Electrocatalyst For Water Oxidation Research Articles

Ultrathin cobalt phosphate enfolded with biomass-derived multishelled carbon onion as a proficient electrocatalyst for the oxygen evolution reaction and its green sustainability assessments

A new member of the carbon family, carbon onion, is formed by flame pyrolysis. Graphitic hands of carbon onion were shakes with cobalt phosphate by mechanochemically, makes potential electrocatalyst for water oxidation.

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.

Efficient and stable Fe3O4@SiO2 core–shell nanospheres for electrochemical water oxidation under neutral conditions

Fe3O4@SiO2 core–shell nanospheres were exploited for the first time to obtain a vigorous electrocatalyst for water oxidation under neutral conditions.

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.

Copper(II) defect-cubane water oxidation electrocatalysts: from molecular tetramers to oxidic nanostructures.

We report on the synthesis and spectroscopic evidence for a sequence of structural transformations of a new defect-cubane type copper complex, [Cu4(pyalk)4(OAc)4](ClO4)(HNEt3), which acts as a pre-catalyst for water oxidation. In situ and post-catalytic studies showed that the tetrameric complex undergoes a structural transformation into dimeric and monomeric species, induced by water molecules and carbonate anions, respectively. Further, the observed electrocatalytic water oxidation activity has been confirmed to arise from in situ-generated Cu(II) oxidic nanostructures at the electrode interface.

Bimetal Leaching Induced Reconstruction of Water Oxidation Electrocatalyst for Enhanced Activity and Stability

Bimetal Leaching Induced Reconstruction of Water Oxidation Electrocatalyst for Enhanced Activity and Stability

A Cobalt(III)−Hydroxo Complex Bearing a Pentadentate Amidate Ligand as an Electrocatalyst for Water Oxidation

AbstractA Co(III)−hydroxo complex, [CoIII(dpaq)OH]ClO4 (1‐OH) bearing a pentadentate ligand, H‐dpaq, (H‐dpaq=(2‐[bis(pyridin‐2‐ylmethyl)]amino‐N‐quinolin‐8‐yl‐acetamidate]) catalyses water oxidation in mildly alkaline medium (pH 8.0) at a potential of 1.4 VNHE with an average Turn‐Over‐Frequency (TOFmax) of 2.8×104 s−1 and faradaic efficiency of 88 %. Post‐electrolysis characterization of the electrode rules out the formation of any heterogeneous electroactive species. Electrochemical results and theoretical calculations confirm the occurrence of both metal and ligand centered PCET processes during anodic scanning. The resulting formally Co(V)−oxo/oxyl intermediate undergoes water nucleophilic attack to install the O−O bond. The role of axial ligand in water oxidation by Co(III)−dpaq system has been examined by comparing the reactivity of the Co‐hydroxide complex (1‐OH) with that of its chloride‐ligated counterpart, [CoIII(dpaq)Cl]Cl (1‐Cl). The results confirm the ability of the Co‐dpaq complexes to bind water/or water derived ligands over chloride or non‐aqueous solvents. The interplay of ligand redox non‐innocence and σ‐donating ability of the N5‐carboxamido ligand helps to store oxidizing equivalents and triggers O−O bond formation.

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.

Pillared-MOF@NiV-LDH Composite as a Remarkable Electrocatalyst for Water Oxidation.

Oxygen evolution reaction (OER) represents a highly important electrochemical transformation in energy storage and conversion technologies. Considering the low rate of this four-electron half-reaction, there is a demand for efficient, stable, and noble-metal-free electrocatalysts to improve the kinetic and economical parameters. In this work, a new pillared-MOF@NiV-LDH nanocomposite based on a CoII metal-organic framework (pillared-MOF) and heterometallic Ni/V-layered double hydroxide (NiV-LDH) was assembled via a simple protocol, characterized, and explored as an electrocatalyst in OER. A remarkable electrocatalytic efficiency of pillared-MOF@NiV-LDH in 1 M KOH is evidenced by a low overpotential (238 mV at 10 mA cm-2 current density) and a small value of the Tafel slope (62 mV dec-1). These parameters are very close to those of the reference IrO2 electrocatalyst and are superior to the majority of the LDH- and MOF-based systems previously applied for OER. Excellent stability of pillared-MOF@NiV-LDH was confirmed by the chronopotentiometry tests for 70 h and linear-sweep voltammetry after 7000 cycles. Features such as rich electroactive sites, porous structure, high surface area, and synergic effect between pillared-MOF and NiV-LDH are likely responsible for the remarkable electrocatalytic efficiency of this electrocatalyst in OER. Despite prior reports on the application of NiV-LDH in OER, the present study describes the first example where this type of LDH is blended with MOF to generate a nanocomposite material. The interface between the two components of the composite can improve the electronic structure and, in turn, the electrocatalytic behavior. The introduction of this composite paves the way toward the synthesis of other multicomponent materials with potential applications in different energy fields.

