Next Article in Journal
Earth-Abundant Electrocatalysts in Proton Exchange Membrane Electrolyzers
Next Article in Special Issue
Enhancement of Hydrogen Productions by Accelerating Electron-Transfers of Sulfur Defects in the CuS@CuGaS2 Heterojunction Photocatalysts
Previous Article in Journal
Increased Aromatics Formation by the Use of High-Density Polyethylene on the Catalytic Pyrolysis of Mandarin Peel over HY and HZSM-5
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Photocatalytic Hydrogen Evolution via Water Splitting: A Short Review

1
Department of Chemistry and Chemical Engineering, Inha University, 100 Inharo, Incheon 22212, Korea
2
Department of Environmental Medical Biology, Wonju College of Medicine, Yonsei University, Wonju 26426, Korea
*
Authors to whom correspondence should be addressed.
Catalysts 2018, 8(12), 655; https://doi.org/10.3390/catal8120655
Submission received: 23 October 2018 / Revised: 6 December 2018 / Accepted: 8 December 2018 / Published: 12 December 2018
(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

Abstract

:
Photocatalytic H2 generation via water splitting is increasingly gaining attention as a viable alternative for improving the performance of H2 production for solar energy conversion. Many methods were developed to enhance photocatalyst efficiency, primarily by modifying its morphology, crystallization, and electrical properties. Here, we summarize recent achievements in the synthesis and application of various photocatalysts. The rational design of novel photocatalysts was achieved using various strategies, and the applications of novel materials for H2 production are displayed herein. Meanwhile, the challenges and prospects for the future development of H2-producing photocatalysts are also summarized.

1. Introduction

The development of renewable green energy sources is a critical challenge for modern society. H2 is environmentally friendly, renewable, and considered to be an ideal candidate for an economically and socially sustainable fuel [1,2,3,4,5,6], and was previously regarded as an alternative energy source. Interestingly, some researchers also found that H2-rich water has neuron effects owing to its antioxidant properties. Although the deep mechanism is not clear, more and more researchers made an effort to study the biological function of H2 [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. To date, almost all H2 gas production processes in the industry are based on natural gas, coal, petroleum, or water electrolysis. These traditional preparation methods are limited due to the associated CO2 emissions and high energy consumption. Hence, it is urgent to develop a low-cost method for efficient H2 generation and, thus, support the emerging H2 economy.
The sun provides an energy output of ~3 × 1024 J per year, which is approximately 12,000 times higher than the current energy demand. Therefore, solar energy can act as a sustainable alternative energy source in the future. To date, the transformation of solar energy into H2 via water splitting is deemed as a desirable H2 preparation method to solve the energy crisis [22,23].
The proper use of H2 requires insight into the physical properties of H2 molecules. As we know, the lengths and strengths of hydrogen bonds are exquisitely sensitive to temperature and pressure. Meanwhile, the charges of H2 molecules also vary with temperature [24] because the spin direction of the nucleus in the H2 molecule changes depending on the temperature, and an energy difference occurs between H2 molecules. The para-H2 fraction changes with temperature, and it is necessary to understand the characteristics of H2 molecules according to temperature [25]. During the reaction, hydrogen can be used safely at room temperature; however, it is rather dangerous in high-temperature environments.
As we know, H2 gas, often called dihydrogen or molecular H2, is a highly flammable gas with a wide range of concentrations between 4% and 75% by volume. Meanwhile, H2 is the world’s lightest gas. The density of H2 is only 1/14 of that of air. At 0 °C, the density of H2 is only 0.0899 g/L at standard atmospheric pressure, which is the smallest-molecular-weight substance; it is mainly used as a reducing agent. The enthalpy of combustion is about −286 kJ/mol, which can be displayed by the following equation: 2H2(g) + O2(g) → 2H2O(l) + 572 kJ (286 kJ/mol). Currently, H2 is the main industrial raw material and the most important industrial gas. It has various applications in the petrochemical, electronic, and metallurgical industry, as well as in food processing, float glass, fine organic synthesis, aerospace, and other fields. At the same time, H2 is also an ideal secondary energy source. Owing to the properties of H2, the aerospace industry uses liquid H2 as fuel. Now, it is common to produce H2 from water gas rather than using high-energy-consuming water. The produced H2 is used in large quantities in the cracking reaction of the petrochemical industry and the production of ammonia. Unfortunately, all H2 production methods are highly energy (thermal and electrical) demanding, which limits their application. Thus, it is crucial to find a new method of H2 production.
Fujishima and Honda first reported photocatalytic water splitting using a TiO2 electrode in 1972 [26]. Research on solar H2 production attracted researchers in various fields, such as (1) chemists for the design and synthesis of various catalysts to investigate structure–property relationships; (2) physicists to fabricate semiconductor photocatalysts with novel electronic structures, as predicted by theoretical calculation; and (3) material scientists to construct unique photocatalytic materials with novel structures and morphologies [27,28,29,30]. When photocatalysts are illuminated at wavelengths which are suitable to their band gap energy, after the excitation, the charge carriers will either combine or transfer to the surface of the photocatalysts to participate in photocatalytic reactions. For the generation of efficient semiconductor photocatalysts, long-lived charge carriers and high stability are required [31,32,33].
Significant developments were made toward H2 generation via water splitting over the last several decades by a number of talented researchers [34,35,36,37,38].
Herein, we attempt to sum up the advances achieved to date. Therefore, we briefly summarize the background related to various photocatalysts for H2 generation and the achievements of high-efficiency photocatalysts. The main synthesis routes and modifications for adjusting the band structure to harvest light and enhance charge separation are also discussed.

2. Principle of H2 Generation via Water Splitting

In the pioneering study by Fujishima and Honda [27], electrochemical cells were made up for the splitting of the water into H2 and O2, as shown in Figure 1. While the TiO2 electrode was under ultraviolet (UV) light irradiation, water oxidation (oxygen evolution) occurred on its surface, while the reduction reaction (H2 evolution) occurred on the surface platinum black electrode. With this study in mind, semiconductor photocatalysts were later developed by Bard et al. in their design of a novel photocatalytic system.
Figure 2a shows a display of hydrogen evolution by photocatalysts. The photocatalytic reaction occurring on the semiconductor photocatalysts can be divided into three parts: (1) obtaining photons with energy exceeding that of the photocatalyst’s band gap, generating electron and hole pairs; (2) separating carriers by migration in the semiconductor photocatalyst; and (3) reaction between these carriers and H2O [39,40,41,42,43,44,45,46]. In addition, electron–hole pairs will combine with each other simultaneously. As shown in Figure 2b, while photocatalysts are involved in hydrogen evolution, the lowest position of the conduction band (CB) should be lower than the reduction position of H2O/H2, while the position of the valence band (VB) should be higher than the potential of H2O/O2 [47,48,49,50].
Various photocatalysts were reported to decompose water into H2 and O2 (Equation (1)). As we know, the hydrogen evolution reaction can be separated into two parts: oxidation for the evolution of O2 (Equation (2)) and water reduction to produce H2 (Equation (3)) [51,52,53,54,55,56]:
H 2 O 2 H 2 + O 2               Δ E 0 = 1.23   V        
H 2 O 4 H + + 4 e + O 2            E 0 = + 1.23   V   v s .   N H E ,   p H = 0
4 H + + 4 e 2 H 2                 Δ E 0 = 0   V   v s .   N H E ,   p H = 0

3. Photocatalysts for Water Splitting

Many photocatalysts were created as photocatalysts for hydrogen evolution. Based on these species, they can be divided into three major parts: (1) graphene-based photocatalyst; (2) graphitic carbon nitride (g-C3N4)-based photocatalysts; and (3) heterojunction photocatalysts (semiconductor–semiconductor or semiconductor–(metal, element)).

3.1. Graphene-Based Photocatalysts

Recently, graphene-based photocatalysts attracted significant attention for enhancing photocatalytic H2 production performance. Graphene is used to enhance photocatalytic efficiency owing to its novel structure and electrochemical properties (Figure 3).
To date, many reports regarding the synthesis of graphene-based photocatalysts with improved photocatalytic efficiency were published. Graphene is a well-known two-dimensional (2D) material, which can improve surface area, and its 2D membrane-like structure imparts unique electrochemical properties [57,58,59,60]. Generally speaking, photocatalysts prepared by simple physical mixing with graphene will involve only a bit of direct contact with the graphene sheets. This small amount of contact between the photocatalyst and graphene results in weak interactions and inhibits charge transfer rates. Hence, the synthesis of photocatalysts with more interactions is highly needed.
Previously, Kim et al. synthesized novel graphene oxide (GO)-TiO2 photocatalysts [58] in 2013, comprising a core–shell nanostructure with enhanced photocatalytic efficiency (Figure 4). The improved H2 production activity compared to that of TiO2 revealed that the utilization of the core–shell structure enhanced photocatalytic efficiency. This novel structural design offers three-dimensional (3D) close contact between the materials and provides more active sites, which will enhance the charge separation rate and H2 production efficiency [61,62,63].
Currently, many researchers are more interested in visible-light-driven photocatalysts, which are achieved using band-gap modification or taking graphene as a photosensitizer to broaden the visible-light adsorption range [64,65,66]. Significant efforts were conducted for building visible-light response systems because of the UV-only response of TiO2, and its nontoxic properties [67]. Recently, it was found that graphene regulating TiO2 involves visible-light adsorption activity. The carbon-layered structure of graphene with enriched π electrons forms bonds with titanium atoms. As a result, this strong interaction will shift the band position and reduce the band gap [68,69,70]. Lee et al. [71] also achieved a lower band gap using a graphene/TiO2 photocatalyst. The improved photocatalytic efficiency of the graphene/TiO2 composite owes to the band-gap regulation, which consequently promotes charge transfer rates through the graphene sheets.

