Oxygen Evolution Reaction Kinetics Research Articles

Unveiling the kinetics of oxygen evolution reaction in defect-engineered B/P-incorporated cobalt-oxide electrocatalysts

Defect-rich transition-metal oxide electrocatalysts hold great promise for alkaline water electrolysis due to their enhanced activity and stability. This study presents a new strategy that significantly improve the OER activity of Co-oxide nanosheets through incorporation of B and P (B/P-CoOx NS), eventually leading to abundant surface defects and oxygen vacancies. The B/P-CoOx NS demonstrates low overpotential of 220 mV to achieve 10 mA/cm2. The electrochemical and kinetic studies coupled with conventional morphological and structural characterizations, reveal that various crystalline defects like vacancies, dislocations, twin planes, and grain boundaries play crucial roles in promoting the OH− ion adsorption, the formation of intermediates, and the desorption of oxygen molecules. The industrial viability of the developed electrocatalyst is substantiated through assessments under harsh industrial conditions of 6 M KOH at 60 °C in a zero-gap single-cell alkaline electrolyzer which achieves 1 A/cm2 at 1.95 V. Chronoamperometry tests (100 h) highlight remarkable robustness of the electrocatalyst. This work establishes a new strategy to fabricate defect-rich OER electrocatalysts, setting a precedent to achieve better OER rates with non-noble materials.

Elevated Water Oxidation by Cation Leaching Enabled Tunable Surface Reconstruction.

Water electrolysis is one promising and eco-friendly technique for energy storage, yet its overall efficiency is hindered by the sluggish kinetics of oxygen evolution reaction (OER). Therefore, developing strategies to boost OER catalyst performance is crucial. With the advances in characterization techniques, an extensive phenomenon of surface structure evolution into an active amorphous layer was uncovered. Surface reconstruction in a controlled fashion was then proposed as an emerging strategy to elevate water oxidation efficiency. In this work, Cr substitution induces the reconstruction of NiFexCr2-xO4 during cyclic voltammetry (CV) conditioning by Cr leaching, which leads to a superior OER performance. The best-performed NiFe0.25Cr1.75O4 shows a ~1500 % current density promotion at overpotential η=300 mV, which outperforms many advanced NiFe-based OER catalysts. It is also found that their OER activities are mainly determined by Ni : Fe ratio rather than considering the contribution of Cr. Meanwhile, the turnover frequency (TOF) values based on redox peak and total mass were obtained and analysed, and their possible limitations in the case of NiFexCr2-xO4 are discussed. Additionally, the high activity and durability were further verified in a membrane electrode assembly (MEA) cell, highlighting its potential for practical large-scale and sustainable hydrogen gas generation.

Elevated Water Oxidation by Cation Leaching Enabled Tunable Surface Reconstruction

AbstractWater electrolysis is one promising and eco‐friendly technique for energy storage, yet its overall efficiency is hindered by the sluggish kinetics of oxygen evolution reaction (OER). Therefore, developing strategies to boost OER catalyst performance is crucial. With the advances in characterization techniques, an extensive phenomenon of surface structure evolution into an active amorphous layer was uncovered. Surface reconstruction in a controlled fashion was then proposed as an emerging strategy to elevate water oxidation efficiency. In this work, Cr substitution induces the reconstruction of NiFexCr2‐xO4 during cyclic voltammetry (CV) conditioning by Cr leaching, which leads to a superior OER performance. The best‐performed NiFe0.25Cr1.75O4 shows a ~1500 % current density promotion at overpotential η=300 mV, which outperforms many advanced NiFe‐based OER catalysts. It is also found that their OER activities are mainly determined by Ni : Fe ratio rather than considering the contribution of Cr. Meanwhile, the turnover frequency (TOF) values based on redox peak and total mass were obtained and analysed, and their possible limitations in the case of NiFexCr2‐xO4 are discussed. Additionally, the high activity and durability were further verified in a membrane electrode assembly (MEA) cell, highlighting its potential for practical large‐scale and sustainable hydrogen gas generation.