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.

Low-temperature synthesized amorphous quasi-high-entropy carbonate electrocatalyst with superior surface self-optimization for efficient water oxidation

Anionic High-entropy materials have seldom been reported as a new library of water oxidation electrocatalysts owing to great difficulty in uniformly distributing multiple elements with different physicochemical properties and harsh synthesis conditions. Herein, a series of amorphous quasi-high-entropy carbonates for the first time is prepared via a facile low-temperature hydrothermal route. The optimized CoCrFeMnMoCO3 with hydrothermal treatment of 6 h can serve as a promising oxygen evolution reaction (OER) electrocatalyst for water splitting on account of amorphous structure rendering more exposed active sites, superior synergistic effect realizing surface component self-optimization, high-valence ferritic species (Fe(3+δ)+) providing high catalytic activity and high-entropy stabilization guaranteeing long-term OER performance, thus exhibiting the low overpotentials of 302 and 355 mV at the current densities of 10 and 100 mA cm−2, respectively, the small Tafel slope of 36.7 mV dec−1, and excellent durability longer than 38 h, dramatically exceeding its corresponding crystalline counterpart and benchmark RuO2 catalyst, as well as yielding the current density of 10 mA cm−2 with impressive low voltage of 1.56 V while used as bifunctional electrocatalyst for overall water splitting. This study lights a broad avenue to design other anionic high-entropy materials as promising OER catalysts.

Construction of NiS@CoFeMoO4/NF nanosheet heterostructures for efficient overall water splitting

Inexpensive and robust earth-abundant electrocatalysts with excellent electrocatalytic reaction kinetics must be developed to realize electrochemical water-splitting. In this study, nickel sulfide@cobalt iron-molybdenum oxide (NiS@CoFeMoO4) nanosheet heterostructures supported on nickel foam were fabricated. The as-built NiS@CoFeMoO4/NF with a sheet-on-sheet morphology delivered a current density of 10 mA cm−2 with a low overpotential of 72 and 200 mV for the hydrogen evolution and oxygen evolution reactions, respectively. The formation of a synergistic heterostructure between NiS and CoFeMoO4/NF via interfacial engineering facilitated the generation of a micro-mesoporous surface and modulation of the charge density at interfaces. Consequently, this configuration outperformed many non-precious-metal-based catalysts as an electrocatalyst for water oxidation.

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.

Freestanding Cactus-Like Dual-Phase Bimetallic Metal–Organic Framework as a High-Efficiency Electrocatalyst for Water Oxidation

Realizing a high-efficiency electrochemical oxygen evolution reaction (OER) is a great challenge in water splitting and metal–air battery fields due to the slow reaction kinetics. Herein, a synchronous dual-phase synthetic strategy is developed to successfully construct a cactus-like dual-phase bimetallic metal–organic framework (MOF) on a nickel foam (NF) substrate (noted as NiFe-MOF@NF). It is constituted by Ni-main NiFe-MOF and Fe-main NiFe-MOF. When functioning as an anode, the freestanding cactus-like dual-phase NiFe-MOF@NF catalyst merely requires a lower overpotential of 277 mV to supply 100 mA cm–2 with robust stability (90% retainment of initial current density after 24 h chronoamperometry measurement). Density functional theory calculations on the NiFe-MOF@NF catalyst reveal that the combination of Ni and Fe has efficiently modulated the electron configuration of metal centers and optimized the absorption/desorption of OER oxygen-containing intermediates. Thus, we demonstrate a novel synchronous dual-phase synthetic strategy to engineer freestanding dual-phase electrocatalysts, which feature multiple synergetic effects considerably boosting OER performance for optimizing the energy conversion and storage system.

Fabrication of the novel NiFe-LDHs @γ-MnOOH nanorod electrocatalyst for effective water oxidation

The development of highly efficient electrocatalysts for water splitting is great critical for the massive production of hydrogen energy. In this work, a kind of novel NiFe-LDHs@γ-MnOOH nanorod electrocatalyst was fabricated via the two-step method. Firstly, γ-MnOOH nanorods were grown in situ on the nickel foam conductive substrate by a simple hydrothermal method. Then, NiFe-LDHs were combined on the γ-MnOOH/NF surface by electrochemical deposition to prepare the NiFe-LDHs@γ-MnOOH/NF core-shell structure catalyst. Due to good charge transfer capability, high exposure of active sites as well as the interfacial interaction between NiFe-LDHs and γ-MnOOH, the obtained core-shell structure catalyst exhibited excellent oxygen evolution reaction (OER) activity in alkaline media. The overpotential of 226 mV at the current density of 10 mA cm−2 for OER could be achieved with a low Tafel slope of 88 mV dec- 1, and almost no current density loss occurred after the 24 h i-t stability testing. Furthermore, this catalyst also possessed good performance in overall water splitting, which could afford a current density of 10 mA cm−2 by 1.69 V cell voltage.

