Outstanding Oxygen Evolution Reaction Activity Research Articles

Efficient electrocatalytic oxygen evolution enabled by porous Eu-Ni(PO3)2 nanosheet arrays

Phosphorous compounds have garnered significant interest as catalysts for the oxygen evolution reaction (OER). However, their catalytic performance often falls short, limiting their widespread application in electrocatalysis. The objective of this work is to improve the OER performance of nickel metaphosphate (Ni(PO3)2) by incorporating rare-earth europium (Eu). The prepared Eu-Ni(PO3)2 exhibits significant electron redistribution and features porous nanosheet arrays. The optimized Eu-Ni(PO3)2 exhibits outstanding OER activity, with an overpotential of 273 mV at 10 mA/cm, rapid OER kinetics with a Tafel slope of 39.4 mV/dec, and excellent electrochemical stability. These results surpass the performance of Ni(PO3)2, many reported Ni-based catalysts, and even commercial RuO2. Operando Raman spectroscopy reveals that the improvement of OER performance on Eu-Ni(PO3)2 is due to the accelerated formation of surface NiOOH active species and the enhanced interfacial water enrichment during OER. Density functional theory (DFT) calculations further demonstrate that Eu doping induces electronic modulation between the Eu sites and adjacent O-Ni sites, resulting in an optimized thermodynamic pathway with balanced adsorption energies for key oxygen intermediates, thus alleviating thermodynamic limitations during OER.

Phase-Regulated built-in electric field intensity mediates reconstructing for efficient water oxidation

The uncontrollable dynamic surface reconstruction of oxygen evolution reaction (OER) catalysts poses a significant impact on the activity and stability of the catalysts. To tackle this issue, a phase-controlled strategy is utilized to fabricate various CoxSy/layered double hydroxides (LDH) heterojunction with adjustable built-in electric field (BIEF) strength. The BIEF formed at the interface leads to an accumulation of OH– on the electron-deficient region of CoxSy side, facilitating its reconstruction and exposing more active sites. Furthermore, it enhances the bond energy of M−O in the electron-rich LDH, reducing LDH reconstruction and enhancing stability. The asymmetrical distribution of interface charges induced by the BIEF effectively modulates the d-band center of the metal sites, optimizing the adsorption/desorption of reaction intermediates. As a result, the designed Co3S4/LDH demonstrates outstanding OER activity and stability. This study introduces a novel approach to regulate the reconstruction of heterogeneous catalysts by leveraging interface effects driven by the BIEF.

In Situ Transformed CoOOH@Co3S4 Heterostructured Catalyst for Highly Efficient Catalytic OER Application.

The deprived electrochemical kinetics of the oxygen evolution reaction (OER) catalyst is the prime bottleneck and remains the major obstacle in the water electrolysis processes. Herein, a facile hydrothermal technique was implemented to form a freestanding polyhedron-like Co3O4 on the microporous architecture of Ni foam, its reaction kinetics enhanced through sulfide counterpart transformation in the presence of Na2S, and their catalytic OER performances comparatively investigated in 1 M KOH medium. The formed Co3S4 catalyst shows outstanding catalytic OER activity at a current density of 100 mA cm-2 by achieving a relatively low overpotential of 292 mV compared to the pure Co3O4 catalyst and the commercial IrO2 catalyst. This enhancement results from the improved active centers and conductivity, which boost the intrinsic reaction kinetics. Further, the optimized Co3S4 catalyst exhibits admirable prolonged durability up to 72 h at varied current rates with insignificant selectivity decay. The energy dispersive X-ray spectroscopy (EDX) and Raman spectra measured after the prolonged OER stability test reveal a partial transformation of the active catalyst into an oxyhydroxide phase (i.e., CoOOH@Co3S4), which acts as an active catalyst phase during the electrolysis process.

Valence Band-Tunable NiFe Electrocatalyst Triggered by the Dynamic Mo Exudation and Re-Deposition for Superior High Current Density Oxygen Evolution Reaction.

