Stable Electrocatalysts For Oxygen Evolution Reaction Research Articles

Synergistic Effect of Cobalt/Ferrocene as a Catalyst for the Oxygen Evolution Reaction.

There is a great deal of interest in the development of electrocatalysts for the oxygen evolution reaction (OER) that are stable and have high activity because this anodic half-reaction is the main bottleneck in water splitting and other key technologies. Cobalt and iron oxide and oxyhydroxide electrocatalysts constitute a cheaper alternative to the highly active and commonly used Ir- and Ru-based catalysts. Most of the described electrocatalysts require tedious synthetic and expensive preparation procedures. We report here a facile and straightforward preparation of an electrocatalyst by a combination of commercial compounds, such as cobalt chloride and ferrocene. A highly active and stable OER electrocatalyst is obtained, which shows a low overpotential in the alkaline medium as a consequence of a synergistic effect between both compounds and is inexpensive.

(Invited) Cost Reduction Strategies in Low Temperature Water Electrolysis with Improved Catalytic Activity

Proton exchange membrane water electrolysis (PEMWE) technology is especially advantageous for green H2 production as a clean energy vector. During the water electrolysis process, the oxygen evolution reaction (OER) requires a large amount of iridium (2-3 mgIr cm−2) as catalyst. This material is scarce and expensive, representing a major bottleneck for large-scale deployment of electrolyzers. Recently, Retuerto et al. have synthesized different Ir double perovskites (Sr2CaIrO6) with the Ir atoms in a high oxidation state (Ir6+/5+) 1 and their catalytic activity was extensively investigated. Specifically, a Ca-based double perovskite (Sr2CaIrO6) has showed the highest OER activity similar to those of Ir or Ir oxides-based catalysts while being stable for the OER in half cell measurements. We report the development of a membrane electrode assembly taking advantage of the high activity of the Sr2CaIrO6 catalyst that has only 0.2 mgIr cm−2, around 10 times lower compared to what it is used in the anodes of commercial PEMWE, showing superior performance and stability. The morphology/structure of the developed anode and Sr2CaIrO6 catalyst, before and after operation in PEMWE, were extensively characterized by X-ray diffraction (XRD, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge structure (XANES). We discuss in this contribution how the finding of this work can provide a strategy to lower the Ir content in commercial PEMWE.Anion exchange membrane water electrolysis (AEMWE) combines the advantages of proton exchange membrane water electrolysis (PEMWE), i.e., high current density while maintaining high efficiency and fast dynamic response with the advantages of alkaline water electrolysis (AWE), i.e., low-cost materials. However, AEMWE technology is still depends on a supporting electrolyte and its durability is low. In this regard, the German Aerospace Center (DLR) is developing novel approaches and cell components. Raney-nickel electrodes were developed via vacuum plasma spraying, reaching performance and stability comparable to SoA MW size PEMWE. The electrodes were further refined, switching to lower cost atmospheric plasma spraying while maintaining high performance. Studying the effect of supporting electrolyte concentration it was found, that lowering the ohmic resistance is by far the largest challenge for high performance AEMWE, especially at low KOH concentrations and electrode kinetics are less impactful. Moreover, a 17% efficiency uplift was achieved by applying a carefully tuned, thermally sprayed, nickel-based macro porous layer (MPL) onto a traditional mesh porous transport layer. Both ohmic and mass transport resistances were found to be lowered by the MPL. FIB-SEM and µCT analysis revealed an ideal structure, i.e., 30-40% porosity, almost exclusively open pores, and a broad pore size distribution2. In a fundamental study3, the mechanism of the OER activity was investigated as well as the effect of trace amounts of iron in Ni(OH)2. X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) TGA analysis lead to the conclusion, that iron stabilized the α-Ni(OH)2which is the most active. CV analysis showed that an important redox switching step is also accelerated by Fe-doping. M. Retuerto, L. Pascual, J. Torrero, M. A. Salam, Á. Tolosana-Moranchel, D. Gianolio, P. Ferrer, P. Kayser, V. Wilke, S. Stiber, V. Celorrio, M. Mokthar, A. S. Gago, K. A. Friedrich, M. A. Peña, J. A. Alonso, D. G. Sanchez, S. Rojas, Highly Active and Stable OER Electrocatalysts Derived from Sr2MIrO6 for Proton Exchange Membrane Water Electrolyzers. Nat. Commun. 2022, 13, 7935. Razmjooei, F.; Morawietz, T.; Taghizadeh, E.; Hadjixenophontos, E.; Mues, L.; Gerle, M.; Wood, B. D.; Harms, C.; Gago, A. S.; Ansar, S. A.; Friedrich, K. A., Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer. Joule 2021, 5 (7), 1776-1799. Wang, L.; Saveleva, V. A.; Eslamibidgoli, M. J.; Antipin, D.; Bouillet, C.; Biswas, I.; Gago, A. S.; Hosseiny, S. S.; Gazdzicki, P.; Eikerling, M. H.; Savinova, E. R.; Friedrich, K. A., Deciphering the Exceptional Performance of NiFe Hydroxide for the Oxygen Evolution Reaction in an Anion Exchange Membrane Electrolyzer. ACS Applied Energy Materials 2022, 5 (2), 2221-2230.