3.2. g-C3N4-Based Photocatalysts

Currently, carbon-nitride-based photocatalysts receive significant attention for their photocatalytic H2 generation owing to a unique electronic structure (Figure 5) [72,73,74,75,76,77]. This section summarizes recent significant achievements in building C3N4-based photocatalysts for H2 evolution. Methods including nanostructure regulation, band-gap modification, dye sensitization, and heterojunction fabrication are highlighted herein.
Recently, carbon nitride attracted significant attention following the pioneering research of Wang et al. in 2009 for photocatalytic hydrogen evolution [78,79]. The assumed structure of C3N4 is a 2D framework with the tri-s-triazine linked by tertiary amines (Figure 6); it is thermally stable and chemically stable. Pioneering studies regarded g-C3N4 as a visible-light-driven phorocatalyst with a band gap of approximately 2.7 eV and an appropriate band position for water splitting [80,81,82,83,84,85]. Hence, g-C3N4 is an ideal candidate for photocatalytic H2 evolution.
H2 generation performance using g-C3N4 can be promoted with noble-metal particles such as Au or Pd, which obtain electrons in the CB to inhibit the charge recombination rate [86,87,88,89,90]. Many researchers are developing metal-free photocatalysts for H2 evolution, and recent reports involved the introduction of non-noble-metal catalysts into g-C3N4 photocatalysts, displaying enhanced photocatalytic performance compared to noble-metal catalysts [91,92,93,94,95]. Hou et al. [86] synthesized MoS2/g-C3N4 composite photocatalysts (Figure 7) in 2018. MoS2/g-C3N4 increased the surface area and decreased the barrier when the electrons transported, thereby improving the charge transfer rate. The formation of band alignment enabled electron transfer from the CB (g-C3N4) to MoS2. Therefore, the MoS2/gC3N4 nanojunction significantly enhanced H2 evolution efficiency, achieving the highest H2 evolution rate and an optimum quantum efficiency of up to 2.1% (420 nm), which was higher than g-C3N4/Pt.

3.3. Metal-Loading-Based Photocatalysts

Metal loading is also regarded as a useful method for photocatalytic enhancement. Song et al. [96] constructed Ag-rGO-TiO2 composite photocatalysts (Figure 8) in 2018. In order to analyze the photocatalytic mechanism of the architectural Ag-TiO2 and Ag-rGO-TiO2 composites, their structures with Ag nanocubes for light absorption and TiO2 nanosheets were well displayed. The difference between Ag-TiO2 and Ag-rGO-TiO2 is the interface between Ag nanocubes and TiO2 nanosheets, which enhances the electron transfer capability. For Ag-TiO2, the direct contact between the two materials results in the formation of Ag (100)/(001) TiO2 interface. Meanwhile, for Ag-rGO-TiO2, both Ag(100)/rGO and rGO/(001) TiO2 interfaces are formed by rGO. As mentioned above, the synergistic effect of Ag(100)/rGO and rGO/(001)TiO2 interfaces, rather than the Ag(100)/(001) TiO2 interface, offers quicker electron transfer. As shown in Figure 8, no Schottky barrier is formed between Ag and TiO2, and the hot electrons on the surface of TiO2 flow back to Ag and then recombine with holes. Meanwhile, for the Ag-rGO-TiO2 sample, no barrier is necessary to facilitate the electron transfer. The electrons generated on the surface of Ag nanocubes with smaller work function flow to rGO via a contact so as to equilibrate the electron Fermi distribution on the interface [97,98]. Moreover, the rGO nanosheets can act as conductive channels, further transferring the electron to the rGO/TiO2 interface. Owing to the light absorption of rGO, the transferred electrons within the rGO nanosheets can be further transferred to the CB of TiO2 under light excitation. The proposed photocatalytic mechanism of Ag-rGO-TiO2 is illustrated in Figure 8.

3.4. Z-Scheme Photocatalysts

An illustration of Z-scheme water splitting is shown in Figure 9. During an H2 evolution reaction, the reactions which happen on the surface of photocatalysts include the reduction of protons by CB electrons and the oxidation of an electron donor (D) by VB holes, yielding the corresponding electron acceptor (A), as follows:
2 H + + 2 e H 2    ( p h o t o r e d u c t i o n   o f   H +   t o   H 2 )
D + n h + A    ( p h o t o o x i d a t i o n   o f   D   t o   A )
On the other hand, the forward reactions on an O2 evolution photocatalyst are as follows:
A   +   n e   D   ( p h o t o r e d u c t i o n   o f   A   t o   D )
2 H 2 O   +   4 h +   O 2   +   4 H +   ( ( p h o t o o x i d a t i o n   o f   H 2 O   t o   O 2 )
where the electron acceptor generated by the paired H2 evolution photocatalyst is converted to D, and the water oxidation process occurs via the valence band holes. Thus, the water-splitting process can be achieved.
Amal et al. reported a Z-scheme photocatalytic water-splitting system using Ru/SrTiO3 and partially reduced GO (PRGO)/BiVO4 (Figure 10) in 2011 [100]. As described in the report, the PRGO/BiVO4 (O2 photocatalyst) and Ru/SrTiO3:Rh (H2 photocatalyst) were attached due to surface charge modification in acidic conditions, as depicted in Figure 10. Under irradiation, electrons are excited from the VB (BiVO4) or an impurity level in Rh (Ru/SrTiO3:Rh) to the CB. We can indicate that the PRGO does not contribute to the electron and hole generation. In other words, the RGO in this work acts as an electron conductor. PRGO transfers the electrons from the CB of BiVO4 to the Ru/SrTiO3:Rh. Meanwhile, the electrons in Ru/SrTiO3:Rh reduce the water to H2 on the surface of the Ru co-catalyst, while the holes left in BiVO4 oxidize the water to O2. Additionally, the PRGO provides a pathway for photogenerated electrons in the BiVO4 photocatalyst. Each reaction can migrate as follows: reduction of water, transfer of electrons to PRGO, and transfer of holes to PRGO for oxidation. Because the majority of the photocatalyst surface is surrounded by water and only relatively small portions are in contact with PRGO [101], most electrons in Ru/SrTiO3:Rh and holes in BiVO4 are used for water splitting.

3.5. Defect Engineering Photocatalyst

Among the various photocatalyst designs, the defect engineering strategy is regarded as an important way of modifying the photocatalysts. Defects are places where the atoms or molecules in the materials are disrupted, and they greatly influence photocatalytic performance. The defects in the lattice of photocatalysts not only act as an electron–hole recombination center, but also break the electronic structure and display a scattering center for electron and hole travel. Nevertheless, the positive effect of defects in photocatalytic performance enhancement were also recognized with the development of defect photocatalysts and the development of the photocatalytic field.
Chen et al. reported the synthesis of a bismuth subcarbonate (Bi2O2CO3, BOC) with controllable defect density (BOC-X) (Figure 11) in 2018. The BOC-X with defect density displayed a photocatalytic nitrogen fixation of 957 μmol·L–1 under irradiation within 4 h, which was 9.4 times higher than that of pristine BOC. This photocatalytic performance enhancement of BOC-X can be attributed to the surface defects. These defects contribute to the defect levels in the forbidden band, which improves the light harvest percentage. Meanwhile, surface defects can also inhibit the electron–hole recombination rate to promote the separation efficiency of charge carriers. Photocatalytic nitrogen fixation by BOC-X is displayed in Figure 11. If the light energy is higher than the band-gap energy, the electrons on the VB surface of BOC-X are transferred to the CB and react with N2 to form NH3. Moreover, some of the VB electrons are transferred to the defect level and then react with N2. However, if the light energy is lower than the band-gap energy, the electrons of BOC-X are also excited from VB to the defect level and then participate in the reaction. Defects modulate the band gap of BOC-X and improve the light absorption range, thereby enhancing the carrier transport, and leading to photocatalytic enhancement.

