Oxygen Evolution Reaction Properties Research Articles

Promoting Oxygen Evolution Electrocatalysis by Coordination Engineering in Cobalt Phosphate.

Understanding the structure-activity correlation is an important prerequisite for the rational design of high-efficiency electrocatalysts at the atomic level. However, the effect of coordination environment on electrocatalytic oxygen evolution reaction (OER) remains enigmatic. In this work, the regulation of proton transfer involved in water oxidation by coordination engineering based on Co3(PO4)2 and CoHPO4 is reported. The HPO4 2- anion has intermediate pKa value between Co(II)-H2O and Co(III)-H2O to be served as an appealing proton-coupled electron transfer (PCET) induction group. From theoretical calculations, the pH-dependent OER properties, deuterium kinetic isotope effects, operando electrochemical impedance spectroscopy (EIS) and Raman studies, the CoHPO4 catalyst beneficially reduces the energy barrier of proton hopping and modulates the formation energy of high-valent Co species, thereby enhancing OER activity. This work demonstrates a promising strategy that involves tuning the local coordination environment to optimize PCET steps and electrocatalytic activities for electrochemical applications. In addition, the designed system offers a motif to understand the structure-efficiency relationship from those amino-acid residue with proton buffer ability in natural photosynthesis.

Enhancing oxygen evolution reaction performance of Ruddlesden–Popper perovskite oxide through heteroatom incorporation

Prior studies have demonstrated that Ruddlesden–Popper (RP) type perovskite oxides exhibit promising electrocatalytic properties for oxygen evolution reaction (OER). However, the limited electrocatalytic activity has impeded their widespread utilization. The incorporation of heteroatoms into the Ruddlesden–Popper type structure has been identified as an effective strategy to enhance the electrocatalytic performance. This research presents the systematic design and synthesis of RP type perovskite oxide LaSrFeO4 (LSFO), followed by the optimization of electrocatalytic activity through Ni substitution at the Fe site of SLFO to create LaSrFe1-xNixO4 (LSFNO-x, x = 0.2, 0.4, and 0.5). Therein, the LSFNO-0.4 sample achieved a current density of 10 mA·cm−2 with an overpotential of only 340 mV. Additionally, it displayed exceptional stability over 120 h in a 1.0 M KOH solution. Both experimental and theoretical studies suggest that the addition of Ni cation increases the Fe − O covalency, and impacts the morphology and surface electron density of LSFO. This substitution results in a greater electrochemically active surface area, improved electron transfer, and optimization of hydrogen/water absorption free energy. This study presents a successful approach for enhancing the OER performance of Ruddlesden–Popper LSFO through the deliberate control of Fe − O covalent bonding.

Rich phosphorus vacancies N-doped C high-entropy metal phosphides for efficient electrocatalytic water oxidation

High-entropy materials have received increasing attention due to their unique physicochemical characteristics and remarkable properties for oxygen evolution reaction (OER). The synthesis of high-entropy metal phosphides (HEMPs) has rarely been reported owing to the incompatibility between different metal ions and phosphorus. Herein, the phosphorus vacancies (Pv) enriched N-doped C HEMPs (N-C@CoNiMnCuFeP/NF) for OER were prepared by a facile ZIF-derived phosphide method. Abundant Pv and amorphous structures increase the active sites and modulate the electronic structure of electrocatalyst to improve the OER performance. Besides, the synergistic effect among the metallic elements is beneficial for enhancing the electrocatalytic activity. Accordingly, HEMP-450 shows outstanding catalytic performance with the overpotential of 199 mV and continuously reacts for 140 hours without performance degradation for OER at 100 mA cm−2. This work demonstrates a simple template strategy for reasonably preparing HEMPs electrocatalyst with rich Pv.

Synergistic Effects in LaNiO3 Perovskites between Nickel and Iron Heterostructures for Improving Durability in Oxygen Evolution Reaction for AEMWE.