Developing energy- and time-efficient strategies to derive high-performance non-precious electrocatalysts for anodic oxygen evolution reaction (OER), especially stably working at industrial-demanding current density, is still a big challenge. In this work, a concise molten salt erosion scenario was devised to rapidly modulate the smooth surface of the commercial NiMo foam substrate into the rough, electronically coupled, and hierarchically porous Ni/Fe/Mo(oxy)hydroxide catalyst layer assembled by the nanosphere array. This self-supported catalyst is super-hydrophilic for the alkaline electrolyte and distinguished by a balanced Mo leaching/surface-readsorption process to tune the metal d band center and electronic perturbation. The altered electronic environment with the favored OER intermediate adsorption behavior attains the outstanding OER activity in terms of a very small overpotential of 230.21 mV at 10 mA cm-2 and an ultra-long stability for 1179.45 h to sustain the initial commercial-level current density of ca. 1000 mA cm-2. This superb performance transcends most of the edge-cutting transition metal peers reported recently and can satisfy the standards of industrial applications. This industrial-compatible synthesis technology holds profound implications for hydrogen production via water splitting and other electrochemical applications.

In Situ Reconstructing NiFe Oxalate Toward Overall Water Splitting.

Surface reconstruction plays an essential role in electrochemical catalysis. The structures, compositions, and functionalities of the real catalytic species and sites generated by reconstruction, however, are yet to be clearly understood, for the metastable or transit state of most reconstructed structures. Herein, a series of NiFe oxalates (NixFe1- xC2O4, x = 1, 0.9, 0.7, 0.6, 0.5, and 0) are synthesized for overall water splitting electrocatalysis. Whilst NixFe1-xC2O4 shows great hydrogen evolution reaction (HER) activity, the in situ reconstructed NixFe1-xOOH exhibits outstanding oxygen evolution reaction (OER) activity. As identified by the in situ Raman spectroscopy and quasi-in situ X-ray absorption spectroscopy (XAS) techniques, reconstructions from NixFe1-xC2O4 into defective NixFe1-xOOH and finally amorphous NixFe1-xOOH active species (R-NixFe1-xOOH) are confirmed upon cyclic voltammetry processes. Specifically, the fully reconstructed R-Ni0.6Fe0.4OOH demonstrates the best OER activity (179mV to reach 10mA cm-2), originating from its abundant real active sites and optimal d-band center. Benefiting from the reconstruction, an alkaline electrolyzer composed of a Ni0.6Fe0.4C2O4 cathode and an in situ reconstructed R-Ni0.6Fe0.4OOH anode achieves a superb overall water splitting performance (1.52 V@10mA cm-2). This work provides an in-depth structure-property relationship understanding on the reconstruction of catalysts and offers a new pathway to designing novel catalyst.

Nickel-Iron Layered Double Hydroxides/Nickel Sulfide Heterostructured Electrocatalysts on Surface-Modified Ti Foam for the Oxygen Evolution Reaction.

Electrochemical approaches for generating hydrogen from water splitting can be more promising if the challenges in the anodic oxygen evolution reaction (OER) can be harnessed. The interface heterostructure materials offer strong electronic coupling and appropriate charge transport at the interface regions, promoting accessible active sites to prompt kinetics and optimize the adsorption-desorption of active species. Herein, we have designed an efficient multi-interface-engineered Ni3Fe1 LDH/Ni3S2/TW heterostructure on in situ generated titanate web layers from the titanium foam. The synergistic effects of the multi-interface heterostructure caused the exposure of rich interfacial electronic coupling, fast reaction kinetics, and enhanced accessible site activity and site populations. The as-prepared electrocatalyst demonstrates outstanding OER activity, demanding a low overpotential of 220 mV at a high current density of 100 mA cm-2. Similarly, the designed Ni3Fe1 LDH/Ni3S2/TW electrocatalyst exhibits a low Tafel slope of 43.2 mV dec-1 and excellent stability for 100 h of operation, suggesting rapid kinetics and good structural stability. Also, the electrocatalyst shows a low overpotential of 260 mV at 100 mA cm-2 for HER activity. Moreover, the integrated electrocatalyst exhibits an incredible OER activity in simulated seawater with an overpotential of 370 mV at 100 mA cm-2 and stability for 100 h of operation, indicating good OER selectivity. This work might benefit further fabricating effective and stable self-sustained electrocatalysts for water splitting in large-scale applications.