3.6. Heterojunction Photocatalysts

During the H2 evolution reaction, the formed electron–hole charges are transferred to the surface of the photocatalyst for the next step of the reaction or recombine with each other [102,103,104,105,106]. To better reveal this point, we assumed it as a simple case [107]: the influence of gravity on a man jumping (Figure 12a,b). When a man (electron) jumps from the ground (VB) to the sky (CB), it can return to the floor immediately (recombination of the electron and hole) owing to gravity. In order to let the people rise off the floor (separation of the charge carrier pairs), an instrument (semiconductor B) can be used (Figure 12c,d). Subsequently, the previously mentioned people can drop to the instrument rather than the ground (inhibition of the electron and hole pair recombination). Although the inhibition of electron–hole recombination rate is an urgent issue, it can be achieved via suitable construction of materials. Many methods were conducted to achieve better electron–hole pair separation rate, such as element combining [108,109], metal doping [110,111], or the use of heterojunctions [112,113]. Among these strategies, heterojunctions were proven to be the most desirable method for achieving efficient photocatalysis due to their improved separation ability of electron–hole pairs (Figure 12d).
A heterojunction is regarded as the connection between two kinds of photocatalysts with different band structures, which leads to a new band arrangement [114,115]. Generally, three kinds of composite photocatalysts are developed (Figure 13). As shown in Figure 13a, the CB and VB of A are a bit over and under the band position of B, respectively [116]. As a result, when the light irradiates, the generated electrons and holes are transferred to the CB and VB of B. Because the generated electrons and holes move to the same photocatalyst, the recombination rate of electron–hole pairs is not efficiently inhibited. The photocatalytic process happens on photocatalyst B with a mild potential requirement; thus, the photocatalytic ability of the photocatalyst using this heterojunction will be lower than others. As dispalyed in Figure 13b, the band positions of CB and VB are over that of photocatalyst B. Hence, during the photocatalytic reaction, the generated electron moves to photocatalyst B, while the holes are transferred to photocatalyst A, which leads to the formation of long lived electron–hole pairs [117,118,119]. Parallel to Figure 13a, the photocatalytic performance of the type-II composite photocatalysts is inhibited by the redox process occurring on B. Meanwhile, as displayed in Figure 13c, the band structure of type-III composite photocatalysts is parallel to type II, apart from the interlaced gap changing into non-overlapping band gaps [120,121]. Thus, the generated electron–hole pairs cannot be transferred between the two photocatalysts, resulting in them being inappropriate for long lived electron–hole pair separation. We can determine that the type-II heterojunctions are desirable for enhancing redox ability due to their optimum structure for long-lived electron–hole separation. In previous reports, great efforts were conducted to synthesize type-II composite photocatalysts, including g-C3N4/TiO2 [122], WO3/BiVO4 [123], WO3/g-C3N4 [124], and BiPO4/g-C3N4 [125].
Yu et al. designed CdS/NiS composites photocatalysts using various heterojunctions in 2012, which greatly enhanced the hydrogen evolution performance. As shown in Figure 14a, around 20 nm of NiS particles were loaded onto the CdS uniformly, which supported a close connection between CdS and NiS. The formation of p–n heterojunctions facilitates charge transfer between the NiS and CdS, and inhibits charge-carrier recombination (Figure 14b,c). We can see that the holes left on the n-type catalyst are transferred to the p-type catalyst, providing a negative specie. The electron–hole pair distribution keeps moving until a Fermi-level equilibrium is achieved [126,127,128]. The generated active species move through the internal electric field of the composite photocatalysts, resulting in long-lived electron–hole pair separation rates. Thus, the electron–hole recombination rate is efficiently inhibited owing to the synergistic effect between the two photocatalysts. The photocatalytic H2 production rate over CdS/NiS composite photocatalysts with 5 wt.% NiS was found to be higher than that of the CdS and 1 wt.% Pt/CdS (Figure 14d). More NiS doping resulted in a reduction in photocatalytic efficiency due to NiS catalysts reducing the number of redox sites during the reaction.

4. Summary and Perspectives

Over the last several decades, photocatalysis was shown to be a promising method for H2 production. Even though the principles controlling photocatalytic activity in the developed semiconductors were identified, several aspects remain unclear. Therefore, practical applications and the commercialization of photocatalytic H2 production require further research. Meanwhile, the charge transfer among photocatalysts due to the influence of structure and electrochemical properties is also not very clear, while the influence of various preparation methods on the catalytic performance is not well understood. The development of improved photocatalysts will benefit from advances in science. Improved building of novel co-catalysts will arise from using efficient catalysts. Many researches are underway investigating new synthesis methods for sample preparation and novel system construction. Herein, we concluded the most prominent achievements associated with H2 production via photocatalysis. We hope this report will assist further research efforts regarding the development of photocatalysts.

Funding

This research was supported by the Korea Evaluation Institute of Industrial Technology (KEIT) through the Carbon Cluster Construction project [10083586, Development of petroleum-based graphite fibers with ultra-high thermal conductivity] funded by the Ministry of Trade, Industry, & Energy (MOTIE, Korea), and the Commercialization Promotion Agency for R&D Outcomes (COMPA) funded by the Ministry of Science and ICT (MSIT) [2018_RND_002_0064, Development of 800 mA·h·g−1 pitch carbon coating materials].

