Electrocatalytic Water Oxidation Research Articles

Electrodeposited NiFe‐LDH on the Surface of Ni‐BDC for Electrocatalytic Water Oxidation

Substrate surface modification with a functional material can effectively enhance the electrocatalytic performance of an electrode on oxygen evolution reaction (OER). In this work, a functional Ni‐BDC MOF nanosheet layer was in‐situ grown on the surface of nickel foam (NF). Consequently, the NiFe layered double hydroxides (NiFe‐LDH) electrodeposited on the modified layer exhibited an excellent activity and an amazing long‐term stability on electrocatalytic OER. In alkaline electrolyte, the well‐designed NiFe‐LDH/Ni‐BDC/NF drives a current density of 100 mA cm‐2 at a small overpotential of 223 mV, with a low Tafel slope of 33.1 mV dec‐1 and an outstanding catalytic stability of more than 10 days under continuous electrocatalysis. Such distinguished performances are attributed to the particular hydrophily and electrical conductivity of the Ni‐BDC layer. This work is an important attempt to bring a simple and effective guideline on fabricating a highly efficient catalytic electrode for OER.

Self-Supported WO3@RuO2 Nanowires for Electrocatalytic Acidic Water Oxidation.

Developing catalysts with high catalytic activity and stability in acidic media is crucial for advancing hydrogen production in proton exchange membrane water electrolyzers (PEMWEs). To this end, a self-supported WO3@RuO2 nanowire structure was grown in situ on a titanium mesh using hydrothermal and ion-exchange methods. Despite a Ru loading of only 0.098 wt %, it achieves an overpotential of 246 mV for the oxygen evolution reaction (OER) at a current density of 10 mA·cm-2 in acidic 0.5 M H2SO4 while maintaining excellent stability over 50 h, much better than that of the commercial RuO2. After the establishment of the WO3@RuO2 heterostructure, a reduced overpotential of the rate-determining step from M-O* to M-OOH* is confirmed by the DFT calculation. Meanwhile, its enhanced OER kinetics are also greatly improved by this self-supported system in the absence of the organic binder, leading to a reduced interface resistance between active sites and electrolytes. This work presents a promising approach to minimize the use of noble metals for large-scale PEMWE applications.

Efficient Alkaline Water Oxidation Electrocatalysis Enabled via the Modulation of Sn‐containing Anions towards NiFe Oxyhydroxide

Despite being considered as efficient non‐noble metal‐based electrocatalysts for alkaline oxygen evolution reaction (OER), NiFe (oxy)hydroxides (NiFeOxHy) typically fall short of meeting practical requirements. To address this challenge, herein, we introduce a facile in situ electrochemical incorporation technique to form Sn‐doped NiFe‐layered double hydroxide (NiFeSn‐LDH) precatalysts. Subsequently, under the alkaline OER process, the precatalyst evolves into stannate ion‐adsorbed NiFe oxyhydroxides (NiFeOOH). The presence of these stable stannate oxyanions plays a key role in mitigating Fe leaching, optimizing the electronic structure of NiFeOOH, and improving its reaction kinetics, thereby significantly enhancing alkaline OER performance. Notably, the nickel foam‐supported NiFeSn‐LDH demonstrated impressive results delivering a large current density of 100 mA cm−2 at an overpotential as low as ~260 mV and maintaining the industrial‐relevant ~500 mA cm−2 current density over 5 days with negligible activity decay, surpassing the performance of most of the transition metal‐based electrocatalysts. Comprehensive advanced characterization of the precatalysts, before and after the OER reactions, has been performed to uncover stable residual stannate ions at the surface of NiFeOxHy and to determine their pivotal role in promoting alkaline OER.