Grain Boundary Defect Engineering in Rutile Iridium Oxide Boosts Efficient and Stable Acidic Water Oxidation.

Proton exchange membrane water electrolysis (PEMWE) is considered a promising technology for coupling with renewable energy sources to achieve clean hydrogen production. However, constrained by the sluggish kinetics of the anodic oxygen evolution reaction (OER) and the acidic abominable environment render the grand challenges in developing the active and stable OER electrocatalyst, leading to low efficiency of PEMWE. Herein, we develop the rutile-type IrO2 nanoparticles with abundant grain boundaries and the continuous nanostructure through the joule heating and sacrificial template method. The optimal candidate (350-IrO2) demonstrates remarkable electrocatalytic activity and stability during the OER, presenting a promising advancement for efficient PEMWE. DFT calculations verified that grain boundaries can modulate the electronic structure of Ir sites and optimize the adsorption of oxygen intermediates, resulting in the accelerated kinetics. 350-IrO2 affords a rapid OER process with 20 times higher mass activity (0.61 A mgIr -1) than the commercial IrO2 at 1.50 V vs. RHE. Benefiting from the reduced overpotential and the preservation of the stable rutile structure, 350-IrO2 exhibits the stability of 200 h test at 10 mA cm-2 with only trace decay of 11.8 mV. Moreover, the assembled PEMWE with anode 350-IrO2 catalyst outputs the current density up to 2 A cm-2 with only 1.84 V applied voltage, long-term operation for 100 h without obvious performance degradation at 1 A cm-2.

Microwave sintering construct 3D NiFeAl micro/nano porous bulk electrode for effective oxygen evolution reaction

The development of oxygen evolution reaction (OER) electrocatalysts is an important strategy to produce hydrogen energy by water splitting. Based on the Kirkendall effect and the capillary action of Al melting, this paper introduced a proper amount of Al into NiFe, and the 3D porous bulk high-efficiency OER electrodes were successfully prepared by microwave sintering. The 3D porous structure can provide abundant active sites for OER. The porous channel accelerates the penetration of O2 and electrolyte, shortens the diffusion path of reagents and products, and reduces the charge transfer resistance. It is worth noting that the NiFeAl porous bulk electrode shows excellent OER performance. The overpotentials are 205 mV and 251 mV at the current density of 10 mA cm−2 and 100 mA cm−2, respectively, and the Tafel slope is as low as 39.3 mV dec−1. Due to the existence of Al in the electrode and continuous etching and reconstruction in 1 M KOH solution, the stability test of the electrode lasts for more than 80 h, and the stability rate is even as high as 99.6%. In this work, a new view is put forward in developing an efficient and stable OER electrocatalysts for the preparation of transition metals.