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Park, S.J.; Lee, S.Y. A study on hydrogen-storage behaviors of nickel-loaded mesoporous MCM-41. J. Colloid Interface Sci. 2010, 346, 194–198. [Google Scholar] [CrossRef] [PubMed]
  2. Catapan, R.C.; Cancino, L.R.; Oliveira, A.A.M.; Schwarz, C.O.; Nitschke, H.; Frank, T. Potential for onboard hydrogen production in an direct injection ethanol fueled spark ignition engine with EGR. Fuel 2018, 234, 441–446. [Google Scholar] [CrossRef]
  3. Im, J.S.; Park, S.-J.; Kim, T.; Lee, Y.-S. Hydrogen storage evaluation based on investigations of the catalyticproperties of metal/metal oxides in electrospun carbon fibers. Int. J. Hydrogen Energy 2009, 34, 3382–3388. [Google Scholar] [CrossRef]
  4. Park, S.-J.; Lee, S.-Y. Hydrogen storage behaviors of platinum-supported multi-walled carbon nanotubes. Int. J. Hydrogen Energy 2010, 35, 13048–13054. [Google Scholar] [CrossRef]
  5. Lee, S.-Y.; Park, S.-J. Effect of platinum doping of activated carbon on hydrogen storage behaviors of metal-organic frameworks-5. Int. J. Hydrogen Energy 2011, 36, 8381–8387. [Google Scholar] [CrossRef]
  6. Baykara, S.Z. Hydrogen: A brief overview on its sources, production and environmental impact. Int. J. Hydrogen Energy 2018, 43, 10605–10614. [Google Scholar] [CrossRef]
  7. Chen, M.; Cui, W.; Zhu, K.; Xie, Y.; Zhang, C.; Shen, W. Hydrogen-rich water alleviates aluminum-induced inhibition of root elongation in alfalfa via decreasing nitric oxide production. J. Hazard. Mater. 2014, 267, 40–47. [Google Scholar] [CrossRef] [PubMed]
  8. Cui, W.; Gao, C.; Fang, P.; Lin, G.; Shen, W. Alleviation of cadmium toxicity in Medicago sativa by hydrogen-rich water. J. Hazard. Mater. 2013, 260, 715–724. [Google Scholar] [CrossRef] [PubMed]
  9. Gao, Q.; Song, H.; Wang, X.T.; Liang, Y.; Xi, Y.J.; Gao, Y.; Guo, Q.J.; LeBaron, T.; Luo, Y.X.; Li, S.C.; et al. Molecular hydrogen increases resilience to stress in mice. Sci. Rep. 2017, 7, 9625. [Google Scholar] [CrossRef]
  10. Giuliani, D.; Ottani, A.; Zaffe, D.; Galantucci, M.; Strinati, F.; Lodi, R.; Guarini, S. Hydrogen sulfide slows down progression of experimental Alzheimer’s disease by targeting multiple pathophysiological mechanisms. Neurobiol. Learn. Mem. 2013, 104, 82–91. [Google Scholar] [CrossRef]
  11. Huang, C.S.; Kawamura, T.; Toyoda, Y.; Nakao, A. Recent advances in hydrogen research as a therapeutic medical gas. Free Radic. Res. 2010, 44, 971–982. [Google Scholar] [CrossRef] [PubMed]
  12. Kumar, R.; Kumar, A.; Langstrom, B.; Darreh-Shori, T. Discovery of novel choline acetyltransferase inhibitors using structure-based virtual screening. Sci. Rep. 2017, 7, 16287. [Google Scholar] [CrossRef]
  13. Li, J.; Wang, C.; Zhang, J.H.; Cai, J.M.; Cao, Y.P.; Sun, X.J. Hydrogen-rich saline improves memory function in a rat model of amyloid-beta-induced Alzheimer’s disease by reduction of oxidative stress. Brain Res. 2010, 1328, 152–161. [Google Scholar] [CrossRef]
  14. Luo, Q.; Lin, Y.X.; Yang, P.P.; Wang, Y.; Qi, G.B.; Qiao, Z.Y.; Li, B.N.; Zhang, K.; Zhang, J.P.; Wang, L.; et al. A self-destructive nanosweeper that captures and clears amyloid beta-peptides. Nat. Commun. 2018, 9, 1802. [Google Scholar] [CrossRef] [PubMed]
  15. Nagata, K.; Nakashima-Kamimura, N.; Mikami, T.; Ohsawa, I.; Ohta, S. Consumption of molecular hydrogen prevents the stress-induced impairments in hippocampus-dependent learning tasks during chronic physical restraint in mice. Neuropsychopharmacol. Off. Publ. Am. Coll. Neuropsychopharmacol. 2009, 34, 501–508. [Google Scholar] [CrossRef]
  16. Nakayama, M.; Itami, N.; Suzuki, H.; Hamada, H.; Yamamoto, R.; Tsunoda, K.; Osaka, N.; Nakano, H.; Maruyama, Y.; Kabayama, S.; et al. Novel haemodialysis (HD) treatment employing molecular hydrogen (H2)-enriched dialysis solution improves prognosis of chronic dialysis patients: A prospective observational study. Sci. Rep. 2018, 8, 254. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  17. Nishimaki, K.; Asada, T.; Ohsawa, I.; Nakajima, E.; Ikejima, C.; Yokota, T.; Kamimura, N.; Ohta, S. Effects of Molecular Hydrogen Assessed by an Animal Model and a Randomized Clinical Study on Mild Cognitive Impairment. Curr. Alzheimer Res. 2018, 15, 482–492. [Google Scholar] [CrossRef] [PubMed]
  18. Ohsawa, I.; Ishikawa, M.; Takahashi, K.; Watanabe, M.; Nishimaki, K.; Yamagata, K.; Katsura, K.; Katayama, Y.; Asoh, S.; Ohta, S. Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals. Nat. Med. 2007, 13, 688–694. [Google Scholar] [CrossRef]
  19. Xiao, H.W.; Li, Y.; Luo, D.; Dong, J.L.; Zhou, L.X.; Zhao, S.Y.; Zheng, Q.S.; Wang, H.C.; Cui, M.; Fan, S.J. Hydrogen-water ameliorates radiation-induced gastrointestinal toxicity via MyD88’s effects on the gut microbiota. Exp. Mol. Med. 2018, 50, e433. [Google Scholar] [CrossRef] [Green Version]
  20. Zhang, L.M.; Jiang, C.X.; Liu, D.W. Hydrogen sulfide attenuates neuronal injury induced by vascular dementia via inhibiting apoptosis in rats. Neurochem. Res. 2009, 34, 1984–1992. [Google Scholar] [CrossRef] [PubMed]
  21. Zhang, Y.; Su, W.J.; Chen, Y.; Wu, T.Y.; Gong, H.; Shen, X.L.; Wang, Y.X.; Sun, X.J.; Jiang, C.L. Effects of hydrogen-rich water on depressive-like behavior in mice. Sci. Rep. 2016, 6, 23742. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  22. Liu, S.; Xin, Z.-J.; Lei, Y.-J.; Yang, Y.; Yan, X.-Y.; Lu, Y.-B.; Li, C.-B.; Wang, H.-Y. Thin Copper-Based Film for Efficient Electrochemical Hydrogen Production from Neutral Aqueous Solutions. ACS Sustain. Chem. Eng. 2017, 5, 7496–7501. [Google Scholar] [CrossRef]
  23. Wang, Z.; Yang, X.; Yang, T.; Zhao, Y.; Wang, F.; Chen, Y.; Zeng, J.H.; Yan, C.; Huang, F.; Jiang, J.-X. Dibenzothiophene Dioxide Based Conjugated Microporous Polymers for Visible-Light-Driven Hydrogen Production. ACS Catal. 2018, 8, 8590–8596. [Google Scholar] [CrossRef]
  24. Zhu, K.; Kang, S.-Z.; Qin, L.; Han, S.; Li, G.; Li, X. Novel and Highly Active Potassium Niobate-Based Photocatalyst for Dramatically Enhanced Hydrogen Production. J. Am. Chem. Soc. 2005, 127, 11447–11453. [Google Scholar] [CrossRef]
  25. Hibino, T.; Kobayashi, K.; Ito, M.; Ma, Q.; Nagao, M.; Fukui, M.; Teranishi, S. Kinetics of the Interconversion of Parahydrogen and Orthohydrogen Catalyzed by Paramagnetic Complex Ions. J. Am. Chem. Soc. 2005, 127, 11447–11453. [Google Scholar]
  26. Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37–38. [Google Scholar] [CrossRef] [PubMed]
  27. Zhang, P.; Song, T.; Wang, T.; Zeng, H. In-situ synthesis of Cu nanoparticles hybridized with carbon quantum dots as a broad spectrum photocatalyst for improvement of photocatalytic H2 evolution. Appl. Catal. B Environ. 2017, 206, 328–335. [Google Scholar] [CrossRef]
  28. Zhang, P.; Song, T.; Wang, T.; Zeng, H. Plasmonic Cu nanoparticle on reduced graphene oxide nanosheet support: An efficient photocatalyst for improvement of near-infrared photocatalytic H2 evolution. Appl. Catal. B Environ. 2018, 225, 172–179. [Google Scholar] [CrossRef]
  29. Zhang, P.; Wang, T.; Zeng, H. Design of Cu-Cu2O/g-C3N4 nanocomponent photocatalysts for hydrogen evolution under visible light irradiation using water-soluble Erythrosin B dye sensitization. Appl. Surf. Sci. 2017, 391, 404–414. [Google Scholar] [CrossRef]
  30. Zhang, P.; Song, T.; Wang, T.; Zeng, H. Effectively extending visible light absorption with a broad spectrum sensitizer for improving the H2 evolution of in-situ Cu/g-C3N4 nanocomponents. Int. J. Hydrogen Energy 2017, 42, 14511–14521. [Google Scholar] [CrossRef]
