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Mbang Eze O, Ertekin Z, Symes MD. Decoupled Water Electrolysis at High Current Densities Using a Solution-Phase Redox Mediator. ENERGY & FUELS : AN AMERICAN CHEMICAL SOCIETY JOURNAL 2025; 39:7129-7136. [PMID: 40236631 PMCID: PMC11995369 DOI: 10.1021/acs.energyfuels.5c00092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/06/2025] [Revised: 03/15/2025] [Accepted: 03/17/2025] [Indexed: 04/17/2025]
Abstract
The electrolysis of water using renewably generated power to give "green" hydrogen is a key enabler of the putative hydrogen economy. Conventional electrolysis systems are effective for hydrogen production when steady power inputs are available, but tend to handle intermittent or low-power inputs much less well, in particular because it becomes very difficult to ensure separation of the hydrogen and oxygen products under intermittent or low-power regimes. Decoupled electrolysis offers one potential solution to the problem of interfacing electrolyzers with intermittent and low-power inputs: by allowing the hydrogen and oxygen products of electrolysis to be produced in separate devices to each other, systems in which gas mixtures are inherently much less likely to form can be designed. However, in general, decoupled electrolysis systems operate at rather low current densities (up to a few hundred mA/cm2), which detracts somewhat from their suitability for applications. Herein, we constructed a flow system device for decoupled hydrogen production using a solution of the polyoxometalate silicotungstic acid as a liquid-phase decoupling agent. This mediator has been explored as a mediator for decoupled hydrogen evolution before, but in this work, we significantly expanded the range of current densities over which decoupling is demonstrated, from 50 mA/cm2 up to 1.35 A/cm2, the latter of which exceeds the current densities at which commercial alkaline electrolyzers operate and which begins to approach those achievable with proton exchange membrane electrolyzers. Essentially complete decoupling of the hydrogen and oxygen generation processes is achieved across this full range of current densities, suggesting that rapid oxygen production with coupled redox mediator reduction is possible without compromising on decoupling efficiency.
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Affiliation(s)
- Obeten Mbang Eze
- School of
Chemistry, University of Glasgow, Glasgow G12 8QQ, United Kingdom
- Department
of Chemistry, University of Cross River
State, Calabar, Cross River State 540281, Nigeria
| | - Zeliha Ertekin
- School of
Chemistry, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Mark D. Symes
- School of
Chemistry, University of Glasgow, Glasgow G12 8QQ, United Kingdom
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Iesalnieks M, Vanags M, Alsiņa LL, Eglītis R, Grīnberga L, Sherrell PC, Šutka A. Efficient Decoupled Electrolytic Water Splitting in Acid through Pseudocapacitive TiO 2. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024; 11:e2401261. [PMID: 38742588 PMCID: PMC11267372 DOI: 10.1002/advs.202401261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Revised: 04/30/2024] [Indexed: 05/16/2024]
Abstract
Water electrolysis remains a key component in the societal transition to green energy. Membrane electrolyzers are the state-of-the-art technology for water electrolysis, relying on 80 °C operation in highly alkaline electrolytes, which is undesirable for many of the myriad end-use cases for electrolytic water splitting. Herein, an alternative water electrolysis process, decoupled electrolysis, is described which performed in mild acidic conditions with excellent efficiencies. Decoupled electrolysis sequentially performs the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), at the same catalyst. Here, H+ ions generated from the OER are stored through pseudocapacitive (redox) charge storage, and released to drive the HER. Here, decoupled electrolysis is demonstrated using cheap, abundant, TiO2 for the first time. To achieve decoupled acid electrolysis, ultra-small anatase TiO2 particles (4.5 nm diameter) are prepared. These ultra-small TiO2 particles supported on a carbon felt electrode show a highly electrochemical surface area with a capacitance of 375 F g-1. When these electrodes are tested for decoupled water splitting an overall energy efficiency of 52.4% is observed, with excellent stability over 3000 cycles of testing. This technology can provide a viable alternative to membrane electrolyzers-eliminating the need for highly alkaline electrolytes and elevated temperatures.
