Effects of Surface Chemistry of Carbon on Hydrogen Evolution Reaction in Lead Carbon Electrodes

Transcription

1 Effects of Surface Chemistry of Carbon on Hydrogen Evolution Reaction in Lead Carbon Electrodes Begüm Bozkaya 1, Jochen Settelein 1, Henning Lorrmann 1, Gerhard Sextl 1, 2 1 Fraunhofer Institute for Silicate Research ISC, Würzburg, Germany 2 University of Würzburg, Germany - - Pb 2+ Pb Pb 2+ Carbon Pb 2+ Pb 2+ Pb Lead

2 Carbon in Negative Plates Pronounced H 2 Evolution H 2 Overpotential Electrocatalytic Activity 1, 2 Current Pb PbSO 4 H 2 COOH O NH A. Allouche, et al., Carbon, 44 (26) LABAT 217, Bulgaria Potential vs. NHE H + + 2e - H 2 1. J. L. Figueiredo, et al., Catalysis Today, 15 (21) 2-7 PbSO 4 Pb Surface area H 3 O + OH O e - e - e - NH 2 Surface active sites

3 Electrocatalytic Activity of Pure Carbons Motivation Carbon - Surface chemistry - Specific surface area No simple correlation with physical properties? Performance Mechanism - Electrocatalytic activity - Double layer capacity - Dynamic charge acceptance - Gassing 3 LABAT 217, Bulgaria

4 Outline MATERIAL Functionalized Carbon Materials MECHANISM Electrocatalytic Activity of Pure Carbons PERFORMANCE Electrochemical Activity of Negative Electrodes 4 LABAT 217, Bulgaria

5 Functionalized Carbon Materials Chemical Treatment HO N Possible effects: Polarity N + ph Adsorption capability Direct synthesis N N H Conductivity Porosity Wet chemical treatment. Gas phase treatment 5 LABAT 217, Bulgaria

6 Counts Counts Counts Counts Functionalized Carbon Materials XPS Surface Functionality C 1s: 95% N 1s:.4% O 1s: 4.6% C 1s 8 6 C 1s: 75% N 1s: 14% O 1s: 11% C 1s Presence of oxygen groups in original O 1s N 1s Incorporation of nitrogen groups by chemical treatment 4 2 O 1s Binding Energy / ev Binding Energy / ev Amount of surface functionality: -N C 1s: 89. N 1s: 6.7 O 1s: 4.3 O 1s C 1s C 1s: 6% N 1s: 23% O 1s: 17% O 1s N 1s -N2 C 1s 8 4 O 1s N 1s Binding Energy / ev Binding Energy / ev 6 LABAT 217, Bulgaria

7 Quantity Adsorbed / cm³/g Quantity Adsorbed / cm³/g Quantity Adsorbed / cm³/g Quantity Adsorbed / cm³/g Functionalized Carbon Materials N 2 Sorption Surface Area Original and mainly consist of micropores Decrease in surface area by chemical treatment Desorption 17 m 2 /g Relative Pressure / p/p Adsorption m 2 /g Relative Pressure / p/p Significant low BET of and -N2 due to the blocked / filled micropores Relative Pressure / p/p 11 m 2 /g m 2 /g -N Relative Pressure / p/p 7 LABAT 217, Bulgaria

8 Functionalized Carbon Materials Summary Activated carbons with different amount of functional groups Porosity decrease by the modification of activated carbon Higher surface functionality resulted in lower BET surface area Carbon [%] Nitrogen [%] Oxygen [%] S BET [m 2 /g] S micro [m 2 /g] -N LABAT 217, Bulgaria

9 Electrocatalytic Activity of Pure Carbons Motivation Carbon - Surface chemistry - Specific surface area Mechanism - Electrocatalytic activity - Double layer capacity Performance - Dynamic charge acceptance - Gassing 9 LABAT 217, Bulgaria

10 Electrocatalytic Activity of Pure Carbons Rotating Disk Electrode Measurements Working electrode: Glassy Carbon Drop casting of carbon from aqueous dispersion.2 cm 2 apparent surface area Motor Counter electrode: Platinum Working electrode Reference electrode: RHE Electrolyte: 1M H 2 SO 4 (de-aerated) Electrolyte Rotating Disk Electrode 1 LABAT 217, Bulgaria

