(e) In a vanadium flow battery, the electrochemical reactions which take place at the electrodes during discharge are: At the positive electrode: (VO2)2SO4 + HSO4 +2e + 2H2(VOSO4) + 2(HO) At the negative electrode: 2(VSO4) + HSO4 V2(SO4)3 +2e + 2H+ E = +0.99 V (vs. SHE) The overall cell reaction is: (VO2)2SO4 + 2(VSO4) +2(HSO4)2(VOSO4) + V2(SO4)3 + 2(HO) (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 HSO4 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)