Enhancement In Oxygen Evolution Reaction Activity Research Articles

Post-treatment induced anisotropic growth of MOF-derived surface modified heterogeneous catalyst for efficient oxygen evolution reaction

The advancement of electrocatalysts exhibiting outstanding performance in the oxygen evolution reaction (OER), crucial for hydrogen production, holds immense significance in addressing energy shortages and mitigating environmental pollution. In this study, a novel approach to synthesizing Co-MOF (Metal-Organic Framework) directly immobilized onto a Ni foam substrate through hydrothermal synthesis is presented. In contrast to conventional methods employing powder-based synthesis with binders, our direct attachment method offers a unique and efficient means of creating robust Co-MOF at Ni foam (Co-MOF@NF) hybrid catalysts. Subsequently, a chemical reduction approach utilizing sodium borohydride was employed to introduce surface modification into the Co-MOF structure. The resulting material, sodium borohydride treated Co-MOF@NF (Red. 1 h Co-MOF@NF), exhibited a remarkable enhancement in OER activity compared to the pristine Co-MOF@NF sample. Notably, Red.1 h Co-MOF@NF demonstrated a substantially reduced overpotential of 235 mV to achieve a current density of 10 mA cm⁻2, in contrast to the 300 mV overpotential required by the pristine Co-MOF@NF under the same conditions. Furthermore, the Red.1 h Co-MOF@NF catalyst displayed exceptional stability, sustaining a current density of 50 mA cm⁻2 for over 48 h, highlighting its promising potential for practical applications. The synergistic effects of direct hydrothermal attachment, surface modification, and improved OER performance make this study a significant contribution to the advancement of efficient and stable electrocatalysts for energy conversion 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.

Strong Interface Coupling Enables Stability of Amorphous Meta-Stable State in CoS/Ni3S2 for Efficient Oxygen Evolution.

Rational design of heterostructure catalysts through phase engineering strategy plays a critical role in heightening the electrocatalytic performance of catalysts. Herein, a novel amorphous/crystalline (a/c) heterostructure (a-CoS/Ni3S2) is manufactured by afacile hydrothermal sulfurization method. Strikingly, the interface coupling between amorphous phase (a-CoS) and crystalline phase (Ni3S2) in a-CoS/Ni3S2 is much stronger than that between crystalline phase (c-CoS) and crystalline phase (Ni3S2) in crystalline/crystalline (c/c) heterostructure (c-CoS/Ni3S2) as control sample, which makes the meta-stable amorphous structure more stable. Meanwhile, a-CoS/Ni3S2 has more S vacancies (Sv)than c-CoS/Ni3S2 because of the presence of an amorphous phase. Eventually, for the oxygen evolution reaction (OER), the a-CoS/Ni3S2 exhibits a significantly lower overpotential of 192mV at 10mAcm-2 compared to the c-CoS/Ni3S2 (242mV). An exceptionally low cell voltage of 1.51V is required to achieve a current density of 50mAcm-2 for overall water splitting in the assembled cell (a-CoS/Ni3S2 || Pt/C). Theoretical calculations reveal that more charges transfer from a-CoS to Ni3S2 in a-CoS/Ni3S2 than in c-CoS/Ni3S2, which promotes the enhancement of OER activity. This work will bring into play a fabrication strategy of a/c catalysts and the understanding of the catalytic mechanism of a/c heterostructures.

Unveiling the role of catalytically active MXene supports in enhancing the performance and durability of cobalt oxygen evolution reaction catalysts for anion exchange membrane water electrolyzers

