Stable Electrocatalysts For Oxygen Evolution Reaction Research Articles

Hierarchically hollow interconnected rings of nickel substituted cobalt carbonate hydroxide hydrate as promising oxygen evolution electrocatalyst

The present work highlights fabrication of nanostructured nickel-substituted cobalt carbonate hydroxide hydrates (NCCHH) through one-step reflux method. It is noted that optimized 30 mol% nickel-substituted cobalt carbonate hydroxide hydrate (NCCHH-30) nanostructures show quite high specific surface area (∼229.55 m2 g−1) owing to the formation of hierarchically hollow interconnected ring-type morphology facilitating the electrode-electrolyte interfacial interaction. As a result, NCCHH-30 showed significant amplification in electrocatalytic oxygen evolution reaction (OER) activity with ultralow overpotential (∼141 mV @ 10 mA cm−2), Tafel slope (∼49 mV dec−1), and excellent durability (12 h and 2000 cycles) in 1.0 M KOH. Notably, to the best of our knowledge, interconnected NCCHH-30 hierarchical hollow rings exhibited the best overpotential (η100 ∼198 mV) value reported for cobalt-based electrocatalysts in alkaline OER. In addition, this material exhibited exceptionally high oxygen evolution performance in comparison to the state-of-the-art commercial RuO2 electrocatalyst in 1.0 M KOH. Such interconnected hierarchically hollow nickel (30 mol%)-substituted cobalt carbonate hydroxide hydrate nanostructured rings could act as an ultraefficient, cost-effective, and stable electrocatalyst for OER in alkaline medium.

Laser Processed Magnetite Nanoparticles Embedded on rGO Composites for Efficient Electrocatalytic Oxygen Evolution Reaction

AbstractThe oxygen evolution reaction (OER) plays a key role in the ongoing global search for effective and clean energy sources. Tremendous efforts have been devoted to finding high‐performance electrocatalysts consisting of nonprecious metals. The search is spent, not only on the designing of new materials, but also on the invention of new fabrication techniques. Recently, laser processing has emerged as a promising route to obtain micron‐thick films of highly graphitic carbons. The laser approach enables a fast one‐step synthesis of highly‐dispersed nanoparticles under ambient temperature and pressure conditions. In this work, a laser is used to fabricate magnetite/reduced graphene oxide (rGO) composite electrodes as electrocatalysts. The graphitization level can be controlled by tuning different laser parameters. The detailed chemical, structural and morphology characterization, and electrochemical measurements are investigated. With only five atomic percentage metal, the designed magnetite‐rGO electrocatalyst lowers the overpotential by 40 mV at 10 mA cm−2 with a smaller Tafel value (63 mV dec−1). Moreover, these studies demonstrate that magnetite‐rGO nanocomposites are stable OER electrocatalysts with only 13.5% activity reduction after 10 h of chronoamperometric operation. This work combines an efficient nanocomposites fabrication method with important implications for energy‐related applications.

Selenium-doped copper oxide nanoarrays: Robust electrocatalyst for the oxygen evolution reaction with ultralow overpotential

The oxygen evolution reaction (OER) is the key anodic reaction in electrochemical water splitting. OER is a four-electron process with sluggish reaction kinetics. RuO2 and IrO2 are the benchmark catalysts for OER. Thus, finding a low-cost, earth-abundant, and stable electrocatalyst for OER is a big challenge. In this work, we report OER over Se-CuO/CF nanoarrays with an ultralow overpotential of 440 mV (at 50 mA/cm2 current density). Se-CuO/CF nanoarray has a TOF of 0.05 s−1 at 300 mV. The catalyst showed consistent OER performance upto1000 cycles run over a period of 10 h. The OER performance of Se-CuO/CF nanoarrays was compared with RuO2/CF catalyst and the overpotential for RuO2/CF nanoarray was only 10 mV lower than Se-CuO/CF 50 mA/cm2 current density. Se-CuO/CF nanoarray showed 50 mV lower overpotential than the state of the art RuO2/CF catalyst at a current density of 100 mA/cm2. The Tafel slope of Se-CuO/CF is 21 mV/decade lower compared to RuO2/CF suggesting faster reaction kinetics of Se-CuO/CF. The electrochemical surface area and the conductivity were increased upon doping Se into CuO/CF nanoarrays which can be attributed to enhanced OER performance of the Se-CuO/CF nanoarrays.