Cation-π interactions regulate electrocatalytic water oxidation over iridium single atoms supported on conjugated polymers

Cation-π interactions regulate electrocatalytic water oxidation over iridium single atoms supported on conjugated polymers

A Multi-Interfacial Material Design Leading Bifunctional Oxygen Reduction and Water Oxidation Electrocatalysis to Zinc–Air Battery Application

A Multi-Interfacial Material Design Leading Bifunctional Oxygen Reduction and Water Oxidation Electrocatalysis to Zinc–Air Battery Application

Deprotonated of layered double hydroxides during electrocatalytic water oxidation for multi‐cations intercalation

AbstractAqueous rechargeable batteries using abundant multi‐ion cations have received increasing attention in the energy storage field for their high safety and low cost. Layered double hydroxides (LDHs) possess a two‐dimensional structure and exhibit great potential as cathodes for multi‐ion intercalation. However, the insufficient active sites of LDHs result in low capacities in the discharging process. Interestingly, the LDHs after the deprotonation process exhibit favorable electrochemical performance of multi‐cation intercalation. The deprotonation process of LDHs has been widely found in the oxygen evolution reaction and energy storage field, where LDHs lose H in laminates and converts to deprotonated γ‐phase MOOHs (MOOs). Herein, we take a comprehensive overview of the dynamics structure transformation of the deprotonation process of LDHs. Furthermore, the development of advanced aqueous battery cathode and metal battery anode based on deprotonated LDHs for energy storage is explored and summarized. Finally, the perspective of deprotonated LDHs in the energy storage field is discussed.

Strain Engineering of High-Entropy Oxides Enriches Highly Active Lattice Oxygen for Electrocatalytic Water Oxidation

Strain Engineering of High-Entropy Oxides Enriches Highly Active Lattice Oxygen for Electrocatalytic Water Oxidation

Fe2W18Fe4@MOF-Ni-100 nanocomposite: Insights into synthesis and application as a promising material towards the electrocatalytic water oxidation

In this research, a new nanocomposite was synthesized via the sol–gel method by encapsulation of tetranuclear sandwich-type hetropolyanion (Na9K[(FeW9O34)2Fe4(H2O)2].32H2O, abbreviated as Fe2W18Fe4, on the surface of MOF-Ni-100 for the first time. The as-prepared nanocomposite (Fe2W18Fe4@MOF-Ni-100) was examined using different microscopy and spectroscopy techniques, including FT-IR, UV–vis, XRD, SEM, EDX, and BET techniques. The assembled Fe2W18Fe4@MOF-Ni-100 nanocomposite served as a potential heterogeneous catalyst in the water oxidation process for the purpose of oxygen evolution reaction (OER) at neutral pH conditions (N2-saturated 0.1 M Na2SO4). The electrochemical characteristics of the Fe2W18Fe4@MOF-Ni-100 nanocomposite was assessed through cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) methods. The desired nanocatalyst displayed a low onset potential of 1.1 V vs. NHE and low overpotential of 269 mV at a current density (j) of 10 mAĊcm−2 with a Tafel slope of 73 mV.dec−1 (pH = 7). Furthermore, the Fe2W18Fe4@MOF-Ni-100 nanocomposite exhibited remarkable stability and retained its catalytic activity even after 200 catalytic cycles.

Introducing Phosphorus into Spinel Nickel Ferrite to Enhance Lattice Oxygen Participation towards Water Oxidation Electrocatalysis

Oxygen evolution reaction (OER) restricts the efficiency of overall water splitting due to its complex transfer process and sluggish intrinsic kinetics. The novel lattice oxygen oxidation mechanism (LOM) could lift the theoretical scaling limits of the traditional adsorbate evolution mechanism (AEM), but increasing the participation of lattice oxygen still remains a great challenge. Herein, we introduce phosphorus into spinel nickel ferrite as electrocatalyst with an overpotential of 264mV at 10mAcm-2 towards water oxidation. Experimental results confirm the enhanced participation of lattice oxygen for OER in P-NiFe2O4. Further theoretical modelling reveals that the incorporated phosphorus results in an upshift of O 2p band center relative to Fermi level and enhances hybridization of the metal-oxygen bond, thus facilitating LOM and accelerating the OER process on spinel NiFe2O4. This work provides some deep insights into the OER mechanism and a sound strategy for improving the electrocatalytic activity of spinel oxides.

