Tailored (La0.2 Pr0.2 Nd0.2 Tb0.2 Dy0.2 )2 Ce2 O7 as a Highly Active and Stable Nanocatalyst for the Oxygen Evolution Reaction.

Designing highly active and robust catalysts for the oxygen evolution reaction is key to improving the overall efficiency of the water splitting reaction. It has been previously demonstrated that evaporation induced self-assembly (EISA) can be used to synthesize highly porous and high surface area cerate-based fluorite nanocatalysts, and that substitution of Ce with 50% rare earth (RE) cations significantly improves electrocatalyst activity. Herein, the defect structure of the best performing nanocatalyst in the series are further explored, Nd2 Ce2 O7 , with a combination of neutron diffraction and neutron pair distribution function analysis. It is found that Nd3 + cation substitution for Ce in the CeO2 fluorite lattice introduces higher levels of oxygen Frenkel defects and induces a partially reduced RE1.5 Ce1.5 O5 + x phase with oxygen vacancy ordering. Significantly, it is demonstrated that the concentration of oxygen Frenkel defects and improved electrocatalytic activity can be further enhanced by increasing the compositional complexity (number of RE cations involved) in the substitution. The resulting novel compositionally-complex fluorite- (La0.2 Pr0.2 Nd0.2 Tb0.2 Dy0.2 )2 Ce2 O7 is shown to display a low OER overpotential of 210 mV at a current density of 10 mAcm-2 in 1M KOH, and excellent cycling stability. It is suggested that increasing the compositional complexity of fluorite nanocatalysts expands the ability to tailor catalyst design.

Mesoporous RE0.5Ce0.5O2-x Fluorite Electrocatalysts for the Oxygen Evolution Reaction.

Developing highly active and stable electrocatalysts for the oxygen evolution reaction (OER) is key to improving the efficiency and practical application of various sustainable energy technologies including water electrolysis, CO2 reduction, and metal air batteries. Here, we use evaporation-induced self-assembly (EISA) to synthesize highly porous fluorite nanocatalysts with a high surface area. In this study, we demonstrate that a 50% rare-earth cation substitution for Ce in the CeO2 fluorite lattice improves the OER activity and stability by introducing oxygen vacancies into the host lattice, which results in a decrease in the adsorption energy of the OH* intermediate in the OER. Among the binary fluorite compositions investigated, Nd2Ce2O7 is shown to display the lowest OER overpotential of 243 mV, achieved at a current density of 10 mA cm-2, and excellent cycling stability in an alkaline medium. Importantly, we demonstrate that rare-earth oxide OER electrocatalysts with high activity and stability can be achieved using the EISA synthesis route without the incorporation of transition and noble metals.

A Molecular Tetrahedral Cobalt-Seleno-Based Complex as an Efficient Electrocatalyst for Water Splitting.

The cobalt-seleno-based coordination complex, [Co{(SePiPr2)2N}2], is reported with respect to its catalytic activity in oxygen evolution and hydrogen evolution reactions (OER and HER, respectively) in alkaline solutions. An overpotential of 320 and 630 mV was required to achieve 10 mA cm-2 for OER and HER, respectively. The overpotential for OER of this CoSe4-containing complex is one of the lowest that has been observed until now for molecular cobalt(II) systems, under the reported conditions. In addition, this cobalt-seleno-based complex exhibits a high mass activity (14.15 A g-1) and a much higher turn-over frequency (TOF) value (0.032 s-1) at an overpotential of 300 mV. These observations confirm analogous ones already reported in the literature pertaining to the potential of molecular cobalt-seleno systems as efficient OER electrocatalysts.

Explosive Fragmentation of Luminescent Diamond Particles.

Development of efficient and cost-effective mass-production techniques for size reduction of high- pressure, high-temperature (HPHT) diamonds with sizes from tens to hundreds of micrometers remains one of the primary goals towards commercial production of fluorescent submicron and nanodiamond (fND). fNDs offer great advantages for many applications, especially in labelling, tracing, and biomedical imaging, owing to their brightness, exceptional photostability, mechanical robustness and intrinsic biocompatibility. This study proposes a novel processing method utilizing explosive fragmentation that can potentially be used for the fabrication of submicron to nanoscale size fluorescent diamond particles. In the proposed method, synthetic HPHT 20 pm and 150 pm microcystalline diamond particles containing color centers are rapidly fragmented in conditions of high explosive detonation. X-ray diffraction and Raman spectroscopy show that the detonation fragmented diamond particles consist of good quality submicron diamonds of ~420-800 nm in size, while fluorescence spectroscopy shows photoluminescence spectra with noticeable changes for large (150 µm) starting microcrystalline diamond particles, and no significant changes in photoluminescence properties for smaller (20 µm) starting microcrystalline diamond particles. The proposed detonation method shows potential as an efficient, cost effective, and industrially scalable alternative to milling for the fragmentation of fluorescent diamond microcrystals into submicron- to nano-size domain.

Effect of Nanodiamond Surface Chemistry on Adsorption and Release of Tiopronin.

Tiopronin is an FDA-approved thiol drug currently used to treat cystinuria and rheumatoid arthritis. However, due to its antioxidant properties, it may be beneficial in a variety of other conditions. One primary obstacle to its wider application is its limited bioavailability, which necessitates administration of high systemic doses to achieve localized therapeutic effects. Incorporation of a drug delivery vehicle can solve this dilemma by providing a means of controlled, targeted release. Functionalized nanodiamond is a promising theranostic platform that has demonstrated great potential for biomedical applications, including drug delivery. Design of nanodiamond theranostic platforms requires comprehensive understanding of drug-platform interactions, and the necessary physical chemical investigations have only been realized for a limited number of compounds. Towards the long-term goal of developing a nanodiamond-tiopronin treatment paradigm, this study aims to shed light on the effects of nanodiamond surface chemistry on adsorption and release of tiopronin. Specifically, adsorption isotherms were measured and fit to Langmuir and Freundlich models for carboxylated, hydroxylated, and aminated nanodiamonds, and release was monitored in solutions at pH 4.0, 5.8, 7.3, and 8.1. Our results indicate that aminated nanodiamonds exhibit the highest loading capacity while hydroxylated nanodiamonds are the most effective for sustained release. Therefore, a high degree of flexibility may be afforded by the use of nanodiamonds with different surface chemistries optimized for specific applications.