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Surfactant- and Binder-Free Hierarchical Platinum Nanoarrays Directly Grown onto a Carbon Felt Electrode for Efficient Electrocatalysis.

ABSTRACT

The future of fuel cells that convert the chemical energy to electricity relies mostly on the efficiency of oxygen reduction reaction (ORR) due to its sluggish kinetics. By effectively bypassing the use of organic surfactants, post-synthesis steps for the immobilization onto electrodes, the catalytic inks preparation using binders, and the common problem of nanoparticles detachment from supports involved in traditional methodologies, we demonstrate a versatile electrodeposition method for growing anisotropic microstructures directly onto a three-dimensional (3D) carbon felt electrode, using platinum nanoparticles as elementary building blocks. The as-synthesized materials are extensively characterized by integrating methods of physical (TGA, XRD, SEM, ICP, XPS) and electroanalytical (voltammetry, EIS) chemistry to examine the intricate relationship of material-to-performance and select the best-performing electrocatalyst to be applied in the model reaction of ORR for its practical integration into a microbial fuel cell (MFC). A tightly optimized procedure enables decorating an electrochemically activated carbon felt electrode by 40-60 nm ultrathin 3D-interconnected platinum nanoarrays leading to a hierarchical framework of ca. 500 nm. Half-cell reactions reveal that the highly rough metallic surface exhibits improved activity and stability towards ORR (Eonset ~1.1 V vs. RHE, p(HO2‒) < 0.1%) and hydrogen evolution reaction (HER, -10 mA cm-2 for only 75 mV overpotential). Owing to its unique features, the developed material shows distinguished performance as an air-breathing cathode in a garden compost MCF exhibiting better current and faster power generation than its equivalent classical double chamber. The enhanced performance of the material obtained herein is explained by the absence of any organic surfactant on the surface of the nanoarrays, the good metal-support interaction, the particular morphology of the nanoarrays, and the reduced aggregation/detachment of particles. It promises a radical improvement in current surface reactions and paves a new way towards electrodes with regulated surface roughness allowing for their successful application in heterogeneous catalysis.