The role of 2D transition metal carbides, also known as MXenes, as active catalyst supports in Co-based oxygen evolution reaction (OER) catalysts was elucidated through a combination of experimental and computation electrochemistry. Through facile seeding of commericial Co nanoparticles on three different MXene supports (Ti3C2Tx, Mo2Ti2C3Tx, Mo2CTx), Co@MXene catalysts were prepared and their electrochemical properties examined for alkaline OER electrocatalysts. The OER activity enhancement of Co was significantly improved for Mo2CTx and Mo2Ti2C3Tx supports, but marginal on the Ti3C2Tx in rotating disk electrode and membrane electrode assembly tests. The Co@Mo2CTx exhibited the highest anion exchange water electrolysis performance of 2.11 A cm−2 at 1.8 V with over 700 h of stable performance, exceeding previous benchmarks for non-platinum group (non-PGM) metal OER catalysts. The superior performance was attributed to the strong chemical interaction of Co nanoparticle with the Mo2CTx MXene support. Insights into the electrochemical and chemical oxidation according to MXene type as related to cell durability, as well the effect of electrical conductivity and inherent boosting of electrocatalytic activity of Mo-based MXenes elucidated through density functional theory (DFT) calculations helped explain the performance and durability enhancement of Mo-based MXene supports over Ti3C2Tx supports.

Oxygen evolution reaction (OER) active sites in BiVO4 studied using density functional theory and XPS experiments.

Bismuth vanadate (BiVO4/BVO) has been widely studied as a photocatalytic water splitting semiconductor material in recent years because of its many advantages, such as its ease of synthesis and suitable band gap (2.4 eV). However, BVO still has some disadvantages, one of which is the low photocatalytic water oxidation activity. It is intriguing and unexpected to note that in the current literature, Bi atoms are taken as the oxygen evolution reaction (OER) active sites, while V metal atoms are not investigated in the OER, and the underlying reason for this remains unknown. In this work, using density functional theory (DFT) calculations and ab initio molecular dynamics simulations, we found that in BVO, the VO4 tetrahedron structure is very stable and there is strong surface reconstruction that leads to the V atoms on the surface having the same coordinates as in the bulk. For some high index surfaces, there are some theoretically predicted unsaturated V sites, but it is very easy to form a VO4 tetrahedron structure again by taking oxygen atoms from water. The other intermediates of OER are difficult to adsorb or desorb on this VO4 structure, which makes the V sites in BVO unsuitable as OER active sites. This VO4 structure remained stable during the molecular dynamics simulation at 300 and 673 K. The XPS characterization of various BVO morphologies validates our primary findings from DFT and molecular dynamics simulations. It reveals the presence of unsaturated Bi sites on the BVO surface, while unsaturated V sites are not observed. This study provides novel insights into the enhancement of OER activity of BVO and offers a fundamental understanding of OER activity in other photocatalysts containing V atoms.

Novel ruthenium-based catalysts with atomic dispersion for oxygen evolution reaction in water electrolysis

This study introduces a method for fabricating ultra-high-performance catalysts designed for the oxygen evolution reaction (OER), employing a combination of ball-milling, autoclave heat treatment procedures, and a two-step heat treatment approach. This method produces catalysts characterized by an atomic dispersion of ruthenium on nitrogen-doped carbon sheets (Ru–O/N–C–NH3). The Ru–O/N–C–NH3 catalyst exhibits exceptional OER activity in alkaline conditions, achieving a mass activity of 16842 A g−1Ru at 1.52 V, and a minimal overpotential of 290 mV at a current density of 10 mA cm−2. Moreover, this catalyst demonstrates enduring stability, showing no significant decay after a 100-h stability test in anion exchange membrane water electrolysis (AEMWE), with a mass activity approximating 62000 A g−1PGM. This is nearly three orders of magnitude greater than the AEMWE that utilizes commercial IrO2 as an anode. The atomic dispersion and the Ru–O/N bonding of the catalyst are substantiated to contribute to the notable enhancement in OER activity.

