Crystalline-dependent surface reconstruction at low applied potential region for enhanced oxygen evolution reaction.

Alkaline water electrolysis is apreferred technology for large-scale green hydrogen production. For most active transition metal-based catalysts during anodic oxygen evolution reaction (OER), the atomic structure of the anodic catalysts' surface often undergoes reconstruction to optimize the reaction path and enhance their catalytic activity. The design and maintenance of highly active sites during this reconstruction process remain critical and challenging for most OER catalysts. In this study, we explored the effects of crystal structures in pre-catalysts on surface reconstruction at low applied potential. Through experimental observation and theoretical calculation, we found out that catalysts with specific crystal structures exhibit superior surface remodeling ability, which enables them to better adapt to the conditions of the oxygen evolution reaction and achieve efficient catalysis. The discharge process enables the formation of abundant phosphorus vacancies on the surface, which in turn affects the efficiency of the entire oxygen evolution reaction. The optimized crystal structure of the catalyst results in an increase as high as 58.5 mA/cm2 for Ni5P4, which is twice as high as that observed for Ni2P. These results provide essential theoretical foundations and technical guidance for designing more efficient catalysts for oxygen evolution reactions.

Cations induced in situ electrochemical amorphization for enhanced oxygen evolution reaction.

Surface reconstruction is widely existed on the surface of transition metal-based catalysts under operando oxygen evolution reaction (OER) condition. The design and optimize the reconstruction process are essential to achieve high electrochemical active surface and thus facilitate the reaction kinetics, whereas still challenge. Herein, we exploit electrolyte engineering to regulate reconstruction on the surface of Fe2O3 catalysts under operando OER conditions. The intentional added cations in electrolyte can participate the reconstruction process and realize a desirable crystalline to amorphous structure conversion, contributing abundant well-defined active sites. Spectroscopic measurements and density functional theory calculation provide insight into the underlying role of amorphous structure for electron transfer, mass transport, and intermediate adsorption. With the assistant of Co2+ cations, the enhanced current density as large as 17.9 % can be achieved at 2.32 V (vs RHE). The present results indicate the potential of electrolyte engineering for regulating the reconstruction process and provide a generalized in-situ strategy for advanced catalysts design.

Symmetrical-waveform alternating current-promoted NiOxHy electrocatalysis for the oxygen evolution reaction.

Here we describe a symmetrical waveform alternating current strategy that provides a solution for obtaining gradient oxygen vacancies (VO) in situ. The unique gradient VO provides multiple stairs to reduce the reaction kinetics and thus contributes to a total increase of up to 84.7% in current density.

Crystalline-Dependent Discharge Process of Locally Enhanced Electrooxidation Activity on Ni2P.

The state-of-the-art transition-based electrocatalysts in alkaline media generally suffer from unavoidable surface reconstruction during oxygen evolution reaction measurements, leading to the collapse and loss of the crystalline matrix. Low potential discharge offers a gentle way for surface reconstruction and thus realizes the manipulation of the real active site. Nevertheless, the absence of a fundamental understanding focus on this discharge region renders the functional phase, either the crystalline or amorphous matrix, for the controllable reconstruction still undecidable. Herein, we report a scenario to employ different crystalline matrices as electrocatalysts for discharge region reconstruction. The representative low crystalline Ni2P (LC-Ni2P) possesses a relatively weak surface structure compared with highly crystalline or amorphous Ni2P (HC-Ni2P or A-Ni2P), which contributes abundant oxygen vacancies after the discharge process. The fast discharge behavior of LC-Ni2P leads to the uniform distribution of these vacancies and thus endows the inner interface with reactant activating functionality. A high increase in current density of 36.7% is achieved at 2.32 V (vs RHE) for the LC-Ni2P electrode. The understanding of the discharge behavior in this study, on different crystalline matrices, presents insights into the establishment of controllable surface reconstruction for an effective oxygen evolution reaction.

Indium doped bismuth subcarbonate nanosheets for efficient electrochemical reduction of carbon dioxide to formate in a wide potential window.

