Exceptional electrostatic phenomenon in ultrathin nanorods: the terminal σ‑hole

An in-depth understanding of the physicochemical properties of nanorods during the initial growth process has a profound impact on the rational design of high-performance nanorods catalysts. Herein, we conducted a systematic DFT study on the transition metal Co, Ni and alloyed nanoclusters/rods systems to simulate an atomic process from the initial nanoclusters growth to nanorods/wires. We found that the highly active sites of nanorods depend on an interesting electrostatic phenomenon. The surface electrostatic potential analysis shows that all nanoclusters and nanorods structures have formed σ-hole. Unlike nanoclusters, the σ-hole only appears at terminal sites in nanorods, called terminal σ-hole. The elemental composition in nanorods has a certain influence on the maximal surface electrostatic potential (VS,max) i.e., terminal σ-hole. Interestingly, we found that the terminal σ-hole formed in nanorods is generally higher in magnitude than smaller nanoclusters. First-principle calculations show that terminal σ-hole is closely related to the physicochemical activities of nanorods. For example, the work function of the directions forming terminal σ-hole is smaller than other directions. More interestingly, we found that in almost all nanorods, compared with other atoms, the d-orbital of the atoms forming terminal σ‑hole shifts close to the Fermi level and exhibits a shallower d-band center, showing higher chemical activity. In short, it is the first time that we discovered terminal σ-hole in nanorods, explained the theoretical basis of terminal σ-hole in nanorod systems, and provided theoretical guidance for the rational design of high-performance nanorods catalysts

Morphology, crystal structure and electronic state one-step co-tuning strategy towards developing superior perovskite electrocatalysts for water oxidation

Here, we use an electrospinning method to control the crystal structure, electronic structure and microstructure of catalysts simultaneously. The electrospun perovskite SmBaSrCoO (SBSC) possesses not only a large specific surface area but also an optimized crystal structure and electronic state, showing an excellent OER activity and durability

Postsynthesis oxygen nonstoichiometric regulation: a new strategy for performance enhancement of perovskites in advanced oxidation

Due to their flexible physiochemical properties and defect-rich structures, perovskite oxides have drawn increasing attention as efficient heterogeneous catalysts for peroxymonosulfate (PMS) activation in wastewater remediation. Herein, we reported a new nondoping strategy of postsynthesis oxygen nonstoichiometric regulation for LaMnO (LMO) at various oxygen partial pressures and calcination temperatures, named as LMO-P-T, to control its interstitial oxygen defect content, resulting in the enhancement of its catalytic activity and stability for degradation of rhodamine B (RhB). The defect structure, charge-transfer capacity, and resistance against metal leaching of LMO were thus improved. Specifically, LMO-5 bar-600 with the highest defect content presented excellent Fenton-like activity, 1.76 times that of LMO. Favorable singlet oxygen was confirmed as the dominant reactive species in the LMO-5 bar-600/PMS system, and the obtained catalysts showed satisfactory activity in a wide initial pH range. This work might provide a universal approach in designing metal oxides catalysts for efficient advanced oxidation

High‐performance platinum‐perovskite composite bifunctional oxygen electrocatalyst for rechargeable Zn–air battery

Constructing highly active electrocatalysts with superior stability at low cost is a must, and vital for the large-scale application of rechargeable Zn-air batteries. Herein, a series of bifunctional composites with excellent electrochemical activity and durability based on platinum with the perovskite Sr(Co0.8Fe0.2)(0.95)P0.05O3-delta (SCFP) are synthesized via a facile but effective strategy. The optimal sample Pt-SCFP/C-12 exhibits outstanding bifunctional activity for the oxygen reduction reaction and oxygen evolution reaction with a potential difference of 0.73 V. Remarkably, the Zn-air battery based on this catalyst shows an initial discharge and charge potential of 1.25 and 2.02 V at 5 mA cm(-2), accompanied by an excellent cycling stability. X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure experiments demonstrate that the superior performance is due to the strong electronic interaction between Pt and SCFP that arises as a result of the rapid electron transfer via the Pt-O-Co bonds as well as the higher concentration of surface oxygen vacancies. Meanwhile, the spillover effect between Pt and SCFP also can increase more active sites via lowering energy barrier and change the rate-determining step on the catalysts surface. Undoubtedly, this work provides an efficient approach for developing low-cost and highly active catalysts for wider application of electrochemical energy devices

Manipulating cation nonstoichiometry towards developing better electrolyte for self-humidified dual-ion solid oxide fuel cells

