testing completed. Altogether, these polymers are excellent innovative materials suited for an application in stent manufacture due to the ease in translation of this one-step synthesis strategy to device production and their excellent in vitro cyto- and hemocompatibility.

Water uptake on mineral dust and soot: a fundamental view of the hydrophilicity of atmospheric particles?

The interaction of water vapour with mineral dust and soot surfaces has been studied in the temperature range 203 K < T < 298 K using a Knudsen cell reactor. For the uptake of water on mineral dust an initial uptake coefficient of gamma(ini) = (6.3 +/- 0.7) x 10(-2) independent of temperature has been determined. In contrast the desorption rate has been found to be strongly temperature dependent with desorption rate constants decreasing from 1 x 10(-3) at 265 K to 1 x 10(-4) at 223 K. In addition, relatively high surface coverages have been determined from which an adsorption enthalpy of -40 kJ mol(-1) is inferred. For the uptake of water on soot the initial uptake coefficient has been found to be independent of temperature with a value of gamma(ini) = (4.7 +/- 0.2) x 10(-2), similar to the case of mineral dust. However, the corresponding desorption rate constants have been found to be three orders of magnitude larger than for mineral dust. Consistent with this finding, low surface coverages with an adsorption enthalpy of -27 kJ mol(-1) have been derived. A comparison of the uptake kinetics and adsorption enthalpies of water on mineral dust and soot leads to the conclusion that water is much stronger interacting with mineral dust than with soot. In terms of a hydrophilicity concept the results suggest, that mineral dust may be regarded as hydrophilic whereas soot is hydrophobic and that fundamental kinetic and thermochemical quantities may be related to that concept.