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Carbon-based single-atom catalysts, a promising candidate in electrocatalysis, offer insights into electron-donating effects of metal center on adjacent atoms. Herein, we present a practical strategy to rationally design a model catalyst with a single zinc (Zn) atom coordinated with nitrogen and sulfur atoms in a multilevel carbon matrix. The Zn site exhibits an atomic interface configuration of ZnN4S1, where Zn's electron injection effect enables thermal-neutral hydrogen adsorption on neighboring atoms, pushing the activity boundaries of carbon electrocatalysts toward electrochemical hydrogen evolution to an unprecedented level. Experimental and theoretical analyses confirm the low-barrier Volmer-Tafel mechanism of proton reduction, while the multishell hollow structures facilitate the hydrogen evolution even at high current intensities. This work provides insights for understanding the actual active species during hydrogen evolution reaction and paves the way for designing high-performance electrocatalysts.
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Sulfur reduction reaction (SRR) facilitates up to 16 electrons, which endows lithium-sulfur (Li-S) batteries with a high energy density that is twice that of typical Li-ion batteries. However, its sluggish reaction kinetics render batteries with only a low capacity and cycling life, thus remaining the main challenge to practical Li-S batteries, which require efficient electrocatalysts of balanced atom utilization and site-specific requirements toward highly efficient SRR, calling for an in-depth understanding of the atomic structural sensitivity for the catalytic active sites. Herein, we manipulated the number of Fe atoms in iron assemblies, ranging from single Fe atom to diatomic and triatomic Fe atom groupings, all embedded within a carbon matrix. This led to the revelation of a "volcano peak" correlation between SRR catalytic activity and the count of Fe atoms at the active sites. Utilizing operando X-ray absorption and X-ray diffraction spectroscopies, we observed that polysulfide adsorption-desorption and electrochemical conversion kinetics varied up and down with the incremental addition of even a single iron atom to the catalyst's metal center. Our results demonstrate that the metal center with exactly two iron atoms represents the optimal configuration, maximizing atom utility and adeptly handling the conversion of varied intermediate sulfur species, rendering the Li-S battery with a high areal capacity of 23.8 mAh cm-2 at a high sulfur loading of 21.8 mg cm-2. Our results illuminate the pivotal balance between atom utilization and site-specific requirements for optimal electrocatalytic performance in SRR and diverse electrocatalytic reactions.
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Oxygen evolution reaction (OER) plays a critical role in energy conversion technologies. Significant progress has been made in alkaline conditions. In contrast, it remains a challenge to develop stable OER electrocatalysts in acidic conditions. Herein, a new strategy is reported to stabilize single atoms integrated into cobalt oxide spinel structure with interstitial carbon (Ru0.27Co2.73O4), where the optimized Ru0.27Co2.73O4 exhibits a low overpotential of 265, 326, and 367 mV to reach a current density of 10, 50, and 100 mA cm2, respectively. More importantly, Ru0.27Co2.73O4 has long-term stability of up to 100 h, representing one of the most stable OER electrocatalysts. X-ray adsorption spectroscopy (XAS) characterization and density functional theory (DFT) calculations jointly demonstrate that the significant catalytic performance of Ru0.27Co2.73O4 is due to the synergistic effect between the Ru and Co sites and the bridging O ligands, as well as the significant reduction of the OER energy barrier. This work provides a new perspective for designing and constructing efficient non-noble metal-based electrocatalysts for water splitting.
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Quasi-2D perovskites show great potential as photovoltaic devices with superior stability, but the power conversion efficiency (PCE) is limited by poor carrier transport. Here, it is simultaneously affected the hole transport layer (HTL) and the perovskite layer by incorporating pyridine-based materials into poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) to address the key problem above in 2D perovskites. With this approach, the enhanced optoelectronic performance of the novel PEDOT:PSS is due to electron transfer between the additives and PEDOT or PSS, as well as a dissociation between PEDOT and PSS based on experimental and theoretical studies, which facilitates the charge extraction and transfer. Concurrently, in-situ X-ray scattering studies reveal that the introduction of pyridine-based molecules alters the transformation process of the perovskite intermediate phase, which leads to a preferred orientation and ordered distribution caused by the PbâN chemical bridge, achieving efficient charge transport. As a result, the pyridine-treated devices achieve an increased short-circuit current density (Jsc) and PCE of over 17%.