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

Porous dehydroxyl cobalt phytate as electrocatalyst for high-efficiency water oxidation

Phytic acid (PA) is a six-fold dihydrogenphosphate ester of inositol with cost-effective, environmentally friendly, and safe properties. Here, we successfully synthesize the dehydroxyl cobalt phytate (PA-Co-400) using PA as phosphorus sources by a one-pot wet-chemistry strategy to prepare the precursor PA-Co and then heat treatment at 400 °C under an N2 atmosphere for dehydroxylation. The average diameter, specific surface area, surface element distribution, and catalytic activity of the catalyst are significantly affected by dehydroxylation temperature. The specific surface area increasesfirstandthendecreases with the treatment temperature from 200 °C to 600 °C. The SEM results indicate that the average diameter of PA-Co-400 particle is 68.90 nm. The as-prepared samples are used as an anode catalyst for electrocatalytic oxygen evolution reaction (OER). The PA-Co-400 exhibits splendid OER performances with an overpotential of 310.31 mV at j10 (η50 = 349.35 mV, η100 = 367.20 mV), which are even comparable to commercial RuO2 (η10 = 310.54 mV, η50 = 389.80 mV, η100 = 450.60 mV). Moreover, the PA-Co-400 has a small Tafel slope of 53.27 mV dec−1, which is lower than commercial RuO2 (81.71 mV dec−1). The ultra-long durability of PA-Co-400 was tested for over 80 h at current densities of 10 mA cm−2 without a significant reduction in 1 M KOH.

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.

Dual-functional fullerene supported NiO-based nanocomposite: Efficient electrocatalyst for OER and photocatalyst for MB dye degradation

Developing effective and noble-metal-free electrocatalysts for the grim oxygen evolution reaction (OER) and photocatalysts for pollutant elimination is critical for long-term energy supply and environmental remediation. Herein a simple sol-gel technique is used to synthesize NiO/C60 electrophotocatalyst and is characterized via different state-of-art techniques. All the characteristic analytical studies have discovered that the structural components dramatically increased the OER and photocatalytic activity for grown NiO/C60 nanocomposite. TEM results showed that the C60 uniformly covering NiO has a particle size of 46 nm. NiO/C60 electrocatalyst has outperformed the overpotential of 310 mV at a current density of 10 mA/cm2. At the applied voltage, electrochemical impedance spectroscopy showed that the catalytically active surfaces of NiO/C60 and charge transfer rate are much greater than simple NiO. It was also discovered that the grown nanocomposite remained stable for 30 h without degrading, outlasting numerous recent noble-metal-free electrocatalysts. In addition, the NiO/C60 has also exhibited excellent photocatalytic reduction efficiency for Methylene blue (MB) dye and completely degraded after 40 min under sunlight with the stability of up to six cycles. Our findings show that NiO-based water oxidation electrocatalysts and efficient photocatalysts may now be produced at a low cost with outstanding performance.

(Invited) Water Splitting and Carbon Dioxide Conversion By Mixed-Anion Materials

Mixed-anion materials that consist more than one anionic species in a single-phase have attracted attention for various applications. Oxynitrides containing d0- or d10-metal cations are typical example of visible-light-driven photocatalysts for water splitting and CO2conversion. In this presentation, recent progress on the development of mixed-anion materials for water splitting and CO2 conversion made by our group will be given. While two-dimensional (2D) undoped layered oxynitrides are potential candidates as high performance visible-light photocatalysts, synthesis of 2D layered oxynitrides is generally difficult because most of them are metastable phases and are not chemically very stable. We found an exceptional example of a 2D layered oxynitride, K2LaTa2O6N (more specifically, K2LaTa2O6N·1.6H2O), which is a Ruddlesden-Popper phase two-layer perovskite analogous to Li2LaTa2O6N and has a band gap of 2.5 eV. This material undergoes in situH+/K+ exchange in aqueous solution while keeping its visible light absorption capability. The protonated, Ir-modified K2LaTa2O6N exhibited photocatalytic activity for H2 evolution from aqueous NaI solution under visible light, outperforming Pt/ZrO2/TaON and Pt/SrTiO3:Rh, which are one of the best-performing oxynitride and oxide photocatalysts for H2 evolution, respectively. The use of mixed-anion materials is of interest not only for photocatalysts but also for catalysts promoting water oxidation and CO2reduction. For example, we found that certain oxyfluorides work as electrocatalysts for water oxidation. A 2D perovskite oxyfluoride Pb3Fe2O5F2 exhibits activity for electrochemical water oxidation to O2, which is 8 times more active than a 3D bulk PbFeO2F.