Supporting Information Pt Nanoparticles Anchored Molecular Self-Assemblies of DNA: An Extremely Stable and Efficient HER Electrocatalyst with Ultra-Low Pt Content Sengeni Anantharaj, $ Pitchiah E. Karthik, # Balasubramanian Subramanian $ and Subrata Kundu $ * $ Electrochemical Materials Science (ECMS) Division, CSIR-Central Electrochemical Research Institute (CECRI), Karaikudi-630006, Tamil Nadu, India. # Department of Chemistry, Indian Institute of Science Education and Research (IISER) Mohali, Punjab, India. * To whom correspondence should be addressed, E-mail: skundu@cecri.res.in; kundu.subrata@gmail.com, Phone: (+ 91) 4565-241487, FAX: +91-4565-227651 Materials. Platinic acid (H 2 PtCl 4 ), sodium borohydride (NaBH 4 ), sodium salt of DNA from salmon testes, 5 wt. % solution of Nafion in propanol and water mixture and the commercial Pt/C 10 wt. % catalyst were obtained from Sigma Aldrich and used without any further purification. Conc. sulphuric acid was obtained from RANKEM, India. Ultra-pure water (18.2 MΩ.cm) was used throughout the synthesis and in electrochemical studies and other places wherever required. A glassy carbon (GC) disc electrode of geometrical surface area 0.0732 cm 2 was used as substrate for working electrode fabrication. Hg/HgSO 4 reference electrode filled with saturated potassium sulphate (K 2 SO 4 ) was used in 0.5 M H 2 SO 4 electrolyte along with a Pt-foil counter electrode were used in a three electrode electrochemical system taken for the HER performance evaluation of our colloidal Pt@DNA molecular self-assemblies. Instruments Used for Materials Characterizations. The synthesized colloidal Pt@DNA molecular self-assemblies were characterized with HR-TEM, (Tecnai TM G 2 TF20) working at an accelerating voltage of 200 kv. TheEnergy Dispersive X-ray Spectroscopy (EDS) analysis was done with the FE-SEM instrument (Oxford)
with a separate EDS detector connected to that instrument and the same instrument was used to study the morphology of the synthesized colloidal Pt@DNA molecular self-assemblies. The XRD analysis was carried out with a scan rate of 5 min -1 in the 2θ range 10-70 using a Bruker X-ray powder diffractometer (XRD) with Cu K α radiation (λ = 0.154 nm). X-ray photoelectron spectroscopic (XPS) analysis was performed using a Theta Probe AR-XPS system (Thermo Fisher Scientific, UK). Electrochemical analyzer CHI6084c version 12.13 was used for the entire HER and related studies. Hg/HgSO 4 reference electrode was used along with a Pt counter electrode while colloidal Pt@DNA molecular self-assemblies modified GC electrodes were used as working electrode. Sample Preparation Methods for Various Characterizations. The synthesized colloidal Pt@DNA molecular self-assemblies were characterized using UV-Vis, TEM, EDS, XRD, XPS and FT-IR analysis studies. The colloidal Pt@DNA molecular self-assemblies were directly used for the absorption measurement in UV-Vis spectrophotometer. The same liquid solution was used for the TEM sample preparation and other thin films preparation. The samples for TEM was prepared by placing a drop of the as synthesized colloidal Pt@DNA molecular self-assemblies onto a carbon coated Cu grid followed by slow evaporation of solvent at ambient conditions. For EDS, XRD, XPS and FT-IR analysis, glass slides were used as substrates for the preparation of thin films. The slides were cleaned thoroughly with acetone and sonicated for about 30 min. The cleaned substrates were covered on one side with the colloidal Pt@DNA molecular self-assemblies and then