Spin States and Spin Order in Perovskite Oxide Oxygen Evolution Electrocatalysts

The ‘power-to-hydrogen’ strategy aims at splitting water into O2 and H2 via the oxygen and hydrogen evolution reactions. The complex four-step oxygen evolution reaction (OER) limits the overall efficiency of hydrogen production. An important reason of the low efficiency is that the production of ground-state (triplet) O2 is a spin-forbidden reaction: in fact, the reactants, OH- or H2O, are diamagnetic, but the final product, O2, is a paramagnetic molecule. Recently, this was well-recognized theoretically1 and the use of spin selective catalysts was described as a possible way to promote the OER.2 . However, it remains complex to understand and exploit intrinsic and extrinsic magnetic features to enhance catalytic performance. Here, we investigate the role of magnetic moments in individual active sites in the catalyst surface layer and the role of spin order in ferromagnetic vs. paramagnetic catalysts, focussing on perovskite oxides.First, we investigated the role of Ni magnetic moment in the the (001), (110) and (111) facet of LaNiO3 electrocatalysts, which we studied using electrochemical measurements, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT+U) calculations.3 The results show a facet-dependent activity, where the (111) overpotential is ~60 mV lower as compared to the other facets. Closer investigation of the (001) and (111) facets reveals a surface transformation to a oxyhydroxide-like NiOO with edge-sharing octahedra,4 and we observed that the transformed surface is thicker for (111) than for (001).3 The detailed DFT+U analysis reveals important distinctions that give rise to the increased activity: the transformed LaNiO3 (111) surface exhibits a better match to the underlying perovskite layer. Moreover, protonation induces reduced Ni3+ with a finite magnetic moment. A moderate Jahn-Teller distortion enables a favorable binding of reaction intermediates. In contrast, the structural mismatch to the underlying LaNiO3(001)-substrate leads to a strong distortion of the transformed layer for this orientation and a weak binding of *O and ultimately to a different potential determining step (PDS), *OH→*O, compared to *O→*OOH for the transformed LaNiO3(111) surface.Second, we experimentally demonstrate the effect of intrinsic magnetic order on the OER on catalytic performance. Thin films of La0.67Sr0.33MnO3 grown by pulsed laser deposition with appropriate magnetic and electronic properties were chosen as well-defined model systems. Using the ferromagnetic to paramagnetic transition at the Curie temperature in these ferromagnetic perovskite oxides, the magnetic order of the catalysts were switched in situ during the OER by changing the temperature. For ferromagnetic films, the decrease in current density with decreasing temperature, induced by the reduction of thermal energy, was suppressed for temperatures below the Curie temperature, indicating that the presence of ferromagnetic ordering below Curie temperature enhances OER activity. This claim is further supported by an enhancement of OER activity for the same ferromagnetic film upon alignment of magnetic domains with an external magnetic field. All in all, our results reveal that the spin state, intrinsic spin order, and extrinsic magnetic fields are decisive for the OER activity. Biz, C., Fianchini, M. & Gracia, J. Strongly Correlated Electrons in Catalysis: Focus on Quantum Exchange. ACS Catal 11, 14249–14261 (2021).Sun, Y. et al. Spin‐Related Electron Transfer and Orbital Interactions in Oxygen Electrocatalysis. Advanced Materials 32, 2003297 (2020).Füngerlings, A. et al. Crystal-facet-dependent surface transformation dictates the oxygen evolution reaction activity in lanthanum nickelate. in preparation (2023).Baeumer, C. et al. Tuning electrochemically driven surface transformation in atomically flat LaNiO3 thin films for enhanced water electrolysis. Nat Mater 20, 674–682 (2021).

Highly mixed high-energy d-orbital states enhance oxygen evolution reactions in spinel catalysts

Design, synthesis, and engineering of electrocatalysts for the oxygen evolution reaction (OER) are essential for attaining desirable electrocatalytic performance towards practical implementation. Emerging spinel-type OER catalysts have not reached the desirable activity and durability, thus demanding critical research to advance the field. To achieve enhanced OER performance for spinel-type OER catalysts, we present an efficient strategy of electronic structure modulation of central metal atoms. Modulation of the electronic properties of the Zn and Co atoms through the counter anionic components (O, S, and Se) regulates the adsorption of oxygen intermediates and thus enhances OER activity, which is systematically demonstrated using Density Functional Theory (DFT) calculation. Although the zinc cobalt selenide catalyst showed the less pronounced trigonal distortion, the mixing of eg orbitals with selenium accounts for the experimentally observed enhancement in OER activity. The result is, in contrast to the benchmark catalyst made of RuO2, ZnCo2Se4@rGO demonstrated lower OER overpotential (η10 = 302 mV) and Tafel slope (58 mV dec−1) as well as greater durability at 10 mA cm−2 for 50 h. The implementation of this strategy in several spinel-type catalysts could improve their electrocatalytic performance.

