High Oxygen Evolution Reaction Activity Research Articles

Ba-leaching-initiated structural destabilization of perovskite Ruthenates during the oxygen evolution reaction

The destabilization of a lattice structure during the oxygen evolution reaction (OER) is one of the most essential aspects for designing and realizing highly efficient electrocatalysts. However, the underlying mechanism of structural evolution or degradation at the microscopic scale on the electrocatalyst surface during the OER has not been elucidated because of the sluggish yet dynamic character of the reaction. To address this issue, the direct observation of the unstable electrocatalytic activity is necessary. In this study, we demonstrate that the structural destabilization of epitaxial cubic perovskite BaRuO3 thin films during the OER originates from Ba leaching, Ru dissolution, and oxygen vacancy. A thin film geometry is adopted to selectively visualize the structural decomposition at the well-defined sample surface. The cubic BaRuO3 thin film initially exhibits high OER activity, which drastically decreases even during the first cyclic voltammetry cycle and is completely lost after the first cycle. The OER activity loss is closely related to the generation of structural defects on the surface, indicating the absence of the Ba and Ru atoms. This study proposes the mechanism underlying the OER activity that can be extended to elucidate the structural destabilization in various Ru- and Ir-based oxide catalysts.

Stepwise Understanding on Hydrolysis Formation of the IrOx Nanoparticles as Highly Active Electrocatalyst for Oxygen Evolution Reaction

AbstractIn this study, we have investigated the synthesis of supported iridium oxide (IrOx) nanoparticles (NPs) through hydrolysis in a surfactant-free aqueous bath as a possible route for the large-scale production of highly active electrocatalyst for oxygen evolution reaction (OER) in acidic water electrolyzers. The process involves (i) formation of Ir-hydroxides complex from an Ir precursor in basic media followed by (ii) protonation in acidic media to form colloidal hydrated IrOx NPs and (iii) conversion and deposition of IrOx NPs on the surface of carbon or TiN support by probe sonication. The IrOx NPs produced through hydrolysis route form highly stable colloidal solution. Since it is essential to precipitate the catalyst NPs from the colloidal solution for their use in water electrolyzer electrode development, here, we investigate the optimal reaction conditions, e.g., pH, temperature, time, and presence of support, for efficient synthesis of the catalyst NPs. The reaction intermediates formed at different reaction steps are explored to get insights into the chemistry of the process. Under the optimal synthesis conditions, 100% precipitation of IrOx NPs was achieved. Further, the precipitated TiN supported IrOx NPs exhibited high OER activity, superior to that of the commercial benchmark IrO2 electrocatalyst. The study provides a scalable synthesis route for highly active, low Ir-content OER electrocatalysts for acidic water electrolyzers. Graphical Abstract

Metallic Ru─Ru Interaction in Ruthenium Oxide Enabling Durable Proton Exchange Membrane Water Electrolysis.

Developing efficient and robust electrocatalysts toward the oxygen evolution reaction (OER) is critical for proton exchange membrane water electrolysis (PEMWE). RuO2 possesses intrinsically high OER activity, but the concurrent electrochemical dissolution leads to rapid deactivation. Here a unique RuO2 catalyst containing metallic Ru─Ru interactions (m-RuO2) is reported, which maintains stability in practical PEMWE for 100h at 60 °C and 1 A cm-2. Experimental and theoretical investigations suggest that the presence of Ru─Ru interactions significantly increases the energy barrier for the formation of RuO2(OH)2, which is a key intermediate for Ru dissolution, and hence substantially mitigates the electrochemical corrosion of m-RuO2. Meanwhile, the Ru4d band center downshifts, accordingly, ensuring the high OER activity, and the participation of lattice oxygen in the OER is also suppressed at the Ru─Ru sites, further contributing to the enhanced durability. Interestingly, such enhanced stability is also dependent on the size of metallic Ru─Ru cluster, where the energy barrier is further increased for Ru3, but is decreased for Ru5. These results highlight the significance of local coordination structure modulation on the electrochemical stability of RuO2 and open a feasible avenue toward the development of robust OER electrocatalysts for high-performance PEMWE.