Electronic structure-modulated NiFe-metal–organic framework nanosheets for enhance electrochemical oxygen Evolution

Oxygen Evolution Reaction (OER) is a critical half-reaction that hinders water decomposition due to its sluggish kinetics. Developing efficient, stable electrocatalysts for OER is crucial for addressing the challenges in energy crisis and green hydrogen production. Compared to single-metal Metal-Organic Frameworks (MOFs), synergistic interactions between metal ions in bimetallic MOFs provide sufficient space for tuning the electronic structure and oxygen-containing intermediate adsorption energies, and therefore bimetallic MOFs shows great potential in enhancing the OER kinetics. In this work, NiFe-MIL-88A nanosheets were synthesized on nickel foam via a facile one-step hydrothermal method. The catalyst exhibited exceptional OER performance in 1.0 M KOH solution. Notably, it achieved a current density of 50 mA cm−2 at a low overpotential of 220 mV and displayed a Tafel slope of 43.2 mV/dec. Furthermore, it had impressive electrocatalytic durability suitable for commercial applications. This work elucidates the performance enhancement of NiFe bimetallic MOF from the perspective of electron migration. In-situ Raman spectroscopy was adopted to investigate the structural reconfiguration of the catalyst to reveal the true catalytic active sites. First-principle calculation demonstrate that introduction of Ni atoms with low electronegativity is conducive to optimizing the catalytic d-band center and ƒe value. This work provides insights for the designing bimetallic MOFs with superior OER performance.

Nitrogen-doped carbon layer encapsulating NiFeP nanosheet arrays as high-performance electrocatalyst for oxygen evolution reaction

With water electrolysis restricted to the slow kinetics of oxygen evolution reaction (OER), developing catalysts with both high activity and durability has become an urgent requirement for the development of current water electrolysis technology. Herein, we successfully prepared nitrogen-doped carbon layer encapsulating NiFe phosphide nanosheet arrays (denoted as N-C@NiFeP) catalysts by using a simple hydrothermal method combined with low temperature plasma technique. Phosphating conversion, carbonization, and nitrogen doping were realized by the same high-efficiency plasma treatment process. The nitrogen-doped carbon-coated structure modifies the NiFeP electronic structure, resulting in remarkable OER performances of N-C@NiFeP nanosheet arrays. The N-C@NiFeP nanosheet arrays possessed a tiny Tafel slope value of 27 mV dec−1 and a low overpotential of 229 mV at 10 mA cm−2. Meanwhile, the N-C@NiFeP nanosheet arrays also exhibited impressive long-term durability of 100 h under sequential OER testing at 100 mA cm−2. Our work was instrumental in paving new pathways for the construction of efficient and stable OER electrocatalysts.

Facile and scalable synthesis of Ni3S2/Fe3O4 nanoblocks as an efficient and stable electrocatalyst for oxygen evolution reaction

This study employed a one-step hydrothermal process to synthesize Ni3S2/Fe3O4 nanoblocks in situ on nickel foam (NF). The resulting Ni3S2/Fe3O4/NF catalyst demonstrates exceptional electrocatalytic activity for the oxygen evolution reaction (OER) and robust long-term stability. It achieves a low overpotential of only 220 mV for a current density of 10 mA cm−2 with a Tafel slope of 54.1 mV dec−1 and remains stable in 1.0 M KOH for 66 h. The binder-free self-supported three-dimensional nanoblocks enhance the reaction region and long-term stability. Electronic interactions between Fe3O4 and Ni3S2, coupled with heterogeneous interfaces, optimize the electronic structure, fostering the formation of highly reactive species. Density-functional theory (DFT) calculations confirm that Ni3S2/Fe3O4, with a heterogeneous interfacial structure, modulates the chemisorption of reaction intermediates on the catalyst surface, optimizing the Gibbs free energies (ΔG) of oxygen-containing intermediates. The synergistic effect between the two active materials within the heterogeneous structure enhances OER catalytic performance. This finding offers a valuable approach to designing efficient and stable OER electrocatalysts.

Ru Single Atoms Integrated into Cobalt Oxide Spinel Structure with Interstitial Carbon for Enhanced Electrocatalytic Water Oxidation.

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, a new strategy is reported to stabilize single atoms integrated into cobalt oxide spinel structure with interstitial carbon (Ru0.27Co2.73O4), where the optimized Ru0.27Co2.73O4 exhibits a low overpotential of 265, 326, and 367mV to reach a current density of 10, 50, and 100mA cm2, respectively. More importantly, Ru0.27Co2.73O4 has long-term stability of up to 100h, representing one of the most stable OER electrocatalysts. X-ray adsorption spectroscopy (XAS) characterization and density functional theory (DFT) calculations jointly demonstrate that the significant catalytic performance of Ru0.27Co2.73O4 is due to the synergistic effect between the Ru and Co sites and the bridging O ligands, as well as the significant reduction of the OER energy barrier. This work provides a new perspective for designing and constructing efficient non-noble metal-based electrocatalysts for water splitting.