Amorphous/crystalline NiFe LDH hierarchical nanostructure for large-current-density electrocatalytic water oxidation

Amorphous structure shows more catalytic active sites but poor conductivity towards oxygen evolution reaction (OER). Herein, we fabricated a novel three-dimensional (3D) self-supported NiFe layered double hydroxides (LDH) catalytic material with amorphous/ crystalline interface, aiming to obtain both excellent catalytic activity and conductivity. This homogeneous hierarchical structure exhibits a high catalytic activity and robustness, giving the industrially required current density of 1000 mA cm−2 at an ultralow overpotential of 359.8 mV with 240-hour stability in 1 M KOH. In-situ electrochemical tests reveal that the amorphous/crystalline interface boosts the intermediates evolution and OER kinetics, which might be ascribed to considerable active sites and fast charge transfer. Moreover, the 3D structure has unique superhydrophilicity and superaerophobicity, which can further accelerate the electrolyte penetration, facilitate the bubbles desorption from the electrode, enhance mass transport, and thus improve OER performance at large current densities. This work provides a feasible way to develop high-performance electrocatalytic material via constructing homogeneous amorphous/crystalline interface.

Construction and enhancement of built-in electric field for efficient oxygen evolution reaction

The construction and regulation of built-in electric field (BIEF) are considered effective strategies for enhancing the oxygen evolution reaction (OER) performance of transition metal-based electrocatalysts. Herein, we present a strategy to regulate the electronic structure of nickel–iron layered double hydroxide (NiFe-LDH) by constructing and enhancing the BIEF induced by in-situ heterojunction transformation. This concept is demonstrated through the design and synthesis of Ag2S@S/NiFe-LDH (p-n heterojunction) and Ag@S/NiFe-LDH (Mott-Schottky heterojunction). Benefiting from the larger BIEF of Mott-Schottky heterojunction, efficient electron transfer occurs at the interface between silver (Ag) and NiFe-LDH. As a result, Ag@S/NiFe-LDH exhibits excellent OER performance, requiring only a 232 mV overpotential at 1 M KOH to achieve a current density of 100 mA cm−2, with a small Tafel slope of 73 mV dec-1, as well as excellent electrocatalytic durability. Density functional theory (DFT) calculations further verified that stronger BIEF in Mott-Schottky heterojunction enhances the electron interaction at the interfaces, reduces the energy barrier for the rate-determining step (RDS), and accelerates the OER kinetics. This work provides an effective strategy for designing catalyst with larger BIEF to enhance electrocatalytic activity.

Heterogenous Fe2P-NiFe layered double hydroxide nanostructures for boosting oxygen evolution reaction

One effective approach to improve the slow kinetics of oxygen evolution reaction (OER) for water splitting is to develop high-performance electrocatalysts. The Fe2P-NiFe LDH/NF catalyst with hetero-interfaces in this work was created using an easy two-step process that involved electrodeposition and hydrothermal processes. In the alkaline electrolyte, the as-prepared Fe2P-NiFe LDH/NF demonstrates improved OER performance. The Fe2P-NiFe LDH/NF catalyst only requires a low overpotential of 200 mV to achieve 10 mA cm−2, indicating the high efficiency for electrochemical reactions. Additionally, the Tafel slope of the catalyst is measured to be 59 mV dec−1. Even at a high current density of 100 mA cm−2, the overpotential of Fe2P-NiFe LDH/NF is only 250 mV, which is noticeably smaller than that of NiFe LDH/NF and commercial IrO2/NF. In addition, the current density of Fe2P-NiFe LDH/NF remains stable without any degradation during a 12 h durability test. By the SEM and TEM results, it showed that Fe2P with a crystalline-amorphous hybrid structure is grown at the edge of NiFe LDH nanosheets. The average length of Fe2P-NiFe LDH nanosheet is about 600 nm, which is longer than that of NiFe LDH nanosheets (about 400 nm). This increased size provides a larger specific area. As a result, more exposed active sites and a synergistic effect at the hetero-interface between Fe2P and NiFe LDH were achieved, which produces a distinct decrease in charge transfer resistance and promotes catalytic performance. Moreover, density functional theory (DFT) calculations emphasize the significance of rationally designed hetero-interfaces in increasing OER activity. It is found that the Fe2P-NiFe LDH/NF with a hetero-interface is an efficient OER catalyst for water splitting.

