absorbers have aroused great attention due to their resonant absorption and localized heating effect. [7][8][9] Nevertheless, this resonant absorption inherently features a narrow bandwidth, which is usually advantageous for applications such as biosensors [10] and resonant energy transfer, [11] but disadvantageous for broadband light absorption. [12,13] Some complex and delicate plasmonic metastructures were thus designed to hybridize proximate surface plasmons [12] or to support multiple resonances [13] in order to broaden the absorption bandwidth. However, the noble metals (i.e., Au and Ag) for plasmonic absorption along with the complicated fabrication procedures are undesirable for large-scale and full-spectrum (300-2500 nm) solar energy harvesting. [14] Zhou et al. creatively fabricated an all-aluminum hybrid plasmonic membrane, which was lowcost and enabled efficient broadband solar absorption. [15] The broadband plasmonic absorber was based on closely packed Al nanoparticles along the side walls of nanopores to induce a plasmon hybridization effect and high-density plasmonic resonances. [15] Among the several mechanisms that cause light absorption in metals, [16] interband transitions (IBTs) are single-electron excitations [17] from occupied levels in one band to unoccupied levels in another band, [18] in contrast to the collectively coherent excitation of electrons for plasmonic absorption. [19] IBTs intrinsically have a broadband attribute because photons the energy of which surpasses the interband threshold of a metal can excite IBTs. This makes IBTs very suitable for full-spectrum solar energy utilization, especially when massive IBTs over the entire solar spectrum can be supported by some transition metals (e.g., Ni, Pd, and Pt) with a high density of electronic states (DOS) near their Fermi levels. [20][21][22] In this work, we designed a Ni-cellulose hybrid metamaterial (NCM) that employs IBTs as the dominant optical absorption mechanism over the entire solar spectrum (Figures S1 and S2, and Note S1 for the detailed demonstration, Supporting Information). Nickel supports strong IBTs in very low energy regions (≈0.5 eV), which greatly increase optical absorption in the near-infrared spectrum compared to plasmonic metals (Au, Ag, and Cu). We densely embedded Ni nanoparticles into the nanogaps of cellulose microfibers via a seed-mediated and nanoconfined growth. This nanoconfinement effect can inhibit Sophisticated metastructures are usually required to broaden the inherently narrowband plasmonic absorption of light for applications such as solar desalination, photodetection, and thermoelectrics. Here, nonresonant nickel nanoparticles (diameters < 20 nm) are embedded into cellulose microfibers via a nanoconfinement effect, producing an intrinsically broadband metamaterial with 97.1% solar-weighted absorption. Interband transitions rather than plasmonic resonance dominate the optical absorption throughout the solar spectrum due to a high density of electronic states near the Fermi level of nickel. Fiel...

Up to now, the field of PEC water splitting is dominated by inorganic semiconductors consisting of earth abundant elements (e.g., silicon, [7-12] metal oxides, [13-16] metal sulfides, [17,18] dichalcogenide, [19] etc.). However, the high cost and poor stability of noble metal (e.g., Pt) as cocatalysts seriously restrict the practical applications of inorganic semiconductors for the PEC hydrogen evolution reaction (HER). Compared with traditional inorganic semiconductors, organic semiconductors (e.g., graphitic carbon nitride [g-C 3 N 4 or polyheptazine], [20-23] polythiophene, [24,25] conjugated covalent organic frameworks [COFs], [26] conjugated acetylenic polymers [CAPs] [27-29]) have attracted increasing attentions benefitting from their tunable bandgaps, engineered band edge positions, and molecular-level desirable active centers. [6] However, the PEC HER performance of current organic photocathodes falls far behind inorganic counterparts mainly due to their severe recombination of photoinduced holes and electrons. Recently, diverse strategies have been explored for promoting the charge separation of organic semiconductors, mainly focusing on the heterojunction or homojunction As attractive materials for photoeletrochemical hydrogen evolution reaction (PEC HER), conjugated polymers (e.g., conjugated acetylenic polymers [CAPs]) still show poor PEC HER performance due to the associated serious recombination of photogenerated electrons and holes. Herein, taking advantage of the in situ conversion of nanocopper into Cu 2 O on copper cellulose paper during catalyzing of the Glaser coupling reaction, a general strategy for the construction of a CAPs/Cu 2 O Z-scheme heterojunction for PEC water reduction is demonstrated. The as-fabricated poly(2,5-diethynylthieno[3,2-b]thiophene) (pDET)/Cu 2 O Z-scheme heterojunction exhibits a carrier separation efficiency of 16.1% at 0.3 V versus reversible hydrogen electrode (RHE), which is 6.7 and 1.4-times higher respectively than those for pDET and Cu 2 O under AM 1.5G irradiation (100 mW cm −2) in the 0.1 m Na 2 SO 4 aqueous solution. Consequently, the photocurrent of the pDET/Cu 2 O Z-scheme heterojunction reaches ≈520 µA cm −2 at 0.3 V versus RHE, which is much higher than pDET (≈80 µA cm −2), Cu 2 O (≈100 µA cm −2), and the state-of-the-art cocatalyst-free organic or organicsemiconductor-based heterojunctions/homojunctions photocathodes (1-370 µA cm −2). This work advances the design of polymer-based Z-scheme heterojunctions and high-performance organic photoelectrodes.

Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for CO2 reduction to alleviate the greenhouse effect. However, the low light absorption, small specific surface area, and rapid charge recombination limit the photocatalytic efficiency of g-C3N4. Herein, we demonstrate a bioinspired nanoarchitecturing strategy to significantly improve the light harvesting and charge separation of the g-C3N4/Au composite, as proven by the remarkable photocatalytic CO2 reduction. Specifically, a biotemplating approach is employed to transfer the sophisticated hierarchical structures and the related light-harvesting functionality of Troides helena butterfly wings to the g-C3N4/Au composite. The resulting g-C3N4/Au composite shows high photocatalytic efficiency under UV–visible excitation with triethanolamine as the sacrificial agent. The yields of CO and CH4 are 331.57 and 39.71 μmol/g/h, respectively, which are ∼36 times and ∼88 times that of pure g-C3N4 under the same conditions. Detailed experiments and the finite-difference time-domain method suggest that the superb photocatalytic activity should be ascribed to the unique periodic hierarchical structure which assists the light absorption and the localized surface plasmon resonance for promoted charge separation in addition to the more effective CO2 diffusion and larger specific surface area. Our work provides a new path for the design and optimization of photocatalysts based on biological structures that are usually unattainable artificially.

Zeroth-order complex dispersion relations of a cylindrical metallic nanowire have been solved out analytically with approximate methods. The analytical solutions are valid for the sections of the dispersion relations whose frequencies are close to the Surface Plasmon frequency. The back bending of the Surface PlasmonPolaritons(SPPs) can be well described by the analytical solutions, confirming that the back bending is originated from the metal Ohmic loss. The utility of the back bending point in the dispersion relation for the measurement of the metallic Ohmic loss has also been suggested.