Efficient Oxygen Evolution Electrocatalysts Research Articles

CoFe(OH)x-Co3O4/NF as highly efficient electrocatalyst for oxygen evolution and urea oxidation reactions at high current densities

The advancement of an affordable and highly effective catalyst for the oxygen evolution reaction (OER) is essential to enhance the performance of overall water splitting (OWS). Here, we report a highly efficient nickel foam (NF)-supported CoFe(OH)x-Co3O4/NF heterostructure catalyst for OER. The CoFe(OH)x-Co3O4/NF heterostructure catalyst contain amorphous phase CoFe(OH)x and crystalline Co3O4, and the synergistic interaction between the two different phases reduces the charge transfer resistance, accelerates the kinetic processes of electrocatalysis and makes the catalysts exhibit excellent catalytic performance. In 1.0 M KOH solution, an overpotential (η) of merely 262 mV is needed to attain a current density of 100 mA cm−2. Even at high current densities demanded for commercial applications, the overpotentials remain very low (η500 = 291 mV, η1000 = 319 mV). The catalytic activity of CoFe(OH)x-Co3O4/NF has exceeded that of most non-noble metal OER catalysts documented in the literature. Furthermore, the CoFe(OH)x-Co3O4/NF catalyst demonstrates superior catalytic stability to OER, with only a 23 mV potential increase after 24 h of stability testing at a high current density of 500 mA cm−2. Owing to the heterostructure, the CoFe(OH)x-Co3O4/NF catalyst also exhibits excellent catalytic performance for the urea oxidation reaction (UOR), and the use of UOR instead of OER at the anode of OWS significantly reduces the cell voltage, thereby reducing the electrolytic energy consumption. The findings in this work offer precious insights into the design of OWS anode catalysts and their important applications in industrial water electrolysis. These insights are crucial for advancing the development of highly efficient and sustainable water electrolysis processes, which is essential for the production of green hydrogen and other valuable chemicals.

Performance of Co9S8/Cu2S@LDH nanowires prepared by dual sulfur sources to promote oxygen evolution performance

Hydrogen production through water electrolysis is an effective method for obtaining clean energy. The oxygen evolution reaction plays a key role in the process of water electrolysis, and the development of efficient and stable oxygen evolution electrocatalysts is crucial to improve the efficiency of hydrogen production. This paper presents the preparation of Co9S8/Cu2S@LDH nanowire catalysts on copper foam using thiourea and sodium sulfide as dual sulfur sources by a hydrothermal method combined with electrochemical deposition. The composition, structure, and performance of the catalysts were investigated using characterization methods of XRD, SEM, Raman, and electrochemical analyses. Also, the mechanism of thiourea's role in the process of sulfurization of dual sulfur sources was also revealed. The results indicate that the introduction of thiourea facilitates the generation of the active center CoOOH and improves the catalytic efficiency of oxygen precipitation with a low overpotential of 199 mV at 10 mA/cm2 in 1.0 M KOH electrolyte. Additionally, the LDH deposited in the outer layer effectively prevents the oxidation of Co9S8/Cu2S and improves the catalyst's stability. Therefore, the prepared Co9S8/Cu2S@LDH nanowire catalyst exhibits high oxygen evolution reaction (OER) catalytic activity and stability in alkaline electrolyte, making it a promising OER catalyst.

Exploring Cu-Doped Co3O4 Bifunctional Oxygen Electrocatalysts for Aqueous Zn-Air Batteries.

