Singapore

Green and eco-friendly geopolymers with high thermal/acid resistance represent potential replacement material for epoxies. However, the intrinsic brittleness hinders widespread applications of this material. We fabricated a new type of geopolymer composites by impregnated with interface engineered 3D skeleton resembling the lotus root structure. Highly porous melamine foam was selected as the 3D skeleton and its interior surface was coated with elastomeric PDMS-polyurea block copolymer. Under loading, the interfacial elastomer could deform and absorb large amount of energy concurrently with crack deflection of melamine foam and delamination of interfaces, thus the toughness was substantially improved as results indicated a transition of fracture behavior from brittle failure mode to a more ductile one. With as low as 2.5 wt. % elastomer, the fracture toughness and work of fracture were increased by 258% and 654%, respectively.

MATERIALS FOR HUMANITY (MH 21)

Biomimetic Geopolymer Composites as A Promising Thermoset Material

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MH 21 is arranged around 6 themes that focus attention on pressing needs that should be addressed to enhance the well-being of communities and provide a forum for presenting breakthrough discoveries.

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We reported the convenient synthesis of carbon dots by one-step hydrothermal method using plastic waste as the precursor. The prepared carbon dots exhibit good water dispersibility, excellent pH stabilities and resistance to photobleaching. Transmission Electron Microscope image indicates that the size of the synthesized carbon dot is 3 nm-10 nm. The effect of produced carbon dots on plant growth was investigated with mung bean as plant model. Plant growth results indicated that carbon dots produced from plastic waste is effective in promoting plant growth in terms of shoot length, wet mass and dry mass, which implied the potential of plastic waste in sustainable agriculture.

Carbon Dots from plastic waste and their potential application in sustainable agriculture

The use of Carbon Fibre Reinforced Polymer (CFRP) composites as high performance replacement for traditional metal alloy-based structures have been ongoing over the past decade. Although some of these CFRP products are reaching their end-of-life, there is still a lack of CFRP waste management and recycling strategies. The main issues plaguing the commercialisation of large scale CFRP recycling includes capital intensive equipment, energy intensive processes and downgraded recyclate with reduced commercial value. We present our technical approach which addresses the abovementioned difficulties.

Maximising value from carbon fibre composite waste

Electrocatalytic dinitrogen reduction reaction (N2RR) is an emerging route for ammonia synthesis at ambient conditions. Albeit the ‘‘π back-donation’’ process enables N2RR activity on transition metals with empty dorbitals, given its dilemma in overcoming hydrogen evolution reaction (HER) competition, exploring p-block-element-based catalysts with relatively inferior HER activity is achievable for high selectivity. The challenge lies in designing rational structure to improve N2RR activity. Here, we synergistically integrate oxygen vacancy (VO) with hydroxyl on Bi4O5 I2 (VOBi4O5 I2 -OH), which render this p-block-element-based material active to mimic ‘‘π back-donation’’ behavior because of sufficient vacant orbitals. In neutral media, the electrocatalytic N2RR performance of VO-Bi4O5 I2 -OH in terms of splendid faradic efficiency (32.4%) is superior to most of the prior reports using p-block-element-based catalysts.

Electrocatalytic Ammonia Production through Mimicking ‘‘π Back-Donation’’

Aqueous Al-ion batteries (AAIBs) are the subject of great interest due to the inherent safety and high theoretical capacity of aluminum. Here, we proposed a new AAIB system consisting of an AlxMnO2 cathode, a zinc substrate-supported Zn−Al alloy anode, and an Al(OTF)3 aqueous electrolyte. Through the in situ electrochemical activation of MnO, the cathode was synthesized to incorporate a two-electron reaction, thus enabling its high theoretical capacity. The anode was realized by a simple deposition process of Al3+ onto Zn foil substrate. The featured alloy interface layer can effectively alleviate the passivation and suppress the dendrite growth, ensuring ultralong-term stable aluminum stripping/ plating. The architected cell delivers a record-high discharge voltage plateau near 1.6 V and specific capacity of 460 mAh g −1 for over 80 cycles. This work provides new opportunities for the development of highperformance and low-cost AAIBs for practical applications.

Architecting a Stable High-Energy Aqueous Al-Ion Battery

As one of the most promising sustainable energy techniques, Li-O2 batteries have attracted tremendous interest. However, the sluggish cathode reactions and the unwanted side reactions by the reactive superoxide intermediates deleteriously compromise the attainable capacity and the reversibility. Herein, we introduce duroquinone (DQ) as a bifunctional soluble catalyst that facilitates electron transfer and stabilizes the aggressive superoxide intermediates. With the assistance of electron paramagnetic resonance (EPR), the prolonged lifetime by the quinone can be observed which proves the stabilization of the superoxide species. By enhancing the solvation of the superoxide species, the oxygen reduction turns from the surface to the solution mechanism in low donor number (DN) electrolyte. Consequently, the Li-O2 battery presents a significantly enlarged discharge capacity and the solution growth of micrometer-sized Li2O2 particles.

Bifunctional soluble catalyst promoting solution discharge of Li-O2 battery

1) The aprotic Li–O2 battery are expected to be the promising next-generation candidates due to their extremely high theoretical gravimetric energy density. 2) However, to realize a commercial rechargeable Li–O2 technology confronts clogging and passivation of the cathode by insoluble nature of discharge product Li2O2 and high charge overpotential for its insulating nature. 3) Crown ethers have been attracting interests due to their ability to coordinate with Li+ , which enhances the ionic conductivity of the electrolyte and improves the battery performance. EXPERIMENTAL Here, we examined dibenzo-24-crown-8 derivative aldehyde (DB24C8-CHO) as an additive in TEGDME electrolyte solutions, which present a significantly low charge overpotential of 0.77 V, and an excellent cycle life (up to 213 cycles) at 500 mA g −1with a fixed capacity of 500 mAh·g -1.

