Enhanced Oxygen Evolution Research Articles

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.

CoNi2S4 cocatalyst modified TiO2 nanorods/nanoflower homojunction for efficient photoelectrochemical water splitting

Photoelectrochemical water splitting is a promising green method for obtaining clean energy, and its core lies in the preparation of high-performance photoanodes. In this study, TiO2 nanorods/nanoflower homojunction photoanodes were prepared using a one-step hydrothermal method, unlike the complex material composite process used in most previous research works, the TiO2 homojunction photoanode obtained through a one-step method combines the advantages of nanorod and nanoflower structures. CoNi2S4 was further used as an oxygen evolution cocatalyst supported on the TiO2 nanorods/nanoflower homojunction photoanodes, enhancing oxygen evolution kinetics. The photogenerated current density of the obtained TiO2 flower-rod/CoNi2S4 composite photoanode at 1.23 V (versus RHE) was 1.64 mA cm−2, which is 2.3 times of that of TiO2 nanorod photoanode. By density function theory calculation, it is confirmed that the loading of CoNi2S4 cocatalyst can significantly reduce the overpotential and enhance the kinetic process of oxygen evolution reaction.

Enhanced oxygen evolution of a new copper-based metal-organic framework through the construction of a heterogeneous structure with bismuth oxyiodide

Herein, a newly developed MOF, Cu-based on 2-amino terephthalic acid (CuATPA) is successfully prepared and utilized as a photoanode material. To achieve high-efficiency electron/hole separation and rapid catalytic kinetics, a heterojunction architecture is designed by combining CuATPA with BiOI. Scanning electron microscopy images reveal the formation of CuATPA nanoplates within the structures of BiOI nanoflakes. Electrochemical characterization demonstrates the excellent photoelectrocatalytic performance of the CuATPA-BiOI nanocomposite. Linear sweep voltammetry reveals a reduced overpotential value for the CuATPA-BiOI nanocomposite, indicating enhanced catalytic activity. Moreover, the CuATPA-BiOI photoanode displays a photo-voltage of 0.43 V compared to 0.23 and 0.24 V for the CuATPA and BiOI photoanodes, respectively, indicating a deeper band bending. The improved photoelectrochemical performance of the nanocomposite is attributed to efficient separation and transfer of photo-generated charge carriers, as evidenced by higher charge density extracted from the Mott-Schottky plot and smaller semicircle radius in the Nyquist plot.

Electric-field-assisted proton coupling enhanced oxygen evolution reaction.

The discovery of Mn-Ca complex in photosystem II stimulates research of manganese-based catalysts for oxygen evolution reaction (OER). However, conventional chemical strategies face challenges in regulating the four electron-proton processes of OER. Herein, we investigate alpha-manganese dioxide (α-MnO2) with typical MnIV-O-MnIII-HxO motifs as a model for adjusting proton coupling. We reveal that pre-equilibrium proton-coupled redox transition provides an adjustable energy profile for OER, paving the way for in-situ enhancing proton coupling through a new "reagent"- external electric field. Based on the α-MnO2 single-nanowire device, gate voltage induces a 4-fold increase in OER current density at 1.7 V versus reversible hydrogen electrode. Moreover, the proof-of-principle external electric field-assisted flow cell for water splitting demonstrates a 34% increase in current density and a 44.7 mW/cm² increase in net output power. These findings indicate an in-depth understanding of the role of proton-incorporated redox transition and develop practical approach for high-efficiency electrocatalysis.

Electron Accumulation Induced by Electron Injection-Incomplete Discharge on NiFe LDH for Enhanced Oxygen Evolution Reaction.

