Efficient Electrocatalyst For Water Oxidation Research Articles

Constructing an efficient electrocatalyst for water oxidation: an Fe-doped CoO/Co catalyst enabled by in situ MOF growth and a solvent-free strategy.

The development of non-precious metal electrocatalysts with high activity for the oxygen evolution reaction (OER) is a crucial and challenging task. In this work, we proposed a solvent-free in situ metal-organic framework (MOF) growth strategy for the fabrication of an Fe-doped CoO/Co electrocatalyst. This approach not only partially granted the MOF's porous structure to the catalyst but also resulted in a tighter combination between the Co metal and CoO, thereby enhancing its electrical conductivity. Furthermore, this method enabled the Fe species to be more uniformly dispersed on CoO/Co, which significantly exposed more active sites for efficient electrocatalysis. The entire synthesis process was solvent-free, except for a small amount of water and ethanol used during catalyst washing. The as-synthesized Fe-CoO/Co electrocatalyst exhibited superior OER activity on a glass carbon electrode, with η = 276 mV at a current density of 10 mA cm-2, even higher than that of the commercial precious IrO2/C catalyst. Additionally, it was also extended to prepare a Ni-doped CoO/Co electrocatalyst by the same procedure with satisfactory OER performance. This work presents a new preparation approach for MOF-derived catalysts with potential applications in energy conversion and beyond.

A transparent iron-incorporated nickel hydroxide electrocatalyst for efficient water oxidation

Transparent electrocatalysts were developed by a facile solution-based method. The highly transparent iron-incorporated nickel hydroxide (FeNi-10) oxygen evolution electrode exhibited low overpotential compared to the benchmark electrocatalyst.

Holistic functional biomimetics: a key to make an efficient electrocatalyst for water oxidation

The performance of a water-oxidation electrocatalyst is determined by the synergistic effect of an active site structure, e− transfer system, and H+ transport system. The holistic functional biomimetic is a promising design strategy.

CeO2/CuO/NiO hybrid nanostructures loaded on N-doped reduced graphene oxide nanosheets as an efficient electrocatalyst for water oxidation and non-enzymatic glucose detection.

In this work, the three-component heterostructure of CeO2/CuO/NiO was synthesized by a co-precipitation procedure and heating at a temperature of 750 °C. Then, CeO2/CuO/NiO nanoparticles were successfully supported on N-doped reduced graphene oxide (N-rGO) by a hydrothermal method. The obtained nanomaterials were used as effective electrocatalysts for the oxygen evolution reaction and glucose sensing in an alkaline medium. The results indicated that when CeO2/CuO/NiO is anchored on N-rGO nanosheets, active catalytic sites increase. On the other hand, N-doped rGO enhances electrical conductivity and electron transfer for water or glucose oxidation. CeO2/CuO/NiO@N-rGO has a large electrochemically active surface area and more active catalytic positions, and thus exhibits high activity for the OER with a low overpotential of 290 mV, a suitable Tafel slope of 110 mV dec-1, and superior stability and durability for at least 10 hours. CeO2/CuO/NiO@N-rGO can also detect glucose with a high sensitivity of 912.7 μA mM-1 cm-2, a low detection limit of 0.053 μM, a wide linear range between 0.001 and 24 mM, and a short response time of about 2.9 s. Moreover, the high selectivity and stability of this electrode for glucose sensing show its potential for clinical applications.

MoO2/Ni0.2Mo0.8N nanorods on nickel foam as a high performance electrocatalyst for efficient water oxidation

MoO2/Ni0.2Mo0.8N nanorods on nickel foam delivered a low overpotential of 264 mV at 10 mA cm−2 in alkaline electrolyte for oxygen evolution reaction due to the synergistic effect as a result of interfacial engineering between MoO2 and Ni0.2Mo0.8N.

An amorphous FeCoNiMnCr high-entropy alloy supported by 2H-MoS2 on carbon cloth as a highly efficient and robust electrocatalyst for water oxidation

Novel electrocatalysts with amorphous FeCoNiMnCr HEA supported by 2H-MoS2 on carbon cloth (FeCoNiMnCr@MoS2-CC) have been designed for OER electrocatalysis. Due to the synergistic effects of FeCoNiMnCr and 2H-MoS2, the FeCoNiMnCr@MoS2-CC electrocatalysts show significantly enhanced electrocatalytic performance for the OER and good stability.

α-MnO2/FeCo-LDH on Nickel Foam as an Efficient Electrocatalyst for Water Oxidation.