The efficiency of oxygen electrocatalysis is a key factor in diverse energy domain applications, including the performance of metal-air batteries, such as aqueous Zinc (Zn)-air batteries. We demonstrate here that the doping of cobalt oxide with optimal amounts of copper (abbreviated as Cu-doped Co3O4) results in a stable and efficient bifunctional electrocatalyst for oxygen reduction (ORR) and evolution (OER) reactions in aqueous Zn-air batteries. At high Cu-doping concentrations (≥5%), phase segregation occurs with the simultaneous presence of Co3O4 and copper oxide (CuO). At Cu-doping concentrations ≤5%, the Cu ion resides in the octahedral (Oh) site of Co3O4, as revealed by X-ray diffraction (XRD)/Raman spectroscopy investigations and molecular dynamics (MD) calculations. The residence of Cu@Oh sites leads to an increased concentration of surface Co3+-ions (at catalytically active planes) and oxygen vacancies, which is beneficial for the OER. Temperature-dependent magnetization measurements reveal favorable d-orbital configuration (high eg occupancy ≈ 1) and a low → high spin-state transition of the Co3+-ions, which are beneficial for the ORR in the alkaline medium. The influence of Cu-doping on the ORR activity of Co3O4 is additionally accounted in DFT calculations via interactions between solvent water molecules and oxygen vacancies. The application of the bifunctional Cu-doped (≤5%) Co3O4 electrocatalyst resulted in an aqueous Zn-air battery with promising power density (=84 mW/cm2), stable cyclability (over 210 cycles), and low charge/discharge overpotential (=0.92 V).

Cobalt molybdenum di-selenide surface modification: A path to improved trifunctional catalysis via partial oxygenation

Efficient, stable, and cost-effective electrocatalysts for hydrogen evolution, oxygen evolution, and oxygen reduction reactions have been in demand for decades. Recently, layered transition metals (Co, Mo, Ni, and Fe) and chalcogen compounds (S/Se/Te) gained prominence in catalysis and device studies. Density functional theory identified the covalency of Co and Mo, oxygenated bimetallic selenium bond, crystal structure distortions, and adsorption properties as crucial for enhanced electrocatalytic activity. Hybridizing the Co and Mo d-orbitals around the Fermi level of 0.463 eV improves bonding with metal surface-adsorbate intermediates validated by partial density of states. Oxygenated cobalt molybdenum selenide (O-CoMoSe2) (210) exhibited remarkable electrocatalytic properties at various active sites, with Gibbs free energy and theoretical overpotential at an active site of Co = 0.086 eV, 0.41 V, and Se = 0.50 V.

NiCo2O4/MXene Hybrid as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reaction

AbstractFor the advancement of electrochemical energy conversion and storage technologies, bifunctional electrocatalysts are crucial for efficiently driving both the oxygen evolution (OER) and reduction reactions (ORR). Cobalt‐based spinel oxides are a class of promising bifunctional electrocatalysts. However their low electrical conductivity and stability may hinder further improvement. A novel composite material composed of NiCo2O4 nanoparticles integrated with emerging two dimensional MXene nanosheets (NiCo2O4/MXene) was developed. The successful integration of NiCo2O4 with MXene brings about a number of attractive structural features. This includes synergistic effects between NiCo2O4 and MXene, highly accessible surface areas, complete exposure of numerous active sites, and excellent electronic conductivity, all of which collectively contribute to the desirability of composite material for OER and ORR. The synthesized NiCo2O4/MXene composite showed extraordinary OER electrocatalytic activity with a lower overpotential of 360 mV at a current density of 10 mA/cm2, and a small Tafel slope of 64 mV/dec compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed). Additionally, NiCo2O4/MXene displays an ORR limiting current density of −4 mA/cm2 and exhibited highest onset potential and half wave potential of 0.92 V and 0.72 V vs. RHE, respectively, for the ORR in alkaline media compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed).

Regulating the Electronic Structure of Metal-Organic Frameworks by Introducing Mn for Enhanced Oxygen Evolution Activity.

The construction of low-cost and highly efficient oxygen evolution electrocatalysts is paramount for clean and sustainable hydrogen energy. In recent years, metal-organic framework (MOF) OER electrocatalysts have attracted tremendous research attention. Herein, we report a simple and facile strategy to construct bimetallic MOFs (named CoMn0.01) for enhancing OER catalytic performance. Significantly, CoMn0.01 exhibited remarkable OER activity (255 mV at 10 mA cm-2) and a low Tafel slope of 66 mV dec-1, superior to those of commercial benchmark electrocatalysts (RuO2, 352 mV, 178 mV dec-1). Besides, the catalyst demonstrated outstanding longevity for 144 h at a current density of 100 mA cm -2. Mn doping can regulate the electronic structure of Co MOFs, which optimizes charge transfer capability and improves conductivity.

