Supplementary Material

Decoration of ultralong carbon nanotubes with Cu2O nanocrystals: a hybrid platform for enhanced photoelectrochemical CO2 reduction

Egon Kecsenovitya,d, Balázs Endrődia,b, Zsuzsanna Pápae, Klára Hernádid, Krishnan Rajeshwarc,*, and Csaba Janákya,b,*

a MTA-SZTE „Lendület” Photoelectrochemistry Research Group, Rerrich Square 1, Szeged, H-6720, Hungary

b Department of Physical Chemistry and Materials Science, University of Szeged, Rerrich Square 1, Szeged, H-6720, Hungary

c Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas 76019, USA

d Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Square 1, Szeged, H-6720, Hungary

e Department of Optics and Quantum Electronics, University of Szeged, Dóm Square 9, Szeged, H-6720, Hungary

*E-mail:rajeshwar@uta.edu (K.R.), janaky@chem.u-szeged.hu (C. J.)

Figures:

(a) (b)

Fig. S1 SEM images of the CVD synthesized MWCNT arrays at different magnifications.

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2016

0.0 0.1 0.2 0.3 0.4 0.5-100

-50

0

50

100

150

200

I (A

)

E (V) vs. Ag/AgCl/3M NaCl

thin CNT film thick CNT film

Fig. S2 CV traces of two CNT/ITO films with different CNT loading (10 and 50 g cm-2)

registered at 50 mV s-1 sweep rate in the same Cu-lactate solution (pH=9) which was used for

the subsequent electrodeposition.

Slightly modified Randles equivalent circuit was applied to evaluate the data from

electrochemical impedance measurements (Fig. S3). This circuit consists of an active solution

(electrolyte) resistance (RS) coupled in series with the parallel combination of the Faradaic

impedance and the double-layer capacitance. Faradaic impedance of such electrode is

commonly described with series combination of the charge transfer resistance (RCT) and a

Warburg element (W). The double layer capacitance was defined by a constant phase element.

Capacitance of the cell (capacitor formed from the working and counter electrodes) was also

introduced in the model, since it has significant contribution to the impedance at high

frequencies (typically above 100 kHz). In the case of the CNT-containing electrode, the

model was improved with an additive, parallel combined capacitance element to describe the

new electrode-electrolyte surface.

(a) (b)

Fig. S3 Equivalent circuits used for the fitting of the impedance spectra for: (a) Cu2O and (b)

CNT/Cu2O electrodes.

0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

3x1010

4x1010

5x1010

6x1010

7x1010

8x1010 CNT/Cu2O 5 kHz

-(Z"

)2 / F-2

E (V) vs. Ag/AgCl/3M NaCl

0.346 V

0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.452.0x1011

4.0x1011

6.0x1011

8.0x1011

1.0x1012

1.2x1012

1.4x1012

1.6x1012

1.8x1012 Cu2O 5 kHz

-(Z"

)2 / F-2

E (V) vs. Ag/AgCl/3M NaCl

0.274 V

Fig. S4 Mott-Schottky plots recorded in 0.1 M sodium acetate solution at 5 kHz for (a) Cu2O

and (b) CNT/Cu2O electrodes.

0 2 4 6 8 10 12 14-1.0

-0.5

0.0

0.5

1.0

E v

s. A

g/A

gCl (

V)

pH

I. Cu2+

III. Cu2O

IV. Cu

II. CuOWater oxidation

Proton reduction

Fig. S5 Pourbaix diagram of Cu.

(a) (b)

(a)

(b)

(c)

(d)

Fig. S6 Comparison of SEM images recorded for Cu2O/CNT (a, b) and Cu2O (c, d) films

deposited with 200 mC charge.