Supporting Information

Transcription

1 Supporting Information Understanding Reduction Kinetics of Aqueous Vanadium(V) and Transformation Products Using Rotating Ring-Disk Electrode Gongde Chen and Haizhou Liu * Department of Chemical and Environmental Engineering, University of California at Riverside, Riverside, CA USA * Corresponding author, haizhou@engr.ucr.edu, phone (951) , fax (951) Submitted to Environmental Science & Technology S1

2 Table of Contents Figure S1 Speciation profiles of vanadium(v) as a function ph at the different vanadium(v) concentration: (A) 2 µm, (B) 20 µm, (C) 200 µm, (D) 2 mm, and (E) 20 mm. [NaClO ] = 0.6 M, and ionic strength = 0.6 M. V 10 is a combination of H 3 V 10 O 3-28, H 2 V 10 O - 28, NaHV 10 O - 28, Na 2 V 10 O - 28, HV 10 O 5-28 and NaV 10 O 5-28 ; V is a combination of V O - 12 and HV O 5-13 ; V 2 is a 2- combination of H 2 V 2 O 7 and HV 2 O S Figure S2 Predominance diagram of vanadium(iv) species as a function of ph. Total [vanadium(iv)] = 10 µm, [NaClO ] = 0.6 M, and ionic strength = 0.6 M.... S5 Text S1 Reactions and equilibrium constants of vanadium(v) and vanadium(iv) species... S6 Figure S3 Correlations between the cathodic peak current of vanadium (V) species and the square root of scan rates. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, and ionic strength = 0.6 M. The EC current at disk electrode potentials of 0.10, -0.5, -0.7, and V was taken for VO + 2, V 10, V and HVO 2-, respectively.... S7 Text S2 Calculations of the electron-transfer number and diffusion coefficient... S8 Text S3 Calculations of rate constant, charge transfer coefficient and intrinsic rate constant... S9 Figure S Koutecky-Levich plots of linear sweep voltammetry of the reduction of vanadium(v) on a rotating gold ring-disk electrode: (A) VO + 2, (B) V 10, (C) V and (D) HVO 2-. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, and scan rate = 50 mv/s.... S11 Figure S5 Koutecky-Levich plots of linear sweep voltammetry of the reduction of VO + 2 at ph=1 on a rotating gold ring-disk electrode in the presence of phosphate: (A) 1 mm, (B) 5 mm, (C) 10 mm and (D) 20 mm. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, and scan rate=50 mv/s.... S12 Figure S6 Tafel plots of linear sweep voltammetry of the reduction of vanadium(v) on a rotating gold ring-disk electrode: (A) VO + 2, (B) V 10, (C) V and (D) HVO 2-. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, and scan rate= 50 mv/s.... S13 Figure S7 Tafel plots of linear sweep voltammetry of the reduction of of VO + 2 at ph=1 on a rotating gold ring-disk electrode in the presence of phosphate: (A) 1 mm, (B) 5 mm, (C) 10 mm S2

3 and (D) 20 mm. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, and scan rate = 50 mv/s.... S1 Text S Calculation of half-life of the intermediate products... S15 Figure S8 Impact of rotation speed on the collection efficiency reduction products produced at a gold rotating ring-disk electrode. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, scan rate = 50 mv/s, and ring potential was fixed at 1.3, 1.0, 0.8, and 0.7 V for VO + 2, V 10, V and HVO 2-, respectively.... S16 Figure S9 Impact of phosphate on the linear sweep voltammetry of vanadium(v) at a rotating gold ring-disk electrode: (A) VO + 2, (B) V 10, (C) V and (D) HVO 2-. Total [vanadium(v)] = S20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, scan rate = 50 mv/s, rotation speed = 200 rpm, and ring potential was fixed at 1.3, 1.0, 0.8, and 0.7 V for VO + 2, V 10, V and HVO 2-, respectively.... S17 Figure S10 Predominance diagram of phosphate as a function of ph. Total [phosphate] = 20 mm, [NaClO ] = 0.6 M, and ionic strength = 0.6 M.... S18 Figure S11 Impact of phosphate on the collection efficiency of the reduction products produced on a rotating ring-disk electrode. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, rotation speed = 200 rpm, scan rate = 50 mv/s, and Ring electrode potential was fixed at 1.5, 1.0, 0.8, and 0.7 V for VO + 2, V 10, V and HVO 2-, respectively.... S19 S3

