Elucidating the Sole Contribution from Electromagnetic Near‐Fields in Plasmon‐Enhanced Cu₂O Photocathodes

Abstract

semiconductor for photoelectrochemical H 2 production as it consists of earth-abundant elements, displays a direct optical band gap ( E g ) suitable for solar energy conversion ( E g = 2.0 eV), and exhibits a so-called "built-in" overpotential for H 2 evolution. [ 2,3 ] Despite these auspicious properties, the performance of Cu 2 Obased photocathodes is ultimately limited by the small optical cross section of this p-type oxide near the band edge. [ 2a-c ] The abrupt decrease in Cu 2 O absorption coeffi cient below 2.5 eV effectively narrows the spectral sensitivity of this ostensibly 2.0 eV band gap semiconductor. [ 2a-c ] Consequently, a signifi cant portion of the solar spectrum ( λ = 500-600 nm) theoretically available for driving H 2 evolution with a Cu 2 O photocathode is often ineffi ciently harvested by the device. [ 2,3 ] Attempts to mitigate this constraint by fabricating thicker semiconductor fi lms have met with limited success: such a strategy ultimately restricts device performance by adversely affecting charge carrier collection due to the incommensurate length scales between the optical penetration depth ( α −1 = 1-3 µm) and the minority carrier diffusion length ( l d ≈ 50 nm). [ 2a , 4 ] Innovative approaches to augment the optical cross section of the semiconductor without signifi cantly altering the internal device architecture are therefore required to achieve viable solar-to-fuel conversion effi ciencies.Plasmonic-metal nanostructures (e.g., Au, Ag, Cu, Al, etc.) offer intriguing opportunities for solar photocatalysis due to their unique ability to confi ne freely propagating optical radiation into subwavelength volumes. [ 5,6 ] Optical excitation at their localized surface plasmon resonance (LSPR) frequency induces a local enhancement (≈10 3 ) of electromagnetic (EM) fi elds near the nanoparticle (NP) surface that can markedly boost the absorption cross section of a nearby semiconductor photocatalyst. [5][6][7] Panchromatic light-harvesting devices are envisioned by tailoring the LSPR frequency to amplify the absorption profi le of the semiconductor in regions of the solar spectrum that would otherwise be incompletely collected by the device. [ 8 ] While promising reports abound, [ 6,7 ] the pursuit of plasmonic photocatalysts is plagued by the daunting complexity of these systems. [ 5,6 ] Numerous plasmonic processes may coexist spatiotemporally, [ 6,9 ] resigning most studies to invoke a multitude of Despite many promising reports of plasmon-enhanced photocatalysis, the inability to identify the individual contributions from multiple enhancement mechanisms has delayed the development of general design rules for engineering effi cient plasmonic photocatalysts. Herein, a plasmonic photocathode comprised of Au@SiO 2 (core@shell) nanoparticles embedded within a Cu 2 O nanowire network is constructed to exclusively examine the contribution from one such mechanism: electromagnetic near-fi eld enhancement. The infl uence of the local electromagnetic fi eld intensity is correlated with ...

Localized Defects on Copper Sulfide Surface for Enhanced Plasmon Resonance and Water Splitting

“…As shown in Figure b, the light absorption of the SD sample can be fitted and resolved into two parts, that is, intrinsic absorption (λ < 1180 nm) and LSPR absorption (λ > 760 nm), by comparing the absorption spectra of SD‐NFAs with that of DF‐NFAs, such absorption ranges are well consistent with these reported in literature . Moreover, the intrinsic and plasma absorption ranges overlap in a rather large wavelength range (760–1180 nm), which is a prerequisite for LSPR to work efficiently . Under the illumination of 300–760 nm light (region I shown in Figure c), which falls in the intrinsic absorption but without overlap with LSPR absorption, the SD‐NFAs yield an average photoresponse of 0.1567 mA cm −2 (at 0.2 V).…”

Shell‐Isolated Plasmonic Nanostructures for Biosensing, Catalysis, and Advanced Nanoelectronics

“…The silica shell acting as an insulator layer prevented direct electron transfer from photoexcited CdS to AuNPs and therefore proved the main contribution of LSPR‐induced electric field in the H 2 generation efficiency. Likewise, very recently, Wei group [ 18 ] exclusively identified the contribution of near electromagnetic field enhancement in the plasmon‐enhanced photoelectrocatalytic reaction of water splitting by using Au@SiO 2 NPs embedded Cu 2 O nanowire network. Other factors, such as resonant photon scattering, hot electron transfer or local photothermal heating can be systematically excluded by experimental results and theoretical analysis.…”

“…Due to the unique physiochemical properties of LSPR, plasmonic nanostructures have been widely used in various fields, including photo(electro)catalysis, [ 1,2 ] biosensing, [ 3–5 ] bioimaging, [ 6,7 ] cancer therapy, [ 8,9 ] nanoelectronics, [ 10–12 ] and optical spectroscopy, such as surface enhanced Raman spectroscopy (SERS) [ 13,14 ] and photoluminescence (PL) ( Figure ). [ 15,16 ] Among all plasmonic nanoparticles (NPs), shell‐isolated plasmonic nanostructures (abbreviated to SHIPNSs, a class of plasmonic core–shell NPs), consisting of plasmonic metal cores and transparent protective layers that does not significantly damp the electromagnetic enhancement, have attracted great attentions in various applications due to the following several outstanding characteristics: 1) multifunctionality and tunability: the shell‐isolated plasmonic NPs possess inner plasmonic metal cores and outer shells made of various inert materials, such as silica, aluminum oxide, MnO 2 , or polymers, in which the properties of the shell and the resulting core/shell NPs can be tuned and modulated much more easily than the metallic cores by shell nanoengineering of various functional materials (e.g., upconversion nanocrystal, [ 17 ] Cu 2 O, [ 18 ] et. al).…”

Modified Absorption and Emission Properties Leading to Intriguing Applications in Plasmonic–Excitonic Nanostructures

“…The enhancement factor values for J ph (photocurrent), PL and electromagnetic field decrease with increasing distance between Au core and Cu 2 O layer as can be seen in Figure 21g. [ 366 ] Also, Cu 2 O film thickness imparted significant effect on device performance as J ph value increases with increase in film thickness and starts decreasing after certain thickness. Moreover, Figure 21g also shows the requirement of less semiconducting material and better device performance was achieved using plasmonic core in contrast to bare Cu 2 O layer.…”