Dual-ion (oxygen ion and proton) conducting electrolyte BaZrCeYYbO (BZCYYb) is one of the most commonly used electrolyte materials for proton conducting fuel cells (PCFCs). Here, we improve conducting property and performance of BZCYYb electrolyte through simply introducing B-site cation deficiency. Dual-ion conductivities for Ba(ZrCeYYb)O (BZCYYb-0.95) electrolyte are improved to a large extent as 2.5 times protonic conductivity (4.6 × 10 S cm at 700 °C) and 6.3 times oxygen ionic conductivity (1.2 × 10 S cm at 900 °C) compared to BZCYYb electrolyte. Low-temperature (1350 °C) sinterability of BZCYYb-0.95 is achieved for the higher concentration of defect compared to the original material (BZCYYb, 1500 °C). Meanwhile, a cell with the BZCYYb-0.95 electrolyte illustrates prominent power density of 794 mW cm at 650 °C, superior to the cell with BZCYYb (643 mW cm) at the same condition. The collaborative diffusions of dual-ion via two different conducting mechanisms enhance the cell performance with BZCYYb-0.95 electrolyte. The cell voltage and power density actually have no observable performance degradation during the course of the 300-h test. Therefore, it indicates the dual-ion diffusions of BZCYYb-0.95 electrolyte as the promising future for practical application

Fibroblasts in metastatic lymph nodes confer cisplatin resistance to ESCC tumor cells via PI16

Abstract Although many studies have compared tumor fibroblasts (T-Fbs) and nontumor fibroblasts (N-Fbs), less is understood about the stromal contribution of metastatic lymph node fibroblasts (LN-Fbs) to the evolving microenvironment. Here, we explored the characteristics of LN-Fbs in esophageal squamous cell carcinoma (ESCC) and the interactions between fibroblasts and ESCC tumor cells in metastatic lymph nodes. Fibroblasts were isolated from tumor, nontumor and metastatic lymph node tissues from different patients with ESCC. Transcriptome sequencing was performed on the fibroblasts. Tumor growth and drug-resistance assays were carried out, and characteristics of T-Fbs, N-Fbs and LN-Fbs were determined. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to assay the culture medium of fibroblasts. The results demonstrated that fibroblasts derived from different tissues had different characteristics. Coculture with LN-Fbs conditioned medium inhibited ESCC tumor cell growth and induced chemoresistance in ESCC cells. LN-Fbs induced chemoresistance to cisplatin in ESCC cells by secreting PI16. Coculture with LN-Fbs conditioned medium decreased cisplatin-induced apoptosis in ESCC cells by regulating the p38 and JNK cell signaling pathways. Survival analyses showed that patients with high PI16 expression in Fbs of lymph nodes exhibited worse overall survival. We also examined PI16 expression in interstitial tissues in ESCC tumor samples of patients receiving platinum-based therapy postsurgery and found that high PI16 expression in tumor interstitial tissues was an independent prognostic factor for ESCC patients. In addition, an in vivo assay demonstrated that PI16 knockdown increased the sensitivity of ESCC cells to cisplatin. Our results suggest that fibroblasts in metastatic lymph nodes decrease apoptosis of ESCC cells via PI16, thereby providing a cisplatin-resistance niche and supporting ESCC tumor cells to survive in metastatic lymph nodes. PI16 is also a potential target for effectively blocking the chemoresistance niche signaling circuit in response to cisplatin

Theoretical Design of Core–Shell 3d-Metal Nanoclusters for Efficient Hydrogen-Evolving Reaction

Co- and Ni-based materials are promising catalysts for the hydrogen evolution reaction (HER) but usually transform into active Co/Ni metal nanoclusters during reductive HER processes, making the rational design of initial states for Co/Ni metal nanoclusters critical. However, the optimal states of Co/Ni metal nanoclusters for the HER are still unclear. Herein, we design 16 pure/alloyed core–shell Co/Ni-metal nanoclusters and give systematic insights into their HER performance and catalysis mechanism, from thermodynamics to kinetics. We find that the HER performance significantly depends on the geometric structures of the Co–Ni metal nanoclusters. Compared to other sized nanoclusters, Co13@Ni20 and Ni@Co12@Ni20 exhibit the optimum HER performance with proton adsorption free energies close to zero, which could be attributed to their special and favorable negative surface electronic structures to adsorb the key protons. Further investigations show that they also exhibit good stability in both thermodynamics and kinetics. Furthermore, we apply metadynamics to directly map the 2D free energy reaction surface and HER pathways, ultimately uncovering the detailed HER mechanism of the best-performing Co13@Ni20 catalyst. Our work helps us understand the optimal states and the catalytic mechanism of active Co/Ni metal nanoclusters for HER

