Excitonic effects mediated by Coulomb interactions between photogenerated electrons and holes play crucial roles in photoinduced processes of semiconductors. In terms of photocatalysis, however, ...efforts have seldom been devoted to the relevant aspects. For the catalysts with giant excitonic effects, the coexisting, competitive exciton generation serves as a key obstacle to the yield of free charge carriers, and hence, transformation of excitons into free carriers would be beneficial for optimizing the charge-carrier-involved photocatalytic processes. Herein, by taking bismuth oxybromide (BiOBr) as a prototypical model system, we demonstrate that excitons can be effectively dissociated into charge carriers with the incorporation of oxygen vacancy, leading to excellent performances in charge-carrier-involved photocatalytic reactions such as superoxide generation and selective organic syntheses under visible-light illumination. This work not only establishes an in-depth understanding of defective structures in photocatalysts but also paves the way for excitonic regulation via defect engineering.
Isolated single atomic site catalysts have attracted great interest due to their remarkable catalytic properties. Because of their high surface energy, single atoms are highly mobile and tend to form ...aggregate during synthetic and catalytic processes. Therefore, it is a significant challenge to fabricate isolated single atomic site catalysts with good stability. Herein, a gentle method to stabilize single atomic site metal by constructing defects on the surface of supports is presented. As a proof of concept, single atomic site Au supported on defective TiO2 nanosheets is prepared and it is discovered that (1) the surface defects on TiO2 nanosheets can effectively stabilize Au single atomic sites through forming the Ti–Au–Ti structure; and (2) the Ti–Au–Ti structure can also promote the catalytic properties through reducing the energy barrier and relieving the competitive adsorption on isolated Au atomic sites. It is believed that this work paves a way to design stable and active single atomic site catalysts on oxide supports.
Single atomic sites of Au are supported on defective TiO2 nanosheets and it is discovered that the surface defects on TiO2 nanosheets can effectively stabilize Au single atomic sites through forming a Ti–Au–Ti structure, and this Ti–Au–Ti structure can also promote the catalytic properties through reducing the energy barrier and relieving the competitive adsorption on isolated Au atomic sites.
It is of great importance to understand the origin of high oxygen-evolving activity of state-of-the-art multimetal oxides/(oxy)hydroxides at atomic level. Herein we report an evident improvement of ...oxygen evolution reaction activity via incorporating iron and vanadium into nickel hydroxide lattices. X-ray photoelectron/absorption spectroscopies reveal the synergistic interaction between iron/vanadium dopants and nickel in the host matrix, which subtly modulates local coordination environments and electronic structures of the iron/vanadium/nickel cations. Further, in-situ X-ray absorption spectroscopic analyses manifest contraction of metal-oxygen bond lengths in the activated catalyst, with a short vanadium-oxygen bond distance. Density functional theory calculations indicate that the vanadium site of the iron/vanadium co-doped nickel (oxy)hydroxide gives near-optimal binding energies of oxygen evolution reaction intermediates and has lower overpotential compared with nickel and iron sites. These findings suggest that the doped vanadium with distorted geometric and disturbed electronic structures makes crucial contribution to high activity of the trimetallic catalyst.
Solar CO2 reduction efficiency is largely limited by poor photoabsorption, sluggish electron–hole separation, and a high CO2 activation barrier. Defect engineering was employed to optimize these ...crucial processes. As a prototype, BiOBr atomic layers were fabricated and abundant oxygen vacancies were deliberately created on their surfaces. X‐ray absorption near‐edge structure and electron paramagnetic resonance spectra confirm the formation of oxygen vacancies. Theoretical calculations reveal the creation of new defect levels resulting from the oxygen vacancies, which extends the photoresponse into the visible‐light region. The charge delocalization around the oxygen vacancies contributes to CO2 conversion into COOH* intermediate, which was confirmed by in situ Fourier‐transform infrared spectroscopy. Surface photovoltage spectra and time‐resolved fluorescence emission decay spectra indicate that the introduced oxygen vacancies promote the separation of carriers. As a result, the oxygen‐deficient BiOBr atomic layers achieve visible‐light‐driven CO2 reduction with a CO formation rate of 87.4 μmol g−1 h−1, which was not only 20 and 24 times higher than that of BiOBr atomic layers and bulk BiOBr, respectively, but also outperformed most previously reported single photocatalysts under comparable conditions.
BiOBr atomic layers with abundant oxygen vacancies were synthesized. The photoresponse of BiOBr extends into the visible range, while charge delocalization around the vacancies contributes to CO2 conversion into COOH*. The material catalyzes visible‐light‐driven CO2 reduction with a CO formation rate of 87.4 μmol g−1 h−1, which is 20 and 24 times greater than that of BiOBr atomic layers and bulk BiOBr, respectively.
Co-N-C catalysts are promising candidates for substituting platinum in electrocatalysis and organic transformations. The heterogeneity of the Co species resulting from high-temperature pyrolysis, ...however, encumbers the structural identification of active sites. Herein, we report a self-supporting Co-N-C catalyst wherein cobalt is dispersed exclusively as single atoms. By using sub-Ångström-resolution HAADF-STEM in combination with XAFS and DFT calculation, the exact structure of the Co-N-C is identified to be CoN
C
-1-2O
, where the Co center atom is coordinated with four pyridinic N atoms in the graphitic layer, while two oxygen molecules are weakly adsorbed on Co atoms in perpendicular to the Co-N
plane. This single-atom dispersed Co-N-C catalyst presents excellent performance for the chemoselective hydrogenation of nitroarenes to produce azo compounds under mild reaction conditions.
