Recent Progress in Extending the Cycle-Life of Secondary Zn-Air Batteries

Secondary Zn-air batteries with stable voltage and long cycle-life are of immediate interest to meet global energy storage needs at various scales. Although primary Zn-air batteries have been widely used since the early 1930s, large-scale development of electrically rechargeable variants has not been fully realized due to their short cycle-life. In this work, we review some of the most recent and effective strategies to extend the cycle-life of Zn-air batteries. Firstly, diverse degradation routes in Zn-air batteries will be discussed, linking commonly observed failure modes with the possible mechanisms and root causes. Next, we evaluate the most recent and effective strategies aimed at tackling individual or multiple of these degradation routes. Both aspects of cell architecture design and materials engineering of the electrodes and the electrolytes will be thoroughly covered. Finally, we offer our perspective on how the cycle-life of Zn-air batteries can be extended with concerted and tailored research directions to pave the way for their use as the most promising secondary battery system of the future

Hydrothermal synthesis of lead free piezoelectric materials

This thesis reports successful synthesis of NKN solid solution powder series with compositions around the morphotropic phase boundary (MPB) hydrothermally at 200°C using a simple KOH and NaOH mixture with Nb2O5 as a precursor powder. Hydrothermal synthesis route adds the green-synthesis advantage to the already less toxic NKN by enabling growth at low temperatures (≤200°C, way below NKN Curie temperature), in water using simple chemicals and recyclable process. More significantly, this thesis demonstrates that the NKN solid solutions can be grown epitaxially over a conductive substrate using the same procedure. Thorough structural studies of hydrothermally grown NKN films and powders described in this thesis have shed light on the significant role of lattice trapped –OH related defects to the films’ electrical properties, crucial in devising strategies to remove the defects effectively and improve the ferro/piezoelectric performance. This thesis envisions to make widespread usage of I-V perovskite based lead-free ferro/piezoelectric materials a step closer to reality and shift the heavy reliance towards the high temperature, energy and labor intensive solid-state based materials synthesis.DOCTOR OF PHILOSOPHY (MSE

Report on industrial attachment with Hewlett-Packard (Singapore) Pte Ltd

This report focuses on, but not limited to, crack die e-test failure behavior of TIJ 2.X generation of HP print heads. The main interest of this project is to characterize the failures, especially, but not limited to, crack die. Means of electrical test and visual inspections are used extensively to identify individual failures

Understanding the defect structure of solution grown zinc oxide

Zinc oxide (ZnO) is a wide bandgap semiconducting oxide with many potential applications in various optoelectronic devices such as light emitting diodes (LEDs) and field effect transistors (FETs). Much effort has been made to understand the ZnO structure and its defects. However, one major issue in determining whether it is Zn or O deficiency that provides ZnO its unique properties remains. X-ray absorption spectroscopy (XAS) is an ideal, atom specific characterization technique that is able to probe defect structure in many materials, including ZnO. In this paper, comparative studies of bulk and aqueous solution grown (≤90 °C) ZnO powders using XAS and x-ray pair distribution function (XPDF) techniques are described. The XAS Zn–Zn correlation and XPDF results undoubtedly point out that the solution grown ZnO contains Zn deficiency, rather than the O deficiency that were commonly reported. This understanding of ZnO short range order and structure will be invaluable for further development of solid state lighting and other optoelectronic device applications

Selective Electrochemical Reduction of Carbon Dioxide to Ethylene and Ethanol on Copper(I) oxide catalysts

10.1021/cs502128qACS Catalysis552814-282

Mechanistic Insights into the Enhanced Activity and Stability of Agglomerated Cu Nanocrystals for the Electrochemical Reduction of Carbon Dioxide to <i>n</i>‑Propanol

The reduction of carbon dioxide (CO₂) to <i>n-</i>propanol (CH₃CH₂CH₂OH) using renewable electricity is a potentially sustainable route to the production of this valuable engine fuel. In this study, we report that agglomerates of ∼15 nm sized copper nanocrystals exhibited unprecedented catalytic activity for this electrochemical reaction in aqueous 0.1 M KHCO₃. The onset potential for the formation of <i>n-</i>propanol was 200–300 mV more positive than for an electropolished Cu surface or Cu⁰ nanoparticles. At −0.95 V (vs RHE), <i>n-</i>propanol was formed on the Cu nanocrystals with a high current density (<i>j</i>_{<i>n</i>‑propanol}) of −1.74 mA/cm², which is ∼25× larger than that found on Cu⁰ nanoparticles at the same applied potential. The Cu nanocrystals were also catalytically stable for at least 6 h, and only 14% deactivation was observed after 12 h of CO₂ reduction. Mechanistic studies suggest that <i>n-</i>propanol could be formed through the C–C coupling of carbon monoxide and ethylene precursors. The enhanced activity of the Cu nanocrystals toward <i>n-</i>propanol formation was correlated to their surface population of defect sites

