Oxygen Evolution Reaction Overpotential Research Articles

Renewable energy storage using hydrogen produced from seawater membrane-less electrolysis powered by triboelectric nanogenerators

Utilization of widely available seawater for hydrogen generation using robust electrolysis methods can provide sustainable solutions to energy carriers. Sea waves at the same time provide abundant renewable energy that can produce the electricity required for seawater electrolysis. This work presents a novel design for a self-powered hydrogen generation based on membrane-less seawater electrolysis integrated with spring-assisted spherical triboelectric nanogenerators. To streamline fabrication and minimize maintenance expenses, water electrolysis is conducted in a membrane-less electrochemical cell reactor. Employing a mathematical model, the system's performance is analyzed across different catalysts, electrolytes, and operational temperatures. The modeling outcomes indicate that elevating the cell's temperature can lower the necessary potential, enhancing overall electrochemical cell efficiency and decreasing capacitor charging duration. The voltage required for the cell to reach 100 mA cm−2 in the seawater decreases from 2.4 V to 1.9 V as the cell temperature increase from 25 °C to 70 °C. This is due to the decline in the hydrogen and oxygen evolution reaction overpotentials for NPNNS and Ti supported PtPd from 351 mV to 246 mV and 568 mV–394 mV, respectively. Furthermore, increase in the temperature results in an additional 19 % improvement in cell efficiency from 78 % to 97 % and producing hydrogen per cycle during electrolysis of seawater increase from 0.015 μmole to 0.020 μmole.

Designing a Phenalenyl-Based Dinuclear Ni(II) Complex: An Electrocatalyst with Two Single Ni Sites for the Oxygen Evolution Reaction (OER).

A new dinuclear Ni(II) complex 1, [Ni2II(dtbh-PLY)2], is synthesized from 9-(2-(3,6-di-tert-butyl-2-hydroxybenzylidene)hydrazineyl)-1H-phenalen-1-one, dtbh-PLYH2 ligand, and structurally characterized by various analytical tools including the single-crystal X-ray diffraction (SCXRD) technique. In the solid state, both Ni(II) metal centers in complex 1 exist in a distorted square planar geometry and display the presence of rare Ni···H-C anagostic interactions to form a one-dimensional (1-D) linear motif in the supramolecular array. Complex 1 is further stabilized in the solid state by π-π-stacking interactions between the highly delocalized phenalenyl rings. The redox features of complex 1 have been analyzed by the cyclic voltammetry (CV) technique in solution as well as in the solid state, revealing the crucial involvement of both the Ni(II) metal centers for undergoing quasi-reversible oxidation reactions on the application of an anodic sweep. A complex 1-modified glassy carbon electrode, GC-1, is employed as an electrocatalyst for oxygen evolution reaction (OER) in 1.0 M KOH, giving an OER onset at 1.45 V, and very low OER overpotential, 300 mV vs the reversible hydrogen electrode (RHE) to reach 10 mA cm-2 current density. Furthermore, GC-1 displayed fast OER kinetics with a Tafel slope of 40 mV dec-1, a significantly lower Tafel slope value than those of previously reported molecular Ni(II) catalysts. In situ electrochemical experiments and postoperational UV-vis, Fourier transform infrared (FT-IR), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) studies were performed to analyze the stability of the molecular nature of complex 1 and to gain reasonable insights into the true OER catalyst.

Fe-Incorporated Metal-Organic Cobalt Hydroxide Toward Efficient Oxygen Evolution Reaction

AbstractMetal-organic cobalt hydroxide emerges as a cost-effective electrocatalyst for the oxygen evolution reaction (OER) in energy conversion. However, the limited active sites and poor conductivity hinder their large-scale application. This study employed salicylate as a bridging ligand to synthesize iron-incorporated metal-organic cobalt hydroxide. The influence of Fe intercalation on Co(OH)(Hsal) (where Hsal denotes o-HOC6H4COO−) was investigated using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Fe0.2Co0.8(OH)(Hsal) demonstrates remarkable electrocatalytic activity, displaying an OER overpotential of 298 mV at 10 mA cm−2 and a Tafel slope of 57.46 mV dec−1. This enhancement can be attributed to improved charge transfer kinetics and increased active sites. This work highlights the crucial role of Fe in improving the efficiency of Co-based oxygen-evolving catalysts (OECs) and its potential for boosting efficient hydrogen generation in alkaline environments. Graphical Abstract

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.