Multi-interface anchoring enables atomic-level dispersion of Ru for efficient water oxidation

Although noble metal-based catalysts are expensive, they are still the most promising oxygen evolution reaction (OER) electrocatalysts. Therefore, it is desirable to reduce the load of the precious metal without affecting the OER performance of the catalyst. In this work, we have innovatively proposed a strategy of interfacial anchoring of Ru atoms and successfully achieve the dispersion of precious metal ruthenium atoms in cross-growing NiS and NiSe multifaceted structures. The dispersion of Ru ensures Ru–NiS/NiSe/NF more active sites and more adequate contact with the electrolyte, which further improves the oxygen production property of the catalyst. As a direct outcome, the target catalyst (Ru–NiS/NiSe/NF) only requires low overpotential of 453 mV to excite a current density of 1000 mA cm−2. Meanwhile, it can remain stable to catalyze the OER for more than 50 h (200 mA cm−2), which gives it great application potential in future large-scale electrolytic water processes. This work provides a new perspective for the efficient utilization of precious metal for designing the efficient and stable OER electrocatalyst.

Rational Construction of a Triple-Phase Reaction Zone Using CuO-Based Heterostructure Nanoarrays for Enhanced Water Oxidation Reaction.

The development of high-efficiency oxygen evolution reaction (OER) electrocatalysts for the production and conversion of clean energy is paramount yet also full of challenges. Herein, we proposed a simple and universal method to precisely fabricate the hierarchically structured CuO/TMOs loaded on Cu foil (CuO/TMOs/CF) (TMO represents Mn3O4, NiO, CoO, and CuO) nanorod-array electrodes as a highly active and stable OER electrocatalyst, employing Cu(OH)2/CF as a self-sacrificing template by the subsequent H2O2-induced chemical deposition (HiCD) and pyrolysis process. Taking CuO/Mn3O4/CF as an example, we systematically investigated its structure-performance relationship via experimental and theoretical explorations. The enhanced OER activity can be ascribed to the rational design of the nanoarray with multiple synergistic effects of abundant active sites, excellent electronic conductivity of the metallic Cu foil substrate, strong interface charge transfer, and quasi-superhydrophilic/superaerophobic property. Consequently, the optimal CuO/Mn3O4/CF presents an overpotential of 293 mV to achieve a current density of 20 mA cm-2 in 1.0 M KOH media, comparable to that of commercial RuO2 (282 mV), delivering excellent durability by the electrolysis of water at a potential of around 1.60 V [vs reversible hydrogen electrode (RHE)] without evident degeneration. This work might offer a feasible scheme for developing a hybrid nanoarray OER electrocatalyst via regulating electron transportation and mass transfer.

Highly efficient and stable vanadium-based electrocatalysts: Stoichiometric iron vanadium sulfides for water-oxidation at large current densities

Rational design of inexpensive electrocatalysts with high activity towards oxygen evolution reaction (OER) consisting of a complex four-electron process is of great importance for developing renewable energies in the form of hydrogen fuel from water electrolysis. Herein, we develop an exceptionally active and stable OER electrocatalyst, stoichiometric iron vanadium sulfide (Fe1.94V1.06S4) grown on nickel foam (NF). This electrocatalyst affords current densities of 100 and 1500 mA cm−2 at low overpotentials of 193 and 253 mV, respectively, and has stable operation time of exceeding 150 h in alkaline electrolyte, which dramatically outperforms most of the recently reported electrocatalysts (typically, the state-of-the-art NiFe-based electrocatalysts). Systematic investigations on the effects of vanadium and its valence state demonstrate that Fe3+ coupled with V2+ in Fe1.94V1.06S4 endows a larger benefit on the OER than the counterparts in FeV2S4 and vanadium-doped pyrrhotite (Fe7−xVxS8). Density functional theory (DFT) simulations reveal the highly conductive stoichiometric iron vanadium sulfides and favored binding energetics of the OER intermediates on them with a derived amorphous Fe–V oxyhydroxide overlayer due to the synergistically optimized the electronic structure. Thus, a novel bimetallic system containing low-valent vanadium is anticipated to work effectively to enable the communities to scrutinize and exploit new electrocatalysts for water splitting.