  31. Zhang, Y.; Park, M.; Kim, H.Y.; Ding, B.; Park, S.J. A facile ultrasonic-assisted fabrication of nitrogen-doped carbon dots/BiOBr up-conversion nanocomposites for visible light photocatalytic enhancements. Sci. Rep. 2017, 7, 45086. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  32. Zhang, Y.; Park, S.-J. Bimetallic AuPd alloy nanoparticles deposited on MoO3 nanowires for enhanced visible-light driven trichloroethylene degradation. J. Catal. 2018, 361, 238–247. [Google Scholar] [CrossRef]
  33. Zhang, Y.; Park, S.-J. Au–pd bimetallic alloy nanoparticle-decorated BiPO4 nanorods for enhanced photocatalytic oxidation of trichloroethylene. J. Catal. 2017, 355, 1–10. [Google Scholar] [CrossRef]
  34. Yu, H.; Xue, Y.; Hui, L.; Zhang, C.; Li, Y.; Zuo, Z.; Zhao, Y.; Li, Z.; Li, Y. Efficient Hydrogen Production on a 3D Flexible Heterojunction Material. Adv. Mater. 2018, 30, e1707082. [Google Scholar] [CrossRef]
  35. Zhang, P.; Song, T.; Wang, T.; Zeng, H. Fabrication of a non-semiconductor photocatalytic system using dendrite-like plasmonic CuNi bimetal combined with a reduced graphene oxide nanosheet for near-infrared photocatalytic H2 evolution. J. Mater. Chem. A 2017, 5, 22772–22781. [Google Scholar] [CrossRef]
  36. Lin, L.; Ren, W.; Wang, C.; Asiri, A.M.; Zhang, J.; Wang, X. Crystalline carbon nitride semiconductors prepared at different temperatures for photocatalytic hydrogen production. Appl. Catal. B Environ. 2018, 231, 234–241. [Google Scholar] [CrossRef]
  37. Im, J.S.; Kwon, O.; Kim, Y.H.; Park, S.-J.; Lee, Y.-S. The effect of embedded vanadium catalyst on activated electrospun CFs for hydrogen storage. Microporous Mesoporous Mater. 2008, 115, 514–521. [Google Scholar] [CrossRef]
  38. Yi, H.; Huang, D.; Qin, L.; Zeng, G.; Lai, C.; Cheng, M.; Ye, S.; Song, B.; Ren, X.; Guo, X. Selective prepared carbon nanomaterials for advanced photocatalytic application in environmental pollutant treatment and hydrogen production. Appl. Catal. B Environ. 2018, 239, 408–424. [Google Scholar] [CrossRef]
  39. Ismail, A.A.; Bahnemann, D.W. Photochemical splitting of water for hydrogen production by photocatalysis: A review. Sol. Energy Mater. Sol. Cells 2014, 128, 85–101. [Google Scholar] [CrossRef]
  40. Cai, J.; Shen, J.; Zhang, X.; Ng, Y.H.; Huang, J.; Guo, W.; Lin, C.; Lai, Y. Light-Driven Sustainable Hydrogen Production Utilizing TiO2 Nanostructures: A Review. Small Methods 2018, 1800184. [Google Scholar] [CrossRef]
  41. Ventura-Espinosa, D.; Sabater, S.; Carretero-Cerdán, A.; Baya, M.; Mata, J.A. High Production of Hydrogen on Demand from Silanes Catalyzed by Iridium Complexes as a Versatile Hydrogen Storage System. ACS Catal. 2018, 8, 2558–2566. [Google Scholar] [CrossRef]
  42. Ji, L.; Lv, C.; Chen, Z.; Huang, Z.; Zhang, C. Nickel-Based (Photo) Electrocatalysts for Hydrogen Production. Adv. Mater. 2018, 30, e1705653. [Google Scholar] [CrossRef] [PubMed]
  43. Ma, Y.; Dong, X.; Wang, Y.; Xia, Y. Decoupling Hydrogen and Oxygen Production in Acidic Water Electrolysis Using a Polytriphenylamine-Based Battery Electrode. Angewandte Chem. 2018, 57, 2904–2908. [Google Scholar] [CrossRef] [PubMed]
  44. Wang, B.; Zeng, C.; Chu, K.H.; Wu, D.; Yip, H.Y.; Ye, L.; Wong, P.K. Enhanced Biological Hydrogen Production from Escherichia coli with Surface Precipitated Cadmium Sulfide Nanoparticles. Adv. Energy Mater. 2017, 7, 1700611. [Google Scholar] [CrossRef]
  45. Xue, Z.; Shen, Y.; Li, P.; Zhang, Y.; Li, J.; Qin, B.; Zhang, J.; Zeng, Y.; Zhu, S. Key Role of Lanthanum Oxychloride: Promotional Effects of Lanthanum in NiLaOy/NaCl for Hydrogen Production from Ethyl Acetate and Water. Small 2018, 14, e1800927. [Google Scholar] [CrossRef] [PubMed]
  46. Zhang, Y.; Yang, H.M.; Park, S.-J. Synthesis and characterization of nitrogen-doped TiO2 coatings on reduced graphene oxide for enhancing the visible light photocatalytic activity. Curr. Appl. Phys. 2018, 18, 163–169. [Google Scholar] [CrossRef]
  47. Zhang, Y.; Park, M.; Kim, H.-Y.; Park, S.-J. In-situ synthesis of graphene oxide/BiOCl heterostructured nanofibers for visible-light photocatalytic investigation. J. Alloy Compd. 2016, 686, 106–114. [Google Scholar] [CrossRef]
  48. Huang, J.; Li, G.; Zhou, Z.; Jiang, Y.; Hu, Q.; Xue, C.; Guo, W. Efficient photocatalytic hydrogen production over Rh and Nb codoped TiO2 nanorods. Chem. Eng. J. 2018, 337, 282–289. [Google Scholar] [CrossRef]
  49. Kim, W.; Monllor-Satoca, D.; Chae, W.-S.; Mahadik, M.A.; Jang, J.S. Enhanced photoelectrochemical and hydrogen production activity of aligned CdS nanowire with anisotropic transport properties. Appl. Surf. Sci. 2019, 463, 339–347. [Google Scholar] [CrossRef]
  50. Han, J.; Liu, Y.; Dai, F.; Zhao, R.; Wang, L. Fabrication of CdSe/CaTiO3 nanocomposties in aqueous solution for improved photocatalytic hydrogen production. Appl. Surf. Sci. 2018, 459, 520–526. [Google Scholar] [CrossRef]
  51. Zhang, Y.; Park, M.; Kim, H.Y.; Ding, B.; Park, S.-J. In-situ synthesis of nanofibers with various ratios of BiOClx/BiOBry/BiOIz for effective trichloroethylene photocatalytic degradation. Appl. Surf. Sci. 2016, 384, 192–199. [Google Scholar] [CrossRef]
  52. Pipitone, G.; Tosches, D.; Bensaid, S.; Galia, A.; Pirone, R. Valorization of alginate for the production of hydrogen via catalytic aqueous phase reforming. Catal. Today 2018, 304, 153–164. [Google Scholar] [CrossRef]
  53. Hibino, T.; Kobayashi, K.; Ito, M.; Nagao, M.; Fukui, M.; Teranishi, S. Direct electrolysis of waste newspaper for sustainable hydrogen production: An oxygen-functionalized porous carbon anode. Appl. Catal. B Environ. 2018, 231, 191–199. [Google Scholar] [CrossRef]
  54. Park, S.; Kim, B.; Lee, Y.; Cho, M. Influence of copper electroplating on high pressure hydrogen-storage behaviors of activated carbon fibers. Int. J. Hydrogen Energy 2008, 33, 1706–1710. [Google Scholar] [CrossRef]
  55. Im, J.S.; Park, S.-J.; Lee, Y.-S. Superior prospect of chemically activated electrospun carbon fibers for hydrogen storage. Mater. Res. Bull. 2009, 44, 1871–1878. [Google Scholar] [CrossRef]
  56. Xiang, Q.; Yu, J. Graphene-Based Photocatalysts for Hydrogen Generation. J. Phys. Chem. Lett. 2013, 4, 753–759. [Google Scholar] [CrossRef]
  57. Kim, H.-I.; Moon, G.-H.; Monllor-Satoca, D.; Park, Y.; Choi, W. Solar Photoconversion Using Graphene/TiO2 Composites: Nanographene Shell on TiO2 Core versus TiO2 Nanoparticles on Graphene Sheet. J. Phys. Chem. C 2011, 116, 1535–1543. [Google Scholar] [CrossRef]
  58. Wu, Z.; Zhou, Z.; Zhang, Y.; Wang, J.; Shi, H.; Shen, Q.; Wei, G.; Zhao, G. Simultaneous photoelectrocatalytic aromatic organic pollutants oxidation for hydrogen production promotion with a self-biasing photoelectrochemical cell. Électrochim. Acta 2017, 254, 140–147. [Google Scholar] [CrossRef]
  59. Kim, B.J.; Lee, Y.S.; Park, S.J. Preparation of platinum-decorated porous graphite nanofibers, and their hydrogen storage behaviors. J. Colloid Interface Sci. 2008, 318, 530–533. [Google Scholar] [CrossRef]
  60. Zhang, Y.; Park, S.-J. Fabrication and characterization of flower-like BiOI/Pt heterostructure with enhanced photocatalytic activity under visible light irradiation. J. Solid State Chem. 2017, 253, 421–429. [Google Scholar] [CrossRef]
  61. Zhang, Y.; Park, S.-J. Incorporation of RuO2 into charcoal-derived carbon with controllable microporosity by CO2 activation for high-performance supercapacitor. Carbon 2017, 122, 287–297. [Google Scholar] [CrossRef]
  62. Panthi, G.; Park, M.; Kim, H.-Y.; Park, S.-J. Electrospun polymeric nanofibers encapsulated with nanostructured materials and their applications: A review. J. Ind. Eng. Chem. 2015, 24, 1–13. [Google Scholar] [CrossRef]
  63. Panthi, G.; Park, M.; Kim, H.-Y.; Lee, S.-Y.; Park, S.-J. Electrospun ZnO hybrid nanofibers for photodegradation of wastewater containing organic dyes: A review. J. Ind. Eng. Chem. 2015, 21, 26–35. [Google Scholar] [CrossRef]
  64. Kim, S.; Park, S. Electroactivity of Pt–Ru/polyaniline composite catalyst-electrodes prepared by electrochemical deposition methods. Solid State Ion. 2008, 178, 1915–1921. [Google Scholar] [CrossRef]