4 Fraction of Vanadium(V) Species VO + 2 H 2 VO - HVO 2- VO ph A Fraction of Vanadium(V) Species VO + HVO H 2 VO - B VO 3- H 2 V 2 O ph Fraction of Vanadium(V) Species VO + HVO C H VO 3-2 VO V 10 H 2 V 2 O 2-7 V O ph Fraction of Vanadium(V) Species Fraction of Vanadium(V) Species VO HVO 2- D ph V 10 VO + V E HVO 2- V O - 12 H 2 VO - VO V 2 V 5 O ph Figure S1 Speciation profiles of vanadium(v) as a function ph at the different vanadium(v) concentration: (A) 2 µm, (B) 20 µm, (C) 200 µm, (D) 2 mm, and (E) 20 mm. [NaClO ] = 0.6 M, and ionic strength = 0.6 M. V 10 is a combination of H 3 V 10 O 28 3-, H 2 V 10 O 28 -, NaHV 10 O 28 -, Na 2 V 10 O 28 -, HV 10 O and NaV 10 O ; V is a combination of V O 12 - and HV O ; V 2 is a combination of H 2 V 2 O 7 2- and HV 2 O V V 5 O 5-15 H 2 VO - V 2 VO 3- S

5 - -5 VO 2+ V 2 O (s) VO(OH) - 3 log[v(vi)] V(OH) + 3 VO(OH) + (VO) 2 (OH) [(VO) 2 (OH) 2 ] ph Figure S2 Predominance diagram of vanadium(iv) species as a function of ph. Total [vanadium(iv)] = 10 µm, [NaClO ] = 0.6 M, and ionic strength = 0.6 M. S5

6 Text S1 Reactions and equilibrium constants of vanadium(v) and vanadium(iv) species HVOO 2 + 3HH + VVOO HH 2 OO (1) llllllkk 1 = HVOO HH + HH 3 VV 10 OO HH 2 OO (2) llllllkk 2 = HVOO HH + HH 2 VV 10 OO HH 2 OO (3) llllllkk 3 = HVOO HH + HHVV 10 OO HH 2 OO () llooookk = HVOO HH + + NNNN + NNNNNNVV 10 OO HH 2 OO (5) llllllkk 5 = HVOO 2 + 1HH + + 2NNNN + NNNNNNVV 10 OO HH 2 OO (6) llllllkk 6 = HVOO 2 + 1HH + + NNNN + NNNNVV 10 OO HH 2 OO (7) llllllkk 7 = HVOO 2 + 5HH + VV 5 OO HH 2 OO (8) llllllkk 8 = HVOO 2 + HH + VV OO 12 + HH 2 OO (9) llllllkk 9 = 2.60 HVOO 2 + 3HH + HHHH OO HH 2 OO (10) llllllkk 10 = HVOO 2 + 2HH + HH 2 VV 2 OO HH 2 OO (11) llllllkk 11 = HVOO 2 + HH + HHHH 2 OO HH 2 OO (12) llllllkk 12 = HVOO 2 + HH + HH 2 VVOO (13) llllllkk 13 = 8.75 HVOO 2 VVOO 3 + HH + (1) llllllkk 1 = VOO 2+ + HH 2 OO VVVV(OOOO) + + HH + (15) llllllkk 15 = 5.9 VOO HH 2 OO VV(OOOO) HH + (16) llllllkk 16 = VOO HH 2 OO [(VVVV) 2 (OOOO) 2 ] HH + (17) llllllkk 17 = 6.69 VOO HH 2 OO VVVV(OOOO) 3 + 3HH + (18) llllllkk 18 = VOO HH 2 OO (VVVV) 2 (OOOO) 5 + 5HH + (19) llllllkk 19 = VV 2 OO (ss) + 2HH + VOO 2+ + HH 2 OO (20) llllllkk 20 =.27 VO(OOOO) 2(ss) + 2HH + VOO HH 2 OO (21) llllllkk 21 = 5.89 S6

7 Peak Current (ma) VO + 2 V 10 V (ph=1) (ph=) (ph=7) HVO - (ph=11) {Scan rate (V/s)} 0.5 Figure S3 Correlations between the cathodic peak current of vanadium (V) species and the square root of scan rates. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, and ionic strength = 0.6 M. The EC current at disk electrode potentials of 0.10, -0.5, -0.7, and V was taken for VO + 2, V 10, V and HVO 2-, respectively. S7

