ABSTRACT: Nanoporous anodic aluminum oxide (AAO) is one of the most popular and cost-effective platform for various applications: from templates and molecular separation to drug delivery and energy generation. Its’ unique optical and electrochemical properties have been extensively explored as a platform for developing biosensing and energy-harvesting nanodevices. Membranes with a small pore diameter (<25 nm) are of particular importance, since their integration in nanodevices is often preferable. The thickness of such membranes usually does not exceed 60 μm. The reason is that much thinner inter-pore walls in sulfuric-AAO membranes, compared to oxalic-AAO or phosphoric-AAO, after long anodisation in the sulfuric acid electrolyte are turning into Al2O3 nanowires, that are blocking the pores. In this work three different approaches have been used to solve this problem: 1) direct anodisation in 0.3M sulfuric acid electrolyte – maximum thickness obtained is 65 μm; 2) step-by-step anodisation in oxalic and sulfuric acid – the attempts to increase the sulfuric-AAO layer thickness above 50 microns lead to delamination of the oxalic-AAO layer; 3) pulse anodisation in 0.3M sulfuric acid electrolyte – appeared to be the most promising method for obtaining membranes that consist of alternating higly ordered nanoporous sulfuric-AAO layers with pore diameters dpore= 20 nm and 40 nm and the total thicknesses of 80 – 100 microns. All anodisation and postanodisation treatment conditions (concentration and type of electrolyte, applied potential between electrodes, temperature and time of anodisation, the way of aluminum layer dissolution, and time of barrier layer etching) were optimized for fabricating robust AAO membranes. The morphology of the AAO membranes was characterized by the means of scanning electron microscopy (SEM).

TRANSLATE is a €3.4 million EU-funded research project that aims to develop a new nanofluidic platform technology to effectively convert waste heat to electricity. This technology has the potential to improve the energy efficiency of many devices and systems, and provide a radically new zero-emission power source. The TRANSLATE project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 964251, for the action of 'The Recycling of waste heat through the Application of Nanofluidic ChannelS: Advances in the Conversion of Thermal to Electrical energy'. More information can be be found on the TRANSLATE project website: https://translate-energy.eu/