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Affiliation(s)
- Mairis Iesalnieks
- Institute of Materials and Surface EngineeringFaculty of Natural Sciences and TechnologyRiga Technical UniversityP. Valdena Street 3/7RigaLV‐1048Latvia
| | - Mārtiņš Vanags
- Institute of Materials and Surface EngineeringFaculty of Natural Sciences and TechnologyRiga Technical UniversityP. Valdena Street 3/7RigaLV‐1048Latvia
| | - Linda Laima Alsiņa
- Institute of Materials and Surface EngineeringFaculty of Natural Sciences and TechnologyRiga Technical UniversityP. Valdena Street 3/7RigaLV‐1048Latvia
| | - Raivis Eglītis
- Institute of Materials and Surface EngineeringFaculty of Natural Sciences and TechnologyRiga Technical UniversityP. Valdena Street 3/7RigaLV‐1048Latvia
| | - Līga Grīnberga
- Institute of Solid State PhysicsUniversity of LatviaRigaLV‐1063Latvia
| | - Peter C. Sherrell
- Applied Chemistry & Environmental ScienceSchool of ScienceRMIT University124 La Trobe StMelbourne3000Australia
| | - Andris Šutka
- Institute of Materials and Surface EngineeringFaculty of Natural Sciences and TechnologyRiga Technical UniversityP. Valdena Street 3/7RigaLV‐1048Latvia
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Slobodkin I, Davydova E, Sananis M, Breytus A, Rothschild A. Electrochemical and chemical cycle for high-efficiency decoupled water splitting in a near-neutral electrolyte. NATURE MATERIALS 2024; 23:398-405. [PMID: 38195864 PMCID: PMC10917665 DOI: 10.1038/s41563-023-01767-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Accepted: 11/20/2023] [Indexed: 01/11/2024]
Abstract
Green hydrogen produced by water splitting using renewable electricity is essential to achieve net-zero carbon emissions. Present water electrolysis technologies are uncompetitive with low-cost grey hydrogen produced from fossil fuels, limiting their scale-up potential. Disruptive processes that decouple the hydrogen and oxygen evolution reactions and produce them in separate cells or different stages emerge as a prospective route to reduce system cost by enabling operation without expensive membranes and sealing components. Some of these processes divide the hydrogen or oxygen evolution reactions into electrochemical and chemical sub-reactions, enabling them to achieve high efficiency. However, high efficiency has been demonstrated only in a batch process with thermal swings that present operational challenges. This work introduces a breakthrough process that produces hydrogen and oxygen in separate cells and supports continuous operation in a membraneless system. We demonstrate high faradaic and electrolytic efficiency and high rate operation in a near-neutral electrolyte of NaBr in water, whereby bromide is electro-oxidized to bromate concurrent with hydrogen evolution in one cell, and bromate is chemically reduced to bromide in a catalytic reaction that evolves oxygen in another cell. This process may lead the way to high-efficiency membraneless water electrolysis that overcomes the limitations of century-old membrane electrolysis.
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Affiliation(s)
- Ilya Slobodkin
- Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel
| | - Elena Davydova
- Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel
| | - Matan Sananis
- Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel
| | - Anna Breytus
- Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel
| | - Avner Rothschild
- Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel.
- The Nancy and Stephen Grand Technion Energy Program (GTEP), Technion - Israel Institute of Technology, Haifa, Israel.
- The Stewart and Lynda Resnick Sustainability Center for Catalysis (RSCC), Technion - Israel Institute of Technology, Haifa, Israel.
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Siracusano S, Giacobello F, Tonella S, Oldani C, Aricò AS. Ce-radical Scavenger-Based Perfluorosulfonic Acid Aquivion ® Membrane for Pressurised PEM Electrolysers. Polymers (Basel) 2023; 15:3906. [PMID: 37835954 PMCID: PMC10575047 DOI: 10.3390/polym15193906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 09/16/2023] [Accepted: 09/22/2023] [Indexed: 10/15/2023] Open
Abstract
A Ce-radical scavenger-based perfluorosulfonic acid (PFSA) Aquivion® membrane (C98 05S-RSP) was developed and assessed for polymer electrolyte membrane (PEM) electrolyser applications. The membrane, produced by Solvay Specialty Polymers, had an equivalent weight (EW) of 980 g/eq and a thickness of 50 μm to reduce ohmic losses at a high current density. The electrochemical properties and gas crossover through the membrane were evaluated upon the formation of a membrane-electrode assembly (MEA) in a range of temperatures between 30 and 90 °C and at various differential pressures (ambient, 10 and 20 bars). Bare extruded (E98 05S) and reinforced (R98 05S) PFSA Aquivion® membranes with similar EWs and thicknesses were assessed for comparison in terms of their performance, stability and hydrogen crossover under the same operating conditions. The method used for the membrane manufacturing significantly influenced the interfacial properties, with the electrodes affecting the polarisation resistance and H2 permeation in the oxygen stream, as well as the degradation rate, as observed in the durability studies.