Regulating the electronic state of SnO2@NiFe-LDH heterojunction: Activating lattice oxygen for efficient oxygen evolution reaction

In Oxygen Evolution Reaction (OER), catalysts with lattice oxygen, utilizing the Lattice Oxygen Mechanism (LOM), directly participate in oxygen evolution, effectively reducing activation energy. NiFe-Layered Double Hydroxides (NiFe-LDHs), rich in surface hydroxyls, are potential for LOM. However, their stability is challenged in alkaline conditions due to metal cation dissolution from the lattice, limiting catalytic efficiency. In this work, we modify NiFe-LDH by combining hydrothermal and electrodeposition techniques, coupling NiFe-LDH with the metal oxide SnO2. This process creates a heterojunction enriched with oxygen vacancies through interfacial and defect engineering. In 1 M KOH solution, this modified catalyst exhibits an OER overpotential of just 209 mV at a current density of 10 mA cm−2. Furthermore, when the current density is increased to 100 mA cm−2, the overpotential only increases by a modest 46 mV. Subsequent DFT investigations reveal that in the heterostructured system, there is an enhanced overlap between the O 2p and metal 3d orbitals, which optimizes the covalency of the metal–oxygen bond and promotes the participation of lattice oxygen in the reduction reaction. The heterojunction, in concert with oxygen vacancies, aligns the energy bands of oxygen and metal closer to the Fermi level, resulting in improved continuity of electronic orbitals near the Fermi level. This synergistic arrangement significantly reduces the energy barrier for the rate-determining step of the OER, substantiating the improved performance and activation of lattice oxygen.

Applied electric field induced the change of spin-electron of the Fe3GeTe2 to improve its oxygen evolution reaction performance

Utilizing density functional theory (DFT) calculations, we investigate the influence of the external electric field on the oxygen evolution reaction (OER) performance of monolayer Fe3GeTe2. Monolayer Fe3GeTe2 has ferromagnetic metal properties and displays excellent electrocatalytic activity. The magnetism mainly comes from FeI atoms, owing to the strong Fe-Te orbitals hybridization, and FeI atoms have great effect on the active site Te atoms. The electric field induces the change of spin-electron and promotes charge redistribution in the Fe3GeTe2, resulting in the changes of the magnetic moment and magnetic anisotropic energy (MAE). Simultaneously, the applied electric field shifts the energy band and decreases the work function which facilitates carrier migration to the surface. Therefore, the OER overpotential is reduced and the catalytic performance is improved. These valuable findings can serve as vital references for the design of 2D magnetic electrocatalysts.

WC nanoparticles and NiFe alloy co-encapsulated in N-doped carbon nanocage for exceptional OER and ORR bifunctional electrocatalysis

Developing earth-abundant electrocatalysts with optimized intrinsic active sites is crucial for enhancing bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance. In this study, we fabricated a hollow structured carbon framework utilizing NiFe Prussian Blue analogs (PBAs) as templates, while polypyrrole (PPy) and phosphotungstic acid (PW12). Pyrrole monomer underwent polymerization on the nanocubic PBA surface in the presence of PW12 (PBA@PPy-PW12). Subsequent carbothermal reduction created an N-doped carbon shell with embedded NiFe alloy and tungsten carbide (WC) nanoparticles. The polymeric PPy-PW12 nature can not only prevent the aggregation of PBA and WC structures but also enhance electrical conductivity by connecting neighboring nanospheres. Moreover, the introduction of WC can significantly enhance the bifunctional electrocatalytic activity of the carbon-based catalyst, which is attributed to synergism between the WC and NiFe materials within the NC layer. Consequently, NiFe/W0.3C@NC exhibited outstanding OER (overpotential = 290 mV for 10 mA/cm2; Tafel slope = 57 mV/dec) and ORR (half wave potential = 0.81 V; Tafel slope = 61 mV/dec) performances. This work presents a promising avenue for developing high-performance electrocatalysts for energy conversion systems that showcase remarkable efficiency, stability, and potential practicability.

Oxygen Radical Coupling on Short-Range Ordered Ru Atom Arrays Enables Exceptional Activity and Stability for Acidic Water Oxidation.