Advances in Noble Metal Electrocatalysts for Acidic Oxygen Evolution Reaction: Construction of Under-Coordinated Active Sites.

Renewable energy-driven proton exchange membrane water electrolyzer (PEMWE) attracts widespread attention as a zero-emission and sustainable technology. Oxygen evolution reaction (OER) catalysts with sluggish OER kinetics and rapid deactivation are major obstacles to the widespread commercialization of PEMWE. To date, although various advanced electrocatalysts have been reported to enhance acidic OER performance, Ru/Ir-based nanomaterials remain the most promising catalysts for PEMWE applications. Therefore, there is an urgent need to develop efficient, stable, and cost-effective Ru/Ir catalysts. Since the structure-performance relationship is one of the most important tools for studying the reaction mechanism and constructing the optimal catalytic system. In this review, the recent research progress from the construction of unsaturated sites to gain a deeper understanding of the reaction and deactivation mechanism of catalysts is summarized. First, a general understanding of OER reaction mechanism, catalyst dissolution mechanism, and active site structure is provided. Then, advances in the design and synthesis of advanced acidic OER catalysts are reviewed in terms of the classification of unsaturated active site design, i.e., alloy, core-shell, single-atom, and framework structures. Finally, challenges and perspectives are presented for the future development of OER catalysts and renewable energy technologies for hydrogen production.

In situ transformation from metal-organic framework into iridium-iron hollow hexagonal rod to promote oxygen evolution reaction

Developing highly efficient and durable electrocatalysts for water oxidation in alkaline media is crucial for hydrogen production in industrialization. IrO2 is a highly promising electrocatalyst for oxygen evolution reaction (OER), but its large-scale is still limited to the sluggish OER kinetics in alkaline solution due to the multi-steps adsorption of -OH and H2O. Herein, we reported a novel in-situ generation from metal-organic framework strategy for preparing hollow hexagonal rod IrFex electrocatalysts (IrFex HHRs). Specifically, the optimized IrFe3 HHRs shows an excellent OER electrocatalytic activity, including low overpotential of 265, 295 and 307 mV at the current density of 10, 50 and 100 mA cm−2, and high stability (100 h). The experimental results revealed that the existent interfacial Fe-O-Ir bonds between Ir and MIL-88A (Fe) can promote electrons transport to improve the electrocatalyst activity. This work represents a new strategy for designing an efficiency electrocatalysts with low iridium content derived from Ir doped-bimetal MOF material.

Structure and oxygen evolution reaction performance of Ni-supported catalysts based on steam-exploded poplar

Using renewable steam-exploded poplar (SEP) as carbon source, nickel metal doped carbon hybrid materials were designed to synthesize catalysts (Ni/SEP) with certain oxygen evolution reaction (OER) properties and were compared with nickel catalysts supported on metal organic framework structure (ZIF67-Ni). The roles of SEP support in Ni-based catalyst were considered. Scanning electron microscope (SEM) images confirmed that the fiber could better hinder the aggregation of metal particles. Fourier transform infrared spectroscopy (FT-IR) indicated the presence of surface OH groups after the reduction process. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses confirmed the major form of metallic Ni in the resulting Ni catalysts. Carbon materials as carriers, the synergetic effect of Ni-doped, and carbon carrier played an important role in facilitating the kinetics of OER, which was similar to the carrier of metal-organic frame material. Notably, the Ni/SEP (11.3 mF/cm-2) and ZIF67-Ni (37.2 mF/cm-2) with better OER performance exhibited a smaller double layer capacitances (Cdl), suggesting the intrinsic OER catalytic activity of the Ni/SEP and ZIF67-Ni were much higher in comparison to the ZIF67-Ni/SEP. Moreover, the inferior performance of Ni/SEP further indicated that the synergistic effect between carbon and Ni/NiO contributes to the enhanced OER activity.

