scholarly journals A Tetranuclear Cobalt (II) Phosphate Possessing a D4R Core: An Efficient Water Oxidation Catalyst

2019 ◽  
Author(s):  
Atanu Dey ◽  
Virendra Kumar ◽  
Shubhadeep Pal ◽  
Anku Guha ◽  
Sumit Bawari ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Oxidation Catalyst ◽  
Phosphate Ester ◽  
Durability Test ◽  
Efficient Catalyst ◽  
Functional Theory ◽  
Faradaic Efficiency ◽  
Alkaline Conditions ◽  
Current Densities

<p>The reaction of Co(OAc)<sub>2</sub>·4H<sub>2</sub>O with the sterically hindered phosphate ester, LH<sub>2</sub>, afforded the tetranuclear complex, [Co<sup>II</sup>(L)(CH<sub>3</sub>CN)]<sub>4</sub>∙5CH<sub>3</sub>CN (<b>1</b>) [LH<sub>2</sub> = <a>2,6</a>‐(diphenylmethyl)‐4‐isopropyl‐phenyl phosphate]. The molecular structure of <b>1</b> reveals that it is a tetranuclear assembly where the Co(II) centers are present in the alternate corners of a cube. The four Co(II) centers are held together by four di-anionic [L]<sup>2-</sup> ligands. The fourth coordination site on Co(II) is taken by an acetonitrile ligand. Changing the Co(II) precursor from Co(OAc)<sub>2</sub>·4H<sub>2</sub>O to Co(NO<sub>3</sub>)<sub>2</sub>.6H<sub>2</sub>O afforded the mononuclear complex [Co<sup>II</sup>(LH)<sub>2</sub>(CH<sub>3</sub>CN)<sub>2</sub>(MeOH)<sub>2</sub>](MeOH)<sub>2 </sub>(<b>2). </b>In<b> 2, </b>the Co(II) is surrounded by two monoanionic [LH]<sup>‒</sup> ligands, and a pair of methanol and acetonitrile solvents in a six-coordinate arrangement. <b>1</b> has been found to be an efficient catalyst for the electrochemical water oxidation under high basic conditions while the mononuclear analogue, <b>2</b>, does not respond towards electrochemical water oxidation. The tetranuclear catalyst has excellent electrochemcial stability and longevity, as established by the chronoamperometry and >1000 cycles durability test in high alkaline conditions. Excellent current densities of 1 and 10 mAcm<sup>‒2</sup> were achieved with the overpotential of 354 and 452 mV respectively. The turnover frequency of this catalyst was calculated as 5.23 s<sup>−1 </sup>with excellent faradaic efficiency of 97%, indicating the selective oxygen evolution (OER) process happening with the aid of this catalyst. A mechanistic insight in to the higher activity of complex <b>1</b> towards OER compared to complex <b>2 </b>is also provided with the help of density functional theory based calculations.</p>

scholarly journals A Tetranuclear Cobalt (II) Phosphate Possessing a D4R Core: An Efficient Water Oxidation Catalyst

2019 ◽  
Author(s):  
Atanu Dey ◽  
Virendra Kumar ◽  
Shubhadeep Pal ◽  
Anku Guha ◽  
Sumit Bawari ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Oxidation Catalyst ◽  
Phosphate Ester ◽  
Durability Test ◽  
Efficient Catalyst ◽  
Functional Theory ◽  
Faradaic Efficiency ◽  
Alkaline Conditions ◽  
Current Densities

<p>The reaction of Co(OAc)<sub>2</sub>·4H<sub>2</sub>O with the sterically hindered phosphate ester, LH<sub>2</sub>, afforded the tetranuclear complex, [Co<sup>II</sup>(L)(CH<sub>3</sub>CN)]<sub>4</sub>∙5CH<sub>3</sub>CN (<b>1</b>) [LH<sub>2</sub> = <a>2,6</a>‐(diphenylmethyl)‐4‐isopropyl‐phenyl phosphate]. The molecular structure of <b>1</b> reveals that it is a tetranuclear assembly where the Co(II) centers are present in the alternate corners of a cube. The four Co(II) centers are held together by four di-anionic [L]<sup>2-</sup> ligands. The fourth coordination site on Co(II) is taken by an acetonitrile ligand. Changing the Co(II) precursor from Co(OAc)<sub>2</sub>·4H<sub>2</sub>O to Co(NO<sub>3</sub>)<sub>2</sub>.6H<sub>2</sub>O afforded the mononuclear complex [Co<sup>II</sup>(LH)<sub>2</sub>(CH<sub>3</sub>CN)<sub>2</sub>(MeOH)<sub>2</sub>](MeOH)<sub>2 </sub>(<b>2). </b>In<b> 2, </b>the Co(II) is surrounded by two monoanionic [LH]<sup>‒</sup> ligands, and a pair of methanol and acetonitrile solvents in a six-coordinate arrangement. <b>1</b> has been found to be an efficient catalyst for the electrochemical water oxidation under high basic conditions while the mononuclear analogue, <b>2</b>, does not respond towards electrochemical water oxidation. The tetranuclear catalyst has excellent electrochemcial stability and longevity, as established by the chronoamperometry and >1000 cycles durability test in high alkaline conditions. Excellent current densities of 1 and 10 mAcm<sup>‒2</sup> were achieved with the overpotential of 354 and 452 mV respectively. The turnover frequency of this catalyst was calculated as 5.23 s<sup>−1 </sup>with excellent faradaic efficiency of 97%, indicating the selective oxygen evolution (OER) process happening with the aid of this catalyst. A mechanistic insight in to the higher activity of complex <b>1</b> towards OER compared to complex <b>2 </b>is also provided with the help of density functional theory based calculations.</p>

scholarly journals Cryomilled Ni-Co-Se Enables Water Oxidation Electrocatalysts Durable at High Current Densities

