Efficient Electrocatalyst For Oxygen Evolution Reaction Research Articles

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.

Lattice Oxygen Redox Mechanisms in the Alkaline Oxygen Evolution Reaction

AbstractUnderstanding of fundamental mechanism and kinetics of the oxygen evolution reaction (OER) is pivotal for designing efficient OER electrocatalysts owing to its key role in electrochemical energy conversion devices. In the past few years, the lattice oxygen oxidation mechanism (LOM) arising from the anodic redox chemistry has attracted significant attention as it involves a direct O─O coupling and thus bypasses thermodynamic limitations in the traditional adsorbate evolution mechanism (AEM). Transition metal‐based oxyhydroxides are generally acknowledged as the real catalytic phase in alkaline media. In particular, their low‐dimensional layered structures offer sufficient structural flexibility to trigger the LOM. Herein, a comprehensive overview is provided for recent advances in anion redox from LOM‐based electrocatalysts. Based on analyses of electronic structure of electrocatalysts and LOM, a strategy is proposed to activate LOM. Possible identification techniques for corroboration of the oxygen redox are also reviewed. In addition, the structural reconstruction process induced by the LOM is focused and the importance of multiple in situ/operando characterizations is highlighted to unveil the structural and chemical origins of the LOM. To conclude, a prospect on the remaining challenges and future opportunities for LOM electrocatalysts is presented.

Interface Engineering of Electrocatalysts for Efficient and Selective Oxygen Evolution in Alkaline/Seawater

Electrochemical water splitting is regarded as an effective technology for producing green hydrogen, which is crucial for addressing energy and environmental challenges. In particular, direct seawater splitting offers significant economic and environmental advantages. However, its efficiency is hindered by the high overpotential required for the oxygen evolution reaction (OER) and the competition from chloride oxidation. This review highlights the potential of interface engineering to overcome these limitations and develop efficient OER electrocatalysts. We comprehensively explore recent advancements in interface engineering for OER in both alkaline and seawater environments. We begin by introducing the mechanisms of freshwater and seawater electrolysis, emphasizing key considerations for OER catalyst design. Subsequently, we review the recent progress made in various interface engineering strategies, analyzing their impact on OER performance in both electrolytes. Finally, we outline promising future directions for developing efficient seawater oxidation catalysts through interface engineering.

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.

Amorphous FeNi alloy nanoparticles encapsulated in N doped carbon shell induced by laser irradiation with enhanced electrocatalytic activity for water oxidation

Tuning crystal structure of metal nanomaterials is an effective approach to optimize electrocatalytic performance. Here, we employ amorphous FeNi alloy nanoparticles encapsulated in N doped carbon shell (A-FeNi@NC) as an efficient electrocatalyst for oxygen evolution reaction (OER) via laser irradiation in H2O. The formation mechanism of amorphous FeNi alloy is due to the rapid heating and cooling rate result from the pulse laser. The following electrochemical measurements indicate that A-FeNi@NC displays much better OER activity compared with the conventional crystalline FeNi alloy nanoparticles encapsulated in N doped carbon shell (C-FeNi@NC). We proposed that amorphous FeNi alloy possess favorable electronic property to optimize electronic state of the external carbon shell and give rise to a higher electrocatalytic activity towards OER. The optimized electronic state of the external carbon shell commonly exists in other amorphous transition metal include FeCo, CoNi and Ni, give birth to a series of efficient electrocatalysts for OER.