N, P-doped NiCo2S4 nanospheres with excellent hydrophilicity for efficient oxygen evolution reaction

The rational design of a robust hydrophilic electrocatalyst is essential for enhancing its oxygen evolution reaction(OER). In this work, a nanosphere catalyst (NiCo2S4) composed of 2D-nanosheets was prepared. Interestingly, The hierarchically porous hydrangea-like N,P-NiCo2S4 structure was formed through the doping of nonmetal elements N and P. With the introduction of N and P, the electronic structure of Ni and Co can be optimized and the charge transfer resistance of NiCo2S4 can be reduced, thus improving the kinetics of OER. More importantly, N and P doping increased the hydrophilicity of NiCo2S4, which may have accelerated the surface reconstruction of NiCo2S4, resulting in the generation of truly active sites. Overall, this work not only optimised the electronic structure of NiCo2S4, but also improved its hydrophilicity through the synergistic interaction between the nonmetal elements N and P, which provided ideas for the development of advanced non-noble metal electrocatalysts.

Research progress on electronic and active site engineering of cobalt‐based electrocatalysts for oxygen evolution reaction

AbstractElectrocatalytic water splitting has been identified as a potential candidate for producing clean hydrogen energy with zero carbon emission. However, the sluggish kinetics of oxygen evolution reaction on the anode side of the water‐splitting device significantly hinders its practical applications. Generally, the efficiency of oxygen evolution processes depends greatly on the availability of cost‐effective catalysts with high activity and selectivity. In recent years, extensive theoretical and experimental studies have demonstrated that cobalt (Co)‐based nanomaterials, especially low‐dimensional Co‐based nanomaterials with a huge specific surface area and abundant unsaturated active sites, have emerged as versatile electrocatalysts for oxygen evolution reactions, and thus, great progress has been made in the rational design and synthesis of Co‐based nanomaterials for electrocatalytic oxygen evolution reactions. Considering the remarkable progress in this area, in this timely review, we highlight the most recent developments in Co‐based nanomaterials relating to their dimensional control, defect regulation (conductivity), electronic structure regulation, and so forth. Furthermore, a brief conclusion about recent progress achieved in oxygen evolution on Co‐based nanomaterials, as well as an outlook on future research challenges, is given.

Spontaneous-Spin-Polarized 2D π-d Conjugated Frameworks Towards Enhanced Oxygen Evolution Kinetics.

Alternative strategies to design sustainable-element-based electrocatalysts enhancing oxygen evolution reaction (OER) kinetics are demanded to develop affordable yet high-performance water-electrolyzers for green hydrogen production. Here, it is demonstrated that the spontaneous-spin-polarized 2D π-d conjugated framework comprising abundant elements of nickel and iron with a ratio of Ni:Fe = 1:4 with benzenehexathiol linker (BHT) can improve OER kinetics by its unique electronic property. Among the bimetallic NiFex:y-BHTs with various ratios with Ni:Fe = x:y, the NiFe1:4-BHT exhibits the highest OER activity. The NiFe1:4-BHT shows a specific current density of 140Ag-1 at the overpotential of 350mV. This performance is one of the best activities among state-of-the-art non-precious OER electrocatalysts and even comparable to that of the platinum-group-metals of RuO2 and IrO2. The density functional theory calculations uncover that introducing Ni into the homometallic Fe-BHT (e.g., Ni:Fe = 0:1) can emerge a spontaneous-spin-polarized state. Thus, this material can achieve improved OER kinetics with spin-polarization which previously required external magnetic fields. This work shows that a rational design of 2D π-d conjugated frameworks can be a powerful strategy to synthesize promising electrocatalysts with abundant elements for a wide spectrum of next-generation energy devices.

