Special Issue "Electrocatalytic Water Oxidation"

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Electrocatalysis".

Deadline for manuscript submissions: 10 January 2022.

Special Issue Editors

Dr. Yurii V. Geletii
E-Mail Website
Guest Editor
Department of Chemistry, Emory University, Atlanta, GA 30322, USA
Interests: artificial photosynthesis; water splitting; water oxidation catalysts; electron transfer reactions
Special Issues, Collections and Topics in MDPI journals
Dr. Qiushi Yin
E-Mail Website
Guest Editor
Department of Chemistry, Emory University, Atlanta, GA 30322, USA
Interests: inorganic chemistry; photoelectrochemical cells; water oxidation catalysis

Special Issue Information

Dear Colleagues,

Water electrolysis to produce oxygen and hydrogen gas is a promising option to convert solar energy to fuel. Electrolyzers using an alkaline solutions as the electrolyte have been commercially available for many years. Electrolyzers using a liquid alkaline solution of sodium or potassium hydroxide as the electrolyte have been commercially available for many years, but their effective electrical efficiency is rather low, 70–80%. Water oxidation on anode is the 4-electron process and requires use of a cost-effective catalyst. Despite numerous efforts, such catalysts for a new generation of electrolyzers are not yet developed. This Special Issue will be mostly focused on understanding of the mechanism of water oxidation in the presence of homogeneous or immobilized molecular catalysts. The catalysts with thorough characterized reactive centers will be also considered.

Dr. Yurii V. Geletii
Dr. Qiushi Yin
Guest Editors

Manuscript Submission Information

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Keywords

  • Water oxidation
  • electron transfer
  • molecular catalyst
  • mechanism of O2 formation

Published Papers (7 papers)

