Enhanced Oxygen Evolution Activity Research Articles

Enhanced Oxygen Evolution Activity at Amorphous Hydroxide/Perovskite Interfaces

Enhanced Oxygen Evolution Activity at Amorphous Hydroxide/Perovskite Interfaces

Tailoring Ni-Fe-B Electronic Effects in Layered Double Hydroxides for Enhanced Oxygen Evolution Activity.

NiFe layered double hydroxides (LDHs) are state-of-the-art catalysts for the oxygen evolution reaction (OER) in alkaline media, yet they still face significant overpotentials. Here, quantitative boron (B) doping is introduced in NiFe LDHs (ranging from 0% to 20.3%) to effectively tailor the Ni-Fe-B electronic interactions for enhanced OER performance. The co-hydrolysis synthesis approach synchronizes the hydrolysis rates of Ni and Fe precursors with the formation rate of B─O─M (M: Ni, Fe) bonds, ensuring precise B doping into the NiFe LDHs. It is demonstrated that B, as an electron-deficient element, acts as an "electron sink" at doping levels from 0% to 13.5%, facilitating the transition of Ni2+ to the active Ni3+δ, thereby accelerating OER kinetics. However, excessive B doping (13.5-20.3%) effectively generates oxygen vacancies in the LDHs, which increases electron density at Ni2+ sites and hinders their transition to Ni3+δ, thereby reducing OER activity. Optimal OER performance is achieved at a B doping level of 13.5%, with an overpotential of only 208mV to reach a current density of 500mA cm-2, placing it among the most effective OER catalysts to date. This Ni-Fe-B electronic engineering opens new avenues for developing highly efficient anode catalysts for water-splitting hydrogen production.

NiFe-spinel oxides with nitrogen-doped carbon quantum dots for enhanced oxygen evolution activity

Designing efficient and stable electro-catalysts for non-precious metal oxygen evolution reactions (OER) is critical to solve the bottleneck of water splitting. The NiFe2O4/NCQDs composite electrode was fabricated by combining nitrogen doped carbon quantum dots (NCQDs) with NiFe2O4 spinel via a hydrothermal method, which showed brilliant OER catalytic performance by modifying on nickel foams (NF). The composites had petal-like structures, and the NiFe2O4 was epitaxially grown on the NF substrates with exposed sites, resulting in enhanced electron transport. The fluorescence quenching of NCQDs was accompanied by binding NCQDs with NiFe2O4, which indicated the energy barrier was greatly reduced during the electron transport as well as electro-catalysis. The higher intrinsic charge transfer was achieved, and the doping combination having a higher conductivity was confirmed. The electrochemical activity of NiFe2O4/NCQDs electrode in OER reaction was evaluated under alkaline conditions. The addition of NCQDs effectively enhanced the OER activity, and over-potentials were decreased from 330 mV to 270 mV at 10 mA cm−2 with Tafel slope lower (66 mV/dec) than counterparts. The NiFe2O4/NCQDs displayed long-term catalytic stability at 1.47 V. Therefore, a facile method for preparing NiFe2O4/NCQDs was developed which had characteristics of low cost, simple process and excellent OER activity.

Regulating the Electronic Structure of Metal-Organic Frameworks by Introducing Mn for Enhanced Oxygen Evolution Activity.

The construction of low-cost and highly efficient oxygen evolution electrocatalysts is paramount for clean and sustainable hydrogen energy. In recent years, metal-organic framework (MOF) OER electrocatalysts have attracted tremendous research attention. Herein, we report a simple and facile strategy to construct bimetallic MOFs (named CoMn0.01) for enhancing OER catalytic performance. Significantly, CoMn0.01 exhibited remarkable OER activity (255 mV at 10 mA cm-2) and a low Tafel slope of 66 mV dec-1, superior to those of commercial benchmark electrocatalysts (RuO2, 352 mV, 178 mV dec-1). Besides, the catalyst demonstrated outstanding longevity for 144 h at a current density of 100 mA cm -2. Mn doping can regulate the electronic structure of Co MOFs, which optimizes charge transfer capability and improves conductivity.

