Supported metal nanoparticles are the most widely investigated heterogeneous catalysts in catalysis community. The size of metal nanostructures is an important parameter in influencing the activity ...of constructed catalysts. Especially, as coordination unsaturated metal atoms always work as the catalytically active centers, decreasing the particle size of the catalyst can greatly boost the specific activity per metal atom. Single‐atom catalysts (SACs), containing single metal atoms anchored on supports, represent the utmost utilization of metallic catalysts and thus maximize the usage efficiency of metal atom. However, with the decreasing of particle size, the surface free energy increases obviously, and tends to aggregate into clusters or particles. Selection of an appropriate support is necessary to interact with isolated atoms strongly, and thus prevents the movement and aggregation of isolated atoms, creating stable, finely dispersed active sites. Furthermore, with uniform single‐atom dispersion and well‐defined configuration, SACs afford great space for optimizing high selectivity and activity. In this review, a detailed discussion of preparing, characterizing, and catalytically testing within this family is provided, including the theoretical understanding of key aspects of SACs materials. The main advantages of SACs as catalysts and the challenges faced for further improving catalytic performance are also highlighted.
In this review, a detailed discussion of preparing, characterizing, and catalytically testing within this family is provided, including the theoretical understanding of key aspects of single atom catalysts (SACs) materials. The main advantages of SACs as catalysts and the challenges faced for further improving catalytic performance are also highlighted.
The fast industrialization process has led to global challenges in the energy crisis and environmental pollution, which might be solved with clean and renewable energy. Highly efficient ...electrochemical systems for clean‐energy collection require high‐performance electrocatalysts, including Au, Pt, Pd, Ru, etc. Graphene, a single‐layer 2D carbon nanosheet, possesses many intriguing properties, and has attracted tremendous research attention. Specifically, graphene and graphene derivatives have been utilized as templates for the synthesis of various noble‐metal nanocomposites, showing excellent performance in electrocatalytic‐energy‐conversion applications, such as the hydrogen evolution reaction and CO2 reduction. Herein, the recent progress in graphene‐based noble‐metal nanocomposites is summarized, focusing on their synthetic methods and electrocatalytic applications. Furthermore, some personal insights on the challenges and possible future work in this research field are proposed.
Recent progress in the study of graphene‐based noble‐metal nanocomposites is reviewed. Different strategies regarding the synthesis of noble‐metal nanostructures on graphene or its derivatives are presented. Their applications in electrocatalysis including the hydrogen evolution reaction, oxygen reduction reaction, alcohol oxidation reaction, and CO2 reduction reaction are discussed.
Through a facile and effective strategy by employing lithium molten salts the controlled synthesis of 2H‐ and 1T‐MoS2 monolayers with high‐yield production is achieved. Both phases of MoS2 monolayers ...exhibit high stabilities. When used as a catalyst for hydrogen evolution, these phased MoS2 monolayers deliver respective advantages in the field of electro‐ and photo‐catalytic hydrogen evolution.
Graphitic carbon nitride (g‐C3N4) has recently emerged as an attractive photocatalyst for solar energy conversion. However, the photocatalytic activities of g‐C3N4 remain moderate because of the ...insufficient solar‐light absorption and the fast electron–hole recombination. Here, defect‐modified g‐C3N4 (DCN) photocatalysts, which are easily prepared under mild conditions and show much extended light absorption with band gaps decreased from 2.75 to 2.00 eV, are reported. More importantly, cyano terminal CN groups, acting as electron acceptors, are introduced into the DCN sheet edge, which endows the DCN with both n‐ and p‐type conductivities, consequently giving rise to the generation of p–n homojunctions. This homojunction structure is demonstrated to be highly efficient in charge transfer and separation, and results in a fivefold enhanced photocatalytic H2 evolution activity. The findings deepen the understanding on the defect‐related issues of g‐C3N4‐based materials. Additionally, the ability to build homojunction structures by the defect‐induced self‐functionalization presents a promising strategy to realize precise band engineering of g‐C3N4 and related polymer semiconductors for more efficient solar energy conversion applications.
The p–n homojunction graphitic carbon nitride (g‐C3N4) photocatalysts with extended light absorption are prepared via in situ bond modulation, which is achieved by low‐temperature heating g‐C3N4 with NaBH4. Such a p–n homojunction endows g‐C3N4 with much increased π‐electron delocalization and highly improved carrier separation and transfer. Consequently, the materials exhibit a fivefold enhanced photocatalytic hydrogen evolution activity under visible light irradiation.
Modular optimization of metal–organic frameworks (MOFs) was realized by incorporation of coordinatively unsaturated single atoms in a MOF matrix. The newly developed MOF can selectively capture and ...photoreduce CO2 with high efficiency under visible‐light irradiation. Mechanistic investigation reveals that the presence of single Co atoms in the MOF can greatly boost the electron–hole separation efficiency in porphyrin units. Directional migration of photogenerated excitons from porphyrin to catalytic Co centers was witnessed, thereby achieving supply of long‐lived electrons for the reduction of CO2 molecules adsorbed on Co centers. As a direct result, porphyrin MOF comprising atomically dispersed catalytic centers exhibits significantly enhanced photocatalytic conversion of CO2, which is equivalent to a 3.13‐fold improvement in CO evolution rate (200.6 μmol g−1 h−1) and a 5.93‐fold enhancement in CH4 generation rate (36.67 μmol g−1 h−1) compared to the parent MOF.
Less is more: A photocatalyst comprising atomically dispersed Co in an extended MOF efficiently reduces CO2. Directional migration of photogenerated excitons from porphyrin to catalytic cobalt centers was witnessed, thereby supplying long‐lived electrons for reduction of CO2 molecules adsorbed on cobalt centers.
