(e) In a vanadium flow battery, the electrochemical reactions which take place at the electrodes during...
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(e) In a vanadium flow battery, the electrochemical reactions which take place at the electrodes during discharge are: At the positive electrode: (VO2)2SO4 + H₂SO4 +2e + 2H2(VOSO4) + 2(H₂O) At the negative electrode: 2(VSO4) + H₂SO4 → V2(SO4)3 +2e + 2H+ E = +0.99 V (vs. SHE) The overall cell reaction is: (VO2)2SO4 + 2(VSO4) +2(H₂SO4)2(VOSO4) + V2(SO4)3 + 2(H₂O) (i) E-0.26 V (vs. SHE) It can be seen that for 2 moles of electrons to be transferred in the cell, 1 mole of (VO2)2SO4, 2 moles of VSO4, and 2 moles of H₂SO4 are required as the active materials. (ii) By considering the molar masses of the required active materials, calculate the theoretical specific energy (Wh/kg) of the vanadium flow battery. (81/3 marks) The actual specific energy of a practical vanadium flow battery is typically approximately 20 Wh/kg. Explain why the actual specific energy of a practical vanadium flow battery is always significantly lower than the theoretical specific energy value based on the active masses of the materials. Give at least two reasons. (3 marks) (e) In a vanadium flow battery, the electrochemical reactions which take place at the electrodes during discharge are: At the positive electrode: (VO2)2SO4 + H₂SO4 +2e + 2H2(VOSO4) + 2(H₂O) At the negative electrode: 2(VSO4) + H₂SO4 → V2(SO4)3 +2e + 2H+ E = +0.99 V (vs. SHE) The overall cell reaction is: (VO2)2SO4 + 2(VSO4) +2(H₂SO4)2(VOSO4) + V2(SO4)3 + 2(H₂O) (i) E-0.26 V (vs. SHE) It can be seen that for 2 moles of electrons to be transferred in the cell, 1 mole of (VO2)2SO4, 2 moles of VSO4, and 2 moles of H₂SO4 are required as the active materials. (ii) By considering the molar masses of the required active materials, calculate the theoretical specific energy (Wh/kg) of the vanadium flow battery. (81/3 marks) The actual specific energy of a practical vanadium flow battery is typically approximately 20 Wh/kg. Explain why the actual specific energy of a practical vanadium flow battery is always significantly lower than the theoretical specific energy value based on the active masses of the materials. Give at least two reasons. (3 marks)
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1 At standard conditions E Ecathode E anode 099 026 125 n 2 F 96500 AG nF E 2 x 96500 x 125 24125... View the full answer
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