Modulating positive charge sites generations and iron oxidation state transitions in FeP4/CoP/C p-n heterojunction toward efficient oxygen evolution

Promoting the formation of positive charge active sites and high oxidation state FeOOH in the heterojunction electrocatalyst can enhance its intrinsic activity for oxygen evolution reaction (OER). However, the current synthesis methods that can simultaneously achieve both properties remain a great challenge. In this work, a feasible strategy for concurrently promoting the generation of positive charge active sites and high oxidation state metal species by constructing a heterojunction between FeP4 and CoP is proposed. Specifically, the p-n heterojunction between FeP4 and CoP is constructed by pyrolysis of MIL88A@FeCoLDH prepared by introducing Co through cation exchange using MIL88A as a template. The experimental and density functional theory calculation analyses suggest the construction of p-n heterojunction can effectively modulate the electron structure, optimize the d-band center, induce the generation of strong space charge region, and shorten the bond length of Fe-O, thus promoting the formation of positive charge active sites and high active species FeOOH and the adsorption ability of oxygen-containing intermediates for enhancing the OER performance. Benefiting from the synergistic effect between positive charge active sites and FeOOH, the obtained FeP4/CoP/C electrocatalyst exhibits a low overpotential of 258 mV for the OER at a current density of 10 mA cm−2 and superior stability at 20 mA cm−2 for 52 h. This work gives insights into the charge regulation effect in the heterojunction for enhancing the OER catalytic activity and provides a general strategy for designing more efficient oxygen evolution electrocatalysts.

Ce doped Ni(OH)2/Ni-MOF nanosheets as an efficient oxygen evolution and urea oxidation reactions electrocatalyst

Metal-organic frameworks (MOFs) are widely recognized as precursors or sacrificial templates for the synthesis of target catalysts on account of their high porosity and high active surface area. Elemental doping strategy is considered as an effective method for the synthesis of efficient and stable catalysts for electrolytic water. Therefore, in this paper, Ce-doped Ni(OH)2 nanoparticles and Ni-MOF nanosheets composites were synthesized by electrodeposition using Ni-MOF as precursor. Catalyst Ce–Ni(OH)2@Ni-MOF/NF displays excellent OER performance, requiring only 193 mV and 279 mV overpotentials to realize current densities of 10 mA cm−2 and 100 mA cm−2, respectively, while the UOR performance was very remarkable, only a potential of 1.28 V was demanded to reach a current density of 10 mA cm−2. In addition, no obvious change in the overpotential was noticed during the stability test of 16 h, indicating good stability of Ce–Ni(OH)2@Ni-MOF/NF. This study provides a meaningful reference for the design of an efficient and stable environmental friendly electrocatalyst.

Optimizing Edge Active Sites via Intrinsic In-Plane Iridium Deficiency in Layered Iridium Oxides for Oxygen Evolution Electrocatalysis.

Improving catalytic activity of surface iridium sites without compromising catalytic stability is the core task of designing more efficient electrocatalysts for oxygen evolution reaction (OER) in acid. This work presents phase transition of a bulk layered iridate Na2IrO3 in acid solution at room temperature, and subsequent exfoliation to produce 2D iridium oxide nanosheets with around 4nm thickness. The nanosheets consist of OH-terminated, honeycomb-type layers of edge-sharing IrO6 octahedral framework with intrinsic in-plane iridium deficiency. The nanosheet material is among the most active Ir-based catalysts reported for acidic OER and gives an iridium mass activity improvement up to a factor of 16.5 over rutile IrO2 nanoparticles. The material also exhibits good catalytic and structural stability and retains the catalytic activity for more than 1300 h. The combined experimental and theoretical results demonstrate that edge Ir sites of the layer are active centers for OER, with structural hydroxyl groups participating in the catalytic cycle of OER via a non-traditional adsorbate evolution mechanism. The existence of intrinsic in-plane iridium deficiency is the key to building a unique local environment of edge active sites that have optimal surface oxygen adsorption properties and thereby high catalytic activity.

