Formulation and mechanism of copper tartrate - a novel anode material for lithium-ion batteries.

Batteries play an increasingly critical role in the functioning of contemporary society. To ensure future proofing of battery technology, new materials and methods that overcome the current shortcomings need to be developed. Here we report the use of the inexpensive and off the shelf metal-carboxylate, copper tartrate, as a high-capacity anode material for lithium-ion batteries, providing a specific capacity of 744 mA h g-1 when cycled at 50 mA g-1. Additionally, an unusual capacity gain with cycling is investigated using advanced techniques including X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and small and ultra-small angle neutron scattering (SANS and USANS), providing insight into the structure-performance relationship of the electrode. Subsequently, a novel method of in situ generation of the active material is demonstrated using the reaction between the parent acid, tartaric acid, and the copper current collector during electrode formulation. This serves to increase and stabilise the electrode performance, as well as to make use of a cheaper feedstock (tartaric acid), and reduce some of the "dead mass" of the copper current collector.

Stability of surface protons in pyridine-catalyzed CO2 reduction at p-GaP photoelectrodes.

Adsorbed protons that develop hydride character have been proposed to play a role in the mechanism of CO2 reduction catalyzed by pyridine on GaP photoelectrodes. Investigating their stability represents an important step towards vetting this mechanism. In this contribution, the relative stability of the adsorbed protons is determined using cluster models with dispersion-corrected density functional theory and continuum solvation. Proton acidity constants computed under typical experimental conditions are compared to the acidity constants of other relevant species. The adsorbed protons are predicted to be very stable, suggesting that they will be present on the surface and available to be reduced to surface hydrides that could possibly react with adsorbed pyridine to form adsorbed dihydropyridine, a previously proposed co-catalyst. However, the high stability of such protons also suggests that the surface does not represent a significant proton source; as a consequence, protons required in the proposed mechanism must be provided by a different source such as the acidified aqueous solution in contact with the electrode surface.

What Is the Role of Pyridinium in Pyridine-Catalyzed CO2 Reduction on p-GaP Photocathodes?

Experimental evidence suggests that pyridinium plays an important role in photocatalytic CO2 reduction on p-GaP photoelectrodes. Pyridinium reduction to pyridinyl has been previously proposed as an essential mechanistic step for this reaction. However, theoretical calculations suggest that this step is not feasible in solution. Here, cluster models and accurate periodic boundary condition calculations are used to determine whether such a reduction step could occur by transfer of photoexcited electrons from the p-GaP photocathode and whether this transfer could be catalyzed by pyridinium adsorption on the p-GaP surface. It is found that both the transfer of photoexcited electrons to pyridinium and pyridinium adsorption are not energetically favored, thus making very unlikely pyridinium reduction to the pyridinyl radical and the proposed mechanisms requiring this reduction step. Given this conclusion, an alternative and energetically viable pathway for pyridinium reduction on p-GaP photoelectrodes is proposed. This pathway leads to the formation of adsorbed species that could react to form adsorbed dihydropyridine, which was proposed previously to play the role of the active catalyst in this system.

Cation induced changes to the structure of cryptophane cages.

Here the monocation complexes of seven anti-cryptophanes are examined with high-resolution ion-mobility mass spectrometry. The relative size of the [cation + cryptophane]+ complexes were compared based on their measured mobilities and derived collisional cross sections. A paradoxical trend of structural contraction was observed for complexes of increasing cation size. Density functional theory confirmed encapsulation occurs for cation = Na+, K+, Rb+, Cs+ and NH4+. However, cation = Li+ preferred oxygen coordination at a linker over encapsulation within the cavity, leading to a slightly larger gas phase structure overall. Protonated cryptophanes yielded much larger collision cross sections via imploded cryptophane structures. Thus, competing physical effects led to the observed non-periodic size trend of the complexes. Trends in complexation from isothermal titration calorimetry and other condensed phase techniques were borne out by the gas phase studies. Further, predicted cavity sizes compared with the gas phase experimental findings reveal more about the encapsulation mechanisms themselves.

Sugar-induced self-assembly of curcumin-based polydopamine nanocapsules with high loading capacity for dual drug delivery.

Many drug delivery carriers reported in the literature require multistep assembly or often have very low drug loading capacities. Here, we present a simple sugar-based strategy that feeds the increased interest in high-loading nanomedicine. The driving force of the supramolecular nanocapsule formation is the interaction between curcumin (CCM) and the monosaccharide fructose. Drug and sugar are simply mixed in an aqueous solution in an open vessel, followed by coating the nanocapsules with polydopamine (PDA) to maintain structural integrity. We show that nanocapsules can still be obtained when other drugs are added, producing dual-drug nanoparticles with sizes of around 150-200 nm and drug loading contents of around 90% depending on the thickness of the PDA shell. This concept is widely applicable for a broad variety of drugs, as long as the drug has similar polarities to CCM. The key to success is the interaction of CCM and the second drug as shown in computational studies. The drug was able to be released from the nanocapsule at a release rate that could be fine-tuned by adjusting the thickness of the PDA layer.