Covalent organic framework‐derived Fe, Co‐nitrogen codoped carbon as a bifunctional electrocatalyst for rechargeable efficient Zn–air batteries

AbstractThe development of cathode materials with controllable physicochemical structures and explicit catalytic sites is important in rechargeable Zn–air batteries (ZABs). Covalent organic frameworks (COFs) have garnered increasing attention owing to their facile synthesis methods, ordered pore structure, and selectivity of functional groups. However, the sluggish kinetics of oxygen evolution reaction (OER) or oxygen reduction reaction (ORR) inhibit their practical applications in ZABs. Herein, nucleophilic substitution is adopted to synthesize pyridine bi‐triazine covalent organic framework (denoted as O‐COF), and meanwhile, ionothermal conversion synthesis is employed to load MOx (M=Fe, Co) onto carbon nanosheet (named as FeCo@NC) to modulate the electronic structure. The Fe, Co‐N codoped carbon material possesses a large portion of pyridinic N and M‐N, high graphitization, and a larger BET surface area. An outstanding bifunctional activity has been exhibited in FeCo@NC, which provides a small voltage at 10 mA cm−2 for OER (E10 = 1.67 V) and a remarkable half‐wave voltage for ORR (E1/2 = 0.86 V). More impressively, when assembling ZABs, it displays notable rate performance, significant specific capacity (783.9 mAh gZn−1), and satisfactory long‐term endurance. This method of regulating covalent organic framework and ionothermal synthesis can be extended to design diverse catalysts.

Iron, Tungsten Dual-Doped Nickel Sulfide as Efficient Bifunctional Catalyst for Overall Water Splitting.

Developing low-cost and highly efficient bifunctional catalysts for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is a challenging problem in electrochemical overall water splitting. Here, iron, tungsten dual-doped nickel sulfide catalyst (Fe/W-Ni3S2) is synthesized on the nickel foam, and it exhibits excellent OER and HER performance. As a result, the water electrolyze based on Fe/W-Ni3S2 bifunctional catalyst illustrates 10mAcm-2 at 1.69V (without iR-compensation) and highly durable overall water splitting over 100h tested under 500mAcm-2. Experimental results and DFT calculations indicate that the synergistic interaction between Fe doping and Ni vacancy induced by W leaching during the in situ oxidation process can maximize exposed OER active sites on the reconstructed NiOOH species for accelerating OER kinetics, while the Fe/W dual-doping optimizes the electronic structure of Fe/W-Ni3S2 and the binding strength of intermediates for boosting HER. This study unlocks the different promoting mechanisms of incorporating Fe and W for boosting the OER and HER activity of Ni3S2 for water splitting, which provides significant guidance for designing high-performance bifunctional catalysts for overall water splitting.

Facet-Dependent Surface Restructuring on Nickel (Oxy)hydroxides: A Self-Activation Process for Enhanced Oxygen Evolution Reaction.

Unraveling the catalyst surface structure and behavior during reactions is essential for both mechanistic understanding and performance optimization. Here we report a phenomenon of facet-dependent surface restructuring intrinsic to β-Ni(OH)2 catalysts during oxygen evolution reaction (OER), discovered by the correlative ex situ and operando characterization. The ex situ study after OER reveals β-Ni(OH)2 restructuring at the edge facets to form nanoporous Ni1-xO, which is Ni deficient containing Ni3+ species. Operando liquid transmission electron microscopy (TEM) and Raman spectroscopy further identify the active role of the intermediate β-NiOOH phase in both the OER catalysis and Ni1-xO formation, pinpointing the complete surface restructuring pathway. Such surface restructuring is shown to effectively increase the exposed active sites, accelerate Ni oxidation kinetics, and optimize *OH intermediate bonding energy toward fast OER kinetics, which leads to an extraordinary activity enhancement of ∼16-fold. Facilitated by such a self-activation process, the specially prepared β-Ni(OH)2 with larger edge facets exhibits a 470-fold current enhancement than that of the benchmark IrO2, demonstrating a promising way to optimize metal-(oxy)hydroxide-based catalysts.