Optimizing the local electronic structure of electrocatalysts can effectively lower the energy barrier of electrochemical reactions, thus enhancing the electrocatalytic activity. However, the intrinsic contribution of the electronic effect is still experimentally unclear. In this work, the electron injection-incomplete discharge approach to achieve the electron accumulation (EA) degree on the nickel-iron layered double hydroxide (NiFe LDH) is proposed, to reveal the intrinsic contribution of EA toward oxygen evolution reaction (OER). Such NiFe LDH with EA effect results in only 262mV overpotential to reach 50 mAcm-2, which is 51mV-lower compared with pristine NiFe LDH (313mV), and reduced Tafel slope of 54.8mVdec-1 than NiFe LDH (107.5mVdec-1). Spectroscopy characterizations combined with theoretical calculations confirm that the EA near concomitant Vo can induce a narrower energy gap and lower thermodynamic barrier to enhance OER performance. This study clarifies the mechanism of the EA effect on OER activity, providing a direct electronic structure modulation guideline for effective electrocatalyst design.

Elemental Charge Engineering in Cobalt and Cobalt–Phosphide Interface for Enhanced Oxygen Evolution and Urea Oxidation Reactions

Elemental Charge Engineering in Cobalt and Cobalt–Phosphide Interface for Enhanced Oxygen Evolution and Urea Oxidation Reactions

The Role of Photo in Oxygen Evolution Reaction: A Review.

Photo enhanced oxygen evolution reaction has recently emerged as an advanced strategy with great application prospects for highly efficient energy conversion and storage. In the course of photo enhanced oxygen evolution reactions, the other works focus has predominantly centered on catalysts while inadvertently overlooking the pivotal role of photo. Consequently, this manuscript embarks upon a comprehensive review of recent advancements in photo-driven, aiming to illuminate this critical dimension. A detailed introduction to the photothermal effect, photoelectronic effect, photon-induced surface plasmon resonance, photo and heterojunction, photo-induced reversible geometric conversion, photo-induced energy barrier reduction, photo-induced chemical effect, photo-charging, and the synthesis of laser/photo-assisted catalysts, offering prospects for the development of each case is provided. A detailed introduction to the photothermal effect, photoelectronic effect, photon-induced surface plasmon resonance, photo and heterojunction, photo-induced reversible geometric conversion, photo-induced energy barrier reduction, photo-induced chemical effect, photo-charging, and the synthesis of laser/photo-assisted catalysts is provided. At the same time, the overpotential and Tafel slope of some catalysts mentioned above at 10mAcm-2 is collected, and calculated the lifting efficiency of light on them, offering prospects for the development of each case.

Enhanced oxygen evolution reaction of 2-dimensional metal-organic frameworks with tunable nitrogen functionalities by ion beam sputtering

Modification of metal–organic frameworks (MOFs) is recently under the spotlight due to their versatile properties and potential applications in electrochemical catalysis. Here, we successfully demonstrate nitrogen doping into the MOF electrocatalyst without noble metals using a facile, tunable ion beam sputtering (IBS) process for the first time and evaluate the role of the incorporated heteroatom. Two-dimensional Ni-naphthalene-2,6-dicarboxylic acid MOF (NiNDC) with large surface area was subjected to nitrogen IBS (NIBS) and exhibited significantly improved performance for oxygen evolution reaction (OER) with a low overpotential of 222 mV at 10 mA cm−2; a Tafel slope of 88 mV dec-1; and over 120 h of stability at 100 mA cm−2. The relationship between the nitrogen functionalities and catalytic activity was elucidated by spectroscopic analysis and electrochemical measurements, i.e., (i) pyridinic N as an electron-withdrawing group that directly enhances the reaction kinetics, (ii) pyrrolic N to stabilize the catalyst and (iii) graphitic N to enhance the electrical conductivity. We found that the electrocatalytic performance was affected by the ratio of the three nitrogen species, which was controllable by the accelerating potential (AP) of NIBS. This study provides insights into the influence of the chemical state of MOF surfaces on catalytic reactions and presents a novel method for effective nitrogen doping.