A Self-Supporting Electrode Material (NiS/NF) as a Stable and Efficient Electrocatalyst for Oxygen Evolution: In Situ Surface Activation of Nickel Sulfide to Nickel Oxide/(Oxy)hydroxide

A Self-Supporting Electrode Material (NiS/NF) as a Stable and Efficient Electrocatalyst for Oxygen Evolution: <i>In Situ</i> Surface Activation of Nickel Sulfide to Nickel Oxide/(Oxy)hydroxide

Biological upcycling of nickel and sulfate as electrocatalyst from electroplating wastewater

Upcycling nickel (Ni) to useful catalyst is an appealing route to realize low-carbon treatment of electroplating wastewater and simultaneously recovering Ni resource, but has been restricted by the needs for costly membranes or consumption of large amount of chemicals in the existing upcycling processes. Herein, a biological upcycling route for synchronous recovery of Ni and sulfate as electrocatalysts, with certain amount of ferric salt (Fe3+) added to tune the product composition, is proposed. Efficient biosynthesis of bio-NiFeS nanoparticles from electroplating wastewater was achieved by harnessing the sulfate reduction and metal detoxification ability of Desulfovibrio vulgaris. The optimal bio-NiFeS, after further annealing at 300 °C, served as an efficient oxygen evolution electrocatalyst, achieving a current density of 10 mA·cm−1 at an overpotential of 247 mV and a Tafel slope of 60.2 mV·dec−1. It exhibited comparable electrocatalytic activity with the chemically-synthesized counterparts and outperformed the commercial RuO2. The feasibility of the biological upcycling approach for treating real Ni-containing electroplating wastewater was also demonstrated, achieving 99.5 % Ni2+removal and 41.0 % SO42− removal and enabling low-cost fabrication of electrocatalyst. Our work paves a new path for sustainable treatment of Ni-containing wastewater and may inspire technology innovations in recycling/ removal of various metal ions.

A highly efficient and long-term durable electrocatalyst for oxygen evolution in alkaline seawater by growing Ni1.5Fe1.5B on the NiMoO4 nanorods

The development of efficient and stable catalysts for the oxygen evolution reaction (OER) that can function effectively in seawater is crucial for addressing the energy crisis. In this study, a low-cost hydrothermal-dip-coating method was employed to synthesize Ni1.5Fe1.5B nanosheets decorated three-dimensional NiMoO4 nanorods anchored on nickel foam (NiMoO4@Ni1.5Fe1.5B). This catalyst exhibits high conductivity and electrochemically active surface areas, which can be attributed to the synergistic effect between NiMoO4 and Ni1.5Fe1.5B, the presence of numerous oxygen vacancies, and the modification of boron. The NiMoO4@Ni1.5Fe1.5B catalyst exhibits exceptional catalytic activity for the oxygen evolution reaction (OER), as evidenced by overpotentials of 235 and 262 mV required to achieve current densities of 100 and 200 mA cm−2, respectively, in 1 M KOH. Notably, the leaching of Mo during the OER in alkaline conditions contributes to the preservation of the 3D core-shell structure of NiMoO4@Ni1.5Fe1.5B, resulting in improved stability and resistance to chloride-induced corrosion. In seawater with a concentration of 1 M KOH, the catalyst requires overpotentials of 261 and 299 mV to achieve current densities of 100 and 200 mA cm−2, respectively, and can operate continuously for 72 h without significant performance degradation.

