scholarly journals An Overview of Significant Achievements in Ruthenium-Based Molecular Water Oxidation Catalysis

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 494 ◽  
Author(s):  
Jayneil Kamdar ◽  
Douglas Grotjahn
Keyword(s):  
Water Splitting ◽  
Water Oxidation ◽  
Fossil Fuels ◽  
Catalyst Activity ◽  
Ruthenium Catalysts ◽  
Hydrogen Gas ◽  
Oxidation Catalysis ◽  
Molecular Water ◽  
Environmental Consequences ◽  
Energy Options

Fossil fuels (coal, oil, natural gas) are becoming increasingly disfavored as long-term energy options due to concerns of scarcity and environmental consequences (e.g., release of anthropogenic CO2). Hydrogen gas, on the other hand, has gained popularity as a clean-burning fuel because the only byproduct from its reaction with O2 is H2O. In recent decades, hydrogen derived from water splitting has been a topic of extensive research. The bottleneck of the water splitting reaction is the difficult water oxidation step (2H2O → O2 + 4H+ + 4e−), which requires an effective and robust catalyst to overcome its high kinetic barrier. Research in water oxidation by molecular ruthenium catalysts enjoys a rich history spanning nearly 40 years. As the diversity of novel ligands continues to widen, the relationship between ligand geometry or electronics, and catalyst activity is undoubtedly becoming clearer. The present review highlights, in the authors’ opinion, some of the most impactful discoveries in the field and explores the evolution of ligand design that has led to the current state of the art.

scholarly journals Thickness-dependent photoelectrochemical properties of a semitransparent Co3O4 photocathode

2018 ◽  
Vol 9 ◽  
pp. 2432-2442 ◽  
Author(s):  
Malkeshkumar Patel ◽  
Joondong Kim
Keyword(s):  
Water Splitting ◽  
Water Oxidation ◽  
Hydrogen Generation ◽  
Hydrogen Gas ◽  
Generation Rate ◽  
Alkaline Electrolyte ◽  
Stoichiometric Ratio ◽  
Gas Generation ◽  
Pec Cells ◽  
Gas Generation Rate

Co3O4 has been widely studied as a catalyst when coupled with a photoactive material during hydrogen production using water splitting. Here, we demonstrate a photoactive spinel Co3O4 electrode grown by the Kirkendall diffusion thermal oxidation of Co nanoparticles. The thickness-dependent structural, physical, optical, and electrical properties of Co3O4 samples are comprehensively studied. Our analysis shows that two bandgaps of 1.5 eV and 2.1 eV coexist with p-type conductivity in porous and semitransparent Co3O4 samples, which exhibit light-induced photocurrent in photoelectrochemical cells (PEC) containing the alkaline electrolyte. The thickness-dependent properties of Co3O4 related to its use as a working electrode in PEC cells are extensively studied and show potential for the application in water oxidation and reduction processes. To demonstrate the stability, an alkaline cell was composed for the water splitting system by using two Co3O4 photoelectrodes. The oxygen gas generation rate was obtained to be 7.17 mL·h−1 cm−1. Meanwhile, hydrogen gas generation rate was almost twice of 14.35 mL·h−1·cm−1 indicating the stoichiometric ratio of 1:2. We propose that a semitransparent Co3O4 photoactive electrode is a prospective candidate for use in PEC cells via heterojunctions for hydrogen generation.

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%.

scholarly journals Photoelectrochemical Water Splitting Reaction System Based on Metal-Organic Halide Perovskites

Materials ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 210 ◽  
Author(s):  
Dohun Kim ◽  
Dong-Kyu Lee ◽  
Seong Min Kim ◽  
Woosung Park ◽  
Uk Sim
Keyword(s):  
Hydrogen Production ◽  
Water Splitting ◽  
Fossil Fuels ◽  
Reaction System ◽  
Hydrogen Gas ◽  
Production Environment ◽  
Organic Halide ◽  
Highly Active ◽  
Production Of Hydrogen ◽  
Metal Organic