The formation of unsaturated IrOx in SrIrO3 by cobalt-doping for acidic oxygen evolution reaction

Electrocatalytic water splitting is a promising route for sustainable hydrogen production. However, the high overpotential of the anodic oxygen evolution reaction poses significant challenge. SrIrO3-based perovskite-type catalysts have shown great potential for acidic oxygen evolution reaction, but the origins of their high activity are still unclear. Herein, we develop a Co-doped SrIrO3 system to enhance oxygen evolution reaction activity and elucidate the origin of catalytic activity. In situ experiments reveal Co activates surface lattice oxygen, rapidly exposing IrOx active sites, while bulk Co doping optimizes the adsorbate binding energy of IrOx. The Co-doped SrIrO3 demonstrates high oxygen evolution reaction electrocatalytic activity, markedly surpassing the commercial IrO2 catalysts in both conventional electrolyzer and proton exchange membrane water electrolyzer.

Photo‐promoted rapid reconstruction induced alterations in active site of Ag@amorphous NiFe hydroxides for enhanced oxygen evolution reaction

AbstractThe dynamic surface self‐reconstruction behavior in local structure correlates with oxygen evolution reaction (OER) performance, which has become an effective strategy for constructing the catalytic active phase. However, it remains a challenge to understand the mechanisms of reconstruction and to accomplish it fast and deeply. Here, we reported a photo‐promoted rapid reconstruction (PRR) process on Ag nanoparticle‐loaded amorphous Ni‐Fe hydroxide nanosheets on carbon cloth for enhanced OER. The photogenerated holes generated by Ag in conjunction with the anodic potential contributed to a thorough reconstruction of the amorphous substrate. The valence state of unsaturated coordinated Fe atoms, which serve as active sites, is significantly increased, while the corresponding crystalline substrate shows little change. The different structural evolutions of amorphous and crystalline substrates during reconstruction lead to diverse pathways of OER. This PRR utilizing loaded noble metal nanoparticles can accelerate the generation of active species in the substrate and increase the electrical conductivity, which provides a new inspiration to develop efficient catalysts via reconstruction strategies.

Tailoring hypervalent Nickel induced by oxygen vacancy toward enhanced oxygen evolution reaction performance in self-supporting NiFe-(oxy)hydroxides electrodes

NiFe-(oxy)hydroxides are the most active transition metal oxide electrocatalysts for oxygen evolution reaction (OER) under the alkaline media. Herein, we controllably manipulated oxygen vacancy (VO)-tunable NiFe-(oxy) hydroxides that their OER performances possessed a volcano-type relationship with VO concentration, positively-correlated with Ni3+/Ni2+ ratio. Theoretical simulations further unearthed the enhanced activation and dissociation of H2O by the inserting of VO. As a result, the optimal sample featuring the Ni3+/Ni2+ ratio of 30.3 % and VO of 23.8 % exhibited the overpotential of 243 mV at the current density of 100 mA cm–2, simultaneously lasting 120 h durability without any attenuation, exceding the most reported NiFe-(oxy)hydroxides. This work offers an innovative view to understand the OER performance using hypervalent Ni ratio induced by VO defects.

Magnetic-Field-Induced Spin Regulation in Electrocatalytic Reactions.

The utilization of a magnetic field to manipulate spin states has emerged as a novel approach to enhance efficiency in electrocatalytic reactions, distinguishing from traditional strategies that focus on tuning activation energy barriers. Currently, this approach is specifically tailored to reactions where spin states change during the catalytic process, such as the oxidation of singlet H2O to triplet O2. In the magnetically enhanced oxygen evolution reaction (OER) procedure, the parallel spin alignment on the ferromagnetic catalyst was induced by the external magnetic field, facilitating the triplet O-O bonding, which is the rate limiting step in OER. This review centers on recent advancements in harnessing external magnetic fields to enhance OER performance, delving into mechanistic approaches for this magnetic promotion. Additionally, we provide a summary of magnetic field application in other electrocatalytic reactions, including oxygen reduction, methanol oxidation, and CO2 reduction.