Electrochemical carbon dioxide (CO2) reduction reaction (E-CO2RR) to formate with high selectivity driven by renewable electricity is one of the most promising routes to carbon neutrality. Herein, we developed a novel indium (In)-doped bismuth subcarbonate (BOC) nanosheets (BOC-In-x NSs) through transformation of In-doped bismuth (Bi) nanoblocks (Bi-In-x NBs). The BOC-In-0.1 NSs achieved a maximum Faraday efficiency of formate (FEformate) nearly 100% with high stability (22 h) and an appreciable average FEformate of 93.5% in a wide potential window of 450 mV. The experimental and theoretical calculations indicate that the incorporation of In into BOC nanosheets enhanced the adsorption of CO2 and the intermediates during the process of E-CO2RR, and reduced the energy barrier for the formation of formate.

Rutin promotes white adipose tissue "browning" and brown adipose tissue activation partially through the calmodulin-dependent protein kinase kinase ß/AMP-activated protein kinase pathway.

Promoting white adipose tissue (WAT) "browning" and brown adipose tissue (BAT) activation could contribute to increasing energy expenditure. We explored the mechanisms by which the natural compound rutin induced adipose tissue differentiation and ameliorated obesity in vivo and in vitro. 3T3-L1 preadipocytes were cultured in adipogenic differentiation media with/out rutin. Male C57BL/6 mice (n = 6) were fed a high-fat diet (HFD) for 12 weeks with/out rutin. In HFD-fed mice, rutin treatment significantly inhibited weight gain, improved the metabolic profile of plasma samples, decreased the weights of epididymal WAT (eWAT), inguina WAT (iWAT), and liver, and adipocyte size. Furthermore, rutin also increased the expression of uncoupling protein 1 (Ucp-1) and other thermogenic markers in the WAT and BAT. In 3T3-L1 cells, rutin effectively reduced the formation of lipid droplets, stimulated the expression of thermogenic markers, and reduced the expression of adipogenic genes. Additionally, rutin markedly upregulated the AMP-activated protein kinase (AMPK) pathway, and these effects were diminished by treatment with the AMPK inhibitor compound C (CC). Pretreatment with the calmodulin-dependent protein kinase kinase ß (CaMKKß) inhibitor STO-609 blocked the induction of thermogenic markers in 3T3-L1 cells by rutin. Our results indicated that rutin increased energy consumption, induced WAT "browning" and BAT activation, and thus was a promising target for the development of new therapeutic approaches to improve adipose tissue energy metabolism.

Highly efficient electrochemical carbon dioxide reduction to syngas with tunable ratios over pyridinic- nitrogen rich ultrathin carbon nanosheets.

Developing nonmetallic carbon-based electrocatalysts that are affordable and have high activity and stability for carbon dioxide (CO2) reduction to syngas is a new and challenging strategy for solving the energy crisis. Here, we prepared a highly active ultrathin nitrogen (N)-doped carbon nanosheet (UNCN) electrocatalyst. By tuning the applied potential of the UNCN-900 (900 represents the carbonization temperature) electrode, we could tune the H2/CO ratio in clean syngas within a wide range with extra-high Faradic efficiency (FE). The maximum FECO reached 91%, which represented the highest value among the reported nonmetallic carbon-based electrocatalysts for CO2 reduction to syngas. According to the results of experiments and density functional theory calculations, we proved that pyridinic-N in UNCNs-900 is the active site of the CO2 reduction reaction (CO2RR) and that graphitic-N may be the active site for the hydrogen evolution reaction. These results provide a useful case for electrochemical CO2 reduction to syngas with a tunable H2/CO ratio using nonmetallic carbon-based electrocatalysts.

Discharge-Induced Enhancement of the Oxygen Evolution Reaction.

