Using this metal as a charge carrier avoids both cross-contamination and electro·deposition because it has four stable oxidation states: plus-two, plus-three, plus-four, and plus-five. For 10 points each:
[10h] Name this transition metal used as the charge carrier in the most common redox flow battery for electric grids.
ANSWER: vanadium [or V]
[10m] To balance charge between the pipes, redox flow batteries rely on one of these semi·permeable barriers made of Nafion. They also separate the compartments of fuel cells.
ANSWER: proton-exchange membranes [or PEMs; or polymer-electrolyte membranes; prompt on membranes orion-exchange membranes]
[10e] The electrolyte of a vanadium redox flow battery is a solution of this compound. This “acid” in a lead-acid battery is prepared using a vanadium catalyst in the contact process.
ANSWER: sulfuric acid [or H2SO4]
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