Surface Reconstruction of Co‐based Catalysts for Enhanced Oxygen Evolution Activity in Anion Exchange Membrane Water Electrolysis

AbstractDeveloping high‐performance and durable electrocatalysts for the oxygen evolution reaction (OER) is of utmost importance for green hydrogen production via anion exchange membrane water electrolysis (AEMWE). Herein, it is presented that a straightforward surface reconstruction strategy for preparing a robust Co‐based OER catalyst with increased mass transfer activity while preserving the active CoOOH phase during the OER. This strategy comprises electrochemical oxidation of electrodeposited Co‐based catalysts prior to heat treatment, allowing for the meticulous control of the oxidation potential to optimize the OER activity. The optimized catalyst exhibits an overpotential of 190 mV at 10 mA cm−2 and a Tafel slope of 32.7 mV dec−1 under half‐cell conditions. In an AEMWE single‐cell system, it shows a current density of 1590 mA cm−2 at 1.8 V and 60 °C and demonstrates a degradation rate of 0.2 mV h−1 during 1000 h of operation at 500 mA cm−2. This study not only provides a simple yet potent strategy to enhance the OER activity but also offers insights regarding the factors enhancing the OER performance.

Origin of Spin‐State Precise Modulation for Enhanced Oxygen Evolution Activity: Effect of Secondary Coordination Sphere

AbstractThe process of oxygen evolution reaction (OER) is crucial for energy storage and conversion, and the spin electronic structure of catalyst significantly influences its catalytic activity. Precisely regulating the spin electronic structures of metal active centers with intermediate spin (IS) states is challenging but important. This study presents a general method for achieving spin‐state precise modulation by altering the secondary coordination sphere (SCS) in Fe‐substituted LaCo1‐xFexO3 perovskites, denoted as Co6‐y−[Co]−Fey (y = 0–6). The concentration‐dependent SCSs can precisely regulate the spin state of Co3+ from high‐spin (HS) to IS and low‐spin (LS) state by tuning the Co─O binding energy of primary coordination sphere (PCS) to ≈567 KJ mol−1. The binding energy demonstrates a strong negative correlation with the spin state of Co3+, serving as a quantitative descriptor for precise spin‐state modulation. Furthermore, a universal optimal doping concentration is proposed for generating IS‐state Co3+ with the best OER activity, ranging from 1/(m+1) to 2/(m+1) in M‐doped ACo1‐xMxOy system with the coordination number of m. As a proof‐of‐concept, the LaCo7/9Fe2/9O3 with IS Co3+ exhibits significantly enhanced OER activity, almost six times higher than the control samples (without IS Co3+). These findings provide new insights into spin‐state modulation for effective OER catalysts.

Ru-anchoring Co-MOF-derived porous Ru-Co3O4 nanomaterials for enhanced oxygen evolution activity and structural stability

Electrocatalytic water electrolysis is intrinsically limited by the slow kinetics of the oxygen evolution reaction (OER) at the anodic electrode. Building on our previous work, we utilized a porous metal-organic...

Unraveling the effect of local dopant environment on NiO6 octahedron perturbation for enhanced oxygen evolution activity

The oxygen evolution reaction (OER) performance in cation-doped materials often exhibits a volcano-like relationship with dopant concentration. However, the influence of dopant content with its associated local environment on the electronic states of electrocatalysts remains unclear. Herein, V is incorporated into Ni(OH)2 to study the underlying mechanism. It is revealed that evenly distributed V can effectively perturb the NiO6 octahedron, leading to strong eg * band broadening and more electronic states around the Fermi level. This phenomenon significantly enhances the electron transfer from electrocatalysts to external circuits. Conversely, the aggregation of V at higher dopant concentration exerts weaker influence on perturbing the NiO6 octahedron. As a result of balance between V doping and aggregation, Ni0.95V0.05OOH, with the strongest NiO6 octahedron distortion, effectuating a remarkably low overpotential of 258 mV at 10 mA cm−2. Furthermore, such a structure-activity relationship is also extended to Fe-doped Ni(OH)2, affirming the universality of the proposed mechanism.

