Oxygen Evolution Reaction Catalytic Activity Research Articles

FeCo‐oxalate Organic Framework as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Developing nonprecious metallic electrocatalysts for water splitting is of vital importance for sustainable environment and energy technologies. As for oxygen evolution reaction (OER), FeCo‐based bimetallic catalysts have been found to act as promising candidates owing to their high intrinsic activity. Herein, a novel FeCo‐oxalate organic framework was grown on nickel foam (FeCo‐OA@NF) under mild conditions. The optimized electrocatalyst shows good OER performance with a low overpotential of 275 mV at the current density of 100 mA cm−2 in alkaline environment, comparable to that of commercial Ru‐based catalyst. Moreover, the quantification of produced oxygen by both gas chromatography and drainage method demonstrates nearly 100% Faradaic efficiency. Except for the contribution of Fe and Co species for the excellent OER catalytic activity, in‐situ Raman spectroscopy reveals that the positive effect of oxalate coordination also makes a difference, which can possibly reduce electron transport resistance and provide more active sites. This work provides a promising approach for the preparation of alkaline oxygen evolution electrocatalysts with low‐cost and high performance.

Convenient construction of electrocatalysts via combustion-assisted corrosion engineering for efficient water oxidation

Developing an efficient strategy for the universal synthesis of electrocatalysts is crucial for advancing the industrialization of water splitting, yet it remains a significant challenge. In this study, we propose combustion-assisted corrosion engineering as a rapid method to fabricate electrocatalysts for the oxygen evolution reaction (OER) within seconds. By utilizing a three-dimensional framework composed of nickel foam and the unique structure of the active species, we enable swift electrolyte diffusion and gas release. Consequently, the optimized S–NiO/NF exhibits remarkable OER catalytic activity, requiring a low overpotential of 236 mV to achieve a current density of 50 mA cm−2 in 1.0 M KOH solution. Notably, the reconfiguration during the OER process leads to the formation of actual catalytic active species, enhancing the number of active centers and thereby improving the catalyst's performance. This research presents a versatile method for industrially fabricating non-noble metal self-supporting electrodes with high efficiency, offering a practical solution for energy conversion and storage.

Self-Assembled Conjugated Coordination Polymer Nanorings: Role of Morphology and Redox Sites for the Alkaline Electrocatalytic Oxygen Evolution Reaction.

Electrocatalytic water splitting provides a sustainable method for storing intermittent energies, such as solar energy and wind, in the form of hydrogen fuel. However, the oxygen evolution reaction (OER), constituting the other half-cell reaction, is often considered the bottleneck in overall water splitting due to its slow kinetics. Therefore, it is crucial to develop efficient, cost-effective, and robust OER catalysts to enhance the water-splitting process. Transition-metal-based coordination polymers (CPs) serve as promising electrocatalysts due to their diverse chemical architectures paired with redox-active metal centers. Despite their potential, the rational use of CPs has faced obstacles including a lack of insights into their catalytic mechanisms, low conductivity, and morphology issues. Consequently, achieving success in this field requires the rational design of ligands and topological networks with the desired electronic structure. This study delves into the design and synthesis of three novel conjugated coordination polymers (CCPs) by leveraging the full conjugation of terpyridine-attached flexible tetraphenylethylene units as electron-rich linkers with various redox-active metal centers [Co(II), Ni(II), and Zn(II)]. The self-assembly process is tuned for each CCP, resulting in two distinct morphologies: nanosheets and nanorings. The electrocatalytic OER performance efficiency is then correlated with factors such as the nanostructure morphology and redox-active metal centers in alkaline electrolytes. Notably, among the three morphologies studied, nanorings for each CCP exhibit a superior OER activity. Co(II)-integrated CCPs demonstrate a higher activity between the redox-active metal centers. Specifically, the Co(II) nanoring morphology displays exceptional catalytic activity for OER, with a lower overpotential of 347 mV at a current density of 10 mA cm-2 and small Tafel slopes of 115 mV dec-1. The long-term durability is demonstrated for at least 24 h at 1.57 V vs RHE during water splitting. This is presumably the first proof that links the importance of nanostructure morphologies to redox-active metal centers in improving the OER activity, and it may have implications for other transdisciplinary energy-related applications.