  65. Park, S.J.; Kim, B.J. Influence of oxygen plasma treatment on hydrogen chloride removal of activated carbon fibers. J. Colloid Interface Sci. 2004, 275, 590–595. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  66. Park, S.-J.; Kim, J.S. Modifications produced by electrochemical treatments oncarbon blacks Microstructures and mechanical interfacial properties. Carbon 2001, 39, 2011–2016. [Google Scholar] [CrossRef]
  67. Chen, W.-T.; Chan, A.; Sun-Waterhouse, D.; Llorca, J.; Idriss, H.; Waterhouse, G.I.N. Performance comparison of Ni/TiO2 and Au/TiO2 photocatalysts for H2 production in different alcohol-water mixtures. J. Catal. 2018, 367, 27–42. [Google Scholar] [CrossRef]
  68. Hou, H.; Liu, H.; Gao, F.; Shang, M.; Wang, L.; Xu, L.; Wong, W.-Y.; Yang, W. Packaging BiVO4 nanoparticles in ZnO microbelts for efficient photoelectrochemical hydrogen production. Electrochim. Acta 2018, 283, 497–508. [Google Scholar] [CrossRef]
  69. Belhadj, H.; Hamid, S.; Robertson, P.K.J.; Bahnemann, D.W. Mechanisms of Simultaneous Hydrogen Production and Formaldehyde Oxidation in H2O and D2O over Platinized TiO2. ACS Catal. 2017, 7, 4753–4758. [Google Scholar] [CrossRef]
  70. Akbarzadeh, R.; Ghaedi, M.; Nasiri Kokhdan, S.; Jannesar, R.; Sadeghfar, F.; Sadri, F.; Tayebi, L. Electrochemical hydrogen storage, photocatalytical and antibacterial activity of Fe Ag bimetallic nanoparticles supported on TiO2 nanowires. Int. J. Hydrogen Energy 2018, 43, 18316–18329. [Google Scholar] [CrossRef]
  71. Chen, C.; Cai, W.M.; Long, M.C.; Zhou, B.X.; Wu, Y.H.; Wu, D.Y.; Feng, Y.J. Synthesis of Visible Light Responsive Graphene Oxide/ TiO2 Composites with p/n Heterojunction. ACS Nano 2010, 4, 6425–6432. [Google Scholar] [CrossRef] [PubMed]
  72. Cao, S.; Yu, J. g-C3N4-Based Photocatalysts for Hydrogen Generation. J. Phys. Chem. Lett. 2014, 5, 2101–2107. [Google Scholar] [CrossRef] [PubMed]
  73. Rather, R.A.; Singh, S.; Pal, B. A C3N4 surface passivated highly photoactive Au-TiO2 tubular nanostructure for the efficient H2 production from water under sunlight irradiation. Appl. Catal. B Environ. 2017, 213, 9–17. [Google Scholar] [CrossRef]
  74. Bian, H.; Ji, Y.; Yan, J.; Li, P.; Li, L.; Li, Y.; Frank Liu, S. In Situ Synthesis of Few-Layered g-C3N4 with Vertically Aligned MoS2 Loading for Boosting Solar-to-Hydrogen Generation. Small 2018, 14, 1703003. [Google Scholar] [CrossRef] [PubMed]
  75. Tian, N.; Zhang, Y.; Li, X.; Xiao, K.; Du, X.; Dong, F.; Waterhouse, G.I.N.; Zhang, T.; Huang, H. Precursor-reforming protocol to 3D mesoporous g-C3N4 established by ultrathin self-doped nanosheets for superior hydrogen evolution. Nano Energy 2017, 38, 72–81. [Google Scholar] [CrossRef]
  76. Xu, X.; Si, Z.; Liu, L.; Wang, Z.; Chen, Z.; Ran, R.; He, Y.; Weng, D. CoMoS2/rGO/C3N4 ternary heterojunctions catalysts with high photocatalytic activity and stability for hydrogen evolution under visible light irradiation. Appl. Surf. Sci. 2018, 435, 1296–1306. [Google Scholar] [CrossRef]
  77. Luo, X.; Wu, Z.; Liu, Y.; Ding, S.; Zheng, Y.; Jiang, Q.; Zhou, T.; Hu, J. Engineering Amorphous Carbon onto Ultrathin g-C3N4 to Suppress Intersystem Crossing for Efficient Photocatalytic H2 Evolution. Adv. Mater. Interfaces 2018, 5, 1800859. [Google Scholar] [CrossRef]
  78. Wang, Y.; Wang, X.; Antonietti, M. Polymeric graphitic carbon nitride as a heterogeneous organocatalyst: From photochemistry to multipurpose catalysis to sustainable chemistry. Angewandte Chem. 2012, 51, 68–89. [Google Scholar] [CrossRef]
  79. Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J.M.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2009, 8, 76–80. [Google Scholar] [CrossRef]
  80. Gao, H.; Yang, H.; Xu, J.; Zhang, S.; Li, J. Strongly Coupled g-C3N4 Nanosheets-Co3O4 Quantum Dots as 2D/0D Heterostructure Composite for Peroxymonosulfate Activation. Small 2018, 14, 1801353. [Google Scholar] [CrossRef]
  81. Chen, Z.; Xia, K.; She, X.; Mo, Z.; Zhao, S.; Yi, J.; Xu, Y.; Chen, H.; Xu, H.; Li, H. 1D metallic MoO2-C as co-catalyst on 2D g-C3N4 semiconductor to promote photocatlaytic hydrogen production. Appl. Surf. Sci. 2018, 447, 732–739. [Google Scholar] [CrossRef]
  82. Kong, L.; Ji, Y.; Dang, Z.; Yan, J.; Li, P.; Li, Y.; Liu, S.F. g-C3N4 Loading Black Phosphorus Quantum Dot for Efficient and Stable Photocatalytic H2 Generation under Visible Light. Adv. Funct. Mater. 2018, 28, 1800668. [Google Scholar] [CrossRef]
  83. Wan, J.; Pu, C.; Wang, R.; Liu, E.; Du, X.; Bai, X.; Fan, J.; Hu, X. A facile dissolution strategy facilitated by H2SO4 to fabricate a 2D metal-free g-C3N4/rGO heterojunction for efficient photocatalytic H2 production. Int. J. Hydrogen Energy 2018, 43, 7007–7019. [Google Scholar] [CrossRef]
  84. Marcì, G.; García-López, E.I.; Palmisano, L. Polymeric carbon nitride (C3N4) as heterogeneous photocatalyst for selective oxidation of alcohols to aldehydes. Catal. Today 2018, 315, 126–137. [Google Scholar] [CrossRef]
  85. Oh, W.-D.; Lok, L.-W.; Veksha, A.; Giannis, A.; Lim, T.-T. Enhanced photocatalytic degradation of bisphenol A with Ag-decorated S-doped g-C3N4 under solar irradiation: Performance and mechanistic studies. Chem. Eng. J. 2018, 333, 739–749. [Google Scholar] [CrossRef]
  86. Hou, Y.; Laursen, A.B.; Zhang, J.; Zhang, G.; Zhu, Y.; Wang, X.; Dahl, S.; Chorkendorff, I. Layered nanojunctions for hydrogen-evolution catalysis. Angewandte Chem. 2013, 52, 3621–3625. [Google Scholar] [CrossRef] [PubMed]
  87. Zhou, J.; Zhao, Y.; Bao, J.; Huo, D.; Fa, H.; Shen, X.; Hou, C. One-step electrodeposition of Au-Pt bimetallic nanoparticles on MoS2 nanoflowers for hydrogen peroxide enzyme-free electrochemical sensor. Electrochim. Acta 2017, 250, 152–158. [Google Scholar] [CrossRef]
  88. Yang, Y.; Gao, P.; Ren, X.; Sha, L.; Yang, P.; Zhang, J.; Chen, Y.; Yang, L. Massive Ti3+ self-doped by the injected electrons from external Pt and the efficient photocatalytic hydrogen production under visible-Light. Appl. Catal. B Environ. 2017, 218, 751–757. [Google Scholar] [CrossRef]
  89. Fang, J.; Gu, J.; Liu, Q.; Zhang, W.; Su, H.; Zhang, D. Three-Dimensional CdS/Au Butterfly Wing Scales with Hierarchical Rib Structures for Plasmon-Enhanced Photocatalytic Hydrogen Production. ACS Appl. Mater. Interfaces 2018, 10, 19649–19655. [Google Scholar] [CrossRef] [PubMed]
  90. Chang, Y.; Yu, K.; Zhang, C.; Yang, Z.; Feng, Y.; Hao, H.; Jiang, Y.; Lou, L.-L.; Zhou, W.; Liu, S. Ternary CdS/Au/3DOM-SrTiO3 composites with synergistic enhancement for hydrogen production from visible-light photocatalytic water splitting. Appl. Catal. B Environ. 2017, 215, 74–84. [Google Scholar] [CrossRef]
  91. Masudy-Panah, S.; Siavash Moakhar, R.; Chua, C.S.; Kushwaha, A.; Dalapati, G.K. Stable and Efficient CuO Based Photocathode through Oxygen-Rich Composition and Au-Pd Nanostructure Incorporation for Solar-Hydrogen Production. ACS Appl. Mater. Interfaces 2017, 9, 27596–27606. [Google Scholar] [CrossRef] [PubMed]
  92. Ortiz, N.; Zoellner, B.; Hong, S.J.; Ji, Y.; Wang, T.; Liu, Y.; Maggard, P.A.; Wang, G. Harnessing Hot Electrons from Near IR Light for Hydrogen Production Using Pt-End-Capped-AuNRs. ACS Appl. Mater. Interfaces 2017, 9, 25962–25969. [Google Scholar] [CrossRef]
  93. Wang, Y.; Zhao, J.; Li, Y.; Wang, C. Selective photocatalytic CO2 reduction to CH4 over Pt/In2O3: Significant role of hydrogen adatom. Appl. Catal. B Environ. 2018, 226, 544–553. [Google Scholar] [CrossRef]
  94. Jiang, J.-Z.; Ren, L.-Q.; Huang, Y.-P.; Li, X.-D.; Wu, S.-H.; Sun, J.-J. 3D Nanoporous Gold-Supported Pt Nanoparticles as Highly Accelerating Catalytic Au-Pt Micromotors. Adv. Mater. Interfaces 2018, 5, 1701689. [Google Scholar] [CrossRef]
