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Despite the groundbreaking advancements in the synthesis of inorganic lead halide perovskite (LHP) nanocrystals (NCs), stimulated from their intriguing size-, composition-, and morphology-dependent optical and optoelectronic properties, their formation mechanism through the hot-injection (HI) synthetic route is not well-understood. In this work, for the first time, in-flow HI synthesis of cesium lead iodide (CsPbI 3 ) NCs is introduced and a comprehensive understanding of the interdependent competing reaction parameters controlling the NC morphology (nanocube vs nanoplatelet) and properties is provided. Utilizing the developed flow synthesis strategy, a change in the CsPbI 3 NC formation mechanism at temperatures higher than 150 °C, resulting in different CsPbI 3 morphologies is revealed. Through comparison of the flow-versus flask-based synthesis, deficiencies of batch reactors in reproducible and scalable synthesis of CsPbI 3 NCs with fast formation kinetics are demonstrated. The developed modular flow chemistry route provides a new frontier for high-temperature studies of solution-processed LHP NCs and enables their consistent and reliable continuous nanomanufacturing for next-generation energy technologies.

Inorganic lead halide perovskite (LHP) quantum dots (QDs) have recently emerged as a promising class of semiconducting materials for next-generation, solution-processed optoelectronic devices. [1] For example, inorganic LHPs have surpassed the performance of conventional IV-VI QDs in photovoltaic devices. [2] The prominence of LHPs among other semiconductor nanocrystals is mainly attributed to their high photoluminescence quantum yield (PLQY), high defect tolerance, facile bandgap tunability, and narrow emission linewidth. The ease of peak emission bandgap tuning (1.7-3.1 eV) makes inorganic LHP QDs a versatile material for widespread applications ranging from solar cells (1.77 eV), [3-6] light-emitting diodes (blue 2.7 eV, green 2.39 eV, and red 1.88 eV), [7-9] and various photocatalytic reactions. [10-12] The peak emission energy of cesium lead halide QDs (CsPbX 3 , X ¼ Cl, Br, I) can be readily tuned by varying i) QD size using the quantum confinement effect, [13-16] ii) ligand composition, [17-19] iii) the chemical composition of the QD through anion, [20-22] and/or cation exchange, [23] and iv) the precursor halide content. [1,24] Despite producing high-quality monodispersed CsPbX 3 QDs, [1] flask-based hot-injection synthetic routes impose major challenges from large-scale manufacturing and reproducibility perspectives. Hot-injection colloidal synthesis requires operating at high temperatures (>150 C), which increases the overall energy costs and necessitates specific reactor design modifications to ensure homogenous, uniform heat distribution across the reactor. Furthermore, manual, flask-based colloidal syntheses are notorious for their lack of reproducibility (batch-to-batch variation and operator error), and difficulty of integration with material diagnostic probes. [13,24,25] Room-temperature colloidal synthesis (e.g., ligand-assisted reprecipitation strategy) [7,26,27] and post-synthesis halide exchange reactions [20-22,28] of CsPbBr 3 QDs are considered attractive alternatives to the hot-injection synthesis strategy for facile and precise bandgap engineering of LHP QDs. QD purification normally involves washing steps that consist of antisolvent addition followed by centrifugation, aliquot disposal, and fresh solvent addition. Moreover, washing and the subsequent redispersal of LHP QDs in fresh solvent disrupts the surface ligands, leading to ligand detachment, [29,30] surface defects (lowering the PLQY), and reduced colloidal stability of the LHP QDs. [30] Removal of the intermediate washing step of halide exchange reactions can enable end-to-end continuous manufacturing of inorganic LHP QDs and accelerate their adoption by chemical and energy technologies.

The aim of this study is to quantify the hydrogen production rate in an anion exchange membrane (AEM) lignin electrolysis cell. Two non-precious and nanostructured metal and metal oxide electrocatalysts were developed and used as the anodic catalysts in a lignin electrolysis process. H 2 production rates, energy consumption rates and faradaic efficiency were measured using β-PbO 2 /MWNTs and Ni-Co/TiO 2 electrocatalysts as the anode, where electrochemical depolymerization of lignin occurs. Our results were then compared with recent efforts for lignin electrolysis in the literature. This work demonstrates that the β-PbO 2 /MWNTs nanocomposite is the more stable and active electrocatalyst in this process. At the end, our results showed that using β-PbO 2 /MWNTs as the anodic electrocatalyst can enhance lignin oxidation rates, with a corresponding increase in the rate of H 2 production at the cathode. As a result, this can lead to high hydrogen evolution rates (∼45.6 mL/h), and increase energy efficiency by 20%, compared to a commercial alkaline water electrolyzer.

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Semiconductors are intriguing due to their unique electrical properties, particularly the behavior of their electrons in the presence of different stimuli (e.g., electric field, magnetic field, light irradiation), which differ greatly from conducting (i.e., metals) and insulating materials. In insulators and semiconductors, the available electronic states are discontinuous, with the existence of a gap between the lower energy states, commonly referred to as the valence band (VB), and the higher energy states, known as the conduction band (CB). The distinguishing factor between these materials is the size of the energy difference between the highest energy state in the VB and the lowest energy state in the CB, called the band gap. In insulators, the band gap is very large, making it difficult, if not impossible, to cause an electron to move from the VB to the CB. By comparison, semiconductors possess narrow to moderate band gaps, implying that it is possible to introduce enough energy to an electron to cause it to move from the VB to the CB, enabling electron transfer, the use of high energy electrons, or the emission of energy (i.e., photons) when the electron returns from the CB to the VB. The wide range of industrial application-specific requirements demands versatility in the target characteristics of semiconductor materials (e.g., size, morphology, composition, band gap, emission wavelength), which are vastly different from those commonly used in thin-film transistors. Typically, the semiconductor materials synthesized for use in the above applications are particulate materials produced across a range of sizes spanning five orders of magnitude (from just a few nm to hundreds of µm), and can be divided into two overarching categories, nano-and microsized particulate materials. Nanosized semiconductor materials, due in large part to their miniscule dimensions, present a variety of intriguing characteristics not observed in microsized semiconductor particles. First and foremost, if the dimensions of the semiconductor material decrease below a certain threshold known as the Bohr radius, the absorption and emission energies become highly dependent on the particle size, a phenomenon known as quantum confinement. [28-30] Moreover, nanosized structures have significantly larger surface-to-volume ratios which increases the surface contribution to the total free energy of the semiconductor materials, making them highly soluble [29] and therefore much easier to process and handle. Thus far, nanosized semiconductor particles have been effectively utilized in sensors, [7] LEDs, [9] Controlled synthesis of semiconductor nano/microparticles has attracted sub stantial attention for use in numerous applications from photovoltaics to photo catalysis and bioimaging due to the breadth of available physicochemical and optoelectronic properties. Microfluidic material synthesis strategies have recently been demonstrated as an effective technique for rapid development, controlled synthesis, and continuous manufacturing of solutionpr...

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