2020 ◽  
Author(s):  
Jehad Abed ◽  
Shideh Ahmadi ◽  
Laura Laverdure ◽  
Ahmed Abdellah ◽  
Colin O'Brien ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Active Sites ◽  
Density Functional ◽  
Nanocrystalline Structure ◽  
Cell Voltage ◽  
Functional Theory ◽  
Water Electrolyser ◽  
Current Densities ◽  
Exchange Membrane ◽  
Synchrotron Spectroscopy

Abstract The oxygen evolution reaction (OER) limits electrocatalysis due to the high overpotential incurred by the poor reaction kinetics; this problem worsens over time if the performance of the OER electrocatalyst diminishes during operation. Here, we report the synthesis of immiscible Ni-Co-Se nanoparticles (<10 nm) for alkaline OER using milling at a cryogenic temperature. Milling at such low temperatures promotes thermodynamically stable nanocrystalline intermetallics with a high density of coordinatively unsaturated active sites. Using operando synchrotron spectroscopy, electron microscopy, and density functional theory we found that during the OER, Se ions leaches out of the nanocrystalline structure activating the electrocatalyst by hydrating and transforming defective Ni and Co sites into active and stable oxyhydroxides. Activated (NiCo)3Se4 electrocatalyst required only an overpotential of 279 mV at 0.5 A.cm-2 and 329 mV at 1 A.cm-2 for 500 hours in 1M KOH. Using anion exchange membrane, we report the lowest cell voltage for an alkaline water electrolyser delivering 2 A.cm-2 at 2 V.

scholarly journals First-Principles Mechanistic Insights into the Hydrogen Evolution Reaction on Ni2P Electrocatalyst in Alkaline Medium

Catalysts ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 307
Author(s):  
Russell W. Cross ◽  
Nelson Y. Dzade
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Density Functional ◽  
Hydrogen Adsorption ◽  
Density Functional Theory Calculations ◽  
Transition Metal Doping ◽  
Experimental Conditions ◽  
Functional Theory ◽  
Alkaline Conditions ◽  
Modification Of The Surface

Nickel phosphide (Ni2P) is a promising material for the electrocatalytic generation of hydrogen from water. Here, we present a chemical picture of the fundamental mechanism of Volmer–Tafel steps in hydrogen evolution reaction (HER) activity under alkaline conditions at the (0001) and (10 1 ¯ 0) surfaces of Ni2P using dispersion-corrected density functional theory calculations. Two terminations of each surface (Ni3P2- and Ni3P-terminated (0001); and Ni2P- and NiP-terminated (10 1 ¯ 0)), which have been shown to coexist in Ni2P samples depending on the experimental conditions, were studied. Water adsorption on the different terminations of the Ni2P (0001) and (10 1 ¯ 0) surfaces is shown to be exothermic (binding energy in the range of 0.33−0.68 eV) and characterized by negligible charge transfer to/from the catalyst surface (0.01−0.04 e−). High activation energy barriers (0.86−1.53 eV) were predicted for the dissociation of water on each termination of the Ni2P (0001) and (10 1 ¯ 0) surfaces, indicating sluggish kinetics for the initial Volmer step in the hydrogen evolution reaction over a Ni2P catalyst. Based on the predicted Gibbs free energy of hydrogen adsorption (ΔGH*) at different surface sites, we found that the presence of Ni3-hollow sites on the (0001) surface and bridge Ni-Ni sites on the (10 1 ¯ 0) surface bind the H atom too strongly. To achieve facile kinetics for both the Volmer and Heyrovsky–Tafel steps, modification of the surface structure and tuning of the electronic properties through transition metal doping is recommended as an important strategy.

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.

Ruthenium-based catalysts for water oxidation: the key role of carboxyl groups as proton acceptors

2020 ◽  
Vol 22 (9) ◽  
pp. 5249-5254 ◽  
Author(s):  
Yuting Liu ◽  
Xiaofang Su ◽  
Wei Guan ◽  
Likai Yan
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Water Oxidation ◽  
Density Functional ◽  
Carboxyl Groups ◽  
Functional Theory

In this work, the mechanism of water oxidation catalyzed by an Ru-based complex [Ru(L)]+ (L = 5,5-chelated 2-carboxy-phen, 2,2′;6′,2′′-terpyridine) was studied by density functional theory (DFT) calculations.

scholarly journals Electrochemical water oxidation on WO3 surfaces: A density functional theory study

2019 ◽  
Vol 321-322 ◽  
pp. 94-99 ◽  
Author(s):  
Ravi Kishore ◽  
Xi Cao ◽  
Xueqing Zhang ◽  
Anja Bieberle-Hütter
Keyword(s):  
Density Functional Theory ◽  
Water Oxidation ◽  
Density Functional ◽  
Density Functional Theory Study ◽  
Functional Theory

Theoretical insights into the reactivity of Fe-based catalysts for water oxidation: the role of electron-withdrawing groups

2018 ◽  
Vol 20 (21) ◽  
pp. 14919-14926 ◽  
Author(s):  
Penglin Xu ◽  
Shaojin Hu ◽  
Hou-Dao Zhang ◽  
Xiao Zheng
Keyword(s):  
Density Functional Theory ◽  
Water Oxidation ◽  
Density Functional ◽  
Catalytic Efficiency ◽  
Oxidation Catalysts ◽  
Functional Theory

The relative catalytic efficiency of a series of Fe-based water oxidation catalysts is elucidated by comprehensive calculations using density functional theory methods.

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