Abstract
The electrochemical CO
2
reduction reaction (CO
2
RR) represents a very promising future strategy for synthesizing carbon-containing chemicals in a more sustainable way. In spite of great ...progress in electrocatalyst design over the last decade, the critical role of wettability-controlled interfacial structures for CO
2
RR remains largely unexplored. Here, we systematically modify the structure of gas-liquid-solid interfaces over a typical Au/C gas diffusion electrode through wettability modification to reveal its contribution to interfacial CO
2
transportation and electroreduction. Based on confocal laser scanning microscopy measurements, the Cassie-Wenzel coexistence state is demonstrated to be the ideal three phase structure for continuous CO
2
supply from gas phase to Au active sites at high current densities. The pivotal role of interfacial structure for the stabilization of the interfacial CO
2
concentration during CO
2
RR is quantitatively analysed through a newly-developed in-situ fluorescence electrochemical spectroscopic method, pinpointing the necessary CO
2
mass transfer conditions for CO
2
RR operation at high current densities.
Dinitrogen reduction to ammonia using transition metal catalysts is central to both the chemical industry and the Earth's nitrogen cycle. In the Haber–Bosch process, a metallic iron catalyst and high ...temperatures (400 °C) and pressures (200 atm) are necessary to activate and cleave NN bonds, motivating the search for alternative catalysts that can transform N2 to NH3 under far milder reaction conditions. Here, the successful hydrothermal synthesis of ultrathin TiO2 nanosheets with an abundance of oxygen vacancies and intrinsic compressive strain, achieved through a facile copper‐doping strategy, is reported. These defect‐rich ultrathin anatase nanosheets exhibit remarkable and stable performance for photocatalytic reduction of N2 to NH3 in water, exhibiting photoactivity up to 700 nm. The oxygen vacancies and strain effect allow strong chemisorption and activation of molecular N2 and water, resulting in unusually high rates of NH3 evolution under visible‐light irradiation. Therefore, this study offers a promising and sustainable route for the fixation of atmospheric N2 using solar energy.
Ultrathin TiO2 nanosheets with abundant oxygen vacancies (VO) are synthesized through a facile copper‐doping strategy, exhibiting remarkable and stable performance for the photofixation of N2 to NH3 at a rate of 78.9 µmol g−1 h−1 under ambient conditions (especially up to 700 nm). The outstanding activity can be attributed to the existence of VO and compressive strain in the nanosheets.
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In recent years, two-dimensional (2D) semiconductor photocatalysts have been widely applied in water splitting, CO2 reduction, N2 fixation, as well as many other important ...photoreactions. Photocatalysts in the form of 2D nanosheet possess many inherent advantages over traditional 3D nanopowder photocatalysts, including improved light absorption characteristics, shorter electron and hole migration paths to the photocatalysts’ surface (thus minimizing undesirable electron-hole pair recombination), and abundant surface defects which allow band gap modulation and facilitate charge transfer from the semiconductor to adsorbates. When synergistically exploited and optimized, these advantages can impart 2D photocatalysts with remarkable activities relative to their 3D counterparts. Accordingly, a wide range of experimental approaches is now being explored for the synthesis of 2D photocatalysts, with computational methods increasingly being used for identification of promising new 2D photocatalytic materials. Herein, we critically review recent literatures related to 2D photocatalyst development and design. Particular emphasis is placed on 2D photocatalyst synthesis and the importance of computational studies for the fundamental understanding of 2D photocatalyst electronic structure, band gap structure, charge carrier mobility and reaction pathways. We also explore the practical challenges of using 2D photocatalysts, such as their difficulty to synthesize in large quantity and also their characterization. The overarching aim of this review is to provide a snapshot of recent work targeting high-performance 2D photocatalysts for efficient solar energy conversion, thus laying a firm base for future advancements in this rapidly expanding area of photocatalysis research.
