Artificial Photosynthesis on TiO2-Passivated InP Nanopillars.
Here, we report photocatalytic CO2 reduction with water to produce methanol using TiO2-passivated InP nanopillar photocathodes under 532 nm wavelength illumination. In addition to providing a stable photocatalytic surface, the TiO2-passivation layer provides substantial enhancement in the photoconversion efficiency through the introduction of O vacancies associated with the nonstoichiometric growth of TiO2 by atomic layer deposition. Plane wave-density functional theory (PW-DFT) calculations confirm the role of oxygen vacancies in the TiO2 surface, which serve as catalytically active sites in the CO2 reduction process. PW-DFT shows that CO2 binds stably to these oxygen vacancies and CO2 gains an electron (-0.897e) spontaneously from the TiO2 support. This calculation indicates that the O vacancies provide active sites for CO2 absorption, and no overpotential is required to form the CO2(-) intermediate. The TiO2 film increases the Faraday efficiency of methanol production by 5.7× to 4.79% under an applied potential of -0.6 V vs NHE, which is 1.3 V below the E(o)(CO2/CO2(-)) = -1.9 eV standard redox potential. Copper nanoparticles deposited on the TiO2 act as a cocatalyst and further improve the selectivity and yield of methanol production by up to 8-fold with a Faraday efficiency of 8.7%.
Jing
J
Qiu
Guangtong
G
Zeng
Mai-Anh
MA
Ha
Mingyuan
M
Ge
Yongjing
Y
Lin
Mark
M
Hettick
Bingya
B
Hou
Anastassia N
AN
Alexandrova
Material Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Ali
A
Javey
Stephen B
SB
Cronin
CO2 reduction; InP; Photoelectrochemical; TiO2-passivation; copper; methanol