dried in air. After the deposition of first layer, subsequent layers were deposited by repeatedly adding more colloidal Pt@DNA molecular self-assemblies solution. Final samples were obtained after 10-12 depositions and then analyzed using the above techniques. Determination of Number of Pt Atoms in both Loaded Pt@DNA and the Pt/C Catalysts. The number Pt atoms in the loaded catalysts is calculated based on Avogadro s method with use of density of the crystal system at which it crystallized during the synthesis and the covalent radii of Ptas follows: For Pt@DNA of loading 15 µg:
Wt. of Pt taken=1.5*10-5 g ρ = 21.45 g/cm 3 V = w/ρ = (1.5*10-5 /21.45)*10 21 = 7*10 14 nm 3 R=139 pm = 0.139 nm V = 1.33*3.14*0.139 3 = 0.01122 nm 3 N = V/V = 7*10 14 /0.01122 = 6.2*10 17 Wt. of Pt = W/N -= 1.5*10-5 /6.2*10 17 = 2.4*10-23 g 1NA=195.08g 1g = 1/195.08 2.4*10-23 = 2.4*10-23 *6.023*10 23 /195.08 = 0.074atoms/NP No of Pt atoms = 0.074*6.2*10 17 = 4.59*10 16 atoms For Pt/C 10 wt. % of loading 20.5 µg: W=2.05*10-5 g ρ=21.45 g/cm 3 V=w/ρ = (2.05*10-5 /21.45)*10 21 = 9.56*10 14 nm 3 R=139 pm = 0.139 nm V = 1.33*3.14*0.139 3 = 0.01122 nm 3 N = V/V = 9.56*10 14 /0.01122 = 8.59*10 16 Wt. of Pt = W/N -= 2.05*10-5 /8.59*10 16 = 2.4*10-22 g 1NA=195.08g 1g = 1/195.08 2.4*10-22 = 2.4*10-22 *6.023*10 23 /195.08 = 0.74atoms/NP No of Pt atoms = 0.74*8.59*10 16 = 6.36*10 16 atoms Determination TOF at an Overpotential of 0.02 V for both Pt@DNA-GC Interface without Binder and the Pt/C-GC Interface with Binder. Turnover frequency for oxygen evolution reactions is usually done in more than one way. Here we have made a primary assumption of 100% activity and participation of all the Fe atoms in OER and the calculated Fe atoms as shown above is used here as surface concentration. The
following equation is used to calculate the TOF value at an overpotential (ŋ) of 359 mv for both Sn-FeHP and FeHP. TOF= i N A / A F n ᴦ Where, i = current N A = Avogadro number A = Geometrical surface area of the electrode F = Faraday constant n = Number of electrons ᴦ = Surface concentration We have taken the HER current density at the overpotential of 20 mv for both Pt@DNA-GC interface without binder and the Pt/C-GC interface with binder. Hence for Pt@DNA-GC interface without binder; TOF ŋ = 26 mv = [(10 10-3 ) (6.023 10 23 )] / [(1) (96485) (2) (4.59 10 16 )] TOF ŋ = 26 mv =15.810s -1 Similarly for Pt/C-GC interface with binder; 10 16 )] TOF ŋ = 26 mv = [(3.12 10-3 ) (6.023 10 23 )] / [(1) (96485) (2) (6.36 TOF ŋ = 26 mv = 0.153s -1
A 0.000050 HUPD of Pt@DNAwithout binder B 0.00002 HUPD CV of Pt@DNAwith binder 0.000025 0.000000 0.00000 j (A) -0.000025 j (A) -0.000050-0.000075 Charge = 10.406 e-6 As ECSA = 10.406 e-6 As/ 210 µc cm -2 = 0.0495 cm 2-0.00002-0.00004 Charge = 5.273 e-6 As ECSA = 5.273 e-6 As/ 210 µc cm -2 = 0.0251 cm 2-0.000100-0.8-0.6-0.4-0.2 0.0 0.2 0.4 0.6 0.8 E / V (vs Hg/HgSO 4 ) -0.8-0.6-0.4-0.2 0.0 0.2 0.4 0.6 0.8 E / V (vs Hg/HgSO 4 ) C 0.0002 HUPD of Pt/C 10 wt. % without nafion D 0.0002 HUPD of Pt/C 10 wt. % with nafion 0.0000 0.0000 j (A) j (A) -0.0002-0.0002-0.0004 Charge = 3.833 e-5 As ECSA = 3.833 e-5 As/ 210 µc cm -2 = 0.16 cm 2-0.0004 Charge = 3.30 e-5 As ECSA = 3.3 e-5 As/ 210 µc cm -2 = 0.15 cm 2-0.8-0.6-0.4-0.2 0.0 0.2 0.4 0.6 0.8 E / V (vs Hg/HgSO 4 ) -0.8-0.6-0.4-0.2 0.0 0.2 0.4 0.6 0.8 E / V (vs Hg/HgSO 4 ) Figure S1: (A-B) are the CV of Pt@DNA without and with binder that show their respective H-UPD peaks as indicated. (C-D) are the CV of Pt/GC without and with binder that show their respective H-UPD peaks as indicated.
