Singapore

Biopolymers such as chitosan, cellulose and alginate from biomass have demonstrated huge potential in many important and rapidly growing applications, it is always challenging to create advanced biopolymer materials cost-effectively. Herein, we present our progress in preparing a series of biopolymer composite materials with unexpected properties using a facile “dry”, thermomechanical method. Chitosan/CMC composite films created in this way showed much better hydrolytic stability, compared to chitosan-only films. This is so despite inclusion of the CMC in the chitosan matrix even increasing the surface hydrophilicity. We propose that our processing method led to the polyelectrolyte complexation between chitosan and CMC generating physical crosslinking points in the materials. These crosslinks stabilised the films in water although hydration disrupted hydrogen bonding between polysaccharide chains leading to dramatically decreased tensile strength and increased elongation at break. 
Besides, we found chitosan/silk peptide (SP) polyelectrolyte-complexed materials prepared in the same way had extraordinary mechanical properties. Moreover, we prepared chitosan/alginate composites using the same processing protocol and demonstrate that inclusion of graphene oxide could enhance polysaccharide plasticisation, leading to enhanced mechanical properties and surface hydrophobicity. 
The method of materials hybridisation without chemical reactions demonstrated in this work could provide an insight into the development of cost-effective biopolymer materials with competitive properties as plastic replacements in certain applications, where biodegradability, biosafety, and biocompatibility are indeed required (e.g. functional food packaging and antimicrobial wound healing).

MATERIALS FOR HUMANITY (MH 21)

Thermomechanically Processed, Polyelectrolyte-Complexed Polysaccharide Composites with Enhanced Hydrolytic Stability and Mechanical Properties

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technical paper

Plastics have become indispensable in the modern society. However, plastics pollution has also become a global environmental crisis that is projected to grow. The most common approaches to manage plastics pollution include mechanical recycling and pyrolytic waste-to-energy processes, but these methods inevitably lead to the increase in greenhouse gas emissions. In this presentation, I will summarize my team’s early contributions to using exclusively Earth-abundant elements and renewable energy to upcycle plastics. In particular, I plan to focus on our efforts at applying molecular vanadium complexes for selective, ambient condition, photoredox C-C cleavage reactions.1 We conducted detailed kinetic measurements to identify the fastest catalyst and the critical functional groups required in the substrates.2 The vanadium photocatalysts were then utilized for the C-C bond cleavage and oxygenation of over 30 substrates, including unactivated, commercially sourced alcohols and even non-biodegradable plastics.3-6 

Figure 1. Photocatalytic upcycling of non-biodegradable polyethylene to formic acid, a liquid organic hydrogen carrier as a fuel.

References
1. Gazi, S.; Ng, W. K. H.; Ganguly, R.; Moeljadi, A. M. P.; Hirao, H.; Soo, H. S. Chem. Sci. 2015, 6, 7130-7142.
2. Gazi, S.; Dokić, M.; Moeljadi, A. M. P.; Ganguly, R.; Hirao, H.; Soo, H. S. ACS Catal. 2017, 7, 4682-4691.
3. Gazi, S.; Dokić, M.; Chin, K. F.; Ng, P. R.; Soo, H. S. Adv. Sci. 2019, 6, 1902020.
4. Dokić, M.; Chin, K. F.; Soo, H. S. Trends Chem. 2020, 2, 485-488.
5. Zhao, X.; Boruah, B.; Chin, K. F.; Dokić, M.; Modak, J. M.; Soo, H. S. Adv. Mater. 2021, in press.
6. Estahbanati, M. R. K; Kong, X. Y.; Eslami, A.; Soo, H. S. ChemSusChem, 2021, in press.

Photocatalytic Upcycling to Sustainably Reuse Plastics

High dielectric constant and low dielectric loss are desirable electrical properties for next generation polymer films for capacitive energy storage. Unfortunately, the dielectric constant of polymers is often limited to 2-5, much lower than that of inorganic dielectrics, because of the nature of hydrocarbon covalent bonds for electronic and atomic polarizations. It is essential to understand the fundamental physics of different types of polarization and the associated loss mechanisms in polymers. Among various approaches for high dielectric constant and low loss polymers, the multilayer film technology is of particular interest because a multilayer film is a unique one-dimensional system with tailored material choices, layer thicknesses, and interfaces. By minimizing the disadvantageous polarizations and enhancing the advantageous polarizations, multilayer films hold promise as advanced dielectrics for future polymer film capacitors.

High Energy Density and High Temperature Multilayer Polymer Films for Capacitive Energy Storage

The continuing growth of membrane technologies for water, solvent and gas separations, as well as other applications, has advanced significantly in the past few decades. However, the short durability of polymeric membranes, which wear out due to continuous fouling cycles and chemical cleaning, is increasingly becoming a waste disposal issue. The purpose of this presentation is to provide an overview of the environmental, energy and economic challenges and possible advantages of implementing sustainable processes in membrane manufacturing, evaluating the sustainability of membrane life-cycle and defining some end-of-life approaches such as reuse, repurposing and recycling. A bird’s eye review of the existing membrane challenges, state-of-art and potential sustainable solutions will be discussed in this presentation with examples from the literature.