Room-Temperature Synthesis of Carbon-Nanotube-Interconnected Amorphous NiFe-Layered Double Hydroxides for Boosting Oxygen Evolution Reaction.

The oxygen evolution reaction (OER) is a key half-reaction in electrocatalytic water splitting. Large-scale water electrolysis is hampered by commercial noble-metal-based OER electrocatalysts owing to their high cost. To address these issues, we present a facile, one-pot, room-temperature co-precipitation approach to quickly synthesize carbon-nanotube-interconnected amorphous NiFe-layered double hydroxides (NiFe-LDH@CNT) as cost-effective, efficient, and stable OER electrocatalysts. The hybrid catalyst NiFe-LDH@CNT delivered outstanding OER activity with a low onset overpotential of 255 mV and a small Tafel slope of 51.36 mV dec-1, as well as outstanding long-term stability. The high catalytic capability of NiFe-LDH@CNT is associated with the synergistic effects of its room-temperature synthesized amorphous structure, bi-metallic modulation, and conductive CNT skeleton. The room-temperature synthesis can not only offer economic feasibility, but can also allow amorphous NiFe-LDH to be obtained without crystalline boundaries, facilitating long-term stability during the OER process. The bi-metallic nature of NiFe-LDH guarantees a modified electronic structure, providing additional catalytic sites. Simultaneously, the highly conductive CNT network fosters a nanoporous structure, facilitating electron transfer and O2 release and enriching catalytic sites. This study introduces an innovative approach to purposefully design nanoarchitecture and easily synthesize amorphous transition-metal-based OER catalysts, ensuring their cost effectiveness, production efficiency, and long-term stability.

Perspectives on the development of highly active, stable, and cost‐effective OER electrocatalysts in acid

AbstractPolymer electrolyte membrane water electrolysis (PEMWE) is an attractive hydrogen energy production technology that offers various advantages such as compact design, high operating pressure, high current densities, and high hydrogen gas purity. However, PEMWE still faces several critical challenges, particularly with respect to the oxygen evolution reaction (OER) at the anode. Highly active, corrosion‐resistant electrocatalytic materials are required for the acidic OER owing to its sluggish kinetics involving four‐electron transfer under harsh anodic potentials. To date, IrO2‐ or RuO2‐based noble metal electrocatalysts have been employed as commercial acidic OER electrocatalysts for PEMWE. However, they remain inadequate in terms of satisfying the industrial activity/stability‐related requirements. Above all, the two noble metals are too rare and expensive, which significantly inhibits widespread commercialization of PEMWE. Therefore, low‐cost, highly active, and highly stable OER electrocatalysts that can operate in acidic media must be urgently developed. This review paper presents various state‐of‐the‐art strategies employed to address the aforementioned issues by classifying them according to objectives such as improving activity, enhancing stability, and reducing cost. Then, finally, we summarize major tasks and strategies to overcome them and put forward a few issues in this field.

Nanostructured Ir-based electrocatalysts for oxygen evolution prepared by galvanic displacement of Co and Ni

Proton exchange membrane (PEM) electrolysers are promising devices to produce hydrogen as a green fuel. Currently, this technology is limited by the sluggish kinetics of the oxygen evolution reaction (OER). In this work, we describe an environmentally safe method for the preparation of Ir oxide thin films (IrO2) for OER. Electrodeposition of Co and Ni was performed in the non-toxic choline chloride:urea deep eutectic solvent (ChCl:urea DES), followed by galvanic displacement reaction (GDR) of Co and Ni by Ir(IV). We evaluated how the GDR conditions, such as the metal replaced (Co or Ni), time and temperature affect both the activity and stability of the deposited IrO2 films on gold substrates. We observed that GDR of Ni at 90 °C induces morphological changes on the IrO2 nanostructures which resulted in higher activity and stability towards OER. We highlight that not only reducing mass loadings of Ir but also tuning the surface morphology and structure controlling the synthesis preparation, as well as investigating the role of the substrate, are key to design more active and stable OER electrocatalysts.