Polar Layered Intermetallic LaCo2P2 as a Water Oxidation Electrocatalyst.

We investigate LaCo2P2 as an electrocatalytic material for oxygen evolution reaction (OER) under alkaline and acidic conditions. This layered intermetallic material was prepared via Sn-flux high-temperature annealing. The electrocatalytic ink, prepared with the ball-milled LaCo2P2 catalyst at the mass loading of 0.25 mg/cm2, shows OER activity at pH = 14, reaching current densities of 10, 50, and 100 mA/cm2 under the overpotential of 400, 440, and 460 mV, respectively. Remarkably, the electrocatalytic performance remains constant for at least 4 days. Transmission electron microscopy reveals the formation of a catalytically active CoOx shell around the pre-catalyst LaCo2P2 core during the alkaline OER. The core serves as a robust support for the in situ-formed electrocatalytic system. Similar studies under pH = 0 reveal the rapid deterioration of LaCo2P2, with the formation of LaPO4 and amorphous cobalt oxide. This study shows the viability of layered intermetallics as stable OER electrocatalysts, although further developments are required to improve the electrocatalytic performance and increase the stability at lower pH values.

A nanoflower composite catalyst in situ grown on conductive iron foam: Revealing the enhancement of OER activity by cooperating of amorphous Ni based nanosheets with spinel NiFe2O4

As a bottleneck step in electrochemical water splitting, oxygen evolution reaction (OER) seriously limits the development of large-scale electrochemical hydrogen production. Rational design and development of an efficient and stable OER electrocatalysts are of enormous importance but still challenging for electrochemical energy conversion. In this work, a unique nanoflower like electrocatalyst consisting of NiFe2O4 nanoparticles wrapped with amorphous Ni based nanosheet on the 3D porous iron foam (IF) substrate (named as Ni-ANS@NiFe2O4/IF) is proposed and the evolution of catalyst morphology and its effect on electrochemical activity were explored. Profiting from the unique nanoflower structure and the coupling of ample active substances with favorable conductive substrates, the prepared Ni-ANS@NiFe2O4/IF exhibits outstanding OER activity with low overpotential of 209, 251, 270 mV to reach a current density of 10, 100 and 200 mA cm−2, and admirable long-term stability. This work may broaden a new vision and avenue for the design of efficient OER catalysts.

Exceptionally active and stable RuO2 with interstitial carbon for water oxidation in acid

<h2>Summary</h2> Oxygen evolution reaction (OER) plays a critical role in energy conversion technologies. Significant progress has been made in alkaline conditions. In contrast, it remains a challenge to develop stable OER electrocatalysts in acidic conditions. Herein, we report a new strategy to stabilize RuO₂ by introducing interstitial carbon (C-RuO₂-RuSe), where the optimized C-RuO₂-RuSe-5 exhibits a low overpotential of 212, 259, and 294 mV to reach a current density of 10, 50, and 100 mA cm⁻², respectively. More importantly, C-RuO₂-RuSe-10 has long-term stability of up to 50 h, representing one of the most stable OER electrocatalysts. X-ray absorption spectroscopy reveals that the Ru–O bonds have been elongated due to the formation of interstitial C. Theoretical calculations show that the elongated Ru–O bonds in RuO₂ enhance its stability and reduce energy barriers for OER. This work provides a new perspective for designing and constructing efficient Ru-based electrocatalysts for water splitting.

Electronic Interaction between In Situ Formed RuO2 Clusters and a Nanoporous Zn3V3O8 Support and Its Use in the Oxygen Evolution Reaction.