Enhanced Oxygen Evolution Activity and Stability of RuO2(110) Surface by Ti Doping

Introduction Developing highly active and durable electrocatalysts for the oxygen evolution reaction (OER) is essential for efficient hydrogen production through polymer electrolyte membrane water electrolysis (PEMWE). Although RuO2 exhibits the highest OER activity among pure transition metal oxide catalysts, its low durability hampers its practical application as an OER catalyst for PEMWE. Recent studies have shown that the incorporation of dissimilar metal elements, such as Ni, Mn, and Cu, effectively enhances the OER activity and stability of RuO2 in acidic electrolytes (1-3). In this study, we focus on Ti, a corrosion-resistant element in the PEMWE environment, and investigate the effects of doping amounts on the OER activity and stability of a RuO2(110) single crystal model catalyst surface. Experimental Non-doped rutile-type TiO2(110) single crystals were used as sample substrates. Ru and Ti, with a total thickness of 40 nm, were deposited onto the substrate at 400 ℃ under 0.5 Pa-O2 partial pressure using the arc-plasma deposition (APD) method. Subsequently, the sample was post-annealed at 400℃ for 1 hour in air using a tube furnace. Hereafter, the samples are denoted as RuO2-Tix (x represents the atomic percentage of doped Ti).Oxygen evolution activity was measured by linear sweep voltammetry (LSV) at a scan rate of 20 mV s-1 in N2-purged 0.1 M HClO4 at room temperature. Chronopotentiometry (CP) was conducted at 1 mA cm-2 for 120 min to evaluate the durability. The electrochemical impedance spectroscopy was conducted at 1.6 V vs. reversible hydrogen electrode (RHE) to measure the solution resistance. All the LSV and CP data were iR-corrected using the Rs values. Out-of-plane X-ray diffraction (XRD) analysis was carried out to evaluate the crystal structure. The dissolution amounts of Ru into the electrolyte after CP were evaluated by inductively coupled plasma mass spectrometry (ICP-MS). Results and Discussions Fig. 1(a) presents the out-of-plane XRD patterns of Ti-doped and non-doped RuO2(110) samples. The results indicate that (110)-oriented Ti-doped and non-doped RuO2 thin films were successfully obtained on TiO2 substrates. However, the peak position of RuO2(110) gradually shifts to the lower angle side, and the peak becomes less distinct with increasing Ti-doping amounts, suggesting that doped Ti is dissolved in the RuO2 crystal lattice and the crystallinity decreases with increasing doping amounts. Initial LSV curves for OER are shown in Fig. 1(b). The current density of RuO2-Ti4, 5, and 7 samples significantly increases at higher potential regions above 1.6 V vs. RHE, while RuO2-Ti2 and 10 exhibit decreased activity. The CP curves presented in (c) demonstrate that Ti doping, especially at 5 and 7 at.%, effectively suppresses the overpotential increase during CP. The dissolution amounts of Ru after 120 min of CP are summarized in (d). The dissolution amounts tend to decrease with increasing Ti-doping amounts. These results clearly show that an appropriate amount of Ti-doping effectively enhances both the OER activity and electrochemical stability of the RuO2(110) surface.AcknowledgmentsThis study was partly supported by JSPS KAKENHI Grant Number 21H01661, 22K19078 and Toyota Mobility Foundation Hydrogen Initiative. References Z. Y. Wu, F. Y. Chen, B. Li, S. W. Yu, Y. Z. Finfrock, D. M. Meira, Q. Q. Yan, P. Zhu, M. X. Chen, T. W. Song, Z. Yin, H. W. Liang, S. Zhang, G. Wang and H. Wang, Nat. Mater., 22, 100 (2023). S. Chen, H. Huang, P. Jiang, K. Yang, J. Diao, S. Gong, S. Liu, M. Huang, H. Wang and Q. Chen, ACS Catal., 10, 1152 (2020). J. Su, R. Ge, K. Jiang, Y. Dong, F. Hao, Z. Tian, G. Chen and L. Chen, Adv Mater, 30, 1801351 (2018). Figure 1

Metal-organic framework-derived cation regulation of metal sulfides for enhanced oxygen evolution activity

