Efficiency of layered photocatalysts such as graphitic carbon nitride (g-CN) is still too low due to the poor utilization of photoexcited-charge carriers. The major drawback is that the weak van der Waals force among g-CN layers is unfavorable for the charge transfer between the adjacent layers and the intrinsically π-conjugated planes with inefficient random in-plane charge migration. Herein, an atomically dispersed Pd layered photocatalyst with both bridged sites of adjacent layers and surface-sites of g-CN is demonstrated, providing directional charge-transfer channels and targeting active sites for photocatalytic water reduction. Both theoretical prediction and empirical characterizations are conducted to achieve the successful synthesis of single-atom engineered Pd/g-CN hybrid and the excellent separation of charge transfer as well as the efficient photocatalytic hydrogen evolution, much better than that of the optimized Pt/g-CN benchmark. The finding in this work provides a rational way for tailoring the performance and engineering of single-atomic noble metal.
In article number https://doi.org/10.1002/adfm.201802169, Jiaguo Yu, Hao Ming Chen, and co‐workers demonstrate the construction of a single‐atom engineered Pd/g‐CN hybrid with directional charge transfer channels and targeting active sites by interlayer intercalation and a surface anchor of Pd atoms. This unique material shows excellent charge transfer/separation and efficient photocatalytic hydrogen evolution.
Real bifunctional electrocatalysts
for hydrogen evolution reaction
and oxygen evolution reaction have to be the ones that exhibit a steady
configuration during/after reaction without irreversible structural
transformation or surface reconstruction. Otherwise, they can be termed
as “precatalysts” rather than real catalysts. Herein,
through a strongly atomic metal–support interaction, single-atom
dispersed catalysts decorating atomically dispersed Ru onto a nickel–vanadium
layered double hydroxide (LDH) scaffold can exhibit excellent HER
and OER activities. Both in situ X-ray absorption
spectroscopy and operando Raman spectroscopic investigation clarify
that the presence of atomic Ru on the surface of nickel–vanadium
LDH is playing an imperative role in stabilizing the dangling bond-rich
surface and further leads to a reconstruction-free surface. Through
strong metal–support interaction provided by nickel–vanadium
LDH, the significant interplay can stabilize the reactive atomic Ru
site to reach a small fluctuation in oxidation state toward cathodic
HER without reconstruction, while the atomic Ru site can stabilize
the Ni site to have a greater structural tolerance toward both the
bond constriction and structural distortion caused by oxidizing the
Ni site during anodic OER and boost the oxidation state increase in
the Ni site that contributes to its superior OER performance. Unlike
numerous bifunctional catalysts that have suffered from the structural
reconstruction/transformation for adapting the HER/OER cycles, the
proposed Ru/Ni3V-LDH is characteristic of steady dual reactive
sites with the presence of a strong metal–support interaction
(i.e., Ru and Ni sites) for individual catalysis in water splitting
and is revealed to be termed as a real bifunctional electrocatalyst.
Solar-driven
photocatalytic reactions can mildly activate hydrocarbon
C–H bonds to produce value-added chemicals. However, the inefficient
utilization of photogenerated carriers hinders the application. Here,
we report reversible photochromic BiOBr (denoted as p-BiOBr) nanosheets that were colored by trapping photogenerated holes
upon visible light irradiation and bleached by water oxidation to
generate hydroxyl radicals, demonstrating enhanced carrier separation
and water oxidation. The photocatalytic coupling and oxidation reactions
of ethylbenzene were efficiently realized by p-BiOBr
in a water-based medium under ambient temperature and pressure (apparent
quantum yield is 14 times that of pristine BiOBr). The p-BiOBr nanosheets feature lattice disordered defects on the surface,
providing rich uncoordinated catalytic sites and inducing structural
distortions and lattice strain, which further leads to an altered
band structure and significantly enhanced photocatalytic performances.
These hole-trapping materials open up the possibility of substantially
elevating the utilization efficiency of photogenerated holes for high-efficiency
photocatalytic activation of various saturated C–H bonds.
Phosphide-based
electrocatalysts exhibit high activities in alkaline
solution toward overall water electrolysis. However, their real phases
during catalysis have not been comprehensively identified, leading
to improper advancement in material recognition and theoretical simulation.
In this work, in situ spatially coherent transmitted X-ray diffraction
and X-ray absorption spectroscopy were developed to probe Fe-doped
cobalt phosphides, presenting superior catalytic activity and reaction
kinetics for overall water electrolysis compared to pristine cobalt
phosphides. The results showed that Fe dopants latched the crystallographic
sites and stabilized the phosphide phase, which are the active species
for hydrogen evolution reaction, while pristine cobalt phosphide transformed
into hydroxides that impede the formation of active substances. Besides,
Fe-doped cobalt phosphides swiftly converted into active-site confined
oxyhydroxide for oxygen evolution reaction, achieving superb overall
catalytic performance. The genuine materials unveiled during the electrocatalysis
suggest that the appropriate catalytic mechanism correlates with the
phase transition and crystalline transformation rate.
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