Cost-efficient sunlight-driven thermoelectric electrolysis over Mo-doped Ni5P4 nanosheets for highly efficient alkaline water/seawater splitting

Thermoelectric water spitting to hydrogen systems has great potential in the production of environment-friendly fuel using renewable solar energy in the future. In this work, we prepared porous nanosheet Mo doping Ni5P4 catalysts on nickel foam with efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in alkaline media. DFT calculations and experimental studies have shown that Mo doping deadeneds the interaction between H and O atomic orbitals of transition state water molecules, effectively weakening the activation energy of H2O dissociation. Therefore, Mo doping is favorable for enhancing HER activity with overpotential at 10 mA cm–2 of 93 mV and Tafel slope of 40.1 mV dec–1 in 1 M KOH. Besides, it exhibits high alkaline OER activity with an ultra-low overpotential of 200 mV at 10 mA cm–2. Moreover, this catalyst only needs 1.537 V in a dual-electrode configuration of the electrolytic cell, which is much lower than the commercial Pt/C-RuO2 couple (1.614 V). In addition, we have developed and constructed a solar thermoelectric generator (TEG) that is capable of floating on water. This TEG has a continuous power output and an exceptionally long lifespan, providing a stable power supply to the synthesized catalyst electrolyzer. It can produce a maximum power output of over 90 mW, meeting the requirement of converting solar radiation heat into usable electricity. As a result, the system achieves productivity of 0.11 mL min–1 H2. This solar thermal energy conversion technology shows the possibility of large-scale industrial production of H2 and provides a new idea for exploring heat source utilization.

Hydrogen Bonds Induced Ultralong Stability of Conductive π-d Conjugated FeCo3(DDA)2 with High OER Activity.

Conductive π-d conjugated metal-organic frameworks (MOFs) have attracted wide concerns in electrocatalysis due to their intrinsic high conductivity. However, the poor electrocatalytic stability is still a major problem that hinders the practical application of MOFs. Herein, a novel approach to enhancing the stability of MOF-based electrocatalyst, namely, the introduction of hydrogen bonds (H-bonds), is reported. Impressively, the π-d conjugated MOF FeCo3(DDA)2 (DDA = 1,5-diamino-4,8-dihydroxy-9,10-anthraceneedione) exhibits ultrahigh oxygen evolution reaction (OER) stability (up to 2000h). The experimental studies demonstrate that the presence of H-bonds in FeCo3(DDA)2 is responsible for its ultrahigh OER stability. Besides that, FeCo3(DDA)2 also displays a prominent OER activity (an overpotential of 260mV vs reversible hydrogen electrode (RHE) at a current density of 10mA cm-2 and a Tafel slope of 46.86mV dec-1). Density functional theory (DFT) calculations further indicate that the synergistic effect of the Fe and Co sites in FeCo3(DDA)2 contributes to its prominent OER performance. This work provides a new avenue of boosting the electrocatalytic stability of conductive π-d conjugated MOFs.

Towards atom-level understanding of metal oxide catalysts for the oxygen evolution reaction with machine learning

Green hydrogen production is crucial for a sustainable future, but current catalysts for the oxygen evolution reaction (OER) suffer from slow kinetics, despite many efforts to produce optimal designs, particularly through the calculation of descriptors for activity. In this study, we develop a dataset of density functional theory calculations of bulk and surface perovskite oxides, and adsorption energies of OER intermediates, which includes compositions up to quaternary and facets up to (555). We demonstrate that per-site properties of perovskite oxides such as Bader charge or band center can be tuned through element substitution and faceting, and develop a machine learning model that accurately predicts these properties directly from the local chemical environment. We leverage these per-site properties to identify promising perovskites with high theoretical OER activity. The identified design principles and promising materials provide a roadmap for closing the gap between current artificial catalysts and biological enzymes such as photosystem II.

Unveiling the Potential of Covalent Organic Framework Electrocatalyst for Enhanced Oxygen Evolution.

The potential for sustainable energy and carbon neutrality has expanded with the development of a highly active electrocatalyst for the oxygen evolution reaction (OER). Covalent Organic Frameworks (COF) have recently garnered attention because of their enormous potential in a number of cutting-edge application sectors, such as gas storage, sensors, fuel cells, and active catalytic supports. A simple and effective COF constructed and integrated by post-alteration plasma modification facilitates high electrocatalytic OER activity under alkaline conditions. Variations in parameters such as voltage and treatment duration have been employed to enhance the factor that demonstrates high OER performance. The overpotential and Tafel slope are the lowest of all when using an optimized parameter, such as plasma treatment for 30 min utilizing 6 kV of voltage, PT-30 COF, measuring 390 mV at a current density of 10 mA.cm-2 and 69 mV.dec-1, respectively, as compared to 652 mV and 235 mV.dec-1 for the Pristine-COF. Our findings provide a method for broadening the scope by post-functionalizing the parent framework for effective water splitting.

Template-assisted strategy for synthesizing transition metal oxyhydroxide for high-efficiency oxygen evolution reaction

Oxyhydroxides have been widely recognized as the true active species for oxygen evolution reaction (OER), while most of them are created via the complicated and time-consuming electrochemical activation process. Here, we develop a facile template-mediated method for directly synthesizing highly active oxyhydroxides toward OER. The optimal FeCoOOH prepared via using Cu2O as a sacrificial template could exhibit outstanding electrocatalytic OER performance, delivering a current density of 10 mA cm−2 with the overpotential of merely 320 mV, and a corresponding Tafel slope of 77.5 mV dec−1. Detailed mechanism study outlines that the extraordinary OER performance of such FeCoOOH originated from the intrinsically high OER activity of oxyhydroxide and the high specific surface area of the particular architecture. This work demonstrates a simple and direct route for the successful fabrication of highly active oxyhydroxides, which may open a new way for the synthesis of other active species.

NdMn1.5Ru0.5O5, a high-performance electrocatalyst with low Ru content for acidic oxygen evolution reaction

A mixed oxide with the crystal structure of the DyMn2O5 family, namely NdMn1.5Ru0.5O5, is reported active for the oxygen evolution reaction (OER) in acidic media. NdMn1.5Ru0.5O5 displays high OER activity of 500 A gRu−1 at 1.5 V. Moreover, is more stable than most Ru oxides reported to date, remaining active for more than 500 cycles between 1.1. and 1.7 V at low scan rate of 10 mV s−1. The high activity and stability are attributed to the Ru cations, as NdMn2O5 exhibits very low OER activity. NdMn1.5Ru0.5O5 has particularly short Ru–Ru distances of 2.60 Å, a value close to the Ru–Ru metallic distances around 2.642 Å. The high activity and durability of NdMn1.5Ru0.5O5 for the OER are also demonstrated in a proton exchange membrane water electrolysis cell by producing a low-loaded anode electrode with 0.5 mgRucm−2. The cell achieves 1.97 V at 0.5 A cm−2, consistent with the performances reported for Ru-based catalysts but with lower Ru loading. This performance is maintained during 100 h of operation. Additionally, NdMn1.5Ru0.5O5 displays visible ORR activity in acidic media, recording an onset potential of 0.85 V at 0.1 mA cm−2. It is noteworthy to highlight the extreme rarity of bifunctional ORR/OER catalysts acidic media.

Nanostructured NiMoO4 electrode materials for efficient oxygen evolution reaction

Bifunctional electrocatalysts derived from earth-abundant transition metals are a promising substitute for noble metals in general water electrolysis, but their low activity and short durability limit their application. Herein, a nickel molybdate nanoparticles decorated on nickel foam (NiMoO4/NF NPs) electrode was fabricated by a facile hydrothermal method at three different time intervals (6, 12, and 24 h) and verified for the oxygen evolution reaction (OER). The constructed electrodes exhibited high OER activity in 1.0 M KOH with overpotentials of 315 mV, 290 mV and 320 mV for NiMoO4-6 h, NiMoO4-12 h, and NiMoO4-24 h, respectively. In addition, the NiMoO4-12 h electrodes displayed remarkable durability with a negligible reduction of 1.28 % at a current density of 10 mA cm−2 for 200 h. This research work delivers a new pathway to improve the electrocatalytic behaviour of the catalysts by synergistically moderating the inherent electrical conductivity, efficient surface moieties, and surface reaction.

Cr dopant regulating d-orbital electronic configuration of NiFe spinel oxide to improve oxygen evolution reaction in Zn-air battery

Significant advancements towards enhancing the catalytic activity of spinel ferrites in oxygen evolution reaction (OER) have been achieved, however, further studies are required on this regard. In this study, Cr-doped spinel ferrite (NiFe2O4) embedded in N-doped C (Cr-NiFe2O4@NC) was synthesized via a high-temperature treatment using an NiFe Prussian blue analog as a precursor and K2Cr2O7 as a Cr source. Owing to the strong octahedral site preference energy, Cr3+ ions were successfully doped into octahedral sites and tailored the electronic configuration of NiFe2O4, as confirmed by XPS. The Cr-substituted Cr-NiFe2O4@NC exhibited the overpotential of 241 mV at 10 mA cm−2, which was smaller than that of NiFe2O4@NC (266 mV) at the same current density. Meanwhile, the Tafel slope of Cr-NiFe2O4@NC (65.32 mV dec−1) was also lower than that of NiFe2O4@NC (86.96 mV dec−1). Therefore, the Cr substitution can improve the electrocatalytic OER performance of NiFe2O4@NC. In particular, an assembled rechargeable Zn-air battery using Cr-NiFe2O4@NC as the cathode catalyst afforded a high power density (61.1 mA cm−2) together with a high specific capacity (740 mA g−1). Amazingly, it could power light-emitting diodes, demonstrating its real-world application. Density functional theory calculations revealed that Cr ion doping led to electron transfer in NiFe2O4, resulting in a density of electronic states close to the Fermi level, which probably regulated the adsorption/desorption behaviors of oxygenate intermediates (*O and *OOH), thus promoting the reaction kinetics of the OER. This study provides a helpful basis for the development of spinel oxides with high electrocatalytic OER activity and durability via cation doping.

Enhanced oxygen evolution reaction of electrodeposited Functionally-Graded Ni-Cu-Fe coating

This study aimed to use a functionally graded (FG) Ni-Cu-Fe coating as an electrocatalyst for oxygen evolution reaction (OER) applications. The coating was applied on a mild carbon steel substrate by an electrodeposition technique, with the current density being progressively increased from 0.5 A/dm2 to 5 A/dm2 at a steady rate of 0.2 (A/dm2)/min during the coating operation. Using this specific method, the Ni content of the FG Ni-Cu-Fe coating changed along the cross-section when increasing the current density, 17 % more than the constant current coating. This technique also affected the surface morphology of the FG Ni-Cu-‌Fe coating and changed it from cauliflower to micro/nanocones when the current density was linearly increased, enhancing active sites significantly and thereby improving electrocatalytic activity. The coating's electrocatalytic behavior was studied by electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and cyclic voltammetry (CV). results showed that the FG Ni-Cu-Fe coating had the smallest overpotential (134 mV) at the current density of 10 mA.cm−2. Also, it had the smallest Tafel slope (24.3 mV.dec− 1) and smallest resistance (598 Ω.cm2) compared to all of the other coatings. The FG Ni-Cu-‌‌Fe coating had higher OER performance because of high Ni content, micro/nanocones morphology with many active sites, and FG nature. The FG Ni-Cu-Fe coating is finally concluded to be a promising and economical catalyst with high OER activity.

Photo-assisted electrocatalysis of NiO/CeO2 heterojunction for efficient oxygen evolution reaction

In recent years, photo-assisted electrocatalysis has attracted significant interest in the field of electrolytic hydrogen production. By integrating electrical and optical energy, supplementary energy is harnessed for the electrocatalytic process, which offers an efficient strategy to enhance the performance of oxygen evolution reaction (OER). Herein, the heterojunction NiO/CeO2 composite nanostructures supported by nickel foam (represented as NiO/CeO2@NF) was selected as the photo-assisted electrocatalyst, through the mutual synergy of voltage and light to improve the catalytic activity of OER in electrolytic water. Under light irradiation, the NiO component undergoes photoexcited to produce photogenerated electrons that move towards the CeO2 component, stimulating the generation and accumulation of more holes accelerating the formation of Ni (III) to improve the reaction efficiency with electrons, thereby boosting the enhancement of OER activity. The results demonstrate that the overpotential corresponding to NiO/CeO2@NF in non-irradiation at 10 mA cm−2 current density was 280 mV, and the NiO/CeO2@NF in light irradiation displays robust OER activity, with lower over-potentials 260 mV at 10 mA cm−2, which 20 mV lower than in non-irradiation. Moreover, NiO/CeO2@NF in light irradiation exhibits high catalytic activity and durability for OER in an alkaline electrolyte, delivering 100 mA cm−2 at 320 mV and outperforming RuO2 under high current densities.

Carbon materials co-doped with nitrogen and sulfur for highly efficient catalytic activity in oxygen reduction and evolution

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) represent crucial steps in the functioning of fuel cells and metal-air batteries. Designing bifunctional oxygen electrode catalysts with high activity for both ORR and OER remains an immense challenge. In this study, we address this challenge by employing in-situ polymerization to design nitrogen and sulfur co-doped carbon materials (NSCs). The resulting NSC-1000–3 exhibits an onset potential of 1.03 V vs. RHE and a half-wave potential (E1/2) of approximately 0.89 V during ORR in an alkaline solution. When compared to commercial Pt/C, it demonstrates a positive shift of 60 mV in the half-wave potential. Furthermore, NSC-1000–3 displays outstanding oxygen evolution performance. At a current density of 10 mA cm−2, its performance matches that of RuO2. This material demonstrates exceptional performance in both ORR and OER, showcasing the synergistic doping effects of nitrogen and sulfur.

Glassy State Hydroxide Materials for Oxygen Evolution Electrocatalysis.

Hydroxides are the archetype of layered crystals with metal-oxygen (M-O) octahedron units, which have been widely investigated as oxygen evolution reaction (OER) catalysts. However, the better crystallinity of hydroxide materials, the more perfect octahedral symmetry and atomic ordering, resulting in the less exposed metal sites and limited electrocatalytic activity. Herein, a glassy state hydroxide material featuring with short-range order and long-range disorder structure is developed to achieve high intrinsic activity for OER. Specifically, a rapid freezing point precipitation method is utilized to fabricate amorphous multi-component hydroxide. Owing to the freezing-point crystallization environment and chaotic M-O (M = Ni/Fe/Co/Mn/Cr etc.) structures, the as-fabricated NiFeCoMnCr hydroxide exhibit a highly-disordered glassy structure, as-confirmed by X-ray/electron diffraction, enthalpic response, and pair distribution function analysis. The as-achieved glassy-state hydroxide materials display a low OER overpotential of 269mV at 20mA cm-2 with a small Tafel slope of 33.3mV dec-1 , outperform the benchmark noble-metal RuO2 catalyst (341mV, 84.9mV dec-1 ) . Operando Raman and density functional theory studies reveal that the glassy state hydroxide converted into disordered active oxyhydroxide phase with optimized oxygen intermediates adsorption under low OER overpotentials, thus boosting the intrinsic electrocatalytic activity.