Multiwall carbon nanotubes supported rhenium doped Co3O4 as an efficient electrocatalyst for water oxidation in alkaline medium

The recent trends for the development of efficient and low cost transition metal (TMs) based anode catalysts for water splitting is crucial and important. Even though, research is continuously progressing in different directions to design catalyst; however, catalytic OER (oxygen evolution reaction) activity has remained insufficient. Till now, various transition metal oxides (TMOs) have been used as efficient and cost-effective electrocatalyst for the oxygen evolution reaction. The catalytic performance of TMOs could be enhanced by doping with the metal, which increases the catalyst's charge transfer and electronic conductivity. Decoration of TMOs with the multi-wall carbon nanotube (MWCNT) further improves catalytic activity by providing numerous active sites. Here, Co3O4/MWCNT and Rhenium (Re) doped Co3O4/MWCNT composite were prepared by simple hydrothermal process and used as electrocatalyst for OER in alkaline medium. Different concentrations of Re (0.05 mmol, 0.1 mmol, 0.2 mmol, 0.3 mmol) were doped and it was observed that the electrochemical results of the 0.2 mmol Re doped Co3O4/ MWCNT (R0.2CO) was most efficient electrocatalyst which offers the OER overpotential of 298 mV/dec to attain the 10 mA cm−2 current density, lower Tafel slope (70 mV/dec), higher value of turn over frequency (0.95), lower value of the charge transfer resistance (3.10Ω) and good stability, demonstrating the better OER catalytic activity as compared to un-doped Co3O4/MWCNT (R0.0CO) catalyst. The investigated catalyst R0.2CO is more efficient catalyst than most of the reported similar type of catalysts and offers comparable electrocatalytic activity with benchmark electrocatalyst RuO2.

Coupling interface constructions of flower-like structure MoSe2–NiWSe2 for efficient oxygen evolution reaction and urea oxidation reaction

Because of its low thermodynamic voltage, the electrocatalytic urea oxidation reaction (UOR) is an effective way to replace the sluggish oxygen evolution reaction (OER) and address the issue of urea-rich water pollution. Herein, we have synthesized MoSe2–NiWSe2 with spherical nanoflower structure consisting of MoSe2 nanosheets and NiWSe2 nanosheets crisscrossed longitudinally and transversely. The results show that the prepared MoSe2–NiWSe2 has a significant competitive advantage in the UOR and OER. With 10 mA cm−2, a mere 200 mV overpotential was required, indicating high OER catalytic activity. MoSe2–NiWSe2-driven UOR might operate at a comparatively low potential of 1.36 V (10 mA cm−2). The overpotential did not significantly alter after 40 h of continuous operation, suggesting it possesses high UOR stability. A built-in electric field that aids in controlling the adsorption and oriented distribution of urea molecules and thus promotes the oxidative properties of water and urea forms at the interface of MoSe2 and NiWSe2, where the difference in electronegativity between the elements Mo and Ni induces self-driven charge transfer and interfacial coupling effects. This work offers a method for creating catalysts that produce more oxygen and clean up urea-rich water contamination.

Noble metal clusters substitution in porous Ni substrate renders high mass-specific activities toward oxygen evolution reaction and methanol oxidation reaction

The sluggish reaction kinetics of the oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) remain obstacles to the commercial promotion of water splitting and direct methanol fuel cells. Considering the vital role of noble metals in electrocatalytic activity, this work focuses on the rational synthesis of Ni-noble metal composite nanocatalysts for overcoming the drawbacks of high cost and susceptible oxidized surfaces of noble metals. The inherent catalytic activity is improved by the altered electronic structure and effective active sites of the catalyst induced by the size effect of noble metal clusters. In particular, a series of Ni-noble metal nanocomposites are successfully synthesized by partially introducing noble metal into Ni with porous interfacial defects derived from Ni-Al layered double hydroxide (LDH). The Ni10Pd1 nanocomposite exhibits high OER catalytic activity with an overpotential of 0.279 V at 10 mA/cm2, surpassing Ni10Ag1 and Ni10Au1 counterparts. Furthermore, the average diameter of Pd clusters gradually increases from 5.57 nm to 44.44 nm with the increased proportion of doped Pd, leading to the passivation of catalytic activity due to the exacerbated surface oxidation of Pd in the form of Pd2+. After optimization, Ni10Pd1 delivers significantly enhanced OER and MOR electroactivities and long-term stability compared to that of Ni2Pd1, Ni1Pd1 and Ni1Pd2, which is conducive to the effective utilization of Pd and alleviation of surface oxidation.