The discovery of efficient and stable electrocatalysts for oxygen evolution reaction (OER) in acid is vital for the commercialization of the proton-exchange membrane water electrolyzer. In this work, we demonstrate that short-range Ru atom arrays with near-ideal Ru-Ru interatomic distances and a unique Ru-O hybridization state can trigger direct O*-O* radical coupling to form an intermediate O*-O*-Ru configuration during acidic OER without generating OOH* species. Further, the Ru atom arrays suppress the participation of lattice oxygen in the OER and the dissolution of active Ru. Benefiting from these advantages, the as-designed Ru array-Co3O4 electrocatalyst breaks the activity/stability trade-off that plagues RuO2-based electrocatalysts, delivering an excellent OER overpotential of only 160 mV at 10 mA cm-2 in 0.5 M H2SO4 and outstanding durability during 1500 h operation, representing one of the best acid-stable OER electrocatalysts reported to date. 18O-labeled operando spectroscopic measurements together with theoretical investigations revealed that the short-range Ru atom arrays switched on an oxide path mechanism (OPM) during the OER. Our work not only guides the design of improved acidic OER catalysts but also encourages the pursuit of short-range metal atom array-based electrocatalysts for other electrocatalytic reactions.

Selective Activation of Methane on Hydroxyapatite Surfaces: Insights from Machine Learning and Density Functional Theory

The electrocatalytic conversion of methane has attracted considerable attention owing to its ability to operate under mild conditions, thereby avoiding peroxidation. Recently, hydroxyapatite (HAP), an environmental-friendly and cost-effective electrocatalyst, was found to have high catalytic selectivity for the methane activation to produce alcohols. However, the overall activation mechanism still remains elusive and thus limits further improvement of the catalytic performance. In this study, we employed machine learning-assisted molecular dynamics simulations to analyze the structural modifications in the HAP with defects during sintering. Density functional theory calculations were performed to explore the catalytic mechanism of methane on various sintered surfaces of HAP. During the sintering of HAP, the presence of H2O or O vacancies causes the migration of H2O and OH species from the bulk phase toward the surface. On the basis of our simulations, the H2O or OH migration reduces the overpotential of oxygen evolution reactions and alters the stability of intermediates. It largely impacts the selectivity of methane activation and different products can be obtained depending on the defect modes. Our mechanistic proposal then fundamentally challenges the prevailing opinion that active sites are exclusively confined to the surface of HAP. Our work may pave the way for designing and synthesizing novel electrocatalysts with enhanced performance and efficiency.

Microflower-like NiFe layered double hydroxide @ g-C3N4 electrocatalysts for enhanced photo-assisted OER and overall water splitting performance

Photo-assisted electrocatalysis has emerged as a cutting-edge area of electrocatalysis in recent times. It relies on the combined influence of electrical and optical energy, offering a novel approach to enhance electrocatalytic efficiency. In this study, we synthesized microflower-like catalysts consisting of NiFe layered double hydroxide and g-C3N4 (known as NiFe-LDH/CN@NF) directly on Ni foam using a one-step hydrothermal technique. Under the irradiation of 300W xenon lamp, the electrocatalytic activities of oxygen evolution reaction (OER) and overall water splitting of NiFe-LDH/CN@NF were significantly enhanced. Under photo-assisted circumstances, the OER overpotential (204mV@10mAcm−2) in KOH electrolyte is 23% lower than in dark conditions; the cell voltage of an electrolytic cell using NiFe-LDH/g-C3N4 as the cathode and anode decreased from 1.65V to 1.58V. According to study on mechanisms, the enhancement in OER can be mainly ascribed to the synergistic impact of photo-driven and electro-driven water oxidation processes. These results validate the broad generalizability of photo-assisted electrocatalysis technology and provide valuable insights into the advanced material design for sustainable energy conversion technologies.