Inspired by the crucial roles of phosphates in natural photosynthesis, we explored an environmental “phosphorylation” strategy for boosting photocatalytic H2 production over g‐C3N4 nanosheets under ...visible light. As expected, a substantial improvement was observed in the rate of H2 evolution to 947 μmol h−1, and the apparent quantum yield was as high as 26.1 % at 420 nm. The synergy of enhanced proton reduction and improved hole oxidation is proposed to account for the markedly increased activity. Our findings may provide a promising and facile approach to highly efficient photocatalysis for solar‐energy conversion.
The right environment for success: A “phosphorylation” strategy inspired by natural photosynthesis was explored to boost photocatalytic H2 production over g‐C3N4 nanosheets. Thus, the addition of a phosphate led to a high apparent quantum yield (AQY). Experimental and theoretical results indicated that the large increase in activity was due to the synergy of enhanced proton reduction and improved hole oxidation (see picture; TEOA=triethanolamine).
Water splitting represents a promising technology for renewable energy conversion and storage, but it is greatly hindered by the kinetically sluggish oxygen evolution reaction (OER). Here, using ...Au-nanoparticle-decorated Ni(OH)2 nanosheets Ni(OH)2–Au as catalysts, we demonstrate that the photon-induced surface plasmon resonance (SPR) excitation on Au nanoparticles could significantly activate the OER catalysis, specifically achieving a more than 4-fold enhanced activity and meanwhile affording a markedly decreased overpotential of 270 mV at the current density of 10 mA cm–2 and a small Tafel slope of 35 mV dec–1 (no iR-correction), which is much better than those of the benchmark IrO2 and RuO2, as well as most Ni-based OER catalysts reported to date. The synergy of the enhanced generation of NiIII/IV active species and the improved charge transfer, both induced by hot-electron excitation on Au nanoparticles, is proposed to account for such a markedly increased activity. The SPR-enhanced OER catalysis could also be observed over cobalt oxide (CoO)–Au and iron oxy-hydroxide (FeOOH)–Au catalysts, suggesting the generality of this strategy. These findings highlight the possibility of activating OER catalysis by plasmonic excitation and could open new avenues toward the design of more-energy-efficient catalytic water oxidation systems with the assistance of light energy.
Highly efficient utilization of solar light with an excellent reduction capacity is achieved for plasmonic Fe@C nanostructures. By carbon layer coating, the optimized catalyst exhibits enhanced ...selectivity and stability applied to the solar‐driven reduction of CO2 into CO. The surface‐plasmon effect of iron particles is proposed to excite CO2 molecules, and thereby facilitates the final reaction activity.
Heterostructured, including heterophase, noble-metal nanomaterials have attracted much interest due to their promising applications in diverse fields. However, great challenges still remain in the ...rational synthesis of well-defined noble-metal heterophase nanostructures. Herein, we report the preparation of Pd nanoparticles with an unconventional hexagonal close-packed (2H type) phase, referred to as 2H-Pd nanoparticles, via a controlled phase transformation of amorphous Pd nanoparticles. Impressively, by using the 2H-Pd nanoparticles as seeds, Au nanomaterials with different crystal phases epitaxially grow on the specific exposed facets of the 2H-Pd, i.e., face-centered cubic (fcc) Au (fcc-Au) on the (002)h facets of 2H-Pd while 2H-Au on the other exposed facets, to achieve well-defined fcc-2H-fcc heterophase Pd@Au core–shell nanorods. Moreover, through such unique facet-directed crystal-phase-selective epitaxial growth, a series of unconventional fcc-2H-fcc heterophase core–shell nanostructures, including Pd@Ag, Pd@Pt, Pd@PtNi, and Pd@PtCo, have also been prepared. Impressively, the fcc-2H-fcc heterophase Pd@Au nanorods show excellent performance toward the electrochemical carbon dioxide reduction reaction (CO2RR) for production of carbon monoxide with Faradaic efficiencies of over 90% in an exceptionally wide applied potential window from −0.9 to −0.4 V (versus the reversible hydrogen electrode), which is among the best reported CO2RR catalysts in H-type electrochemical cells.
The rational design and synthesis of anisotropic 3D nanostructures with specific composition, morphology, surface structure, and crystal phase is of significant importance for their diverse ...applications. Here, the synthesis of well‐crystalline lotus‐thalamus‐shaped Pt‐Ni anisotropic superstructures (ASs) via a facile one‐pot solvothermal method is reported. The Pt‐Ni ASs with Pt‐rich surface are composed of one Ni‐rich “core” with face‐centered cubic (fcc) phase, Ni‐rich “arms” with hexagonal close‐packed phase protruding from the core, and facet‐selectively grown Pt‐rich “lotus seeds” with fcc phase on the end surfaces of the “arms.” Impressively, these unique Pt‐Ni ASs exhibit superior electrocatalytic activity and stability toward the hydrogen evolution reaction under alkaline conditions compared to commercial Pt/C and previously reported electrocatalysts. The obtained overpotential is as low as 27.7 mV at current density of 10 mA cm−2, and the turnover frequency reaches 18.63 H2 s−1 at the overpotential of 50 mV. This work provides a new strategy for the synthesis of highly anisotropic superstructures with a spatial heterogeneity to boost their promising application in catalytic reactions.
Well‐crystalline lotus‐thalamus‐shaped Pt‐Ni anisotropic superstructures (ASs) with unique hexagonal‐close‐packed/face‐centered‐cubic crystal phases and Pt‐rich surface are synthesized via a simple one‐pot solvothermal method. The obtained Pt‐Ni ASs exhibit superior electrocatalytic activity and stability toward the hydrogen evolution reaction under alkaline conditions compared to commercial Pt/C and other reported electrocatalysts.
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