Perspectives of sustainable development, life cycle and end of life in polymeric membranes

Membrane separations consume less than 90% of the energy required in incumbent industrial separation processes (absorption, distllation etc), and is widely considered as a "green" alternative for industrial separations. However, the manufacturing process of polymer membranes negates the "green" benefits of low energy. This is due to the mandatory use of oil-derived plastics and hazardous solvents e.g. NMP and n-hexane. At the Scale-Up Lab at The University of Edinburgh, we have deployed Green Chemistry concepts in tandem with additive manufacturing to imbue sustainability into polymer membrane fabrication. In this presentation, I will share with you key aspects of our work, including recycling plastic waste into high performance additives for mixed matrix membranes and replacing oil-derived plastics and overcoming the use of hazardous solvents in thin-film composite membrane fabrication.

Replacing plastics and hazardous solvents in polymer membrane fabrication


The needed massive deployment of lithium ion batteries (LIBs), in particular to satisfy the demand from the Electric Vehicle sector, encourage battery manufacturers to multiply the number of giga-factories to reduce the cost of production. Such a production consists of a complex process involving multiple steps, such as the slurry preparation, its coating, drying, calendering, electrolyte filling and formation. The choice of the manufacturing parameters along the process strongly impact the overall LIB cell performance. However, the optimization of the manufacturing parameters to obtain the desired characteristics of LIB cells is currently based on a forward "trial and error" approach. This approach is inefficient in terms of time and cost due to the infinite number of possibilities for adjusting the manufacturing parameters. The integration of Industry 4.0 concepts into giga-factories such as Artificial Intelligence (AI) and multiscale modeling is essential to accelerate the manufacturing process optimization and significantly raise the work efficiency of scientists, engineers and production line operators. Here I present our efforts in developing a digital twin of battery manufacturing [1], supported on a combination of physical and AI/machine learning models trained with data arising from in house high throughput characterizations. This digital twin allows simulating the different steps along the manufacturing process, predicting the resulting electrode properties and evaluating the associated electrochemical performance upon battery cell cycling. The predictive capabilities of this digital twin are illustrated with results for different electrode formulations, paving the way towards manufacturing digital optimization. Finally, data standardization challenges to ease the wide use of these tools in the battery field will be briefly discussed.

[1] www.erc-artistic.eu 


Digitalization of Battery Manufacturing through Artificial Intelligence and Multiscale Modeling

Advanced two-dimensional (2D) materials have attracted significant interest due to their extraordinary physical and chemical properties over the past decade. Understanding and controlling the growth of novel 2D crystal materials for energy strorage application is central for the performance of the batteries. One of the greatest challenges besetting the development of battery technologies is fast charging, especially within flexible or compact designs. We discuss how the design of low dimensional nanostructure can correlate with the ion transportation efficiency, the activity of electrochemical reaction and energy storage based on chemical transformation. We have also studied the prospects of fast prototyping and scalability for 2D materials-based devices.

Design and Synthesis Low-dimensional Nanomaterials for Energy Storage Applications

Mixed Sn-Pb perovskites have shown their potentials in photovoltaics as a promising alternative to traditional silicon and other inorganic compounds. To achieve efficient devices, high-quality Sn-Pb perovskite thick films with well-packed, smooth, pinhole/void-free features are highly desirable for boosting spectral absorption. Herein, we propose an approach of double-side crystallization tuning through low-temperature space-restricted annealing in MA-free Sn-Pb perovskite films with over 1 μm thickness. Through simultaneously retarding the crystallization in the top of precursor films and promoting the crystal growth of the bottom of precursor films, we achieve high-quality and block-like thick Sn-Pb perovskite films with improved crystallinity and reduced trap density [1]. The high-quality Sn-Pb perovskite can also be fabricated on metal/ silicon substrates for direct integration with CMOS electronics for efficient photodiode imaging arrays [2]. Meanwhile, we develop the approach of in-situ tin(II) inorganic complex anti-solvent process to uniquely form the quasi core-shell structure of Pb-Sn perovskite-tin(II) complex as well as heterojunction perovskite structure. The Pb-Sn perovskite solar cells (SCs) achieves a high power conversion efficiency upto 19.03% with a fill factor over 0.8. Remarkably, the device fail time under continuous light illumination is extended by over 18.5 folds reaching 560 h [3]. To realize the integration of Sn-Pb perovskite for tandem cell applications, we also develop a new thermionic emission-based interconnecting layer (ICL) structure with the enhanced solvent-resistance feature. Fundamentally, thermionic emission plays a critical role in the electron transport process in the ICL, which is confirmed through both experimental and theoretical studies [4]. The works not only demonstrate the solid potential of Sn-Pb perovskite in SCs and photodetectors but also promoting all perovskite tandem SCs for low-cost photovoltaics. 

[1] Adv. Funct. Mat. DOI:10.1002/adfm.202010532. [2] H.L. Zhu, W.C.H. Choy, et al, ACS Nano, 13, 11800, 2019. [3] C. Li, W.C.H. Choy, et al, Adv. Energy Mater., 10, 1903013, 2020. [4] C. Li, W.C.H. Choy, et al, Adv. Energy Mater., 8, 1801954, 2018.


