SÍNTESE DE NANOPARTÍCULAS À BASE DE COBRE PARA APLICAÇÃO COMO ÂNODOS DE CÉLULAS A COMBUSTÍVEL MICROFLUÍDICAS IMPRESSAS EM 3D ALIMENTADAS POR METANOL

Abstract

Technological advances have increased the demand for low-power energy converters to supply portable devices such as laptops, smartphones, and smartwatches. This demand arises from growing social automation – communication mediated by electronic devices – and the widespread use of portable systems in healthcare, defense, and entertainment. In this context, miniaturized fuel cells (µFCs) have emerged as promising alternatives. However, their commercial implementation remains limited by: (i) unstable catalysts with low electrocatalytic activity and (ii) architectures that restrict power output. This work aimed to synthesize new materials for application as anodes in microfluidic µFCs. A simple, rapid, small-scale, and surfactant-free route was proposed for the synthesis of Cu nanoparticles (NPs) at room temperature under three distinct conditions: stationary (ST), magnetic stirring (MS), and ultrasonic bath (US). The catalytic activity toward methanol electrooxidation in alkaline medium was evaluated using electrochemical and spectroelectrochemical techniques, revealing higher current densities for the US-synthesized NPs. In situ FTIR analyses confirmed that all materials promote methanol oxidation to carbonate via a formate intermediate, without detectable CO formation. The US sample exhibited superior performance, associated with a higher surface proportion of Cu(OH)2, lower carbon contamination, and greater availability of active sites. At higher potentials, this sample further displayed distinct behavior, involving an additional step of formate formation and its subsequent conversion to carbonate (or CO2 in the thin-layer configuration), suggesting a more efficient reaction mechanism. Finally, a mixed-media µFC was constructed and fed with methanol in alkaline medium and sodium persulfate in acidic medium. The device, comprising a Carbon Paper™ (CP) anode modified with US-synthesized Cu NPs and a metal-free CP cathode, achieved a maximum current density of 0.56 mA cm-2 and a peak power density of 26 µW cm-2 at 100 µL min-1. These results confirm that the membrane-free configuration optimizes the performance of each half-cell and demonstrate the feasibility of µFCs with noble-metal-free anodes and fully metal-free cathodes, representing a promising alternative for sustainable energy conversion technologies.

Keywords: fuel cell; microfluidic; methanol electrooxidation; copper anode; metal-free cathode; in situ FTIR; energy conversion.