Heteroatom doping serves as an important strategy to improve the oxygen evolution reaction (OER) activity of transition-metal compounds, while the investigation of intrinsic active sites and mechanisms remains insufficient. In this work, a facile cation regulation strategy is reported to boost the OER activity of metal sulfides via pyrolysis of the Ni-Co bimetallic metal-organic framework. The obtained Ni-substituted CoS nanoparticles on nitrogen-doped mesoporous carbon (Ni-CoS/NC) catalyst achieves a current density of 10 mA cm−2 at a small overpotential of 270 mV with a Tafel slope of 37 mV dec−1 in 1.0 mol L−1 KOH. Through a combination of spectroscopy study and theoretical computations, the activity origin is revealed at the atomic level. The CoxNi1–xOOH serves as the real active site for the OER generated by the Ni-CoS/NC reconstruction under oxidation potential during OER. The Ni substitution results in a strong electronic interaction between the two metals, thus generating more negatively charged Co atoms and more positively charged Ni atoms in the electrocatalyst. The metal sites with regulated electronic structure exhibit enhanced surface adsorption of OOH* and reduce the OER overpotential. Meanwhile, the conductive porous carbon scaffold facilitates electron transfer, mass diffusion, and the accessibility of active sites. This work not only provides a feasible cation regulation strategy for the design of high-performance electrocatalysts for low-cost energy storage and conversion systems, but also yields fresh insight into the activity enhancement mechanisms and intrinsic active sites.

Electronic Structure Regulation and Surface Reconstruction of Iron Diselenide for Enhanced Oxygen Evolution Activity.

Regulating the electronic structure of active sites and monitoring the evolution of the active component is essential to improve the intrinsic activity of catalysts for electrochemical reactions. Herein, a highly efficient pre-electrocatalyst of iron diselenide with rich Se vacancies achieved by phosphorus doping (denoted as P-FeSe2 ) for oxygen evolution reaction (OER) is reported. Systematically experimental and theoretical results show that the formed Se vacancies with phosphorus doping can synergistically modulate the electronic structure of FeSe2 and facilitate OER kinetics with the resulting enhanced electrical conductivity and electrochemical surface area. Importantly, the in situ formed FeOOH species on the surface of the P-FeSe2 nanorods (denoted as P-FeOOH(Se)) during the OER process acts as an active component to efficiently catalyze OER and exhibits a low overpotential of 217 mV to reach 10 mA cm-2 with good durability. Promisingly, an alkaline electrolyzer assembled with P-FeOOH(Se) and Pt/C electrodes requires an ultra-low cell voltage of 1.50 V at 10 mA cm-2 for overall water splitting, which is superior to the RuO2 || Pt/C counterpart and most of the state-of-the-art electrolyzers, demonstrating the high potential of the fabricated electrocatalyst by P doping strategy to explore more highly efficient selenide-based catalysts for various reactions.

Regulating the Electronic Structure of Ruddlesden-Popper-Type Perovskite by Chlorine Doping for Enhanced Oxygen Evolution Activity.

Developing economical, efficient, and durable oxygen evolution catalysts is crucial for achieving sustainable energy conversion and storage. Ruddlesden-Popper-type perovskite oxides are at the forefront of oxygen evolution reaction (OER) research. However, their activity and stability are far from satisfactory. Therefore, we emphasize the paradigm shift in designing efficient perovskite-type OER catalysts through anion defect engineering. The Cl anion-doped A2BO4-type perovskite oxides, SrLaCoO4-xClx (SLCOClx), were employed as highly efficient OER catalysts, wherein Cl could tune the electronic structure of SrLaCoO4 (SLCO) to enhance the OER activity effectively. Especially, SLCOCl0.15 demonstrates significantly enhanced OER activity, and the overpotential is only 370 mV at 10 mA·cm-2, which is significantly better than that of SLCO (510 mV). As confirmed by experience results and density functional theory (DFT) calculation, due to the doping of Cl, obviously increasing the ratio of Co2+/Co3+, more abundant oxygen vacancies (O22-/O-) are generated, and the electrical conductivity is increased, which together promote the improvement of OER activity.