Oxidation State Engineering in Octahedral Ni by Anchored Sulfate to Boost Intrinsic Oxygen Evolution Activity

Promoting the electron occupancy of active sites to unity is an effective method to enhance the oxygen evolution reaction (OER) performance of spinel oxides, but it remains a great challenge. Here, an in situ approach is developed to modify the valence state of octahedral Ni cations in NiFe2O4 inverse spinel via surface sulfates (SO42-). Different from previous studies, SO42- is directly anchored on the spinel surface instead of forming from uncontrolled conversion or surface reconstruction. Experiment and theoretical calculations reveal the precise adsorption sites and spatial arrangement for SO42- species. As a main promoting factor, surface SO42- effectively converts the crystal field stable Ni state (t2g6eg2) to the near-unity eg electron state (t2g6eg1). Moreover, the inevitable oxygen vacancies (Vo) further optimize the energy barrier of the potential-determining step (from OH* to O*). This co-modification strategy enhances turnover frequency-based electrocatalytic activity about two orders higher than the control sample without surface sulfates. This work may provide insight into the OER activity enhancement mechanism by the oxyanion groups.

Promoting the electrocatalytic oxygen evolution reaction on NiCo2O4 with infrared-thermal effect: A strategy to utilize the infrared solar energy to reduce activation energy during water splitting

Utilization of the infrared (IR) solar energy remains a challenging task for traditional photo(electro)catalysis. Taking advantage of the IR-thermal effect to facilitate sluggish electrocatalytic reactions emerges as a promising way to utilize the IR band of the solar spectrum. In this work, nickel foam (NF) supported NiCo2O4 nanoneedles (NF/NiCo2O4 NNs) were prepared to promote the oxygen evolution reaction (OER) via the IR-thermal effect, with the NF/NiCo2O4 NNs acting as both the IR absorbing antennae and the OER active anode. The potential required to deliver a current density of 200 mA cm−2 is negatively shifted from 1.618 V in the dark to 1.578 V under IR irradiation, and the Tafel slope is also decreased from 106 to 89 mV dec−1. We demonstrate that the enhancement of OER activity is due to the localized temperature rise under IR irradiation. We measured the electrochemical activation energy of OER on NF/NiCo2O4 with and without IR irradiation, and the results reveal that IR irradiation reduces the kinetic energy barrier of the OER by IR-thermal effect and then facilitates OER kinetics. This work highlights a new approach to utilizing the IR portion of the sunlight to produce renewable hydrogen energy via water splitting.

Tuning Electronic Structure of CuCo2O4 Spinel via Mn‐Doping for Enhancing Oxygen Evolution Reaction

AbstractCobalt‐based spinel oxide is a promising electrocatalyst for oxygen evolution reaction (OER) because of its low cost, excellent activity and stability. Herein, we designed the CuMnxCo2O4 electrocatalyst with tunable electronic structure via Mn‐doping to enhance OER performance. Results showed that the CuMn0.5Co2O4 catalyst prepared by calcined at 600°C exhibited high crystalline without impurity phase, and possessed the enhanced Co2+/Co3+ ratio and high concentration of oxygen vacancies, which were facilitated to enhance OER performance. Electrochemical test results showed the CuMn0.5Co2O4 catalyst had high OER performance with a low overpotential of 340 mV at the current density of 10 mA ⋅ cm−2 and a smaller Tafel slope of 69.8 mV ⋅ dec−1. TOF and ECSA results illustrated that the more intrinsic catalytic activity on the CuMn0.5Co2O4 catalyst. After 1000 cycles, the catalyst exhibited high stability with the 8 1.7 % of current retention rate. The OER activity enhancement mechanism of was further analyzed, which were mainly ascribed to the conversion of variable Co2+/Co3+ and enhanced oxygen vacancies.