The electrocatalytic activity of transition‐metal‐based compounds is strongly related to the spin states of metal atoms. However, the ways for regulation of spin states of catalysts are still ...limited, and the underlying relationship between the spin states and catalytic activities remains unclear. Herein, for the first time, by taking NiII‐based compounds without high or low spin states for example, it is shown that their spin states can be delocalized after introducing structural distortion to the atomic layers. The delocalized spin states for Ni atoms can provide not only high electrical conductivity but also low adsorption energy between the active sites and reaction intermediates for the system. As expected, the ultrathin nanosheets of nickel‐chalcogenides with structural distortions show dramatically enhanced activity in electrocatalytic oxygen evolution compared to their corresponding bulk samples. This work establishes new way for the design of advanced electrocatalysts in transition‐metal‐based compounds via regulation of spin states.
Delocalized spin states in transition‐metal‐based compounds by introducing structural distortion to their confined 2D atomic layers can enhance activity in electrocatalytic oxygen evolution. This work establishes new way for the design of advanced electrocatalysts in transition‐metal‐based compounds via regulation of spin states.
Rational design of non‐noble materials as highly efficient, economical, and durable bifunctional catalysts for oxygen evolution and reduction reactions (OER/ORR) is currently a critical obstacle for ...rechargeable metal‐air batteries. A new route involving S was developed to achieve atomic dispersion of Fe‐Nx species on N and S co‐decorated hierarchical carbon layers, resulting in single‐atom bifunctional OER/ORR catalysts for the first time. The abundant atomically dispersed Fe‐Nx species are highly catalytically active, the hierarchical structure offers more opportunities for active sites, and the electrical conductivity is greatly improved. The obtained electrocatalyst exhibits higher limiting current density and a more positive half‐wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions. Moreover, a rechargeable Zn–air battery device comprising this hybrid catalyst shows superior performance compared to Pt/C catalyst. This work will open a new avenue to design advanced bifunctional catalysts for reversible energy storage and conversion devices.
In isolation: Atomically dispersed iron–nitrogen sites supported on hierarchical carbon nanotubes co‐decorated with nitrogen and sulfur are efficient electrocatalytic sites for oxygen‐evolution and ‐reduction reactions. The hybrid material demonstrates good stability in alkaline solutions, allowing incorporation into a rechargeable zinc–air battery as an air cathode.
Semihydrogenation of acetylene in the ethylene feed is a vital step for the industrial production of polyethylene. Despite their favorable reaction activity and ethylene selectivity, the Pd‐based ...intermetallic compound and single‐atom alloy catalysts still suffer from the limitation of atomic utilization derived from the partial exposure of active Pd atoms. Herein, a hard‐template Lewis acid doping strategy is reported that can overcome the inefficient utilization of Pd atoms. In this strategy, N‐coordinated isolated single‐atomic Pd sites are fully embedded on the inner walls of mesoporous nitrogen‐doped carbon foam nanospheres (ISA‐Pd/MPNC). This synthetic strategy has been proved to be applicable to prepare other ISA‐M/MPNC (M = Pt and Cu) materials. This ISA‐Pd/MPNC catalyst with both high specific surface area (633.8 m2 g−1) and remarkably thin pore wall (1–2 nm) exhibits higher activity than that of its nonmesoporous counterpart (ISA‐Pd/non‐MPNC) catalyst by a factor of 4. This work presents an efficient way to tailor and optimize the catalytic activity and selectivity by atomic‐scale design and structural control.
A mesoporous nitrogen‐doped carbon nanosphere catalyst, on which isolated single‐atom Pd sites are uniformly dispersed, is prepared successfully via a hard‐template Lewis acid doping strategy. An efficient way to tailor and optimize the catalytic activity and selectivity by atomic‐scale design and structural control is thus presented.
The chemical coupling interaction has been explored extensively to boost heterogeneous catalysis, but the insight into how chemical coupling interaction works on CO2 electroreduction remains unclear. ...Herein we demonstrate how the chemical coupling interaction between porous In2O3 nanobelts and reduced graphene oxide (rGO) could substantially improve the electrocatalytic activity toward CO2 electroreduction. Such an In2O3–rGO hybrid catalyst showed 1.4-fold and 3.6-fold enhancements in Faradaic efficiency and specific current density for the formation of formate at −1.2 V versus reversible hydrogen electrode relative to the catalyst prepared by physically loading of In2O3 nanobelts onto rGO, respectively. The density functional theory calculations and electrochemical analysis together revealed that the chemical coupling interaction boosted CO2 electroreduction activity by improving electrical conductivity and stabilizing key intermediate HCOO–*. The present work not only deepens an understanding of chemical coupling effect but also provides an effective lever to optimize the catalytic performance toward CO2 electroreduction.
Abstract
The widespread use of proton exchange membrane water electrolysis requires the development of more efficient electrocatalysts containing reduced amounts of expensive iridium for the oxygen ...evolution reaction (OER). Here we present the identification of 6H-phase SrIrO
3
perovskite (6H-SrIrO
3
) as a highly active electrocatalyst with good structural and catalytic stability for OER in acid. 6H-SrIrO
3
contains 27.1 wt% less iridium than IrO
2
, but its iridium mass activity is about 7 times higher than IrO
2
, a benchmark electrocatalyst for the acidic OER. 6H-SrIrO
3
is the most active catalytic material for OER among the iridium-based oxides reported recently, based on its highest iridium mass activity. Theoretical calculations indicate that the existence of face-sharing octahedral dimers is mainly responsible for the superior activity of 6H-SrIrO
3
thanks to the weakened surface Ir-O binding that facilitates the potential-determining step involved in the OER (i.e., O* + H
2
O → HOO* + H
+
+
e
¯
).
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