Size optimization of IrOx nanoparticles synthesized by Br mediation for enhanced PEM water electrolysis

We have creatively developed a hydrothermal approach to synthesize ultra-small IrOx nanoparticles with precise size control at 1.6 nm by carefully modulating KBr concentrations. Br ions are adsorbed onto the surface of IrOx and modulate the free energy through adsorption, thereby controlling the nanoparticle size to achieve ultra-small IrOx. The tailored IrOx nanoparticles are aimed to be high-performance electrocatalysts for efficient oxygen evolution reaction. The optimized nanoparticles exhibited an ultra-low overpotential of 230 mV to reach 10 mA/cm2 for oxygen evolution reaction in acid and showed negligible degradation after 50 h operation at 10 mA/cm2. When assembled in a proton exchange membrane electrolyzer, the catalyst enabled the device to reach 1 A/cm2 at only 1.69 V with excellent durability over 100 h at 1 A/cm2. Through detailed cost accounting, it was determined that 1 kg of hydrogen could be produced for a remarkably low, significantly below prevailing cost targets. This work not only develops an effective strategy to enhance oxygen evolution reaction efficiency by tailoring IrO2 particle size, but also shows the great potential for scalable application in industrial water electrolysis.

Rapid Construction of Double Crystalline Prussian Blue Analogue Hetero-Superstructure.

The controllable construction of complex metal-organic coordination polymers (CPs) merits untold scientific and technological potential, yet remains a grand challenge of one-step construction and modulating simultaneously valence states of metals and topological morphology. Here, a thiocyanuric acid (TCA)-triggered strategy is presented to one-step rapid synthesis a double-crystalline Prussian blue analogue hetero-superstructure (PBA-hs) that comprises a Co3[Fe(CN)6]2 cube overcoated with a KCo[Fe(CN)6] shell, followed by eight self-assembled small cubes on vertices. Unlike common directing surfactants, TCA not only acts as a trigger for the fast growth of KCo[Fe(CN)6] on the Co3[Fe(CN)6]2 phase resulting in a PBA-on-PBA hetero-superstructure, but also serves as a flange-like bridge between them. By combining experiments with simulations, a deprotonation-induced electron transfer (DIET) mechanism is proposed for formation of second phase in PBA-hs, differing from thermally and photo-induced electron transfer processes. To prove utility, the calcined PBA-hs exhibits enhanced oxygen evolution reaction performance. This work provides a new method to design of novel CPs for enriching chemistry and material science. This work offers a practical approach to design novel CPs for enriching chemistry and material science.

Ultrasound-Assisted Synthesis of High-Entropy Materials for Enhanced Oxygen Evolution Electrocatalysis

High-entropy materials (HEMs) play a significant role in the electrocatalytic oxygen evolution reaction (OER) due to their unique properties. However, there are still challenges in the preparation of HEMs for OER catalysts. In this study, the FeCoNiMnCr catalyst is synthesized for the first time using the ultrasonic hydrothermal-sintering technique and exhibits excellent performance for OER electrocatalysis. There is an optimal ultrasonic hydrothermal time and power for achieving the best OER performance. The results demonstrate that the performance of FeCoNiMnCr catalysts prepared through ultrasonic hydrothermal sintering (US-FeCoNiMnCr) is significantly improved compared with the traditional hydrothermal-sintering method. The US-FeCoNiMnCr catalyst exhibits an overpotential of 228 mV at the current density of 10 mA cm−2 and a Tafel slope as low as 45.39 mV dec−1 in an alkaline medium. Moreover, the US-FeCoNiMnCr catalyst demonstrates remarkable stability in electrocatalytic OER with a minimal potential increase observed even after 48 h. This work not only provides valuable insights into high-entropy material synthesis, but also presents a powerful electrocatalyst for water electrolysis.

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.