Identifying high-efficiency Ni-based alloys/(oxy)hydroxides electrocatalysts for oxygen evolution reaction through a rapid screening method

Ni-based (oxy)hydroxides, as a kind of cost-effective oxygen evolution reaction (OER) electrocatalysts to replace precious Ru/Ir-based catalysts, have attracted comprehensive attention. Recently, the nickel utilization has also come under interest in the latest prices soar of nickel. Herein, 41 kinds of Ni-M (oxy)hydroxides (M = Fe, Cu, Co and Cr) are prepared via a quick electrodeposition method to screen Ni-M (oxy)hydroxides. It is observed that OER activity and durability of Ni-M (oxy)hydroxides heavily depend on the content of M, and the Fe plays the best role on OER activity enhancement. The optimum Ni8Fe2/Ni(OH)2/FeOOH (NiFe-8) exhibit a low overpotential of 270 mV at a current density of 10 mA cm−2 and Tafel slope of 83 mV dec−1, which are lower than those of other Ni-M (oxy)hydroxides. In addition, the designed NiFe-8 shows superior cycling stability (10,000 times), self-adapting function during 33.01–49.65 h resulting in a 55.56 h long-term operation durability with 15.94 mA cm−2 ending activity. Such performance together with low preparation cost, Ni-based materials are favorable for enterprises to improve their economic benefit as well as open up an opportunity for mass-producing of them.

Operando identification of active sites in Co-Cr oxyhydroxide oxygen evolution electrocatalysts

Identifying the active sites and their dynamic changes is of critical significance for designing efficient oxygen evolution reaction (OER) catalysts, but remains challenging owing to the complexity in structure and reaction process. Herein, using various operando characterizations, we identify the origin of a 12-time enhancement of OER activity over pure cobalt oxyhydroxide achieved by confining high-valance chromium into its lattice. Operando X-ray absorption spectroscopy reveals in-situ generation of high-valence Cr state with shortened CrO bond relative to original state, indicating potential-dependent formation of OER intermediates on Cr sites. Operando electrochemical impedance and infrared spectroscopy provide direct spectroscopic evidence of OOH* on Cr site. Combined with theoretical calculations, the confined Cr is identified as the active site with improved bonding strength with O*, exhibiting a lower overpotential than that on Co site. This study elucidates the dynamic behaviour of active sites and provides guiding for improving OER catalysts via introducing high-valance metals.

Role of Noble- and Base-Metal Speciation and Surface Segregation in Ni2–xRhxP Nanocrystals on Electrocatalytic Water Splitting Reactions in Alkaline Media