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Photocatalytic CO2 reduction holds promise as a future technology for the manufacture of fuels and commodity chemicals. However, factors controlling product selectivity remain poorly ...understood. Herein, we compared the performance of a homologous series of Zn-based layered double hydroxide (ZnM-LDH) photocatalysts for CO2 reduction. By varying the trivalent or tetravalent metal cations in the ZnM-LDH photocatalysts (M = Ti4+, Fe3+, Co3+, Ga3+, Al3+), the product selectivity of the reaction could be precisely controlled. ZnTi-LDH afforded CH4 as the main reduction product; ZnFe-LDH and ZnCo-LDH yielded H2 exclusively from water splitting; whilst ZnGa-LDH and ZnAl-LDH generated CO. In-situ diffuse reflectance infrared measurements, valence band XPS and density function theory calculations were applied to rationalize the CO2 reduction selectivities of the different ZnM-LDH photocatalysts. The analyses revealed that the d-band center (εd) position of the M3+ or M4+ cations controlled the adsorption strength of CO2 and thus the selectivity to carbon-containing products or H2. Cations with d-band centers relatively close to the Fermi level (Ti4+, Ga3+ and Al3+) adsorbed CO2 strongly yielding CH4 or CO, whereas metal cations with d-band centers further from the Fermi level (Fe3+ and Co3+) adsorbed CO2 poorly, thereby yielding H2 only (from water splitting). Our findings clarify the role of trivalent and tetravalent metal cations in LDH photocatalysts for the selective CO2 reduction, paving new ways for the development of improved LDH photocatalyst with high selectivities to specific products.
Designing bifunctional catalysts capable of driving the electrochemical hydrogen evolution reaction (HER) and also H2 evolution via the hydrolysis of hydrogen storage materials such as ammonia borane ...(AB) is of considerable practical importance for future hydrogen economies. Herein, we systematically examined the effect of tensile lattice strain in CoRu nanoalloys supported on carbon quantum dots (CoRu/CQDs) on hydrogen generation by HER and AB hydrolysis. By varying the Ru content, the lattice parameters and Ru‐induced lattice strain in the CoRu nanoalloys could be tuned. The CoRu0.5/CQDs catalyst with an ultra‐low Ru content (1.33 wt.%) exhibited excellent catalytic activity for HER (η=18 mV at 10 mA cm−2 in 1 M KOH) and extraordinary activity for the hydrolysis of AB with a turnover frequency of 3255.4 mol(H2)
mol−1(Ru) min−1 or 814.7 mol(H2)
mol−1(cat) min−1 at 298 K, respectively, representing one of the best activities yet reported for AB hydrolysis over a ruthenium alloy catalyst. Moreover, the CoRu0.5/CQDs catalyst displayed excellent stability during each reaction, including seven alternating cycles of HER and AB hydrolysis. Theoretical calculations revealed that the remarkable catalytic performance of CoRu0.5/CQDs resulted from the optimal alloy electronic structure realized by incorporating small amounts of Ru, which enabled fast interfacial electron transfer to intermediates, thus benefitting H2 evolution kinetics. Results support the development of new and improved catalysts HER and AB hydrolysis.
Ultra‐low Ru induced CoRu nanoalloy lattice strain for robust hydrogen evolution reaction (HER) and hydrolysis of ammonia borane (AB) bifunctional hydrogen production is introduced. The CoRu0.5/CQDs displayed excellent stability during each reaction, including seven alternating cycles of HER and AB hydrolysis.
The selective hydrogenation of acetylene to ethylene in an ethylene‐rich gas stream is an important process in the chemical industry. Pd‐based catalysts are widely used in this reaction due to their ...excellent hydrogenation activity, though their selectivity for acetylene hydrogenation and durability need improvement. Herein, the successful synthesis of atomically dispersed Pd single‐atom catalysts on nitrogen‐doped graphene (Pd1/N‐graphene) by a freeze‐drying‐assisted method is reported. The Pd1/N‐graphene catalyst exhibits outstanding activity and selectivity for the hydrogenation of C2H2 with H2 in the presence of excess C2H4 under photothermal heating (UV and visible‐light irradiation from a Xe lamp), achieving 99% conversion of acetylene and 93.5% selectivity to ethylene at 125 °C. This remarkable catalytic performance is attributed to the high concentration of Pd active sites on the catalyst surface and the weak adsorption energy of ethylene on isolated Pd atoms, which prevents C2H4 hydrogenation. Importantly, the Pd1/N‐graphene catalyst exhibits excellent durability at the optimal reaction temperature of 125 °C, which is explained by the strong local coordination of Pd atoms by nitrogen atoms, which suppresses the Pd aggregation. The results presented here encourage the wider pursuit of solar‐driven photothermal catalyst systems based on single‐atom active sites for selective hydrogenation reactions.
Pd single‐atom catalysts on nitrogen‐doped graphene are successfully fabricated. A Pd1/N‐graphene catalyst (Pd loading of 2.3 wt%) exhibits outstanding activity and selectivity for the selective hydrogenation of acetylene in the presence of excess ethylene under photothermal or direct thermal heating at 125 °C, which is attributed to the suppression of C2H4 hydrogenation to C2H6 by Pd‐N4 surface sites.
