Electrochemical Oxygen Evolution Research Articles

Hydrothermal electrochemical flow reactor to independently control temperature, pressure, and potential for manganese oxide electrodeposition

Electrodeposition has been widely applied for the fabrication of functional materials; however, most previous deposition processes were limited to temperatures of less than 100 °C. Furthermore, reaction pressure was concomitantly determined with the reaction temperature, hindering the full exploration of synthetic conditions. Here, we developed a hydrothermal electrochemical flow reactor equipped with flowing system and that enables the independent control of temperature and pressure and applied this reactor to the synthesis of manganese oxides (MnOx) for electrochemical oxygen evolution reaction. Systematic investigation of temperature and pressure revealed that the crystallinity and morphology of MnOx was influenced by deposition temperature, with particle size decreasing under higher pressure (4 MPa). Electrodeposition at higher temperature (160 °C) at 1 MPa generated a mixed phase of ε- and γ- MnO2, which showed superior electrochemical water oxidation activity to samples prepared at lower temperature (80 and 100 °C, respectively), achieving a current density of 10 mA cm−2 for at least 100 h under acidic conditions (pH 2.3). Our results show that the hydrothermal electrochemical flow reactor allows expanding synthetic parameters for the synthesis of highly functional catalytic materials.

Ligand-engineered Ni-based metal–organic frameworks for electrochemical oxygen evolution reaction

Regulating morphology and crystal structure of metal–organic frameworks (MOFs), as well as fabricating bimetallic MOFs have been widely proposed to optimize the electronic structure of MOFs and thus enhance electrochemical oxygen evolution reaction (OER) activity. Distinguish from these conventional and complex strategies, this work mainly focuses on the convenient ligand-engineering strategy to optimize the electronic structure of Ni-MOFs. Specifically, the electron-rich ferrocene (Fc) unit is linked into the ligand of Ni-MIL-53-NH2 by the stable covalent bond on the basis of Schiff-base reaction. Noticeably, the resulting Ni-MIL-53-Fc exhibits significantly enhanced OER activity compared to parent Ni-MIL-53-NH2, achieving 6.6-times improvement of TOF value from 0.19 to 1.25 s−1 at the overpotential of 350 mV. Further characterizations confirm that the incorporation of Fc unit can enhance the charge transfer, which induces more electrons aggregated in the Ni active sites and thus improves the intrinsic activity of Ni sites toward OER activity. This ligand-engineering strategy can be extended to fabricate highly active and stable catalysts toward other electrocatalytic reactions.

Hierarchically Multiscale Vertically Oriented NiFeCo Nanoflakes for Efficient Electrochemical Oxygen Evolution at High Current Densities

AbstractCrucial advancements in versatile catalyst systems capable of achieving high current densities under industrial conditions, bridging the gap between fundamental understanding and practical applications, are pivotal to propel the hydrogen economy forward. In this study, vertically oriented hierarchically multiscale nanoflakes of NiFeCo electrocatalysts are presented, developed by surface modification of a porous substrate with nano‐structured nickel. The resulting electrodes achieve remarkably low overpotentials of 139 mV at 10 mAcm−2 and 248 mV at 500 mAcm−2. Further, scaled‐up electrodes are implemented in a water‐splitting electrolyser device exhibiting a stable voltage of 1.82 V to deliver a constant current density of 500 mA cm−2 for over 17 days. Moreover, the role of the unique structures on electrochemical activity is systematically investigated by fractal analysis, involving computation of structure factors such as Minkowski connectivity, fractal dimension, and porosity using scanning electron microscope images. It is found that such structures offer higher surface area than typical layered double hydroxide structures due to morphological coherence that results in a superhydrophilic surface, while the base Ni layer boosts the charge transfer. This study demonstrates a Ni/NiFeCo(OH)x heterostructure with highly porous morphology, a key to unlocking extremely efficient oxygen evolution reaction activity with exceptional stability. Moreover, fractal analysis is presented as a valuable tool to evaluate the electrochemical performance of catalysts for their structured morphology.