Unveiling the Role of Electrocatalysts Activation for Iron‐Doped Ni Oxyhydroxide in Enhancing the Catalytic Performance of Oxygen Evolution Reaction

Water electrolysis using renewable electricity is a promising strategy for high‐purity hydrogen production. To realize the practical application of water electrolysis, an electrocatalyst with high redox properties and low cost is essential for enhancing the sluggish oxygen evolution reaction. Herein, we fabricated Fe‐doped nickel oxalate (Fe‐NiC2O4) directly grown on nickel (Ni) foam as an efficient electrocatalyst for the alkaline oxygen evolution reaction using a facile one‐step hydrothermal method. Fe‐NiC2O4 served as a precursor for obtaining highly active Fe‐doped Ni oxyhydroxide (Fe‐NiOOH) via in situ electrochemical oxidation. Consequently, 0.75Fe‐NiOOH was demonstrated to be the optimal electrocatalyst, exhibiting outstanding oxygen evolution reaction activity with a low overpotential of 220 mV at a current density of 100 mA cm−2 and a Tafel slope of 20.5 mV dec−1. Furthermore, Fe‐NiOOH maintained its oxygen evolution reaction activity without performance decay during long‐term electrochemical measurements, owing to the phase transformation from nickel oxyhydroxide (NiOOH) to γ‐NiOOH (gamma nickel oxyhydroxide). These performances significantly surpass those of recently reported transition‐metal‐based electrocatalysts.

Sulfate modified Fe(OH)x/NF nanosheets with oxygen vacancies for enhanced oxygen evolution

The development of cost-effective and high-performance electrocatalysts for oxygen evolution reaction (OER) would be beneficial to future renewable energy storage. Herein, sulfate modified Fe(OH)x nanosheets grown on nickel foam (S–Fe(OH)x/NF) with rich undercoordinated atom centers and oxygen vacancies were fabricated through a facile hydrothermal method. The optimal sample S2–Fe(OH)x/NF exhibits outstanding OER activity with an ultralow overpotential of 261 mV to obtain a current density of 200 mA cm−2. The impressive catalytic activity is primarily attributed to the introduction of the undercoordinated atom (Fe) center, which offer rich active sites, as well as the creation of oxygen vacancies (Vo) that enhance the electron density and the intrinsic conductivity. This work opens up an in-depth understanding of transition metal oxides for OER mechanism by sulfate-decorated and a new prospect for designing highly efficient electrocatalysts.

Electronic Structure Modification of MnO2 Nanosheet Arrays with Enhanced Water Oxidation Activity and Stability by Nitrogen Plasma.

The strategic design of catalysts for the oxygen evolution reaction (OER) is crucial in tackling the substantial energy demands associated with hydrogen production in electrolytic water splitting. Despite extensive research on birnessite (δ-MnO2) manganese oxides to enhance catalytic activity by modulating Mn3+ species, the ongoing challenge is to simultaneously stabilize Mn3+ while improving overall activity. Herein, oxygen (O) vacancies and nitrogen (N) doping have been simultaneously introduced into the MnO2 through a simple nitrogen plasma approach, resulting in efficient OER performance. The optimized N-MnO2v electrocatalyst exhibits outstanding OER activity in alkaline electrolyte, reducing the overpotential by nearly 160 mV compared to pure pristine MnO2 (from 476 to 312 mV) at 10 mA cm-2, and a small Tafel slope of 89 mV dec-1. Moreover, it demonstrates excellent durability over a 122 h stability test. The introduction of O vacancies and incorporation of N not only fine-tune the electronic structure of MnO2, increasing the Mn3+ content to enhance overall activity, but also play a crucial role in stabilizing Mn3+, thereby leading to exceptional stability over time. Subsequently, density functional theory calculations validate the optimized electronic structure of MnO2 achieved through the two engineering methods, effectively lowering the intermediate adsorption free energy barrier. Our synergistic approach, utilizing nitrogen plasma treatment, opens a pathway to concurrently enhance the activity and stability of OER electrocatalysts, applicable not only to Mn-based but also to other transition metal oxides.