The fundamental understanding of the surface reconstruction induced by the applied potential is of great significance for enhancing the oxygen evolution reaction (OER). Here, we show that a previously overlooked discharge current in the low applied potential region also leads to in situ electrochemical activation of a nitrogen-doped nickel oxyhydroxide surface. We exploit the fact that doping of heteroatoms weakens the surface structure, and hence, a weak discharge current originating from the capacitive nature of nickel oxyhydroxide has a strong structure-reforming ability to promote the formation of nitrogen and oxygen vacancies. The current density at 1.4 V (vs. Hg/HgO) can dramatically increase by as much as 31.3 % after discharge in the low applied potential region. This work provides insight into in situ enhancement of the OER and suggests that the low applied potential region must be a primary consideration in evaluating the origin of the activity of electrocatalysts.

Phosphorus doped nickel selenide for full device water splitting.

The lack of high active and stable electrocatalysts has impeded the development of electrochemical water splitting device, which is promising technique for renewable energy conversion system. Here, we report a one-step protocol to synthesize P doped NiSe2 (P-NiSe2) by selenylation process derived from nickel foam with assistant of NaH2PO2 and Se powder. The P-NiSe2 could be directly used as working electrode and shows the superior electrochemical activity, offering current density of 10 mA cm-2 with overpotential of 270 mV for OER and 71 mV for HER. The enhanced electrochemical activity can be ascribed to the P atom doping. The P atom doping leads to the high valence state of Ni active sites, which have high catalytic ability towards OER. Moreover, the P doping makes the d-band center of Ni atoms in P-NiSe2 move close to Fermi level, facilitating the HER kinetics with respect to proton adsorption and hydrogen desorption. When employed P-NiSe2 as both anodic and cathodic electrode in alkaline water electrolyzer, a current density of 10 mA cm-2 can be achieved at 1.58 V. Our work highlights the importance of P doping in determining the surface electron configuration for full device water splitting and the facile synthesis protocol would be promising for realistic applications.

Self-supported nickel sulfide derived from nickel foam for hydrogen evolution and oxygen evolution reaction: effect of crystal phase switching.

Designing and fabricating economically viable, high active and stable electrocatalysts play an important role for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Crystal phase is the crucial factor that governs the electrochemical property and electrocatalytic reaction pathways. Here, a one-step nickel foam derived sulfidation method was presented to synthesize self-supported NiS2 and Ni3S2. The crystal phase-dependent chemical properties related to electrocatalytic behavior were evaluated by a series of advanced characterization and density functional theory calculations. Overall, the self-supported Ni3S2 shows high electrochemical activity towards both HER and OER in alkaline conditions, which afford the current density of 10 mA cm-2 with overpotentials of 245 mV for OER and 123 mV for HER, respectively. When employed the self-supported Ni3S2 as the bifunctional electrocatalysts for overall water splitting, the entire device provides the current density of 10 mA cm-2 at 1.61 V. These results indicate that the electrocatalytic properties can be exert greater improved by controlling the crystal phase, offering the prospect for advanced materials design and development.

Ink-Assisted Synthetic Strategy for Stable and Advanced Composite Electrocatalysts with Single Fe Sites.

The oxygen evolution reaction is critical to the efficiency of many energy technologies that store renewable electricity in chemical form. However, the rational design of high-performance and stable catalysts to drive this reaction remains a formidable challenge. Here, a facile ink-assisted strategy to construct a series of stable and advanced composite electrocatalysts with single Fe sites for permitting seriously improved performance characteristics is reported. As revealed by a suit of characterization techniques and theoretical methods, the improved electrocatalytic performance and stability can be attributed to the unique coordination states of Fe in the form of distorted FeO4 C and the interfacial effect in the composite system that optimize and stabilize single Fe sites in changing to better configurations for intermediates adsorption. The findings provide a novel strategy to in-depth understanding of practical guidelines for the electrocatalyst design for energy conversion devices.

Nickel foam derived nitrogen doped nickel sulfide nanowires as an efficient electrocatalyst for the hydrogen evolution reaction.

