Cathodic current flowing through a Pt wire as a function of time measured in a 20M NaOH solution at −10 V applied bias. The Pt wire was 0.13 mm in diameter and submerged 1 mm into the electrolyte. The submerged part of the wire was atomized completely into a suspension of nanoparticles after 255 s. The measured current density is much lower than the one expected during spark discharge (∼100 A/cm2). 36,39 Apparent oscillations are due to the intermittent hydrogen bubble formation at the electrode.
SEM images of a platinum wire (a) before and (b) after cathodic corrosion in a solution containing 10M NaOH at −10 V applied potential for 1000 s. Figures (c)–(f) show zoom-in images of the corroded electrode, revealing rough electrode surface and agglomerates of nanoparticles on it.
Cyclic voltammograms of the same Pt wire before (grey) and after (black) cathodic corrosion for 1000 s at −10 V in a solution containing 10M NaOH. The voltammograms were recorded in a de-aerated solution of 0.5M H2SO4 at a sweep rate of 50 mV/s. The current in the grey voltammogram, which was acquired prior to corrosion, is magnified 16 times. The Pt wire was 0.13 mm in diameter and submerged 1 mm into the electrolyte.
(a) Time dependence of the average ac currents flowing during (grey) anodic and (black) cathodic half-cycles of the −10 V to +10 V, 100 Hz, applied ac voltage in a 20M NaOH. The Pt wire was 0.13 mm in diameter and submerged 2.5 mm into the electrolyte. (b) Current (black) and voltage (grey) during a single ac cycle.
Dependence of the atomization time of a Pt wire on the limits of the square wave ac voltage applied. Circles represent the measurements, in which the upper value of the square wave was fixed at +10 V, and the lower one systematically varied between −20 and −0.5 V. Squares represent the measurements, in which the lower value of the square wave was fixed at −10 V, and the upper one varied from −1 to 30 V. Where available, several measured values of etching time are plotted for the same ac voltage. For each point on the graph, 1 mm of a Pt wire was completely atomized, and the atomization time was recorded. The experiments were conducted in a solution containing 1M NaOH. The frequency of the applied ac voltage was f = 100 Hz. A glassy carbon electrode was used as a counter-electrode.
TEM images of Pt nanoparticles that were formed during cathodic corrosion of a Pt wire. Although the nanoparticles agglomerate, individual particles can be distinguished.
SEM images of Pt electrodes that were subjected to cathodic corrosion in tetraalkylammonium hydroxide solutions. Figures (a) and (b) show a polycrystalline Pt electrode after treatment for 10 min at −10 V dc in a solution containing 2.7M TMAH. The Pt electrode in (c) and (d) was treated with −10 to 0 V ac voltage (100 Hz block waveform) for 10 min in the same solution. Figures (e) and (f) show a third Pt electrode that was treated with −10 to +1.5 V ac voltage for 10 min in a solution of 0.5M TEAH. In (f) certain surface termination, possibly (100), appears enhanced by corrosion. Although cathodic corrosion is visible even after application of a negative dc voltage to a Pt electrode, it becomes more apparent after an ac voltage treatment, especially if the upper limit of the ac voltage is positive.
SEM images of the same polycrystalline Pt electrode after flame-annealing (a), (b), subsequent cathodic polarization for 10 min at −10 V dc in a solution containing 2M H2SO4 (c), (d), and in a solution containing 1M H2SO4 and 1M Na2SO4 (e), (f). Images (b), (d), and (f) show a zoom-in of the same area marked by a square in (c). While slight deposits in (d) are possibly due to contamination, clear morphological changes in (f) reveal the extent of cathodic corrosion in a Na+-containing electrolyte.
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