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"Lin, X"
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Influence of iron doping on tetravalent nickel content in catalytic oxygen evolving films
Iron doping of nickel oxide films results in enhanced activity for promoting the oxygen evolution reaction (OER). Whereas this enhanced activity has been ascribed to a unique iron site within the nickel oxide matrix, we show here that Fe doping influences the Ni valency. The percent of Fe3+ doping promotes the formation of formal Ni4+, which in turn directly correlates with an enhanced activity of the catalyst in promoting OER. The role of Fe3+ is consistent with its behavior as a superior Lewis acid.
Journal Article
Seeded growth of single-crystal two-dimensional covalent organic frameworks
Covalent organic framework (COF) materials have been difficult to characterize structurally and to exploit because they tend to form powders or amorphous materials. Ma et al. studied a variety of three-dimensional COFs based on imine linkages (see the Perspective by Navarro). They found that the addition of aniline inhibited nucleation and allowed the growth of crystals large enough for single-crystal x-ray diffraction studies. Evans et al. describe a two-step process in which nanoscale seeds of boronate ester–linked two-dimensional COFs can be grown into micrometer-scale single crystals by using a solvent that suppresses the nucleation of additional nanoparticles. Transient absorption spectroscopy revealed superior charge transport in these crystallites compared with that observed in conventional powders. Science , this issue p. 48 , p. 52 ; see also p. 35 Micrometer-scale single crystals of two-dimensional boronate ester–linked frameworks can be grown in a two-step process. Polymerization of monomers into periodic two-dimensional networks provides structurally precise, layered macromolecular sheets that exhibit desirable mechanical, optoelectronic, and molecular transport properties. Two-dimensional covalent organic frameworks (2D COFs) offer broad monomer scope but are generally isolated as powders comprising aggregated nanometer-scale crystallites. We found that 2D COF formation could be controlled using a two-step procedure in which monomers are added slowly to preformed nanoparticle seeds. The resulting 2D COFs are isolated as single-crystalline, micrometer-sized particles. Transient absorption spectroscopy of the dispersed COF nanoparticles revealed improvement in signal quality by two to three orders of magnitude relative to polycrystalline powder samples, and suggests exciton diffusion over longer length scales than those obtained through previous approaches. These findings should enable a broad exploration of synthetic 2D polymer structures and properties.
Journal Article
Detection of high-valent iron species in alloyed oxidic cobaltates for catalysing the oxygen evolution reaction
Iron alloying of oxidic cobaltate catalysts results in catalytic activity for oxygen evolution on par with Ni-Fe oxides in base but at much higher alloying compositions. Zero-field
57
Fe Mössbauer spectroscopy and X-ray absorption spectroscopy (XAS) are able to clearly identify Fe
4+
in mixed-metal Co-Fe oxides. The highest Fe
4+
population is obtained in the 40–60% Fe alloying range, and XAS identifies the ion residing in an octahedral oxide ligand field. The oxygen evolution reaction (OER) activity, as reflected in Tafel analysis of CoFeO
x
films in 1 M KOH, tracks the absolute concentration of Fe
4+
. The results reported herein suggest an important role for the formation of the Fe
4+
redox state in activating cobaltate OER catalysts at high iron loadings.
The capturing of high valent iron in a catalytic reaction is important but difficult task. Here, the authors report identification of a high-valent Fe(IV)-species with different spectroscopic tools such as Mössbauer spectroscopy and X-ray absorption spectroscopy during the course of an oxygen evolving reaction.
Journal Article
Teclistamab in Relapsed or Refractory Multiple Myeloma
In this phase 1–2 study involving patients with relapsed or refractory myeloma, a bispecific antibody (teclistamab) that mediates T-cell activation and subsequent lysis of myeloma cells expressing B-cell maturation antigen induced responses in 63% of the patients, including a complete response in nearly 40%.
Journal Article
Intrinsically patterned two-dimensional materials for selective adsorption of molecules and nanoclusters
PtSe
2
and CuSe monolayers obtained by selenization of a metal substrate are shown to intrinsically form periodic patterns by varying the amount of Se atoms deposited. These patterns are used for the localized absorption of molecules and nanoclusters.
Two-dimensional (2D) materials have been studied extensively as monolayers
1
,
2
,
3
,
4
,
5
, vertical or lateral heterostructures
6
,
7
,
8
. To achieve functionalization, monolayers are often patterned using soft lithography and selectively decorated with molecules
9
,
10
. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe
2
can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.
Journal Article
Two-dimensional perovskitoids enhance stability in perovskite solar cells
Two-dimensional (2D) and three-dimensional (3D) perovskite heterostructures have played a key role in advancing the performance of perovskite solar cells
1
,
2
. However, the migration of cations between 2D and 3D layers results in the disruption of octahedral networks, leading to degradation in performance over time
3
,
4
. We hypothesized that perovskitoids, with robust organic–inorganic networks enabled by edge- and face-sharing, could impede ion migration. We explored a set of perovskitoids of varying dimensionality and found that cation migration within perovskitoid–perovskite heterostructures was suppressed compared with the 2D–3D perovskite case. Increasing the dimensionality of perovskitoids improves charge transport when they are interfaced with 3D perovskite surfaces—this is the result of enhanced octahedral connectivity and out-of-plane orientation. The 2D perovskitoid (A6BfP)
8
Pb
7
I
22
(A6BfP:
N
-aminohexyl-benz[f]-phthalimide) provides efficient passivation of perovskite surfaces and enables uniform large-area perovskite films. Devices based on perovskitoid–perovskite heterostructures achieve a certified quasi-steady-state power conversion efficiency of 24.6% for centimetre-area perovskite solar cells. We removed the fragile hole transport layers and showed stable operation of the underlying perovskitoid–perovskite heterostructure at 85 °C for 1,250 h for encapsulated large-area devices in ambient air.
We find that 2D–3D perovskitoid passivation applied to perovskite solar cells impedes cation migration and decreases carrier recombination at the interface, providing enhanced operating stability at elevated temperatures and increased power conversion efficiencies.
Journal Article
Spin–vibronic coherence drives singlet–triplet conversion
Design-specific control over the transitions between excited electronic states with different spin multiplicities is of the utmost importance in molecular and materials chemistry
1
–
3
. Previous studies have indicated that the combination of spin–orbit and vibronic effects, collectively termed the spin–vibronic effect, can accelerate quantum-mechanically forbidden transitions at non-adiabatic crossings
4
,
5
. However, it has been difficult to identify precise experimental manifestations of the spin–vibronic mechanism. Here we present coherence spectroscopy experiments that reveal the interplay between the spin, electronic and vibrational degrees of freedom that drive efficient singlet–triplet conversion in four structurally related dinuclear Pt(II) metal–metal-to-ligand charge-transfer (MMLCT) complexes. Photoexcitation activates the formation of a Pt–Pt bond, launching a stretching vibrational wavepacket. The molecular-structure-dependent decoherence and recoherence dynamics of this wavepacket resolve the spin–vibronic mechanism. We find that vectorial motion along the Pt–Pt stretching coordinates tunes the singlet and intermediate-state energy gap irreversibly towards the conical intersection and subsequently drives formation of the lowest stable triplet state in a ratcheting fashion. This work demonstrates the viability of using vibronic coherences as probes
6
–
9
to clarify the interplay among spin, electronic and nuclear dynamics in spin-conversion processes, and this could inspire new modular designs to tailor the properties of excited states.
Many aspects of materials chemistry rely on singlet–triplet spin conversion, but spin–vibronic effects are shown to accelerate the process when vibronic coupling causes the quantum-mechanical mixing of spin states.
Journal Article