Perovskite materials that aren't stable during the oxygen evolution reaction (OER) are unsuitable for anion-exchange membrane water electrolyzers (AEMWE). But through manipulating their electronic structures, their performance can further increase. Among the first-row transition metals, nickel and iron are widely recognized as prominent electrocatalysts; thus, the researchers are looking into how combining them can improve the OER. Recent research has actively explored the design and study of heterostructures in this field, showcasing the dynamic exploration of innovative catalyst configurations. In this study, a heterostructure is used to manipulate the electronic structure of LaNiO3 (LNO) to improve both OER properties and durability. Through adsorbing iron onto the LNO (LNO@Fe) as γ iron oxyhydroxide (γ-FeOOH), the binding energy of nickel in the LNO exhibited negative shifts, inferring nickel movement toward the metallic state. Consequently, the electrochemical properties of LNO@Fe are further improved. LNO@Fe showed excellent performance (1.98Acm-2, 1m KOH, 50°C at 1.85V) with 84.1% cell efficiency in AEMWE single cells, demonstrating great improvement relative to LNO. The degradation for the 850h durability analysis of LNO@Fe is ≈68mVkh-1, which is ≈58 times less than that of LNO.

The reconstruction of equal-mole bimetal organic framework to heterostructure for effective oxygen evolution reaction

Oxygen evolution reaction (OER) is one of the most important issues for hydrogen production from water splitting. During the OER process, electrochemical reconstruction is widely observed for the majority of electrocatalysts, which is strongly related to the formation and evolution of real active species. Herein, bimetal metal-organic framework (MOF) with an equal ratio of Co and Fe sites is screened to exhibit the superior OER property. An obvious reconstruction is observed to transform single MOF phase into the heterostructure composed of active CoOOH and FeOOH. Meanwhile, the generation of Co3+ species is more reliant on the blessing of electricity and electrolyte than that of Fe3+ species. As a result, the optimal electrocatalyst shows the overpotential of 267 mV at 10 mA/cm2 and ultra-low Tafel slope of 24.7 mV/dec with a stable OER performance.

Nickel Sulfide Modified NiCu Nanoalloy with Excellent Oxygen Evolution Reaction Properties Prepared through Electrospinning and Heat Treatment

Nickel Sulfide Modified NiCu Nanoalloy with Excellent Oxygen Evolution Reaction Properties Prepared through Electrospinning and Heat Treatment

FeCo2S4@NiCo-LDH heterostructures as self-supported electrode for highly efficient overall water splitting

The development of highly stable and cost-effective catalysts to enhance hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an urgent issue nowadays. Herein, we present a bifunctional heterogeneous structure of electrocatalyst FeCo2S4@NiCo-LDH with good catalytic activity and high stability. By the use of the facile hydrothermal and electrodeposition methods, FeCo2S4@NiCo-LDH heterostructures are prepared on nickel foam, of which the corresponding experimental HER and OER overpotentials are 285, 135 mV at 50 mA cm−2, respectively. The results demonstrate that the HER and OER properties of FeCo2S4 and NiCo-LDH are synchronized and significantly improved, and there was an enhancement in the overall water splitting activity of the FeCo2S4@NiCo-LDH heterostructures.

Construction of mesoporous Ni-Co-Mo oxide/sulfide composite composite nanosheet arrays as bifunctional material for charge storage and oxygen evolution reaction applications

At present, energy conversion and energy storage devices are gradually integrated together, which puts forward higher requirements for the design and construction of electrode materials. Herein, bi-functional Co-Mo oxides and Ni/Co sulfides (NCMOS) composite nanosheet arrays on Ni foam are constructed for supercapacitors and oxygen evolution reaction (OER) of water splitting. The Ni-Co-Mo nanosheet precursor is firstly synthesized by stepwise hydrothermal processes and then converted into Ni-Co sulfide and Co-Mo oxide by in-situ sulfurization. The nanoarray and in-situ sulfurization of active materials bring more reactive active sites, optimize reaction kinetics, and shorten the transport path of electrons and charges, which enhance energy storage performance and OER catalytic activity of NCMOS material. In terms of supercapacitor applications, NCMOS exhibits high specific capacity (1332.1 C g–1) and good cycle stability. For OER application, NiCMOS shows lower OER overpotential (290 mV at 100 mA cm–2), smaller Tafel slope (87.2 mV dec–1) and excellent catalytic stability in oxygen evolution for 60 h. The excellent charge storage and OER properties suggest that bi-functional oxide/sulfide composites have great potential in energy conversion and storage-integrated devices.