Transition-metal phosphides have proven to be surprisingly active electrocatalysts for electrochemical water splitting, but the nature of the “active” catalyst depends strongly on the solution pH, the identity of the metals, and whether the reactions are anodic [oxygen evolution reaction (OER)] or cathodic [hydrogen evolution reaction (HER)]. In order to understand the origin of this activity, the synthesis of well-defined, compositionally controlled precatalysts is needed, as are detailed catalytic studies and physicochemical characterization/activity assessment of catalysts at different stages. While base-metal phosphides of Ni and Co have the advantage of being earth-abundant, in alkaline media, they are less active and less stable than noble-metal phosphides such as Rh2P. As a means to combine the abundant nature of base metals with the activity and stability of noble metals, the first synthesis of colloidal Ni2–xRhxP nanocrystals by arrested precipitation routes is reported along with their composition-dependent activity for electrocatalytic HER and OER. Phase-pure samples of Ni2–xRhxP were realized at the Ni-rich (hexagonal, Fe2P-type) end (x = 0.00, 0.25, 0.50) and Rh-rich (cubic, antifluorite-type) end (x = 1.75, 2.00). When assessed in terms of current density normalized to electrochemical surface area (ECSA) at a fixed potential, the most active precatalyst for OER is Ni1.75Rh0.25P, and for HER, it is Rh1.75Ni0.25P. Evaluation of X-ray photoelectron spectroscopy, transmission electron microscopy/energy-dispersive spectroscopy and ECSA data before and after 10 h stability runs were performed. The data reveal surface compositions to be considerably richer in Ni and poorer in Rh and P relative to the bulk composition, particularly for Ni0.25Rh1.75P, where the surface ratio of Ni/Rh is nearly 2:1 and increases to 4:1 after HER catalysis. In all cases, surface phosphorus is completely depleted post catalysis, suggesting a sacrificial role for phosphide under alkaline conditions. Moreover, the activity of “Rh1.75Ni0.25P” for HER decreases over time, even as the ECSA continues to rise, attributed to a decrease in the more active and stable Rh sites relative to Ni on the surface. In contrast, the enhancement in OER activity of Ni2P with 12.5% Rh incorporation is attributed to restructuring upon phase segregation of Rh, suggesting that the noble metal may also play a sacrificial role and not directly participate in OER catalysis. The roles of minority noble metals (Rh) in base-metal phosphides for OER and of minority base metals in noble-metal (Rh) phosphides for HER are discussed in light of related data on Co2–xRhxP.

Controlling the D-band for improved oxygen evolution performance in Ni modulated ultrafine Co nanoparticles embedded in Nitrogen-doped carbon microspheres

Despite the challenges on tuning the d-band structure of transition metals, the d-band is of great importance for promoting the interaction between catalytic and intermediates during the oxygen evolution reaction (OER) process. Herein, ultrafine Co nanoparticles embedded in the surface layer of nitrogen-doped carbon microspheres are prepared through an in-situ co-coordination strategy, and its d-band is modulated by introducing different Ni amounts. The introduction of Ni in the Co crystal lattice can tune the d-band center and unpaired electrons, which collectively result in an enhancement of OER activity and kinetics. By investigating the catalysts with Ni content from 0% to 75%, it is concluded that the catalyst with 25% Ni shows optimal OER activity, lower overpotential (285 mV at 10 mA cm−2) and higher current densities (73.75 mA cm−2 at 1.63 V). Moreover, the good stability is also demonstrated with the negligible decrease on current densities after 3000 CV cycles or 100 h of continuous test in alkaline media. This concept of modulating the d-band structure by introducing a transition metal with different contents in another transition metal crystal lattice could present an alternative pathway to the development of highly active catalytic materials for OER and beyond.

Sonoactivated polycrystalline Ni electrodes for alkaline oxygen evolution reaction

The development of cost-effective and active water-splitting electrocatalysts is an essential step toward the realization of sustainable energy. Its success requires an intensive improvement in the kinetics of the anodic half-reaction of the oxygen evolution reaction (OER), which determines the overall system efficiency to a large extent. In this work, we designed a facile and one-route strategy to activate the surface of metallic nickel (Ni) for the OER in alkaline media by ultrasound (24 kHz, 44 W, 60% acoustic amplitude, ultrasonic horn). Sonoactivated Ni showed enhanced OER activity with a much lower potential at + 10 mA cm−2 of + 1.594 V vs. RHE after 30 min ultrasonic treatment compared to + 1.617 V vs. RHE before ultrasonication. In addition, lower charge transfer resistance of 11.1 Ω was observed for sonoactivated Ni as compared to 98.5 Ω for non-sonoactivated Ni. In our conditions, ultrasound did not greatly affect the electrochemical surface area (Aecsa) and Tafel slopes however, the enhancement of OER activity can be due to the formation of free OH• radicals resulting from cavitation bubbles collapsing at the electrode/electrolyte interface.