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Understanding the correlation between the structural evolution of electrocatalysts and their catalytic activity is both essential and challenging. In this study, we investigate this correlation in the context of the oxygen evolution reaction (OER) by examining the influence of structural disorder during and after dynamic structural evolution on the OER activity of Fe-Ni (oxy)hydroxide catalysts using operando X-ray absorption spectroscopy, alongside other experiments and theoretical calculations. The Debye-Waller factors obtained from extended X-ray absorption fine structure analyses reflect the degree of structural disorder and exhibit a robust correlation with the intrinsic OER activities of the electrocatalysts. The enhanced OER activity of in situ-generated metal (oxy)hydroxides derived from different pre-catalysts is linked to increased structural disorder, offering a promising approach for designing efficient OER electrocatalysts. This strategy may inspire similar investigations in related electrocatalytic energy-conversion systems.
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Although Ru-based materials are among the outstanding catalysts for the oxygen evolution reaction (OER), the instability issue still haunts them and impedes the widespread application. The instability of Ru-based OER catalysts is generally ascribed to the formation of soluble species through the over-oxidation of Ru and structural decomposition caused by involvement of lattice oxygen. Herein, an effective strategy of selectively activating the lattice oxygen around Ru site is proposed to improve the OER activity and stability. Our synthesized spinel-type electrocatalyst of Ru and Zn co-doped Co3O4 showed an ultralow overpotential of 172â mV at 10â mA cm-2 and a long-term stability reaching to 100â hours at 10â mA cm-2 for alkaline OER. The experimental results and theoretical simulations demonstrated that the lattice oxygen site jointly connected with the octahedral Ru and tetrahedral Zn atoms became more active than other oxygen sites near Ru atom, which further lowered the reaction energy barriers and avoided generating excessive oxygen vacancies to enhance the structural stability of Ru sites. The findings hope to provide a new perspective to improve the catalytic activity of Ru-incorporated OER catalysts and the stability of lattice-oxygen-mediated mechanism.
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Developing efficient electrocatalysts for the oxygen evolution reaction (OER) is paramount to the energy conversion and storage devices. However, the structural complexity of heterogeneous electrocatalysts makes it a great challenge to elucidate the dynamic structural evolution and OER mechanisms. Here, we develop a controllable atom-trapping strategy to extract isolated Mo atom from the amorphous MoOx -decorated CoSe2 (a-MoOx @CoSe2 ) pre-catalyst into Co-based oxyhydroxide (Mo-CoOOH) through an ultra-fast self-reconstruction process during the OER process. This conceptual advance has been validated by operando characterizations, which reveals that the initially rapid Mo leaching can expedite the dynamic reconstruction of pre-catalyst, and simultaneously trap Mo species in high oxidation state into the lattice of in situ generated CoOOH support. Impressively, the OER kinetics of CoOOH has been greatly accelerated after the reverse decoration of Mo species, in which the Mo-CoOOH affords a markedly decreased overpotential of 297â mV at the current density of 100â mA cm-2 . Density functional theory (DFT) calculations demonstrate that the Co species have been greatly activated via the effective electron coupling with Mo species in high oxidation state. These findings open new avenues toward directly synthesizing atomically dispersed electrocatalysts for high-efficiency water splitting.