  95. Lang, Q.; Chen, Y.H.; Huang, T.L.; Yang, L.N.; Zhong, S.X.; Wu, L.J.; Chen, J.R.; Bai, S. Graphene ‘bridge’ in transferring hot electrons from plasmonic Ag nanocubes to TiO2 nanosheets for enhanced visible light photocatalytic hydrogen evolution. Appl. Catal. B Environ. 2018, 220, 182–190. [Google Scholar] [CrossRef]
  96. Zhang, Y.; Park, S.-J. Facile construction of MoO3@ZIF-8 core-shell nanorods for efficient photoreduction of aqueous Cr (VI). Appl. Catal. B Environ. 2019, 240, 92–101. [Google Scholar] [CrossRef]
  97. Kamijyo, K.; Takashima, T.; Yoda, M.; Osaki, J.; Irie, H. Facile synthesis of a red light-inducible overall water-splitting photocatalyst using gold as a solid-state electron mediator. Chem. Commun. 2018, 54, 7999–8002. [Google Scholar] [CrossRef] [PubMed]
  98. Maeda, K.; Domen, K. Photocatalytic Water Splitting: Recent Progress and Future Challenges. J. Phys. Chem. Lett. 2010, 1, 2655–2661. [Google Scholar] [CrossRef]
  99. Iwase, A.; Ng, Y.H.; Ishiguro, Y.; Kudo, A.; Amal, R. Reduced graphene oxide as a solid-state electron mediator in Z-scheme photocatalytic water splitting under visible light. J. Am. Chem. Soc. 2011, 133, 11054–11057. [Google Scholar] [CrossRef] [PubMed]
  100. Zhang, Y.; Park, S.-J. Formation of hollow MoO3/SnS2 heterostructured nanotubes for efficient light-driven hydrogen peroxide production. J. Mater. Chem. A 2018, 6, 20304–20312. [Google Scholar] [CrossRef]
  101. Xu, C.; Qiu, P.; Li, L.; Chen, H.; Jiang, F.; Wang, X. Bismuth Subcarbonate with Designer Defects for Broad-Spectrum Photocatalytic Nitrogen Fixation. ACS Appl. Mater. Interfaces 2018, 10, 25321–25328. [Google Scholar] [CrossRef] [PubMed]
  102. Kobayashi, R.; Takashima, T.; Tanigawa, S.; Takeuchi, S.; Ohtani, B.; Irie, H. A heterojunction photocatalyst composed of zinc rhodium oxide, single crystal-derived bismuth vanadium oxide, and silver for overall pure-water splitting under visible light up to 740 nm. Phys. Chem. Chem. Phys. PCCP 2016, 18, 27754–27760. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  103. Iwashina, K.; Iwase, A.; Ng, Y.H.; Amal, R.; Kudo, A. Z-schematic water splitting into H2 and O2 using metal sulfide as a hydrogen-evolving photocatalyst and reduced graphene oxide as a solid-state electron mediator. J. Am. Chem. Soc. 2015, 137, 604–607. [Google Scholar] [CrossRef] [PubMed]
  104. Yu, X.; Liu, G.; Li, W.; An, L.; Li, Z.; Liu, J.; Hu, P. Mesocrystalline Ta2O5 nanosheets supported Pd Pt nanoparticles for efficient photocatalytic hydrogen production. Int. J. Hydrogen Energy 2018, 43, 8232–8242. [Google Scholar] [CrossRef]
  105. Low, J.; Yu, J.; Jaroniec, M.; Wageh, S.; Al-Ghamdi, A.A. Heterojunction Photocatalysts. Adv. Mater. 2017, 29, 1601694. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  106. Zhu, M.; Zhai, C.; Fujitsuka, M.; Majima, T. Noble metal-free near-infrared-driven photocatalyst for hydrogen production based on 2D hybrid of black Phosphorus/WS2. Appl. Catal. B Environ. 2018, 221, 645–651. [Google Scholar] [CrossRef]
  107. Do, J.Y.; Lee, J.H.; Park, N.-K.; Lee, T.J.; Lee, S.T.; Kang, M. Synthesis and characterization of Ni2−xPdxMnO4/γ-Al2O3 catalysts for hydrogen production via propane steam reforming. Chem. Eng. J. 2018, 334, 1668–1678. [Google Scholar] [CrossRef]
  108. Qin, Z.; Xue, F.; Chen, Y.; Shen, S.; Guo, L. Spatial charge separation of one-dimensional Ni2P-Cd0.9Zn0.1S/g-C3N4 heterostructure for high-quantum-yield photocatalytic hydrogen production. Appl. Catal. B Environ. 2017, 217, 551–559. [Google Scholar] [CrossRef]
  109. Hu, Z.; Wang, X.; Dong, H.; Li, S.; Li, X.; Li, L. Efficient photocatalytic degradation of tetrabromodiphenyl ethers and simultaneous hydrogen production by TiO2-Cu2O composite films in N2 atmosphere: Influencing factors, kinetics and mechanism. J. Hazard. Mater. 2017, 340, 1–15. [Google Scholar] [CrossRef]
  110. Iervolino, G.; Vaiano, V.; Sannino, D.; Rizzo, L.; Galluzzi, A.; Polichetti, M.; Pepe, G.; Campiglia, P. Hydrogen production from glucose degradation in water and wastewater treated by Ru-LaFeO3/Fe2O3 magnetic particles photocatalysis and heterogeneous photo-Fenton. Int. J. Hydrogen Energy 2018, 43, 2184–2196. [Google Scholar] [CrossRef]
  111. Imran, M.; Yousaf, A.B.; Kasak, P.; Zeb, A.; Zaidi, S.J. Highly efficient sustainable photocatalytic Z-scheme hydrogen production from an α-Fe2O3 engineered ZnCdS heterostructure. J. Catal. 2017, 353, 81–88. [Google Scholar] [CrossRef]
  112. Subha, N.; Mahalakshmi, M.; Myilsamy, M.; Neppolian, B.; Murugesan, V. Direct Z-scheme heterojunction nanocomposite for the enhanced solar H2 production. Appl. Catal. A Gen. 2018, 553, 43–51. [Google Scholar] [CrossRef]
  113. Zhang, J.; Yan, W.; An, Z.; Song, H.; He, J. Interface–Promoted Dehydrogenation and Water–Gas Shift toward High-Efficient H2 Production from Aqueous Phase Reforming of Cellulose. ACS Sustain. Chem. Eng. 2018, 6, 7313–7324. [Google Scholar] [CrossRef]
  114. Vinodgopal, K.; Kamat, P.V. Enhanced rates of photocatalytic degradation of an azo dye using SnO2/TiO2 coupled semiconductor thin films. Environ. Sci. Technol. 1995, 29, 841–845. [Google Scholar] [CrossRef] [PubMed]
  115. Ranjit, K.; Viswanathan, B. Synthesis, characterization and photocatalytic properties of iron-doped TiO2 catalysts. J. Photochem. Photobiol. A 1997, 108, 79–84. [Google Scholar] [CrossRef]
  116. Monai, M.; Montini, T.; Fonda, E.; Crosera, M.; Delgado, J.J.; Adami, G.; Fornasiero, P. Nanostructured Pd Pt nanoparticles: Evidences of structure/performance relations in catalytic H2 production reactions. Appl. Catal. B Environ. 2018, 236, 88–98. [Google Scholar] [CrossRef]
  117. Wang, Q.; He, J.; Shi, Y.; Zhang, S.; Niu, T.; She, H.; Bi, Y.; Lei, Z. Synthesis of MFe2O4 (M = Ni, Co)/BiVO4 film for photolectrochemical hydrogen production activity. Appl. Catal. B Environ. 2017, 214, 158–167. [Google Scholar] [CrossRef]
  118. Xu, J.; Gao, J.; Qi, Y.; Wang, C.; Wang, L. Anchoring Ni2P on the UiO-66-NH2/g-C3N4-derived C-doped ZrO2/g-C3N4 Heterostructure: Highly Efficient Photocatalysts for H2 Production from Water Splitting. ChemCatChem 2018, 10, 3327–3335. [Google Scholar] [CrossRef]
  119. Wang, Z.; Jin, Z.; Wang, G.; Ma, B. Efficient hydrogen production over MOFs (ZIF-67) and g-C3N4 boosted with MoS2 nanoparticles. Int. J. Hydrogen Energy 2018, 43, 13039–13050. [Google Scholar] [CrossRef]
  120. Fu, J.; Zhu, B.; You, W.; Jaroniec, M.; Yu, J. A flexible bio-inspired H2- production photocatalyst. Appl. Catal. B Environ. 2018, 220, 148–160. [Google Scholar] [CrossRef]
  121. Zhang, S.; Liu, X.; Liu, C.; Luo, S.; Wang, L.; Cai, T.; Zeng, Y.; Yuan, J.; Dong, W.; Pei, Y.; et al. MoS2 Quantum Dot Growth Induced by S Vacancies in a ZnIn2S4 Monolayer: Atomic-Level Heterostructure for Photocatalytic Hydrogen Production. ACS Nano 2018, 12, 751–758. [Google Scholar] [CrossRef] [PubMed]
  122. Li, K.; Gao, S.; Wang, Q.; Xu, H.; Wang, Z.; Huang, B.; Dai, Y.; Lu, J. In-Situ-Reduced Synthesis of Ti(3)(+) Self-Doped TiO(2)/g-C(3)N(4) Heterojunctions with High Photocatalytic Performance under LED Light Irradiation. ACS Appl. Mater. Interfaces 2015, 7, 9023–9030. [Google Scholar] [CrossRef] [PubMed]
  123. Hong, S.J.; Lee, S.; Jang, J.S.; Lee, J.S. Heterojunction BiVO4/WO3 electrodes for enhanced photoactivity of water oxidation. Energy Environ. Sci. 2011, 4, 1781–1787. [Google Scholar] [CrossRef]
  124. Huang, L.; Xu, H.; Li, Y.; Li, H.; Cheng, X.; Xia, J.; Xu, Y.; Cai, G. Visible-light-induced WO3/g-C3N4 composites with enhanced photocatalytic activity. Dalton Trans. 2013, 42, 8606–8616. [Google Scholar] [CrossRef] [PubMed]
  125. Pan, C.; Xu, J.; Wang, Y.; Li, D.; Zhu, Y. Dramatic Activity of C3N4/BiPO4 Photocatalyst with Core/Shell Structure Formed by Self-Assembly. Adv. Funct. Mater. 2012, 22, 1518–1524. [Google Scholar] [CrossRef]