In the development of hydrogen-based technology, a key challenge is the sustainable production of hydrogen in terms of energy consumption and environmental aspects. However, existing methods mainly rely on fossil fuels due to their cost efficiency, and as such, it is difficult to be completely independent of carbon-based technology. Electrochemical hydrogen production is essential, since it has shown the successful generation of hydrogen gas of high purity. Similarly, the photoelectrochemical (PEC) method is also appealing, as this method exhibits highly active and stable water splitting with the help of solar energy. In this article, we review recent developments in PEC water splitting, particularly those using metal-organic halide perovskite materials. We discuss the exceptional optical and electrical characteristics which often dictate PEC performance. We further extend our discussion to the material limit of perovskite under a hydrogen production environment, i.e., that PEC reactions often degrade the contact between the electrode and the electrolyte. Finally, we introduce recent improvements in the stability of a perovskite-based PEC device.

scholarly journals Molecular water oxidation catalysis by zwitterionic carboxylate bridge-functionalized bis-NHC iridium complexes

2019 ◽  
Vol 9 (6) ◽  
pp. 1437-1450 ◽  
Author(s):  
Raquel Puerta-Oteo ◽  
M. Victoria Jiménez ◽  
Jesús J. Pérez-Torrente
Keyword(s):  
Water Oxidation ◽  
Oxidation Catalysis ◽  
Molecular Water ◽  
Iridium Complexes ◽  
Intermediate Species ◽  
Carboxylate Bridge ◽  
Water Oxidation Catalysis ◽  
High Valent

Carboxylate functionalized bis-NHC ligands allow for the stabilization of high-valent iridium intermediate species involved in homogeneous water oxidation catalysis.

scholarly journals Dye-sensitized photoelectrochemical water oxidation through a buried junction

2018 ◽  
Vol 115 (27) ◽  
pp. 6946-6951 ◽  
Author(s):  
Pengtao Xu ◽  
Tian Huang ◽  
Jianbin Huang ◽  
Yun Yan ◽  
Thomas E. Mallouk
Keyword(s):  
Solar Cell ◽  
Water Splitting ◽  
Water Oxidation ◽  
Molecular Water ◽  
Phosphate Solution ◽  
Oxidation Catalysts ◽  
Faradaic Efficiency ◽  
Dye Sensitized ◽  
Electrode Potentials ◽  
Oxide Electrodes

Water oxidation has long been a challenge in artificial photosynthetic devices that convert solar energy into fuels. Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) provide a modular approach for integrating light-harvesting molecules with water-oxidation catalysts on metal-oxide electrodes. Despite recent progress in improving the efficiency of these devices by introducing good molecular water-oxidation catalysts, WS-DSPECs have poor stability, owing to the oxidation of molecular components at very positive electrode potentials. Here we demonstrate that a solid-state dye-sensitized solar cell (ss-DSSC) can be used as a buried junction for stable photoelectrochemical water splitting. A thin protecting layer of TiO2 grown by atomic layer deposition (ALD) stabilizes the operation of the photoanode in aqueous solution, although as a solar cell there is a performance loss due to increased series resistance after the coating. With an electrodeposited iridium oxide layer, a photocurrent density of 1.43 mA cm−2 was observed in 0.1 M pH 6.7 phosphate solution at 1.23 V versus reversible hydrogen electrode, with good stability over 1 h. We measured an incident photon-to-current efficiency of 22% at 540 nm and a Faradaic efficiency of 43% for oxygen evolution. While the potential profile of the catalyst layer suggested otherwise, we confirmed the formation of a buried junction in the as-prepared photoelectrode. The buried junction design of ss-DSSs adds to our understanding of semiconductor–electrocatalyst junction behaviors in the presence of a poor semiconducting material.

Pivotal role of the redox-active tyrosine in driving the water splitting catalyzed by photosystem II

2020 ◽  
Vol 22 (1) ◽  
pp. 273-285 ◽  
Author(s):  
Shin Nakamura ◽  
Matteo Capone ◽  
Daniele Narzi ◽  
Leonardo Guidoni
Keyword(s):  
Hydrogen Bond ◽  
Photosystem Ii ◽  
Water Splitting ◽  
Oxidation State ◽  
Water Oxidation ◽  
Oxidation Catalysis ◽  
Pivotal Role ◽  
Redox Active ◽  
Water Oxidation Catalysis

TyrZ oxidation state triggers hydrogen bond modification in the water oxidation catalysis.

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