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Research

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Article
Tafel Slope Analyses for Homogeneous Catalytic Reactions
Catalysts 2021, 11(1), 87; https://doi.org/10.3390/catal11010087 - 11 Jan 2021
Viewed by 809
Abstract
Tafel analysis of electrocatalysts is essential in their characterization. This paper analyzes the application of Tafel-like analysis to the four-electron nonelectrochemical oxidation of water by the stoichiometric homogeneous 1-electron oxidant [Ru(bpy)3]3+ to dioxygen catalyzed by homogeneous catalysts, [Ru4O [...] Read more.
Tafel analysis of electrocatalysts is essential in their characterization. This paper analyzes the application of Tafel-like analysis to the four-electron nonelectrochemical oxidation of water by the stoichiometric homogeneous 1-electron oxidant [Ru(bpy)3]3+ to dioxygen catalyzed by homogeneous catalysts, [Ru4O4(OH)2(H2O)4(γ-SiW10O36)2]10− (Ru4POM) and [Co4(H2O)2(PW9O34)2]10– (Co4POM). These complexes have slow electron exchange rates with electrodes due to the Frumkin effect, which precludes the use of known electrochemical methods to obtain Tafel plots at ionic strengths lower than 0.5 M. The application of an electron transfer catalyst, [Ru(bpy)3]3+/2+, increases the rates between the Ru4POM and electrode, but a traditional Tafel analysis of such a complex system is precluded due to a lack of appropriate theoretical models for 4-electron processes. Here, we develop a theoretical framework and experimental procedures for a Tafel-like analysis of Ru4POM and Co4POM, using a stoichiometric molecular oxidant [Ru(bpy)3]3+. The dependence of turnover frequency (TOF) as a function of electrochemical solution potential created by the [Ru(bpy)3]3+/[Ru(bpy)3]2+ redox couple (an analog of the Tafel plot) was obtained from kinetics data and interpreted based on the suggested reaction mechanism. Full article
(This article belongs to the Special Issue Electrocatalytic Water Oxidation)
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Article
Ir-Sn-Sb-O Electrocatalyst for Oxygen Evolution Reaction: Physicochemical Characterization and Performance in Water Electrolysis Single Cell with Solid Polymer Electrolyte
Catalysts 2020, 10(5), 524; https://doi.org/10.3390/catal10050524 - 08 May 2020
Cited by 1 | Viewed by 959
Abstract
Mixed oxide Ir-Sn-Sb-O electrocatalyst was synthesized using thermal decomposition from chloride precursors in ethanol. Our previous results showed that Ir-Sn-Sb-O possesses electrocatalytic activity for an oxygen evolution reaction (OER) in acidic media. In the present work, the physicochemical characterization and performance of Ir-Sn-Sb-O [...] Read more.
Mixed oxide Ir-Sn-Sb-O electrocatalyst was synthesized using thermal decomposition from chloride precursors in ethanol. Our previous results showed that Ir-Sn-Sb-O possesses electrocatalytic activity for an oxygen evolution reaction (OER) in acidic media. In the present work, the physicochemical characterization and performance of Ir-Sn-Sb-O in an electrolysis cell are reported. IrO2 supported on antimony doped tin oxide (ATO) was also considered in this study as a reference catalyst. Scanning electron microscopy (SEM) images indicated that Ir-Sn-Sb-O has a mixed morphology with nanometric size. Energy dispersive X-ray spectroscopy (EDS) showed a heterogeneous atomic distribution. Transmission electron microscopy (TEM) analysis resulted in particle sizes of IrO2 and ATO between 3 to >10 nm, while the Ir-Sn-Sb-O catalyst presented non-uniform particle sizes from 3 to 50 nm. X-ray diffraction (XRD) measurements indicated that synthesized mixed oxide consists of IrO2, IrOx, doped SnO2 phases and metallic Ir. The Ir-Sn-Sb-O mixed composition was corroborated by temperature programmed reduction (TPR) measurements. The performance of Ir-Sn-Sb-O in a single cell electrolyser showed better results for hydrogen production than IrO2/ATO using a mechanical mixture. Ir-Sn-Sb-O demonstrated an onset potential for water electrolysis close to 1.45 V on Ir-Sn-Sb-O and a current density near to 260 mA mg−1 at 1.8 V. The results suggest that the mixed oxide Ir-Sn-Sb-O has favorable properties for further applications in water electrolysers. Full article
(This article belongs to the Special Issue Electrocatalytic Water Oxidation)
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Article
The Positive Effect of Iron Doping in the Electrocatalytic Activity of Cobalt Hexacyanoferrate
Catalysts 2020, 10(1), 130; https://doi.org/10.3390/catal10010130 - 16 Jan 2020
Cited by 5 | Viewed by 1512
Abstract
The lack of an earth-abundant, robust, and fast electrocatalyst for the oxygen evolution reaction (water oxidation) is a major bottleneck for the development of an scalable scheme towards the production of electrolytic hydrogen and other synthetic fuels from renewable energy and natural feedstocks. [...] Read more.
The lack of an earth-abundant, robust, and fast electrocatalyst for the oxygen evolution reaction (water oxidation) is a major bottleneck for the development of an scalable scheme towards the production of electrolytic hydrogen and other synthetic fuels from renewable energy and natural feedstocks. While many transition metal oxides work reasonably well in basic media, very few alternatives are available in neutral or acidic media. One promising candidate comes from the Prussian blue family, cobalt hexacyanoferrate. This electrocatalyst offers robust activity in a large pH range ( 0 < pH < 13 ), although current densities are limited due to slow charge transfer kinetics. Herein, we report how the partial substitution of catalytically active Co centres by additional Fe boosts current densities, reaching over 100 mA/cm 2 , more than double the performance of the parent Co 2 [Fe(CN) 6 ]. Those new results clearly increase the opportunity for this catalyst to become relevant in industrial-ready electrolyser architectures. Full article