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Affiliation(s)
- Stefania Siracusano
- CNR-ITAE, Institute of Advanced Energy Technologies, National Research Council, Via Salita S. Lucia Sopra Contesse 5, 98126 Messina, Italy; (F.G.); (A.S.A.)
| | - Fausta Giacobello
- CNR-ITAE, Institute of Advanced Energy Technologies, National Research Council, Via Salita S. Lucia Sopra Contesse 5, 98126 Messina, Italy; (F.G.); (A.S.A.)
| | - Stefano Tonella
- Solvay Specialty Polymers, Viale Lombardia 20, 20021 Bollate (MI), Italy; (S.T.); (C.O.)
| | - Claudio Oldani
- Solvay Specialty Polymers, Viale Lombardia 20, 20021 Bollate (MI), Italy; (S.T.); (C.O.)
| | - Antonino S. Aricò
- CNR-ITAE, Institute of Advanced Energy Technologies, National Research Council, Via Salita S. Lucia Sopra Contesse 5, 98126 Messina, Italy; (F.G.); (A.S.A.)
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Zheng X, Lv F, Liu X, Zheng Z, Chen Y. Decoupled alkaline water electrolysis by a K 0.5MnO 2-Ti mediator via K-ion insertion/extraction. Chem Commun (Camb) 2023; 59:2138-2141. [PMID: 36727267 DOI: 10.1039/d2cc05775a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Conventional one-step water electrolyzers generate H2 accompanied by O2 evolution, and may cause gas mixing and high cell voltage inputs. Herein, using the potassium ion battery material of K0.5MnO2-Ti as a mediator, we effectively decoupled the H2 and O2 evolution of alkaline water electrolysis temporally, thereby achieving a membrane-free pathway for H2 production. As a mediator electrode for charge storage, the K0.5MnO2-Ti exhibited a stable capacity of 100 mA h g-1 at 0.1 A g-1 owing to the reversible K-ion insertion/extraction mechanism. The decoupled water electrolysis device exhibited the step voltages for hydrogen and oxygen production of 1.02 and 0.57 V at 5 mA, respectively. A nearly unity Faradaic efficiency and sustained production of pure H2 has been demonstrated at a constant current density. We anticipate that this mediator demonstrated here may provide a route for the practical application of the decoupling strategy.
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Affiliation(s)
- Xuewen Zheng
- International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, China.
| | - Fei Lv
- International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, China.
| | - Xuan Liu
- International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, China.
| | - Zhihao Zheng
- International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, China.
| | - Yubin Chen
- International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, China.
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Zhang W, Liu M, Gu X, Shi Y, Deng Z, Cai N. Water Electrolysis toward Elevated Temperature: Advances, Challenges and Frontiers. Chem Rev 2023. [PMID: 36749705 DOI: 10.1021/acs.chemrev.2c00573] [Citation(s) in RCA: 47] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Since severe global warming and related climate issues have been caused by the extensive utilization of fossil fuels, the vigorous development of renewable resources is needed, and transformation into stable chemical energy is required to overcome the detriment of their fluctuations as energy sources. As an environmentally friendly and efficient energy carrier, hydrogen can be employed in various industries and produced directly by renewable energy (called green hydrogen). Nevertheless, large-scale green hydrogen production by water electrolysis is prohibited by its uncompetitive cost caused by a high specific energy demand and electricity expenses, which can be overcome by enhancing the corresponding thermodynamics and kinetics at elevated working temperatures. In the present review, the effects of temperature variation are primarily introduced from the perspective of electrolysis cells. Following an increasing order of working temperature, multidimensional evaluations considering materials and structures, performance, degradation mechanisms and mitigation strategies as well as electrolysis in stacks and systems are presented based on elevated temperature alkaline electrolysis cells and polymer electrolyte membrane electrolysis cells (ET-AECs and ET-PEMECs), elevated temperature ionic conductors (ET-ICs), protonic ceramic electrolysis cells (PCECs) and solid oxide electrolysis cells (SOECs).
