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In this work, an alcohol dehydrogenase (ADH) enzyme was used for ethanol oxidation in an air-breathing type microfluidic fuel cell. A bioanode was prepared using a catalytic ink prepared by using a mixture of ADH enzyme, tetrabutylammonium bromide, and Nafion and subsequently immobilized on TiO 2 nanotubes, previously synthesized by electrochemical anodization. Several techniques were used to determine the successful immobilization of the enzyme and the operational parameters of the bioanode (temperature and pH). Using scanning electrochemical microscopy, the photocatalytic activity was confirmed in the bioanode from the enhanced oxidizing current densities while preserving the enzymatic activity. Finally, the as-prepared bioanode was evaluated in a microfluidic device using a Pt/C commercial as the cathode, obtaining a good performance over an open circuit potential greater than 0.9 V.

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An air‐breathing nanofluidic fuel cell (AB‐NFC) was evaluated using ethanol as the fuel. Two Pd electrocatalysts, one commercial (ETEK) and one synthesized (Pd IL), were tested as anodes and using carbon nanofoam as three‐dimensional flow‐through electrodes. It was found from the polarization and power density curves that despite differences in particle sizes, both of the electrocatalysts exhibited similar power densities in an alkaline AB‐NFC (15.4 to 15.8 mW cm−2). Nevertheless, the Pd IL provided stability over time to the AB‐NFC while performing at a higher ethanol concentration (1.5 M), which was related to its greater tolerance to poisoning compared to the commercial Pd. The cell performance of the AB‐NFC was enhanced by changing the pH of the cathodic electrolyte from an alkaline to an acidic pH. The net cell efficiency increased 44 % with a power density near 100 mW cm−2, which is one of the best power densities reported to date for membraneless micro/nanofluidic fuel cells.

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Titanium oxide nanotubes (TNTs) were anodically grown in ethylene glycol electrolyte. The influence of the anodization time on their physicochemical and photoelectrochemical properties was evaluated. Concomitant with the anodization time, the NT length, fluorine content, and capacitance of the space charge region increased, affecting the opto-electronic properties (bandgap, bathochromic shift, band-edge position) and surface hydrophilicity of TiO2 NTs. These properties are at the origin of the photocatalytic activity (PCA), as proved with the photooxidation of methylene blue.