A nanoflower composite catalyst in situ grown on conductive iron foam: Revealing the enhancement of OER activity by cooperating of amorphous Ni based nanosheets with spinel NiFe2O4

As a bottleneck step in electrochemical water splitting, oxygen evolution reaction (OER) seriously limits the development of large-scale electrochemical hydrogen production. Rational design and development of an efficient and stable OER electrocatalysts are of enormous importance but still challenging for electrochemical energy conversion. In this work, a unique nanoflower like electrocatalyst consisting of NiFe2O4 nanoparticles wrapped with amorphous Ni based nanosheet on the 3D porous iron foam (IF) substrate (named as Ni-ANS@NiFe2O4/IF) is proposed and the evolution of catalyst morphology and its effect on electrochemical activity were explored. Profiting from the unique nanoflower structure and the coupling of ample active substances with favorable conductive substrates, the prepared Ni-ANS@NiFe2O4/IF exhibits outstanding OER activity with low overpotential of 209, 251, 270 mV to reach a current density of 10, 100 and 200 mA cm−2, and admirable long-term stability. This work may broaden a new vision and avenue for the design of efficient OER catalysts.

Chromium doping: A new approach to regulate electronic structure of cobalt carbonate hydroxide for oxygen evolution improvement

Highly efficient catalysts are required to solve the intrinsically sluggish kinetics of oxygen evolution reaction (OER). Herein, chromium doped cobalt carbonate hydroxide nanowire array on Ni foam (Cr-CoCH/NF) has been synthesized for the enhancement of OER activity and stability. Compared with pure CoCH/NF, Cr0.2-CoCH/NF, the optimal doping of Cr, shows a low overpotential of 203 mV at the current density of 10 mA cm−2 and a small Tafel slope of 84 mV dec−1 in 1.0 M NaOH. In addition, there is little deterioration in electrocatalytic performance after 1000-cycle cyclic voltammetry and the high activity can be maintained over 25 h. Density functional theory calculations reveal the Cr doping can regulate the electronic structure of nearby Co active center to achieve great enhancement of OER activity.

SmCo5 with a Reconstructed Oxyhydroxide Surface for Spin-Selective Water Oxidation at Elevated Temperature.

The efficiency of electrolytic hydrogen production is limited by the slow reaction kinetics of oxygen evolution reaction (OER). Surface-reconstructed ferromagnetic (FM) catalysts with a spin-pinning effect at the FM/oxyhydroxide interface could enhance the spin-dependent OER kinetics. However, in real-life applications, electrolyzers are operated at elevated temperature, which may disrupt the spin orientations of FM catalysts and limit their performance. In this study, we prepared surface-reconstructed SmCo5 /CoOx Hy , which possesses polarized spins at the FM/oxyhydroxide interface that lead to excellent OER activity. These interfacial polarized spins could be further aligned through a magnetization process, which further enhanced the OER performance. Moreover, the operation temperature was elevated to mimic the practical operation conditions of water electrolyzers. It was found that the OER activity enhancement of the magnetized SmCo5 /CoOx Hy catalyst could be preserved up to 60 °C.

SmCo5 with a Reconstructed Oxyhydroxide Surface for Spin‐Selective Water Oxidation at Elevated Temperature

AbstractThe efficiency of electrolytic hydrogen production is limited by the slow reaction kinetics of oxygen evolution reaction (OER). Surface‐reconstructed ferromagnetic (FM) catalysts with a spin‐pinning effect at the FM/oxyhydroxide interface could enhance the spin‐dependent OER kinetics. However, in real‐life applications, electrolyzers are operated at elevated temperature, which may disrupt the spin orientations of FM catalysts and limit their performance. In this study, we prepared surface‐reconstructed SmCo5/CoOxHy, which possesses polarized spins at the FM/oxyhydroxide interface that lead to excellent OER activity. These interfacial polarized spins could be further aligned through a magnetization process, which further enhanced the OER performance. Moreover, the operation temperature was elevated to mimic the practical operation conditions of water electrolyzers. It was found that the OER activity enhancement of the magnetized SmCo5/CoOxHy catalyst could be preserved up to 60 °C.