Molecular Imprinted BiVO4 Microswimmers for Selective Target Recognition and Removal.

Analogous to photosynthetic systems, photoactive semiconductor-based micro/nanoswimmers display biomimetic features that enable unique light harvesting and energy conversion functions and interactions with their surroundings. However, these artificial swimmers are usually non-selective and provide ineffective target recognition, resulting in poor surface analyte binding that affects the overall reactivity and motion efficiency. Here, the surface engineering of light-driven BiVO4 microswimmers by molecular imprinting polymerization is presented. After embedding surface recognition sites, the modified microswimmers can self-propel in a solution of a target molecule, without requiring toxic fuels, and degrade the target selectively in a pollutant mixture. These findings show that optimizing the design of semiconductor-based microswimmers with specific target recognition cavities on their surface is a promising strategy to achieve selective capture and degradation of organic pollutants, which is otherwise impossible because of the non-selective behavior of photogenerated reactive radicals. Moreover, this study provides a unique strategy to enhance the motion capabilities of single-component photocatalytic microswimmers in a specific chemical environment.

Sustainable oxygen evolution electrocatalysis in aqueous 1 M H2SO4 with earth abundant nanostructured Co3O4.

Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) able to work in acidic working conditions are elusive. While many first-row transition metal oxides are competitive in alkaline media, most of them just dissolve or become inactive at high proton concentrations where hydrogen evolution is preferred. Only noble-metal catalysts, such as IrO2, are fast and stable enough in acidic media. Herein, we report the excellent activity and long-term stability of Co3O4-based anodes in 1 M H2SO4 (pH 0.1) when processed in a partially hydrophobic carbon-based protecting matrix. These Co3O4@C composites reliably drive O2 evolution a 10 mA cm-2 current density for >40 h without appearance of performance fatigue, successfully passing benchmarking protocols without incorporating noble metals. Our strategy opens an alternative venue towards fast, energy efficient acid-media water oxidation electrodes.

Quantification of the Effect of an External Magnetic Field on Water Oxidation with Cobalt Oxide Anodes.

Here, we quantify the effect of an external magnetic field (ß) on the oxygen evolution reaction (OER) for a cobalt oxide|fluorine-doped tin oxide coated glass (CoOx|FTO) anode. A bespoke apparatus enables us to precisely determine the relationship between magnetic flux density (ß) and OER activity at the surface of a CoOx|FTO anode. The apparatus includes a strong NdFeB magnet (ßmax = 450 ± 1 mT) capable of producing a magnetic field of 371 ± 1 mT at the surface of the anode. The distance between the magnet and the anode surface is controlled by a linear actuator, enabling submillimeter distance positioning of the magnet relative to the anode surface. We couple this apparatus with a finite element analysis magnetic model that was validated by Hall probe measurements to determine the value of ß at the anode surface. At the largest tested magnetic field strength of ß = 371 ± 1 mT, a 4.7% increase in current at 1.5 V vs the normal hydrogen electrode (NHE) and a change in the Tafel slope of 14.5 mV/dec were observed. We demonstrate through a series of OER measurements at sequential values of ß that the enhancement consists of two distinct regions. The possible use of this effect to improve the energy efficiency of commercial water electrolyzers is discussed, and major challenges pertaining to the accurate measurement of the phenomenon are demonstrated.

Bifunctional Oxygen Electrocatalysis on Mixed Metal Phthalocyanine-Modified Carbon Nanotubes Prepared via Pyrolysis.

Non-precious-metal catalysts are promising alternatives for Pt-based cathode materials in low-temperature fuel cells, which is of great environmental importance. Here, we have investigated the bifunctional electrocatalytic activity toward the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of mixed metal (FeNi; FeMn; FeCo) phthalocyanine-modified multiwalled carbon nanotubes (MWCNTs) prepared by a simple pyrolysis method. Among the bimetallic catalysts containing nitrogen derived from corresponding metal phthalocyanines, we report the excellent ORR activity of FeCoN-MWCNT and FeMnN-MWCNT catalysts with the ORR onset potential of 0.93 V and FeNiN-MWCNT catalyst for the OER having EOER = 1.58 V at 10 mA cm-2. The surface morphology, structure, and elemental composition of the prepared catalysts were examined with scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The FeCoN-MWCNT and FeMnN-MWCNT catalysts were prepared as cathodes and tested in anion-exchange membrane fuel cells (AEMFCs). Both catalysts displayed remarkable AEMFC performance with a peak power density as high as 692 mW cm-2 for FeCoN-MWCNT.

Redefining the Mechanistic Scenario of Carbon-Sulfur Nucleophilic Coupling via High-Valent Cp*CoIV Species.

The potential access to CoIV species for promoting transformations that are particularly challenging at CoIII still remains underexploited in the context of Cp*Co-catalyzed C-H functionalization reactions. Herein, we disclose a combined experimental and computational strategy for uncovering the participation of Cp*CoIV species in a Cp*Co-mediated C-S bond-reductive elimination. These studies support the intermediacy of high-valent Cp*Co species in C-H functionalization reactions, under oxidative conditions, when involving nucleophilic coupling partners.

Effect of Mechanochemical Recrystallization on the Thermal Hysteresis of 1D FeII-triazole Spin Crossover Polymers.

The thermal hysteresis in the cooperative spin crossover (SCO) polymer [Fe(trz)(Htrz)2]n[BF4]n (1) has been tuned by a simple ball milling grinding process. Mechanical treatment affects the size and morphology of the crystallite domains, as confirmed by multiple complementary techniques, including ESEM, DLS, and PXRD data. Upon milling, the regular cubic shape particles recrystallize with slightly different unit cell parameters and preferential orientation. This macroscopic change significantly modifies the thermally induced SCO behavior, studied by temperature-dependent magnetic susceptibility, X-ray diffraction, and DSC analysis. Transition temperatures downshift, closer to room temperature, while hysteresis widens, when particle sizes are actually decreasing. We relate this counterintuitive observation to subtle modifications in the unit cell, offering new alternatives to tune and enhance SCO properties in this class of 1D-cooperative polymers.