The catalytic activity and durability of RuO2 clusters toward the oxygen evolution reaction (OER) are strongly associated with their support; however, how the electronic interaction would enhance the catalytic performance is still not quite clear. Herein, hierarchical nanoporous and single-crystal Zn3V3O8 nanosheets are adopted to anchor in situ formed RuO2 clusters. X-ray photoelectron analysis reveals significant binding energy changes of both Ru and V due to the creation of strong Ru-O-V bonding interaction, which would lead to the reconstruction of the electronic structure of the Zn3V3O8 matrix and RuO2 clusters. The ultrastrong electronic interaction also results in superior OER activity, indicated by a small overpotential at 10 mA cm-2 (228 mV) and a shallow Tafel slope of 46 mV dec-1. First-principles simulation further reveals the synergistic effect derived from the unique RuO2@Zn3V3O8 couple, which effectively regulates the electronic structure for the OER process. In addition, the created interfacial chemical bond and the confined microporous structure of the Zn3V3O8 substrate could prevent the RuO2 clusters from detachment and aggregation, making the nanocomposite a promising long-term stable OER electrocatalyst.

Dense Crystalline–Amorphous Interfacial Sites for Enhanced Electrocatalytic Oxygen Evolution

AbstractThe crystalline‐amorphous (c–a) heterostructure is verified as a promising design for oxygen evolution reaction (OER) catalysts due to the concerted advantages of the crystalline and amorphous phase. However, most heterostructures via asynchronous heterophase synthesis suffer from the limited synergistic effect because of the sparse c–a interfaces. Here, a highly efficient and stable OER electrocatalyst with dense c–a interfacial sites is reported by hybridizing crystalline Ag and amorphous NiCoMo oxides (NCMO) on the nickel foam (NF) via synchronous dual‐phase synthetic strategy. In 1 m KOH, the as‐obtained Ag/NCMO/NF catalyst exhibits a low OER overpotential of 243 mV to attain 10 mA cm−2 and a small Tafel slope of 67 mV dec−1. Theoretical calculations indicate that the c–a interface can efficiently modulate the electronic structure of the interfacial sites and lower the OER overpotential. Besides, in situ Raman spectroscopy results demonstrate that the c–a interfacial sites can promote the irreversible phase transition to the metal oxy(hydroxide) active phase, and the dense c–a interfaces can stabilize the active phase during the whole OER process.

Atomic Cation-Vacancy Engineering of NiFe-Layered Double Hydroxides for Improved Activity and Stability towards the Oxygen Evolution Reaction.

NiFe-layered double hydroxides (NiFe-LDH) are among the most active catalysts developed to date for the oxygen evolution reaction (OER) in alkaline media, though their long-term OER stability remains unsatisfactory. Herein, we reveal that the stability degradation of NiFe-LDH catalysts during alkaline OER results from a decreased number of active sites and undesirable phase segregation to form NiOOH and FeOOH, with metal dissolution underpinning both of these deactivation mechanisms. Further, we demonstrate that the introduction of cation-vacancies in the basal plane of NiFe LDH is an effective approach for achieving both high catalyst activity and stability during OER. The strengthened binding energy between the metals and oxygen in the LDH sheets, together with reduced lattice distortions, both realized by the rational introduction of cation vacancies, drastically mitigate metal dissolution from NiFe-LDH under high oxidation potentials, resulting in the improved long-term OER stability. In addition, the cation vacancies (especially M3+ vacancies) accelerate the evolution of surface γ-(NiFe)OOH phases, thereby boosting the OER activity. The present study highlights that tailoring atomic cation-vacancies is an important strategy for the development of active and stable OER electrocatalysts.

Atomic Cation‐Vacancy Engineering of NiFe‐Layered Double Hydroxides for Improved Activity and Stability towards the Oxygen Evolution Reaction

AbstractNiFe‐layered double hydroxides (NiFe‐LDH) are among the most active catalysts developed to date for the oxygen evolution reaction (OER) in alkaline media, though their long‐term OER stability remains unsatisfactory. Herein, we reveal that the stability degradation of NiFe‐LDH catalysts during alkaline OER results from a decreased number of active sites and undesirable phase segregation to form NiOOH and FeOOH, with metal dissolution underpinning both of these deactivation mechanisms. Further, we demonstrate that the introduction of cation‐vacancies in the basal plane of NiFe LDH is an effective approach for achieving both high catalyst activity and stability during OER. The strengthened binding energy between the metals and oxygen in the LDH sheets, together with reduced lattice distortions, both realized by the rational introduction of cation vacancies, drastically mitigate metal dissolution from NiFe‐LDH under high oxidation potentials, resulting in the improved long‐term OER stability. In addition, the cation vacancies (especially M3+ vacancies) accelerate the evolution of surface γ‐(NiFe)OOH phases, thereby boosting the OER activity. The present study highlights that tailoring atomic cation‐vacancies is an important strategy for the development of active and stable OER electrocatalysts.