Interfacial electronic structure modulation enables PdAg/NiOx an advanced oxygen evolution electrocatalyst

Hydrogen production by electrolysis of water is one of the solutions to energy problems and environmental pollution. The design of efficient oxygen evolution electrocatalyst remains a challenging. One way to improve catalytic performance is to change the morphology and structure of the catalyst. Herein, a two-dimensional (2D) flake nano-flower heterostructured catalyst was designed on nickel foam (NF) substrate by simple hydrothermal and thermal annealing reactions. Benefiting from the porous nanosheet structure and synergistic effect between PdAg and NiOx, which facilitates electrolyte transport, the PdAg/NiOx nanosheets deliver a low overpotential (253 mV @ 10 mA cm−2) for oxygen evolution reaction (OER) and has excellent stability. In addition, the addition of PdAg alloy regulates the electronic structure of the active component Ni, which also makes for further improving the electrocatalytic OER performance. This work not only offers a promising strategy of in situ anchoring PdAg alloy on NiOx nanosheet but also provide a new way for the application of alloy heterogeneous interfaces to high performance OER catalysts.

Interconnected nickel cobalt vanadate quasi-spheres as an efficient and stable oxygen evolution electrocatalyst in alkaline media

The present work reports the one-step hydrothermal fabrication of carbon fiber paper (CFP) supported interconnected nickel cobalt vanadate (Ni3-xCoxV2O8) microparticles. The CFP substrate was selected for its conductive support and strong adhesion to materials, thereby improving durability. Crystal structure analysis confirmed the successful incorporation of Co into the Ni3V2O8 lattice, resulting in a single orthorhombic phase of Ni3-xCoxV2O8 without altering the crystal structure. Compositional tuning was achieved by varying Ni/Co molar feeding ratios to optimize electrocatalytic oxygen evolution reaction (OER) performance in 1 M KOH. The compositionally tuned interconnected NiCo2V2O8 microspheres exhibited improved OER activity compared to its individual counterparts and other compositions. It exhibited a low OER overpotential of ∼ 351 mV to reach a current density of 50 mA cm−2 and good long-term stability for 20 h, without any performance decay. These results suggest that the NiCo2V2O8 could serve as a cost-effective alternative to valuable electrocatalysts for the alkaline OER.

Motivating Inert Strontium Manganate with Iridium Dopants as Efficient Electrocatalysts for Oxygen Evolution in Acidic Electrolyte.

The search for high-performance and low-cost electrocatalysts in acid conditions still remains a challenging target. Herein, iridium (Ir) doped strontium manganate (named as Irx -SMO) is proposed as an efficient and durable low-iridium electrocatalyst for water oxidation in acidic media. The Ir0.1 -SMO with 75% less iridium in comparison to that of iridium dioxide (IrO2 ) exhibits excellent performance for oxygen evolution reaction (OER), which is even better than most of the iridium-based oxide electrocatalysts. The theoretical outcomes confirm the activation of the inert manganese sites in strontium manganate by the incorporation of iridium dopants. This work reveals the boosted effect of the iridium dopants on the OER activity of strontium manganate, providing a strategy to tune the activity of manganese-based perovskites in electrocatalysis.

In situ construction of S-doped NiFe-layered double hydroxide nanoarrays on porous reduced graphene oxide as efficient oxygen evolution electrocatalysts for electrolytic cells

The application of NiFe-layered double hydroxide (NiFe-LDH) as electrocatalysts for oxygen evolution reaction (OER) is seriously limited owing to low conductivity, insufficient active sites and self-aggregation. The construction of anion-doped NiFe-LDH nanoarray structures with ideal electrochemical activity is an effective strategy. Herein, we report a facile solvothermal approach for the synthesis of S-doped NiFe-LDH nanosheets loaded in situ on porous reduced graphene oxide (rGO) to form a composite with nanosheet array structure (S-NiFe-LDH/rGO) for OER. The S-NiFe-LDH/rGO nanosheet array ensures a large specific surface area, abundant accessible active sites and high stability. The moderate S doping in NiFe-LDH can tune the local electronic structures of Ni and Fe to optimize the binding of metal sites with reaction intermediates, thus enhancing the OER activity. The S-NiFe-LDH/rGO electrocatalyst shows the small OER overpotential of 264 mV at 10 mA cm−2 and the low Tafel slope of 55 mV dec−1. Moreover, S-NiFe-LDH/rGO displays good durability and structural stability due to the strong anchoring effect. The assembled two-electrode S-NiFe-LDH/rGO||Pt electrolytic cell exhibits a low cell voltage of 1.53 V at 10 mA cm−2, which is superior to the RuO2||Pt benchmark cell (1.60 V), indicating the practical feasibility for water electrolysis. This design strategy provides a promising insight into the fabrication of advanced OER non-noble metal electrocatalysts.