Co-Ni co-sputter deposited bimetallic thin film catalysts for alkaline hydrogen and oxygen evolution reactions

Co-Ni bi-metallic thin films with different stoichiometries have been deposited by magnetron co-sputtering technique on Ni foam (NF), Si and carbon paper substrates. The structural and morphological characterisations of these films have been done by X-ray diffraction, X-ray absorption spectroscopy and Field Emission Scanning Electron Microscope measurements. The performances of these films for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been evaluated through electrochemical measurements like Linear Sweep Voltammetry, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy measurements. Operando X ray absorption near edge spectroscopy measurements have also been carried out during HER and OER to decipher the redox reaction mechanisms. It has been observed that the HER and OER performance of all the Co Ni bi-metallic thin films on NF are found to be better than that of bare NF. The CoNi sample with composition of 58.7 % Co and 41.3 % Ni shows the best catalytic activity and stability towards HER and OER reactions. Though the HER activity is not the best but is comparable to many results reported in the literature, however the catalyst shows excellent OER activity with overpotential of 214 mV for 10 mA/cm2 current density. This is much better than that of the OER benchmark catalyst RuO2 and most of those reported in the literature. The OER is kinetically slower than HER and requires more overpotential, hence a significant improvement in the catalytic OER activity will definitely enhance the overall water splitting activity and hydrogen production efficiency. Thus the Co-Ni bi-metallic catalyst prepared by an easily scalable and highly reproducible magnetron co-sputtering technique has significant potential to emerge out as a technologically viable water splitting catalyst.

Rapid Defect Engineering in FeCoNi/FeAl2O4 Hybrid for Enhanced Oxygen Evolution Catalysis: A Pathway to High-Performance Electrocatalysts.

Rational modulation of surface reconstruction in the oxygen evolution reaction (OER) utilizing defect engineering to form efficient catalytic activity centers is a topical interest in the field of catalysis. The introduction of point defects has been demonstrated to be an effective strategy to regulate the electronic configuration of electrocatalysts, but the influence of more complex planar defects (e.g., twins and stacking faults), on their intrinsic activity is still not fully understood. This study harnesses ultrasonic cavitation for rapid and controlled introduction of different types of defects in FeCoNi/FeAl2O4 hybrid coatings, optimizing OER catalytic activity. Theoretical calculations and experiments demonstrate that the different defects optimize the coordination environment and facilitate the activation of surface reconstruction into true catalytic activity centers at lower potentials. Moreover, it demonstrates exceptional durability, maintaining stable oxygen production at a high current density of 300 mA cm-2 for over 120 hours. This work not only presents a novel pathway for designing advanced electrocatalysts but also deepens our understanding of defect-engineered catalytic mechanisms, showcasing the potential for rapid and efficient enhancement of electrocatalytic performance.

Rapid Defect Engineering in FeCoNi/FeAl2O4 Hybrid for Enhanced Oxygen Evolution Catalysis: A Pathway to High‐Performance Electrocatalysts

Rational modulation of surface reconstruction in the oxygen evolution reaction (OER) utilizing defect engineering to form efficient catalytic activity centers is a topical interest in the field of catalysis. The introduction of point defects has been demonstrated to be an effective strategy to regulate the electronic configuration of electrocatalysts, but the influence of more complex planar defects (e.g., twins and stacking faults), on their intrinsic activity is still not fully understood. This study harnesses ultrasonic cavitation for rapid and controlled introduction of different types of defects in FeCoNi/FeAl2O4 hybrid coatings, optimizing OER catalytic activity. Theoretical calculations and experiments demonstrate that the different defects optimize the coordination environment and facilitate the activation of surface reconstruction into true catalytic activity centers at lower potentials. Moreover, it demonstrates exceptional durability, maintaining stable oxygen production at a high current density of 300 mA cm−2 for over 120 hours. This work not only presents a novel pathway for designing advanced electrocatalysts but also deepens our understanding of defect‐engineered catalytic mechanisms, showcasing the potential for rapid and efficient enhancement of electrocatalytic performance.