(This article belongs to the Special Issue Electrocatalytic Water Oxidation)
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Article
Oxygen Evolution Reaction of Co-Mn-O Electrocatalyst Prepared by Solution Combustion Synthesis
Catalysts 2019, 9(6), 564; https://doi.org/10.3390/catal9060564 - 24 Jun 2019
Cited by 8 | Viewed by 2235
Abstract
High-performance oxygen evolution reaction (OER) electrocatalysts are needed to produce hydrogen for energy generation through a carbon-free route. In this work, the solution combustion synthesis (SCS) method was employed to synthesize mixed phases of Co- and Mn-based oxides, and the relationships between the [...] Read more.
High-performance oxygen evolution reaction (OER) electrocatalysts are needed to produce hydrogen for energy generation through a carbon-free route. In this work, the solution combustion synthesis (SCS) method was employed to synthesize mixed phases of Co- and Mn-based oxides, and the relationships between the crystalline structure and the catalytic properties in the mixed phases were established. The mixed phases of Co- and Mn-based oxides shows promising OER properties, such as acceptable overpotential (450 mV for 10 mA∙cm−2) and Tafel slope (35.8 mV∙dec−1), highlighting the use of the mixed phases of Co- and Mn-based oxides as a new efficient catalysts for water splitting. Electronic structure of the mixed phases of Co- and Mn based oxides is studied in detail to give insight for the origin of high catalytic activities. In addition, excellent long-term stability for OER in alkaline media is achieved for the mixed phase of Co- and Mn based oxides. Full article
(This article belongs to the Special Issue Electrocatalytic Water Oxidation)
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Article
Engineering Ternary Copper-Cobalt Sulfide Nanosheets as High-performance Electrocatalysts toward Oxygen Evolution Reaction
Catalysts 2019, 9(5), 459; https://doi.org/10.3390/catal9050459 - 17 May 2019
Cited by 11 | Viewed by 2030
Abstract
The rational design and development of the low-cost and effective electrocatalysts toward oxygen evolution reaction (OER) are essential in the storage and conversion of clean and renewable energy sources. Herein, a ternary copper-cobalt sulfide nanosheets electrocatalysts (denoted as CuCoS/CC) for electrochemical water oxidation [...] Read more.
The rational design and development of the low-cost and effective electrocatalysts toward oxygen evolution reaction (OER) are essential in the storage and conversion of clean and renewable energy sources. Herein, a ternary copper-cobalt sulfide nanosheets electrocatalysts (denoted as CuCoS/CC) for electrochemical water oxidation has been synthesized on carbon cloth (CC) via the sulfuration of CuCo-based precursors. The obtained CuCoS/CC reveals excellent electrocatalytic performance toward OER in 1.0 M KOH. It exhibits a particularly low overpotential of 276 mV at current density of 10 mA cm−2, and a small Tafel slope (58 mV decade−1), which is superior to the current commercialized noble-metal electrocatalysts, such as IrO2. Benefiting from the synergistic effect of Cu and Co atoms and sulfidation, electrons transport and ions diffusion are significantly enhanced with the increase of active sites, thus the kinetic process of OER reaction is boosted. Our studies will serve as guidelines in the innovative design of non-noble metal electrocatalysts and their application in electrochemical water splitting Full article
(This article belongs to the Special Issue Electrocatalytic Water Oxidation)
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Article
Solvothermally Doping NiS2 Nanoparticles on Carbon with Ferric Ions for Efficient Oxygen Evolution Catalysis
Catalysts 2019, 9(5), 458; https://doi.org/10.3390/catal9050458 - 17 May 2019
Cited by 7 | Viewed by 1449
Abstract
Exploring efficient non-precious metal based electrocatalysts for the oxygen evolution reaction (OER) is a prerequisite to implement the widespread application of a water electrolyzer and metal-air batteries. Herein, Fe-doped NiS2 nanoparticles on a carbon matrix (Fe-NiS2/C) are facilely prepared via [...] Read more.
Exploring efficient non-precious metal based electrocatalysts for the oxygen evolution reaction (OER) is a prerequisite to implement the widespread application of a water electrolyzer and metal-air batteries. Herein, Fe-doped NiS2 nanoparticles on a carbon matrix (Fe-NiS2/C) are facilely prepared via a two-step solvothermal process, where Ni-containing metal organic frameworks (Ni-MOFs) are vulcanized in situ and carbonized by a solvothermal method to form abundant NiS2 nanoparticles homogeneously distributed on a carbon matrix (NiS2/C), followed by doping with ferric ions via a similar solvothermal treatment. The resulting Fe-NiS2/C nanoparticle composites show a rougher surface than the NiS2/C parent, likely due to the formation of more structural defects after ferric ion doping, which maximizes the exposure of active sites. Moreover, ferric ion doping can also regulate the surface electronic state to reduce the activation energy barrier for OER on NiS2/C sample. With these merits, the best sample Fe-NiS2/C-30 only requires a potential of +1.486 V (vs. RHE) to reach an OER current density of 10 mA cm−2 and can retain 96.85% of its initial current after continuous working for about 10 h in 1.0 M KOH aqueous solution, along with a small Tafel slope of 45.66 mV/dec, outperforming a commercial RuO2 catalyst. The results in this work enrich the method to tailor the catalytic activity of transition metal sulfides for electrochemical energy technologies. Full article
(This article belongs to the Special Issue Electrocatalytic Water Oxidation)
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Review