Metal-organic framework-derived boron-doped iron-cobalt tannate nanoparticles as a high-efficiency electrocatalyst for oxygen evolution reaction

Electrocatalytic oxygen evolution reaction (OER) is an important half reaction for energy conversion and storage, which possesses low OER efficiency due to the multistep proton-coupled electron transfer. Herein, B-doped iron-cobalt tannate nanoparticles (B-doped FeCoTA) are synthesized by one-step hydrothermal method. It is proved that the optimized B-doped FeCoTA exhibits excellent electrocatalytic performance for OER with a low overpotential of 306 mV at a current density of 10 mA cm−2, a small Tafel slope of 28 mV dec−1, a high double-layer capacitance of 6.31 mF cm−2 and excellent OER stability with a low potential of 1.55 V (vs RHE) at 10 mA cm−2, which is ascribed to the synergistic effect between bimetallic and heteroatom doping. The B incorporation can greatly enhance the electrical conductivity between metals, facilitate electron transfer and material exchange, thus greatly reducing reaction dynamics and strengthening OER performance. This work can provide a good strategy for the design and development of new efficient and stable OER electrocatalysts.

Fe‐Induced Electronic Transfer and Structural Evolution of Lotus Pod‐Like CoNiFePx@P,N‐C Heterostructure for Sustainable Oxygen Evolution

Transition metal phosphides with metallic properties are a promising candidate for electrocatalytic water oxidation, and developing highly active and stable metal phosphide‐based oxygen evolution reaction catalysts is still challenging. Herein, we present a facile ion exchange and phosphating processes to transform intestine‐like CoNiPx@P,N‐C into lotus pod‐like CoNiFePx@P,N‐C heterostructure in which numerous P,N‐codoped carbon‐coated CoNiFePx nanoparticles tightly anchors on the 2D carbon matrix. Meanwhile, the as‐prepared CoNiFePx@P,N‐C enables a core‐shell structure, high specific surface area, and hierarchical pore structure, which present abundant heterointerfaces and fully exposed active sites. Notably, the incorporation of Fe can also induce electron transfer in CoNiPx@P,N‐C, thereby promoting the oxygen evolution reaction. Consequently, CoNiFePx@P,N‐C delivers a low overpotential of 278 mV (vs RHE) at a current density of 10 mA cm−1 and inherits excellent long‐term stability with no observable current density decay after 30 h of chronoamperometry test. This work not only highlights heteroatom induction to tune the electronic structure but also provides a facile approach for developing advanced and stable oxygen evolution reaction electrocatalysts with abundant heterointerfaces.

Epitaxial Design of Complex Nickelates as Electrocatalysts for the Oxygen Evolution Reaction

AbstractThe oxygen evolution reaction (OER) is a crucial process in electrochemical water splitting, a promising technology to renewably yield hydrogen gas from water. Designing and developing earth‐abundant, efficient, and stable OER electrocatalysts to replace the most widely used but scarce RuO2 and IrO2 are thus of critical interest. Recently, ABO3‐structured perovskite oxides, especially rare‐earth nickelates, are extensively studied for their potential use as OER electrocatalysts. In particular, the epitaxial synthesis of complex oxide thin films allows flexible and precise control over the materials so that their structure–stability–property relationships can be established. Using nickelate thin films as model systems, this review illustrates how epitaxial design allows researchers to test different hypotheses and proposed descriptors, as well as formulate new design principles. Following a brief introduction to the background of OER mechanisms, proposed activity descriptors, and synthesis methods, various epitaxial design strategies are surveyed including strain tuning, composition control, surface termination/orientation selection, defect engineering, and interface design. These have led to precise control over the atomic structures and electronic properties of nickelates which in turn determine their electrochemical performance. Finally, the remaining challenges and perspectives toward a deeper understanding and use of complex oxides as OER catalysts are discussed.