MOF-derived MnCe3.67C6Permeable microflower: A robust electrocatalyst for oxygen evolution reaction

To enhance the accessibility of hydrogen fuel production, there is a pressing need for the development of efficient catalysts possessing abundant catalytic active sites, robust stability, and a substantial surface area conducive to both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In this study, we present a novel electrocatalyst derived from a metal-organic framework (MOF) precursor, specifically MnCe3.67C6, synthesized through a cost-effective and straightforward pyrolysis process. This process involves the transformation of carefully designed porous spongy conjoined tapeworm like morphology at 973.15 K carburized temperature and which transform into conjoined nanowires when carburization temperature increases from 1073.15 to 1273.15 K into aggregated nanospheres, with the MOF serving as a carbon template. The structural, morphological, and compositional characteristics of the resulting MnCe3.67C6 catalyst were thoroughly investigated using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Remarkably, the MnCe3.67C6 catalyst exhibits outstanding OER activity, manifesting a significantly reduced potential of 231 mV at current density of 10 mAcm−2 in alkaline media, thereby facilitating efficient charge transfer. Furthermore, the fabricated MnCe3.67C6-700 electrocatalyst demonstrates a decreased Tafel slope of 68mVdec−1, indicative of a favorable kinetic mechanism for the resultant material. The electrochemical active surface increases considerably after fabrication of composite MnCe3.67C6-700 (Cdl = 77 mFcm−2) as compared to Mn–Ce/MOF (Cdl = 34 mFcm−2). Moreover, the higher OER activity is also complemented with extraordinary stability of MnCe3.67C6-700 that is capable of performing oxygen evolution reaction for more than 150 h, making it attractive candidate for the commercial utilization. Notably, the enhanced catalytic performance of MnCe3.67C6 can be attributed primarily to the well-dispersed cerium on the carbon surface, which provides an enlarged active surface area replete with catalytic sites, as well as the dynamic charge transfer of electrons depicted in XPS spectrum, thereby enhancing electrochemical properties and paving the way for future applications.

Simultaneous Interface Engineering and Phase Tuning of CeO2-Decorated Catalysts for Boosted Oxygen Evolution Reaction.

Heterogeneous catalysts have attracted extensive attention among various emerging catalysts for their exceptional oxygen evolution reaction (OER) capabilities, outperforming their single-component counterparts. Nonetheless, the synthesis of heterogeneous materials with predictable, precise, and facile control remains a formidable challenge. Herein, a novel strategy involving the decoration of catalysts with CeO2 is introduced to concurrently engineer heterogeneous interfaces and adjust phase composition, thereby enhancing OER performance. Theoretical calculations suggest that the presence of ceria reduces the free energy barrier for the conversion of nitrides into metals. Supporting this, the experimental findings reveal that the incorporation of rare earth oxides enables the controlled phase transition from nitride into metal, with the proportion adjustable by varying the amount of added rare earth. Thanks to the role of CeO2 decoration in promoting the reaction kinetics and fostering the formation of the genuine active phase, the optimized Ni3FeN/Ni3Fe/CeO2-5% nanoparticles heterostructure catalyst exhibits outstanding OER activity, achieving an overpotential of just 249mV at 10mAcm-2. This approach offers fresh perspectives for the conception of highly efficient heterogeneous OER catalysts, contributing a strategic avenue for advanced catalytic design in the field of energy conversion.

Short-time potentiostatic assisted borate to induce the generation of ultrathin NiFe LDH active phase for industrial-level water oxidation

Self-supported NiFe-based oxygen evolution reaction (OER) catalysts with high activity and durability are essential for the industrialization of green hydrogen. Herein, Boron-interfered NiFe LDH nanosheets (B2-NiFe-(a-10)) with abundant wrinkle structure are prepared by introducing nonmetallic sources into the surface reconstruction of layered double hydroxide (NiFe LDH) through a novel short-time potential constant activation strategy. It enhances interactions with the electrolyte, decreases Arrhenius activation energy (Ea), accelerates efficient charge transfer and O2 escape rate. The as-reconstructed B2-NiFe-(a-10) exhibits outstanding alkaline OER activity with an ultralow overpotential of 290 mV at 100 mA cm−2 and excellent durability (100 h). Additionally, density functional theory calculations further reveal that the interaction optimizes the adsorption of oxygenated intermediates (*OH→*O), induces the center of the d-band toward the Fermi energy level, and lowers the dissociation barrier of H2O. Moreover, the anion-exchange membrane water electrolyzer (AEMWE) achieves a current density of 1 A cm−2 at 1.97 V.