A High-Performance Li–O2 Battery with dibenzo-24-crown-8 derivative aldehyde additives

The inability of the current energy storage system to meet the requirements of industry is driving the development of emerging battery devices. Rechargeable lithium-oxygen batteries are expected to be a possible solution for the development of alternative batteries with high energy density. However, the lithium-oxygen batteries are still in the prototype stage due to obstacles that are mainly related to the slow electrode dynamics, especially the high charge overpotential. To overcome these bottlenecks, the introduction of photo assistance into the lithium-oxygen system has attracted great research interest. Herein, we explored the application of WO3 with different crystal planes in photo-assisted lithium-oxygen batteries. At a current density of 0.04 mA cm-2, the 3-WO3-nanosheet shows a charge overpotential of about 3.1 V and is able to work for 95 cycles at 0.04 mAh cm-2.

Improving Lithium-Oxygen Battery Performance via Photocatalysis

Pore structure of hard carbon has a fundamental influence on the electrochemical properties in sodium-ion batteries (SIBs). Ultra-micropores (< 0.5nm) of hard carbon can function as ionic sieves to reduce the diffusion of slovated Na + but allow the entrance of naked Na + into the pores, which can reduce the interficial contact between the electrolyte and the inner pores without sacrificing the fast diffusion kinetics. Herein, a molten diffusion-carbonization method is proposed to transform the micropores (> 1 nm) inside carbon into ultra-micropores (< 0.5 nm). Consequently, the designed carbon anode displays an enhanced capacity of 346 mAh g -1 at 30 mA g -1 with a high ICE value of ~ 80.6% and most of the capacity (~90%) is below 1 V. Moreover, the high-loading electrode (~ 19mg cm-2 ) exhibits a good temperature endurance with a high areal capacity of 6.14 mAh cm-2 at 25℃ and 5.32 mAh cm-2 at -20 ℃. Based on the in-situ X-ray diffraction (XRD) and ex-situ solid-state nuclear magnetic resonance (NMR) results, the designed ultra-micropores provide the extra Na+ storage sites, which mainly contributes to the enhanced capacity. This proposed strategy shows good potential for the development of high-performance SIBs.

From Micropores to Ultra-micropores inside Hard Carbon: Towards Enhanced Capacity in Room/Low-Temperature Sodium-Ion Storage

Electromechanical Failure Mechanism of All-solid-state Li-ion Batteries based on a NASICON-type Solid-state Electrolyte 
Linchun He, Stefan Adams
Department of Materials Science and Engineering, National University of Singapore

All-solid-state lithium batteries (ASSLiB) are promising candidates for next-generation energy storage. Beyond design requirements and concerns of conventional batteries, the undeformable nature of solid-state electrolytes (SSEs)1 raises new issues for ASSLiBs such as poor interface bonding, limited contact area and cathode utilization.2 Moreover, volume changes of electrodes during Li-ion (de)intercalation are restricted by the SSE, resulting in large internal stresses that may drive crack creation. Such cracks reduce the utilization of electrodes and the available cross-section of the SSE for ion transport. Increased currents in the remaining connected regions turn this into a self-accelerating aging process. Hence it is essential to synergize understanding of the ion transport with insight into mechanochemical processes in the SSE or at its interfaces to overcome these obstacles.
Here, we demonstrate and analyze a model bulk ASSLiB with MnO2-CNT nanocomposite anode, high voltage LiNi0.5Mn1.5O4 cathode and ambient-stable Li1.5Al0.5Ge(PO4)3 (LAGP) as SSE. This ASSLiB has a discharge capacity of 82 mAh g-1 at 0.15 C at 23.8°C. Electrochemical impedance studies reveal a decrease in impedance by solid interface layer formation, followed by an increase over extended cycling. Electrochemical evaluation and first-principle calculations are used to explore the aging processes. Li4P2O7, Li3PO4, Ge5P6O25, AlPO4 and GeO are identified as products of the decomposition of LAGP, which is assisted by Li-ions and free electrons from voids and grain boundaries. Finite element method (FEM) simulations reveal that the volume expansion on forming the decomposition products causes maximum internal stresses of 2.5 to 125 GPa (for Li excess ratios from 0 to 6), resulting in crack formation and growth within the SSE on multiple cycling. 
1. C. Chen, Y. Sun, L. He et al., ACS Appl. Mater. Interfaces (2020).
2. L. He, C. Chen, M. Kotobuki et al., J. Mater. Chem. A 7, 9748 (2019).



Electromechanical Failure Mechanism of All-solid-state Li-ion Batteries based on a NASICON-type Solid-state Electrolyte

Understanding the alkali interaction with the organic functional groups is significant for molecular-level design of potential anode materials.In this work,we investigate the chemical and electronic interactions between Li/Na and PTCDA/PTCDI during the deposition processes. The change of molecular electronic structures has been studied by X-ray photo electron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), synchrotron-based near edge X-ray absorption fine structure (NEXAFS), and corroborated by density functional theory (DFT) calculations.

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Biomimetic Geopolymer Composites as A Promising Thermoset Material

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