Effect of mixed-valence of manganese on water oxidation activity of La1-xCaxMnO3 (0 ≤ x ≤ 1) solid solutions

The water oxidation reaction is one of the crucial process involves 4e- and 4H+ transfer, which causes a high energy barrier and makes the water-splitting process a slow kinetic reaction. Herein, we have systematically observed the water oxidation activity of La1-xCaxMnO3 (0≤ x ≤ 1) solid solutions by tuning the valence of Mn ion through selective substitution of La3+ with Ca2+. With increasing Ca concentration in La1-xCaxMnO3 solid solutions, the water oxidation activity increases up to x = 0.5 and then decreases. Mixed-valence of Mn generated due to substitution of La3+ with Ca2+, which leads to the double exchange mechanism. This could results in high electrical conduction and a faster electron transfer rate because of the rapid charge exchange between Mn3+ and Mn4+ ions, which pinpoints the reason behind the enhanced oxygen evolution activity. Our findings will be a promising way to relate the Mn mixed-valence with its catalytic activity to design and development of efficient water oxidation catalysts.

Lithium Electrochemical Tuning Engineering in an Aqueous System of LiCoO2 for Enhanced Oxygen Evolution Activity

LiCoO2 is a promising catalyst for oxygen evolution reaction (OER), yet its OER activity is still unsatisfactory. Here, the delithiated LiCoO2 nanoparticles (NLCO-x cycle) are prepared via a new lithium electrochemical tuning in an aqueous two-electrode system for promoting OER in alkaline solutions. As a result, quantitative deintercalation of Li+ can be achieved through an aqueous two-electrode system and the OER performance of NLCO-5 cycle is significantly improved over that of pristine LiCoO2, with a low overpotential of 365 mV at 10 mA cm−2, a small Tafel slope of 55 mV dec−1, and low charge transfer resistance. Performance improvement results from electrochemical delithiation tuning the electronic structure of LiCoO2. The Li+ deintercalation process is accompanied by the partial oxidation of Co3+ to Co4+ and the increase of oxygen vacancies, which is associated with the enhanced intrinsic activity of the catalyst. This work paves a simple avenue for reasonable design of effective oxygen electrocatalysts by electrochemical tuning in aqueous systems.

Enhanced Oxygen Evolution Activity Aroused from Interfacial Electron Transfer and Synergism in Co(OH)2/MIL-88A Heterostructure

The oxygen evolution reaction (OER) is a critical process in the operation of electrochemical water splitting. Metal-organic frameworks (MOFs) are applied in the field of OER electrocatalysis because of their unique structure, but the high impedance and unstable framework during pyrolysis remain unresolved. Here, MIL-88A (iron-based MOF) was modified by hydrolysis and loading Co(OH)2 to improve the catalytic activity. The electrochemical results showed that the Co(OH)2/MIL-88A achieved the optimized performance with the current density of 10 mA cm−2 at 278 mV (vs RHE). Density functional calculations (DFT) combined with characterization tests suggest that electrons transfer from Co(OH)2 to MIL-88A at the interface of the heterostructure, leading to a larger hole electron pair density. D-band theory calculations demonstrated that the synergistic effect of MIL-88A and Co(OH)2 in heterostructure strengthens the adsorption between active sites and adsorbate. The above proofs are the source of the excellent OER performance of the Co(OH)2/MIL-88A. The finding has certain reference significance for the heterogeneous treatment of iron-based MOF catalysts.

Partial crystallization of Co–Fe oxyhydroxides towards enhanced oxygen evolution activity

Developing high-performance noble-metal-free electrocatalysts for the oxygen evolution reaction (OER) is of great significance for the large-scale implement of electrochemical water splitting. Here, we demonstrate that cobalt-iron oxyhydroxide (CoFe0.8(OH)x) with appropriate crystallization exhibits excellent OER activity with a low overpotential of only 246 mV, which is much lower than that achieved on amorphous one. Kinetic experiments indicate that the OER active sites should be di-μ-oxo bridged Fe–Co, on which lower energy barrier is attained than that on Fe–O and Co–O sites. Partial crystallization is beneficial to the lattice contraction, the formation of Co–O–Fe sites, and the decrease of charge transfer resistance, thus accelerating OER process.

Cu2S Nanoflakes Decorated with NiS Nanoneedles for Enhanced Oxygen Evolution Activity.