Synthesis and OER catalytic activity of quasi zeolitic imidazolate Framework-67 having two and three dimensional morphology

Zeolitic imidazolate framework-67 (ZIF-67), in two and three dimensional (2D/3D) morphologies have been synthesized at room temperature using different solvent media, and annealed at 350 and 920 °C to derive the modified ZIF-67 based catalysts. All the ZIF-67 based catalysts were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscopy, Thermogravimetric analysis, N2 gas adsorption method, and Positron annihilation lifetime spectroscopy. It has been observed that catalytic activity of the ZIF-67 based catalysts towards oxygen evolution reaction (OER) depends on the morphology and annealing-induced modifications in active sites. Among different morphologies of as-synthesized ZIF-67, 2D ZIF-67 (nanosheet and disc like morphology) exhibits the best electrocatalytic activity in as-synthesized as well as in the annealed form in comparison to 3D ZIF-67 (rhombic dodecahedron) owing to their better electronic properties. All the types of ZIF-67 annealed at 920 °C show the lower Tafel slopes suggesting higher OER rate.

Perovskite for Electrocatalytic Oxygen Evolution at Elevated Temperatures.

The development of advanced electrolysis technologies such as anion exchange membrane water electrolyzer (AEMWE) is central to the vision of a sustainable energy future. Key to the realization of such AEMWE technology lies in the exploration of low-cost and high-efficient catalysts for facilitating the anodic oxygen evolution reaction (OER). Despite tremendous efforts in the fundamental research, most of today's OER works are conducted under room temperature, which deviates significantly with AEMWE's operating temperature (50-80 °C). To bridge this gap, it is highly desirable to obtain insights into the OER catalytic behavior at elevated temperatures. Herein, using the well-known perovskite catalyst Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as a proof of concept, the effect of temperature on the variation in OER catalytic activity and stability is evaluated. It is found that the BSCF's activity increases with increasing temperature due to enhanced lattice oxygen participation promoting the lattice oxygen-mediated OER process. Further, surface amorphization and cation leaching of BSCF become more pronounced as temperature increases, causing a somewhat attenuated OER stability. These new understandings of the fundamental OER catalysis over perovskite materials at industrial-relevant temperature conditions are expected to have strong implications for the research of OER catalysts to be deployed in practical water electrolyzers.

Surface functionalization of nickel foam with two-dimensional conjugated MOFs Fe3(hexaiminotriphenylene)2 for highly efficient oxygen evolution reaction

The design of high-efficient, low-cost, and stable electrocatalysts for oxygen evolution reaction (OER) is highly demanding for energy conversion applications. Metal-organic frameworks (MOFs), with large surface area and flexible molecular species, can supply atom-dispersed metal active coordination sites (M−NX, M−SX, M−OX) for OER and have been regarded as potential catalysts for practical applications. However, it is still challenging to use MOFs as OER catalysts directly due to their low conductivity and poor stability. Herein, we successfully synthesized a 2D c-MOF of Fe3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) on the surface of nickel foam (NF) by using a layer-by-layer self-assembly strategy. The Fe3(HITP)2/NF-x electrode (x = 5, 10, 15, 20 is the number of cycles) exhibited impressive OER catalytic activity in alkaline electrolyte (1 M KOH), which is superior or comparable to most of the transition metal-based materials reported. Typically, Fe3(HITP)2/NF-15 were able to fully expose the Fe-N4 catalytic sites with an overpotential of 224 mV at a current density of 10 mA·cm−2 and a Tafel slope of 45.4 mV·dec-1. This was mainly attributed to the higher ECSA value, better kinetic process, and fast charge transfer ability of Fe3(HITP)2/NF. In addition, the current density of Fe3(HITP)2/NF-15 remained at 97.3 % of the initial current density after 24 h i-t stability test, showing excellent catalytic stability. This work provided a novel design strategy for the direct application of MOFs to OER applications.