Oxygen evolution reaction kinetics and photoluminescence studies of zinc stannate (ZnSnO3/Zn2SnO4) nanoparticles synthesized via [formula omitted] mediated route

A groundbreaking method utilizing Aloebarbadensismiller gel to synthesize novel zinc stannate nanoparticles in two distinct phases, followed by calcination at 600 °C, has been developed. Structural, optical, and electrochemical analyses were meticulously conducted to explore the impact of phase variation. X-ray diffraction confirmed the formation of face-centered perovskite and inverse spinel cubic structures for ZnSnO3 and Zn2SnO4 nanoparticles respectively, with irregular sizes and shapes observed in both phases. Energy-dispersive X-ray spectroscopy confirmed their purity. Tauc’s plot revealed direct energy band gaps of 3.45 eV and 3.4 eV for ZnSnO3 and Zn2SnO4 respectively, with photoluminescence emission spectra displaying distinct peaks at 646 nm and 647 nm. The study identified higher defect levels in the inverse spinel structure. Notably, the synthesized nanoparticles exhibited promising characteristics for light-emitting diodes and display technology, with color-correlated temperatures (6810 and 6695 K) suggesting their potential application. Furthermore, the nanoparticles demonstrated remarkable performance in oxygen evolution reaction (OER) studies, with low overpotentials (η10) in the range of 269 mV and 273 mV along with a minimal Tafel slope of 76 mV dec−1 and stable electrochemical behavior over 45 h at a current density of 20 mA/cm2, indicating their efficacy as electrocatalysts. The current work unveils the novel synthesis of zinc stannate nanoparticles through an Aloebarbadensismiller gel, a method that stands out for its eco-friendly and cost-effective nature. We delve into uncharted territory by investigating these nanoparticles’ oxygen evolution reaction kinetics and photoluminescence properties, shedding light on their potential applications in energy conversion and sensing technologies. This pioneering study contributes to the understanding of zinc stannate nanoparticles’ behavior, paving the way for transformative advancements in various fields.

Spin Crossover and Exchange Effects on Oxygen Evolution Reaction Catalyzed by Bimetallic Metal Organic Frameworks.

Bimetallic metal-organic frameworks (BMOFs) have shown a superior oxygen evolution reaction (OER) performance, attributed to the synergistic effects of dual metal sites. However, the significant role of these dual-metal synergies in the OER is not yet fully understood. In this study, we employed density functional theory to systematically investigate the OER performance of NiAl- and NiFe-based BMOFs by examining all possible spin states of each intermediate across diverse external potentials and pH environments. We found that the spin state featuring a shallow hole trap state and Ni ions with a higher oxidation state serve as strong oxidizing agents, promoting the OER. An external potential-induced spin crossover was observed in each intermediate, resulting in significant changes in the overall reaction and activation energies due to altered energy levels. Combining the constant potential method and the electrochemical nudged elastic band method, we mapped the minimum free energy barriers of the OER under varied external potential and pH by considering the spin crossover effect for both NiAl and NiFe BMOFs. The results showed that NiFe exhibits better OER thermodynamics and kinetics, which is in good agreement with experimentally measured OER polarization curves and Tafel plots. Moreover, we found that the improved OER kinetics of NiFe not only is attributed to lower barriers but also is a result of improved electrical conductivity arising from the synergistic effects of Ni-Fe dual-metal sites. Specifically, replacing the second metal Al with Fe leads to two significant outcomes: a reduction in both the band gap and the effective hole mass compared to NiAl, and the initiation of super- and double-exchange interactions within the Ni-F-Fe chain, thereby enhancing electron transfer and hopping and leading to the improved OER kinetics.

Designing a Phenalenyl-Based Dinuclear Ni(II) Complex: An Electrocatalyst with Two Single Ni Sites for the Oxygen Evolution Reaction (OER).