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Metallic MoS2 (i.e., 1T-MoS2 ) is considered as the most promising precious-metal-free electrocatalyst with outstanding hydrogen evolution reaction (HER) performance in acidic media comparable to Pt. However, sluggish kinematics of HER in alkaline media and its inability for the oxygen evolution reaction (OER), hamper its development as bifunctional catalysts. The instability of 1T-MoS2 further impedes its applications for scaling up, calling an urgent need for simple synthesis to produce stable 1T-MoS2 . In this work, the challenge of 1T-MoS2 synthesis is first addressed using a direct one-step hydrothermal method by adopting ascorbic acid. 1T-MoS2 with flower-like morphology is obtained, and transition metals (Ni, Co, Fe) are simultaneously doped into 1T-MoS2 . Ni-1T-MoS2 achieves an enhanced bifunctional catalytic activity for both HER and OER in alkaline media, where the key role of Ni doping as single atom is proved to be essential for boosting HER/OER activity. Finally, a Ni-1T-MoS2 ||Ni-1T-MoS2 electrolyzer is fabricated, reaching a current density of 10 mA cm-2 at an applied cell voltage of only 1.54 V for overall water splitting.
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Molibdeno , Agua , Catálisis , Medios de Cultivo , Hidrógeno , OxígenoRESUMEN
The differential XAFS technique holds promise for detecting surface changes, which benefits many chemical applications. Phase-sensitive detection (PSD) analysis based on modulated excitation spectroscopy experiments is expected to obtain a high-quality difference spectrum, while the mathematical relationship and experiment parameters remain to be discussed. In this article, an approach to obtaining the difference spectrum from the PSD demodulated spectrum is described and its applicability in different experiment settings is discussed. The results indicate that the demodulated spectrum is almost equal to the difference spectrum when the modulating period is 20 times larger than the relaxation time constant. This approach was subsequently applied to an electrochemical modulation experiment and the demodulated spectrum was analyzed. A reversible lattice shrinking is observed via the fitting of demodulated spectra, which is proportional to the charge amount on the electrode. This approach could be used to quantitatively analyze the modulated excitation XAS data and holds promise for a wide range of electrochemical studies.
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The tritium recovery behaviors and related mechanisms in lithium-based breeding materials are the major concerns in fusion reactors. In the present work, the energetics of intrinsic point defects and H-related defects in Li2O has been investigated by the first-principles method. The results show that the formation energies, charge states and relative stability of the intrinsic point defects and H-related defects in Li2O under working conditions vary with the energy level. Based on the defect properties and migration process, a model of the tritium trapping and migration mechanisms in Li2O is proposed: (1) the bred tritium is first trapped by oxygen vacancies; (2) subsequently the tritium detrapped from oxygen vacancies is retrapped by lithium vacancies, forming T substituents; and (3) the T substituents hop along the Li lattice.
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Cr is a commonly existing impurity in α-Al2O3, and thus the role of Cr in the process of intrinsic point defects in α-Al2O3 has been studied based on first-principle calculations. The results show that Cr has significant influence on the formation, charge state, relative stability and equilibrium configuration of isolated intrinsic point defects in α-Al2O3, resulting in the variation of defect process. Specifically, depending on the O-condition, the possible defect types, the dominant defects and the defect formation energies will be altered in α-Al2O3 after Cr doping. Generally speaking, Cr is favorable for the formation of Schottky defects, Frenkel defects and antisite pairs, giving a different insight to the defect process in α-Al2O3.
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The interaction of helium with an α-Al2O3(0001) surface was studied by density functional theory (DFT), with consideration of the effects of He-coverage, surface defects, He-coadsorption and van der Waals interaction, respectively. Adsorption energies of helium atoms are very small as expected for a physisorbed state, varying from -20 to -5 meV, which is attributed to the small overlap between Al 3sp, O 2sp and He 1s states. A correlation is obtained for the adsorption energies and the He to nearest-neighbor Al atom distances on a clean (0001) surface. The He atom prefers to bound atop the Al site of the fourth atomic layer (Al4 hollow site), and the favorable site around an O-vacancy is atop the site of the O vacancy with less stability. The competition between O-He attraction and Al-He repulsion makes the He stable sites. As He-coverage on the surface increases, He atoms tend to form clusters, and coadsorption configuration is not solely determined by the most stable site but also by the He-He distance. The two co-adsorbed He atoms absorb on hollow sites Al4 and Al3, with a He-He distance of 2.767 Å. The OBS dispersion corrected DFT energies are 2.2-4.4 times larger than the non-corrected DFT values and He-surface distances are smaller. Finally, implications on H/He interaction within α-Al2O3 as a tritium permeation barrier are discussed.