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Review
Recent Advances in Transition Metal Carbide Electrocatalysts for Oxygen Evolution Reaction
Catalysts 2020, 10(10), 1164; https://doi.org/10.3390/catal10101164 - 11 Oct 2020
Cited by 12 | Viewed by 1188
Abstract
The electrolysis of water is considered to be a primary method for the mass production of hydrogen on a large scale, as a substitute for unsustainable fossil fuels in the future. However, it is highly restricted by the sluggish kinetics of the four-electron [...] Read more.
The electrolysis of water is considered to be a primary method for the mass production of hydrogen on a large scale, as a substitute for unsustainable fossil fuels in the future. However, it is highly restricted by the sluggish kinetics of the four-electron process of the oxygen evolution reaction (OER). Therefore, there is quite an urgent need to develop efficient, abundant, and economical electrocatalysts. Transition metal carbides (TMCs) have recently been recognized as promising electrocatalysts for OER due to their excellent activity, conductivity, and stability. In this review, widely-accepted evaluation parameters and measurement criteria for different electrocatalysts are discussed. Moreover, five sorts of TMC electrocatalysts—including NiC, tungsten carbide (WC), Fe3C, MoC, and MXene—as well as their hybrids, are researched in terms of their morphology and compounds. Additionally, the synthetic methods are summarized. Based on the existing materials, strategies for improving the catalytic ability and new designs of electrocatalysts are put forward. Finally, the future development of TMC materials is discussed both experimentally and theoretically, and feasible modification approaches and prospects of a reliable mechanism are referred to, which would be instructive for designing other effective noble-free electrocatalysts for OER. Full article
(This article belongs to the Special Issue Electrocatalytic Water Oxidation)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Influence of Active Site Iron Substitution in the Water Oxidation Electrocatalytic Activity of Cobalt Hexacyanoferrate

Author: José Ramón Galán-Mascarós

Title: Tafel Slope Analyses for Homogeneous Catalytic Reactions
Authors: Geletii*, Yu. V. et al
Affiliation: Department of Chemistry, Emory University, Atlanta, GA 30322, USA
Abstract: This paper analyzes the application of Tafel plots to the four-electron oxidation of water to dioxygen catalyzed by a homogeneous catalyst, [Ru4O4(OH)2 (H2O)4(γ-SiW10O36)2]10-, (Ru4POM). We show that this approach can be useful to fully characterize and compare the activity of different catalysts (or the same catalyst under different experimental conditions such as pH, ionic strength, etc).

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