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Cite This: ACS Appl. Mater. Interfaces 2019, 11, 5579−5580
Learning from Natural Leaves: Going Green with Artificial Photosynthesis Forum
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nm. The experimental results are consistent with the density functional theory (DFT) calculations, confirming the robustness of FeP/g-C3N4 nanohybrids. Engineering a well-defined semiconductor heterojunction via interface engineering is propitious to ameliorate charge separation. Ye’s group has reported the design of a conformal BiVO4-layer/WO3-nanoplate-array heterojunction photoanode decorated with cobalt phosphate (Co-Pi) as an O2 evolution cocatalyst via photoassisted electrodeposition technique. The enhancement of photoelectrocatalytic (PEC) activity stemmed from the type II nature of the BiVO4/WO3 heterojunction and the role of Co-Pi to facilitate the H2O oxidation kinetics and stability. Apart from the addition of Se and the construction of heterointerfaces, facet control of a semiconductor in contact with the electrolyte plays a predominant role in the PEC performance. Wang and co-workers unraveled the mechanisms of how the dissimilar facets of hematite (i.e., exposed with {012} and {001} facets) would have an effect on the charge dynamics in a solar water oxidation reaction. In order to realize overall water splitting, Abe’s group synthesized platelike RuO2/ Bi4NbO8Cl particles for boosted O2 evolution activity followed by loading with a H2-evolving photocatalyst Ru/SrTiO3:Rh along with an Fe3+/Fe2+ redox mediator to enable water splitting into H2 and O2 through the Z-scheme pathway. Other than water splitting, photocatalytic CO2 reduction to form a closed carbon circular economy renders a magnificent prospect for solar energy conversion. Yu et al. designed a ternary TiO2−MnOx−Pt hybrid nanocomposite for enhanced CO2 conversion to CH4 and CH3OH. Benefiting from the merits of the aforementioned facet engineering of {001}- and {101}-exposed TiO2, the metal−semiconductor junction between Pt and TiO2 {101} facet, and the p−n junction between MnOx and TiO2 {001} facet, this cooperative and synergistic effect maximized the migration and separation of electron−hole pairs. Typically, semiconductor materials with high-energy conduction bands are widely explored for the CO2 fixation. Less emphasis has been put forward for the use of lowenergy conduction band semiconductors. Ozin’s group has employed Pd nanocrystal modified WO3 nanowire photocatalysts for hydrogenation of CO2. Fascinatingly, the hydrogen tungsten bronze, HyWO3−x, as the catalytically active species produced by means of the H2 spillover effect by Pd, was effective in capturing and reducing CO2 to CO with an extremely high selectivity of 99%. Ishitani et al. deposited a Ru(II)−Re(I) supramolecular photocatalyst and a Ru(II) redox photosensitizer on a NiO electrode (poly-RuRe/NiO) to function as an efficient photocathode for the reduction of
ith the escalating development of industry and rapid growth of population in the 21st century, the energy requirement has posed numerous significant challenges. In the age of Anthropocene, it is of utmost significance to search for alternative sources of clean energy, enhance the energy efficiency, and simultaneously preserve the environment.1 At present, massive consumption of carbon-based fossil fuels for the generation of energy and electricity across the globe has come at a cost; the combustion of carbon in fossil fuels discharges tremendous amounts of CO2, the concentration of which in the atmosphere reached a record high last year. In October 2018, the CO2 concentration in the atmosphere rose to above 406 ppm based on the Mauna Loa station, which is beyond the safety limit of 350 ppm. In an attempt to mitigate the contemporary descending resources of fossil fuels and an increasing aggravated environmental crisis, the exploration of renewable energy using sunlight has been regarded as an appealing strategy.2−10 To date, many groups are increasing their research efforts in the development of functional materials and interfaces for artificial photosynthesis motivated by the natural photosynthesis process that takes place in plants (Figure 1). This issue of ACS Applied Materials & Interfaces features a Forum on Artificial Photosynthesis: Harnessing Materials and Interfaces for Sustainable Fuels. The continuous upsurge in demand for renewable energy has motivated the creation of this Forum to provide the readership with articles that highlight the state-of-the-art advancement in new materials and interfaces for artificial photosynthesis. This Forum consists of 10 articles authored by some of the leading research groups in the field. Among all renewable energy processes, water splitting for hydrogen (H2) and oxygen (O2) evolution has underpinned a blossoming interest in the field of photocatalysis and photoelectrocatalysis. Taking