A new dinuclear Ni(II) complex 1, [Ni2II(dtbh-PLY)2], is synthesized from 9-(2-(3,6-di-tert-butyl-2-hydroxybenzylidene)hydrazineyl)-1H-phenalen-1-one, dtbh-PLYH2 ligand, and structurally characterized by various analytical tools including the single-crystal X-ray diffraction (SCXRD) technique. In the solid state, both Ni(II) metal centers in complex 1 exist in a distorted square planar geometry and display the presence of rare Ni···H-C anagostic interactions to form a one-dimensional (1-D) linear motif in the supramolecular array. Complex 1 is further stabilized in the solid state by π-π-stacking interactions between the highly delocalized phenalenyl rings. The redox features of complex 1 have been analyzed by the cyclic voltammetry (CV) technique in solution as well as in the solid state, revealing the crucial involvement of both the Ni(II) metal centers for undergoing quasi-reversible oxidation reactions on the application of an anodic sweep. A complex 1-modified glassy carbon electrode, GC-1, is employed as an electrocatalyst for oxygen evolution reaction (OER) in 1.0 M KOH, giving an OER onset at 1.45 V, and very low OER overpotential, 300 mV vs the reversible hydrogen electrode (RHE) to reach 10 mA cm-2 current density. Furthermore, GC-1 displayed fast OER kinetics with a Tafel slope of 40 mV dec-1, a significantly lower Tafel slope value than those of previously reported molecular Ni(II) catalysts. In situ electrochemical experiments and postoperational UV-vis, Fourier transform infrared (FT-IR), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) studies were performed to analyze the stability of the molecular nature of complex 1 and to gain reasonable insights into the true OER catalyst.

Dual Doping of B and Fe Activated Lattice Oxygen Participation for Enhanced Oxygen Evolution Reaction Activity in Alkaline Freshwater and Seawater

AbstractThe exploitation of highly activity oxygen evolution reaction (OER) electrocatalysts is critical for the application of electrocatalytic water splitting. Triggering the lattice oxygen mechanism (LOM) is expected to provide a promising pathway to overcome the sluggish OER kinetics, however, effectively enhancing the involvement of lattice oxygen remains challenging. In this study, the fabrication of B, Fe co‐doped CoP (B, Fe─CoP) nanofibers is reported, which serve as highly efficient OER electrocatalyst through phosphorization and boronation treatment of Fe‐doped Co3O4 nanofibers. Experimental results combined with theoretical calculations reveal that simultaneous incorporation of both B and Fe can more effectively trigger the participation of lattice oxygen in CoFe oxyhydroxides reconstructed from B, Fe─CoP nanofibers compared to incorporating only B or Fe. Therefore, the optimized B, Fe─CoP nanofibers exhibit superb OER activity with low overpotentials of 361 and 376 mV at 1000 mA cm−2 in alkaline freshwater and alkaline natural seawater, respectively. The present work provides significant guidelines and innovative design concepts for the development of OER electrocatalysts following the LOM pathway.

Multifunctional carbon armor: Synchronously improving oxygen reaction kinetics, mass transfer dynamics, and robustness of transition metal alloy based hybrid catalyst

Construction of robust protective cover on delicate active sites is a frequently-used scheme to enhance the durability of air-cathode catalyst working in harsh environment, thus the lifespan of rechargeable Zinc-air batteries (ZABs). Paradoxically, this would degrade the activity due to the constricted accessibility of active sites to reactants. Herein, carbon nanotubes with abundant mesoporous defects and Fe-N4 species were elaborately designed to be multifunctional protective armor to encapsulate Ni3Fe nano-alloys (Ni3Fe@CNTs/Fe-N4) for bifunctional oxygen electrocatalyst. In/ex-situ spectroscopy analysis and theoretical calculations reveal that the constructed mesoporous carbon defects effectively facilitate the multiphase mass transfer and the oxygen evolution reaction kinetics via strong electrons coupling with packaged Ni3Fe nano-alloys. Meanwhile, the synchronously introduced Fe-N4 moieties could serve as oxygen reduction active sites. Thus, the obtained Ni3Fe@CNTs/Fe-N4 hybrid electrocatalyst simultaneously exhibits remarkable bifunctional catalytic activity (E1/2=0.86/Ej=10=1.59 V vs RHE) and durability over 450 h in the chronoamperometric test at 1.59 V, endowing the assembled Zn-air batteries (ZABs) with a high power density (150 mW cm−2) and lifespan (307 h), much better than that employing benchmark Pt/C+RuO2 mixed catalyst. This work demonstrates an innovative design route for the multifunctional armor to concurrently enhance the durability, activity and robustness of air-cathode-catalyst for ZABs.