(111) Intensity (a.u) (110) (200) (311) 20 30 40 50 60 70 80 90 2θ Figure S2: The X-ray diffraction (XRD) pattern of the Pt@DNA thin films fabricated on glass substrates.
250000 Surve scan of Pt@DNA molecular self-assemblies 200000 Na 1s 150000 cps 100000 50000 O KLL O 1s N 1s Pt 4d C 1s Pt 4f P 2s P 2p 0 1200 1000 800 600 400 200 0 Binding Energy (ev) Figure S3: The X-ray photoelectron survey spectrum of the Pt@DNA thin films fabricated on glass substrates.
A B Figure S4: (A) EIS spectra of Pt@DNA with and without binder. (B) EIS spectra of Pt/C with and without binder.
Figure S5: EIS spectra acquired at 1 st and 10 th day of aging study of Pt@DNA-GC interface without binder.
-25-20 i-t response @ 0.03 V v RHE after 10 days in 0.5 M H 2 SO 4 j ECSA (macm -2 ) -15-10 -5 200 300 400 500 600 700 800 900 1000 Time (min) Figure S6: Post-aging chronoamperometric analysis on Pt@DNA-GC interface without binder.
0-10 LSV of Pt@DNA 10 th day Post-aging and post-chronoamperometric LSV j geo (macm -2 ) -20-30 -40-50 -0.5-0.4-0.3-0.2-0.1 0.0 0.1 E / V (vs RHE) Figure S7: Post-aging and Post-chronoamperometric LSV analysis on Pt@DNA-GC interface without binder.
-0.3-0.2-0.1 E / V (vs RHE) 0.0 0.1 0.2 0.3 Pt@DNA post-ageing and chronoamperometry 0.028 V/dec 0.4-2.50-2.25-2.00-1.75-1.50-1.25-1.00-0.75 log j (macm -2 ) Figure S8: Post-aging and Post-chronoamperometric Tafelanalysis on Pt@DNA-GC interface without binder.
Figure S9: (A-B) are the optical images of water droplet on Pt@DNA coated FTO before and after aging and post-aging studies. (C-D) are the optical images of water droplet on DNA coated FTO before and after aging and post-aging studies. (E-F) are the optical images of water droplet on bare FTO before and after aging and post-aging studies.
A 1.000 Only FTO B 1.02 1.00 DNA coated FTO before aging DNA coated FTO after aging Transmittance (%) 0.995 0.990 0.985 0.980 Transmittance (%) 0.98 0.96 0.94 0.92 0.975 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm -1 ) 0.90 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm -1 ) C 1.000 DNA coated FTO before electrocatalysis and aging DNA coated FTO after electrocatalysis and aging Transmittance (%) 0.995 0.990 0.985 0.980 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm -1 ) Figure S10: (A) The FT-IR spectrum of bare FTO. (B) FT-IR spectra obtained before and after aging on DNA coated FTO. (C) FT-IR spectra obtained before and after aging on Pt@DNA coated FTO.
Scheme S1: Synthesis scheme of Pt@DNA colloids with varying DNA concentrations.