the merit of oxysulfoselenide semiconductors with the ability of harvesting longer wavelengths compared with the pristine oxysulfides, Domen’s group has successfully developed La 5Ti 2 Cu(S1−xSex)5O7 photocatalysts with an improved absorption edge of 720 nm for H2 evolution by annealing La5Ti2CuS5O7 oxysulfide with Se powder in evacuated quartz tubes. In addition to oxysulfoselenide semiconductors, Ong’s group designed sub-5 nm ultrafine zero-dimensional (0D) iron phosphide (FeP) nanodots decorated on the two-dimensional (2D) porous graphitic carbon nitride (g-C3N4) as noble-metalfree photocatalysts. Herein, this work addresses the primary issues raised in several literature reports: how do we ensure uniform-sized transition metal phosphides with high purity loaded on the 2D nanosheets? In regard to that, the 0D/2D heterojunction interface was successfully developed via the gasphase phosphorization of Fe3O4/g-C3N4 nanocomposites. The incorporation of FeP nanodots cocatalysts not only effectively ameliorate electron−hole separation but also function as active sites for H2 generation without the presence of Pt precious metal, recording the apparent quantum yield of ∼1.6% at 420 © 2019 American Chemical Society
Special Issue: Artificial Photosynthesis: Harnessing Materials and Interfaces for Sustainable Fuels Published: February 13, 2019 5579
DOI: 10.1021/acsami.9b00245 ACS Appl. Mater. Interfaces 2019, 11, 5579−5580
ACS Applied Materials & Interfaces
Editorial
Figure 1. A path to artificial photosynthesis, aiming to transform sunlight into chemical fuels. (2) Ong, W.-J.; Tan, L.-L.; Ng, Y. H.; Yong, S.-T.; Chai, S.-P. Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are we a Step Closer to Achieving Sustainability? Chem. Rev. 2016, 116, 7159− 7329. (3) Peng, J.; Chen, X.; Ong, W.-J.; Zhao, X.; Li, N. Surface and Heterointerface Engineering of 2D MXenes and Their Nanocomposites: Insights into Electro- and Photocatalysis. Chem. 2019, 5, 18. (4) Luo, C.; Ren, X.; Dai, Z.; Zhang, Y.; Qi, X.; Pan, C. Present Perspectives of Advanced Characterization Techniques in TiO2-Based Photocatalysts. ACS Appl. Mater. Interfaces 2017, 9, 23265−23286. (5) Kamat, P. V. Semiconductor Surface Chemistry as Holy Grail in Photocatalysis and Photovoltaics. Acc. Chem. Res. 2017, 50, 527−531. (6) Li, Z.; Luan, Y.; Qu, Y.; Jing, L. Modification Strategies with Inorganic Acids for Efficient Photocatalysts by Promoting the Adsorption of O2. ACS Appl. Mater. Interfaces 2015, 7, 22727−22740. (7) Huang, M. H.; Naresh, G.; Chen, H.-S. Facet-Dependent Electrical, Photocatalytic, and Optical Properties of Semiconductor Crystals and Their Implications for Applications. ACS Appl. Mater. Interfaces 2018, 10, 4−15. (8) Chen, X.; Li, N.; Kong, Z.; Ong, W.-J.; Zhao, X. Photocatalytic Fixation of Nitrogen to Ammonia: State-of-the-Art Advancement and Future Prospects. Mater. Horiz. 2018, 5, 9−27. (9) Su, T.; Shao, Q.; Qin, Z.; Guo, Z.; Wu, Z. Role of Interfaces in Two-Dimensional Photocatalyst for Water Splitting. ACS Catal. 2018, 8, 2253−2276. (10) Banerjee, T.; Gottschling, K.; Savasci, G.; Ochsenfeld, C.; Lotsch, B. V. H2 Evolution with Covalent Organic Framework Photocatalysts. ACS Energy Lett. 2018, 3, 400−409.
CO2 to CO with a high Faradaic efficiency of 85% under visible light illumination. Brudvig’s group designed a silatrane-containing porphyrin molecule and a silatrane-containing ruthenium complex for surface binding, which were found to possess high electrochemical stability from pH 2 to 11. Similar to the previous oxysulfoselenide and oxyhalide, metal (oxy)hydroxide nanosheets (MOxHy, M = Ni, Co, Fe and combinations thereof) are remarkable materials in electrochemical O2 evolution reaction in alkaline solution. Boettcher’s group examined the structural evolution of Ni1−δCoδOxHy nanosheets with changing ratios of Ni to Co during the electrochemical cycling. This investigation provides new inroads in understanding the influence of nanostructure and stoichiometric composition on the structural dynamics in the nanoscale system. Last but not least, we hope that the readers of ACS Applied Materials and Interfaces will enjoy reading these articles at the cutting edge of new materials for artificial photosynthesis. We sincerely thank all the authors who have contributed to this Forum and believe that these studies will cast favorable prospects in the design of next-generation nanomaterials for renewable energy technologies.
Wee-Jun Ong, Guest Editor
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Xiamen University Malaysia
AUTHOR INFORMATION
ORCID
Wee-Jun Ong: 0000-0002-5124-1934 Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
(1) Lewis, N. S.; Nocera, D. G. Powering the Planet: Chemical Challenges in Solar Energy Utilization. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 15729−15735. 5580
DOI: 10.1021/acsami.9b00245 ACS Appl. Mater. Interfaces 2019, 11, 5579−5580