The ever-expanding human societies on the one hand and the diminishing fossil fuel resources on the other have driven man to find a suitable, cheap, clean, and accessible source of energy. Water splitting is a good solution to this crisis. Because of the slow kinetics of water oxidation reaction, it is important to select efficient and durable electrocatalysts to improve the reaction kinetics. In this research, α-MnO2/FeCo-LDH catalysts on nickel foam were developed for water oxidation, which exhibited good catalytic performance and stability in a 0.1 M KOH solution. The electrocatalysts were synthesized by hydrothermal methods and characterized by XRD, FTIR, Raman, SEM, TEM, EDS, and MAP techniques. The proposed modified electrode has large exchange current, low overpotential, and small Tafel slope. Here, only an overpotential of 210 mV is required to achieve a current density of 5 mA cm2 with a Tafel slope of 70.4 mV dec-1 in an alkaline solution.

CoOx Supported on α‐MoC for Efficient Electrocatalytic Oxygen Evolution Reaction

AbstractIt is particularly significant to apply stable and low‐cost catalysts in electrochemical water oxidation. It has been reported that molybdenum carbides have exceptional water dissociation ability in thermal catalysis. However, its role in electrocatalytic water oxidation, in which water dissociation is the key initial step, has not yet been paid attention to. Herein, cobalt oxide (CoOx) nanoparticles, by an incipient‐wetness impregnation method, were successfully supported on the surface of nitrogen‐doped porous carbon homogeneously distributed ultrafine α‐MoC nanoparticles with nitrogen‐doped porous carbon (α‐MoC/NC) and worked as efficient electrocatalysts for water oxidation. By regulating the loading amounts of cobalt oxide and the calcination temperature, a series of mesoporous CoOx@α‐MoC/NC composites were obtained. The optimal electrocatalyst exhibited low oxygen evolution overpotential (10 mA cm−2, 410 mV) and an excellent anodic stability. Experimental results implied that the synergistic effect between cobalt oxide and α‐MoC/NC can facilitate water oxidation, with the latter having the ability to dissociate water molecules.

Ultra-low palladium engineered nickel sulfide heterostructure supported on 3D nickel foam as a highly efficient and stable electrocatalyst for water oxidation

• 0.1PdNiS/NF requires only 275 mV overpotential to achieve a current density of 10 mAcm -2 , which is less than NiS/NF (385 mV) and commercial RuO 2 /NF (370 mV). • The Tafel slope of 0.1PdNiS/NF (65 mVdec -1 ) is lower than NiS/NF (132 mVdec -1 ) and commercial RuO 2 /NF. • 0.1PdNiS/NF demonstrated exceptional durability for approximately 14 hours at 10 mAcm -2 . • TOF of 0.1PdNiS was calculated to be 1.31 s -1 at an overpotential of 320 mV, which is greater than the NiS/NF (0.5 s -1 ). Electrochemical water splitting (EWS) has been a crucial process in the production of green fuels (oxygen and hydrogen) for a sustainable energy economy. One of the key processes in the EWS is water oxidation or the oxygen evolution reaction (OER). It is highly desirable to create cost-effective, efficient, and robust electrocatalysts for OER. Here, we present ultra-low Pd doped NiS-NiS 2 heterostructure on NF (0.1PdNiS/NF) grown in-situ by acid etching followed by a simple hydrothermal sulfurization method for excellent OER electrocatalytic activity in alkaline media. Interestingly, low overpotential of 275 mV is required for the 0.1PdNiS/NF to achieve a current density of 10 mAcm -2 , which is less than both NiS/NF (385 mV) and commercial RuO 2 /NF (370 mV). Because of the strong electronic interaction between Pd and NiS, 0.1PdNiS/NF has a small Tafel slope of 65 mV/dec and has shown excellent durability for approximately 14h. Therefore, the findings described above provide significant insights in the design of high-performance OER catalysts with ultra-low precious metal loading.

Atmospheric-Water-Induced Reversible Structural Transformation of a Two-Dimensional Ni(II)-Based Ferromagnetic MOF: A Highly Efficient Water Oxidation Electrocatalyst and Colorimetric Water Sensor

Atmospheric-Water-Induced Reversible Structural Transformation of a Two-Dimensional Ni(II)-Based Ferromagnetic MOF: A Highly Efficient Water Oxidation Electrocatalyst and Colorimetric Water Sensor

Controlled Electrophoretic Deposition Strategy of Binder-Free CoFe2O4 Nanoparticles as an Enhanced Electrocatalyst for the Oxygen Evolution Reaction.

