Spinels can serve as alternative low-cost bifunctional electrocatalysts for oxygen reduction/evolution reactions (ORR/OER), which are the key barriers in various electrochemical devices such as metal-air batteries, fuel cells and electrolysers. However, conventional ceramic synthesis of crystalline spinels requires an elevated temperature, complicated procedures and prolonged heating time, and the resulting product exhibits limited electrocatalytic performance. It has been challenging to develop energy-saving, facile and rapid synthetic methodologies for highly active spinels. In this Article, we report the synthesis of nanocrystalline M(x)Mn(3-x)O(4) (M = divalent metals) spinels under ambient conditions and their electrocatalytic application. We show rapid and selective formation of tetragonal or cubic M(x)Mn(3-x)O(4) from the reduction of amorphous MnO(2) in aqueous M(2+) solution. The prepared Co(x)Mn(3-x)O(4) nanoparticles manifest considerable catalytic activity towards the ORR/OER as a result of their high surface areas and abundant defects. The newly discovered phase-dependent electrocatalytic ORR/OER characteristics of Co-Mn-O spinels are also interpreted by experiment and first-principle theoretical studies.

We report here on the synthesis and photophysical/electrochemical properties of a series of novel triphenylamine (TPA)-based organic dyes (TPAR1, TPAR2, TPAR4, and TPAR5) as well as their application in dye-sensitized nanocrystalline TiO2 solar cells (DSCs). In the four designed dyes, the TPA group and the rhodanine-3-acetic acid take the role of the basic electron donor unit and the electron acceptor, respectively. It was found that introduction of a CH2CH− group into the TPA unit exhibited better photovoltaic performance due to the increase of the electron-density donor moiety and that introduction of a methine (−CHCH−) unit to the π bridge resulted in a red-shift and broadening of the absorption spectrum due to expansion of the π-conjugation system. Density functional theory (DFT) calculation indicated that the electron distribution moved from the donor unit to the electron acceptor under light irradiation, which means efficient intramolecular charge transfer. In particular, the DSCs based on TPAR4 showed the best photovoltaic performance:  a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 81%, a short-circuit photocurrent density (J sc) of 18.2 mA cm-2, an open-circuit photovoltage (V oc) of 563 mV, and a fill factor (ff) of 0.61, corresponding to an overall conversion efficiency of 5.84% under AM 1.5 irradiation (100 mW cm-2). This work suggests that the molecular-designed triphenylamine dyes are promising in the application of DSCs.

A series of new conjugated metal-free organic dyes (TC1, TC2, TC3, and TC4) comprising triphenylamine (TPA) moieties as the electron donor and cyanoacetic acid moieties as the electron acceptor/anchoring groups were designed at the molecular level and developed for the use in dye-sensitized solar cells (DSCs). Quantum chemical calculations have been performed to gain insight into structural, electronic, and optical properties of the as-synthesized sensitizers. The time-dependent density functional theory calculations allowed assignment of the experimental spectroscopic data. It is found that the photovoltaic performance of the DSCs with the as-synthesized dyes can be improved by enhancing the electron-donor ability and extending the π-conjugated bridge of the dyes. In particular, the DSCs based on 2-cyano-5-(4-(phenyl(4-vinylphenyl)amino)phenyl) penta-2,4-dienoic acid dye ( TC4) showed an open circuit voltage of 652 mV, a short circuit photocurrent density of 11.5 mA cm -2 , and a fill factor of 0.64, corresponding to an overall light to electricity conversion efficiency of 4.82% under AM 1.5 irradiation (100 mW cm -2 ). This result reveals that efficient electron injection from the excited sensitizer to the conduction band of titania film occurs, owing to the more delocalizing electrons of the bridge and donor part of the dyes.

Recently, metal nanoclusters (MNCs) emerged as a new class of luminescent materials and have attracted tremendous interest in the area of luminescence-related applications due to their excellent luminous properties (good photostability, large Stokes shift) and inherent good biocompatibility. However, the origin of photoluminescence (PL) of MNCs is still not fully understood, which has limited their practical application. In this mini-review, focusing on the origin of the photoemission emission of MNCs, we simply review the evolution of luminescent mechanism models of MNCs, from the pure metal-centered quantum confinement mechanics to ligand-centered p band intermediate state (PBIS) model via a transitional ligand-to-metal charge transfer (LMCT or LMMCT) mechanism as a compromise model.

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