Metasurface Photoelectrodes for Enhanced Solar Fuel Generation

Abstract

volume is close to the surface, thereby reducing charge carrier recombination because the diffusion length from their excitation site to the catalyst-electrolyte interface is minimized. [7] Third, nanostructuring of photocatalysts increases the surface area compared to a planar film, enabling denser loading of active sites per geometric area. Whereas dissipation losses in metals limit the efficiencies of plasmonic resonances, high refractive index semiconductor photocatalyst nanoresonators are capable of also supporting Mieresonances in the form of electric and magnetic multipoles with negligible dissipation losses compared to metals. [8][9][10] Of particular interest are nonradiative excitations, such as the anapole, which lead to light confinement into the resonator and therefore high electromagnetic field strengths within the material. [11][12][13] In this type of excitation, far-field scattering is minimized and near-field energy inside the material reaches its maximum, making it particularly attractive, e.g., for photo catalytic applications. In a previous study, we demonstrated on the single particle level that resonant coupling of the anapole excitation wavelength to electronic transitions in substoichiometric TiO 2−x leads to enhanced electron-hole pair generation rates and catalytic yields under sub-bandgap excitation. [14] The upscaling from single particles to periodic arrays is accompanied by the emergence of lattice resonances, regardless of their metallic or dielectric character.

Catalytic Metasurfaces Empowered by Bound States in the Continuum

“…We show that strong electromagnetic near-fields within the semiconductor material are crucial for the enhancement of such processes, providing guidelines for boosting light−matter interactions and photocatalytic activity. 13,15,53,54 Furthermore, we find that strong near-fields are readily achieved in…”

“…This finding highlights the potential of this strategy to circumvent the intrinsic trade-off between light absorption and photocarrier recombination on ultrathin photocatalytic films. We show that strong electromagnetic near-fields within the semiconductor material are crucial for the enhancement of such processes, providing guidelines for boosting light–matter interactions and photocatalytic activity. ,,, Furthermore, we find that strong near-fields are readily achieved in metasurfaces composed of TiO 2– x with low extinction coefficient through precise matching of intrinsic and radiative losses (i.e., by utilizing BICs with narrow line widths). This brings another dimension for the field of photocatalysis, where the use of semiconductors with high extinction coefficients is usually preferred.…”

“…Hence, obtaining strong light absorption in ultrathin semiconductors has been of great scientific and technological interest for many years, making it one of the essential aspects for the efficient generation of photocarriers, as well as the development of ultrafast optoelectronic devices − and surface-active photocatalysts. , However, ultrathin films of many naturally occurring semiconductor materials provide only limited freedom for controlling the spectral location and magnitude of light absorption, since their intrinsic optical properties are fixed . In contrast, ultrathin metasurfaces constructed from two-dimensional subwavelength arrays of semiconductor structures have shown tremendous potential for concentrating and controlling light on the nanoscale, positioning them as an ideal toolkit for engineering the light absorption in catalytic materials. − Indeed, recent examples have shown that such artificial materials can increase the internal quantum efficiency of semiconductors and metals when shaping them into catalytic metasurfaces. , …”

“…8−20 Indeed, recent examples have shown that such artificial materials can increase the internal quantum efficiency of semiconductors and metals when shaping them into catalytic metasurfaces. 13,14 All-dielectric metasurfaces underpinned by the physics of bound states in the continuum (BIC) have seen surging interest due to their spectral selectivity, strong light confinement, and giant enhancement of electromagnetic fields, 21−29 sparking applications in diverse fields including nanoscale lasing, 30−36 biomolecular sensing, 37−40 and nonlinear photonics. 41−44 However, to the best of our knowledge, BICs have not yet been tailored for photocatalytic applications.…”

Multimetallic Metasurfaces for Enhanced Electrocatalytic Oxidations in Direct Alcohol Fuel Cells

“…In contrast, plasmonic metasurfaces offer exciting opportunities in tailoring optical response by designing periodic arrays of plasmonic units on planar substrates. [23][24][25] The unit cell symmetry and the substrate properties provide new degrees of freedom to design electromagnetic (EM) properties, which cannot be supported by simple metallic nanostructures.…”