Hollow-structured cobalt sulfide electrocatalyst for alkaline oxygen evolution reaction: Rational tuning of electronic structure using iron and fluorine dual-doping strategy

Utilizing renewable electricity for water electrolysis offers a promising way for generating high-purity hydrogen gases while mitigating the emission of environmental pollutants. To realize the water electrolysis, it is necessary to develop highly active and precious metal-free electrocatalyst for oxygen evolution reaction (OER) which incurs significant overpotential due to its complicated four-electron transfer mechanism. Hence, we propose a facile preparation method for hollow-structured Fe and F dual-doped CoS2 nanosphere (Fe-CoS2-F) as an efficient OER electrocatalyst. The uniform hollow and porous structure of Fe-CoS2-F enlarge the specific surface area and increase the number of exposed active sites. Furthermore, the Fe and F dual-dopants synergistically contributed to the adjustment of electronic structure, thereby promoting the adsorption/desorption of oxygen-containing reaction intermediates on active sites during the alkaline OER procedure. As a result, the prepared Fe-CoS2-F exhibits outstanding OER activity, characterized by a low overpotential of 298 mV to achieve a current density of 10 mA cm−2 and a Tafel slope as small as 46.0 mV dec−1. Based on computational theoretical calculations, the introduction of the dual-dopants into CoS2 structure reduce the excessively strong adsorption energy of reaction intermediate in the rate determining step, leading to effectively promoted electrocatalytic cycle for OER in alkaline environment. This study presents an effective strategy for preparing noble metal-free OER electrocatalysts with promising potential for large-scale industrial water electrolysis.

Activity trends of Pd clusters supported on C2N for oxygen evolution and reduction reactions

Developing highly efficient electrocatalysts for the oxygen evolution reaction (OER) and reduction reaction (ORR) is crucial for future renewable energy technology. Here, we use first-principles calculations combined with genetic algorithm to determine the structures of various Pd clusters supported on experimentally available C2N monolayer and evaluate the OER and ORR performance. Our findings show that the activity of the supported Pd clusters is closely linked to the local geometrical and electronic structure of the active site. Furthermore, we establish the activity trends of the clusters based on the adsorption free energies of intermediates. In particular, C2N supported Pd7 and Pd8 clusters exhibit outstanding OER activity with low overpotentials. We identify a volcano relation for the OER on the clusters, suggesting that the high activity of the cluster is related to the moderate adsorption strength of intermediates. Mechanistic analysis indicates that the second water formation is the potential-determining step for ORR on the clusters due to the strong adsorption of *OH. Additionally, we identify a linear scaling relationship between the ORR overpotentials and adsorption free energies of *OH, demonstrating that reducing the adsorption strength of reaction intermediates on Pd clusters can improve the activity. This work unravels the activity trends of cluster catalysts and provides strategies for the rational design of highly efficient single-cluster catalysts for OER and ORR.

Superaerophilic/Superaerophobic NiFe-LDHs Electrode for Enhancing Overall Water Splitting in Alkaline Media.

Overall water splitting, as a critical approach to producing green hydrogen, is greatly impeded by the mass transfer of gaseous bubbles and dissolved gas molecules. Herein, a bifunctional superaerophilic/superaerophobic (SAL/SAB) NiFe layered-double-hydroxides (LDHs) electrode has been developed, which can drive H2 and O2 bubbles out of the reaction system by asymmetric Laplace pressure and accelerate dissolved gases diffusion through reducing their diffusion distance. Consequently, the SAL/SAB NiFe-LDHs electrode exhibits excellent HER activity with an overpotential of -76 mV at -10 mA cm-2 and outstanding oxygen evolution reaction activity with an overpotential of 253 mV at 100 mA cm-2. The bifunctional SAL/SAB NiFe-LDHs electrode is further utilized in overall water splitting, which can achieve 10 mA cm-2 with a cell voltage of 1.54 V. This work provides an efficient strategy to improve the efficiency of overall water splitting and can stimulate new electrode design in various gas-involved processes.