Unravelling the trifunctional electrochemical properties of WSe2 nanosheets for self-powered hydrogen production

Two dimensional materials have received increasing recognition for their utility in electrochemical energy storage and conversion devices, as well as for self-powered systems. In this work, we are reporting the trifunctional electrochemical properties (such as energy-storage, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)) of WSe2 nanosheets (prepared by a solvothermal method) towards the development of a self-powered system for uninterrupted hydrogen (H2) production. First, we have examined the energy storage properties of the WSe2 nanosheets in the form of flexible solid-state supercapacitor (FSSC) that shows the presence of ion-intercalation pseudocapacitance in the WSe2 nanosheets. The fabricated WSe2 FSSC possess a high device capacitance, energy density, and power density with 119% capacitance retention over 5,000 cycles. Second, we explored the electrocatalytic properties of WSe2 nanosheets that indicated they possess effective HER and OER properties with low overpotential (115 mV for HER and 312 mV for OER), respectively. Finally, a proof-of-concept self-powered system comprising a solar cell, WSe2 FSSC, and lab-scale WSe2 electrolyzer (with a low overpotential of 1.604 V at 10 mA cm−2) was demonstrated to overcome the power fluctuation issues for effective and uninterrupted H2 production.

Co/Ni-MOF as a bifunctional electrode material for electrochemical sensor and oxygen evolution reaction

In recent years, the demand for economical multifunctional materials has increased significantly. In this paper, Co/Ni-based bimetallic-organic frameworks (Co/Ni-MOFs) materials were prepared, which showed good electrochemical recognition and oxygen evolution bifunctional activity in alkaline environment. The electrochemical test showed that the response time of the material to glucose was less than 3 s, the sensitivity was 2.0826 μAmM−1 cm−2, and the detection limit was 8.84 μM. The material also exhibits a good overpotential of 410 mV at a current density of 100 mA cm−2 and Tafel slope of 451 mV dec−1. The results show that Co/Ni-MOFs can be used as an electrocatalyst for electrochemical sensors and water splitting reactions.

Electrochemical oxygen evolution coupled structure and capacity decay of single-crystal LiNi0.6Co0.2Mn0.2O2 cathode materials

Understanding the oxygen evolution of layered oxide cathode materials at high cut-off voltages is an enormous challenge. Herein, the single-crystal LiNi0.6Co0.2Mn0.2O2 (SC622) cathodes have been studied to investigate the relationship between electrochemical oxygen evolution behavior, structural degradation, and electrochemical performance at high cut-off voltages. The oxygen evolution behavior can be detected at around 4.6 V (with 84 % lithium extraction) via in-situ differential electrochemical mass spectrometry and ex-situ synchrotron soft X-ray absorption spectroscopy tests. Density functional theory results show that lattice oxygen atoms are lost easily from the surficial region but stable in the bulk area at high voltages. This provides scientific theoretical fundamentals for using SC622 cathode material at high cut-off voltages. Excessive lithium extraction results in uneven distribution of lithium inside SC622 grains, leading to lattice distortion and uneven deformation, eventually causing slippage and cracks. These bulk damages accelerate oxygen release and severely degrade the electrochemical performance of SC622. Both surface doping and fluorinated electrolyte can suppress the oxygen evolution of SC622 cathode materials at an ultrahigh cut-off voltage of 4.7 V. However, an appropriately high cut-off voltage, such as 4.5 V, maybe a more pragmatic strategy, achieving a “sweet point” of high specific energy and long cycle-life of cathode materials such as SC622.

Multiple oxyanions modification on nickel–iron layered double hydroxides for enhanced oxygen evolution reaction

The electrochemical oxygen evolution reaction (OER) holds paramount significance as a pivotal stage within electrochemical water-splitting processes, particularly in hydrogen production. Highly efficient OER electrocatalysts with inherent capability to effectively lower the energy barrier and promote fast kinetics are in high demand. In this research, we have introduced a novel strategy of modifying the non-precious metal benchmark catalyst, NiFe layered double hydroxide (LDH), through multiple oxyanions. Our approach involved incorporating MoS42− as a source of modified anions to enhance the performance of LDH in OER. Under specific conditions of the hydrothermal reaction, a majority of the sulfur (S) within the MoS42− anions underwent oxidization, resulting in the formation of SO42− and MoOxS4-x2- groups. As a result, NiFe LDH composites that were modified with multiple oxyanionic moieties, were successfully fabricated. Thanks to the synergistic effects of these oxyanions, which accelerate the generation of active NiOOH species, the optimized NiFe LDH-MoS4-0.1/NF sample exhibited a significantly low overpotential of 228 and 270 mV at current densities of 10 and 100 mA cm−2, respectively, along with a low Tafel slope of 35.5 mVdec−1 in 1 M KOH electrolyte solution. Our study underscored the importance of embracing diverse oxyanions modification strategy to amplify the performance of OER, opening up numerous opportunities for energy conversion and storage applications.