  126. Zhang, J.; Qiao, S.Z.; Qi, L.; Yu, J. Fabrication of NiS modified CdS nanorod p-n junction photocatalysts with enhanced visible-light photocatalytic H2-production activity. Phys. Chem. Chem. Phys. PCCP 2013, 15, 12088–12094. [Google Scholar] [CrossRef]
  127. Heo, Y.-J.; Zhang, Y.; Rhee, K.Y.; Park, S.-J. Synthesis of PAN/PVDF nanofiber composites-based carbon adsorbents for CO2 capture. Compos. Part B Eng. 2019, 156, 95–99. [Google Scholar] [CrossRef]
  128. Zhang, Y.; Park, M.; Kim, H.Y.; Park, S.J. Moderated surface defects of Ni particles encapsulated with NiO nanofibers as supercapacitor with high capacitance and energy density. J. Colloid Interface Sci. 2017, 500, 155–163. [Google Scholar] [CrossRef]
Figure 1. Schematic of a photoelectrochemical cell (PEC). Reproduced with permission from Reference [26]; copyright (1972), Nature Publishing Group.
Figure 1. Schematic of a photoelectrochemical cell (PEC). Reproduced with permission from Reference [26]; copyright (1972), Nature Publishing Group.
Catalysts 08 00655 g001
Figure 2. Schematic illustration of hydrogen evolution over photocatalysts. Reproduced with permission from Reference [39]; copyright (2014), Elsevier.
Figure 2. Schematic illustration of hydrogen evolution over photocatalysts. Reproduced with permission from Reference [39]; copyright (2014), Elsevier.
Catalysts 08 00655 g002
Figure 3. Proposed mechanism of graphene-based photocatalysts. Reproduced with permission from Reference [56]; copyright (2013), American Chemical Society.
Figure 3. Proposed mechanism of graphene-based photocatalysts. Reproduced with permission from Reference [56]; copyright (2013), American Chemical Society.
Catalysts 08 00655 g003
Figure 4. Schematic display of synthetic process of graphene oxide (GO)/TiO2 and TiO2/GO. Reproduced with permission from Reference [57]; copyright (2012), American Chemical Society.
Figure 4. Schematic display of synthetic process of graphene oxide (GO)/TiO2 and TiO2/GO. Reproduced with permission from Reference [57]; copyright (2012), American Chemical Society.
Catalysts 08 00655 g004
Figure 5. Proposed mechanism of graphitic carbon nitride (g-C3N4)-based photocatalysts. Reproduced with permission from Reference [72]; copyright (2014), American Chemical Society.
Figure 5. Proposed mechanism of graphitic carbon nitride (g-C3N4)-based photocatalysts. Reproduced with permission from Reference [72]; copyright (2014), American Chemical Society.
Catalysts 08 00655 g005
Figure 6. Schematic display of the structure of g-C3N4. Reproduced with permission from Reference [72]; copyright (2014), American Chemical Society.
Figure 6. Schematic display of the structure of g-C3N4. Reproduced with permission from Reference [72]; copyright (2014), American Chemical Society.
Catalysts 08 00655 g006
Figure 7. Schematic display of charge transfer on MoS2/g-C3N4 heterostructures during water splitting. Reproduced with permission from Reference [72]; copyright (2014), American Chemical Society.
Figure 7. Schematic display of charge transfer on MoS2/g-C3N4 heterostructures during water splitting. Reproduced with permission from Reference [72]; copyright (2014), American Chemical Society.
Catalysts 08 00655 g007
Figure 8. Schematic illustrating photocatalytic mechanism for Ag-TiO2 and Ag-rGO-TiO2 samples under visible-light irradiation. Reproduced with permission from Reference [95]; copyright (2018), Elsevier.
Figure 8. Schematic illustrating photocatalytic mechanism for Ag-TiO2 and Ag-rGO-TiO2 samples under visible-light irradiation. Reproduced with permission from Reference [95]; copyright (2018), Elsevier.
Catalysts 08 00655 g008
Figure 9. Diagram of photocatalytic water splitting using a Z-Scheme system. Reproduced with permission from Reference [98]; Copyright (2010), American Chemical Society.
Figure 9. Diagram of photocatalytic water splitting using a Z-Scheme system. Reproduced with permission from Reference [98]; Copyright (2010), American Chemical Society.
Catalysts 08 00655 g009
Figure 10. (a) Schematic display of a suspension of Ru/SrTiO3 and partially reduced GO (PRGO)/BiVO4 in water. (b) Mechanism of water splitting using Z-scheme system consisting of Ru/SrTiO3 and PRGO/BiVO4 under irradiation. Reproduced with permission from Reference [99]; copyright (2018), American Chemical Society.
Figure 10. (a) Schematic display of a suspension of Ru/SrTiO3 and partially reduced GO (PRGO)/BiVO4 in water. (b) Mechanism of water splitting using Z-scheme system consisting of Ru/SrTiO3 and PRGO/BiVO4 under irradiation. Reproduced with permission from Reference [99]; copyright (2018), American Chemical Society.
Catalysts 08 00655 g010
Figure 11. Mechanism of photocatalytic nitrogen fixation on defective Bi2O2CO3. Reproduced with permission from Reference [101]; copyright (2010), American Chemical Society.
Figure 11. Mechanism of photocatalytic nitrogen fixation on defective Bi2O2CO3. Reproduced with permission from Reference [101]; copyright (2010), American Chemical Society.
Catalysts 08 00655 g011
Figure 12. Schematic display of (a) the influence of gravity on a person jumping, (b) electron–hole pair combination using a photocatalyst, (c) utilization of a stool to keep the person from returning to the ground, (d) electron–hole pairs separated in composite catalyst. Reproduced with permission from Reference [105]; copyright (2010), John Wiley & Sons, Inc.
Figure 12. Schematic display of (a) the influence of gravity on a person jumping, (b) electron–hole pair combination using a photocatalyst, (c) utilization of a stool to keep the person from returning to the ground, (d) electron–hole pairs separated in composite catalyst. Reproduced with permission from Reference [105]; copyright (2010), John Wiley & Sons, Inc.
Catalysts 08 00655 g012
Figure 13. Schematic display of three kinds of electron–hole pair separation among composite photocatalysts: (a) type-Ⅰ, (b) type-Ⅱ, (c) type-Ⅲ heterojunctions. Reproduced with permission from Reference [105]; copyright (2017), John Wiley & Sons, Inc.
Figure 13. Schematic display of three kinds of electron–hole pair separation among composite photocatalysts: (a) type-Ⅰ, (b) type-Ⅱ, (c) type-Ⅲ heterojunctions. Reproduced with permission from Reference [105]; copyright (2017), John Wiley & Sons, Inc.
Catalysts 08 00655 g013
Figure 14. (a) SEM image of CdS/NiS composite catalysts; (b,c) illustration of electron–hole pairs with CdS/NiS composite photocatalysts; (d) contrast of photocatalytic efficiency of CdS with different NiS content. Reproduced with permission from Reference [105]; copyright (2017), John Wiley & Sons, Inc.
Figure 14. (a) SEM image of CdS/NiS composite catalysts; (b,c) illustration of electron–hole pairs with CdS/NiS composite photocatalysts; (d) contrast of photocatalytic efficiency of CdS with different NiS content. Reproduced with permission from Reference [105]; copyright (2017), John Wiley & Sons, Inc.
Catalysts 08 00655 g014

Share and Cite

MDPI and ACS Style

Zhang, Y.; Heo, Y.-J.; Lee, J.-W.; Lee, J.-H.; Bajgai, J.; Lee, K.-J.; Park, S.-J. Photocatalytic Hydrogen Evolution via Water Splitting: A Short Review. Catalysts 2018, 8, 655. https://doi.org/10.3390/catal8120655

AMA Style

Zhang Y, Heo Y-J, Lee J-W, Lee J-H, Bajgai J, Lee K-J, Park S-J. Photocatalytic Hydrogen Evolution via Water Splitting: A Short Review. Catalysts. 2018; 8(12):655. https://doi.org/10.3390/catal8120655

Chicago/Turabian Style

Zhang, Yifan, Young-Jung Heo, Ji-Won Lee, Jong-Hoon Lee, Johny Bajgai, Kyu-Jae Lee, and Soo-Jin Park. 2018. "Photocatalytic Hydrogen Evolution via Water Splitting: A Short Review" Catalysts 8, no. 12: 655. https://doi.org/10.3390/catal8120655

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop