Oxygen Evolution Reaction Research Articles

XPS investigation of CuxO-functionalized amorphous carbon nitride

In this work, we report the x-ray photoelectron spectroscopy characterization of a novel nanocomposite (photo)electrocatalyst for the oxygen evolution reaction, based on amorphous carbon nitride (aCN) functionalized with CuxO nanoparticles (NPs). The specimen has been fabricated employing two sequential plasma-assisted processes, involving the initial aCN deposition onto conductive glass via magnetron sputtering, followed by carbon nitride functionalization with CuxO (x = 1, 2) NPs by radio frequency-sputtering. The results reported herein include the survey spectrum and the high-resolution C 1s, N 1s, O 1s, Cu 2p, and Cu LMM signals. The most significant spectral features are analyzed and critically discussed.

Recent Advances in Rechargeable Zn-Air Batteries

Rechargeable Zn-air batteries are considered to be an effective energy storage device due to their high energy density, environmental friendliness, and long operating life. Further progress on rechargeable Zn-air batteries with high energy density/power density is greatly needed to satisfy the increasing energy conversion and storage demands. This review summarizes the strategies proposed so far to pursue high-efficiency Zn-air batteries, including the aspects of the electrocatalysts (from noble metals to non-noble metals), the electrode chemistry (from the oxygen evolution reaction to the organic oxidation reaction), electrode engineering (from powdery to free-standing), aqueous electrolytes (from alkaline to non-alkaline) and the battery configuration (from liquid to flexible). An essential evaluation of electrochemistry is highlighted to solve the challenges in boosting the efficiency of rechargeable metal-air batteries. In the end, the perspective on current challenges and future research directions to promote the industrial application of rechargeable Zn-air batteries is provided.

Bamboo-Like Carbon Nanotube-Encapsulated Fe2C Nanoparticles Activate Confined Fe2O3 Nanoclusters Via d-p-d Orbital Coupling for Alkaline Oxygen Evolution Reaction.

The efficient anion exchange membrane water electrolysis is challenging with low cell voltage and long-term stability at large current density, due to the unstable anodic oxygen evolution reaction (OER). Fe-based electrocatalysts are potential candidates for the anodic OER. In Fe-based materials, iron oxides always show better stability in alkaline solution but lower OER activity. However, the catalysts in previous study are difficult to continuously and effectively activate iron oxides supported on carbon during electrocatalysis. Herein, a new class of electrocatalyst: bamboo-like carbon nanotubes (B-CNT)-encapsulated Fe2C nanoparticles (NPs) supported Fe2O3 nanoclusters (NCs), named Fe2O3/B-CNT@Fe2C is reported. Theoretical calculations and experimental results reveal that B-CNT-encapsulate Fe2C NPs activate Fe2O3 NCs by the d-p-d orbital coupling, thereby weakening the adsorption of OOH* intermediate during OER process. The electrolyzer based on the electrocatalyst requires only 1.48 V to reach 1.0 A cm-2 and shows a long-term stability at 1.0 A cm-2 for 1600 h, comparable to the best-reported values for the anion exchange membrane water electrolyzer (AEMWE).

Structural and Phase Engineering of a Hierarchical 2D-2D Nickel MOF/Hydroxide-Derived Ni0.85Se/NiTe2 Heterointerface for Robust HER, OER, and Overall Water Splitting.

The development of a nonnoble metal-based cost-effective, efficient, and durable bifunctional electrocatalyst is crucial to achieving the goal of carbon neutrality. In this study, a structural and interfacial engineering approach is employed to design a 2D-2D hierarchical nickel MOF/nickel hydroxide-derived nickel selenide/nickel telluride dual-phase material through a single-step selenotellurization process. The rational design of highly ordered nanoarchitectures provides well-defined voids and ample pathways for ion diffusion. Furthermore, hierarchical nickel selenide/nickel telluride works synergistically at heterojunctions, providing a local ion enrichment mechanism for the catalytic process. As a result, Ni0.85Se/NiTe2@Ni-NH@CC needs an overpotential of 69 and 240 mV to deliver a current density of 10 mA cm-2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, with an outstanding stability observed for over 100 h. Moreover, the Ni0.85Se/NiTe2@Ni-NH@CC (+, -) device exhibits excellent overall water-splitting performance with a cell voltage of 1.50 V at 10 mA cm-2 and can be operated steadily for >100 h at 100 mA cm-2. Density functional theory (DFT) calculations indicate favorable kinetics for H-adsorption at the selenotelluride heterojunction, thereby promoting the HER. This work highlights a new approach for designing a unique nanoarchitecture of MOF/hydroxide-derived selenotelluride heterojunctions for high-efficiency energy conversion applications.

CeO2‐Accelerated Surface Reconstruction of CoSe2 Nanoneedle Forms Active CeO2@CoOOH Interface to Boost Oxygen Evolution Reaction for Water Splitting

AbstractInterface engineering is an efficient strategy to create high‐performance electrocatalysts for water splitting. In the present work, CeO2@CoSe2 nanoneedle on carbon cloth (CeO2@CoSe2/CC) demonstrates high efficiency for oxygen evolution reaction (OER) and water splitting. CeO2 with abundant O vacancies facilitates the adsorption of OH− and boosts the reconstruction of CoSe2 into CoOOH at lower potentials. The in situ generated active CeO2@CoOOH heterointerface upshifts the d‐band center of Co site, thereby decreasing the free energy of rate‐determining step (RDS) (*O to *OOH) during the OER process. It delivers a low OER overpotential of 245 mV at 10 mA cm−2. CeO2@CoSe2/CC is also found to be active for hydrogen evolution reaction (HER, 138 mV overpotential at 10 mA cm−2), profiting from CeO2‐facilitated *H2O dissociation and *H adsorption on CoSe2. The overall water splitting is achieved over the CeO2@CoSe2/CC bifunctional electrode with a low electrolysis voltage of 1.54 V at 10 mA cm−2. This work offers valuable insights into CeO2‐assisted surface reconstruction as well as provides water electrolysis catalysts through interface engineering.

Cation Migration-Induced Lattice Oxygen Oxidation in Spinel Oxide for Superior Oxygen Evolution Reaction.

Activating the lattice oxygen can significantly improve the kinetics of oxygen evolution reaction (OER), however, it often results in reduced stability due to the bulk structure degradation. Here, we develop a spinel Fe0.3Co0.9Cr1.8O4 with active lattice oxygen by high-throughput methods, achieving high OER activity and stability, superior to the benchmark IrO2. The oxide exhibits an ultralow overpotential (190 mV at 10 mA cm-2) with outstanding stability for over 170 h at 100 mA cm-2. Soft X-ray absorption- and Raman-spectroscopies, combined with 18O isotope-labelling experiments, reveal that lattice oxygen activation is driven by Cr oxidation, which induces a cation migration from CrO6octahedrons toCrO4tetrahedrons. The geometry conversion creates accessible non-bonding oxygen states, crucial for lattice oxygen oxidation. Upon oxidation, peroxo O-O bond is formed and further stabilized by Cr6+ (CrO4 tetrahedra) via dimerization. This work establishes a new approach for designing efficient catalysts that feature active and stable lattice oxygen without compromising structural integrity.

Cation Migration‐Induced Lattice Oxygen Oxidation in Spinel Oxide for Superior Oxygen Evolution Reaction

Activating the lattice oxygen can significantly improve the kinetics of oxygen evolution reaction (OER), however, it often results in reduced stability due to the bulk structure degradation. Here, we develop a spinel Fe0.3Co0.9Cr1.8O4 with active lattice oxygen by high‐throughput methods, achieving high OER activity and stability, superior to the benchmark IrO2. The oxide exhibits an ultralow overpotential (190 mV at 10 mA cm–2) with outstanding stability for over 170 h at 100 mA cm–2. Soft X‐ray absorption‐ and Raman‐spectroscopies, combined with 18O isotope‐labelling experiments, reveal that lattice oxygen activation is driven by Cr oxidation, which induces a cation migration from CrO6 octahedrons to CrO4 tetrahedrons. The geometry conversion creates accessible non‐bonding oxygen states, crucial for lattice oxygen oxidation. Upon oxidation, peroxo O–O bond is formed and further stabilized by Cr6+ (CrO4 tetrahedra) via dimerization. This work establishes a new approach for designing efficient catalysts that feature active and stable lattice oxygen without compromising structural integrity.

Maximizing Bifunctionality for Overall Water Splitting by Integrating H2 Spillover and Oxygen Vacancies in CoPBO/Co3O4 Composite Catalyst

In the pursuit of utilizing renewable energy sources for green hydrogen (H2) production, alkaline water electrolysis has emerged as a key technology. To improve the reaction rates of overall water electrolysis and simplify electrode manufacturing, development of bifunctional electrocatalysts is of great relevance. Herein, CoPBO/Co3O4 is reported as a binary composite catalyst comprising amorphous (CoPBO) and crystalline (Co3O4) phases as a high‐performing bifunctional electrocatalyst for alkaline water electrolysis. Owing to the peculiar properties of CoPBO and Co3O4, such as complementing Gibbs free energy values for H‐adsorption (ΔGH) and relatively smaller difference in their work functions (ΔΦ), the composite exhibits H2 spillover (HS) mechanism to facilitate the hydrogen evolution reaction (HER). The outcome is manifested in the form of a low HER overpotential of 65 mV (at 10 mA cm−2). Moreover, an abundant amount of surface oxygen vacancies (Ov) are observed in the same CoPBO/Co3O4 composite that facilitates oxygen evolution reaction (OER) as well, leading to a mere 270 mV OER overpotential (at 10 mA cm−2). The present work showcases the possibilities to strategically design non‐noble composite catalysts that combine the advantages of HS phenomenon as well as Ov to achieve new record performances in alkaline water electrolysis.

Improved Catalyst Performance for the Oxygen Evolution Reaction under a Chiral Bias

Improved Catalyst Performance for the Oxygen Evolution Reaction under a Chiral Bias

Electron‐Penetrating in Heterointerface Engineering for Oxygen Evolution Reaction in Seawater Splitting

AbstractThe interfacial electric field (IEF) between heterogeneous units plays an important role in the electronic modulation of active centers during oxygen evolution reaction (OER). However, the weak electronic coupling between spatially separated IEFs limits the deep activation of metal sites on the surface of the catalyst. Herein, a proof‐of‐concept strategy is provided that imbed MS2 (M = Ni3Fe) species with high spin Fe orbits into heterogeneous units to promote the electron penetrating between IEFs. By designing a Fe2O3@MS/MS2@MOy model catalyst, the electronic interaction between adjacent IEFs is effectively enhanced for the deep oxidation of bimetals on the surface, breaking the competing relationship between adsorbed evolution mechanism (AEM) and lattice oxygen mechanism (LOM) of catalysts during OER. As a result, the onset overpotential of the synthesized electrode is only 171 mV, and it maintains excellent stability for more than 2300 h at a current density of 10 mA cm−2 in 1 M KOH + 0.5 M NaCl electrolyte.

Enhance the Proportion of Fe3+ in NiFe-Layered Double Hydroxides by utilizing Citric Acid to Improve the Efficiency and Durability of the Oxygen Evolution Reaction.

NiFe-layered double hydroxides (NiFe-LDH) are a type of catalyst known for their exceptional catalytic performance during the oxygen evolution reaction (OER). In this study, citric acid was incorporated into the synthesis process of NiFe-LDH, resulting in the NiFe-LDH-CA catalyst with superior OER performance. The catalytic efficacy was evaluated using linear sweep voltammetry (LSV), which demonstrated a significant reduction in the overpotential for OER from 320 mV to 240 mV at a current density of 100 mA cm-2. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) indicate that the distribution of nickel valence states showed no significant difference between two samples. However, the NiFe-LDH-CA exhibits a markedly higher proportion of Fe3+ ions in its iron content. In-situ Raman spectroscopes reveal that Fe3+ broadens the redox potential of nickel and Pourbaix diagrams indicate that higher Fe3+ levels could facilitate the interaction with oxygen active sites. Based on the analysis of test data, we propose a hypothesis that the high proportion of Fe3+ in catalysts may accelerate the oxygen evolution process by modulating the redox potential of nickel and engaging with reactive oxygen species. This provides valuable insights into how to improve the reaction rate of nickel-based catalysts.

Targeted Topological Routine Regulation of RuNiOx Precursors for Excellent Alkaline Overall Water Splitting

Designing efficient and stable electrocatalysts for the hydrogen and oxygen evolution reactions (HER and OER) is crucial for green hydrogen production via the water‐splitting system. The bifunctional electrocatalyst offers a promising strategy due to the simplified preparation process and reduced expenses. However, the single‐component bifunctional catalysts often struggle to match the redox potential of water and to achieve proper adsorption/desorption of Gibbs free energy for both H and O intermediates simultaneously. Herein, through precisely controlling the topological transformation path of the RuNiOx precursor, we successfully prepared high‐performance RuNi/Ni and Ru/NiO heterostructure electrocatalysts for the HER and OER, respectively. The energy level matching between the fabricated electrocatalyst and water oxidation/reduction potential confirms the feasibility of HER and OER. The synergistic effect between the active sites ensures rapid, intermediate adsorption/desorption kinetics. As a result, the assembled alkaline overall water splitting setup achieves a current density of 1 A cm‐2 at 2 V and maintains stable operation at 100 mA cm‐2 for 100 hours.

In Situ Anodic Transition and Cathodic Contamination Affect the Overall Voltage of Alkaline Water Electrolysis

NiFe (oxy)hydroxide has been widely used as a benchmark anodic catalyst for oxygen evolution reactions (OERs) in alkaline water electrolysis devices; however, the energy saving actually takes contributions from both the anodic OER and cathodic hydrogen evolution reaction (HER). In this work, we observe the catalytic promotion upon the in situ-derived NiFe (oxy)hydroxide from the NiFe alloy monolithic electrode and also point out that the coupled nickel cathode is contaminated, leading to the loss of HER activity and a reduction in overall efficiency. It is found that Ni2+ and Fe3+ cations are inevitably detached from the anode into the electrolyte and electrodeposited on the nickel cathode after the three-month industrial simulation. This research presents the significant enhancement of the oxygen evolution catalysis using an in situ aging process and emphasizes that the catalytic application should not only be isolated on the half reaction, but a reasonable coupled electrode match to get rid of the contamination from the electrolyte is also of great significance to sufficiently present the intrinsic catalytic yielding for the real application.

3D-stacked electrospun iron-doped nickel cobalt oxide nanofibers as integrated electrodes for anion exchange membrane water electrolysis

The commercialization of anion-exchange membrane water electrolysis (AEMWE) requires the development of highly active, stable, and cheap anode catalysts for the oxygen evolution reaction (OER). In this study, we proposed electrospun iron-doped NiCo2O4 (NCO) nanofibers on nickel foam (NF) and evaluated the performances of the resulting samples (FeX-NCO/NF; X = iron loading in NCO (0, 5, 10, and 15 at %)) as unitized anodes for the OER. Among the fabricated electrodes, Fe10-NCO/NF exhibited the lowest overpotential of 352 mV at a current density of 50 mA cm−2 in a half-cell test owing to its improved intrinsic activity. In an AEMWE single-cell test, Fe10-NCO/NF as anode showed high current density (932 mA cm-2 at 1.8 V) and long-term stability for 150 h The improved AEMWE performance of Fe10-NCO/NF was attributed to efficient mass transport enabled by superhydrophilic three-dimensional porous structure featuring stacked nanofibers.

Tracking Water Dissociation on RuO2(110) Using Atomic Force Microscopy and First-Principles Simulations.

The interaction between interfacial water and transition metal oxides is a primary enabling step for the oxygen evolution reaction (OER). RuO2 is a prototypical OER electrocatalyst whose ability to activate interfacial water molecules is essential to its OER activity. We image the dissociation of surface water into OH* and O* on RuO2(110), where * denotes adsorbed species, using atomic force microscopy. Starting from the surface-bound water molecules, which form a one-dimensional network along the rows of Ru surface sites, increasing the oxidative potential strips hydrogen away and transforms the water molecules into OH* and O*. This oxidative step changes the pattern of the adsorbates from one- to two-dimensional. First-principles calculations with interfacial polarization, capacitive charging, and adsorbate interactions attribute this evolution to the cooperative dehydrogenation of adsorbed water and OH* on RuO2. We use these results to map the surface phase diagram of RuO2(110) and provide a quantitative interpretation of its cyclic voltammetry. Our result provides the visualization of the water dissociation on a conductive oxide surface, a critical step in the OER, and demonstrates that the water activation is a collective phenomenon at RuO2(110) electrodes.

Enhancing Oxygen Reduction Reaction Electrocatalytic Performance of Nickel‐Nitrogen‐Carbon Catalysts through Coordination Environment Engineering†

Comprehensive SummarySingle‐atom catalysts (SACs) have attracted significant attention due to their high atomic utilization and tunable coordination environment. However, the catalytic mechanisms related to the active center and coordination environment remain unclear. In this study, we systematically investigated the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalytic activities of NiN4, NiN3, NiN3H2, NiN4X, NiN3X, and NiN3H2X (X denotes axial ligand) through density functional theory (DFT) calculations. This study unveils two distinct reaction pathways for ORR and OER, involving proton‐electron pairs adsorbed from both the solution and the catalyst surface. The overpotential is the key parameter to evaluate the catalytic performance when proton‐electron pairs are adsorbed from the solution. NiN3 and NiN3H2 show promise as pH‐universal bifunctional electrocatalysts for both ORR and OER. On the other hand, when proton‐electron pairs are adsorbed from the catalyst surface, the reaction energy barrier becomes the crucial metric for assessing catalytic activity. Our investigation reveals that NiN3H2 consistently exhibits optimal ORR activity across a wide pH range, regardless of the source of proton‐electron pair (solvent or catalyst surface).

Research Progress of High-entropy Oxides for Electrocatalytic Oxygen Evolution Reaction.

High-entropy oxides (HEOs), similar to high-entropy materials (HEMs), have "four-core effects", i. e., high-entropy effect, delayed diffusion effect, lattice distortion effect and cocktail effect, which have attracted more and more attention in the scientific field of renewable energy technology due to their unique structural characteristics, variable chemical composition and corresponding functional properties. HEOs have become potential candidates for electrocatalytic oxygen evolution reaction (OER), which is a key half reaction for electrolytic CO2, nitrogen reduction, and water electrolysis. However, the precise synthesis of HEOs with a wide range of components and structures is challenging, not to mention their active and stable operation for OER. In this paper, we review the recent advancements in the electrocatalytic oxygen evolution facilitated by HEOs in water electrolysis. We analyze these developments from the perspectives of activity and stability in acid and alkaline conditions, respectively. Furthermore, we summarize the design from the aspect of element composition, structure, morphology, and catalyst-support interactions, along with related reaction mechanism of HEOs. Additionally, we discuss the current challenges faced by HEOs in the field of OER and suggest potential directions for the future development of HEOs beyond water electrolysis application.

Role of Surfactants on Electrocatalytic Activity of Co/Al Layered Double Hydroxides For Hydrogen and Oxygen Generation