Nitrogen and molybdenum co-doped CoP nanohoneycombs on 3D nitrogen-doped porous graphene as enhanced electrocatalyst for oxygen evolution reaction

The four-electron transfer process involved in anodic oxygen evolution reaction (OER) of electrocatalytic water splitting causes the sluggish kinetics and significantly limiting the efficiency of energy conversion. It's urgent to explore low-cost, efficient and stable electrocatalysts for OER. In the work, we design the nitrogen and molybdenum co-doped CoP with nanohoneycombs structure on three-dimensional (3D) nitrogen-doped porous graphene (N/Mo–CoP@NPG) as an efficient OER electrocatalyst. The N/Mo–CoP@NPG delivers the current density of 10 mA cm−2 at a low overpotential value of 201 mV in 1.0 M KOH, meanwhile the electrocatalytic activity shows no obvious degradation after 50 h. The NPG substrate provides plentiful ligaments for growth of N/Mo–CoP nanohoneycombs and 3D network for rapid electronic transfer. Additionally, doping N and Mo atoms into CoP synergistically modifies the micromorphology and electronic structure, benefiting the electrocatalytic ability. This work offers a promising strategy to improve the electrocatalytic activity of transition metal phosphides.

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

One‐Step Synthesis of Carbon‐Protected Co3O4 Nanoparticles toward Long‐Term Water Oxidation in Acidic Media

The design and development of highly efficient and stable oxygen evolution reaction (OER) electrocatalysts in acid media are important for various renewable technologies. Herein, an advanced Co3O4 electrocatalyst supported on a mesoporous hydrophobic carbon paper (Co/29BC) is formed via a simple one‐step thermal decomposition of cobalt nitrate. Through this novel approach, the amorphous carbon layer resulting from the thermal decomposition of carbon‐containing species in the mesoporous layer provides enhanced electronic conduction and protection against corrosion to the Co3O4 nanoparticles. Equally important, the OER performance is found to be correlated with the morphology and surface composition of Co3O4. With optimized Co3+ active sites and oxygen vacancies at the metal oxide surface, the Co3O4 catalyst shows superior OER performance and durability in a proton exchange membrane (PEM) water electrolyzer, with a small overpotential (350 mV) at a constant current density of 10 mA cm−1 for over 50 h. Accordingly, this work provides new insights toward the design of high‐performance and highly stable OER electrocatalysts in corrosive acidic environments.

Amorphous Ni1–xFex Oxyhydroxide Nanosheets with Integrated Bulk and Surface Iron for a High and Stable Oxygen Evolution Reaction

Ni-based electrocatalysts, especially with Fe, are attractive electrocatalysts for oxygen evolution reaction (OER) due to their exhilarating surface properties and anticipated synergistic effect. Herein, amorphous Ni1–xFex oxyhydroxide nanosheets (x: 0, 0.25, 0.50, 0.75, and 1) with integrated bulk and surface Fe were synthesized by facile electrodeposition as an active and stable electrocatalyst for OER. Different ratios of Fe and Ni precursors were deposited on nickel foam cathodically for bulk Fe (FeB) embodiment. Then, surface Fe (FeS) was integrated through anodic cycling from Fe-containing KOH. Benefiting from the amorphous structure and integration between FeB and FeS, high activity and stability were achieved. Accordingly, FeB+S-NIFE25 has demonstrated the highest OER activity, with the lowest overpotential of 300 mV at a current density of 50 mA cm–2, a Tafel slope as low as 30 mV dec–1, and robust stability exceeding 100 h for continuous oxygen generation while the same material (NIFE25) in the absence of FeS, has demonstrated relatively a higher overpotential of 340 mV and a Tafel slope of 65 mV dec–1. Computation simulation also calculated that the NIFEX composites containing both FeB and FeS demonstrated weak binding energies enhancing OH– density at the reaction interface facilitating O2 generation. It is probable that the synergy between FeB and FeS coupled with an amorphous structure induces higher OER activity and stability and can be readily applied to generate cheap and clean hydrogen energy.