Dual-site segmentally synergistic catalysis mechanism: boosting CoFeSx nanocluster for sustainable water oxidation

Efficient oxygen evolution reaction electrocatalysts are essential for sustainable clean energy conversion. However, catalytic materials followed the conventional adsorbate evolution mechanism (AEM) with the inherent scaling relationship between key oxygen intermediates *OOH and *OH, or the lattice-oxygen-mediated mechanism (LOM) with the possible lattice oxygen migration and structural reconstruction, which are not favorable to the balance between high activity and stability. Herein, we propose an unconventional Co-Fe dual-site segmentally synergistic mechanism (DSSM) for single-domain ferromagnetic catalyst CoFeSx nanoclusters on carbon nanotubes (CNT) (CFS-ACs/CNT), which can effectively break the scaling relationship without sacrificing stability. Co3+ (L.S, t2g6eg0) supplies the strongest OH* adsorption energy, while Fe3+ (M.S, t2g4eg1) exposes strong O* adsorption. These dual-sites synergistically produce of Co-O-O-Fe intermediates, thereby accelerating the release of triplet-state oxygen ( ↑ O = O ↑ ). As predicted, the prepared CFS-ACs/CNT catalyst exhibits less overpotential than that of commercial IrO2, as well as approximately 633 h of stability without significant potential loss.

Phytic-acid-doped conductive hydrogels as alkaline seawater electrocatalysts with anomalous chloride promoted oxygen evolution reaction

The side reaction mainly caused by chloride ions in seawater is the key bottleneck restricting the development of efficient and stable oxygen evolution reaction (OER) electrocatalysts for direct seawater splitting. Recent researches on OER catalysts in seawater mostly concentrate on the repulsive force of Cl− to reduce its adverse impact. Here, we verified that Cl− doping into phytic acid based polypyrrole conductive hydrogel has no significant negative effect; On the contrary, it is beneficial to enhance its activity in seawater. A series of characterization techniques show that doping Cl in the polypyrrole conductive hydrogel can improve the conductivity and promote the electron transfer in the OER process. Therefore, we achieved direct alkaline seawater electrolysis using a non-metallic PA-PPy/CP anode in an alkaline electrolysis cell.

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

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

Single Transition-Metal Atom Anchored on a Rhenium Disulfide Monolayer: An Efficient Bifunctional Electrocatalyst for the Oxygen Evolution and Oxygen Reduction Reactions.

Developing efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) bifunctional electrocatalysts is attractive for rechargeable metal-air batteries. Meanwhile, single metal atoms embedded in 2D layered transition metal chalcogenides (TMDs) have become a very promising catalyst. Recently, many attentions have been paid to the 2D ReS2 electrocatalyst due to its unique distorted octahedral 1T' crystal structure and thickness-independent electronic properties. Here, the catalytic activity of different transition metal (TM) atoms embedded in ReS2 using the density functional theory is investigated. The results indicate that TM@ReS2 exhibits outstanding thermal stability, good electrical conductivity, and electron transfer for electrochemical reactions. And the Ir@ReS2 and Pd@ReS2 can be used as OER/ORR bifunctional electrocatalysts with a lower overpotential for OER (ηOER) of 0.44 V and overpotentials for ORR (ηORR) of 0.26 V and 0.27 V, respectively. The excellent catalytic activity is attributed to the optimal adsorption strength for oxygen intermediates coming from the effective modulation of the electronic structure of ReS2 after Ir/Pd doping. The results can help to deeply understand the catalytic activity of TM@ReS2 and develop novel and highly efficient OER/ORR electrocatalysts.

The Electrocatalytic Oxygen Evolution Reaction Activity of Rationally Designed NiFe-Based Glycerates

The electrocatalytic oxygen evolution reaction (OER) is an arduous step in water splitting due to its slow reaction rate and large overpotential. Herein, we synthesized glycerate-anion-intercalated nickel–iron glycerates (NiFeGs) using a one-step solvothermal reaction. We designed various NiFeGs by tuning the molar ratio between Ni and Fe to obtain Ni4Fe1G, Ni3Fe1G, Ni3Fe2G, and Ni1Fe1G, which we tested for their OER performance. We initially analyzed the catalytic performance of powder samples immobilized on glassy carbon electrodes using a binder. Ni3Fe2G outperformed the other NiFeG compositions, including NiFe layered double hydroxide (LDH). It exhibited an overpotential of 320 mV at a current density of 10 mA cm–2 in an electrolytic solution of pH 14. We then synthesized carbon paper (CP)-modified Ni3Fe2G as a self-supported electrode (Ni3Fe2G/CP), and it exhibited a high current density (100 mA cm−2) at a low overpotential of 300 mV. The redox peak analysis for the NiFeGs revealed that the initial step of the OER is the formation of γ-NiOOH, which was further confirmed by a post-Raman analysis. We extensively analyzed the catalyst’s stability and lifetime, the nature of the active sites, and the role of the Fe content to enhance the OER performance. This work may provide the motivation to study metal-alkoxide-based efficient OER electrocatalysts that can be used for alkaline water electrolyzer applications.