NiFe-based tungstate@layered double hydroxide heterostructure supported on graphene as efficient oxygen evolution reaction catalyst

Oxygen evolution reaction (OER) plays a key role in water splitting and rechargeable metal–air batteries, thus eagerly demanding efficient, robust, and low-cost electrocatalysts. Two-dimension layered double hydroxides (LDHs) have been widely recognized as one of the most promising OER catalysts due to the high activity and large specific surface area. However, the insufficient electrical conductivity and resistance against corrosion seriously restrict their capabilities of charge transport and long-term stability. Herein, a NiFe-based heterostructure catalyst is proposed by the coupling of NiFe-based LDH (termed NiFe-LDH) nanosheets and amorphous NiFe-tungstate (termed NiFeWO4) nanoparticles, both of which possess the same stoichiometric Ni/Fe ratio (3:1), on graphene substrate (termed NiFeWO4@NiFe-LDH/G). Attributed to the synergy of individual components, NiFeWO4@NiFe-LDH/G exhibits superb electrocatalytic activity for OER in an alkaline electrolyte, with extremely low overpotential of 222 mV at a current density of 10 mA cm-2 and Tafel slope of 32.1 mV dec-1, far surpassing the benchmark IrO2 catalyst. Furthermore, NiFeWO4@NiFe-LDH/G exhibits superior stability and durability to IrO2. Comprehensive characterizations and electrochemical measurements together with DFT calculations reveal that the hetero-assembly of NiFe-LDH and NiFeWO4 generates more efficient NiFe active sites than that of the individual components via a strong chemical binding interaction, which can modulate the electronic structures and optimize the energetics of active sites for OER intermediates. As a result, a low cell voltage of 1.48 V is achieved for the water splitting in two-electrode Pt/C‖NiFeWO4@NiFe-LDH/G electrolysis cell at 10 mA cm-2, overwhelmingly prevailing over the 1.69 V for the Pt/C‖IrO2 benchmark cell. This work provides an ingenious heterostructure design for efficient and stable OER electrocatalysts.

Interfacial electronic coupling in Mn3O4/C@FeOOH nano-octahedrals regulates intermediate adsorption for highly efficient oxygen evolution reaction

Exploiting high-efficient low-cost metal-based electrocatalysts for oxygen evolution reaction (OER) in alkaline media is still urgent and challenging. Herein, a hierarchical nanostructure of manganese oxide/carbon@iron oxyhydroxide (denoted as Mn3O4/C@FeOOH) nano-octahedrons via a three-step approach. The optimal electrocatalyst Mn3O4/C@FeOOH was achieved and delivered a low overpotential of 295 mV at 10 mA cm−2, a small Tafel slope of 47.6 mV dec−1 and a decent stability toward long-term electrolysis of 16 h with only 2.2% degradation. The excellent OER performance of the hybrid Mn3O4/C@FeOOH could be attributed to the synergistic effects of the individual counterparts, namely, the structural support of the amorphous carbon skeleton to maintain the integrity of microstructures, the enhanced conductivity imparted by the uniformly dispersed Mn3O4 and graphite nanoparticles, and the partial electron redistribution between the Mn3O4/C and FeOOH interface, optimizing the adsorption/desorption of intermediate oxygenated species. This work provides a novel strategy to prepare an efficient and stable electrocatalyst for OER in alkaline media.

Cover Picture: Durable Nickel‐Iron (Oxy)hydroxide Oxygen Evolution Electrocatalysts through Surface Functionalization with Tetraphenylporphyrin (Angew. Chem. Int. Ed. 51/2022)

State-of-the-art nickel–iron oxyhydroxide catalysts suffer from loss of iron under oxygen evolution reaction (OER) potential. In their Research Article (e202214541), Jaeyoung Lee and co-workers develop a stable OER electrocatalyst by adding tetraphenylporphyrin protective layers. They accelerate the redeposition of eluted iron onto the electrocatalyst by forming a nonpolar–polar interface. This not only prolongs the iron population but also the lifetime of the electrocatalyst. State-of-the-art nickel–iron oxyhydroxide catalysts suffer from loss of iron under oxygen evolution reaction (OER) potential. In their Research Article (e202214541), Jaeyoung Lee and co-workers develop a stable OER electrocatalyst by adding tetraphenylporphyrin protective layers. They accelerate the redeposition of eluted iron onto the electrocatalyst by forming a nonpolar–polar interface. This not only prolongs the iron population but also the lifetime of the electrocatalyst. Sonochemistry Biosensors