Based on the previous research work in our laboratory, we have designed and synthesized a small-molecule,hole transport material(HTM) POZ6-2 using phenoxazine(POZ) as central unit and dicyanovinyl units as electron-withdrawing terminal groups. Through the introduction of a 2-ethyl-hexyl bulky chain into the POZ core unit, POZ6-2 exhibits good solubility in organic solvents. In addition, POZ6-2 possesses appropriate energy levels in combination with a high hole mobility and conductivity in its pristine form. Therefore, it can readily be used as a dopant-free HTM in perovskite solar cells(PSCs) and a conversion efficiency of 10.3% was obtained. The conductivity of the POZ6-2 layer can be markedly enhanced via doping in combination with typical additives, such as 4-tert-butylpyridine(TBP) and lithium bis(trifluoromethanesulfonyl) imide(Li TFSI).Correspondingly, the efficiency of the PSCs was further improved to 12.3% using doping strategies. Under the same conditions, reference devices based on the well-known HTM Spiro-OMe TAD show an efficiency of 12.8%.
Ming ChengCheng ChenBo XuYong HuaFuguo ZhangLars KlooLicheng Sun
Understanding the seven coordination and O-O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earthabundant metals.This work reports the synthesis,characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda(H2 bnda=2,2’-bi(nicotinic acid)-6,6’-dicarboxylic acid)featuring steric hindrance and enhanced hydrophilicity on the backbone.Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda(H_(2)bda=2,2’-bipyridine-6,6’-dicarboxylic acid),Ru-pda(H_(2)pda=1,10-phenanthroline-2,9-dicarboxylic acid),and Ru-biqa(H_(2)biqa=(1,1’-biisoquinoline)-3,3’-dicarboxylic acid),we emphasized that seven coordination clearly determines presence of Ru^(Ⅴ)=O with high spin density on the ORu^(Ⅴ)=O atom,i.e.oxo with radical properties,which is one of the necessary conditions for reacting through the O-O coupling pathway.However,an additional factor to make the condition sufficient is the favorable intermolecular faceto-face interaction for the generation of the pre-reactive[Ru^(Ⅴ)=O…O=Ru^(Ⅴ)],which may be significantly influenced by the secondary coordination environments.This work provides a new understanding of the structure-activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O-O bond formation.
Two efficient single-site Ru water oxidation catalysts [Ru(bda)(pic)(Ln)](bda = 2,2'-bipyridine-6,6'-dicarboxylic acid, pic = picoline, L1 = 4,5-bipyridine-2,7-di-tert-butyl-9,9-dimethylxanthene, L2 = 4-pyridine-5-phenyl-2,7-di-tert-butyl-9,9-dimethylxanthene) were only synthesized containing different xanthene ligands at the axial site. These complexes have been thoroughly characterized by spectroscopic(UV-vis, NMR) and electrochemical(CV and DPV) techniques. Kinetic analysis proved that the mechanism of water oxidation comprises the water nucleophilic attack process on high-valence ruthenium species.It is found that the catalyst 1 displayed higher activity than catalyst 2 on water oxidation, caused by the protonation of the axial ligand L1 with a free pyridine.
Development of efficient molecular devices for overall water splitting has always been a hotspot of research to realize clean and sustainable energy conversion. In the case, long-term durability of molecular devices is a crucial factor to determine their practical application. Here, an efficient composite molecular anode was assembled by immobilization of charge-neutral mononuclear Ru1 complex on COOHfunctionalized multiwalled carbon nanotubes(MWCNTs COOH) sticking on a glassy carbon(GC) electrode(Ru1/MWCNTsCOOH/GC). The prepared hybrid anode showed a low onset overpotential of only 380 mV for electrocatalytic water oxidation. Moreover, the anode displayed a steady catalytic current density of1.25 mA/cm^2 for more than 5 h at the overpotential of 580 m V, a high TON of 186000(5 h), a TOF of10.3 s-1 and a faradic efficiency of 96%, indicating the significant efficiency and extremely durability.The excellent durability of the molecular anode should be attributed to the key charge-neutral catalytic intermediates(Ru1 ad) of the catalytic step and the two long flexible carbon chains of the catalyst.
Water molecule contains one oxygen and two hydrogen atoms,making it a potential oxygen and hydrogen source.Electrocatalytic organic reduction and oxidation using water as oxygen and/or hydrogen donors provide an environmentally friendly and sustainable strategy to replace traditional chemical-driven stoichiometric reactions that use sacrificial reagents.Furthermore,the development of electrochemical synthesis provides a potential application for low tension photoelectricity,which is not cost-effective during boosted voltage and application.In the last decade,electrocatalytic redox reactions of organic molecules in aqueous media had shown progress owing to the development of electrode materials and water-splitting technology.This paper highlights several electrocatalytic systems and corresponding mechanisms for both hydrogenation and oxidative transformation of representative compounds.The activation process of protons and water on the working electrode surface has received special focus.Furthermore,paired electrolysis using water as the oxygen and hydrogen source has been demonstrated.This paired system combines hydrogenation and oxidation half-reactions in one cell using water as the hydrogen and oxygen source,resulting in high atomic and electron utilization rates.
The oxygen evolution reaction(OER) is a key step in the overall water splitting process. Numerous electrocatalysts have been developed to lower the overpotential and accelerate the kinetics of the OER. In this work, a simple soaking and heating treatment was used to form a stable and efficient Fe_xNi_(1-x)O_y/CP electrode. The electrode combined nickel and iron oxides on a commercial carbon paper were used for electrocatalytic water oxidation. The best Fe_xNi_(1-x)O_y/CP electrode(Ni/Fe = 15/1) displayed a current density of 10 mA/cm^2 at a low overpotential of 290 mV in 0.1 M KOH solution with a Tafel slope of 52 mV/dec.A higher current density of ~50 mA/cm^2 at the same overpotential and a lower Tafel slope of 43 mV/dec was obtained for this electrode in 1.0 M KOH solution. Excellent durability of the Fe_xNi_(1-x)O_y/CP electrode in 1.0 M KOH solution was confirmed under a high current density of 136 mA/cm^2 at an overpotential of 340 mV.