Sub-10 nm mixing and alloying of Cu-Ag and Cu-Ni via accelerated solid diffusion

Development of nanoscale multicomponent solid inorganic materials is often hindered by slow solid diffusion kinetics and poor precursor mixing in conventional solid-state synthesis. These shortcomings can be alleviated by combining nanosized precursor mixtures and low temperature reaction, which could reduce crystal growth and accelerate the solid diffusion at the same time. However, high throughput production of nanoparticle mixtures with tunable composition via conventional synthesis is very challenging. In this work, we demonstrate that ∼10 nm homogeneous mixing of sub-10 nm nanoparticles can be achieved via spark nanomixing at room temperature and pressure. Kinetically driven Spark Plasma Discharge nanoparticle generation and ambient processing conditions limit particle coarsening and agglomeration, resulting in sub-10 nm primary particles of as-deposited films. The intimate mixing of these nanosized precursor particles enables intraparticle diffusion and formation of Cu/Ni nanoalloy during subsequent low temperature annealing at 100 °C. We also discovered that cross-particle diffusion is promoted during the low-temperature sulfurization of Cu/Ag which tends to phase-segregate, eventually leading to the growth of sulfide nanocrystals and improved homogeneity. High elemental homogeneity, small diffusion path lengths, and high diffusibility synergically contribute to faster diffusion kinetics of sub-10 nm nanoparticle mixtures. The combination of ∼10 nm homogeneous precursors via spark nanomixing, low-temperature annealing, and a wide range of potentially compatible materials makes our approach a good candidate as a general platform toward accelerated solid state synthesis of nanomaterials.Agency for Science, Technology and Research (A*STAR)National Research Foundation (NRF)The authors acknowledge funding from the Accelerated Materials Development for Manufacturing Program (Grant A1898b0043) and the Structural Metals and Alloys Program (Grant A18B1b0061) fund by the Agency for Science, Technology and Research. A.D.H. acknowledges Career Development Award (Grant 192D8230) from Agency for Science, Technology and Research. K.H. also acknowledges support from the NRF Fellowship (Grant NRF-NRFF13-2021-0011)

Local microenvironment tuning induces switching between electrochemical CO 2 reduction pathways

Gas diffusion layers (GDL) have become a critical component in electrochemical CO2 reduction (CO2R) systems because they can enable high current densities needed for industrially relevant productivity. Besides this function, it is often assumed that the choice of catalyst and electrolyte play much more important roles than the GDL in influencing the observed product selectivity. Here, we show that tuning of the GDL pore size can be used to control the local microenvironment of the catalyst and hence, effect significant changes in catalytic outcomes. This concept is demonstrated using sputtered Ag films on hydrophobic PTFE substrates with 6 different pore sizes. Although Ag is known to be a predominantly CO generating catalyst, we find that smaller pore sizes favor the generation of formate up to a faradaic efficiency of 43%. Combined experimental and simulation results show that this is due to the influence of the pore size on CO2 mass transport, which alters the local pH at the electrode, resulting in reaction pathway switching between CO and formate. Our results highlight the importance of the local microenvironment as an experimental knob that can be rationally tuned for controlling product selectivity: a key consideration in the design of CO2R systems

Towards a greener electrosynthesis: pairing machine learning and 3D printing for rapid optimisation of anodic trifluoromethylation

Applying electro-organic synthesis in flow configuration can potentially reduce the pharmaceutical industry\u27s carbon footprint and simplify the reaction scale-up. However, the optimisation of such reactions has remained challenging and resource consuming due to the convoluted interplay between the various input experimental parameters. Herein, we demonstrate the advantage of integrating a machine learning (ML) algorithm within an automated flow microreactor setup to assist in the optimisation of anodic trifluoromethylation. The ML algorithm is able to optimise six reaction parameters concurrently and increase the reaction yield of anodic trifluoromethylation by >270% within two iterations. Further, we discovered that electrode passivation and even higher reaction yields could be achieved by integrating 3D-printed metal electrodes into the microreactor. By coupling multiple analytical tools such as AC voltammetry, kinetic modelling, and gas chromatography, we gained holistic insights into the trifluoromethylation reaction mechanism, including potential sources of Faradaic efficiency and reactant losses. More importantly, we confirmed the multiple electrochemical and non-electrochemical steps involved in this reaction. Our findings highlight the potential of synergistically combining ML-assisted flow systems with advanced analytical tools to rapidly optimise complex electrosynthetic reaction sustainably