Semiconductor photocatalysis attracts widespread interest in water splitting, CO2 reduction, and N2 fixation. N2 reduction to NH3 is essential to the chemical industry and to the Earth's nitrogen ...cycle. Industrially, NH3 is synthesized by the Haber–Bosch process under extreme conditions (400–500 °C, 200–250 bar), stimulating research into the development of sustainable technologies for NH3 production. Herein, this study demonstrates that ultrathin layered‐double‐hydroxide (LDH) photocatalysts, in particular CuCr‐LDH nanosheets, possess remarkable photocatalytic activity for the photoreduction of N2 to NH3 in water at 25 °C under visible‐light irradiation. The excellent activity can be attributed to the severely distorted structure and compressive strain in the LDH nanosheets, which significantly enhances N2 chemisorption and thereby promotes NH3 formation.
Layered‐double‐hydroxide (LDH) nanosheets are shown to exhibit outstanding visible‐light‐driven photocatalytic activity for the reduction of N2 to NH3 under ambient conditions. Irradiation of CuCr‐LDH nanosheets in N2‐saturated water with 500 nm monochromatic light produces NH3. The excellent activity can be attributed to the severely distorted structure and compressive strain of the LDH nanosheets, promoting NH3 formation.
Photocatalysis is an ideal and promising green technology to drive numerous chemical reactions for valued chemicals production under very mild conditions, thereby providing solutions to global energy ...and environment issues related to burning fossil fuels. Over the past decade, layered double hydroxides (LDHs), as the members in two‐dimensional materials family, have attracted much attention due to their many advantages in photocatalysis, such as facile synthesis, low cost and powerful tunability of composition. In this review, we provide a synthetic overview of recent research advances of LDH‐based photocatalysts, with the main discussion of the design strategies to improve their photocatalytic performance, including component control, defect engineering, hybridization, and topological transformation. Structure‐performance correlations and tailor‐made material synthesis strategies are elaborated to discuss how to realize high‐performance LDH‐based photocatalysts for three important reactions (i.e., water splitting, CO2 conversion, and N2 reduction) to generate desirable solar fuels. Further, the remaining challenges and future perspectives of LDH‐based photocatalysts are summed up, aiming to inspire brand new solutions for pushing forward the development of LDH‐based photocatalysis.
As a broad platform for material design, LDH‐based materials have exhibited exciting photocatalytic performance and application prospect. The design strategies for high‐performance LDH‐based photocatalysts are summarized in this review, which provide a systematic and in‐depth understanding of LDH‐based photocatalysts. The remaining challenges and future perspectives of LDH‐based photocatalysts are also proposed to further push forward the development of LDH‐based photocatalysis.
Abstract
Photocatalytic two-electron oxygen reduction to produce high-value hydrogen peroxide (H
2
O
2
) is gaining popularity as a promising avenue of research. However, structural evolution ...mechanisms of catalytically active sites in the entire photosynthetic H
2
O
2
system remains unclear and seriously hinders the development of highly-active and stable H
2
O
2
photocatalysts. Herein, we report a high-loading Ni single-atom photocatalyst for efficient H
2
O
2
synthesis in pure water, achieving an apparent quantum yield of 10.9% at 420 nm and a solar-to-chemical conversion efficiency of 0.82%. Importantly, using in situ synchrotron X-ray absorption spectroscopy and Raman spectroscopy we directly observe that initial Ni-N
3
sites dynamically transform into high-valent O
1
-Ni-N
2
sites after O
2
adsorption and further evolve to form a key *OOH intermediate before finally forming HOO-Ni-N
2
. Theoretical calculations and experiments further reveal that the evolution of the active sites structure reduces the formation energy barrier of *OOH and suppresses the O=O bond dissociation, leading to improved H
2
O
2
production activity and selectivity.
The widespread use of polyolefin plastics in modern societies generates huge amounts of plastic waste. With a view toward sustainability, researchers are now seeking novel and low-cost strategies for ...recycling and valorizing polyolefin plastics. Herein, we report the successful development of a photothermal catalytic recycling system for transforming polyolefin plastics into liquid/waxy fuels under concentrated sunlight or xenon lamp irradiation. Photothermal heating of a Ru/TiO
catalyst to 200-300 °C in the presence of polyolefin plastics results in intimate catalyst-plastic contact and controllable hydrogenolysis of C-C and C-H bonds in the polymer chains (mediated by Ru sites). By optimizing the reaction temperature and pressure, the complete conversion of waste polyolefins into valuable liquid fuels (86% gasoline- and diesel-range hydrocarbons, C
-C
) is possible in short periods (3 h). This work demonstrates a simple and efficient strategy for recycling waste polyolefin plastics using abundant solar energy.
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