Increasing Electrocatalytic Oxygen Evolution Efficiency through Cobalt-Induced Intrastructural Enhancement and Electronic Structure Modulation.

Electrolytic water splitting using surplus electricity represents one of the most cost‐effective and promising strategies for hydrogen production. The high overpotential of the oxygen‐evolution reaction (OER) caused by the multi‐electron transfer process with a high chemical energy barrier, however, limits its competitiveness. Here, a highly active and stable OER electrocatalyst was designed through a cobalt‐induced intrastructural enhancement strategy combined with suitable electronic structure modulation. A carved carbon nanobox was embedded with tri‐metal phosphide from a uniform Ni−Co−Fe Prussian blue analogue (PBA) nanocube by sequential NH3 ⋅ H2O etching and thermal phosphorization. The sample exhibited an OER activity in an alkaline medium, reaching a current density of 10 mA cm−2 at an overpotential of 182 mV and displayed a small Tafel slope of 47 mV dec−1, superior to the most recently reported OER electrocatalysts. Moreover, it showed impressive electrocatalytic durability, increasing by approximately 2.7 % of operating voltage after 24 h of continuous testing. The excellent OER activity and stability are ascribed to a favorable transfer of mass and charge provided by the porous carbon shell, synergistic catalysis between the three‐component metal phosphides originating from appropriate electronic structure modulation, more exposed catalytic sites on the hollow structure, and chainmail catalysis resulting from the carbon protective layer. It is foreseen that this successfully demonstrated design concept can be easily extended to other heterogeneous catalyst designs.

Amorphous cobalt-manganese sulfide electrode for efficient water oxidation: Meeting the fundamental requirements of an electrocatalyst

Design and development of efficient and low-cost electrocatalysts for oxygen evolution reaction (OER) remain a challenge due to high overpotential, low stability, and scalability issues. As a realistic solution, herein, amorphous (Co-Mn)S tailored into nanosheets is demonstrated as a highly efficient and stable electrocatalyst for OER. Thin films of (Co-Mn)S are deposited on stainless steel (SS) substrates via a scalable successive ionic layer adsorption and reaction (SILAR) method for the first time. The stoichiometric tuning of composition has effectively augmented the electrocatalytic activity and OER performance by modification of electronic structure and binding strength with the intermediates. The tailored nanosheet like morphology resulted in achieving high current density at low overpotential. Benefited from the synergy of redox chemical properties and a binder-free deposition, (Co3Mn2)S thin film electrocatalyst achieved a current density of 10 mA cm−2 at an overpotential of 243 mV in 1 M KOH electrolyte. On top of that, the electrocatalyst displayed excellent stabilities over 100 h of continuous water oxidation without any apparent change. In view of the simple yet scalable approach of synthesis, and excellent OER performance, amorphous (Co-Mn)S thin film electrocatalyst could be deliberated as a promising candidate for large application of OER.

Oxygen-Evolution Activity of p-n Heterojunction NiO-SnO2 Ceramic on Ti Substrate Fabricated Using a Simple Layer-by-Layer Method.

To expand the application of p–n heterojunction NiO–SnO2 ceramic materials from gas sensors and photoelectrocatalysts to oxygen-evolution reaction (OER) catalysts, we fabricated two NiO–SnO2 ceramics on a Ti plate (NSCTs) using a simple layer-by-layer method. The prepared NSCTs (NSCT-480 and NSCT-600) were characterized and analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance ultraviolet–visible spectroscopy (DRUV–vis), and X-ray photoelectron spectroscopy (XPS). The OER activity and stability were measured by linear sweep voltammetry, cyclic voltammetry, chronoamperometry, amperometric i–t curve, and chronopotentiometry in a 1.0 mol/L NaOH solution at normal temperature and pressure. After 500 cycles, the lower overpotential (η = 194 mV at 1 mA/cm2) indicated that NSCT-600 offered adequate performance as an OER electrocatalyst. Moreover, the changes observed with cyclic voltammetry, SEM, XRD, and XPS during the OER test revealed that the redox cycle of Ni2+/Ni3+, morphology, and crystal faces of NiO and SnO2 were three critical factors. The data proved that the NiO–SnO2 ceramic is a stable OER electrocatalyst. The results of this study will provide a guide for the design and fabrication of p–n heterojunction metal-oxide ceramic electrocatalysts with a high OER performance.