Ni3S2 has been validated as an effective electrocatalyst for the oxygen evolution reaction, attributable to its suitable electronic configuration. However, pure Ni3S2 towards the hydrogen evolution reaction (HER) exhibits relatively low catalytic activity. Herein, a one-step annealing strategy is demonstrated for the synthesis of Ni3S2 nanowires on nickel foam (NF) through N doping towards vigorous HER performance both in acid and alkaline solution. The 1D N-Ni3S2 nanowires, integrated onto a 3D NF electrode, show a high catalytic current density of 10 mA cm-2 at a low overpotential of 196 mV and a small Tafel slope of 63 mV dec-1 in an acid electrolyte. In an alkaline medium, the N-Ni3S2 NWs exhibit a low overpotential of 105 mV at the current density of 10 mA cm-2, which is lower than other reported Ni3S2-based HER catalysts. The superior HER catalytic performance is attributed to its unique structural features, both the morphology and electronic structure. Our work provides profound guidance for the design and optimization of electrocatalysts for an efficient HER.

Metal-organic frameworks-derived synthesis of porous FeP nanocubes: an effective peroxidase mimetic.

Starting with metal-organic frameworks (MOFs), a facile process was demonstrated toward the synthesis of porous FeP nanocubes. Herein, Prussian blue nanocubes were used as iron-based MOFs precursors, and converted into FeP nanocubes through the thermal phosphidation reaction. Then, the FeP nanocubes were exploited as a peroxidase mimetic, which not only has the advantages of low cost, high stability, and easy preparation, but also follows Michaelis-Menten behaviors and shows strong affinity to substrates. On the basis of high catalytic activity of FeP nanocubes, a rapid, and convenient approach was developed for the colorimetric detection of H2O2 from 2µM to 130µM and with a detection limit of 0.62µM. The good catalytic activity and high stability make the porous FeP nanocubes a useful catalyst for a wide range of potential applications in catalysis and biotechnology.

Single molecular recognition force spectroscopy study of a DNA aptamer with the target epithelial cell adhesion molecule.

The epithelial cell adhesion molecule (EpCAM) is a tumor-specific antigen for malignancies of the epithelialis lineage. In this study the interaction between the DNA-based EpCAM aptamer (SYL3C) and EpCAM was explored using single molecular recognition force spectroscopy (SMFS). The capability of aptamer SYL3C to recognize the EpCAM protein and the kinetic parameters were investigated.

Metal-organic frameworks derived CoxFe1-xP nanocubes for electrochemical hydrogen evolution.

Designing and developing active, cost-effective and stable electrocatalysts for hydrogen evolution reaction (HER) are still an ongoing challenge. Herein, we report the synthesis of binary transition metal phosphide (CoxFe1-xP) nanocubes with different Co and Fe ratios through a phosphidation process using metal-organic frameworks (MOFs) as templates. MOF templates contribute well-defined nanocube architectural features after phosphidation, while a suitable phosphidation temperature could allow formation of a crystal structure and maintain the well-defined structure. The incorporation of a binary transition metal results in redistribution of the valence electrons in CoxFe1-xP. The changes imply anionic states of the P and Fe atoms, which act as active sites and thus have stronger electron-donating ability. When CoxFe1-xP nanocubes are employed as electrocatalysts, these characteristic features facilitate the performance of HER. Remarkably, Co0.59Fe0.41P nanocubes prepared at 450 °C afford a current density of 10 mA cm(-2) at a low overpotential of 72 mV in acidic conditions and 92 mV in alkaline conditions. Co0.59Fe0.41P nanocubes also exhibit a small Tafel slope of 52 mV decade(-1) in acidic conditions and 72 mV decade(-1) in alkaline conditions. Moreover, Co0.59Fe0.41P nanocubes show good stability in both acidic and alkaline conditions. Our method produces the highly active HER catalyst based on binary transition metal MOF templates, providing a new avenue for designing excellent electrocatalysts.

Surfactant-assisted fabrication of 3D Prussian blue-reduced graphene oxide hydrogel as a self-propelling motor for water treatment.

