Spiky/hollow metal nanoparticles have applications across a broad range of fields. However, the current bottom-up methods for producing spiky/hollow metal nanoparticles rely heavily on the use of strongly adsorbing surfactant molecules, which is undesirable because these passivate the product particles’ surfaces. Here we report a high-yield surfactant-free synthesis of spiky hollow Au–Ag nanostars (SHAANs). Each SHAAN is composed of >50 spikes attached to a hollow ca. 150 nm diameter cubic core, which makes SHAANs highly plasmonically and catalytically active. Moreover, the surfaces of SHAANs are chemically exposed, which gives them significantly enhanced functionality compared with their surfactant-capped counterparts, as demonstrated in surface-enhanced Raman spectroscopy (SERS) and catalysis. The chemical accessibility of the pristine SHAANs also allows the use of hydroxyethyl cellulose as a weakly bound stabilizing agent. This produces colloidal SHAANs that remain stable for >1 month while retaining the functionalities of the pristine particles and allows even single-particle SERS to be realized.

Pickering emulsions represent an important class of functional materials with potential applications in sustainability and healthcare. Currently, the synthesis of Pickering emulsions relies heavily on the use of strongly adsorbing molecular modifiers to tune the surface chemistry of the nanoparticle constituents. This approach is inconvenient and potentially a dead-end for many applications since the adsorbed modifiers prevent interactions between the functional nanosurface and its surroundings. Here, we demonstrate a general modifier-free approach to construct Pickering emulsions by using a combination of stabilizer particles, which stabilize the emulsion droplet, and a second population of unmodified functional particles that sit alongside the stabilizers at the interface. Freeing Pickering emulsions from chemical modifiers unlocks their potential across a range of applications including plasmonic sensing and interfacial catalysis that have previously been challenging to achieve. More broadly, this strategy provides an approach to the development of surface-accessible nanomaterials with enhanced and/or additional properties from a wide range of nano-building blocks including organic nanocrystals, carbonaceous materials, metals and oxides.

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This study investigates the cycling performance and failure mechanisms of sodium-ion pouch cells with layered NaCa0.03[Mn0.39Fe0.31Ni0.22Zn0.08]O2 positive electrodes and hard carbon negative electrodes. Charge/discharge cycling between different lower and upper cut-off voltages at C/5 and 40°C showed better capacity retention, lower voltage polarization, and less gassing when the upper cut-off voltage was limited to 3.80 V. Electrodes harvested from pouch cells after cycling were reassembled in symmetric coin cells to reveal the origin of voltage polarization by electrochemical impedance spectroscopy. The negative electrode charge transfer resistance dominated the full cell impedance and increased considerably after 100 cycles at 40°C with standard alkyl carbonate electrolyte. The positive electrode impedance was less significant but increased dramatically when the full cell voltage was 4.00 V. Furthermore, ultra-high precision coulometry used for the in-situ detection of sodium plating at 40°C, revealed significant plating at charging rates greater C/2. Based on this failure analysis, long-lived sodium-ion cells with 97% capacity retention after 450 cycles at 40°C could be realized by selecting appropriate voltage cut-offs, C-rates, and effective electrolyte additives that lowered the cell resistance and suppressed gas generation.

Incorporation of plasmonic metal nanomaterials can significantly enhance the visible light response of semiconductor photocatalysts via localized surface plasmon resonance (LSPR) mechanisms. However, the surfaces of plasmonic metal nanomaterials are often covered with surfactant molecules, which is undesired when the nanomaterials are used for photocatalytic hydrogen evolution, since surfactant molecules could significantly compromise the nanomaterials' cocatalyst functionalities by blocking the active sites and/or by inhibiting the surface charge transfer process. Herein, we demonstrate a method that assembles Au nanoparticles (NPs) into Au colloidosomes (AuCSs) without modifying their surfaces with surfactants. The resulting AuCSs were then coupled with CdS for the formation of Au−CdS composite photocatalysts through an in situ deposition method. The assembly of Au NPs induced a broader and stronger LSPR response for AuCSs, while the absence of surfactants allowed them to act efficiently as cocatalysts. This essentially enhanced the electron−hole pair generation rate and further their utilization efficiency, leading to an extremely high hydrogen evolution rate of 235.8 mmol•g −1 •h −1 under simulated sunlight excitation.