Abstract
In this work, we studied the combination of nitrogen-doped carbon quantum dots (N-CQD), a hydroxide-ion conducting ionomer based on polysulfone (PSU) and polyaniline (PANI), to explore the complementary properties of these materials in high-performance nanostructured electrodes for the oxygen reduction reaction (ORR) in alkaline solution. N-CQD were made by hydrothermal synthesis from glucosamine hydrochloride (GAH) or glucosamine hydrochloride and N-Octylamine (GAH-Oct), and PSU were quaternized with trimethylamine (PSU-TMA). The nanocomposite electrodes were prepared on carbon paper by drop-casting. Furthermore, we succeeded in preparing PSU-TMA + PANI + GAH-Oct fibers by electrospinning. The capacitance of the electrodes was investigated by cyclic voltammetry and impedance spectroscopy, which gave similar trends. The ORR was investigated by linear sweep voltammetry at rotating disk electrode speeds between 250 and 2000 rpm in an oxygen-saturated 1 M KOH solution. Koutecky–Levich plots showed that four electrons were exchanged for nanocomposite electrodes containing CQD. The highest reduction currents were measured for the electrodes containing GAH-Oct. The Tafel plots gave the lowest slope and the most positive half-wave potential for PSU-TMA + PANI + GAH-Oct fibers. The best electrocatalytic activity of this electrode could be related to the high amount of graphitic nitrogen in GAH-Oct. Long-term cycling tests showed no significant modification of the onset potential, but a change of the current in the mass transport limited region, indicated the evolution of the microstructure of the nanocomposite ORR electrode modifying the mass transport conditions during the first 400 cycles before reaching stationary conditions. FTIR spectra were used to study possible electrode degradation after the ORR in 1 M KOH: the only change was due to the reaction of PANI emeraldine salt to emeraldine base, whereas the other constituents of the multiphase electrode did not show any degradation.
Highlights
IntroductionThe oxygen reduction reaction (ORR) is of particular theoretical and practical interest, for example in the respiratory reduction of O2 in cell metabolism [1] or the cathode of fuel cells [2–4] or other electrochemical devices [5]
We studied the electrocatalytic properties for the oxygen reduction reaction (ORR) of nanocomposites combining a hydroxide ion-conducting ionomer (PSU-TMA), polyaniline (PANI), and carbon quantum dots (CQD) prepared by hydrothermal synthesis from glucosamine (GAH) without, and with, N-octylamine (GAH-Oct)
The best electrocatalytic activity was found for PSU were quaternized with trimethylamine (PSU-TMA) + PANI + glucosamine hydrochloride (GAH)-Oct fibers
Summary
The oxygen reduction reaction (ORR) is of particular theoretical and practical interest, for example in the respiratory reduction of O2 in cell metabolism [1] or the cathode of fuel cells [2–4] or other electrochemical devices [5] It is well-known that the ORR is difficult in acidic conditions, where Pt or other noble metals are needed as electrocatalysts if a four-electron reduction is desired. Less expensive electrocatalysts, such as polyaniline (PANI), might be used in acidic media if a two-electron reduction pathway to hydrogen peroxide that generates less power is acceptable [6–8].
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