A facile synthesis of hierarchical CoFe2O4 nanosheets for efficient oxygen evolution in neutral medium

It is of great significance to develop electrocatalysts that are abundant in Earth's crust, highly efficient, and exceptionally durable for the oxygen evolution reaction (OER), particularly in neutral medium. Herein, the hierarchical CoFe2O4 nanosheets supported on iron foam (CoFe2O4/IF) were prepared by the ambient spontaneous redox reaction between iron foam and Co2+ at room temperature. The chemical composition and structure of as-prepared CoFe2O4/IF nanosheets were characterized by XRD, XPS, SEM and TEM. The CoFe2O4/IF. The as-obtained CoFe2O4/IF electrode presents excellent electrocatalytic OER activity with an overpotential of 429 mV at 10 mA cm−2 and maintains the stability of 50 h in 1 M PBS. The outstanding electrocatalytic OER activity of CoFe2O4/IF can be credited to the decreased transfer resistance and unique structural features. In addition, the CoFe2O4/IF presented here holds promise for noble-metal-free OER electrocatalyst.

Synergistic effect of a bamboo-like Bi2S3 covered Sm2O3 nanocomposite (Bi2S3-Sm2O3) for enhanced alkaline OER.

The availability of hydrogen energy from water splitting through the electrocatalytic route is strongly dependent on the efficiency, durability, and cost of the electrocatalysts. Herein, a novel Bi2S3-covered Sm2O3 (Bi2S3-Sm2O3) nanocomposite electrocatalyst was developed by a hydrothermal route for the oxygen evolution reaction (OER). The electrochemical properties were studied in 1.00 mol KOH solution after coating the target material on the stainless-steel substrate (SS). Physical analysis via XRD, FTIR, IV, TEM/EDX, and XPS revealed that the Bi2S3-Sm2O3 composite possesses metallic surface states, thereby displaying unconventional electron dynamics and purity of phases. The Bi2S3-Sm2O3 composite shows outstanding OER activity with a low overpotential of 197 mV and a Tafel slope of 74 mV dec-1 at a 10 mA cm-2 current density as compared to pure Bi2S3 and Sm2O3. Meanwhile, the composite catalyst retains high stability even after 100 h of the chronoamperometry test. Thus, this work unveils a new avenue for the speedy flow of electrons, which is attributed to the synergetic effect between Bi2S3 and Sm2O3, as well as enriched interfacial defects, which exhibit greater oxygen adsorption capability with improved electronic assemblies in the active interfacial region. In addition, the introduced porous structure in core-shell Bi2S3-Sm2O3 provides extraordinary electrical properties. Thus, this article offers a realistic framework for electrochemical energy generation.

Iron Phosphates as Highly Efficient Precatalysts for Oxygen Evolution Reaction and Their in Situ Electrochemical Conversion