Ligand and Strain Synergistic Effect in NiFeP0.32 LDH for Triggering Efficient Oxygen Evolution Reaction.

Developing efficient water-splitting electrocatalysts to accelerate the slow oxygen evolution reaction (OER) kinetics is urgently desired for hydrogen production. Herein, ultralow phosphorus (P)-doped NiFe LDH (NiFePx LDH) with mild compressive strain is synthesized as an efficient OER electrocatalyst. Remarkably, NiFePx LDH with the phosphorus mass ratio of 0.32wt.% and compressive strain ratio of 2.53% (denoted as NiFeP0.32 LDH) exhibits extraordinary OER activity with an overpotential as low as 210mV, which is superior to that of commercial IrO2 and other reported P-based OER electrocatalysts. Both experimental performance and density function theory (DFT) calculation demonstrate that the doping of P atoms can generate covalent Fe─P coordination bonds and lattice distortion, thus resulting in the consequent depletion of electrons around the Fe active center and the downward shift of the d-band center, which can lead to a weaker adsorption ability of *O intermediate to improve the catalytic performance of NiFeP0.32 LDH for OER. This work provides novel insights into the distinctive coordinated configuration of P in NiFePx LDH, which can result in superior catalytic performance for OER.

The ultra-high oxygen evolution activity of Fe modified NiPt alloy assisted by Pt pre-oxidation in alkaline electrolyte

Constructing ultra-high activity, highly efficient and robust oxygen evolution reaction (OER) electrocatalysts, especially at large current density, plays a key role in the development of the electrolytic water industry but remains challenging. Highly dispersed alloy compound with large electrolyte contact area and excellent internal conductivity is considered as a kind of ideal candidate. Here, we have rationally designed and synthesized a nickel-platinum alloy with octahedral structure loaded on the surface of the carbon layer (NiPt/C). Under the in-situ modulation of the iron-containing electrolyte, the Fe modified NiPt/C catalyst displays an amazing OER activity in 1 M KOH, and only requires low overpotentials of 183 and 242 mV to reach 100 and 1000 mA cm−2, respectively. The comprehensive characterization analysis and property measurements reveal that the pre-oxidation of Pt at OER potential contribute to the rapid production of nickel hydroxide, thus promoting the deposition of more iron active sites on its surface. Moreover, the Pt/C/CP(−)//NiPt/C/CP(+) couple embedded in anion-exchange membrane water electrolyser also displays a low cell voltage of 2.03 V at 1000 mA cm−2 with significant electrochemical stability, which endows it a great potential in the field of hydrogen production and electrochemical energy storage.

Transition metal Co induce CoSe2/NiWSe2 interface structural reorganization for efficient oxygen evolution reaction and urea oxidation reaction