Monoclinic SrIrO3: an easily synthesized conductive perovskite oxide with outstanding performance for overall water splitting in alkaline solution

Fabricating efficient bifunctional catalysts for both hydrogen/oxygen evolution reactions (HER/OER) in an easy and mass-productive way is highly attractive for alkaline water electrolyzers. Perovskite oxides show compositional flexibility and high property tunability, while poor electrical conductivity and relatively low HER activity hamper their application in overall water splitting. Here, a conductive monoclinic SrIrO3 perovskite is developed as an excellent alkaline electrocatalyst with bifunctionality which can be easily synthesized under normal conditions. Toward the HER, it experiences progressive surface self-reconstruction during the activation process because of lattice Sr2+ leaching, eventually leading to a remarkable apparent activity with an approximately 11-fold enhancement at 200 mV overpotential relative to the fresh sample. Experimental and theoretical evidence reveals that etching of lattice Sr2+ in relatively less-stable SrIrO3 compared to IrO2 is crucial for triggering this self-reconstruction. Toward the OER, no obvious surface reconstruction occurs, and an overpotential of only 300 mV is required to realize 10 mA cmgeo–2, significantly lower than that for most perovskites reported previously (340–450 mV). The activated SrIrO3 from HER operation can be used alternatively as an OER electrocatalyst with further improved performance. A SrIrO3-based two-electrode water-splitting cell shows exceptional performance, that is, 1.59 V@10 mA cmgeo–2 with negligible performance degradation over 10 h

Super-exchange interaction induced overall optimization in ferromagnetic perovskite oxides enables ultrafast water oxidation

Oxygen evolution reaction (OER) is crucial in many renewable electrochemical technologies including regenerative fuel cells, rechargeable metal–air batteries, and water splitting. It is found that abundant active sites with favorable electronic structure and high electrical conductivity play a dominant role in achieving high electrocatalytic efficiency of perovskites, thus efficient strategies need to be designed to generate multiple beneficial factors for OER. Here, highlighted is an unusual super-exchange effect in ferromagnetic perovskite oxide to optimize active sites and enhance electrical conductivity. A systematic exploration about the composition-dependent OER activity in SrCo Ru O (denoted as SCRx) (x = 0.0–1.0) perovskite is displayed with special attention on the role of super-exchange interaction between high spin (HS) Co and Ru ions. Induced by the unique Co–O–Ru super-exchange interactions, the SCR0.1 is endowed with abundant OER active species including Co/Co, Ru, and O /O, high electrical conductivity, and metal–oxygen covalency. Benefiting from these advantageous factors for OER electrocatalysis, the optimized SCR0.1 catalyst exhibits a remarkable activity with a low overpotential of 360 mV at 10 mA cm, which exceeds the benchmark RuO and most well-known perovskite oxides reported so far, while maintaining excellent durability. This work provides a new pathway in developing perovskite catalysts for efficient catalysis

Fast cation exchange of layered sodium transition metal oxides for boosting oxygen evolution activity and enhancing durability

Cost-effective electrocatalysts with high activity and long durability for the oxygen evolution reaction (OER) are key to water splitting and rechargeable metal-air batteries. Here, we report the development of a superior OER electrocatalyst with outstanding activity, favorable durability, and stable particulate morphology based on an ex situ ultra-fast cation exchange strategy that can result in fine tuning of the atom arrangement inside the oxide lattice, thus optimizing the electrocatalytic performance. O3-phase NaCoFeO (O-NCF) is selected as the starting material, and the sodium in the oxide lattice is rapidly exchanged (several minutes) with hydronium ions (HO) in an acidic solution. The as-derived structure fine-tuned sample displays excellent OER performances in alkaline media with an ultra-low overpotential of only 234 mV at 10 mA cm in oxide-based electrocatalysts and an ultra-small Tafel slope of 34 mV dec. The exchange of HO with Na does not affect the oxidation state of cobalt and iron cations inside the oxide lattice, while protons in the inserted HO promote the formation of the hydroxyl group to improve activity. As a general strategy, such cation exchange strategy can also be applied to many other layered sodium transition metal oxides