8 Text S2 Calculations of the electron-transfer number and diffusion coefficient The electron-transfer number (n) and diffusion coefficient of vanadium(v) species (D, cm/s) were calculated through combing the slope of Koutecky-Levich plots (Figure in the main text) from Equation 1 with the slope from correlation of cathodic peak current vs. square root of scan rates (Figure S1) from Equations 2 below: 1 1 = = 1 + ii ii KK ii DD ii KK nnnnnnDD 2/3 ωω 1/2 θθ 1/6 CC 0 (1) II pp = ( )nn 3/2 AADD 1/2 CC 0 VV 1/2 (2) i is the current measured on the disk electrode (A), i K represents the kinetic current in the absence of diffusion limitation (A), i D is the diffusion current (A), F is Faradic constant (C/mol), A is the electrode surface area (cm 2 ), ω is angular frequency of the rotation (s -1 ), υ is the kinematic viscosity of the solution (cm 2 /s), V is the scan rate (V/s) and C 0 is the bulk concentration of vanadium(v) species (mol/cm 3 ). S8

9 Text S3 Calculations of rate constant, charge transfer coefficient and intrinsic rate constant The kinetic current of vanadium(v) reduction at different potentials was determined by the intercept of Koutecky-Levich plots (Figure S3 and Figure S). The rate constant of vanadium(v) reduction (k) was further calculated from Equation 3: 1 kk = ii kk /nnnnnncc 0 (3) Where k is the rate constant at a targeted potential (cm/s), i k is the kinetic current of vanadium(v) reduction, n is the electron-transfer number, F is Faradic constant (C/mol), A is the electrode surface area (cm 2 ), and C 0 is the bulk concentration of vanadium(v) species (mol/cm 3 ). To obtain charge transfer coefficient (α), Tafel analysis was conducted on RRDE data of vanadium(v) reduction with rotation speed from 1600 to 2700 rpm (Figure S5 and Figure S6). α was determined from the slope of the Tafel plots at three rotation speeds (Equation ) and the average was taken in Table 2 of the main text, logii = logii 0 ααnnff ηη () 2.3RRRR Where i is the measured current (A), i 0 is the exchange current (A), α is the charge transfer coefficient, n is the electron-transfer number, η is overpotential (the difference between applied potential and reduction onset potential, V), R is gas constant (J/(mol K)), and T is the temperature (K). The intrinsic rate constants were calculated based on Bulter-Volmer electrode kinetics (Equation 5) 1 kk 0 = kk/ exp αααααααα (5) RRRR S9

10 Where k 0 is the intrinsic rate constant (cm/s), k is the rate constant at a targeted potential (cm/s), α is the charge transfer coefficient, n is the electron-transfer number, F is Faradic constant (C/mol), η is overpotential (the difference between applied potential and reduction onset potential, V), R is gas constant (J/(mol K), and T is the temperature (K). With multiple rate constants at different overpotentials and the average charge transfer coefficient, multiple intrinsic rate constants (k 0 ) were calculated based on Equation 5. The average intrinsic rate constant was used in Table 2 of the main text. S10

11 1/i (ma -1 ) V -0.6 V -0.7 V -0.8 V -0.9 V A 1/i (ma -1 ) V V V -0.2 V V V B VO + 2 (ph=1) ω -1/2 (s 1/2 ) -6 V 10 (ph=) ω -1/2 (s 1/2 ) 1/i (ma -1 ) V V -0.6 V V V V V C 1/i (ma -1 ) V V V V V D V (ph=7) ω -1/2 (s 1/2 ) HVO 2- (ph=11) ω -1/2 (s 1/2 ) Figure S Koutecky-Levich plots of linear sweep voltammetry of the reduction of vanadium(v) on a rotating gold ring-disk electrode: (A) VO 2 +, (B) V 10, (C) V and (D) HVO 2-. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, and scan rate = 50 mv/s. S11

12 V -0.6 V -0.7 V -0.8 V -0.9 V A V -0.6 V -0.7 V -0.8 V -0.9 V B 1/i (ma -1 ) /i (ma -1 ) ω -1/2 (s 1/2 ) ω -1/2 (s 1/2 ) V -0.6 V -0.7 V -0.8 V -0.9 V C V -0.6 V -0.7 V -0.8 V -0.9 V D 1/i (ma -1 ) /i (ma -1 ) ω -1/2 (s 1/2 ) ω -1/2 (s 1/2 ) Figure S5 Koutecky-Levich plots of linear sweep voltammetry of the reduction of VO + 2 at ph=1 on a rotating gold ring-disk electrode in the presence of phosphate: (A) 1 mm, (B) 5 mm, (C) 10 mm and (D) 20 mm. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, and scan rate=50 mv/s. S12

