An ultrathin two-dimensional Zn porphyrin-based metal-organic framework (Zn-MOF nanosheets) is developed and used for the first time in photoreduction of CO2 to CO. Consequently, two novelty noble-metal-free hybrid photocatalytic systems are established and displayed outstanding photocatalytic activity and selectivity for CO evolution under mild photocatalytic reaction conditions. The insight revealed Zn-MOF nanosheets as photo sensitizer displays a better charge transport ability and longer lifetime of the photogenerated electron-hole pairs than the Zn-MOF bulk, which are confirmed by photoelectrochemical impedance and photoluminescence (PL) measurements. These studies show that the development of noble-metal-free photocatalytic systems and various MOF-based materials for photocatalytic applications are promising.

X1 (MeO-TPD) is an inexpensive and easily synthesized pi-conjugated molecule that has been used as a hole-transport material (HTM) in solid-state dye-sensitized solar cells (ssDSSCs), achieving relatively high efficiency. In this paper, we characterize the physicochemical properties of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and show that it is a promising p-dopant in a spin-coating solution with X1 as the HTM. The doped ssDSSCs showed an increase in short-circuit current density from 5.38 mA cm(-2) to 7.39 mA cm(-2), and their overall power conversion efficiency increased from 2.9% to 4.3%. Also, ssDSSCs with DDQ-doped X1 were more stable than the undoped samples, demonstrating that DDQ can act as a p-type dopant in X1 as an HTM for highly efficient, stable ssDSSCs.

Research on the storage of solar energy in terms of hydrogen or carbon-based fuels by using sunlight to split water or to reduce CO2, respectively, has gained significant attention in recent years. Among reported water-splitting systems, one approach has focused on hybrid systems with molecular catalysts or molecular light-harvesting systems that are combined with nanostructured materials. In this perspective we summarize recent developments in operation and fabrication strategies for various water-splitting devices constructed from electrodes (electrochemical cells) or photoelectrodes (photoelectrochemical cells) using molecular engineering. We also provide insights into the factors that influence device efficiency and stability, and provide guidelines for future fabrication strategies for more advanced devices.

The reaction of CuCl2 with 2,9-dimethyl-1,10-phenanthroline (dmp) does not lead to the formation of [Cu(dmp)(2)](Cl)(2) but instead to [Cu(dmp)(2)Cl]Cl, a 5-coordinated complex, in which one chloride is directly coordinated to the metal center. Attempts at removing the coordinated chloride by changing the counterion by metathesis were unsuccessful and resulted only in the exchange of the noncoordinated chloride, as confirmed from a crystal structure analysis. Complex [Cu-(dmp)(2)Cl]PF6 exhibits a reversible cyclic voltammogram characterized by a significant peak splitting between the reductive and oxidative waves (0.85 and 0.60 V vs NHE, respectively), with a half-wave potential E-1/2 = 0.73 V vs NHE. When reduced electrochemically, the complex does not convert into [Cu(dmp)(2)](+), as one may expect. Instead, [Cu(dmp)(2)](+) is isolated as a product when the reduction of [Cu(dmp)(2)Cl]PF6 is performed with L-ascorbic acid, as confirmed by electrochemistry, NMR spectroscopy, and diffractometry. [Cu(dmp)(2)](2+) complexes can be synthesized starting from Cu(II) salts with weakly and noncoordinating counterions, such as perchlorate. Growth of [Cu(dmp)(2)](ClO4)(2) crystals in acetonitrile results in a 5-coordinated complex, [Cu(dmp)(2)(CH3CN)](ClO4)(2), in which a solvent molecule is coordinated to the metal center. However, solvent coordination is associated with a dynamic decoordination-coordination behavior upon reduction and oxidation. Hence, the cyclic voltammogram of [Cu(dmp)(2)(CH3CN)](2+) is identical to the one of [Cu(dmp)(2)](+), if the measurements are performed in acetonitrile. The current results show that halide ions in precursors to Cu(II) metal-organic coordination compound synthesis, and most likely also other multivalent coordination centers, are not readily exchanged when exposed to presumed strongly binding and chelating ligand, and thus special care needs to be taken with respect to product characterization.

As a champion hole-transporting material (HTM), 2,27,7-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD) has been widely used in solid-state dye-sensitized solar cells (ssDSCs). Owing to the low conductivity of Spiro-OMeTAD, a chemical doping strategy is commonly used to enhance its hole-transporting properties. In this study, we report a strong electron acceptor, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an additive for Spiro-OMeTAD along with its application in ssDSCs. We show that the conductivity of Spiro-OMeTAD increases from 5.31 x 10(-5) to 2.22 x 10(-4) Scm upon the addition of 0.04% DDQ, and the power conversion efficiency (PCE) of the ssDSCs also increases. By utilizing a donor-pi-acceptor sensitizer with a high coefficient and an HTM with an optimized doping ratio, we were able to achieve a high PCE of 6.37% for the ssDSCs under 10 0mWcm(-2) AM1.5G simulated illumination, in comparison to the PCE of the pristine device, which was only 3.50%. An increase in the application of benzoquinone-based materials for organic electronics is expected, especially for solar-cell applications.