Heterostructure of Fe-Doped CoMoOx/CoMoOx as an Efficient Electrocatalyst for Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) plays a crucial role as a counter half-reaction for both electrochemical hydrogen production through water splitting and the generation of valuable carbon compounds via CO2 reduction. To overcome the sluggish kinetics of the OER, significant efforts have been devoted to developing cost-effective, sustainable, and efficient electrocatalysts, with transition-metal-based catalysts emerging as promising candidates. Herein, we successfully synthesized a core-shell type nanostructure of Fe-doped CoMoOx/CoMoOx (CMFO), which exhibits excellent electrocatalytic properties for OER. The presence of an amorphous layer of Fe-doped CoMoOx with abundant oxygen vacancies, along with the stability of a key OER intermediate, *O, contributes to the enhanced activity of CMFO catalyst compared to pristine CoMoOx (CMO). The optimized catalyst of CMFO-550 achieved much lower overpotential and Tafel slope and also exhibited better remarkable long-term stability for over 90 h compared to CMO-550. These findings highlight the potential of CMFO-550 as a cost-effective and highly efficient electrocatalyst for the OER. The successful development of this core-shell nanostructure opens up a new opportunity for the design and synthesis of advanced electrocatalysts for the OER, with implications for various applications in energy conversion and storage.

In Situ Modulation of Oxygen Vacancies on 2D Metal Hydroxide Organic Frameworks for High-Efficiency Oxygen Evolution Reaction.

The discovery of non-precious catalysts for replacing the precious metal of ruthenium in the oxygen evolution reaction (OER) represents a key step in reducing the cost of green hydrogen production. The 2D d-MHOFs, a new 2D materials with controllable oxygen vacancies formed by controlling the degree of coordination bridging between metal hydroxyl oxide and BDC ligands are synthesized at room temperature, exhibit excellent OER properties with low overpotentials of 207 mV at 10mA cm-2 . High-resolution transmission electron microscopy images and density functional theory calculations demonstrate that the introduction of oxygen vacancy sites leads to a lattice distortion and charge redistribution in the catalysts, enhancing the OER activity of 2D d-MHOFs comprehensively. Synchrotron radiation and in situ Raman/Fourier transform infrared spectroscopy indicate that part of oxygen defect sites on the surface of 2D d-MHOFs are prone to transition to highly active metal hydroxyl oxides during the OER process. This work provides a mild strategy for scalable preparation of 2D d-MHOFs nanosheets with controllable oxygen defects, reveals the relationship between oxygen vacancies and OER performance, and offers a profound insight into the basic process of structural transformation in the OER process.

Efficient and Stable Dual-Active-Site of Core-Shell NiFe-Layered Double Hydroxide Anchored on FeMnON-N-Doped Carbon Nanotubes as Bifunctional Oxygen Electrocatalysts for Zn-Air Batteries