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Affiliation(s)
- Weizhe Zhang
- Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Haidian District, Beijing 100084, China.,Beijing Institute of Smart Energy, Changping District, Beijing 102209, China
| | - Menghua Liu
- Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Haidian District, Beijing 100084, China.,Beijing Institute of Smart Energy, Changping District, Beijing 102209, China
| | - Xin Gu
- Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Haidian District, Beijing 100084, China
| | - Yixiang Shi
- Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Haidian District, Beijing 100084, China.,Beijing Institute of Smart Energy, Changping District, Beijing 102209, China
| | - Zhanfeng Deng
- Beijing Institute of Smart Energy, Changping District, Beijing 102209, China
| | - Ningsheng Cai
- Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Haidian District, Beijing 100084, China
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Mulkapuri S, Ravi A, Nasani R, Kurapati SK, Das SK. Barrel-Shaped-Polyoxometalates Exhibiting Electrocatalytic Water Reduction at Neutral pH: A Synergy Effect. Inorg Chem 2022; 61:13868-13882. [PMID: 36006778 DOI: 10.1021/acs.inorgchem.2c01811] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Two copper-based barrel-shaped polyoxometalates (POMs), namely, [{H3O}4{Na6(H2O)22}][{CuI (H2O)3}2{CuII (H2O)}3{B-α-BiIIIWVI9O33}2]·7H2O (NaCu-POM) and Li4[{NH4}2{H3O}3{Li(H2O)5}][{CuII(SH)}{(CuIICuI1.5)(B-α-BiIIIWVI9O33)}2]·9H2O (LiCu-POM) have been synthesized and structurally characterized. The single-crystal X-ray diffraction analyses of NaCu-POM and LiCu-POM reveal the presence of penta- and hexa-nuclear copper wheels per formula units, respectively; these copper wheels are sandwiched between two lacunary Keggin anions {B-α-BiIIIWVI9O33}9- (BiW9) to form the barrel-shaped title POM compounds. In both the compounds NaCu-POM and LiCu-POM, the mixed-valent copper centers are present in their respective penta- and hexa-nuclear copper wheels, established by X-ray photoelectron spectroscopy (XPS) as well as by bond valence sum (BVS) calculations. Compound LiCu-POM additionally shows the presence of a sulfhydryl ligand (SH-), coordinated to one of the copper centers of its {Cu6}-wheel, that is expected to be generated from the in situ reduction of sulfate anion present in the concerned reaction mixture (lithium-ion in ammonia solution may be the reducing agent). Interestingly, the title compounds, NaCu-POM and LiCu-POM exhibit an efficient electrocatalytic hydrogen evolution reaction (HER) by reducing water at neutral pH. Detailed electrochemical studies including controlled experiments indicate that the active sites for this electrocatalysis are the W(VI) centers of the title compounds, not the copper centers. However, a relevant tri-lacunary Keggin cluster anion {PVWVI9O33}7- (devoid of copper ion) does not show comparable HER as shown by the title compounds. The intra-cluster cooperative interactions of the mixed-valent copper centers (CuII/CuI) with the tungsten centers (W6+) make the overall system electrocatalytically active toward water reduction to molecular hydrogen at neutral pH. High Faradaic efficiencies (89 and 92%) and turnover frequencies (1.598 s-1 and 1.117 s-1) make the title compounds NaCu-POM and LiCu-POM efficient catalysts toward electrochemical water reduction to molecular hydrogen.
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Affiliation(s)
- Sateesh Mulkapuri
- School of Chemistry, University of Hyderabad, P.O. Central University, Hyderabad 500046, India
| | - Athira Ravi
- School of Chemistry, University of Hyderabad, P.O. Central University, Hyderabad 500046, India
| | - Rajendar Nasani
- School of Chemistry, University of Hyderabad, P.O. Central University, Hyderabad 500046, India
| | - Sathish Kumar Kurapati
- School of Chemistry, University of Hyderabad, P.O. Central University, Hyderabad 500046, India.,Department of Chemistry, Chaitanya Bharathi Institute of Technology Hyderabad, Gandipet, Hyderabad 500075, India
| | - Samar K Das
- School of Chemistry, University of Hyderabad, P.O. Central University, Hyderabad 500046, India
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Stergiou AD, Symes MD. Organic transformations using electro-generated polyoxometalate redox mediators. Catal Today 2022. [DOI: 10.1016/j.cattod.2021.05.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Mulkapuri S, Ravi A, Mukhopadhyay S, Kurapati SK, Siby V, Das SK. WVI‒OH Functionality on polyoxometalates for water reduction to molecular hydrogen. Inorg Chem Front 2022. [DOI: 10.1039/d2qi00421f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
ABSTRACT: Grafting a WVI‒(OH)2 functionality on polyoxometalates (POMs)’ surface makes the concerned POM compounds, Na6[{CoII(H2O)3}2{WVI(OH)2}2{BiIIIWVI9O33)2}]·8H2O (1) and Na4(Himi)2[{MnII(H2O)3}2{WVI(OH)2}2{BiIIIWVI9O33)2}]·28H2O (2) prominent heterogeneous electrocatalysts for water reduction to molecular hydrogen. We have...
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Enhanced performance of a PtCo recombination catalyst for reducing the H2 concentration in the O2 stream of a PEM electrolysis cell in the presence of a thin membrane and a high differential pressure. Electrochim Acta 2020. [DOI: 10.1016/j.electacta.2020.136153] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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