PDF Publication Title:
Text from PDF Page: 005
Journal of The Electrochemical Society, 2021 168 020531 Figure 2. Open circuit potential (OCP) measured using the Pt–Pt electrode pair in different combinations of electrolytes separated by a zeolite membrane: (a) Neutral-Acid; (b) Neutral-Base; (c) Neutral-Neutral; (d) Acid-Acid; (e) Base-Base; (f) Acid-Base. Electrolyte concentrations: 1 M H2SO4, 1 M KOH, 1 M KNO3. potential, which is a clear indication of a potential shift by a change in pH. Similarly, reduction of the anionic redox couple S42- was carried out in the base-base and base-acid electrolytes combination at a Ni foam electrode, as shown in Fig. 4B. There is a reduction plateau started at −350 mV (Fig. 4B curve b) for during the forward scan, and a similar oxidation plateau appeared at −250 mV during the reverse scan for the S42−/2S22− redox couple in a 1M NaOH electrolyte at each half-cell. The observation of a plateau-like reduction/oxidation peak was attributed to the convection phe- nomena because of microchannels in the Ni-foam electrode. On the other hand, base-acid electrolyte combination showed reduction and oxidation plateaus at −360 mV and −260 mV, respectively, with a 10 mV negative shift in the redox potential for the S42−/2S22− redox couple (Fig. 4B curve a). The slight change in potential shift according to pH could be due to reduction, where electrons are released from the electrode. In total, the effect of a pH change was more prominent in the positive half-cell than the negative half-cell. Migration analysis.—For the migration of vanadium and sulfur ions, with a separate zeolite membrane dividing the half cells, a homemade electrolytic cell was constructed and used with a slightly higher current density (10 mA cm−2). Samples collected periodically from the opposite half-cell to either vanadium or sulfur ions containing half-cell during electrolysis were analyzed by UV-visible spectroscopy. Figure 5A shows the UV-visible spectra of known 0.1 m M V4+ in the 1 M KOH solution (Fig. 5 curve a), where an absorbance peak around 515 nm was found. After 1 h, the absor- bance peak at the 515 nm region of an electrolyzed sample collected from the opposite half-cell to the vanadium half-cell had vanished (Fig. 5A curve b). This shows that no crossover of vanadium ions from the acid electrolyte (1M V4+ in 1M H2SO4) to the base electrolyte (1 M NaOH) occurred via the zeolite membrane. This trend was monitored for up to 50 h. of electrolysis time (inset figure in Fig. 5A), which confirmed that vanadium ion migration via the zeolite membrane was completely restricted. A similar zeolite membrane-divided electrolysis experiment was conducted for sulfur ion migration, and the obtained results are depicted in Fig. 5B. The UV-visible spectra for the 0.01 M Na2S4 in 1 M NaOH solution showed an absorbance maximum at 300 nm (Fig. 5B curve a).40 After one hour, the absorbance peak at 300 nm of the electrolyzed Figure 3. EIS measurements for the different combinations of electrolytes separated by Nafion324 (A) and zeolite (B) membranes. (a) Acid-Acid; (b) Acid-Base; (c) Base-Base. Electrolyte concentrations: 5 M H2SO4, 10 M KOH. Electrodes = Pt–Pt (4 cm2). sample (after basified to pH 12) disappeared (Fig. 5B curve b), confirming that the migration of sulfur ions via the zeolite membrane had been prevented. The inset figure of Fig. 5B shows that no absorbance peak appeared for the sulfur ion up to the 50h electrolysis time, which confirms that zeolite prevented the migra- tion of sulfur ions to the opposite side of the half-cell. Charging and discharging analysis.—CV showed that the potential window of the V4+ (anodic half-cell) and S42− (cathodic half-cell) had a potential difference of 1.05 V (vs Ag/AgCl) in acid- base electrolyte combination at each half-cell when a graphite electrode was used as the working electrode. At the same time, the theoretically derived potentials for the vanadium ion7 and sulfur ion31 were 1.0 V (in acid) and −0.45 V (in base), as given below: Positive half-cell reaction: VO2+ +2H+ +e- VO2+ +H2O (1.00 V vsSHE) [1] Negative half-cell reaction: -- Na2S4 + 2NaOH + 2e 2Na2S2 + 2OH (-0.45 V vs SHE) [2]PDF Image | Single Zeolite Membrane for Crossover
PDF Search Title:
Single Zeolite Membrane for CrossoverOriginal File Name Searched:
Muthuraman_2021_168_020531.pdfDIY PDF Search: Google It | Yahoo | Bing
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
Heat Pumps CO2 ORC Heat Pump System Platform More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)