The bifunctional air electrodes with numerous dual-active sites and low cost are desirable to modify the performance of Zn-air batteries (ZABs). Metal–oxygen-nitrogen–carbon substrate (M = Mn, Fe, Ni, etc.) and NiFe-layered double hydroxide (NiFe-LDH) nanosheets are excellent catalysts in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes, respectively. Hereby, we investigate a bifunctional electrocatalytic substrate with a 3D core–shell hierarchical architecture by anchoring high OER-active NiFe-LDH on ORR-active FeMnZIF-8@gC3N4-derived FeMnON-N doped carbon nanotubes bamboo like (NiFe-LDH@FeMnON-NC). This nanocomposite has unique features such as robust synergistic effects, high conductivity, balance, and optimization of surface chemical valences of Fe, Mn, and Ni atoms to boost the bifunctional ORR and OER properties and stability in ZABs. The NiFe-LDH@FeMnON-NC nanocomposite not only exhibited superior OER electroactivity with a low onset overpotential of 235 mV (10 mA cm−2) but also had excellent ORR activity with a current density of −5.48 mA cm−2 and onset potential of 1.04 V, which is better than or comparable to those of commercial Pt/C and RuO2. Rechargeable ZABs constructed by bifunctional NiFe-LDH@FeMnON-NC have a peak power density (235.41 mW cm−2), open-circuit potential (OCV) (1.53 V), small discharge/charge band gap of 0.74 V and excellent discharge stability.

Anisotropic structural carbon skeleton decorated with Co nanoparticles towards oxygen evolution reaction

Hierarchical carbon skeletons derived from natural wood can be employed as the substrates to fabricate self-supported catalysts. The typically three sections (cross section, radial section, and tangential section) of wood would significantly affect the electrocatalytic performance. Therefore, the correlations between anisotropy structure of wood derived hierarchical carbon skeletons and oxygen evolution reaction (OER) performances was systematically investigated. The cross-sectional wood-derived carbon decorated with Co nanoparticles requires an overpotential of 370 mV to deliver 50 mA cm−2 superior to those of radial-sectional and tangential-sectional counterparts. The cross-section of wood derived carbon skeleton possesses higher content of Co nanoparticles, which is accounted for the enhanced OER catalytic activity. This work highlights the critical contribution of anisotropy of carbon skeletons in promoting the OER properties and provides a new paradigm for designing advanced electrocatalysts.

Insights on MOF-derived metal-carbon nanostructures for oxygen evolution.

Electrochemical water splitting has been regarded a promising method for the production of green hydrogen, addressing the need for efficient energy conversion and storage. However, it is severely hindered by the oxygen evolution reaction (OER) because of its multi-step four-electron transfer pathway with sluggish reaction kinetics. Microporous metal-organic-frameworks (MOFs), by virtue of large specific surface area, high porosity, tunable composition and morphology, find widespread use as precursors of metal-carbon nanostructures. The resulting carbon nanomaterials can well inherit the characteristics and advantages of the crystalline MOF precursors, and exhibit versatile application prospects in the fields of environment and energy, particularly in OER. Herein, a meticulous overview of the synthesis strategy for MOF-derived metal-carbon nanostructures and the origins of their enhanced OER properties has been demonstrated. We comprehensively illustrate these aspects across three dimensions: MOF selection, metal introduction, and carbon structures. Finally, the challenges and future prospects for this emerging field will be presented.

Activation of Commercial Stainless-Steel Electrodes for Highly Efficient and Stable Anion-Exchange Membrane Electrolysis

Commercial stainless steel (SS) is gaining interest as a promising electrode material to be widely used for green hydrogen production from alkaline water electrolysis. Herein, low-cost 304-type SS meshes (SM) were engineered through a simple 2-step activation process, i.e., chemical etching and electrochemical activation. The modified electrodes exhibited comparable hydrogen and oxygen evolution reaction properties with commercially, noble metal-based electrodes available. The modified stainless steel-based electrodes were assembled and tested in an AEM electrolyzer cell, which displays more than 300 mV-voltage drops compared to the bare stainless steel-based cells. The in-situ impedance spectroscopy revealed a significant decrease in the resistances due to interfacial contact, charge transfer, and mass transport. In addition, we identified nanocrystalline Fe-NiCr2O4 and nanocrystalline Ni(OH)2/Fe(OH)2 active species for SS used in hydrogen and oxygen evolution side respectively which could explain the significantly higher performance. In addition, we also developed an electrolyzer system to assess the long-term durability of our cell reactors in which our cells exhibited exceptional durability at 5.0 A (1.0 A cm-2) for 250 h. Our results exemplify that such an approach has the potential for upscaling and deployment in the next-generation, low-cost AEM electrolysis for green hydrogen production.