Internal and External Cultivation Strategy toward Efficient Electrochemical Oxygen Evolution in Cobalt Pentlandite

Internal and External Cultivation Strategy toward Efficient Electrochemical Oxygen Evolution in Cobalt Pentlandite

Quench-induced surface engineering of NiO/NiSex hybrid for highly enhanced electrochemical oxygen evolution reaction

To achieve sustainable production of hydrogen fuel through electrochemical water splitting, efficient and low-cost electrocatalysts for the kinetically sluggish oxygen evolution reaction (OER) are urgently desirable. Herein, a calcination-quenching strategy to synthesize core-shell NiO@NiSex nanorods (NiSex is the core and NiO is the shell) with tailored surface compositions and structures is reported. In the calcination step, a NiO@NiSex nanostructure supported on nickel foam (NF) (denoted as NiO@NiSex/NF) was formed via oxidative calcination of highly conductive NiSe in situ grown on NF (denoted as NiSe/NF). Subsequently, the as-obtained NiO@NiSex/NF electrode at the high temperature state was rapidly placed in a cold iron salt solution to achieve the quenching process. The results conclusively demonstrated that the quenching process resulted in iron doping and vacancies generation on the surface of NiO, effectively reconfiguring the desired surface of the catalyst, thus giving rise to notably enhanced electrocatalytic performance for OER in alkaline media. As a result, the quenched-engineered NiO@NiSex/NF electrode requires ultralow overpotentials of 231 and 265 mV to yield current densities of 10 and 100 mA cm−2, respectively, and presents a very low Tafel slope of 28.9 mV dec−1 as well as excellent durability, with the performance superior to most of metal oxide catalysts reported to date. This work extends the use of quenching chemistry in fabrication of high-performance metal oxide catalysts for energy related applications.

Insights into mechanisms on electrochemical oxygen evolution substitution reactions

The high total energy consumption of water electrolysis systems is often attributed to the slow kinetics of oxygen evolution reaction (OER). To address this issue, substituting small molecule oxidation reaction that is thermodynamically more advantageous for OER at the anode can significantly increase its energy conversion efficiency. Diversified oxidation substrates can ensure efficient conversion of the cathodic reaction while generating high value-added products or pollutant degradation at the anode. However, the complexity of the elemental composition of the substrate requires an in-depth study of the reaction mechanism. This review focuses on the mechanism of electrooxidation of different substrate molecules, such as ethanol, urea, and hydrazine. Additionally, it introduces some design ideas and strategies for high-performance electrocatalysts in conjunction with reaction path selectivity. The work also foresees the challenges in achieving industrial transformation in this field.

Engineering 2D heterostructured VS2-rGO-Ni nanointerface to stimulate electrocatalytic water splitting and supercapacitor applications

The electrochemical oxygen evolution reaction (OER) is a key anodic response that turns renewable energy into fuels. Overcoming the obstacles (sluggish kinetics) in OER requires the development of a highly active electrocatalyst with excellent stability. For the first time, this study presents a new kind of nanostructured morphology of VS2-rGO-Ni ternary system for alkaline OER. A systematic investigation was carried out to optimize the excellent electrocatalyst using different arrays in the binary and ternary composites. The homogeneous and well-interconnected network structure is identified between the VS2 nanosheets (∼20 nm thickness) and rGO layered structure, including the dispersion of Ni nanoparticles. The OER performances of VS2-rGO-Ni-3 (rVN-3) in 1 M KOH were excellently stimulated, where the overpotential was lowered to 192 mV at 10 mA cm−2. After 2500 CV cycles and chronopotentiometry tests (10 mA cm−2), the electrocatalyst showed long-term stability without losing much activity. Although, the electrocatalysts were assembled in rVN-3||rVN-3 required cell voltage of 1.70 V which is able to achieve the threshold current density. The interfacial interaction between the VS2, rGO and Ni in the ternary composite leads to synergistic effect that significantly promotes the adsorption of oxygenated intermediates for an excellent OER process. Moreover, rVN-3 provided a reasonable supercapacitor performances, which confirms the multi characteristics properties. The nanostructured morphology with a well-connected network structure provides a large active surface for interacting with charge species and stable performance.