Construction of mesoporous Ni-Co-Mo oxide/sulfide composite composite nanosheet arrays as bifunctional material for charge storage and oxygen evolution reaction applications

At present, energy conversion and energy storage devices are gradually integrated together, which puts forward higher requirements for the design and construction of electrode materials. Herein, bi-functional Co-Mo oxides and Ni/Co sulfides (NCMOS) composite nanosheet arrays on Ni foam are constructed for supercapacitors and oxygen evolution reaction (OER) of water splitting. The Ni-Co-Mo nanosheet precursor is firstly synthesized by stepwise hydrothermal processes and then converted into Ni-Co sulfide and Co-Mo oxide by in-situ sulfurization. The nanoarray and in-situ sulfurization of active materials bring more reactive active sites, optimize reaction kinetics, and shorten the transport path of electrons and charges, which enhance energy storage performance and OER catalytic activity of NCMOS material. In terms of supercapacitor applications, NCMOS exhibits high specific capacity (1332.1 C g–1) and good cycle stability. For OER application, NiCMOS shows lower OER overpotential (290 mV at 100 mA cm–2), smaller Tafel slope (87.2 mV dec–1) and excellent catalytic stability in oxygen evolution for 60 h. The excellent charge storage and OER properties suggest that bi-functional oxide/sulfide composites have great potential in energy conversion and storage-integrated devices.

Cooperative Effects Drive Water Oxidation Catalysis in Cobalt Electrocatalysts through the Destabilization of Intermediates.

A barrier to understanding the factors driving catalysis in the oxygen evolution reaction (OER) is understanding multiple overlapping redox transitions in the OER catalysts. The complexity of these transitions obscure the relationship between the coverage of adsorbates and OER kinetics, leading to an experimental challenge in measuring activity descriptors, such as binding energies, as well as adsorbate interactions, which may destabilize intermediates and modulate their binding energies. Herein, we utilize a newly designed optical spectroelectrochemistry system to measure these phenomena in order to contrast the behavior of two electrocatalysts, cobalt oxyhydroxide (CoOOH) and cobalt-iron hexacyanoferrate (cobalt-iron Prussian blue, CoFe-PB). Three distinct optical spectra are observed in each catalyst, corresponding to three separate redox transitions, the last of which we show to be active for the OER using time-resolved spectroscopy and electrochemical mass spectroscopy. By combining predictions from density functional theory with parameters obtained from electroadsorption isotherms, we demonstrate that a destabilization of catalytic intermediates occurs with increasing coverage. In CoOOH, a strong (∼0.34 eV/monolayer) destabilization of a strongly bound catalytic intermediate is observed, leading to a potential offset between the accumulation of the intermediate and measurable O2 evolution. We contrast these data to CoFe-PB, where catalytic intermediate generation and O2 evolution onset coincide due to weaker binding and destabilization (∼0.19 eV/monolayer). By considering a correlation between activation energy and binding strength, we suggest that such adsorbate driven destabilization may account for a significant fraction of the observed OER catalytic activity in both materials. Finally, we disentangle the effects of adsorbate interactions on state coverages and kinetics to show how adsorbate interactions determine the observed Tafel slopes. Crucially, the case of CoFe-PB shows that, even where interactions are weaker, adsorption remains non-Nernstian, which strongly influences the observed Tafel slope.

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.

Cerium Dioxide as an Electron Buffer to Stabilize Iridium for Efficient Water Electrolysis

AbstractSustaining the steady state for highly active non‐stoichiometric iridium (Ir)‐based oxide (IrOx) at low Ir loading remains challenging primarily due to the continuous oxidation and sequent dissolution of Ir active sites during the oxygen evolution reaction (OER). In this context, a new iridium–cerium (Ce) substitution solid solution oxide (SSO) has been developed, featuring uniformly dispersed Ir atoms within Ce dioxide (CeO2) matrix as electron buffer, which delivers remarkable acidic OER catalytic activity and enhanced stability. The electron‐buffering capacity of CeO2 facilitates the charge transfer toward Ir atoms, leading to abundant active low‐valence Ir sites and effectively prevent their oxidation and dissolution. As a result, Ir─Ce SSO demonstrates an overpotential of merely 238 mV@10 mA cm−2. Proton exchange membrane water electrolyzer employing Ir─Ce SSO at a low Ir loading of 396 µgIr cm−2 operates consistently for over 100 h@500 mA cm−2. Density functional theory (DFT) calculations corroborate that the electron‐buffering effect of CeO2 enriches the density of IrIII and substantially increases the dissolution energy barrier of Ir atoms. This study presents a viable approach to addressing the issues of instability and low efficiency in Ir‐based OER electrocatalysts for acidic water electrolysis.