Enhance the water oxidation performance of electrodeposited Ni(OH)2 through structure modulation by glutamic acid

Ni(OH)2 has been extensively studied as a promising electrocatalyst for the oxygen evolution reaction (OER). However, enhancing its OER properties is still required and challenging. Here we reported that the OER activity of Ni(OH)2 can be improved with the structure modulation by glutamic acid (GA) through a simple co-electrodeposition process. The coordination effect of GA leads to the reduction of Ni2+ ions and enhances the generation of NiOOH sites during the activation process by cyclic voltammetry. The Ni(OH)2-GA anode shows remarkably enhanced OER activity than pristine Ni(OH)2 in alkaline media. Additionally, Fe-doping realizes further improvement in the OER activity of Ni(OH)2-GA, suggesting the possibility of achieving highly efficient electrocatalysts with cheap materials and an easy fabrication process.

Understanding the synergistic catalysis effect on the dual-metal-N4 embedding single-walled carbon nanotubes from first principles

Developing high-efficiency electrocatalysts for the oxygen evolution reaction (OER) remains a crucial bottleneck on the way to the water splitting for producing clean fuel (H2). Compared with single atom catalysis (SACs), dual-atom catalysts (DACs) have attracted great interest due to higher OER catalytic efficiency. In this work, the OER properties of dual-metal-N4 embedding armchair single-walled carbon nanotubes (D-MN4/CNTs) were systematic studied by density functional theory (DFT) simulations. Our results indicate that CoN4 embedding armchair CNTs exhibit higher OER activity than the corresponding planar structure, especially for CoN4 embedding in armchair CNT (4, 4) (CNT4). For MN4-CoN4 co-embedding CNTs, the TiN4-CoN4/CNTs have good OER synergistic effect with the lowest overpotential. Besides, the diameter of CNTs have a significant impact on the OER efficiency. The lowest reaction overpotential 0.47 V were obtained in TiN4-CoN4/CNT4 with a 5.69 Å tube diameter. Interestingly, compressive stress will further enhance the synergistic effect between two metal atoms in the OER reaction. The OER overpotential of CoN4-TiN4 embedding armchair CNT4 can reduce to 0.40 V under the −4 % uniaxial compression strain. These works were expected to better understand the synergistic mechanisms and design high-efficiency dual-atom OER electrocatalysts.

Electrochemical Investigations of Double Perovskite M2NiMnO6 (Where M = Eu, Gd, Tb) for High-Performance Oxygen Evolution Reaction

Double perovskites are known for their special structures which can be utilized as catalyst electrode materials for electrochemical water splitting to generate carbon-neutral hydrogen energy. In this work, we prepared lanthanide series metal-doped double perovskites at the M site such as M2NiMnO6 (where M = Eu, Gd, Tb) using the solid-state reaction method, and they were investigated for an oxygen evolution reaction (OER) study in an alkaline medium. It is revealed that the catalyst with a configuration of Tb2NiMnO6 has outstanding OER properties such as a low overpotential of 288 mV to achieve a current density of 10 mAcm−2, a lower Tafel slope of 38.76 mVdec−1, and a long cycling stability over 100 h of continuous operation. A-site doping causes an alteration in the oxidation or valence states of the NiMn cations, their porosity, and the oxygen vacancies. This is evidenced in terms of the Mn4+/Mn3+ ratio modifying electronic properties and the surface which facilitates the OER properties of the catalyst. This is discussed using electrochemical impedance spectroscopy (EIS) and electrochemical surface area (ECSA) of the catalysts. The proposed work is promising for the synthesis and utilization of future catalyst electrodes for high-performance electrochemical water splitting.