Heat Treatment for Enhancing Ir-Based Catalysts Enclosed in a Carbon Layer for Electrochemical Oxygen Evolution Reaction

Heat Treatment for Enhancing Ir-Based Catalysts Enclosed in a Carbon Layer for Electrochemical Oxygen Evolution Reaction

Elucidating the Role of Mass Transfer in Electrochemical Redox Reactions on Electrospun Fibers

Mass transfer can tune the surface concentration of reactants and products and subsequently influence the catalytic performance. The morphology of nanomaterials plays an important role in the mass transfer of reaction microdomains, but related studies are lacking. Herein, a facile electrospinning technique utilizing cellulose was employed to fabricate a series of carbon nanofibers with different diameters, which exhibited excellent electrochemical nitrate reduction reaction and oxygen evolution reaction activities. Furthermore, the microstructure of electrocatalysts could influence the gas–liquid–solid interfacial mass transfer, resulting in different electrochemical performances.Graphical abstract

Structure‐property Relationship of Double Perovskite Oxide towards Trifunctional Electrocatalytic Activity: Strategy for Designing and Development

AbstractIn the present scenario, the paramount significant roles of various heterogeneous catalysts stimulate the modern technologies to underpin the benchmark requirements for the generation of sustainable energy by reducing toxic fossil fuel emissions. Such critical role necessitates further development of cost‐effective highly efficient and earth‐abundant multifunctional or trifunctional electrocatalysts to promote the advancement of electrochemical overall water splitting performances, yet it is extremely desirable. In this review context, we present the development of double perovskite (DP) oxides as robust trifunctional catalysts for electrochemical oxygen evolution reaction (OER), oxygen reduction reaction (ORR) and hydrogen evolution reactions (HER) by rational design of multiple cationic redox sites with stoichiometric oxygen amount. Particularly, we highlight the importance of the structural modifications via doping, surface structure and oxygen stoichiometry as key parameters to tune the electrocatalytic activities and understand the insight into activity and mechanism of this oxide family. This perspective also describes controlled synthesis protocols including the surface structure of double perovskite oxides are key techniques for realizing a correlation between structure‐activity relationships of these materials. Finally, it is concluded by outlining the several aspects of optimization strategies and computational opportunities can expand the future scope of double perovskite oxides as robust trifunctional electrocatalysts.

Spatially and Chemically Resolved Visualization of Fe Incorporation into NiO Octahedra during the Oxygen Evolution Reaction.

The activity of Ni (hydr)oxides for the electrochemical evolution of oxygen (OER), a key component of the overall water splitting reaction, is known to be greatly enhanced by the incorporation of Fe. However, a complete understanding of the role of cationic Fe species and the nature of the catalyst surface under reaction conditions remains unclear. Here, using a combination of electrochemical cell and conventional transmission electron microscopy, we show how the surface of NiO electrocatalysts, with initially well-defined surface facets, restructures under applied potential and forms an active NiFe layered double (oxy)hydroxide (NiFe-LDH) when Fe3+ ions are present in the electrolyte. Continued OER under these conditions, however, leads to the creation of additional FeOx aggregates. Electrochemically, the NiFe-LDH formation correlates with a lower onset potential toward the OER, whereas the formation of the FeOx aggregates is accompanied by a gradual decrease in the OER activity. Complementary insight into the catalyst near-surface composition, structure, and chemical state is further extracted using X-ray photoelectron spectroscopy, operando Raman spectroscopy, and operando X-ray absorption spectroscopy together with measurements of Fe uptake by the electrocatalysts using time-resolved inductively coupled plasma mass spectrometry. Notably, we identified that the catalytic deactivation under stationary conditions is linked to the degradation of in situ-created NiFe-LDH. These insights exemplify the complexity of the active state formation and show how its structural and morphological evolution under different applied potentials can be directly linked to the catalyst activation and degradation.

