Reducing overpotential and increasing current density remain a great challenge for promoting the application of transition metalsbased layered double hydroxides (LDHs). Herein, Ni nanoparticles (∼10 nm) decorated NiFe LDH ultrathin (thickness: ∼2 nm) nanosheets (Ni NP/NiFe LDH) were successfully synthesized which exhibited advanced electrocatalytic activity and long-term stability on both oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The onset potentials for OER and UOR are 1.50 V and 1.34 V, respectively, both are lower than NiFe LDH under the same conditions. Moreover, the peak current density of UOR was 300 mA/cm 2 , which is much larger than reported precious-metal free UOR catalysts. The excellent catalytic performance of Ni NP/NiFe LDH composite for OER and UOR is proposed to result from the abundant exposed active sites, small charge transfer resistance, and the synergistic effects between NiFe LDH and anchored Ni nanoparticles. This work provides inspiring ideas and helpful guidelines in design of low-cost but highly efficient electrochemical catalysts. The global energy crisis and environmental contamination have prompted intense research into the development of sustainable energy conversion and storage systems.1-10 Water splitting and direct urea fuel cell (DUFC) as promising approaches to produce clean energy recyclable, have been widely investigated recently. Nevertheless, oxygen evolution reaction (OER: 2H 2 O === O 2 + 4H + + 4e − ) suffers from a sluggish kinetics owing to a 4e-transfer process, which is frequently an obstacle to the whole water splitting. Same as OER, urea oxidation reaction (UOR: CO(NH 2 ) 2 + H 2 O === N 2 + 3H 2 + CO 2 ) is also under a multistep proton-coupled electron transfer process, which remains to be a great challenge for DUFC. As a consequence, the sluggish kinetics of OER and UOR lead to considerable overpotential and decrease the efficiency of energy conversion and storage. To achieve efficient energy conversion, much effort has been devoted to the research for robust yet stable electrochemical catalysts with reduced overpotentials. Precious metal based catalysts have shown significant electrocatalytic properties, 11-13 but their high cost and scarcity hamper the commercialization of the technique. Therefore, developing functional nanomaterials composed of cost-effective and abundant elements are on great demand.Owing to the unique physicochemical properties (e.g. tunable metal species/ratios, and exchangeable interlayer spacings, etc.), layered double hydroxides (LDHs) [23][24][25][26][27] and among which, NiFe LDH showed the best performance.28 Nevertheless, reducing the overpotential and increasing the current density remain under intensive pursuit for promoting the application of NiFe LDH. For example, the introduction of conductive materials (graphene, carbon nanotube, etc.) into LDH systems can improve the conductivity of the catalysts 21,22 and hence further enhance their catalytic performance. Herein, we report a bifunctional catalyst ...

FeNi-O porous nanosheets were synthesized and they exhibited advanced OER performance that was investigated experimentally and theoretically.

The exploitation of high‐performance nonlinear optical (NLO) materials is necessitated by the broad application of ultra‐intensive and ultra‐fast lasers. The superb nonlinear absorption and electronic‐structure‐related NLO response of M3HHTP2 are introduced here, where M is Co(II), Ni(II), or Cu(II) and HHTP is 2,3,6,7,10,11‐hexahydroxytriphenylene. With the laser excitation at 532 nm, the Cu3HHTP2 exhibits a two‐photon absorption (2PA) cross‐section of 1.38 ± 0.11 × 107 GM, a value much larger than those of most reported NLO materials so far. The NLO response of M3HHTP2 correlates strongly with the number of metal d electrons. With metal d electrons number increasing from 7 to 10, the optical nonlinearity of M3HHTP2 under the laser excitation at 532 nm varies from three‐photon absorption (3PA) in Co3HHTP2, a combination of 3PA and 2PA in Ni3HHTP2, to 2PA in Cu3HHTP2. Abundant metal d electrons can mitigate the ground‐state depletion, and therefore the 2PA is enhanced. Accordingly, the superb nonlinear absorption of Cu3HHTP2 can be associated with abundant d electrons in Cu.

Layered double hydroxides (LDH) have attracted tremendous attention in a variety of areas, including catalysis, energy storage, drug delivery, etc. Herein, we report a simple coprecipitation method to prepare highly active electrochemical catalysts of FeNiCo LDH at room temperature. In alkaline media, the as-obtained FeNi2Co2 LDH shows superior electrocatalytic activity toward water oxidation with an overpotential of 232 mV at 10 mA/cm2 and a low Tafel slope of 48 mV/dec, comparable to most of the reported noble-metal free OER catalysts. The suitable electronic structures as well as reduced charge transfer resistance that promote the electrons transfer during the OER process are proposed to be the two critical factors that lower the overpotential of the catalytic reaction.

Herein it is reported that electrochemical ion-intercalation is a convenient and effective strategy toward materials with giant nonlinear optical (NLO) absorption. Alkali-metal ions (i.e., Li + , Na + , K + ) are electrochemically intercalated into SnS 2 nanosheets. All ion-intercalated samples exhibit remarkably enhanced optical nonlinearity compared with an untreated sample, and Liintercalated SnS 2 (Li 0.952 Sn II 0.398 Sn IV 0.563 S 2 ) possesses optimized strong NLO performance. Li 0.952 Sn II 0.398 Sn IV 0.563 S 2 exhibits strong saturable absorption, and the corresponding nonlinear absorption coefficient (β eff ) is -1.7 × 10 4 cm GW -1 for the laser excitation at 515 nm. Li 0.952 Sn II 0.398 Sn IV 0.563 S 2shows prominent reverse saturable absorption with the laser excitation at 800 nm (β eff : 2.8 × 10 4 cm GW -1 ) and 1030 nm (β eff : 1.4 × 10 4 cm GW -1 ). All β eff values are larger than most of the reported inorganic NLO materials at corresponding wavelengths. The optical limiting threshold of Li 0.952 Sn II 0.398 Sn IV 0.563 S 2 is 8 × 10 -4 J cm -2 , two orders of magnitude smaller (better) than the benchmark composite (e.g., SWNT-NH-TPP). Ion intercalation introduces abundant in-gap defects. The excitation of electrons in in-gap states to conduction band intensifies the Pauli-blocking effect and therefore promotes the saturable absorption under the 515 nm laser excitation, while the in-gap defect states acting as effective excitation pathway facilitate excited-state absorption for 800 and 1030 nm laser.

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