Metal vacancy-enriched layered double hydroxide for biomass molecule electrooxidation coupled with hydrogen production.

The electrochemical oxidation of biomass molecules coupling with hydrogen production is a promising strategy to obtain both green energy and value-added chemicals; however, this strategy is limited by the competing oxygen evolution reactions and high energy consumption. Herein, we report a hierarchical CoNi layered double hydroxides (LDHs) electrocatalyst with abundant Ni vacancies for the efficient anodic oxidation of 5-hydroxymethylfurfural (HMF) and cathodic hydrogen evolution. The unique hierarchical nanosheet structure and Ni vacancies provide outstanding activity and selectivity toward several biomass molecules because of the finely regulated electronic structure and highly-exposed active sites. In particular, a high faradaic efficiency (FE) at a high current density (99% at 100 mA cm-2) is achieved for HMF oxidation, and a two-electrode electrolyzer is assembled based on the Ni vacancies-enriched LDH, which realized a continuous synthesis of highly-pure 2,5-furandicarboxylic acid products with high yields (95%) and FE (90%).

Active hydrogen boosts electrochemical nitrate reduction to ammonia.

Electrochemical nitrate reduction to ammonia is a promising alternative strategy to the traditional Haber-Bosch process but suffers from a low Faradaic efficiency and limited ammonia yield due to the sluggish multi-electron/proton-involved steps. Herein, we report a typical hollow cobalt phosphide nanosphere electrocatalyst assembled on a self-supported carbon nanosheet array synthesized with a confinement strategy that exhibits an extremely high ammonia yield rate of 8.47 mmol h-1 cm-2 through nitrate reduction reaction, which is highly superior to previously reported values to our knowledge. In situ experiments and theoretical investigations reveal that the dynamic equilibrium between the generation of active hydrogen on cobalt phosphide and its timely consumption by nitrogen intermediates leads to a superior ammonia yield with a high Faradaic efficiency. This unique insight based on active hydrogen equilibrium provides new opportunities for large-scale ammonia production through electrochemical techniques and can be further used for carbon dioxide capture.

Flame-Assisted Synthesis of O-Coordinated Single-Atom Catalysts for Efficient Electrocatalytic Oxygen Reduction and Hydrogen Evolution Reaction.

Single-atom catalysts (SACs) exhibit intriguing performance in electrocatalysis owing to their maximized atom utilizations and unique electronic structures, but effective anchoring metal atoms with defined coordination structure on hierarchical integrated electrode remain a challenge. Herein, a fast and facial flame-assisted strategy is developed to construct oxygen-coordinated SACs on integrated carbon nanotube (CNT) arrays with promising applications in electrocatalysis. Density functional theory calculations show that oxygen in carbon substrate imparts homogeneous sites for the efficient anchoring of metal atoms, thereby enabling SACs to disperse uniformly and firmly and thus bringing optimized activities. Moreover, the integrated CNT array with abundant oxygen-containing groups is constructed and has been used as an efficient matrix for anchoring metal atoms (CNT-O@M) via a flame-assisted method. The as-prepared CNT-O@M (M = Co and Pt as typical examples) shows excellent activities in electrocatalytic oxygen reduction reaction and hydrogen evolution reaction with utilization of active site as high as 75.7%, which is superior to the reported SACs. Particularly, the performance of CNT-O@M can maintain stably under various harsh conditions, showing a promising prospect in the long-time applications. The methodology and concept proposed in this work could be extended to the synthesis of a variety of integrated SACs for efficient electrocatalysis.

NiSn Atomic Pair on an Integrated Electrode for Synergistic Electrocatalytic CO2 Reduction.

The development of efficient electrocatalysts for the CO2 reduction reaction (CO2 RR) remains a challenge. Demonstrated here is a NiSn atomic-pair electrocatalyst (NiSn-APC) on a hierarchical integrated electrode, which exhibits a synergistic effect in simultaneously promoting the activity and selectivity of the CO2 RR to formate. The NiSn atomic pair consists of adjacent Ni and Sn, each coordinated with four nitrogen atoms (N4 -Ni-Sn-N4 ). The as-prepared NiSn-APC displays exceptional activity for the CO2 RR to formate with a turnover frequency of 4752 h-1 , a formate productivity of 36.7 mol h-1 gSn -1 and an utilization degree of active sites (57.9 %), which are superior to previously reported single-atomic catalysts. Both experimental data and density-functional theory calculations verify the electron redistribution of Sn imposed by adjacent Ni, which reduces the energy barrier of the *OCHO intermediate and makes this potential-determining step thermodynamically spontaneous. This synergistic catalysis provides a successful paradigm for rational design and preparation of atomic-pair electrocatalysts with enhanced performance.

