scholarly journals From Ru-bda to Ru-bds: a step forward to highly efficient molecular water oxidation electrocatalysts under acidic and neutral conditions

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jing Yang ◽  
Lei Wang ◽  
Shaoqi Zhan ◽  
Haiyuan Zou ◽  
Hong Chen ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Bond Formation ◽  
Density Functional Theory Calculations ◽  
Oxidation Catalyst ◽  
Nucleophilic Attack ◽  
Molecular Water ◽  
Formation Mechanisms ◽  
Equatorial Position ◽  
Neutral Conditions

AbstractSignificant advances during the past decades in the design and studies of Ru complexes with polypyridine ligands have led to the great development of molecular water oxidation catalysts and understanding on the O−O bond formation mechanisms. Here we report a Ru-based molecular water oxidation catalyst [Ru(bds)(pic)2] (Ru-bds; bds2− = 2,2′-bipyridine-6,6′-disulfonate) containing a tetradentate, dianionic sulfonate ligand at the equatorial position and two 4-picoline ligands at the axial positions. This Ru-bds catalyst electrochemically catalyzes water oxidation with turnover frequencies (TOF) of 160 and 12,900 s−1 under acidic and neutral conditions respectively, showing much better performance than the state-of-art Ru-bda catalyst. Density functional theory calculations reveal that (i) under acidic conditions, the high valent Ru intermediate RuV=O featuring the 7-coordination configuration is involved in the O−O bond formation step; (ii) under neutral conditions, the seven-coordinate RuIV=O triggers the O−O bond formation; (iii) in both cases, the I2M (interaction of two M−O units) pathway is dominant over the WNA (water nucleophilic attack) pathway.

scholarly journals Switching the O-O Bond Formation Pathways of Ru-pda Water Oxidation Catalyst by Third Coordination Sphere Engineering

Research ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yingzheng Li ◽  
Shaoqi Zhan ◽  
Lianpeng Tong ◽  
Wenlong Li ◽  
Yilong Zhao ◽  
...  
Keyword(s):  
Coordination Sphere ◽  
Water Oxidation ◽  
Density Functional ◽  
Electrochemical Polymerization ◽  
Bond Formation ◽  
Kinetic Studies ◽  
Oxidation Catalyst ◽  
Nucleophilic Attack ◽  
Formation Pathway ◽  
Axial Ligands

Water oxidation is a vital anodic reaction for renewable fuel generation via electrochemical- and photoelectrochemical-driven water splitting or CO2 reduction. Ruthenium complexes, such as Ru-bda family, have been shown as highly efficient water-oxidation catalysts (WOCs), particularly when they undergo a bimolecular O-O bond formation pathway. In this study, a novel Ru(pda)-type (pda2– =1,10-phenanthroline-2,9-dicarboxylate) molecular WOC with 4-vinylpyridine axial ligands was immobilized on the glassy carbon electrode surface by electrochemical polymerization. Electrochemical kinetic studies revealed that this homocoupling polymer catalyzes water oxidation through a bimolecular radical coupling pathway, where interaction between two Ru(pda)–oxyl moieties (I2M) forms the O-O bond. The calculated barrier of the I2M pathway by density-functional theory (DFT) is significantly lower than the barrier of a water nucleophilic attack (WNA) pathway. By using this polymerization strategy, the Ru centers are brought closer in the distance, and the O-O bond formation pathway by the Ru (pda) catalyst is switched from WNA in a homogeneous molecular catalytic system to I2M in the polymerized film, providing some deep insights into the importance of third coordination sphere engineering of the water oxidation catalyst.

scholarly journals Two-transition-metal water oxidation catalysts. Faster rates via electronic structure tuning

2021 ◽  
Author(s):  
Craig Hill ◽  
Meilin Tao ◽  
Qiushi Yin ◽  
Alexey Kaledin ◽  
Natalie Uhlikova ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Active Sites ◽  
Density Functional ◽  
Molecular Model ◽  
Kinetic Studies ◽  
Oxidation Catalyst ◽  
Molecular Water ◽  
Oxidation Catalysts ◽  
Order Of Magnitude ◽  
Cobalt Nickel Oxide

Abstract Mixed 3d-metal oxides are some of the most promising water oxidation catalysts (WOCs), but it is very difficult to know the active site structures and thus structure-catalytic activity correlations at the molecular level in such insoluble materials. This study reports a molecular water oxidation catalyst, [Co2Ni2(PW9O34)2]10- (Co2Ni2P2), that constitutes a molecular model of the heterogeneous WOC, cobalt-nickel oxide. Both Co2Ni2P2 and its isostructural analogue, [Co4(PW9O34)2]10- (Co4P2), have the same CoO5(H2O) active sites but Co2Ni2P2 is an order of magnitude faster than Co4P2. Co2Ni2P2 is prepared by a new synthesis, and both the location and percent occupancy of Co and Ni in Co2Ni2P2 (Co outside and Ni inside the central belt are >97% for each) is confirmed by multiwavelength synchrotron X-radiation anomalous dispersion scattering (synchrotron XRAS), a technique applied for the first time to such complexes. Density functional theory (DFT) studies predicated and reveal that Co4P2 and Co2Ni2P2 have greatly altered frontier orbitals, while stopped-flow kinetic studies and DFT calculations indicate that water oxidation by both complexes follows analogous multi-step mechanisms, including Co-OOH formation, with the energetics of most steps being lower for Co2Ni2P2 than for Co4P2.

