An official website of the United States government
Renewable energy-driven hydrogen production from electrocatalytic and photocatalytic water splitting has been widely recognized as a promising approach to utilize green energy resources and hence reduces our dependence on legacy fossil fuels as well as alleviates net carbon dioxide emissions. The realization of large-scale water splitting, however, is mainly impeded by its slow kinetics, particularly because of its sluggish anodic half reaction, the oxygen evolution reaction (OER), whose product O 2 is ironically not of high value. In fact, the co-production of H 2 and O 2 in conventional water electrolysis may result in the formation of explosive H 2 /O 2 gas mixtures due to gas crossover and reactive oxygen species (ROS); both pose safety concerns and shorten the lifetimes of water splitting cells. With these considerations in mind, replacing the OER with thermodynamically more favorable organic oxidation reactions is much more preferred, which will not only substantially reduce the voltage input for H 2 evolution from water and avoid the generation of H 2 /O 2 gas mixtures and ROS, but also possibly lead to the co-production of value-added organic products on the anode. Indeed, such an innovative strategy for H 2 production integrated with valuable organic oxidation has attracted increasing attention in both electrocatalysis and photocatalysis. This feature article showcases the most recent examples along this endeavor. As exemplified in the main text, the oxidative transformation of a variety of organic substrates, including alcohols, ammonia, urea, hydrazine, and biomass-derived intermediate chemicals, can be integrated with energy-efficient H 2 evolution. We specifically highlight the importance of oxidative biomass valorization coupled with H 2 production, as biomass is the only green carbon source whose scale is comparable to fossil fuels. Finally, the remaining challenges and future opportunities are also discussed.
more »
« less
Visible-light-driven organic transformations integrated with H 2 production on semiconductors
Due to its clean and sustainable nature, solar energy has been widely recognized as a green energy source in driving a variety of reactions, ranging from small molecule activation and organic transformation to biomass valorization. Within this context, organic reactions coupled with H 2 evolution via semiconductor-based photocatalytic systems under visible light irradiation have gained increasing attention in recent years, which utilize both excited electrons and holes generated on semiconductors and produce two types of value-added products, organics and H 2 , simultaneously. Based on the nature of the organic reactions, in this review article we classify semiconductor-based photocatalytic organic transformations and H 2 evolution into three categories: (i) photocatalytic organic oxidation reactions coupled with H 2 production, including oxidative upgrading of alcohols and biomass-derived intermediate compounds; (ii) photocatalytic oxidative coupling reactions integrated with H 2 generation, such as C–C, C–N, and S–S coupling reactions; and (iii) photo-reforming reactions together with H 2 formation using organic plastics, pollutants, and biomass as the substrates. Representative heterogeneous photocatalytic systems will be highlighted. Specific emphasis will be placed on their synthesis, characterization, and photocatalytic mechanism, as well as the organic reaction scope and practical application.
more »
« less
- Award ID(s):
- 1914546
- PAR ID:
- 10207452
- Date Published:
- Journal Name:
- Materials Advances
- Volume:
- 1
- Issue:
- 7
- ISSN:
- 2633-5409
- Page Range / eLocation ID:
- 2155 to 2162
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The burgeoning field of semiconductor‐mediated organic conversion is of paramount significance, with zinc indium sulfide (ZnIn2S4) emerging as a standout candidate owing to its benign nature, optimal bandgap, extensive light absorption spectrum, remarkable physicochemical properties, and straightforward synthesis. This review examines the latest breakthroughs and the trajectory of ZnIn2S4‐based photocatalysts in the realm of selective organic transformation. We start with a distinct overview of the intrinsic physical attributes of ZnIn2S4and the underlying mechanisms driving its efficacy in photocatalytic organic transformations. Subsequently, the preparation methods of ZnIn2S4are summarized. The main focus is the state‐of‐the‐art photocatalytic application of various ZnIn2S4‐based photocatalysts, such as redox reactions, the construction of C−C, C−S and S−S bonds, and the cleavage of C−O, C−C, and C=C bonds. In the conclusion part, we provide our perspectives on the prospective advancements and the remaining challenges that lie ahead in the optimization of ZnIn2S4‐based photocatalysts, with the ultimate goal of enhancing their efficacy for a diverse array of photosynthetic applications. It is anticipated to inspire the strategic engineering of ZnIn2S4and other semiconductor‐based photocatalysts for various artificial photosynthesis reactions.more » « less