Current energy issues have prompted demand for the innovations in constructing a clean and sustainable energy platforms. One of examples for energy carrier to actualize a zero carbon society is hydrogen, which is a promising carbon-free fuel with an excellent weight energy density. Hydrogen production through alkaline water electrolysis using renewable energy resources (light and wind)-derived electricity is an attractive ecofriendly and cost-effective technology because cheap nonprecious electrocatalysts can be employed in alkaline media. However, oxygen evolution reaction (OER) at the anode side in the water electrolysis is basically slow and prevents the widespread applications of water electrolysis. Thus, highly efficient and cheap electrocatalysts for OER are highly desirable.Iron (Fe)-based compounds have recently received much attention as OER electrocatalysts because Fe is a quite earth-abundant metallic element that is a very cheap and non-toxic. Therefore, Fe is a promising candidate as electrocatalyst for OER. Due to the insufficient OER activity on simple Fe oxides, previous studies have attempted to enhance the activity by incorporating Fe and other metallic elements.[1,2] Recently, we established a novel comprehensive structural descriptor for the OER on Fe-based simple and multimetal oxides;[3] i.e., shorter minimum Fe–O bond length in the crystalline structures led to higher OER activity regardless of elemental composition, Fe–O coordination number, and crystal category. Thus, this descriptor enabled us to quickly develop excellent OER catalyst, Ba0.65Ca0.35Fe12O19, comprising extremely short Fe–O bond lengths.[4] Furthermore, we found that post-spinel CaFe2O4 catalyzes OER via "multi-iron-site mechanism" involving a reaction intermediate with O–O direct formation on multiple Fe atoms, and CaFe2O4 consequently displayed outstanding OER activity despite the long Fe–O bond length.[5] However, we speculate that OER activity of Fe-based oxides cannot be further enhanced based on crystal structures, and it necessitates to employ another type of compounds.In this study, we report the OER performances of Fe-based phosphates in alkaline media. We selected three kinds of Fe-based phosphates with distinct crystal structures: trigonal FePO4, trigonal Fe3O3(PO4), and monoclinic Fe4(P2O7)3. The electrochemical measurements and post-characterizations identified the Fe-based phosphates as efficient precatalysts that can be electrochemically converted into highly active Fe-based compounds. Notably, the OER performances of the electrochemically converted Fe-based compounds overcame those of the above-mentioned most active Fe-based multimetal oxides and any previously reported crystalline OER electrocatalysts. Therefore, the Fe-based phosphates are promising candidates as OER precatalysts, which can be in situ converted into excellent OER electrocatalysts, and have further advantages of low price, environmental friendliness, and easy production.[6] The part of this paper is based on results obtained from a project, JPNP14021, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). This paper was funded in part by the JSPS KAKENHI Grant-in-Aid (18H01786), the JST PRESTO (JPMJPR15S3) and CREST (JPMJCR16P3) programs, the Tokuyama Science Foundation, and the “Creation of Life Innovative Materials for Interdisciplinary and International Researcher Development” program of the MEXT. The authors thank Dr. Takeshi Aihara in Tokyo Institute of Technology for fruitful discussions.

Nest-like NiFe-LDH derived from the ethylene glycol-assisted hydrothermal route: A highly efficient electrocatalyst for water oxidation in neutral solutions

Water oxidation is an optimistic pathway for hydrogen generation with high quality. In this work, nest-like nickel iron-layered double hydroxide (NiFe-LDH) nanomaterials were successfully prepared using the ethylene glycol-assisted hydrothermal strategy. Morphological and structural studies showed that in the assistance of ethylene glycol (EG), morphologies of the NiFe-LDH nanomaterials were modified, and their surface areas were enhanced. The nano nest-like NiFe-LDH-EG3 derived with 3.0 mL of EG exhibited an excellent oxygen evolution reaction (OER) activity with a low overpotential of about 400 mV at a current density of 10 mA/cm2 and a Tafel slope of 79 mV/dec in neutral media, and such an outstanding OER activity was attributed to the modified morphology, good crystallinity, and high surface area of the nest-like NiFe-LDH-EG3.

Metal-organic framework-derived Fe/NiS heterostructure-embedded nanosheets coupled with carbon nanotubes for excellent oxygen evolution reaction

Developing efficient and stable electrocatalysts to speed up the slow kinetics of oxygen evolution reaction (OER) is both an opportunity and a challenge. Herein, we present a metal-organic framework (MOF)-derived highly active OER catalyst (NiFe-MOF-S@CNT) composed of Fe/NiS heterostructure-embedded nanosheets interconnected by carbon nanotubes network via a direct two-step solvothermal method. The optimized NiFe-MOF-S@CNT catalyst demonstrates outstanding OER activity: it requires an ultralow overpotential of 237 mV to deliver a current density of 10 mA/cm2 (η10) with a small Tafel slope of 42.3 mV/dec, surpassing the commercial RuO2 (η10 = 295 mV) and most other transition metal catalysts. Benefiting from the mesoporous structure and large specific surface area, the MOF-derived NiFe-MOF-S@CNT nanosheets facilitate enhancing mass transfer and electrolyte penetration. Additionally, the incorporation of Fe/NiS heterostructures within the nanosheets, along with carbon nanotubes, generates interfacial effects, promoting electronic interactions and exposing more active sites, thus significantly boosting OER activity. The backbone of carbon nanotubes not only enhances conductivity but also prevents agglomeration of the metal phase, ensuring uniform dispersion of active sites. This work offers a cost-effective and green approach for synthesizing highly efficient transition metal-based sulfides and also paves the way for advancing OER electrocatalysis for various energy applications.