Bioinspired Engineering
Bioinspiration constitutes a new branch of research and innovation which targets to design new devices from our understanding of biological systems. It is renewed from the use of new types of characterization techniques such as high-resolution imaging and ultrafast spectroscopy.
The NQS group has thus recently developed modeling and simulations of light-converting devices inspired from photosynthesis.
Modeling and simulations of light-converting devices
1. Bioinspired photosystems
The first activity addresses the time-resolved charge transfer following light interaction inside a molecular nanojunction inspired by the two-branch reaction center of photosystem 1 [Robert E. Blankenship, Molecular Mechanism of Photosynthesis, Third Edition 2021, Wiley], in which the excitation-vibration interaction is expected beneficial and here mimicked by an external AC drive, see Fig. 1A).
Photocurrent oscillations are analyzed in terms of optical and tunnel resonances in between the excited states involved in absorption and transport (Fig. 1B)). Performance enhancement is stated from the DC response of the proposed optoelectronic nanodevice, as shown Fig. 1C).
Fig. 1: A) Schematic of the bioinspired nanojunction study, B) time-resolved photocurrent as a function of the drive period, C) corresponding DC particle current enhancement as a function of the drive period [F. Michelini et al., in preparation].
2. Hydrogen production
The second activity concerns the production of hydrogen with an hybrid system inspired by the Z-scheme architecture at the heart of photosynthesis. This system, shown Fig. 2, is based on a van der Waals heterojunction made of two transition metal dichalcogenide (TMDs) monolayers, e.g. MoS2 as anode and WSe2 as cathode.
Such a combination provides three key features.
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First, its large surface-to-volume ratio enables the generated carriers to directly interact with the water molecules.
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Second, a MoS2 anode exhibits excellent oxygen evolution reaction performance in acidic solution, comparable to noble IrO2 electrocatalysts.
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Third, the selected TMDs offer adequate band gaps and a type II band alignment offering an efficient Z-scheme.
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To support the active region, we propose to consider it embedded in a transparent and mesoporous oxide which will also act as membranes to separate the produced O2 and H2 gases. Furthermore, they will be patterned into a photonic crystal to enhance the optical absorption.
In the group we have developed a multi-scale model of this system. Optical properties of the materials are first obtained with ab initio models.
An empirical model which couples the optical, electronic and electrochemical properties has been then implemented.
Our results show that 10% efficiency is achievable.
Fig. 2: A) The system is composed of an active part, supported by a transparent mesoporous oxide. The latter has the role of bringing water to the surface of the TMDCs. Photonic crystals are necessary to increase the absorption of photons. The active part is divided into two distinct regions. B) Representation of the band diagram (as a function of thickness energy) in the first region. EH+/H2 and EH2O/O2are the reaction potentials of the reduction of H+ to H2 and the oxidation of H2O and O2, respectively. This region is the seat of carrier generation and electrochemical reactions. C) representation of the band diagram in the second region, without hBN. The second region allows the recombination of excess carriers.