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Little is known about hydrogen interaction with helium, an extrinsic defect, present in α-Al2O3 TPBs due to tritium decay and (n, a) reaction. Using density functional theory (DFT), the stability, structure and diffusion of He-related complexes at the different positions (VAl(3-), V, Oi(2-) and octahedral interstitial sites (OISs)) in α-Al2O3, as well as the interactions with H, are determined under H2-rich conditions. A He atom favors occupation of Al vacancies, the centers of OISs or forms a dumbbell around Al vacancies, forming Hei, HeAl(3-), Hei-HeAl(3-), [V-Hei](0) and [Oi(2-)-He](2-) complexes, among of which HeAl(3-) forms most readily. VAl(3-) can attract He to form small stable He-HeAl(3-) clusters, whereas only a He atom is trapped by an OIS, V and Oi(2-). Hei is more likely to diffuse into VAl(3-) and V than diffuse along the c-axis from one OIS to another. Hi(+) trapping into HeAl(3-) and [V-Hei](0) is thermodynamically and kinetically feasible, whereas dissociation of [Hei-H(+)](+) is more feasible. Forms of H-He complex defects in α-Al2O3 are Hei, Hi(+), [Hei-H(+)](+), [HeAl(3-)-H(+)](2-) and [HO(+)-Hei](+). HeAl(3-) and [V-Hei](0) present will increase the activation energy of H migration in α-Al2O3, which is favored for low H transport of TPBs.
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First-principles plane-wave pseudopotential calculations have been performed to study the charge states and energetics of intrinsic point defects as vacancies, interstitials and antisite atoms in α-Al2O3, and thus a new perspective on the process of intrinsic point defects has been proposed. Considering the various charge states for each intrinsic point defects, V(Al)(3-), V(O)(0), Al(i)(3+), O(i)(2-), Al(O)(3+), and O(Al)(3-), not all in their fully ionized states are found to be most stable and in pure Al2O3. From the formation energies of individual point defects, the antisite atom O(Al) will be readily formed in α-Al2O3 in an O-rich environment. By combination of charge states and formation energies, the defect types of Schottky, Al Frenkel and antisite pairs formed are found to be dependent on the O condition, and the most stable Schottky defect type is not the commonly considered {3V(O)(2+):2V(Al)(3-)}. There are two types of possible O Frenkel defects under both O conditions, yet the most stable defect is {O(i)(1+):V(O)(1-)} rather than the commonly believed {O(i)(2+):V(O)(2-)}. The bizarre configuration and the charge state of Schottky and Frenkel defects predicated in this work provide a new perspective on the process of intrinsic point defects in α-Al2O3.
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It is crucial to understand hydrogen interactions with intrinsic point defects in the hydrogen permeation barrier (HPB) of α-Al2O3, finding underlying reasons for the not-so-low H-permeability of the barrier, and thereby produce samples with tailored defects for optimal performance. Using density functional theory (DFT), the formation energies of intrinsic point defects in an α-Al2O3 lattice, including extrinsic H-related defects (H(i), V(Al)-H complex, HO(i) and H(O)), in all possible charged states, are first calculated under HPB working conditions, to determine the dominant basic defect species for hydrogen. We find that the stable forms of H-related defects in α-Al2O3 are charged H interstitials (H(i)(q), where q is the charge state of the defect) and hydrogenation of the bulk V(Al)(3-) ([V(Al)(3-)-H(+)](q)), under hydrogen-rich conditions. As the system reaches equilibrium, H in α-Al2O3 is mainly present in the H(i)(+) state, and preferentially exists in the form of [V(Al)(3-)-H(+)] and H(O)(+). Migration processes of the dominant defects are further investigated, predicting that H(i)(+) is the predominant diffusion species in α-Al2O3. [V(Al)(3-)-H(+)](2-) and H(O)(+) can release trapped hydrogen during high temperature annealing, contributing to the H-transport in α-Al2O3. The formation energy is much higher than the migration energy for H(i)(+), suggesting that the migration of H(i)(+) is the bottleneck for creating low enough H-permeation in α-Al2O3, and corresponding strategies for optimum H-suppressing performance for an α-Al2O3 HPB are proposed.