Coordinating Adsorption and Catalytic Activity of Polysulfide on Hierarchical Integrated Electrodes for High-Performance Flexible Li-S Batteries.

Lithium-sulfur (Li-S) batteries have been known to be a promising substitute because of their much higher theoretical energy density than that of traditional Li-ion batteries. However, the low utilization of sulfur caused by the poor conductivity of sulfur and shuttle of lithium polysulfides (LiPSs) severely restrict the commercial application of Li-S batteries, especially in flexible wearable devices. Herein, a hierarchical nitrogen-doped carbon nanotube (NCNT)@Co-Co3O4 nanowire array (NWA)-integrated electrode was developed based on the rational design of density functional theory calculations, which shows simultaneous confinement adsorption and catalysis conversion of LiPSs. In situ Raman spectra further proved that the NCNT@Co-Co3O4 NWAs exhibit sufficient adsorption capacity and high catalytic conversion of LiPSs. As a result, the NCNT@Co-Co3O4@S electrode exhibited the desirable specific capacity and excellent cyclic stability at both low and high sulfur loadings. Moreover, pouch cells with the NCNT@Co-Co3O4@S cathode show higher capacity under flat or bending states and longer cycle stability than that of the reported results. This work provides a new approach for the development of high-performance Li-S batteries toward future wearable electronics.

Hierarchical Carbon Microtube@Nanotube Core-Shell Structure for High-Performance Oxygen Electrocatalysis and Zn-Air Battery.

Zinc-air batteries (ZABs) hold tremendous promise for clean and efficient energy storage with the merits of high theoretical energy density and environmental friendliness. However, the performance of practical ZABs is still unsatisfactory because of the inevitably decreased activity of electrocatalysts when assembly into a thick electrode with high mass loading. Herein, we report a hierarchical electrocatalyst based on carbon microtube@nanotube core-shell nanostructure (CMT@CNT), which demonstrates superior electrocatalytic activity for oxygen reduction reaction and oxygen evolution reaction with a small potential gap of 0.678 V. Remarkably, when being employed as air-cathode in ZAB, the CMT@CNT presents an excellent performance with a high power density (160.6 mW cm-2), specific capacity (781.7 mAhg Zn -1 ) as well as long cycle stability (117 h, 351 cycles). Moreover, the ZAB performance of CMT@CNT is maintained well even under high mass loading (3 mg cm-2, three times as much as traditional usage), which could afford high power density and energy density for advanced electronic equipment. We believe that this work is promising for the rational design of hierarchical structured electrocatalysts for advanced metal-air batteries.

A sensing element based on a bent and elongated grooved polymer optical fiber.

An experimental and numerical investigation is performed into the power loss induced in grooved polymer optical fibers (POFs) subjected to combined bending and elongation deformations. The power loss is examined as a function of both the groove depth and the bend radius. An elastic-plastic three-dimensional finite element model is constructed to simulate the deformation in the grooved region of the deformed specimens. The results indicate that the power loss increases significantly with an increasing bending displacement or groove depth. Specifically, the power loss increases to as much as 12% given a groove depth of 1.1 mm and a bending displacement of 10 mm. Based on the experimental results, an empirical expression is formulated to relate the power loss with the bending displacement for a given groove depth. It is shown that the difference between the estimated power loss and the actual power loss is less than 2%.

[The relations between dental fluorosis and economic status in Shuicheng, a fluorosis-endemic County in Guizhou province].

OBJECTIVE: To discuss the relations of dental fluorosis and the social economic status in fluorosis-stricken villages where drying the corn by burning coal was prevail. METHODS: A total of 6 fluorosis-endemic villages and one non-endemic village were involved in the study. The general fluorine intake and the concentrations of fluorine in corn, in the pupils' were tested. Dental fluorosis among the pupils was also examen. A individual interview or household questionnaire survey was conducted to probe the economic condition and staple food structure in 600 adults. RESULTS: The fluorosis prevalence was lower in the villages of transportation convenience, higher income, less coal-dried corn intake. There was a declining trend of dental fluorosis in the corresponding age groups (r: 0.912, 0.916; P < 0.05); There was no significant changes in age-specified dental fluorosis in the low income villages. The correlation (r) of corn fluorine concentration and student's age-specified dental fluorosis prevalence and disparity was 0.755 - 0.980 (P < 0.05) and 0.302 - 0.811; The urine fluorine concentrations were 0.811 and 0.915 (P < 0.05). It was assumed that there was a negative correlation between family cash income and the dental fluorosis. CONCLUSIONS: The corn fluorine concentration is closely related to age-specified dental fluorosis. With the economic improvement, taking less coal-burned corn is the one of major factors in reducing the of dental fluorosis in these areas.