Boosting hydrogen production via water and urea oxidation using a facile fabricated alkali-etched ZIF-67@Ni(OH)2 electrocatalyst

Designing an operative and stable metal electrocatalyst for hydrogen production via water and urea oxidation has been in the spotlight for the past few years. In this work, we have deposited Ni(OH)2 at various time spans of 1, 3 and 5 h over alkali-etched ZIF-67 via facile strategy. The optimum Ni(OH)2@etched ZIF-67 (5 h) (NEZ-3) heterostructure demonstrates excellent OER and UOR performance with a lower overpotential of 240 mV and 1.32 V, respectively at 10 mA cm−2. Moreover, the NEZ-3 electrocatalyst attains smaller Tafel values of 106 and 35 mV dec−1 with remarkable stability of 60 and 48 h for OER/UOR performance at 10 mA cm−2. Specifically, the two-cell electrolyzer requires a lower cell voltage of 1.73 V (OER) and 1.48 V (UOR) with an excellent durability of 20 h at 10 mA cm−2, respectively. Additionally, the water displacement method is used to examine the 4-electron transfer process (OER) of NEZ-3 electrocatalyst with a Faradaic efficiency of 87.53 %. Notably, the porous structure, introduction of oxygen defects (Ov), higher oxidation state of Ni3+, and abundant active sites in NEZ-3 electrocatalyst are the foremost reasons for the superior electrocatalytic water and urea oxidation reactions. Therefore, this research work delivers a simple methodology in emerging a highly active, stable, and cost-effective multifunctional electrocatalysts towards energy conversion applications.

Tuning Electrocatalytic Water Oxidation Activity: Insights from the Active-Site Distance in LnCu6 Clusters.

Atomically precise metal clusters serve as a unique model for unraveling the intricate mechanism of the catalytic reaction and exploring the complex relationship between structure and activity. Herein, three series of water-soluble heterometallic clusters LnCu6, abbreviated as LnCu6-AC (Ln = La, Nd, Gd, Er, Yb; HAC = acetic acid), LnCu6-IM (Ln = La and Nd; IM = Imidazole), and LnCu6-IDA (Ln = Nd; H2IDA = Iminodiacetic acid) are presented, each featuring a uniform metallic core stabilized by distinct protected ligands. Crystal structure analysis reveals a triangular prism topology formed by six Cu2+ ions around one Ln3+ ion in LnCu6, with variations in Cu···Cu distances attributed to different ligands. Electrocatalytic oxygen evolution reaction (OER) shows that these different LnCu6 clusters exhibit different OER activities with remarkable turnover frequency of 135s-1 for NdCu6-AC, 79s-1 for NdCu6-IM and 32s-1 for NdCu6-IDA. Structural analysis and Density Functional Theory (DFT) calculations underscore the correlation between shorter Cu···Cu distances and improves OER catalytic activity, emphasizing the pivotal role of active-site distance in regulating electrocatalytic OER activities. These results provide valuable insights into the OER mechanism and contribute to the design of efficient homogeneous OER electrocatalysts.

Iridium Oxide Coordinatively Unsaturated Active Sites Govern the Electrocatalytic Oxidation of Water

AbstractA special membrane electrode assembly to measure operando X‐ray absorption spectra and resonant photoemission spectra of mesoporous templated iridium oxide films is used. These films are calcined to different temperatures to mediate the catalyst activity. By combining operando resonant photoemission measurements of different films with ab initio simulations these are able to unambiguously distinguish µ2‐O (bridging oxygen) and µ1‐O (terminal oxygen) in the near‐surface regions of the catalysts. The intrinsic activity of iridium oxide scales with the formation of µ1‐O (terminal oxygen) is found. Importantly, it is shown that the peroxo species do not accumulate under reaction conditions. Rather, the formation of µ1‐O species, which are active in O−O bond formation during the OER, is the most oxidized oxygen species observed, which is consistent with an O−O rate‐limiting step. Thus, the oxygen species taking part in the electrochemical oxidation of water on iridium electrodes are more involved and complex than previously stated. This result highlights the importance of employing theory together with true and complementary operando measurements capable of probing different aspects of catalysts surfaces during operation.

