Electrolysis of ammonia in an aqueous solution can generate hydrogen gas at room temperature. An anode reaction of nitrogen gas desorption on ammonia electrolysis has a much larger overvoltage than that of a cathode reaction, and one of the useful electrode catalysts for the anode reaction is platinum (Pt). In this study, in order to increase the surface area of Pt three-dimensionally, Pt nanoparticles are held on a sponge-like film of carbon nanotubes (CNTs) that has a large surface area of 5000–10000 cm2 per 1 cm2 of the CNT film. The electrodes were adapted to the ammonia electrolysis to increase the current density with a low overvoltage. The Pt nanoparticles were deposited on the CNTs by a polyol method at various temperatures, and the Pt nanoparticles supported on the CNT (Pt-CNT) electrodes were fabricated by vacuum filtration of the Pt-CNT dispersion. The size of the deposited Pt nanoparticles was approximately 2–3 nm. The maximum electrochemical surface area of the Pt nanoparticles was more than 250 cm2 per unit electrode area of 1 cm2. The Pt-CNT film electrode with a large surface area of the Pt catalyst increased the current density of the anode reaction compared with the Pt plate or the Pt-black electrodes. The Pt-CNT decreased both the activation overvoltage corresponding to the high Pt surface area and the concentration overvoltage corresponding to the three-dimensional structure of the CNT films. Moreover, it is clarified that the deactivation of the catalysts by the anode reaction does not occur below −0.2 V (vs Hg|HgO) for the Pt-CNT electrodes.
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