Laser assisted oxygen vacancy engineering on Fe doped CoO nanoparticles for oxygen evolution at large current density

Exploring cost-effective non-noble metal-based catalysts with high activity and stability is of great significance for energy conversion and storage involving oxygen evolution reaction (OER). Here, we employed a laser irradiation technique to synthesis Fe doped CoO nanoparticles with ultrafine size (≈ 5.4 nm) and abundant oxygen vacancies (Fe-Ov-CoO). The ultrafine size of Fe-Ov-CoO nanoparticles provides more active sites to be exposed. Fe doping and oxygen vacancy promote the intrinsic activity and electron transfer rates of Fe-Ov-CoO, giving rise to high activity and stability catalyst for OER. Fe-Ov-CoO delivers a large current density of 1000 mA cm−2 at an overpotential of 548 mV, which is much better than commercial RuO2. Moreover, Fe-Ov-CoO presents a remarkable long-term stability with negligible degeneration at a high current density of 500 mA cm−2 for 120 h. This work provides a new route to develop OER electrocatalyst with high activity and stability.

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.

Tensile straining of iridium sites in manganese oxides for proton-exchange membrane water electrolysers

Although the acidic oxygen evolution reaction (OER) plays a crucial role in proton-exchange membrane water electrolysis (PEMWE) devices, challenges remain owing to the lack of efficient and acid-stable electrocatalysts. Herein, we present a low-iridium electrocatalyst in which tensile-strained iridium atoms are localized at manganese-oxide surface cation sites (TS-Ir/MnO2) for high and sustainable OER activity. In situ synchrotron characterizations reveal that the TS-Ir/MnO2 can trigger a continuous localized lattice oxygen-mediated (L-LOM) mechanism. In particular, the L-LOM process could substantially boost the adsorption and transformation of H2O molecules over the oxygen vacancies around the tensile-strained Ir sites and prevent further loss of lattice oxygen atoms in the inner MnO2 bulk to optimize the structural integrity of the catalyst. Importantly, the resultant PEMWE device fabricated using TS-Ir/MnO2 delivers a current density of 500 mA cm−2 and operates stably for 200 h.

Mesoporous hydrogel electrodes with flexible frameworks exhibiting enhanced mass transport for the oxygen evolution reaction.

Mesoporous hydrogel electrodes with unique flexible mesopores surrounded by CoOOH nanosheets were prepared via the electrochemical deposition of hybrid cobalt hydroxide nanosheets, exhibiting high oxygen evolution reaction activity at a high current density owing to the enhanced mass transport of oxygen molecules.

Co3O4/activated carbon nanocomposites as electrocatalysts for the oxygen evolution reaction.

The Oxygen Evolution Reaction (OER) is crucial in various processes such as hydrogen production via water splitting. Several electrocatalysts, including metal oxides, have been evaluated to enhance the reaction efficiency. Zeolitic Imidazolate Framework-67 (ZIF-67) has been employed as a precursor to produce Co3O4, showing high OER activity. Additionally, the formation of composites with carbon-based materials improves the activity of these materials. Thus, this work focuses on synthesizing ZIF-67 and commercial activated carbon (AC) composites, which were used as precursors to obtain Co3O4/C electrocatalysts by calculating ZIF-67/CX (X = 10, 30, and 50, the mass percentage of AC). The obtained materials were thoroughly characterized by employing X-ray powder diffraction (XRD), confirming the cobalt oxide structure with a sphere-like morphology as observed in the TEM images. The presence of oxygen vacancies was confirmed by infrared spectroscopy and EPR measurements. The electrocatalytic performance in the OER was investigated by linear sweep voltammetry (LSV), which revealed an overpotential of 325 mV at 10 mA cm-2 and a Tafel slope value of 65.32 mV dec-1 for Co3O4/C10, superior in activity to several previously reported studies in the literature and electrochemical stability of up to 8 hours. The reduced value of charge transfer resistance, high double-layer capacitance, and the presence of Co3+ ions justify the superior performance of the Co3O4/C10 electrocatalyst.