The kinetic-sluggish oxygen evolution reaction (OER) is the main obstacle in electrocatalytic water splitting for sustainable production of hydrogen energy. Efficient water electrolysis can be ensured by lowering the overpotential of the OER by developing highly active catalysts. In this study, a controlled electrophoretic deposition strategy was used to develop a binder-free spinel oxide nanoparticle-coated Ni foam as an efficient electrocatalyst for water oxidation. Oxygen evolution was successfully promoted using the CoFe2O4 catalyst, and it was optimized by modulating the electrophoretic parameters. When optimized, CoFe2O4 nanoparticles presented more active catalytic sites, superior charge transfer, increased ion diffusion, and favorable reaction kinetics, which led to a small overpotential of 287 mV for a current density of 10 mA cm-2, with a small Tafel slope of 43 mV dec-1. Moreover, the CoFe2O4 nanoparticle electrode exhibited considerable long-term stability over 100 h without detectable activity loss. The results demonstrate promising potential for large-scale water splitting using Earth-abundant oxide materials via a simple and cheap fabrication process.

Binder-Free Fabrication of Prussian Blue Analogues Based Electrocatalyst for Enhanced Electrocatalytic Water Oxidation.

Developing a cost-effective, efficient, and stable oxygen evolution reaction (OER) catalyst is of great importance for sustainable energy conversion and storage. In this study, we report a facile one-step fabrication of cationic surfactant-assisted Prussian blue analogues (PBAs) Mx[Fe(CN)5CH3C6H4NH2]∙yC19H34NBr abbreviated as SF[Fe-Tol-M] (where SF = N-tridecyl-3-methylpyridinium bromide and M = Mn, Co and Ni) as efficient heterogeneous OER electrocatalysts. The electrocatalysts have been characterized by Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS). In the presence of cationic surfactant (SF), PBAs-based electrodes showed enhanced redox current, high surface area and robust stability compared to the recently reported PBAs. SF[Fe-Tol-Co] hybrid catalyst shows superior electrochemical OER activity with a much lower over-potential (610 mV) to attain the current density of 10 mA cm−2 with the Tafel slope value of 103 mV·dec−1 than that for SF[Fe-Tol-Ni] and SF[Fe-Tol-Mn]. Moreover, the electrochemical impedance spectroscopy (EIS) unveiled that SF[Fe-Tol-Co] exhibits smaller charge transfer resistance, which results in a faster kinetics towards OER. Furthermore, SF[Fe-Tol-Co] offered excellent stability for continues oxygen production over extended reaction time. This work provides a surface assisted facile electrode fabrication approach for developing binder-free OER electrocatalysts for efficient water oxidation.

Porous CoNiOOH nanosheets derived from the well-mixed MOFs as stable and highly efficient electrocatalysts for water oxidation

The development of efficient and stable electrocatalysts is of great significance for improving water splitting. Among them, transition metal oxyhydroxides show excellent performance in oxygen evolution reactions (OER), but there are certain difficulties in direct preparation. Recently, Metal–organic frameworks (MOFs) as precatalysts or precursors have shown promising catalytic performance in OER and can be decomposed under alkaline conditions. Therefore, using a mild and controllable way to convert MOFs into oxyhydroxides and retaining the original structural advantages is crucial for improving the catalytic activity. Herein, a rapid electrochemical strategy is used to activate well-mixed MOFs to prepare Co/Ni oxyhydroxide nanosheets for efficient OER catalysts, and the structural transformation in this process was investigated in detail by using scanning electron microscope, X-ray diffraction, Raman, X-ray photoelectron spectroscopy and electrochemical methods. It is discovered that electrochemical activation can promote ligand substitution of well-mixed MOFs to form porous oxyhydroxide nanosheets and tune the electronic structure of the metal (Co and Ni), which can lead to more active site exposure and accelerate charge transfer. In addition, the change of structure also improves hydrophilicity, as well as benefiting from the strong synergistic effect between multiple species, the optimal a-MCoNi–MOF/NF has excellent OER performance and long-term stability. More obviously, the porous CoNiOOH nanosheets are formed in situ during electrochemical activation process through structural transformation and acts as the active centers. This work provides new insights for mild synthesis of MOFs derivatives and also provides ideas for the preparation of highly efficient catalysts.