High efficiency electrocatalyst of LaCr0.5Fe0.5O3 nanoparticles on oxygen-evolution reaction

Due to the multistep proton-coupled electron transfer, it remains a huge challenge to accelerate the kinetics of oxygen evolution reaction (OER). Here, we demonstrate that perovskite-type LaCr0.5Fe0.5O3 nanoparticles can be used as highly active and stable OER electrocatalysts, where it shows a low overpotential of 390 mV at 10 mA/cm2, a small Tafel slope of 114.4 mV/dec and excellent stability with slight current decrease after 20 h, superior than that of their individual counterparts (LaFeO3 and LaCrO3). This finding confirms that the present hybrid material would be an effective means to electrocatalyst for catalyzing OER.

Water Oxidation in Acidic Solutions: Beyond Noble Metals

Water oxidation, a kinetically demanding half-reaction, plays a vital role in hydrogen production through electrochemical water-splitting. Thus, the development of efficient and stable oxygen evolution reaction electrocatalysts has become a central theme for basic research in the field of renewable energy. Substantial progress has been made in developing robust and inexpensive noble metal-free heterogeneous electrocatalysts for water oxidation operating under alkaline and neutral pH conditions. There is, however, a scarcity of active and stable electrocatalysts for acidic water oxidation, which is an ideal pH condition for high purity hydrogen production and offers several other technological advantages. Low performance and poor stability of existing water oxidation electrocatalysts based on non-noble metals are mainly attributed to the dissolution of respective elements in acidic solution. Considering these challenging aspects, we constructed the water oxidations catalysts based on thermodynamically and acid-stable oxides, which are incorporated with catalytically active species (transition metal-based water oxidation catalysts). Specifically, the highly-disordered mixed metal oxide, based on cobalt, iron, and lead, produced in situ exhibits excellent OER performance with unprecedented stability, through self-healing mechanism, under harsh operating conditions of pH 0 and temperature 80 °C. Importantly, the Cobalt-iron-lead oxide demonstrates the capability of operating at industrially relevant rates of 0.5 A cm-2 at low OER overpotentials of 0.7 V. These findings highlight the new strategy to design highly active and acid-stable, noble metal-free, OER electrocatalysts that can essentially operate indefinitely. Our most recent developments focused on replacement of lead with alternative, less toxic components. The presentation will also highlight these new systems, some of which demonstrate outstanding stability even without a self-healing mechanism.

Carbon-Supported IrCoOx nanoparticles as an efficient and stable OER electrocatalyst for practicable CO2 electrolysis

The development of an efficient and stable oxygen evolution reaction (OER) electrocatalyst operating under pH-neutral conditions is vital for the realization of sustainable CO2 reduction reaction (CO2RR) systems in the future. For commercializing this system, it is also important to be able to use general-purpose water as an electrolyte. Here, we explore, characterize and validate a new IrCoOx mixed metal oxide as efficient and stable OER catalyst, before we investigate and proof its suitability as counter electrode to a CO2RR cathode operating under pH-neutral conditions. More specifically, carbon-supported IrCoOx core-shell nanoparticles exhibited a highly efficient OER catalytic activity and stability compared to state-of-art reference IrOx catalysts in CO2-saturated 0.5 M KHCO3 tap-water. IrCoOx/C also exhibited a significantly improved electrochemical oxidation and corrosion resistance than IrOx, resulting in a beneficial suppression of Ir dissolution. The application of IrCoOx/C in the CO2 electrolyzer displayed superior CO space-time yields over prolonged electrolyzer tests.