Highly active Mo-modified NiCoP/NiCoN flower-like sphere: Controlled phase engineering for efficient water splitting

Reasonable design and preparation of a versatile catalyst for the ultra-high efficiency energy conversion system has remarkable practical significance. Herein, a facile phase engineering strategy is employed to synthesize molybdenum modified nickel cobalt nitride and nickel cobalt phosphide flower-like sphere heterostructure (labeled as Mo-NiCoP/NiCoN FS) to improve the performance of Mo-NiCoN FS. The significant geometric structure advantages, the exposure to abundant active centers and the interfacial effect of heterostructure of the target product is evaluated in detail. When the as-obtained Mo-NiCoP/NiCoN FS is applied to the electrochemical bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), it demonstrates remarkable electrocatalytic activity, high-conductivity and excellent corrosion resistance compared with Mo-NiCoN FS with a single phase. As a result, Mo-NiCoP/NiCoN FS indicates a low overpotential towards HER (204 mV at 10 mA/cm2) and OER (262 mV at 10 mA/cm2) compared with Mo-NiCoN (234 mV for HER and 357 mV for OER at 10 mA/cm2) in an alkaline medium and it exhibits excellent activity and stability during the dual-electrode full water-splitting. Therefore, the advanced nano-catalyst with superior activity developed through the controllable phase engineering method illustrates a potential application prospect in high efficiency energy equipment water-splitting and fuel-cells.

Spin-State Modulation on Metal-Organic Frameworks for Electrocatalytic Oxygen Evolution.

Electrochemical oxygen evolution reaction (OER) kinetics are heavily correlated with hybridization of the transition metal d-orbital and oxygen intermediate p-orbital, which dictates the barriers of intermediate adsorption/desorption on the active sites of catalysts. Herein, a strategy is developed involving strain engineering and coordination regulation to enhance the hybridization of Ni 3d and O 2p orbitals, and the as-synthesized Ni-2,6-naphthalenedicarboxylic acid metal-organic framework (DD-Ni-NDA) nanosheets deliver a low OER overpotential of 260mV to reach 10mAcm-2 . By integrating an alkaline anion exchange membrane electrolyzer and Pt/C electrode, 200 and 500mAcm-2 current densities are reached with cell voltages of 1.6 and 2.1V, respectively. When loaded on a BiVO4 photoanode, the nanosheet enables highly active solar-driven water oxygen. Structural characterizations together with theoretical calculations reveal that the spin state of the centre Ni atoms is regulated by the tensile strain and unsaturated coordination defects in DD-Ni-NDA, and such spin regulation facilitates spin-dependent charge transfer of the OER. Molecular orbital hybridization analysis reveals the mechanism of OH* and OOH* adsorption energy regulation by changes in the DD-Ni-NDA spin state, which provides a deeper understanding of the electronic structure design of catalysts for the OER.

Trifunctional cobalt–molybdenum metal–organic framework for electrochemical oxygen evolution reaction and aromatic nitrosensing applications

Trifunctional cobalt–molybdenum metal–organic framework for electrochemical oxygen evolution reaction and aromatic nitrosensing applications

Chemically synthesized ZnFe2O4 electrodes for electrochemical oxygen evolution reaction and supercapacitor applications

Chemically synthesized ZnFe2O4 electrodes for electrochemical oxygen evolution reaction and supercapacitor applications

Lithium-Ion Battery Cathode-Electrolyte Interface

The global energy crisis, consumption of fossil fuels, and the associated environmental issues have stimulated extensive interest in searching for sustainable energy storage and conversion systems. Rechargeable lithium-ion batteries (LIBs) are widely used in mobile devices, hybrid, and electric vehicles. Electrode-electrolyte interface has a strong impact on battery capacity decrease and long-term cycling stability. In order to improve fundamental understanding of the involved phenomena to accelerate the rational design of cathode materials and stable interface, Li(Ni,Co,Mn)O2 (NCM) is a cathode material for rechargeable LIB and also a promising electrocatalyst for oxygen evolution reaction (OER). Their battery performance and catalytic activity are highly correlated to their structures. Multiple processes occurring at the cathode/electrolyte interface led to overall performance degradation. One failure mechanism is the dissolution of transition metals from the cathode. Our efforts employ thin film as a model cathode to monitor the Mn dissolution. Using LiMn2O4 and NCM as cathode materials, we will focus on electrochemical characterization, cation mixing, oxygen evolution, and thin film deposition with controlled crystal structures and composition. We will further introduce our work employing the scanning electrochemical microscope to study LIBs degradation and cathode-electrolyte interface in situ and in real-time.