Investigating the role of 3D hierarchical Ni-CAT/NiFe-LDH/CNFs in enhancing the oxygen evolution reaction and Zn-air battery performance

NiFe layered double hydroxide (NiFe-LDH) is an efficient and widely available catalyst for the oxygen evolution reaction (OER), but further improvement of its OER property remains a challenge. Therefore, a conductive Ni-organic framework is triumphantly synthesized in-situ on NiFe-LDH/carbon nanofibers (Ni-CAT/NiFe-LDH/CNFs) through a hydrothermal treatment. This configuration utilizes the exposed surface area and the electron transfer pathways of Ni-CAT and CNFs, resulting in exceptional OER kinetics in alkaline conditions. A low overpotential of 370 mV at 10 mA cm−2 and a small Tafel slope of 79 mV dec−1 are achieved. The liquid-state Zn-air batteries, featuring Ni-CAT/NiFe-LDH/CNFs catalyst as an air cathode, indicate a significant peak power density of 292.1 mW cm−2 and an extended cycle durability of over 66 h. Solid-state Zn-air batteries demonstrate stable cycling at various flat/bent/flat states, showing great potential for flexible electronic device applications. According to experimental measurements and computational analysis, the in-situ growth of Ni-CAT on the NiFe-LDH matrix can optimize intermediate adsorption and alter hydrophilicity, resulting in improved performance of Zn-air batteries.

A novel sea urchin like nanostructure as a bifunctional catalyst for overall water splitting

The aim of this study is to construct a high-activity platinum-anchored WO3 electrocatalyst and investigate the effect of platinum content on the catalytic performance. This strategy compared the electrocatalytic performance under acidic conditions by discussing the platinum content and significantly enhances the electrocatalytic activity through nanoscale structure creation and electronic synergies. Therefore, anchoring Pt atoms on WO3 nanoarrays is very important for boosting the activity and stability of electrocatalysis via a hydrothermal co-precipitation approach, Ptx/WO3@NF (x = 0.1 mmol∼0.3 mmol) named as Pt1/WO3, Pt2/WO3 and Pt3/WO3, which enhanced hydrogen evolution reaction(HER) and oxygen evolution reaction (OER) activities. The prepared Pt2/WO3@NF microspheres showed excellent electrocatalytic activity. When the current density was 10 mA cm−2, the HER overpotential was 77 mV, the OER overpotential was 126 mV, and the two-electrode water decomposition voltage was 1.4418 V. The bifunctional catalyst shows excellent stability, with virtually no decay in the curves after 100 h stability tests. In addition, nanosheet surface has abundant defects and interface structure, which can maintain excellent conductivity of catalyst and expose more active sites clarify the increased H2 adsorption for HER activity enhancement. The synthesis of a bifunctional electrocatalyst with both HER and OER properties, presents a novel and intriguing concept that contributes to the advancement of green hydrogen development.

“Polyoxometalate electron sponge” induces the accurate regulation of electron states at Ni sites to enhance oxidation of water

Because of their special features, NiFe-LDHs (nickel iron layered double hydroxides) are prospective OER (oxygen evolution reaction) catalysts that might be utilized to catalyse the electrolysis of water and produce hydrogen to address the energy crisis. In this work, the electronic structure and electrocatalytic performance of the NiFe-LDH were accurately regulated by optimizing the Ni sites, which was enabled by adjacent metal sites coordinated with the “polyoxometalate electron sponge”. With extension of the modification time, the Ni 2p binding energy, the Ni3+/Ni2+ ratio and the OER properties were gradually tuned, which indicated accurate regulation of active Ni sites by the “polyoxometalate electron sponge” on a temporal scale. Additionally, NiFe-LDH-PW12-12 h (NiFe-LDH modified by polyoxometalate anions for 12 h) showed the highest OER performance along with fast electron transfer, superior reaction kinetics and electrochemical durability, with an overpotential ∼68 mV lower than that of NiFe-LDH. This work provides an accurate strategy for regulating the electronic structures of active metal sites for the OER.