Insight into the Anticorrosion Behaviors of Phase-Transformed Cobalt Hydroxides for Long-Term Electrocatalytic Water Oxidation in Saline Electrolytes

Insight into the Anticorrosion Behaviors of Phase-Transformed Cobalt Hydroxides for Long-Term Electrocatalytic Water Oxidation in Saline Electrolytes

Electrocatalytic water oxidation with manganese phosphates

As inspired by the Mn4CaO5 oxygen evolution center in nature, Mn-based electrocatalysts have received overwhelming attention for water oxidation. However, the understanding of the detailed reaction mechanism has been a long-standing problem. Herein, homologous KMnPO4 and KMnPO4•H2O with 4-coordinated and 6-coordinated Mn centers, respectively, are prepared. The two catalysts constitute an ideal platform to study the structure-performance correlation. The presence of Mn(III), Mn(IV), and Mn(V) intermediate species are identified during water oxidation. The Mn(V)=O species is demonstrated to be the substance for O−O bond formation. In KMnPO4•H2O, the Mn coordination structure did not change significantly during water oxidation. In KMnPO4, the Mn coordination structure changed from 4-coordinated [MnO4] to 5-coordinated [MnO5] motif, which displays a triangular biconical configuration. The structure flexibility of [MnO5] is thermodynamically favored in retaining Mn(III)−OH and generating Mn(V)=O. The Mn(V)=O species is at equilibrium with Mn(IV)=O, the concentration of which determines the intrinsic activity of water oxidation. This study provides a clear picture of water oxidation mechanism on Mn-based systems.

Hydrothermal synthesis of InTiS3 and Ag2InTiS4 for electrocatalytic water oxidation and photocatalytic dye degradation application

Hydrothermal synthesis of InTiS3 and Ag2InTiS4 for electrocatalytic water oxidation and photocatalytic dye degradation application

Synergistic modulation of the localized electrons and lattice distortion of cobalt-nickel phosphide motivates intrinsic activity through heteroatoms for efficient electrocatalytic water oxidation

The development of non-precious metal-based catalysts for efficient renewable energy conversion remains a significant challenge. In this study, we synthesized petal-shaped spherical electrocatalysts based on cobalt–nickel phosphate (NiCoP) doped with Mo at different concentrations (Mo-NiCoP; 0.05 %, and 0.1 %) using a facile process. Mo doping provides abundant active sites for electrochemical water oxidation. The 0.1 %Mo-NiCoP electrocatalyst exhibited superior electrocatalytic activity for the oxygen evolution reaction (OER), with a low overpotential of 277 mV, compared to NiCoP (313 mV), 0.05 %Mo-NiCoP (292 mV), and noble-metal catalysts for OER. Additionally, the long-term stability of 0.1 %Mo-NiCoP under a fixed voltage for 20 h revealed only a minor decline in current density. The results of density functional theory calculations suggest that the exceptional electrocatalytic activity of Mo-NiCoP is due to the optimized adsorption energy barrier of intermediates in the OER process, the modulation of the electronic structure, and the introduction of rich lattice disorder defects in NiCoP by the Mo heteroatoms. This work presents a practical and economical approach to fabricating ternary transition-metal phosphates for water oxidation.

Lattice oxygen activation and local electric field enhancement by co-doping Fe and F in CoO nanoneedle arrays for industrial electrocatalytic water oxidation

Oxygen evolution reaction (OER) is critical to renewable energy conversion technologies, but the structure-activity relationships and underlying catalytic mechanisms in catalysts are not fully understood. We herein demonstrate a strategy to promote OER with simultaneously achieved lattice oxygen activation and enhanced local electric field by dual doping of cations and anions. Rough arrays of Fe and F co-doped CoO nanoneedles are constructed, and a low overpotential of 277 mV at 500 mA cm−2 is achieved. The dually doped Fe and F could cooperatively tailor the electronic properties of CoO, leading to improved metal-oxygen covalency and stimulated lattice oxygen activation. Particularly, Fe doping induces a synergetic effect of tip enhancement and proximity effect, which effectively concentrates OH− ions, optimizes reaction energy barrier and promotes O2 desorption. This work demonstrates a conceptual strategy to couple lattice oxygen and local electric field for effective electrocatalytic water oxidation.

Electrocatalytic Water Oxidation by Mononuclear Copper Complexes of Bis-amide Ligands with N4 Donor: Experimental and Theoretical Investigation.