Synthesis of MFe2O4 (M=Ni, Co) Nanoparticles by a Bicontinuous Microemulsion Method for the Oxygen Evolution Reaction

AbstractDeveloping efficient and low‐cost electrocatalysts for the oxygen evolution reaction (OER) is crucial for sustainable hydrogen production through water splitting. In this study, CoFe2O4 and NiFe2O4 nanoparticles as electrocatalysts were prepared via an inexpensive method involving the use of bicontinuous microemulsions as nanoreactors. The crystalline structure, morphology, and elemental composition of the electrocatalysts were characterized by XRD, Raman spectroscopy, TEM, and EDS elemental mapping. The electronic structure and textural properties were examined using XPS and the nitrogen adsorption‐desorption method. The OER measurements were carried out in a standard three‐electrode system. CoFe2O4 demonstrated relatively higher OER catalytic activity than NiFe2O4 in 1 M KOH solution, with a smaller overpotential of 410 mV to achieve a current density of 10 mA cm−2 and a smaller Tafel slope of 80 mV dec−1. In contrast, NiFe2O4 offered a higher overpotential of 450 mV to reach the same current density. The superior performance of CoFe2O4 is ascribed to higher ECSA, better conductivity, and lower charge transfer resistance. However, both electrocatalysts showed stability up to more than three hours of continuous performance.

Fabrication and characterization of Nickel-coated 3D printed electrodes for enhanced oxygen evolution reaction in acidic media at various temperatures

Additive manufacturing (AM), often referred to as 3D printing, is a new technology that allows objects to be created by adding layer by layer, as opposed to traditional manufacturing processes. Therefore, the rapid and cost-effective AM method can facilitate research and development efforts in the field of electrochemistry. In this study, oxygen evolution reaction (OER) electrodes are fabricated by a 3D printing technique utilizing carbon-based (PP filament) and graphene-based PLA filaments (BM filament). Electrodes are then coated with Ni by electrochemical deposition method at different temperatures. Electrochemical analysis of Ni coated PP and BM electrodes is made in acidic environments (0.5 M H2SO4) using different characterization techniques. The results indicate that PP/Ni-50 and BM/Ni-50 electrodes have the highest catalytic activity for OER in acidic media. PP/Ni-50 and BM/Ni-50 electrodes exhibited a superior double layer (Cdl) value than other Ni coated 3D printed electrode samples, and their active surface areas are calculated as 0.201 cm2 and 0.286 cm2, respectively. A larger active surface area leads to an increase in the number of active sites, causing the OER process to be more effective. Consequently, increasing the active surface area of electrode samples is crucial for improving the efficiency and effectiveness of the Oxygen Evolution Reaction (OER) process, especially in the context of renewable energy and sustainable technology applications.

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.

Ionic liquid in-situ functionalized carbon nanotube film as self-supported metal-free electrocatalysts for oxygen evolution

The oxygen evolution reaction (OER) is a critical cathode reaction for hydrogen production from water splitting. However, due to the sluggish kinetics of OER, the water-splitting process is impeded. Thus, it is imperative to develop efficient and low-cost electrocatalysts that reduce the overpotential and improve the kinetics of OER. Herein, an in-situ synthesis strategy was applied to prepare the ionic liquid functionalized carbon nanotube (IL-CNT) that served as a metal-free electrocatalyst for OER. This powder material exhibited exceptional electrocatalytic activity for OER, with an overpotential of 335 mV at 10 mA cm−2 and a Tafel slope of 71 mV dec-1. Then, it was found that catalytic activity was influenced by the IL anion. Moreover, this IL-CNT powder could self-assemble to form carbon film during preparation, exhibiting outstanding catalytic activity for OER (a low overpotential of 153 mV at 10 mA cm−2), which was highly beneficial for practical application. Based on the theoretical calculations and experimental results, these in-situ functionalization sites on CNT surface played a significant role in regulating their electron structure. This, in turn, promoted electron transfer and hydroxyl adsorption, resulting in a substantial increase in catalytic activity for the OER.