Electronic Supplementary Information

Perovskite oxide LaCoO3 cocatalyst for efficient photocatalytic reduction of CO2 with visible light

Jiani Qin, Lihua Lin, Xinchen Wang*

State Key Laboratory of Photocatalysis on Energy and Environment, College of

Chemistry, Fuzhou University, Fuzhou 350002, People’s Republic of China

Email: wangxc@fzu.edu.cn

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2018

Experimental section

Synthesis of coralline-like LaCoO3 material: In a typical synthesis, the equal molar

mass of Co(NO3)3·6H2O and La(NO3)3·6H2O were dissolved in a small amount of

deionized water with vigorous stirring, when the two were dissolved and mixed

completely, certain amount of citric acid was added as a complexing agent. The molar

ratio of the added citric acid and the total metal salts was 1:1. Then viscous gel was

obtained by heating the mixture solution at 80 ºC oil bath. Move the gel to a 100 ºC

electron oven and keeping several hours. The pink spongy material obtained was

crushed and calcined at 600 ºC for 6 hours on a muffle furnace with air atmosphere.

The final black powder was the target material LaCoO3.

Characterization: Powder X-ray diffraction (XRD) measurements were conducted on

a Bruker D8 Advance diffractometer with Cu Ka1 radiation. The morphologies and

energy dispersive X-ray (EDX) spectrum of the sample were obtained by a Hitachi New

Generation SU8010 field emission scanning electron microscope (FESEM).

Transmission electron microscopy (TEM) was performed on a JEOL model JEM 2010

EX instrument. The nitrogen adsorption–desorption and CO2 adsorption isotherms were

collected by a Micromeritics ASAP2020 equipment. A Thermo ESCALAB250

instrument with a monochromatized Al Ka line source (200 W) was employed for X-

ray photoelectron spectroscopy (XPS) measurements. UV–Vis diffuse reflectance

spectra (UV–Vis DRS) were performed on a Varian Cary 500 Scan UV-Vis

spectrophotometer with barium sulfate as the reference. Inductively coupled plasma

mass spectrometry (ICP-MS, X Series II Thermo Scientific) was employed to analyze

the supernatant of the reaction mixture. A BAS Epsilon Electrochemical System with a

conventional three electrode cell was used to measure the Mott-Schottky curves. A Pt

plate and an Ag/AgCl electrode were used as the counter electrode and the reference

electrode, respectively. The working electrode was prepared by dip-coating 20 μL

LaCoO3 catalyst slurry (3 mg mL-1 in water) on indium-tin oxide (ITO) glasses, and the

active area is confined to 0.25 cm2. After air-drying, the film electrodes were further

dried at 300 ℃ for 30 min to improve adhesion. A 0.2 M Na2SO4 aqueous solution was

chosen as the supporting electrolyte and was purged with nitrogen to remove O2 before

any measurements. For the Mott-Schottky experiment, the potential ranged from -0.4

to 0.1 V (vs. Ag/AgCl), and the frequency were controlled at 500, 1000, and 1500 Hz.

An Agilent 7820A gas chromatography equipped was used to analyze the produced

gases, which equipped with a thermal conductivity detector (TCD) and a TD-01 packed

column, and using high purity argon as the carrier gas. The products of the 13CO2

isotopic experiment were analyzed by HP 5973 GC-MS.

Photocatalytic performance: In the established photocatalytic CO2 reduction reaction

system, 300 W Xenon Lamp with a 420 nm cut-off filter was used for the light source,

a circulation condensate equipment was employed to control the reaction temperature

at 30 ºC. For the reaction, [Ru(bpy)3]Cl2·6H2O (8 mg) and LaCoO3 (1 mg) were

dispersed into a CO2-saturated MeCN/H2O/TEOA (3:2:1, v/v/v) mixture solution with

magnetic stirring in an airtight reactor. After the reaction, the produced gases were

analysed by a gas chromatography.

Table S1 Comparison of catalytic activity of perovskite LaCoO3 with spinel cobalt

oxides under similar reaction conditions.

Entry Cocatalyst CO / μmol H2 / μmol CO+H2 / μmol Ref.

