A critical review in strategies to improve photocatalytic water splitting towards hydrogen production

Photocatalytic water splitting using sunlight is a promising technology capable of providing high energy yield without pollutant byproducts. Herein, we review various aspects of this technology including chemical reactions, physiochemical conditions and photocatalyst types such as metal oxides, sulfides, nitrides, nanocomposites, and doped materials followed by recent advances in computational modeling of photoactive materials. As the best-known catalyst for photocatalytic hydrogen and oxygen evolution, TiO2 is discussed in a separate section, along with its challenges such as the wide band gap, large overpotential for hydrogen evolution, and rapid recombination of produced electron-hole pairs. Various approaches are addressed to overcome these shortcomings, such as doping with different elements, heterojunction catalysts, noble metal deposition, and surface modification. Development of a photocatalytic corrosion resistant, visible light absorbing, defect-tuned material with small particle size is the key to complete the sunlight to hydrogen cycle efficiently. Computational studies have opened new avenues to understand and predict the electronic density of states and band structure of advanced materials and could pave the way for the rational design of efficient photocatalysts for water splitting. Future directions are focused on developing innovative junction architectures, novel synthesis methods and optimizing the existing active materials to enhance charge transfer, visible light absorption, reducing the gas evolution overpotential and maintaining chemical and physical stability.

https://www.mdpi.com/1420-3049/21/7/900/pdf

Photocatalytic Water Splitting—The Untamed Dream: A Review of Recent Advances

Degradation of methylene blue and methyl orange by palladium-doped TiO2 photocatalysis for water reuse: Efficiency and degradation pathways

Inside-and-Out Semiconductor Engineering for CO2 Photoreduction: From Recent Advances to New Trends

Enhanced Removal of Various Dyes from Aqueous Solutions by UV and Simulated Solar Photocatalysis over TiO2/ZnO/rGO Composites

Pt/TiO 2 –ZnO photocatalytic materials were prepared for the generation of hydrogen gas from water splitting. The photocatalysts were characterized by X-ray diffraction (XRD), UV-visible spectra (UV–Vis), scanning electron microscope (SEM) and transmission electron microscope (TEM). The absorption wavelength of TiO 2 was shifted to longer wavelength on Pt/TiO 2 –ZnO. A 400 W mercury arc lamp with a cutoff filter which filter out all the wavelengths under 400 nm as the visible light source. It reached up to the optimum value of 203 µmolh −1 g −1 on TiO 2 –ZnO (Ti/Zn = 10). A catalyst of 0.5 wt% Pt/TiO 2 –ZnO (Ti/Zn = 10) was used and a best hydrogen production rate through water splitting was reaching to 2150 µmolh −1 g −1 . The 0.1 wt% Pt/TiO 2 –ZnO showed a satisfying long-term stability, and 88% and 77% of initial hydrogen productivity still remained after 7 days and 14 days, respectively.

Hydrogen production by photocatalytic water-splitting on Pt-doped TiO2–ZnO under visible light

In this study, various Pd-loaded TiO2 nanowire (Pd/TiO2 NW) catalysts were prepared using the hydrothermal method, and their photocatalytic activity toward the photoreduction of CO2 into methane (CH4) and carbon monoxide (CO) was evaluated. The photocatalysts were characterized by X-ray diffraction, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, UV–vis spectroscopy, X-ray photoelectron spectroscopy and photoluminescence analysis. The addition of Pd on TiO2 NWs can improve the production yield of CO2 photoreduction to CH4 and CO. The 0.5 wt% Pd/TiO2 NWs showed optimal CO and CH4 yields of 50.4 and 26.7 µmol/g, respectively. Moreover, the 0.5 wt% Pd/TiO2 NWs could be used repeatedly with only a small loss of photocatalytic activity noted after 30 days. Furthermore, a mechanism for the photoreduction of CO2 was proposed. Therefore, Pd/TiO2 NWs are an efficient photocatalyst for the reduction of CO2 to CH4 and CO.

Preparation of Pd/TiO2 nanowires for the photoreduction of CO2 into renewable hydrocarbon fuels

A Pt-deposited C–HS–TiO 2 hollow sphere prepared through a simple template approach as well as their implementation as a photocatalyst for water splitting. The obtained Pt-deposited C–HS–TiO 2 hollow spheres are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV–vis absorption spectrum (UV–vis), and transmission electron microscope (TEM). The results show that hollow spherical morphology was successfully synthesized. Compared with commercial P-25 TiO 2 and C–TiO 2 hollow sphere, Pt-deposited C–HS–TiO 2 hollow spheres exhibit significant improvement in photoactivity under the visible light irradiation. It can be attributed to the enhanced visible light absorption by the deposited Pt. Furthermore, 1.0 wt% Pt/C–HS–TiO 2 presents an ultra-high photocatalytic water splitting activity. The maximum production rate of hydrogen at a reaction temperature of 25 °C is measured as 2857 µmol/h. In addition, 1.0 wt% Pt/C–HS–TiO 2 exhibits excellent long-term stability and durability of photocatalytic activity. The rate of visible light water splitting has no significant change. After 22 days of operation, an 8% loss of the initial activity occurs. Finally, the probable mechanism of hydrogen production by water splitting under visible light irradiation is proposed in this study.

Kang-Yang Su

Papers

Hydrogen production by photocatalytic water-splitting on Pt-doped TiO2–ZnO under visible light

Preparation of Pd/TiO2 nanowires for the photoreduction of CO2 into renewable hydrocarbon fuels

Efficient hydrogen production by water-splitting over Pt-deposited C–HS–TiO2 hollow spheres under visible light