Abstract
Here, a facile approach to enhance the performance of solar‐driven photoelectrochemical (PEC) water splitting is described by means of the synergistic effects of a hybrid network of plasmonic Au nanoparticles (NPs) decorated on multiwalled carbon nanotubes (CNTs). The device based on TiO2–Au:CNTs hybrid network sensitized with colloidal CdSe/(CdSexS1− x)5/(CdS)1 core/alloyed shell quantum dots (QDs) yields a saturated photocurrent density of 16.10 ± 0.10 mA cm−2 [at 1.0 V vs reversible hydrogen electrode (RHE)] under 1 sun illumination (AM 1.5G, 100 mW cm−2), which is ≈26% higher than the control device. The in‐depth mechanism behind this significant improvement is revealed through a combined experimental and theoretical analysis for QDs/TiO2–Au:CNTs hybrid network and demonstrates the multifaceted impact of plasmonic Au NPs and CNTs: i) hot‐electron injection from Au NPs into CNTs and TiO2; ii) near‐field enhancement of the QDs absorption and carrier generation/separation processes by the plasmonic Au NPs; iii) enhanced photoinjected electron transport due to the highly directional pathways offered by CNTs. These results provide fundamental insights on the properties of QDs/TiO2–Au:CNTs hybrid network, and highlights the possibility to improve the performance of other solar technologies.
Highlights
Solar-driven hydrogen (H2) generation is a promising approach for the direct conversion of solar energy into a clean and renewable fuel, to partially address the future energy demands and related environmental issues.[1]
The addition of a precise amount of carbon nanotubes (CNTs) in TiO2 mesoporous paste boosts the performance of solar technologies thanks to improved electron transport and reduced carrier recombination within the photoanode.[24c,26] Recently, Lee et al demonstrated that plasmonic metal NPs–CNTs hybrid networks lead to significant suppression of charge trapping and related nonradiative recombination that are typical of plasmonic NPs.[22a]. To the best of our knowledge, there is no report exploring the use of plasmonic metal NPs–CNTs hybrid networks in colloidal quantum dots (QDs) based PEC
The interplanner spacing of Au NPs is around 2.35 Å, which corresponds to (111) planes of face centered cubic phase of Au (JPCD file No: 00-004-0784), whereas the distance between the adjacent graphene layers within CNTs is around 3.4 Å, consistent with previous reports.[22a,27] Selected area electron diffraction (SAED) pattern of Au NPs is displayed in Figure 1d, composed of several concentric rings corresponding to (111), (200), (220) and (311) planes of the face-centered cubic phase structure of Au (JPCD file No: 00-004-0784)
Summary
It has been shown that combining localized surface plasmon resonance (LSPR) of noble metal (e.g., Au or Ag) nanoparticles (NPs) with wide-bandgap semiconductors (e.g., TiO2) is a promising approach to enhance the light harvesting efficiency of solar technologies.[20] These plasmonic NPs work as nanoantennas that localize the impinging light’s energy, to transfer a fraction of it to its environment through different optical and charge-transfer mechanisms.[21] plasmonic effects only originate from nanoscale noble metal crystals, and their proximity to other systems causes charge trapping, thereby hampers device performance.[22] To address this issue, we propose to use 1D materials capable of promoting the efficient separation and transport of photogenerated charge carriers.[23] In this context, carbon nanomaterials such as multiwall carbon nanotubes (CNTs), graphene, graphene nanoribbons, and graphene oxide may be useful for enhancing charge carrier transport and collection.[24] In particular, CNTs could be the most suitable candidates due to their unique transport and structural properties.[25] The addition of a precise amount of CNTs in TiO2 mesoporous paste boosts the performance of solar technologies thanks to improved electron transport and reduced carrier recombination within the photoanode.[24c,26] Recently, Lee et al demonstrated that plasmonic metal NPs–CNTs hybrid networks lead to significant suppression of charge trapping and related nonradiative recombination that are typical of plasmonic NPs.[22a] To the best of our knowledge, there is no report exploring the use of plasmonic metal NPs–CNTs hybrid networks in colloidal QD based PEC devices for H2 production. The long-term stability of the PEC device based on a QDs/TiO2–Au:CNTs photoanode is better than the PEC devices based on QDs/TiO2 photoanode
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