1 LaCoO3 44.2 12.5 56.7 This work

2 NiCo2O4 21.0 4.0 25.0 [1]

3 MnCo2O4 27.0 8.0 35.0 [2]

4 ZnCo2O4 25.1 8.7 33.8 [3]

Reaction conditions: Ru(bpy)3Cl2·6H2O (8 mg), cocatalyst (1 mg), TEOA (1 ml), solvent (5 ml,

MeCN : H2O = 3: 2), λ≧420 nm, 30 ℃, 1 h.

[1] Z. Wang, M. Jiang, J. Qin, H. Zhou and Z. Ding, Phys. Chem. Chem. Phys., 2015, 17, 16040.

[2] S. Wang, Y. Hou and X. Wang, ACS Appl. Mater. Interfaces, 2015, 7, 4327.

[3] S. Wang, Z. Ding and X. Wang, Chem. Commun., 2015, 51, 1517.

Table S2 The effect of volume ratio of MeCN/H2O on CO2 photoreaction performance.

Entry VMeCN / VH2O CO / μmol H2 / μmol Sel.CO / %

1 5/0 4.1 6.7 38.0

2 4/1 31.2 19.5 61.5

3 3/2 28.5 9.1 75.8

4 2/3 13.7 2.8 83.0

5 1/4 2.2 0.1 95.7

6 0/5 0.6 0.04 93.8

Table S3 Comparison of CO2 photoreduction performance of similar reaction systems.

Catalyst Photosensitizer lightCO-evolving rate

/ μmol h-1 g-1Refs.

LaCoO3 [Ru(bpy)3]2+ 420 nm 44200 This work

Co3O4 [Ru(bpy)3]2+ 420 nm 3523 [4]

Ni-MOF [Ru(bpy)3]2+ 420 nm 15866 [5]

CoSn(OH)6 [Ru(bpy)3]2+ 400 nm 18700 [6]

[4] C. Gao, Q. Meng, K. Zhao, H. Yin, D. Wang, J. Guo, S. Zhao, L. Chang, M. He, Q. Li, H. Zhao, X. Huang, Y. Gao, and Z. Tang, Adv. Mater., 2016, 28, 6485.

[5] K. Niu, Y. Xu, H. Wang, R. Ye, H. Xin, F. Lin, C. Tian, Y. Lum, K. Bustillo, M. Doeff, M. Koper, J. Ager, Sci. Adv., 2017, 3, e1700921.

[6] X. Lin, Y. Gao, M. Jiang, Y. Zhang, Y. Hou, W. Dai, S. Wang, Z. Ding, Appl. Catal. B: Environ., 2018, 224, 1009.

Fig. S1 XPS spectra of the prepared coralline-like perovskite LaCoO3 material: (a) survey spectrum and the high-resolution spectra of (b) Co 2p, (c) La 3d and (d) O 1s.

Fig. S2 (a) N2 adsorption-desorption isotherms at 77K and (b) CO2 adsorption isotherm at 273K.

Fig. S3 GC-MS spectra of 13C-labelled isotropic experiment.

Fig. S4 XRD spectra (a) and XPS patterns (b and c) of the LaCoO3 sample before and after photocatalytic reactions.

Fig. S5 Mott-Schottky plots of the prepared LaCoO3 material.

0

5

10

15

20

25

30

35

8:316:1 8:1

Prod

uced

Gas

(m

ol)

mRu : mLaCoO3

CO H2

160:1

Fig. S6 Yields of CO and H2 as a function of the mass ratio of Ru/LaCoO3 in the CO2 reduction reaction system.

0 30 60 90 120 150 180

0

20

40

60

80

100

120

Prod

uced

Gas

(m

ol)

Time (min)

CO H2

fresh Ru

Fig. S7 Yields of CO and H2 as a function of reaction time.

The apparent quantum yield (AQY) was conducted under the same reaction conditions. The incident light was used a low-power 420 nm LED lamp. The AQY is calculated as following:

AQY (%) = 2(number of the produced molecule)/(number of photons) 100%

The calculation procedures of apparent quantum yield are in the following:

2H+ H2 2e- 1h 0.3 mol

CO2 CO 2e- 1h 1.4 mol

Major parameters:

Light intensity: I = 19.8 mWcm-2

P = ItS, (t = 3600s, S = 1 cm2)

E = nhv, (h = 6.626×10-34 js, = 420 nm)

So, AQY = 1.36 %.