Metal sulfides are considered excellent materials for oxygen evolution reaction because of their excellent conductivity and high electrocatalytic activity. In this report, the NiS-Cu2S composites were prepared on copper foam (NiS-Cu2S-CF) using a facile synthetic strategy. The scanning electron microscopy results confirmed that the NiS nanoneedles were successfully grown on Cu2S nanoflakes, greatly increasing the active sites. Particularly, the optimized 15% NiS-Cu2S-CF composite demonstrated excellent oxygen evolution activity with a small overpotential of 308 mV@20 mA cm−2, which is significantly smaller than that of noble metal-based electrocatalysts and other NiS-Cu2S-CF composites. The enhanced oxygen evolution activity is attributed to the unique morphology that can provide ample active sites, rich ion-transfer pathways, and the synergistic effect between NiS and Cu2S, which can boost the electron transfer rate.

Modulating the oxidation states in nickel–iron layered double hydroxides by natural cooling for enhanced oxygen evolution activity

Modulating the relationship of oxidation state–OER activity by natural cooling.

Novel strategy to enhance the desalination performance of flow-electrode capacitive deionization process via the assistance of electro-catalytic water splitting

• Porous nickel foam was used as the current collector in FCDI system. • Functionalized current collectors with enhanced water splitting activity were prepared. • Desalination performance of F-NFM-FCDI was enhanced via the assistance of electro-catalytic water splitting. • The enhanced desalination performance of F-NFM-FCDI was attributed to the increased ion concentration in flow-electrode. Flow-electrode capacitive deionization (FCDI) has gained lots of attention for the continuous operation, fast and scalable desalination process. However, the flow electrode slurry is poorly conductive and resulting in the high ions transport resistance, which restricts its desalination efficiency. In this work, a novel FCDI system was constructed by using the porous nickel foam (NFM) as the current collector, and its desalination performance was enhanced via the assistance of electro-catalytic water splitting. In detail, the functionalized current collectors (NFM-Co 3 O 4 with enhanced oxygen evolution activity and NFM-Co(OH) 2 with enhanced hydrogen evolution activity) were prepared through a two-step procedure of electrodeposition and subsequently anodic reaction/cathodic reaction. A desalination efficiency of 90.22% was obtained by the FCDI system adopted functionalized NFM (F-NFM-FCDI) after 100 min operation at applied voltage of 2.0 V, which was much higher than that of the FCDI system adopted bare NFM (NFM-FCDI, 65.37%). Moreover, F-NFM-FCDI system possessed higher charge efficiency (CE) of 81.24% and lower normalized energy consumption (NEC) of 237.54 J·mmol −1 under this condition. Mechanism analysis demonstrated that the enhancement on the desalination performance of F-NFM-FCDI system was attributed to the improved conductivity in flow-electrode chamber, which was due to the increase in the concentration of H + and OH – caused by the enhanced electro-catalytic water splitting reaction during charging. In summary, this work provided a novel and facile strategy to improve the desalination performance of FCDI system by coupling with electro-catalytic water splitting.

Facile synthesis of nitrogen, phosphorus and sulfur tri-doped carbon nanosheets as efficient oxygen electrocatalyst for rechargeable Zn-air batteries

The rechargeable Zn-air battery plays vital roles in renewable energy storage and conversion, but the scarcity of highly efficient air cathode electrocatalysts severely hampers its commercial popularizing. Heteroatoms-doped carbon materials have attracted many interests, because the resulted dopants synergistic effect always brings about extraordinary electrocatalytic activities. Herein, a simple pyrolysis strategy of thiourea, phytic acid and graphene oxide was developed to prepare N, P and S tri-doped carbon nanosheets, featuring sheet structure with specific surface area of 479 m2 g−1 and sufficient dopants (3.78 at% N, 7.97 at% P, and 1.36 at% S). Benefiting from the dominated graphitic and pyridinic N moieties, as well as abundant P-C and S-C functional groups, all of which are desired active species for oxygen electrochemistry, the synthesized tri-doped carbon nanosheets exhibit superior oxygen reduction performance and enhanced oxygen evolution activity in alkaline electrolyte. As the air cathode electrocatalysts for rechargeable Zn-air batteries, the decreased charge–discharge potential gaps and robust cycling stability are observed, even superior to those of noble-metal Pt/C benchmarks. The interconnected porous architecture with high surface area, multiple active species, and significant electric conductivity capability are considered as main factors for the enhanced electrochemical activities of this tri-doped carbon material.