Heterointerface engineering of hollow CoP/CeO2 p-n heterojunction for efficient electrocatalytic oxygen evolution

Heterointerface engineering is a promising strategy to realize electronic redistribution and enhance oxygen evolution reaction (OER) activity. However, preparing and designing heterojunction with appropriate band structures and outstanding performance remains a challenge. Herein, a novel hollow CoP/CeO2 heterojunction (h-CoP/CeO2) is constructed by electrospinning and a selective phosphorization process. Hollow structure can create more active sites and promote the intimate contact between catalysts and electrolyte to facilitate the mass and charge transfer. Mott-Schottky plots demonstrate p-n heterojunction is formed between p-CoP and n-CeO2, which induces a strong intrinsic field and redistribution of charges. Attributed to its hollow structure and p-n heterojunction, the optimal h-CoP/CeO2 prepared with appropriate PVP content and [Co/Ce] ratio exhibits remarkable alkaline OER activity (overpotential = 198 mV at 10 mA cm−2, Tafel slope = 83 mV dec−1). This result is better than or comparable to previous reports. Besides, h-CoP/CeO2 acing as a co-catalyst can improve the photoelectrochemical (PEC) performance of TiO2 nanorods, which not only increases the photocurrent density, but also reduces the onset potential (negatively shifted 58 mV for TiO2/CoP-CeO2). This study provided a new insight for constructing hollow heterojunction with uniform distribution of each component to enhance OER and PEC performance.

Synthesis of bimetal-decorated N-doped carbon nanoparticles for enhanced oxygen evolution reaction

Electrochemical hydrogen generation from the most plausible splitting water is severely hindered by OER (oxygen evolution reaction). Hence, the Fe4Co6@NDC amorphous sheet-like lamellar potential electrocatalyst prepared through simple solvothermal synthesis towards OER with low overpotential 307 mV @ 10 mA cm−2, Tafel slope of −55 mV dec-1 and turnover frequency of 0.0396 s−1, compared to 393 mV, Tafel slope of −81 mV dec-1, and a turnover frequency of 0.0136 s−1 at an IrO2 on an inert glassy carbon electrode, under the same conditions in 1 M KOH. The iron: cobalt adjacent ratio (4:6) could give a cooperative synergistic effect for OER, further nitrogen-doped carbon substrate (NDC) offers even metal anchoring sites has provided higher ECSA of 10.202 cm2 and also provides low resistive (5.6 Ω) material. Full cell water splitting Fe4Co6@NDC/NF (anode)//PtC/NF (cathode) with cell potential 1.58 V and the same setup will be used with perennial solar energy source only consumes 1.57 V enhanced hydrogen generation. We anticipate that the developed Fe4Co6@NDC electrocatalyst will be used as a formidable OER catalyst for a clean electrochemical energy conversion process.

Unlocking the potential of Heusler alloy Ni2CuSn as an electro(pre)catalyst for enhanced oxygen evolution reaction performance

Unlocking the potential of Heusler alloy Ni2CuSn as an electro(pre)catalyst for enhanced oxygen evolution reaction performance

Modulating Electronic Structure of Iridium Single-Atom Anchored on 3D Fe-Doped β-Ni(OH)2 Catalyst with Nanopyramid Array Structure for Enhanced Oxygen Evolution Reaction.

Developing high-performance electrocatalysts for oxygen evolution reaction (OER) is crucial in the pursuit of clean and sustainable hydrogen energy, yet still challenging. Herein, a spontaneous redox strategy is reported to achieve iridium single-atoms anchored on hierarchical nanosheet-based porous Fe doped β-Ni(OH)2 pyramid array electrodes (SAs Ir/Fe-β-Ni(OH)2), which exhibits high OER performance with a low overpotential of 175mV at 10mAcm-2 and a remarkable OER current density in alkaline electrolyte, surpassing Fe-β-Ni(OH)2/NF and IrO2 by 31 and 38 times at 1.43V versus RHE, respectively. OER catalytic mechanism demonstrates that the conversion of *OH→*O and the active lattice O content can be significantly improved due to the modulation effect of the Ir single atoms on the local electronic structure and the redox behavior of FeNi (oxy) hydroxide true active species. This work provides a promising insight into understanding the OER enhancement mechanism for Ir single-atoms modified FeNi-hydroxide systems.