Urea-containing wastewater has become an increasingly serious environmental and energy problem. The use of electrochemical urea oxidation reaction (UOR) technology to treat wastewater containing urea has gained considerable significance. The regulation of the composition and electronic properties of the catalyst by doping transition metal elements is crucial for the development of oxygen evolution reaction (OER) and UOR catalysts with high catalytic activity. In this paper, WSe2, CoSe2, NiWSe2 and CoSe2/NiWSe2 were synthesized by hydrothermal method combined with annealing treatment. Compared with WSe2, CoSe2, and NiWSe2, the OER and UOR catalytic activity of CoSe2/NiWSe2 are significantly improved. For OER, a low overpotential of 1.44 V is all that is needed to reach a current density of 10 mA cm−2. The overpotential of UOR is only 1.32 @ 10 mA cm−2, and it can still maintain excellent electrochemical stability after 30 h. The electronic structure of CoSe2/NiWSe2 is changed by the incorporation of Co, thereby improving the conductivity and accelerating the reaction kinetics. CoSe2 particles are uniformly distributed on the layered NiWSe2 nanosheets, which promotes the charge transfer and synergistic effect at the interface between CoSe2 and NiWSe2. The nanoflower-like structure with thin edges enriches the active sites of CoSe2/NiWSe2. Therefore, the transition metal element doping technology can provide a new method for the development of efficient OER and UOR electrocatalysts and provide a new way to reduce the overall energy consumption during urea degradation.

CoO supported NiFe layered double hydroxide sandwich-like nanosheets on hierarchical carbon framework for efficient electrocatalytic oxygen evolution.

Exploration of greatly efficient and steady non-noble oxygen evolution reaction (OER) electrocatalysts is of great significance in improving the overall efficiency of energy density systems such as regenerative fuel cells, water electrolyzes, and metal-air batteries. Herein, inspired by hierarchical 3D porous structures with open microchannels of natural wood, CoO@NiFe LDH sandwich-like nanosheets were anchored on the carbonized wood (CW) via electrodeposition and calcination strategies. The strong interactions between CoO nanosheets and NiFe LDH nanosheets endow CoO@NiFe LDH/CW electrocatalyst with high catalytic properties toward the OER comparable to CoO/CW and NiFe LDH/CW. The optimized CoO@NiFe LDH/CW electrocatalyst demonstrates good OER catalytic performance with an overpotential of 230 mV at 100 mA cm-2. This work presents an innovative approach to utilize renewable resources for constructing advanced free-standing catalysts.

Correlating Structural Disorder in Metal (Oxy)hydroxides and Catalytic Activity in Electrocatalytic Oxygen Evolution

AbstractUnderstanding the correlation between the structural evolution of electrocatalysts and their catalytic activity is both essential and challenging. In this study, we investigate this correlation in the context of the oxygen evolution reaction (OER) by examining the influence of structural disorder during and after dynamic structural evolution on the OER activity of Fe−Ni (oxy)hydroxide catalysts using operando X‐ray absorption spectroscopy, alongside other experiments and theoretical calculations. The Debye–Waller factors obtained from extended X‐ray absorption fine structure analyses reflect the degree of structural disorder and exhibit a robust correlation with the intrinsic OER activities of the electrocatalysts. The enhanced OER activity of in situ‐generated metal (oxy)hydroxides derived from different pre‐catalysts is linked to increased structural disorder, offering a promising approach for designing efficient OER electrocatalysts. This strategy may inspire similar investigations in related electrocatalytic energy‐conversion systems.

Correlating Structural Disorder in Metal (Oxy)hydroxides and Catalytic Activity in Electrocatalytic Oxygen Evolution.

Understanding the correlation between the structural evolution of electrocatalysts and their catalytic activity is both essential and challenging. In this study, we investigate this correlation in the context of the oxygen evolution reaction (OER) by examining the influence of structural disorder during and after dynamic structural evolution on the OER activity of Fe-Ni (oxy)hydroxide catalysts using operando X-ray absorption spectroscopy, alongside other experiments and theoretical calculations. The Debye-Waller factors obtained from extended X-ray absorption fine structure analyses reflect the degree of structural disorder and exhibit a robust correlation with the intrinsic OER activities of the electrocatalysts. The enhanced OER activity of in situ-generated metal (oxy)hydroxides derived from different pre-catalysts is linked to increased structural disorder, offering a promising approach for designing efficient OER electrocatalysts. This strategy may inspire similar investigations in related electrocatalytic energy-conversion systems.

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

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

Questing for High-Performance Electrocatalysts for Oxygen Evolution Reaction: Importance of Chemical Complexity, Active Phase, and Surface-Adsorbed Species.

