Effect of Amino Acid Additives on the Positive Electrolyte of Vanadium Redox Flow Batteries

Two amino acids (L-glutamate and L-arginine) have been used respectively as an additive in a positive electrolyte containing 2.0 M VOSO 4 and 3.0 M H 2 SO 4 for all-vanadium redox flow batteries. The effects of each additive on the thermal stability and electrochemical properties of the positive electrolyte are investigated. The thermal stability tests show that the addition of L-glutamate to the positive electrolyte could delay the initiation of precipitation in the electrolyte for 12 hours at 40°C and 5 hours at 50°C. Cyclic voltammetry results suggest that the electrochemical reversibility of V(IV)/V(V) redox couple in the electrolyte has been improved by the addition of either L-glutamate or L-arginine. The diffusion coefficient of V(IV) has been increased from 0.47∼1.30 × 10 −6 cm 2 /s in the pristine electrolyte to 0.54 ∼1.50 × 10 −6 cm 2 /s in the electrolyte with L-glutamate and 0.70 ∼1.93 × 10 −6 cm 2 /s in the electrolyte with L-arginine. The discharge capacity loss (312.4 mAh) of the cell with L-glutamate in the positive electrolyte is smaller compared to that (503.8 mAh) of the cell with the pristine positive electrolyte. The columbic efficiency and energy efficiency of the cell are also increased by 1.7% and 2.0%, respectively, by the addition of L-glutamate in the positive electrolyte of the cell.