High Performance Photovoltaic devices based High Quality and Thick Sn-Pb Perovskites

Significant progress has been recently reported in solar water splitting, but two major challenges remain. First, although solar-to-hydrogen (STH) efficiency as high as 30% has been demonstrated, the use of expensive and non-scalable III-V semiconductors is required. On the other hand, low-cost metal-oxide based devices, using mainly BiVO4 as the absorber, have only achieved STH efficiency of < 10%, due to the limited absorption of BiVO4. Novel metal oxide semiconductors with a bandgap of 1.7-1.9 eV, which are stable and efficient, are therefore desired. The second challenge is related to the scale-up of the devices, from laboratory experiments to large-area device demonstrations. Several efforts exist, but the performance of the large-area devices is still significantly smaller (up to a factor of 5) as compared to the small-area equivalent. In this talk, I will outline our efforts in overcoming the two challenges above. The first is on the development of  SnWO4 (Eg = 1.9 eV) as a novel photoanode, which suffers from poor stability. This could be overcome by depositing NiOx as a protection layer, but it is also accompanied by the reduction of the photovoltage. We performed a thorough α-SnWO4/NiOx interface investigation by means of synchrotron-based hard X-ray photoelectron spectroscopy,[1] which reveals the presence of an interfacial oxide layer (likely to be SnO2). Control experiments show that such a layer can indeed be responsible for the reduction of photovoltage; its formation must therefore be avoided to overcome the photovoltage limitation. Concerning the scale-up of devices, I will discuss our approach in quantifying the different loss mechanisms associated with scaling-up photoelectrodes using a combination of multiphase multiphysics simulations and in-situ quantitative analysis of the fluid dynamics as well as pH of the electrolyte.[2-4] Based on these insights, electrochemical engineering strategies to overcome the losses associated with scale-up are offered.

1. Schnell et al. Adv. Energy Mater. 11 2021 2003183
2. Abdi et al. Sust. Energy Fuels 4 2020 2734
3. Obata et al. Energy Environ. Sci. 13 2020 5104
4. Obata et al. Cell Rep. Phys. Sci. 2 2021 100358

Development and scale-up of complex oxide-based devices for solar water splitting

The quality of the perovskite films has an important effect on the performance of the perovskite solar cells. In this talk, we demonstrate the nucleation process plays a crucial role in the formation of the perovskite films with various morphologies. The low supersaturation results in films with porous morphologies because of the secondary nucleation. The high supersaturation results in films with compact morphologies due to the homogeneous nucleation. By adjusting the proportion of homogeneous nucleation and secondary nucleation based on an interface precipitation process induced by the antisolvent of n-hexane, we achieve perovskite films from porous morphologies to compact morphologies. The perovskite film with the three layers of structures has high light absorbance and large area of interface between perovskite and the hole transport materials, which result in high efficiency of the corresponding solar cells. In particular, surface of the carbon electrode is rather rough and the porous perovskite film enhances the interfacial contact area between carbon electrode and perovskite film. With the optimized perovskite films and carbon electrodes, we accomplish the fabrication of carbon based large-area and stable perovskite solar modules with the efficiency of over 13%. In addition, the morphology of TiO2 electron transport layer has also important influence on the efficiency of the solar cells. Based on the stable carbon-based perovskite solar cells, a kW-scale demonstration application of perovskite solar cells has been established.

Effect of film morphologies on performance of perovskite solar cells and modules

While numerous research groups have contributed to significant advancement of three-dimensional (3D) halide perovskites for use in photovoltaic applications, the number of publications reporting the development and fundamental properties of the materials of lower dimensionalities remains relatively small. Two-dimensional (2D) hybrid metal halide perovskites possessing the general chemical formulas (RNH3)2MX4 and (NH3RNH3)MX4 (R corresponds to an organic functional group, M a group 14 metal dication, and X a halide) are derived from their 3D congeners by slicing the inorganic lattice along specific crystallographic axes (e.g., the (100)- or (110)-planes). This can be induced through incorporation of moderately sized organic cations, such as 2-phenylethylammonium and 1-butylammonium, and it yields alternating 2D layers of organic cations and single Pb-atom-thick inorganic lattices. These are referred to as n = 1 2D hybrid metal halide perovskites, where n refers to the number of contiguous 2D inorganic layers, i.e., not separated by organic cations. The resulting 2D materials possess synthetic versatility and moisture stability greater than that of pure 3D perovskites. However, they are, generally, considered ill-suited for photovoltaic applications because their reduced dimensionality manifests in poor charge transport and compromised visible light absorption. In addition, they typically possess high excitonic binding energy values as a result of the dielectric mismatch between the organic and inorganic constituents. In this talk, I will present and review the factors that control the performance of n = 1 2D halide perovskite photovoltaics, including the judicious choice of organic and group 14 metal cations and selection of charge-transport materials that are compatible with perovskite layers. Key challenges and potential pathways for achieving efficient solar cells will then be identified and discussed.

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