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Pressure-induced structural phase transitions play a pivotal role in unlocking novel material functionalities and facilitating innovations in materials science. Nonetheless, unveiling the mechanisms of densification, which relies heavily on precise and comprehensive structural analysis, remains a challenge. Herein, we investigated the archetypalB4 âB1 phase transition pathway in ZnO by combining x-ray absorption fine structure (XAFS) spectroscopy with machine learning. Specifically, we developed an artificial neural network (NN) to decipher the extended-XAFS spectra by reconstructing the partial radial distribution functions of Zn-O/Zn pairs. This provided us with access to the evolution of the structural statistics for all the coordination shells in condensed ZnO, enabling us to accurately track the changes in the internal structural parameteruand the anharmonic effect. We observed a clear decrease inuand an increased anharmonicity near the onset of theB4 âB1 phase transition, indicating a preference for the iT phase as the intermediate state to initiate the phase transition that can arise from the softening of shear phonon modes. This study suggests that NN-based approach can facilitate a more comprehensive and efficient interpretation of XAFS under complexin-situconditions, which paves the way for highly automated data processing pipelines for high-throughput and real-time characterizations in next-generation synchrotron photon sources.
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Hydrogen spillover widely occurs in a variety of hydrogen-involved chemical and physical processes. Recently, metal-organic frameworks have been extensively explored for their integration with noble metals toward various hydrogen-related applications, however, the hydrogen spillover in metal/MOF composite structures remains largely elusive given the challenges of collecting direct evidence due to system complexity. Here we show an elaborate strategy of modular signal amplification to decouple the behavior of hydrogen spillover in each functional regime, enabling spectroscopic visualization for interfacial dynamic processes. Remarkably, we successfully depict a full picture for dynamic replenishment of surface hydrogen atoms under interfacial hydrogen spillover by quick-scanning extended X-ray absorption fine structure, in situ surface-enhanced Raman spectroscopy and ab initio molecular dynamics calculation. With interfacial hydrogen spillover, Pd/ZIF-8 catalyst shows unique alkyne semihydrogenation activity and selectivity for alkynes molecules. The methodology demonstrated in this study also provides a basis for further exploration of interfacial species migration.
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BACKGROUND: There is growing evidence indicating the insulin-like growth factor 1 receptor (IGF-1R) plays a critical role in the progression of human colorectal carcinomas. IGF-1R is an attractive drug target for the treatment of colon cancer. Picropodophyllin (PPP), of the cyclolignan family, has recently been identified as an IGF-1R inhibitor. The aim of this study is to determine the therapeutic response and mechanism after colorectal carcinoma treatment with PPP. METHODS: Seven colorectal carcinoma cell lines were treated with PPP. Following treatment, cells were analyzed for growth by a cell viability assay, sub-G1 apoptosis by flow cytometry, caspase cleavage and activation of AKT and extracellular signal-regulated kinase (ERK) by western blot analysis. To examine the in vivo therapeutic efficacy of PPP, mice implanted with human colorectal carcinoma xenografts underwent PPP treatment. RESULTS: PPP treatment blocked the phosphorylation of IGF-1R, AKT and ERK and inhibited the growth of TP53 wild-type but not mutated colorectal carcinoma cell lines. The treatment of PPP also induced apoptosis in TP53 wild-type cells as evident by the presence of sub-G1 cells and the cleavage of caspase-9, caspase-3, DNA fragmentation factor-45 (DFF45), poly (ADP-ribose) polymerase (PARP), and X-linked inhibitor of apoptosis protein (XIAP). The loss of BAD phosphorylation in the PPP-treated TP53 wild type cells further suggested that the treatment induced apoptosis through the BAD-mediated mitochondrial pathway. In contrast, PPP treatment failed to induce the phosphorylation of AKT and ERK and caspase cleavage in TP53 mutated colorectal carcinoma cell lines. Finally, PPP treatment suppressed the growth of xenografts derived from TP53 wild type but not mutated colorectal carcinoma cells. CONCLUSIONS: We report the association of TP53 mutations with the resistance of treatment of colorectal carcinoma cells in culture and in a xenograft mouse model with the IGF-1R inhibitor PPP. TP53 mutations often occur in colorectal carcinomas and could be used as a biomarker to predict the resistance of colorectal carcinomas to the treatment by this IGF-1R inhibitor.