Rational design of advanced electrocatalysts for oxygen evolution reaction (OER) is of vital importance for the development of sustainable energy. Entropy engineering is emerging as a promising approach for the design of efficient OER electrocatalysts. However, other multi-anion/cation electrocatalysts with compositional complexity, particularly the medium-entropy and other non-equimolar cation/anion complex electrocatalysts, have not received noteworthy attention. In this perspective, we review and highlight the importance of compositionally complex catalysts and propose a concept of chemical complexity to correlate the OER catalytic activity with the contributions from the pairwise cation-anion interactions. Then, we offer a new view on the active catalytic sites being the hydroxylated reacting interface in an alkaline solution. Further, we argue that the common discrepancies between computationally predicted OER activities and experimental results stem from lack of considerations of surface-adsorbed species in modeling the active catalytic phases or sites. This perspective would facilitate achieving a renewed and profound understanding of the OER mechanism and promote efficient design of OER electrocatalysts for renewable energy conversion and storage.

In-based coordination polymer-derived carbon nanoribbons with abundant CoP nanoparticles in carbon nanotubes for water oxidation.

The sluggish oxygen evolution reaction (OER) in overall electrocatalytic water splitting poses a significant challenge in hydrogen production. A series of transition metal phosphides are emerging as promising electrocatalysts, effectively modulating the charge distribution of surrounding atoms for OER. In this study, a highly efficient OER electrocatalyst (CoP-CNR-CNT) was successfully synthesized through the pyrolysis and phosphatization of a Co-doped In-based coordination polymer, specifically InOF-25. This process resulted in evenly dispersed CoP nanoparticles encapsulated in coordination polymer-derived carbon nanoribbons. The synthesized CoP-CNR-CNT demonstrated a competitive OER activity with a smaller overpotential (η10) of 295.7 mV at 10 mA cm-2 and a satisfactory long-term stability compared to the state-of-the-art RuO2 (η10 = 353.7 mV). The high OER activity and stability can be attributed to the high conductivity of the carbon network, the abundance of CoP particles, and the intricate nanostructure of nanoribbons/nanotubes. This work provides valuable insights into the rational design and facile preparation of efficient non-precious metal-based OER electrocatalysts from inorganic-organic coordination polymers, with potential applications in various energy conversion and storage systems.

Low-Pressure Plasma-Processed NiCo Metal–Organic Framework for Oxygen Evolution Reaction and Its Application in Alkaline Water Electrolysis Module

Ar, Ar/H2 (95:5), and Ar/O2 (95:5) plasmas are used for treating the NiCo metal–organic framework (MOF), and the plasma-processed NiCo MOF is applied for catalyzing the oxygen evolution reaction (OER) in a 1 M KOH electrolyte. Linear sweep voltammetry measurements show that after plasma treatment with Ar/H2 (95:5) and Ar gases, the overpotential reaches 552 and 540 mV, respectively, at a current density of 100 mA/cm2. The increase in the double-layer capacitance further confirms the enhanced oxygen production activity. We test the Ar plasma-treated NiCo MOF as an electrocatalyst at the OER electrode and Ru as an electrocatalyst at the hydrogen evolution reaction (HER) electrode in the alkaline water electrolysis module. The energy efficiency of the electrolyzer with the Ar plasma-processed NiCo-MOF catalyst increases from 54.7% to 62.5% at a current density of 500 mA/cm2 at 25 °C. The alkaline water electrolysis module with the Ar plasma-processed catalyst also exhibits a specific energy consumption of 5.20 kWh/m3 and 4.69 kWh/m3 at 25 °C and 70 °C, respectively. The alkaline water electrolysis module performance parameters such as the hydrogen production rate, specific energy consumption, and energy efficiency are characterized at temperatures between 25 °C and 70 °C. Our experimental results show that the NiCo MOF is an efficient OER electrocatalyst for the alkaline water electrolysis module.