Replacing the solid metal cathode in an electrolytic cell with a plasma (gas discharge) allows the reduction of metal salt solutions to metal nanoparticles. Here, we apply gravimetric analysis to quantify the charge transfer (faradaic) efficiency of this reduction process and understand reaction pathways at the plasma-liquid interface. Silver powder synthesized from aqueous solutions of silver nitrate is collected and the weight is compared to the theoretical amount of silver obtained by applying Faraday’s law of electrolysis. We find that the faradaic efficiencies are near 100% when the initial silver nitrate concentration is large (>100 mM), but are much less than 100% at low salt concentrations (<15 mM) or at high applied currents (>6 mA). These results are explained in terms of reaction kinetics involving solvated electrons and two important reactions: the reduction of silver ions (Ag+) and the second order recombination of solvated electrons which releases hydrogen gas.
Bibliographical noteFunding Information:
This work was supported by the U. S. Army Research Office under grant No. W911NF-14-1-0241 and the National Science Foundation under grant No. SNM-1246715. R.H. thanks the CWRU SOURCE Summer Fellowship program for support. We are also grateful to Amy Aube for help with the experimental setup.
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