-
Abstract Visible‐light‐driven C−C bond formation utilizing ketyl radical (Cketyl) species has attracted increasing attention recently, as it provides a direct route for the synthesis of complex molecules. However, the most‐developed homogeneous photocatalytic systems for the generation and utilization of ketyl radicals usually entail noble metal‐based (e. g., Ru and Ir) photosensitizers, which suffer from not only high cost but also potential degradation and hence pose challenges in product separation and purification. In contrast, readily accessible, inexpensive, and recyclable semiconductors represent a class of attractive and alternative photocatalysts but remain much less explored for photocatalytic ketyl radical initiated C−C bond formation. This work demonstrates that a wide range of industrially important chemicals, including substituted chromanes and tertiary alcohols, can be produced on ZnIn2S4under visible light irradiation through intramolecular cyclization (Cketyl−Csp2) and intermolecular cross‐coupling (Cketyl−Csp3) reactions, respectively, using ketyl radicals. A suite of experimental studies aided by computational investigation were carried out to shed light on the mechanistic insights of these two types of ketyl radical initiated C−C coupling reactions on ZnIn2S4.more » « less
-
Plasmon-driven photocatalysis has emerged as a paradigm-shifting approach, based on which the energy of photons can be judiciously harnessed to trigger interfacial molecular transformations on metallic nanostructure surfaces in a regioselective manner with nanoscale precision. Over the past decade, the formation of aromatic azo compounds through plasmon-driven oxidative coupling of thiolated aniline-derivative adsorbates has become a testbed for developing detailed mechanistic understanding of plasmon-mediated photochemistry. Such photocatalytic bimolecular coupling reactions may occur not only between thiolated aniline-derivative adsorbates but also between their nonthiolated analogs. How the nonthiolated adsorbates behave differently from their thiolated counterparts during the plasmon-driven coupling reactions, however, remains largely unexplored. Here, we systematically compare an alkynylated aniline-derivative, para-ethynylaniline, to its thiolated counterpart, para-mercaptoaniline, in terms of their adsorption conformations, structural flexibility, photochemical reactivity, and transforming kinetics on Ag nanophotocatalyst surfaces. We employ surface-enhanced Raman scattering as an in situ spectroscopic tool to track the detailed structural evolution of the transforming molecular adsorbates in real time during the plasmon-driven coupling reactions. Rigorous analysis of the spectroscopic results, further aided by density functional theory calculations, lays an insightful knowledge foundation that enables us to elucidate how the alteration of the chemical nature of metal–adsorbate interactions profoundly influences the transforming behaviors of the molecular adsorbates during plasmon-driven photocatalytic reactions.more » « less
-
Electro- and photocatalytic reduction of N 2 to NH 3 —the nitrogen reduction reaction (NRR)—is an environmentally- and energy-friendly alternative to the Haber-Bosch process for ammonia production. There is a great demand for the development of novel semiconductor-based electrocatalysts with high efficiency and stability for the direct conversion of inert substrates—including N 2 to ammonia—using visible light irradiation under ambient conditions. Herein we report electro-, and photocatalytic NRR with transition metal dichalcogenides (TMDCs), viz MoS 2 and WS 2 . Improved acid treatment of bulk TMDCs yields exfoliated TMDCs (exTMDCs) only a few layers thick with ∼10% S vacancies. Linear scan voltammograms on exMoS 2 and exWS 2 electrodes reveal significant NRR activity for exTMDC-modified electrodes, which is greatly enhanced by visible light illumination. Spectral measurements confirm ammonia as the main reaction product of electrocatalytic and photocatalytic NRR, and the absence of hydrazine byproduct. Femtosecond-resolved transient absorption studies provide direct evidence of interaction between photo-generated excitons/trions with N 2 adsorbed at S vacancies. DFT calculations corroborate N 2 binding to exMoS 2 at S-vacancies, with substantial π -backbonding to activate dinitrogen. Our findings suggest that chemically functionalized exTMDC materials could fulfill the need for highly-desired, inexpensive catalysts for the sustainable production of NH 3 using Sunlight under neutral pH conditions without appreciable competing production of H 2 .more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0MA00327A
