Abstract
The Chiral Induced Spin Selectivity (CISS) effect is the ability of chiral materials to selectively conduct electrons with a preferential spin, depending on the handedness of the material itself. The CISS effect has major implications in various fields, from biology to molecular electronics, and can have a huge impact on several technological applications. This project aims to design new chiral catalysts in order to exploit the CISS effect for improving the efficiency of the electrochemical oxygen evolution reaction (OER) in the water splitting process, so as to lower the energy needed for hydrogen production. These new chiral catalysts will be cheaper, greener and more efficient than the rare metal-based catalysts currently in use. This will be possible by exploiting the spin-polarization of the electrons, granted by the spin-filtering properties of the chiral catalyst, to reduce the energy barrier required for the formation of triplet ground state molecular oxygen at the electrode surface and to increase the selectivity of the reaction by shutting off the parasitic reactions leading instead to singlet state hydrogen peroxide. The catalysts that we propose to develop belong to the class of Chiral Electrically Conductive Coordination Polymers (CECCPs). These materials consist in a 3D network of multidentate chiral organic ligands acting as linkers and metal ions acting as nodes and are capable of efficiently conducting electric charges. During the project we will synthesize new chiral organic ligands that are suitable for the formation of CECCPs, synthetize the catalysts by solvothermal or mechanochemical techniques, characterize them via spectroscopic and electrical studies, test their activity towards the OER by electrochemical measurements, and study the structure-properties relationships concerning the catalytic and spin-filtering abilities of the CECCPs. The characterization of the materials will also exploit a new in-operando XAS measurement technique that will allow us to monitor in real time the stability of the catalyst and the formation of reaction intermediates, thus permitting to define the mechanism of the spin-polarized OER. As a practical outcome of the project, we will be able to produce a proof-of-concept catalyst that performs at least as well as the current state-of-the-art catalysts based on rare metal but contains only 1st row transition metals such as nickel, cobalt or iron.
Results achieved
All the synthesized materials in the framework of CHICOPEA project were thoroughly characterized using multiple techniques to guarantee chemical purity and, more importantly, to understand their structures. Chemical composition of the catalysts has been determined by combustion analysis, while their thermal behaviour has been studied using DSC and TGA. XRD and XRDP analyses have been already discussed above. A complete morphological analysis supporting the MOF layer deposition has been accomplished. First, microscopy techniques have been calibrated and tested to perform ad-hoc measurements on the prepared samples. The conditions to obtain well defined crystalline MOFs areas on conducting surfaces for conductive AFM characterization have been clearly settled. Because the powdered materials were not suitable for accurate transport measurements, crystalline MOFs grown directly from self-assembled monolayers on gold of thiols bearing a carboxylic acid functionality have been prepared and structurally characterized, paving the way for a fine tuned crystalline growth of chiral MOF. The respective catalytic efficiency is still under study. Electronic circular dichroism (ECD) is a powerful spectroscopic technique used to characterize the chiroptical properties of chiral metal–organic frameworks (MOFs) in the solid state. It measures the differential absorption of left- and right-circularly polarized light by a material, providing direct insight into its chiral electronic transitions. In chiral MOFs, the spatial arrangement of metal nodes and organic linkers creates an asymmetric environment that can induce distinct ECD signals, even in the absence of inherently chiral building blocks. Solid-state ECD is particularly valuable because it probes the material in its functional form without requiring dissolution, preserving structural integrity and long-range order. The resulting spectra can reveal information about the absolute configuration, degree of chirality, and electronic coupling within the framework, as well as host–guest interactions when chiral molecules are adsorbed. Overall, ECD serves as a sensitive and non-destructive tool for confirming chirality and studying structure–property relationships in advanced porous materials. We did characterize the prepared samples with ECD. While electronic circular dichroism (ECD) is highly effective for probing chiral electronic transitions and provides sensitive, rapid confirmation of chirality, it does not always offer sufficient structural detail to fully understand the origin of that chirality. For this reason, vibrational circular dichroism (VCD) was also employed as a complementary technique. VCD probes vibrational transitions in the infrared region, which are directly associated with specific functional groups and local bonding environments. This allows for a more detailed characterization of the molecular structure, including conformational preferences and the absolute configuration at a finer level than ECD alone. In the case of chiral MOFs in the solid state, ECD primarily reflects the overall chiral arrangement of the framework and long-range electronic interactions, whereas VCD provides insight into the local chirality of the organic linkers and their coordination environment around the metal centres. Using both techniques together enables a more comprehensive understanding: ECD confirms the presence of global chirality and electronic coupling, while VCD validates the stereochemical assignment and reveals subtle structural features that may not be apparent in the ECD spectra. Therefore, combining ECD and VCD ensures a more robust and reliable characterization of chiral materials by bridging information from both electronic and vibrational perspectives. For the characterization of the synthesised Chiral MOFs we did develop a micro Raman Optical Activity (ROA) setup for the study of the sample in form of powder, crystals and/or in device in situ/in operando. A micro–Raman optical activity (micro-ROA) setup was designed to extend conventional Raman optical activity measurements to microscopic, spatially resolved analysis, making it particularly suitable for heterogeneous and solid-state samples. The system was built around monochromatic laser sources (514.5 and 785 nm) that were directed into a high-resolution optical microscope and tightly focused onto the sample through a high numerical aperture objective. The scattered light is collected in a backscattering geometry, which is especially advantageous for opaque or solid materials. In this modified configuration, instead of using a photo-elastic modulator (PEM), the polarization control is obtained with a combination of a quarter-wave plate (λ/4) and a linear polarizer. By carefully adjusting the orientation of the λ/4 plate relative to the incident linearly polarized light, left- and right-circularly polarized light can be generated in a controlled manner. Switching between polarization states can be performed by rotating the λ/4 plate or the polarizer, providing a simpler and more accessible alternative to PEM-based modulation. The difference in Raman scattering intensity between these left and right circular polarization states constitutes the ROA signal, which is extracted using polarization optics and analysed with a high-sensitivity spectrometer equipped with a CCD detector. The “micro” configuration enables precise targeting of micrometre-scale regions, allowing the investigation of structural heterogeneity, crystal domains, or surface features within chiral materials such as MOFs. A key advantage of this setup is its ability to characterize samples directly in the solid state without requiring dissolution or extensive preparation, thereby preserving their native structure. Moreover, its compatibility with microscope-based measurements allows in situ and operando studies, enabling the investigation of materials within working devices or under realistic conditions (e.g., during catalysis or adsorption processes). This makes micro-ROA a powerful tool for correlating local chiral structure with functional properties, combining chemical specificity from Raman spectroscopy with stereochemical sensitivity from optical activity, all at high spatial resolution. As a benchmark for the built setup we did use Camphor which is a common pure chiral material. Below is reported the data obtained with the micro-ROA assembled in our lab.Project details
Unibo Team Leader: Tommaso Salzillo
Unibo involved Department/s:
Dipartimento di Chimica Industriale "Toso Montanari"
Coordinator:
Università degli studi di Modena e Reggio Emilia - UNIMORE(Italy)
Total Unibo Contribution: Euro (EUR) 42.575,00
Project Duration in months: 24
Start Date:
30/11/2023
End Date:
28/02/2026