scholarly journals Aluminum Doping Effect on Surface Structure of Silver Ultrathin Films

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 648
Author(s):  
Han Yan ◽  
Xiong Xu ◽  
Peng Li ◽  
Peijie He ◽  
Qing Peng ◽  
...  
Keyword(s):  
Density Functional ◽  
Near Infrared ◽  
Single Layer ◽  
Density Functional Theory Calculations ◽  
Light Transmittance ◽  
Formation Mechanisms ◽  
Silver Surface ◽  
Silver Films ◽  
Migration Pathway ◽  
Surface Morphologies

Ultrathin silver films with low loss in the visible and near-infrared spectrum range have been widely used in the fields of metamaterials and optoelectronics. In this study, Al-doped silver films were prepared by the magnetron sputtering method and were characterized by surface morphology, electrical conductivity, and light transmittance analyses. Molecular dynamics simulations and first-principles density functional theory calculations were applied to study the surface morphologies and migration pathway for the formation mechanisms in Al-doped silver films. The results indicate that the migration barrier of silver on a pristine silver surface is commonly lower than that of an Al-doped surface, revealing that the aluminum atoms in the doping site decrease the surface mobility and are conducive to the formation of small islands of silver. When the islands are dense, they coalesce into a single layer, leading to a smoother surface. This might be the reason for the observably lower 3D growth mode of silver on an Al-doped silver surface. Our results with electronic structure insights on the mechanism of the Al dopants on surface morphologies might benefit the quality control of the silver thin films.

scholarly journals Sn-Doped Hematite for Photoelectrochemical Water Splitting: The Effect of Sn Concentration

2020 ◽  
Vol 234 (4) ◽  
pp. 683-698 ◽  
Author(s):  
Siyuan Zhang ◽  
Hamidreza Hajiyani ◽  
Alexander G. Hufnagel ◽  
Jonathan Kampmann ◽  
Benjamin Breitbach ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Atomic Layer ◽  
Solubility Limit ◽  
Metallic State ◽  
Equilibrium Solubility ◽  
Functional Theory ◽  
Sn Doping ◽  
Layer Deposition

AbstractHematite-based photoanodes have been intensively studied for photoelectrochemical water oxidation. The n-type dopant Sn has been shown to benefit the activity of hematite anodes. We demonstrate in this study that Sn-doped hematite thin films grown by atomic layer deposition can achieve uniform doping across the film thickness up to at least 32 mol%, far exceeding the equilibrium solubility limit of less than 1 mol%. On the other hand, with the introduction of Sn doping, the hematite crystallite size decreases and many twin boundaries form in the film, which may contribute to the low photocurrent observed in these films. Density functional theory calculations with a Hubbard U term show that Sn doping has multiple effects on the hematite properties. With increasing Sn4+ content, the Fe2+ concentration increases, leading to a reduction of the band gap and finally to a metallic state. This goes hand in hand with an increase of the lattice constant.

scholarly journals Stabilization of a molecular water oxidation catalyst on a dye−sensitized photoanode by a pyridyl anchor

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Yong Zhu ◽  
Degao Wang ◽  
Qing Huang ◽  
Jian Du ◽  
Licheng Sun ◽  
...  
Keyword(s):  
Water Splitting ◽  
Phosphonic Acid ◽  
Water Oxidation ◽  
Oxidation Catalyst ◽  
Molecular Water ◽  
Applied Bias ◽  
Surface Loading ◽  
Dye Sensitized ◽  
Monomeric Structure ◽  
Molecular Catalysts

Abstract Understanding and controlling the properties of water-splitting assemblies in dye-sensitized photoelectrosynthesis cells is a key to the exploitation of their properties. We demonstrate here that, following surface loading of a [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) chromophore on nanoparticle electrodes, addition of the molecular catalysts, Ru(bda)(L)2 (bda  =  2,2′-bipyridine-6,6′-dicarboxylate) with phosphonate or pyridyl sites for water oxidation, gives surfaces with a 5:1 chromophore to catalyst ratio. Addition of the surface-bound phosphonate derivatives with L = 4-pyridyl phosphonic acid or diethyl 3-(pyridin-4-yloxy)decyl-phosphonic acid, leads to well-defined surfaces but, following oxidation to Ru(III), they undergo facile, on-surface dimerization to give surface-bound, oxo-bridged dimers. The dimers have a diminished reactivity toward water oxidation compared to related monomers in solution. By contrast, immobilization of the Ru-bda catalyst on TiO2 with the 4,4′-dipyridyl anchoring ligand can maintain the monomeric structure of catalyst and gives relatively stable photoanodes with photocurrents that reach to 1.7 mA cm−2 with an optimized, applied bias photon-to-current efficiency of 1.5%.

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