Anodic deposition of highly efficient nickel iron oxide electrocatalysts for water oxidation and role of anions in catalyst deposition

Nickel iron oxide has acquired significant interest as a highly efficient electrocatalyst for the oxygen evolution reaction. Although anodic deposition is beneficial for its preparation, anodically deposited nickel iron oxide presents poor performance, and the detailed mechanism of its formation is ambiguous, limiting its extensive applications. In this study, we examined the anodic deposition of nickel iron oxide using electroanalytical techniques combined with an electrochemical quartz crystal microbalance. In particular, the effects of anions were investigated to determine whether the formation of a nickel iron oxide film sensitively depends on the counter anions of the metal precursors. The anions not only provide buffering to retain the solution pH but also play a significant role in scavenging the surface protons to facilitate the growth of the catalyst film. We established a modified protocol to anodically deposit nickel iron oxide electrocatalysts excellent for water oxidation, with the best ever reported performance. These findings presented important but previously neglected aspects of anodic deposition, providing implications for nonprecious metal electrocatalysts.

High-nuclearity cobalt(II)-containing polyoxometalate anchored on nickel foam as electrocatalyst for electrochemical water oxidation studies

Polyoxometalates (POMs) are known for their unique structural properties and have attracted widespread attention in the field of storage devices, energy conversion materials, catalysis, electronics and molecular sensing. This article focuses on the anchoring of high nuclearity 16-cobalt(II)-containing POM that is, Na30.5K1.5[{Co4(OH)3PO4}4(A-α-GeW9O34)4]٠116H2O (Co16-GeW9) using 3-aminopropyl triethoxysilane (APTS) as chemical linker over nickel foam (NiF) and is tested as electrocatalyst for water oxidation studies. The fabricated POM-based electrode (Co16-GeW9@NiF) has been characterized by UV–visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. Co16-GeW9 @NiF has been tested for its electrocatalytic water oxidation activity in 1 M KOH (pH 14) and sodium phosphate buffer (pH 7) with NaNO3 as a supporting electrolyte. The catalyst exhibited excellent electrocatalytic oxygen evolution reaction (OER) activity with overpotential of 370 mV at 10 mA/cm2 and a Tafel slope of 84 mV/dec in 1 M KOH, while overpotential of 530 mV at 10 mA/cm2 and a Tafel slope of 153 mV/dec in sodium phosphate buffer. The immobilization of POM over NiF could generate a way for developing efficient electrocatalysts for water oxidation in both neutral and basic pH.

Enhanced OER performance of NiFeB amorphous alloys by surface self-reconstruction

The design and development of cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalysts are urgently desirable during the water-splitting process. Here, NixFe80-xB20 (x = 70, 60, 50, 40, 30, hereafter referred to as NFB) amorphous alloys, with high mechanical strength, excellent corrosion resistance, and unique atomic structure, are fabricated as efficient water oxidation electrocatalysts in alkaline solutions. Ni40Fe40B20 amorphous ribbons achieve only 319 mV of overpotential at 10 mA·cm−2 with a Tafel slope of 56 mV dec−1 and exhibit excellent long-term stability for 24 h at 10 mA·cm−2 and 100 mA·cm−2 in 1 M KOH solution, which outperform the commercial RuO2 electrocatalyst. It is worth noting that the OER performance of NixFe80-xB20 amorphous electrocatalysts after long-term chronopotentiometry test displays more effectively, which can be ascribed to the surface construction. Meanwhile, the analysis of the morphology and structure of the electrocatalysts reveal that continuous oxidation during the OER process induces the structural reorganization on the surface of the electrocatalysts, which can enhance the electron transfer process and adsorption of the reaction intermediates to optimize the OER performance. This study provides a shred of evidence for surface self-reconstruction of NiFeB amorphous alloys electrocatalysts during the OER process and promotes the application of amorphous alloys as functional materials in the water-splitting field.