The development of efficient molecular catalysts for visible-light driven CO2 reduction, based on abundant materials, is necessary to meet energy demands and address environment problems. In this work, a Co(bpy)(2)Cl-2 catalyst was developed and showed high efficiency and durability for the photocatalytic reduction of CO2 and protons. Yields of CO and H-2 as high as 62.3 and 69.9 mu mol were achieved and the turnover numbers (TONs) reached 6230 and 6990, respectively, under light irradiation (lambda > 420 nm) for 4 h, indicating that the mixture gases could be a candidate as syngas. The apparent quantum yield was determined to be 2.1% for CO. Mechanistic studies revealed oxidative quenching of the photosensitizer Ru(bpy)(3)Cl-2 by the catalyst. The photocatalytic performance, flexible synthesis and non-noble metal catalyst in our system show great promise for the practical application of Co(bpy)(2)Cl-2 to photocatalytic reduction of CO2.

The development of an efficient, stable, and low-cost hole-transporting material (HTM) is of great significance for perovskite solar cells (PSCs) from future commercialization point of view. Herein, we specifically synthesize a dicationic salt of X60 termed X60(TFSI)(2), and adopt it as an effective and stable "doping" agent to replace the previously used lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) for the low-cost organic HTM X60 in PSCs. The incorporation of this dicationic salt significantly increases the hole conductivity of X60 by two orders of magnitude from 10(-6) to 10(-4) S cm(-1). The dramatic enhancement of the conductivity leads to an impressive power conversion efficiency (PCE) of 19.0% measured at 1 sun illumination (100 mW cm(-2), AM 1.5 G), which is comparable to that of the device doped with LiTFSI (19.3%) under an identical condition. More strikingly, by replacing LiTFSI, the PSC devices incorporating X60(TFSI)(2) also show an excellent long-term durability under ambient atmosphere for 30 days, mainly due to the hydrophobic nature of the X60(TFSI)(2) doped HTM layer, which can effectively prevent the moisture destroying the perovskite layer. The present work paves the way for the development of highly efficient, stable, and low-cost HTM for potential commercialization of PSCs.

As a cost-effective catalyst for the oxygen evolution reaction (OER), the potential use of FeOOH is hindered by its intrinsic poor electron conductivity. Here, the significant enhancement of OER activity and long-term stability of electrodeposited FeOOH on zeolitic imidazolate framework-derived N-doped porous carbons (NPCs) are reported. In alkaline media, FeOOH/NPC supported on nickel foam as a 3D electrode delivers a current density of 100 mA cm(-2) at a small overpotential of 230 mV and exhibits a low Tafel slope of 33.8 mV dec(-1) as well as excellent durability, making it one of the most active OER catalysts. Such high performance is attributed to a combined effect of the excellent electron conductivity of NPC and the synergy between FeOOH and NiO derived from Ni substrate.

Perovskite hydroxide CoSn(OH)(6) nanoparticles were synthesized and used for the first time in the photocatalytic reduction of CO2 to CO. Under mild reaction conditions and using [Ru(bpy)(3)](PF6)(2) as the photosensitizer, a high photocatalytic efficiency of 19.3 mu mol for CO evolution with a high selectivity of 86.46% was obtained. The photocatalytic TEOA activity and CO selectivity were further improved by adding weak Bronsted acids, as proton sources, to the system.

Developing earth-abundant, active, and robust electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a vital challenge for efficient conversion of sustainable energy sources. Herein, metal-semiconductor hybrids are reported with metallic nanoalloys on various defective oxide nanowire arrays (Cu/CuOx, Co/CoOx, and CuCo/CuCoOx) as typical Mott-Schottky electrocatalysts. To build the highway of continuous electron transport between metals and semiconductors, nitrogen-doped carbon (NC) has been implanted on metal-semiconductor nanowire array as core-shell conductive architecture. As expected, NC/CuCo/CuCoOx nanowires arrays, as integrated Mott-Schottky electrocatalysts, present an overpotential of 112 mV at 10 mA cm(-2) and a low Tafel slope of 55 mV dec(-1) for HER, simultaneously delivering an overpotential of 190 mV at 10 mA cm(-2) for OER. Most importantly, NC/CuCo/CuCoOx architectures, as both the anode and the cathode for overall water splitting, exhibit a current density of 10 mA cm(-2) at a cell voltage of 1.53 V with excellent stability due to high conductivity, large active surface area, abundant active sites, and the continuous electron transport from prominent synergetic effect among metal, semiconductor, and nitrogen-doped carbon. This work represents an avenue to design and develop efficient and stable Mott-Schottky bifunctional electrocatalysts for promising energy conversion.