Guangtong Zeng

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%.

Artificial Photosynthesis on TiO 2 -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%.

Enhanced Photocatalytic Reduction of CO2 to CO through TiO2 Passivation of InP in Ionic Liquids

A robust and reliable method for improving the photocatalytic performance of InP, which is one of the best known materials for solar photoconversion (i.e., solar cells). In this article, we report substantial improvements (up to 18×) in the photocatalytic yields for CO2 reduction to CO through the surface passivation of InP with TiO2 deposited by atomic layer deposition (ALD). Here, the main mechanisms of enhancement are the introduction of catalytically active sites and the formation of a pn-junction. Photoelectrochemical reactions were carried out in a nonaqueous solution consisting of ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4), dissolved in acetonitrile, which enables CO2 reduction with a Faradaic efficiency of 99% at an underpotential of +0.78 V. While the photocatalytic yield increases with the addition of the TiO2 layer, a corresponding drop in the photoluminescence intensity indicates the presence of catalytically active sites, which cause an increase in the electron-hole pair recombination rate. NMR spectra show that the [EMIM](+) ions in solution form an intermediate complex with CO2(-), thus lowering the energy barrier of this reaction.

Correction: Plasmon-enhanced water splitting on TiO2-passivated GaP photocatalysts

Correction for ‘Plasmon-enhanced water splitting on TiO2-passivated GaP photocatalysts’ by Jing Qiu et al., Phys. Chem. Chem. Phys., 2014, 16, 3115–3121.

Prevention of surface recombination by electrochemical tuning of TiO2-passivated photocatalysts

We present a systematic study of photoluminescence (PL) spectroscopy of TiO2-passivated GaAs as a function of electrochemical potential in an ionic liquid solution. We observe a 7X increase in the PL intensity as the GaAs transitions from accumulation to depletion due to the applied potential. We attribute this to the excellent control over the surface Fermi level enabled by the high capacitance of the electrochemical double layer and TiO2. This allows us to control the surface carrier concentration and corresponding non-radiative recombination rate. In addition to photoluminescence (PL) spectroscopy, we also measured the capacitance-potential (i.e., C-V) characteristics of these samples, which indicate flat band potentials that are consistent with these regimes of ion accumulation observed in the photoluminescence measurements. We have also performed electrostatic simulations of these C-V characteristics, which provide a detailed and quantitative picture of the conduction and valence band profiles and ch...

Correction to Artificial Photosynthesis on TiO2-Passivated InP Nanopillars.

Letter pubs.acs.org/NanoLett Artificial Photosynthesis on TiO 2 ‑Passivated InP Nanopillars Jing Qiu, ‡ Guangtong Zeng, † Mai-Anh Ha, ∥ Mingyuan Ge, † Yongjing Lin, ⊥ Mark Hettick, ⊥ Bingya Hou, § Anastassia N. Alexandrova, ∥,⊥ Ali Javey, # and Stephen B. Cronin* ,†,§ Department of Chemistry, ‡ Department of Materials Science, and § Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States Department of Chemistry and Biochemistry, ⊥ California NanoSystems Institute, University of California Los Angeles, Los Angeles, California 90025, United States Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States S Supporting Information ABSTRACT: Here, we report photocatalytic CO 2 reduction with water to produce methanol using TiO 2 -passivated InP nanopillar photocathodes under 532 nm wavelength illumination. In addition to providing a stable photocatalytic surface, the TiO 2 -passivation layer provides substantial enhancement in the photoconversion efficiency through the introduction of O vacancies associated with the nonstoichiometric growth of TiO 2 by atomic layer deposition. Plane wave-density functional theory (PW-DFT) calculations confirm the role of oxygen vacancies in the TiO 2 surface, which serve as catalytically active sites in the CO 2 reduction process. PW-DFT shows that CO 2 binds stably to these oxygen vacancies and CO 2 gains an electron (−0.897e) spontaneously from the TiO 2 support. This calculation indicates that the O vacancies provide active sites for CO 2 absorption, and no overpotential is required to form the CO 2 − intermediate. The TiO 2 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 (CO 2 /CO 2 − ) = −1.9 eV standard redox potential. Copper nanoparticles deposited on the TiO 2 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%. KEYWORDS: Photoelectrochemical, InP, copper, CO 2 reduction, TiO 2 -passivation, methanol CO 2 − intermediate is so high, a cocatalyst is usually added to lower the energy barrier of this intermediate species. Lastly, the surface recombination rate of the photon-induced electron hole pairs should be as low as possible. InP is a promising material for CO 2 reduction since its band gap of 1.34 eV is well-matched to the solar spectrum. Furthermore, the surface-recombination velocity of untreated InP is low (ca. 10 4 cm/s for n-type and 10 5 cm/s for p-type). 7 Nanotexturing of InP can further enhance the photon-to-chemical energy conversion efficiency due to the increase in surface area and reduced reflection. 8 CO 2 reduction to methanol on p-InP has been reported at relatively high applied potentials of −1.3 V (vs SCE) and with low Faraday efficiencies (around 1%). 3 Both the poor selectivity for methanol production with respect to H 2 and severe photo- W ith the rising level of CO 2 in the earth’s atmosphere, artificial photosynthesis (i.e., a process that utilizes sunlight to convert water and carbon dioxide into carbohy- drates) has begun to receive increasing attention by researchers around the world. In 1978, Halmann et al. reported the first photocatalytic reduction of CO 2 to hydrocarbons, including formic acid, formaldehyde, and methanol. This pioneering work utilized p-type GaP under 365 nm wavelength illumination with an applied overpotential of −1.4 V (vs SCE). 1 Many attempts have since been made to reduce CO 2 to hydrocarbons under UV illumination. 2−4 However, few researchers have achieved photoreduction under visible illumination due to the limited selection of materials. 5 For optimum solar utilization, the band gap of the semiconductor should lie in the range of 1.2−1.4 eV, as derived in the Schokley−Quiesser limit. 6 Also, the position of the conduction band (i.e., electron affinity) must be as close as possible to the CO 2 to CO 2 − redox potential (−1.9 V vs NHE) in order to minimize the applied overpotential required to drive this reaction. 7 Since the energy needed to reach the