Three-dimensional Prussian blue-reduced graphene oxide hydrogel was synthesized with the assistance of sodium dodecyl sulfate (SDS) through a facile hydrothermal method. The hydrogel exhibited strong mechanical properties and was successfully applied as a self-propelling motor for water treatment. During the self-propelling degradation process, SDS facilitated the rapid liberation of oxygen bubbles from the motor and the oxygen bubbles assisted the rapid diffusion of hydroxyl radicals. In addition, the well-defined structure increased the number of reaction sites and the synergy between reduced graphene oxide and Prussian blue, which accelerated the degradation efficiency. The self-propelling motor had an average velocity of 0.026 ± 0.013 cm s(-1) in 7.5% H2O2 and 0.069 ± 0.032 cm s(-1) in 22.5% H2O2. Moreover, the self-propelling motor maintained high degradation efficiency even after cycling for 9 times. These excellent properties make the self-propelling motor an ideal candidate for water treatment.

Modifying candle soot with FeP nanoparticles into high-performance and cost-effective catalysts for the electrocatalytic hydrogen evolution reaction.

Developing inexpensive and highly efficient non-precious-metal electrocatalysts has been proposed as a promising alternative to platinum-based catalysts for the hydrogen evolution reaction (HER). Herein, we report novel FeP NPs supported on inexpensive and available candle soot (FeP-CS) derived from Fe3O4-CS hybrid precursors obtained after a phosphidation reaction. As HER electrocatalysts, the FeP-CS hybrids exhibit high electrocatalytic ability for HER with a Tafel slope of 58 mV dec(-1), a low onset overpotential of 38 mV, a large exchange current density of 2.2 × 10(-1) mA cm(-2) and an overpotential of 112 mV to obtain a current of 10 mA cm(-2). The present work shows significant advance in designing and developing non-precious-metal electrocatalysts for hydrogen evolution reaction.

FeP nanoparticles grown on graphene sheets as highly active non-precious-metal electrocatalysts for hydrogen evolution reaction.

A synthetic route to FeP-GS hybrid sheets that show good stability and high electrocatalytic activity for hydrogen evolution reaction is reported. The materials are prepared via thermal phosphidation of pre-synthesized Fe3O4-GS hybrid sheets.

Facile synthesis of three dimensional hierarchical Co-Al layered double hydroxides on graphene as high-performance materials for supercapacitor electrode.

A facile simple hydrothermal method combined with a post-solution reaction is developed to grow interconnected three dimensional (3D) hierarchical Co-Al layered double hydroxides (LDHs) on reduced graphene oxide (rGO). The obtained 3D hierarchical rGO-LDHs are characterized by field emission scanning electron microscopy, X-ray diffraction, and X-ray photo-electron spectroscopy. As LDHs nanosheets directly grow on the surface of rGO via chemical covalent bonding, the rGO could provide facile electron transport paths in the electrode for the fast Faradaic reaction. Moreover, benefiting from the rational 3D hierarchical structural, the rGO-LDHs demonstrate excellent electrochemical properties with a combination of high charge storage capacitance, fast rate capability and stable cycling performance. Remarkably, the 3D hierarchical rGO-LDHs exhibit specific capacitance values of 599 F g(-1) at a constant current density of 4 A g(-1). The rGO-LDHs also show high charge-discharge reversibility with an efficiency of 92.4% after 5000 cycles.

One-pot solvothermal synthesis of graphene-supported TiO2 (B) nanosheets with enhanced lithium storage properties.

A facile process was developed for the synthesis of graphene-supported TiO2 (B) nanosheets (GTBN) composite based on the hydrothermal treatment titanium (III) chloride and graphene oxide in an ethylene glycol. The morphology and microstructure of the composites were examined by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectroscopy. The obtained GTBN show a high thermal stability and the phase transformation of TiO2 (B) to anatase can be prevented by graphene after pyrolysis of GTBN at 350°C for 2h. Furthermore, GTBN exhibited high rate performance and stability of lithium ion batteries, due to the enhanced conductivity of the electrode and accommodation to volume/strain changes during lithium insertion-extraction.