Unveiling complete lactate oxidation through a hybrid catalytic cascade

Abiotic, Hybrid, and Biological Electrocatalytic Materials Applied in Microfluidic Fuel Cells: A Comprehensive Review

This article provides an overview of the work reported in the past decade in the field of microfluidic fuel cells. To develop appropriate research, the most commonly used electrocatalytic materials were considered and a new classification was proposed based on their nature: abiotic, hybrid, or biological. This classification allowed the authors to discern the information collected. In this sense, the types of electrocatalysts used for the oxidation of the most common fuels in different environments, such as glucose, ethanol, methanol, glycerol, and lactate, were presented. There are several phenomena presented in this article. This information gives an overview of where research is heading in the field of materials for electrocatalysis, regardless of the fuel used in the microfluidic fuel cell: the synthesis of abiotic and biological materials to obtain hybrid materials that allow the use of the best properties of each material.

Carbon Nanotube PtSn Nanoparticles for Enhanced Complete Biocatalytic Oxidation of Ethylene Glycol in Biofuel Cells

We report a hybrid catalytic system containing metallic PtSn nanoparticles deposited on multiwalled carbon nanotubes (Pt₆₅Sn₃₅/MWCNTs), prepared by the microwave-assisted method, coupled to the enzyme oxalate oxidase (OxOx) for complete ethylene glycol (EG) electrooxidation. Pt₆₅Sn₃₅/MWCNTs, without OxOx, showed good electrochemical activity toward EG oxidation and all the byproducts. Pt₆₅Sn₃₅/MWCNTs cleaved the glyoxilic acid C-C bond, producing CO₂ and formic acid, which was further oxidized at the electrode. Concerning EG oxidation, the catalytic activity of the hybrid system (Pt₆₅Sn₃₅/MWCNTs+OxOx) was twice the catalytic activity of Pt₆₅Sn₃₅/MWCNTs. Long-term electrolysis revealed that Pt₆₅Sn₃₅/MWCNTs+OxOx was much more active for EG oxidation than Pt₆₅Sn₃₅/MWCNTs: the charge increased by 65%. The chromatographic results proved that Pt₆₅Sn₃₅/MWCNTs+OxOx collected all of the 10 electrons per molecule of the fuel and was able to catalyze EG oxidation to CO₂ due to the associative oxidation between the metallic nanoparticles and the enzymatic pathway. Overall, Pt₆₅Sn₃₅/MWCNTs+OxOx proved to be a promising system to enhance the development of enzymatic biofuel cells for further application in the bioelectrochemistry field.

Cooperative Photocatalysis with 4-Amino-TEMPO for Selective Aerobic Oxidation of Amines over TiO2 Nanotubes

Attaching π-conjugated molecules onto TiO₂ can form surface complexes that could capture visible light. However, to make these TiO₂ surface complexes durable, integrating 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or its analogues as a redox mediator with photocatalysis is the key to constructing selective chemical transformations. Herein, sodium 6,7-dihydroxynaphthalene-2-sulfonate (DHNS) was obtained by extending the π-conjugated system of catechol by adding a benzene ring and a substituent sodium sulfonate (-SO₃ ^- Na⁺ ). The DHNS-TiO₂ showed the best photocatalytic activity towards the blue light-induced selective aerobic oxidation of benzylamine. Compared to TEMPO, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) could rise above 70% in conversion of benzylamine over the DHNS-TiO₂ photocatalyst. Eventually, a wide range of amines could be selectively oxidized into imines with atmospheric O₂ by cooperative photocatalysis of DHNS-TiO₂ with 4-amino-TEMPO. Notably, superoxide (O₂ ^•- ) is crucial in coupling the photocatalytic cycle of DHNS-TiO₂ and the redox cycle of 4-amino-TEMPO. This work underscores the design of surface ligands for semiconductors and the selection of a redox mediator in visible light photocatalysis for selective chemical transformations.