Regulating multiscale structures of nickel-iron-based electrocatalysts for efficient water oxidation

The oxygen evolution reaction (OER) has been widely studied as an efficient process in energy conversion, yet the majority of studies focus on the strategies to boost the intrinsic activity of the catalyst, rather than considering the enhancement of its mass transfer ability. Herein, we produce efficient NiFe-based OER electrocatalysts with rich oxygen vacancies and abundant transport channels by an argon plasma-engraving strategy. Compared with pristine NiFe, the obtained best NiFe-plasma catalyst yields a 12.5-fold increased current density (from 80 to ∼1,000 mA cm −2 ) at an overpotential of 300 mV, surpassing most OER catalysts in alkaline solution. Density functional theory calculations disclose that the introduction of oxygen vacancies improve the intrinsic activity and electronic conductivity, while finite element method calculations demonstrate that the construction of catalytic interface and the creation of nanoscale transport channels facilitates mass transfer. • Plasma simultaneously produces oxygen vacancies and slit pores on NiFe • FEM calculation illustrates that the slit pores can facilitate mass transport • The obtained NiFe-plasma catalyst yields a 12.5-fold increased current density Wang et al. prepare efficient NiFe-based OER electrocatalysts with abundant oxygen vacancies and transport channels by plasma engraving. Owing to the synergistic effect between high intrinsic catalytic activity and preferable mass transfer ability, the NiFe-P-200-15 exhibits a small overpotential of 302 mV to reach 1.0 A cm −2 in alkaline electrolyte.

One step synthesis of Co-Ni bimetallic organic frameworks as a highly active and durable electrocatalyst for efficient water oxidation

As a half-reaction in the water decomposition, the oxygen evolution reaction (OER) has limited the development and practical application of water splitting due to the kinetic speed and high overpotential. Therefore, it still exists a challenge to exploit high-performance and durable electrocatalysts for OER. Herein, a one-step hydrothermal approach was designed to prepare Co-Ni bimetallic organic frameworks (MOFs) on nickel foam (NF) substrate as a highly efficient electrocatalyst for OER under alkaline conditions. The prepared MIL-53(Co-Ni)/NF has excellent OER catalytic activity, which requires only an overpotential of 197 mV to achieve 20 mA cm−2. The proposed electrocatalyst exhibits long-term durability (>60 h) and a high turnover frequency (TOF) of 0.2806 mol O2 s−1 at 350 mV. Systematic study revealed that the coordination between Co-Ni played a significant role to improve OER performance. The present results demonstrated that bimetallic organic frameworks could be utilized to fabricate promising water-oxidation catalysts in energy conversion.

Oxygen vacancy-rich amorphous FeNi hydroxide nanoclusters as an efficient electrocatalyst for water oxidation

In this work, a one-pot strategy is presented to directly synthesize amorphous FexNiy hydroxide nanoclusters (denoted as ANC-FexNiy, <2 nm) with oxygen vacancies induced by ionic liquids. The ANC-FexNiy catalyst presents abundant catalytic sites and high intrinsic conductivity. As such, the optimized ANC-Fe1Ni2 exhibits high activity in oxygen evolution reaction (OER) with a Tafel slope of 39 mV dec–1 and an overpotential of 266 mV at 10 mA cm−2. Notably, the optimized ANC-Fe1Ni2 shows an extraordinarily large mass activity of 3028 A gFeNi–1 at the overpotential of 300 mV, which is ∼24-fold of commercial RuO2 catalyst. The superior activity of these FexNiy hydroxide nanoclusters is ascribed to (i) the amorphous and distorted structure with abundant oxygen vacancies, and (ii) enhanced active site density by downsizing the ANC-FexNiy clusters. This strategy provides a novel route for enhancing OER electrocatalytic performance and highly encouraging for the future application of amorphous metal hydroxides in catalysis.

Cobalt Formate, a Functional MOF: Electrocatalytic Water Oxidation

Cobalt formate dihydrate, Co(HCOO)[Formula: see text]H2O (Co-MOF), a known crystalline substance, is a three-dimensional coordination polymer. The compound crystallizes in a monoclinic space group [Formula: see text]. In this work, we are reporting a unique synthesis method to prepare this MOF without using any formate salt or formic acid. The source of formate in compound Co-MOF is dimethylformamide (DMF) solvent used in the relevant synthesis. This metal–organic framework (MOF) containing compound, which can be described as a functional MOF, has recently been exploited for hydrogen isotope separation. This functional material has never been used as an electrocatalyst. In this work, we have demonstrated that this water insoluble compound Co-MOF can be used as heterogeneous electrocatalyst for oxygen evolution reaction (OER) by water oxidation at neutral pH. An overpotential of 275.5[Formula: see text]mV versus RHE was required to attain a current density of 1[Formula: see text]mAcm[Formula: see text]. The relevant Faradic efficiency (89.93%) and the turn over frequency (TOF) of 0.277[Formula: see text]s[Formula: see text] make the material an efficient electrocatalyst for water oxidation to molecular oxygen at neutral pH.