The present work describes electrocatalytic water oxidation of three monomeric copper complexes [CuII(L1)] (1), [CuII(L2)(H2O)] (2), and [CuII(L3)] (3) with bis-amide tetradentate ligands: L1 = N,N'-(1,2-phenylene)dipicolinamide, L2 = N,N'-(4,5-dimethyl-1,2-phenylene)bis(pyrazine-2-carboxamide), L3 = N,N'-(1,2-phenylene)bis(pyrazine-2-carboxamide), for the production of molecular oxygen by the oxidation of water at pH 13.0. Ligands and all complexes have been synthesized and characterized by single crystal XRD, analytical, and spectroscopic techniques. X-ray crystallographic data show that the ligand coordinates to copper in a dianionic fashion through deprotonation of two -NH protons. Cyclic voltammetry study shows a reversible copper-centered redox couple with one ligand-based oxidation event. The electrocatalytic water oxidation occurs at an onset potential of 1.16 (overpotential, η ≈ 697 mV), 1.2 (η ≈ 737 mV), and 1.23 V (η ≈ 767 mV) for 1, 2, and 3 respectively. A systematic variation of the ligand scaffold has been found to display a profound effect on the rate of electrocatalytic oxygen evolution. The results of the theoretical (density functional theory) studies show the stepwise ligand-centered oxidation process and the formation of the O-O bond during water oxidation passes through the water nucleophilic attack for all the copper complexes. At pH = 13, the turnover frequencies have been experimentally obtained as 88, 1462, and 10 s-1 (peak current measurements) for complexes 1, 2, and 3, respectively. Production of oxygen gas during controlled potential electrolysis was detected by gas chromatography.

Surface reconstruction of La0.6Sr0.4Co0.8Ni0.2O3-δ perovskite nanofibers for oxygen evolution reaction

Perovskites have become promising alternatives to precious metal-catalyzed oxygen evolution reaction (OER). Herein, we report the synthesis of several perovskite nanofibers, specifically La0.6Sr0.4CoxNi1-xO3-δ (LSCN), and investigate their electrocatalytic water oxidation activity in alkaline electrolytes. La0.6Sr0.4Co0.8Ni0.2O3-δ (LSCN-0.8) is selected and immersed in an aqueous NaBH4 solution for 1 h for surface reconstruction. The perovskite nanofibers' electrocatalytic OER activity and stability are rigorously evaluated using a standard three-electrode system. Results reveal that even a slight Co substitution for Ni content within the LSCN perovskite structure has a notable impact on electrocatalytic activity. Moreover, LSCN-0.8 exhibits an overpotential of 363 mV at 20 mA cm−2 in 1 M KOH. However, significant improvement is observed after the surface reconstruction process. The optimized LSCN-0.8 (now called LSCN-2) displays the lowest OER overpotential (320 mV) under the same conditions. Furthermore, the LSCN-2 nanostructure demonstrates exceptional electrode stability, as evidenced by only a slight decrease in electrocatalytic performance during 5000 cycles of linear sweep voltammetry.

Novel Heterostructure-Based CoFe and Cobalt Oxysulfide Nanocubes for Effective Bifunctional Electrocatalytic Water and Urea Oxidation.

The development of effective oxygen evolution reaction (OER) and urea oxidation reaction (UOR) on heterostructure electrocatalysts with specific interfaces and characteristics provides a distinctive character. In this study, heterostructure nanocubes (NCs) comprising inner cobalt oxysulfide (CoOS) NCs and outer CoFe (CF) layered double hydroxide (LDH) are developed using a hydrothermal methodology. During the sulfidation process, the divalent sulfur ions (S2- ) are released from the breakdown of the sulfur source and react with the Co-precursors on the surface leading to the transformation of CoOH nanorods into CoOS nanocubes. Further, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analyses reveal that the interactions at the interface of the CF@CoOS NCs significantly altered the electronic structure, thus enhancing the electrocatalytic performance. The optimal catalysts exhibited effective OER and UOR activities, the attained potentials are 1.51 and 1.36V. This remarkable performance is attributable to the induction of electron transfer from the CoFe LDH to CoOS, which reduces the energy barrier of the intermediates for the OER and UOR. Furthermore, an alkaline water and urea two-cell electrolyzer assembled using CF@CoOS-2 NCs and Pt/C as the anode and cathode requires a cell voltage of 1.63 and 1.56V along with a durability performance.