11 Current Density / ma/cm 2 Current Density / ma/cm 2 Electrocatalytic Activity of Pure Carbons Cyclic Voltammetry Hydrogen Evolution 5 mv/s 5 mv/s st Cycle -N th Cycle -N Potential vs RHE / V Potential vs RHE / V H 2 evolution overpotentials: -N2 > > > Increased surface treatment led to lower activity towards H 2 evolution 11 LABAT 217, Bulgaria

12 Current Density / ma/cm 2 Electrocatalytic Activity of Pure Carbons Cyclic Voltammetry Double Layer mv/s -N2.4.2 S BET [m 2 /g] N2 * C DL [F/cm 2 ] 1.4 x x x x 1-2 *Capacitance between.2v.25v Potential vs RHE / V Similar capacitance of, and -N2 Surface chemistry as important as BET Higher capacitance of due to the presence of nitrogen groups 12 LABAT 217, Bulgaria

13 Current Density / ma/cm 2 Current Density / ma/cm 2 Electrocatalytic Activity of Pure Carbons Summary Lower activity of carbon towards H 2 evolution by higher nitrogen content Increased double layer capacitance by higher nitrogen content th Cycle -N N Potential vs RHE / V Potential vs RHE / V 13 LABAT 217, Bulgaria

14 Electrocatalytic Activity of Pure Carbons Motivation Carbon - Surface chemistry - Specific surface area Mechanism - Electrocatalytic activity - Double layer capacity Performance - Dynamic charge acceptance - Gassing 14 LABAT 217, Bulgaria

15 Electrochemical Activity of Negative Electrodes Electrode Pasting and Cell Assembly 2V Test-cell 2V laboratory cells Enhanced flooded batteries (EFB) 2 positive, 1 negative electrode Carbon additives:, and 1 Ah capacity Manual pasting of electrodes Cell assembly Container formation Paste Manufactured electrodes 15 LABAT 217, Bulgaria

16 Current / A/Ah Current Density / ma/cm 2 Electrochemical Activity of Negative Electrodes Cyclic Voltammetry Hydrogen Evolution Negative plates with 1 wt.% carbon Pure carbon electrodes.5 1 mv/s Pb / PbSO 4 5 mv/s. -.5 PbSO 4 / Pb H 2 evolution Potential vs RHE / V Potential vs RHE / V 5 th Cycle Different activity of negative electrodes towards H 2 evolution: > > Similar observation obtained from the cyclic voltammetry of pure carbons 16 LABAT 217, Bulgaria

17 Current / A/Ah Current Density / ma/cm 2 Electrochemical Activity of Negative Electrodes Cyclic Voltammetry Double Layer Negative plates with 1 wt.% carbon Pure carbon electrodes mv/s mv/s Potential vs RHE / V Potential vs RHE / V Double layer capacitance of negative electrodes: ~ > No direct correlation between the capacitance of lead-carbon plates and pure carbons 17 LABAT 217, Bulgaria

18 Average Current / A/Ah Electrochemical Activity of Negative Electrodes Charge Acceptance After charge 8% SoC qdca of cells from EN After discharge 9% SoC Carbon [%] Nitrogen [%] Oxygen [%] S BET [m 2 /g] Charge acceptance of negative electrodes : ~ > Despite the low BET, high charging currents of 18 LABAT 217, Bulgaria

19 Current / A/Ah Av. Current / A/Ah Electrochemical Activity of Negative Electrodes Summary Lower activity of carbon in terms of H 2 evolution by higher nitrogen doping High charge acceptance of negative electrodes even with a very low BET carbon.5 Pb / PbSO After discharge 9% SoC PbSO 4 / Pb H 2 evolution Potential vs RHE / V.4.2. BET [m 2 /g] N [%] LABAT 217, Bulgaria

20 Electrocatalytic Activity of Pure Carbons Conclusion Carbon - Surface chemistry - Specific surface area Optimized carbon additive by sufficient nitrogen content and porosity Performance - Dynamic charge acceptance - Gassing Mechanism - Electrocatalytic activity - Double layer capacity 2 LABAT 217, Bulgaria

21 Thank you for your attention! Begüm Bozkaya 21 LABAT 217, Bulgaria