Phosphate functionalised titania for heavy metal removal from acidic sulfate solutions.

Adsorbent materials based on titania and phosphate are ideal for treatment of solutions contaminated with heavy metals under acidic conditions, due to their inherent chemical stability and low pKa. Herein, phosphate functionalised titania has been investigated for the first time for removal of heavy metals (Cr, Fe, Cu, Eu, U) under conditions relevant to acid mine drainage (pH 2-5 sulfuric acid). Successful functionalisation was found to depend on the phase of titania used, with anatase preferred according to computational results from density functional theory. The effect of phosphate ligand structure was explored, revealing that the phosphate ethyl ester maximised heavy metal removal. The presence and concentration of counterions (sulfate, nitrate, ammonium) also impacted the speciation and binding of heavy metal cations, demonstrating the importance of adsorbent testing under realistic conditions. Increasing the porosity of the titania framework enhanced heavy metal removal, while maintaining selectivity for the toxic heavy metals over non-toxic cations Na and K. As such, phosphate functionalised titania shows great promise for heavy metal remediation in acidic sulfate environments.

Superatomic solid solutions.

In atomic solids, substitutional doping of atoms into the lattice of a material to form solid solutions is one of the most powerful approaches to modulating its properties and has led to the discovery of various metal alloys and semiconductors. Herein we have prepared solid solutions in hierarchical solids that are built from atomically precise clusters. Two geometrically similar metal chalcogenide clusters, Co6Se8(PEt3)6 and Cr6Te8(PEt3)6, were combined as random substitutional mixture, in three different ratios, in a crystal lattice together with fullerenes. This does not alter the underlying crystalline structure of the [cluster][C60]2 material, but it influences its electronic and magnetic properties. All three solid solutions showed increased electrical conductivities compared with either the Co- or Cr-based parent material, substantially so for two of the Co:Cr ratios (up to 100-fold), and lowered activation barriers for electron transport. We attribute this to the existence of additional energy states arising from the materials' structural heterogeneity, which effectively narrow transport gaps.

Hydride Shuttle Formation and Reaction with CO2 on GaP(110).

Adsorbed hydrogenated N-heterocycles have been proposed as co-catalysts in the mechanism of pyridine (Py)-catalyzed CO2 reduction over semiconductor photoelectrodes. Initially, adsorbed dihydropyridine (DHP*) was hypothesized to catalyze CO2 reduction through hydride and proton transfer. Formation of DHP* itself, by surface hydride transfer, indeed any hydride transfer away from the surface, was found to be kinetically hindered. Consequently, adsorbed deprotonated dihydropyridine (2-PyH- *) was then proposed as a more likely catalytic intermediate because its formation, by transfer of a solvated proton and two electrons from the surface to adsorbed Py, is predicted to be thermodynamically favored on various semiconductor electrode surfaces active for CO2 reduction, namely GaP(111), CdTe(111), and CuInS2 (112). Furthermore, this species was found to be a better hydride donor for CO2 reduction than is DHP*. Density functional theory was used to investigate various aspects of 2-PyH- * formation and its reaction with CO2 on GaP(110), a surface found experimentally to be more active than GaP(111). 2-PyH- * formation was established to also be thermodynamically viable on this surface under illumination. The full energetics of CO2 reduction through hydride transfer from 2-PyH- * were then investigated and compared to the analogous hydride transfer from DHP*. 2-PyH- * was again found to be a better hydride donor for CO2 reduction. Because of these positive results, full energetics of 2-PyH- * formation were investigated and this process was found to be kinetically feasible on the illuminated GaP(110) surface. Overall, the results presented in this contribution support the hypothesis of 2-PyH- *-catalyzed CO2 reduction on p-GaP electrodes.

The Role of Surface-Bound Dihydropyridine Analogues in Pyridine-Catalyzed CO2 Reduction over Semiconductor Photoelectrodes.

We propose a general reaction mechanism for the pyridine (Py)-catalyzed reduction of CO2 over GaP(111), CdTe(111), and CuInS2(112) photoelectrode surfaces. This mechanism proceeds via formation of a surface-bound dihydropyridine (DHP) analogue, which is a newly postulated intermediate in the Py-catalyzed mechanism. Using density functional theory, we calculate the standard reduction potential related to the formation of the DHP analogue, which demonstrates that it is thermodynamically feasible to form this intermediate on all three investigated electrode surfaces under photoelectrochemical conditions. Hydride transfer barriers from the intermediate to CO2 demonstrate that the surface-bound DHP analogue is as effective at reducing CO2 to HCOO- as the DHP(aq) molecule in solution. This intermediate is predicted to be both stable and active on many varying electrodes, therefore pointing to a mechanism that can be generalized across a variety of semiconductor surfaces, and explains the observed electrode dependence of the photocatalysis. Design principles that emerge are also outlined.