Controllable construction of NiFe MOF/LDH heterojunction with interfacial charge transfer as efficient oxygen evolution electrocatalyst

Herein, a facile partial hydrolysis strategy has been developed to construct NiFe MOF/LDH heterojunction using NiFe MOF as the precursor. While preserving the basic structure of MOF, LDH species along with electroactive phase interfaces were in-situ generated in NiFe MOF/LDH. The obtained catalyst exhibited an ultralow overpotential of 207 mV to reach the current density of 10 mA cm−2 and performed excellent stability towards OER. Both experimental and theoretical investigations demonstrated that the strong interfacial charge transfer in NiFe MOF/LDH heterojunction could improve the conductivity and optimize the adsorption of O-intermediates, thus enhancing the OER kinetics. This study may provide a novel platform to construct heterojunction materials with interfacial charge transfer for electrocatalytic applications.

Cobalt (Oxy)hydroxide Nanosheets Supported on Nickel Foam as Efficient Electrocatalysts for Oxygen Evolution

Cobalt (Oxy)hydroxide Nanosheets Supported on Nickel Foam as Efficient Electrocatalysts for Oxygen Evolution

Nano-NiFe LDH assembled on CNTs by electrostatic action as an efficient and durable electrocatalyst for oxygen evolution

The development of non noble metal electrocatalysts with high OER catalytic activity has become an urgent demand for water cracking. In this work, NiFe LDH nanobulks grown on CNTs were prepared by a green and simple one pot hydrothermal method. The acidified CNTs usually include hydroxyl, carboxyl and other oxygen-containing functional groups, which make the carbon tubes have a certain negative charge. The negatively charged CNTs can interact with the positively charged NiFe LDH nanobulks in an electrostatic manner, resulting in a self-assembly reaction to slow down the agglomeration of NiFe LDH nanobulks, better highlight the advantages of two-dimensional material structure, and expose greater specific surface area of activity. The introduction of CNTs can enhance the conductivity of the composite, accelerate the charge transfer in the reaction process, and further improve the OER catalytic performance of NiFe LDH/CNTs catalyst materials.

Three-dimensional carbon network-supported black phosphorus-cobalt heterojunctions: An efficient electrocatalyst for high-rate oxygen evolution

Black phosphorus (BP), as a burgeoning two-dimensional material, has shown good electrocatalytic activity due to its unique electronic structure and abundant active sites.However, the presence of lone pair electrons in black phosphorus leads to its poor stability and rapid degradation in an oxygen/water environment, which greatly limits its practical application. Herein, BP-Co heterojunctions were synthesized on carbon nanotube@nitrogen-doped carbon (BP-Co/CNT@NC) by the pyrolysis of ZnCo-zeolitic imidazolate frameworks and subsequent solvothermal treatment. The BP-Co Schottky junction improved the electrocatalytic stability of BP, modulated its electronic structure, improved its conductivity and electron transfer during the electrocatalytic reaction. Density functional theory calculation was used to confirm the electron transfer and redistribution at the interface between BP and Co, which constructed an oppositely charged region and formed a strong built-in field. Energy band configuration analysis revealed a narrowed band gap because of the formation of BP-Co Schottky junction. Consequently, the optimized BP-Co/CNT@NC exhibited a superior oxygen evolution reaction (OER) performance, a low overpotential of 370 mV@100 mA/cm2, with a small Tafel slope of 40 mV/dec and good long-term stability. Particularly, the catalyst has an excellent OER performance at the high current density of 100–400 mA/cm2. This strategy improves the stability of BP electrocatalysts and strengthens their utilization in electrocatalytic applications.