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Neoplasias Colorrectales/genética , Neoplasias Colorrectales/metabolismo , Resistencia a Antineoplásicos/genética , Mutación , Podofilotoxina/análogos & derivados , Receptor IGF Tipo 1/antagonistas & inhibidores , Proteína p53 Supresora de Tumor/genética , Animales , Apoptosis/efectos de los fármacos , Apoptosis/genética , Línea Celular Tumoral , Neoplasias Colorrectales/patología , Modelos Animales de Enfermedad , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Humanos , Ratones , Fosforilación/efectos de los fármacos , Podofilotoxina/farmacología , Proteínas Proto-Oncogénicas c-akt/metabolismo , Receptor IGF Tipo 1/metabolismo , Carga Tumoral/efectos de los fármacos , Carga Tumoral/genética , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
The low-rate capability and fast capacity decaying of the molybdenum dioxide anode material have been a bottleneck for lithium-ion batteries (LIBs) due to low carrier transport, drastic volume expansion and inferior reversibility. Furthermore, the lithium-storage mechanism is still controversial at present. Herein, we fabricate a new kind of MoO2 nanoparticles with nitrogen-doped multiwalled carbon nanotubes (MoO2/N-MCNTs) as anode for LIBs. The strong chemical bonding (MoOC) endows MoO2/N-MCNTs a strong metal oxide-support interaction (SMSI), rendering electron/ion transfer and facilitate significant Li+ intercalation pseudocapacitance, which is evidenced by both theoretical computation and detailed experiments. Thus, the MoO2/N-MCNTs exhibits high-rate performance (523.7 mAh/g at 3000 mA g-1) and long durability (507.8 mAh/g at 1000 mA g-1 after 500 cycles). Furthermore, pouch-type full cell composed of MoO2/N-MCNTs anodes and commercial LiNi0.6Co0.2Mn0.2O2 (NCM622) cathodes demonstrate impressive rate performance and cyclic life, which displays an unparalleled energy density of 553.0 Wh kg-1. Ex-situ X-ray absorption spectroscopy (XAS) indicates the enhanced lithium-storage mechanism is originated from a partially irreversible phase transition from Li0.98MoO2 to Li2MoO4 via delithiation. This work not only provides fresh insights into the enhanced lithium-storage mechanism but also proposes new design principles toward efficient LIBs.
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Hard carbons (HCs) have gained much attention for next-generation high energy density lithium-ion battery (LIB) anode candidates. However, voltage hysteresis, low rate capability, and large initial irreversible capacity severely affect their booming application. Herein, a general strategy is reported to fabricate heterogeneous atom (N/S/P/Se)-doped HC anodes with superb rate capability and cyclic stability based on a three-dimensional (3D) framework and a hierarchical porous structure. The obtained N-doped hard carbon (NHC) exhibits an excellent rate capability of 315 mA h g-1 at 10.0 A g-1 and a long-term cyclic stability of 90.3% capacity retention after 1000 cycles at 3 A g-1. Moreover, the as-constructed pouch cell delivers a high energy density of 483.8 W h kg-1 and fast charging capability. The underlying mechanisms of lithium storage are illustrated by electrochemical kinetic analysis and theoretical calculations. It is demonstrated that heteroatom doping imposes significant effects on adsorption and diffusion for Li+. The versatile strategy in this work opens an avenue for rational design of advanced carbonaceous materials with high performance for LIB applications.