13 A B log i log i rpm 200 rpm 2000 rpm VO + 2 (ph=1) rpm 200 rpm 2000 rpm V 10 (ph=) η η log i C log i D rpm 200 rpm 1600 rpm V (ph=7) rpm 2000 rpm 1600 rpm HVO 2- (ph=11) η η Figure S6 Tafel plots of linear sweep voltammetry of the reduction of vanadium(v) on a rotating gold ring-disk electrode: (A) VO 2 +, (B) V 10, (C) V and (D) HVO 2-. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, and scan rate= 50 mv/s. S13

14 log i rpm 200 rpm 2000 rpm A η log i 3.0 B rpm 200 rpm 2000 rpm η log i rpm 200 rpm 2000 rpm C η log i rpm 200 rpm 2000 rpm D η Figure S7 Tafel plots of linear sweep voltammetry of the reduction of of VO + 2 at ph=1 on a rotating gold ring-disk electrode in the presence of phosphate: (A) 1 mm, (B) 5 mm, (C) 10 mm and (D) 20 mm. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, and scan rate = 50 mv/s. S1

15 Text S Calculation of half-life of the intermediate products Half-life of the intermediate products of vanadium(v) was calculated based Equations 6 and 7. 2 NN 0 NN = (νν DD )1 3 ( kk ωω ) (6) tt 1/2 = llll2 kk (7) where N is the experimental collection efficiency, N 0 is theoretical collection efficiency (2%), ν is the kinematic viscosity of the electrolyte (cm 2 /s), D is the diffusion coefficient of the intermediate products (cm 2 /s), ω is the rotation speed (rad/s), k is first-order decay rate constant of the reduction product (s -1 ), and t 1/2 is the half-life of the intermediate products (s). S15

16 Collection efficicency (%) V 10 VO + 2 (ph=) (ph=1) HVO 2- (ph=11) (ph=7) V Rotation speed (rpm) Figure S8 Impact of rotation speed on the collection efficiency reduction products produced at a gold rotating ring-disk electrode. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, scan rate = 50 mv/s, and ring potential was fixed at 1.3, 1.0, 0.8, and 0.7 V for VO + 2, V 10, V and HVO 2-, respectively. S16

17 Current (µa) Ring Background Electrolyte A µm 1 µm µm Disk 10 µm 20 µm Disk electrode potential (V vs. Ag/AgCl) Current (µa) Ring Background Electrolyte C Current (µa) -5 0 µm -10 Disk 1 µm 5 µm µm 20 µm Disk electrode potential (V vs. Ag/AgCl) Current (µa) Ring Background Electrolyte Disk B 0 µm 1 µm 5 µm 10 µm 20 µm Disk Electrode Potential (V vs. Ag/AgCl) Ring Background Electrolyte Disk D 0 µm 1 µm 5 µm 10 µm 20 µm Disk electrode potential (V vs. Ag/AgCl) Figure S9 Impact of phosphate on the linear sweep voltammetry of vanadium(v) at a rotating gold ring-disk electrode: (A) VO + 2, (B) V 10, (C) V and (D) HVO 2-. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, scan rate = 50 mv/s, rotation speed = 200 rpm, and ring potential was fixed at 1.3, 1.0, 0.8, and 0.7 V for VO + 2, V 10, V and HVO 2-, respectively. S17

18 0-2 H 3 PO H 2 PO - NaHPO - Na 2 PO - - NaH 2 PO log [PO ] HPO 2- Na 2 HPO PO NaPO ph Figure S10 Predominance diagram of phosphate as a function of ph. Total [phosphate] = 20 mm, [NaClO ] = 0.6 M, and ionic strength = 0.6 M. S18

19 Collection efficicency (%) B V 10 (ph= ) VO + 2 (ph= 1) HVO 2- (ph=11) (ph=7) [Phosphate] (mm) V Figure S11 Impact of phosphate on the collection efficiency of the reduction products produced on a rotating ring-disk electrode. Total [vanadium(v)] = 20 mm, [NaClO ] = 0.6 M, ionic strength = 0.6 M, rotation speed = 200 rpm, scan rate = 50 mv/s, and Ring electrode potential was fixed at 1.5, 1.0, 0.8, and 0.7 V for VO + 2, V 10, V and HVO 2-, respectively. S19

20 References 1. Bard, A. J.; Faulkner, L. R., Electrochemical methods: fundamentals and applications. 2nd ed.; Wiley New York: Albery, W.-J.; Bruckenstein, S., Ring-disc electrodes. Part 5. First-order kinetic collection effciencies at the ring electrode. Transactions of the Faraday Society 1966, 62, S20