AbstractLayered double hydroxides (LDHs) have recently attracted much attention in the scientific community as a prominent catalyst for oxygen evolution reaction (OER) because they are economical, extremely stable, and highly active. Literature on LDH alone and their hybrids for catalyzing water oxidation are readily available, but LDH catalyzing hydrogen evolution reaction (HER) is meager. Here, we synthesized Co/Al‐based LDH systems that efficiently perform as bifunctional electrocatalysts for both HER and OER. Exfoliation of this layered material via anion intercalation into a few layers further enhanced its activity. In this work, we reported the synthesis of Co/Al LDHs via coprecipitation followed by hydrothermal method and different surfactant‐functionalized LDHs (with anionic surfactant: SDS, cationic surfactant: CTAB, and nonionic surfactant: PEG 4000). SDS‐modified LDH (s LDH) showed notable stability and competent results in hydrogen evolution in addition to oxygen evolution. The exfoliation of s LDH caused enhancement in the high specific surface area about 6.8 times compared to pristine LDH, as evident from BET data. The onset potential for HER as obtained from the polarization curve for s LDH is −0.41 V versus RHE, with Tafel slope of 67.4 mV/dec. Similarly, OER onset potential and corresponding Tafel slope are 1.53 V versus RHE at 10 mA/cm2 and 90.2 mV/dec, respectively.

Isolated FeN3 sites anchored hierarchical porous carbon nanoboxes for hydrazine‐assisted rechargeable Zn‐CO2 batteries with ultralow charge voltage

AbstractZn‐CO2 batteries (ZCBs) are promising for CO2 conversion and electric energy release. However, the ZCBs couple the electrochemical CO2 reduction (ECO2R) with the oxygen evolution reaction and competitive hydrogen evolution reaction, which normally causes ultrahigh charge voltage and CO2 conversion efficiency attenuation, thereby resulting in ~90% total power consumption. Herein, isolated FeN3 sites encapsulated in hierarchical porous carbon nanoboxes (Fe‐HPCN, derived from the thermal activation process of ferrocene and polydopamine‐coated cubic ZIF‐8) were proposed for hydrazine‐assisted rechargeable ZCBs based on ECO2R (discharging process: CO2 + 2H+ → CO + H2O) and hydrazine oxidation reaction (HzOR, charging process: N2H4 + 4OH− → N2 + 4H2O + 4e−). The isolated FeN3 endows the HzOR with a lower overpotential and boosts the ECO2R with a 96% CO Faraday efficiency (FECO). Benefitting from the bifunctional ECO2R and HzOR catalytic activities, the homemade hydrazine‐assisted rechargeable ZCBs assembled with the Fe‐HPCN air cathode exhibited an ultralow charge voltage (decreasing by ~1.84 V), excellent CO selectivity (FECO close to 100%), and high 89% energy efficiency. In situ infrared spectroscopy confirmed that Fe‐HPCN can generate rate‐determining *N2 and *CO intermediates during HzOR and ECO2R. This paper proposes FeN3 centers for bifunctional ECO2R/HzOR performance and further presents the pioneering achievements of ECO2R and HzOR for hydrazine‐assisted rechargeable ZCBs.

Nickel Phosphide: The Effect of Phosphorus Content on the Activity and Stability toward Oxygen Evolution Reaction in Alkaline Medium.

In this work a systematic study of the effect of the metal to phosphorus ratio in Ni-P nanoparticles on their catalytic activity with respect to the OER is reported. To this end, nickel phosphide nanoparticles are synthesized through two different synthesis routes, one involving in-situ phosphidation and one involving ex-situ phosphidation. In-situ phosphidation is performed via two steps route in a one-pot synthesis, in which Ni nanoparticles are formed at 220 °C, but not isolated, and then transformed to phase-pure either Ni12P5 or Ni2P nanocrystallites. In the second synthesis method (ex-situ phosphidation), nickel nanoparticles with an excess amount of trioctylphosphine (TOP) as a capping agent are synthesized and separated from the solution, then subsequently annealed in three different atmospheres, leading to the formation of three types of NixPy viz. [NixPy-H2/Ar], [NixPy-Ar], and [NixPy-air]. [NixPy-air] nanoparticles shows the best electrocatalytic activity among the annealed nanoparticles in Ar and H2/Ar but lower than Ni12P5 nanoparticles. However, [NixPy-air] shows very high stability in comparison with other synthesized nanoparticles. Moreover, the effect of the adventitious and spiked Fe in the electrolyte is studied on the electrocatalytic activity of all synthesized nanoparticles.