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  1. Electrolysis of water to generate hydrogen fuel is an attractive renewable energy storage technology. However, grid-scale freshwater electrolysis would put a heavy strain on vital water resources. Developing cheap electrocatalysts and electrodes that can sustain seawater splitting without chloride corrosion could address the water scarcity issue. Here we present a multilayer anode consisting of a nickel–iron hydroxide (NiFe) electrocatalyst layer uniformly coated on a nickel sulfide (NiSx) layer formed on porous Ni foam (NiFe/NiSx-Ni), affording superior catalytic activity and corrosion resistance in solar-driven alkaline seawater electrolysis operating at industrially required current densities (0.4 to 1 A/cm2) over 1,000 h. A continuous, highly oxygen evolution reaction-active NiFe electrocatalyst layer drawing anodic currents toward water oxidation and an in situ-generated polyatomic sulfate and carbonate-rich passivating layers formed in the anode are responsible for chloride repelling and superior corrosion resistance of the salty-water-splitting anode.

     
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  2. Abstract

    Unusual photophysical properties of organic–inorganic hybrid perovskites have not only enabled exceptional performance in optoelectronic devices, but also led to debates on the nature of charge carriers in these materials. This study makes the first observation of intense terahertz (THz) emission from the hybrid perovskite methylammonium lead iodide (CH3NH3PbI3) following photoexcitation, enabling an ultrafast probe of charge separation, hot‐carrier transport, and carrier–lattice coupling under 1‐sun‐equivalent illumination conditions. Using this approach, the initial charge separation/transport in the hybrid perovskites is shown to be driven by diffusion and not by surface fields or intrinsic ferroelectricity. Diffusivities of the hot and band‐edge carriers along the surface normal direction are calculated by analyzing the emitted THz transients, with direct implications for hot‐carrier device applications. Furthermore, photogenerated carriers are found to drive coherent terahertz‐frequency lattice distortions, associated with reorganizations of the lead‐iodide octahedra as well as coupled vibrations of the organic and inorganic sublattices. This strong and coherent carrier–lattice coupling is resolved on femtosecond timescales and found to be important both for resonant and far‐above‐gap photoexcitation. This study indicates that ultrafast lattice distortions play a key role in the initial processes associated with charge transport.

     
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