Effect of heat treatment on improving OER activity of NiFeOOH based aerogels: A combined experimental and theoretical study

Enhanced catalytic activity of oxygen evolution reaction (OER) catalysts is necessary to lower the cost of green hydrogen production. This study focuses on the use of a simple strategy of heat treatment to enhance the catalytic activity of NiFeOOH-based aerogels. The study shows that heat treatment of this aerogel at 150 °C leads to significant improvement in its catalytic activity, as evident in the staircase voltammetry results. To understand how heat treatment improves the catalytic activity, a DFT+U calculation was carried out on heat-treated and non-heat-treated catalysts. The calculation shows that the overpotential for OER decreases with heat treatment, which is related to the relative stability of the intermediates in heat-treated and non-heat-treated catalysts. Also, it has been found that heat treatment decreases work function, which might improve charge transfer and, thus, catalytic activity. Our calculations are in line with the experimental results that show the release of crystalline water at 150 °C which enhances the catalytic activity, and the formation of dense NiFeOx phase at higher temperatures which results in lower activity.

WO3-x as an activation medium to prompt overall water splitting of NiFe-based electrocatalyst

The efficient oxygen evolution reaction (OER) is crucial for various electrochemical processes, especially for overall water splitting (OWS). In this study, we focus on the utilization of WO3-x as an activation medium to enhance the OER performance of NiFe-based electrocatalysts. Firstly, we synthesize WO3-x nanowires supported on nickel foam (NF) and then incorporate NiFe on WO3-x nanowires by a simple hydrothermal method. The WO3-x self-supported NiFe (Oxy)hydroxide (denoted as NiFe-W-O/NF) shows a three-dimensional stereostructure composed of ultrathin nanosheets (∼ 4.0 nm). This unique structure provides a large open surface for fuller diffusion of the electrolyte while exposing more active sites. The electronic interaction of tri-centers of NiFeW accelerates the surface reconstruction process of γ-NiOOH and FeOOH, which are converted into the main active species in a short time. The electrochemical measurements confirm that the NiFe-W-O/NF has low OER overpotentials (233 mV at 10 mA cm−2, 298 mV at 100 mA cm−2) and excellent stability (100 h in total) in 1 M KOH electrolyte. In addition, the NiFe-W-O/NF || NiFe-W-O/NF battery also exhibits a low cell voltage (1.52 V at 10 mA cm−2) with a stable lifetime (50 h) under alkaline conditions. These results highlight the great potential of NiFe-W-O/NF for practical applications.

Metal–organic framework–derived trimetallic particles encapsulated by ultrathin nitrogen-doped carbon nanosheets on a network of nitrogen-doped carbon nanotubes as bifunctional catalysts for rechargeable zinc–air batteries

Economical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts with high activity aimed at replacing precious metal catalysts for rechargeable zinc-air batteries (ZABs) must be developed. In this study, a multiple hierarchical-structural material is developed using a facile dielectric barrier discharge (DBD) plasma surface treatment, solvothermal reaction, and high-temperature carbonization strategy. This strategy allows for the construction of nanosheets using nitrogen-doped carbon (NC) material-encapsulated ternary CoNiFe alloy nanoparticles (NPs) on a network of NC nanotubes (NCNTs), denoted as CoNiFe–NC@p–NCNTs. Precisely, the presence of abundant CoNiFe alloy NPs and the formation of M–N–C active sites created by transition metals (cobalt, nickel, and iron) coupled with NC can provide superior OER/ORR bifunctional properties. Moreover, the prepared NC layers with a multilevel pore structure contribute to a larger specific surface area, exposing numerous active sites and enhancing the uniformity of electron and mass movement. The CoNiFe0.08–NC@p–NCNTs show remarkable dual functionality for electrochemical oxygen reactions (ORR half-wave potential of 0.811 V, limiting current density of 5.73 mA cm−2 measured with a rotating disk electrode at a rotation speed of 1600 rpm, and OER overpotential of 351 mV at 10 mA cm−2), which demonstrates similar ORR performance to 20 wt% Pt/C and better OER performance than the commercial RuO2. A liquid ZAB prepared using the proposed material has excellent bifunctionality with an open-circuit voltage of 1.450 V and long-term cycling stability of 230 h@10 mA cm−2.

Solar enhanced oxygen evolution reaction with transition metal telluride.

The photo-enhanced electrocatalytic method of oxygen evolution reaction (OER) shows promise for enhancing the effectiveness of clear energy generation through water splitting by using renewable and sustainable source of energy. However, despite benefits of photoelectrocatalytic (PEC) water splitting, its uses are constrained by its low efficiency as a result of charge carrier recombination, a large overpotential, and sluggish reaction kinetics. Here, we illustrate that Nickel telluride (NiTe) synthesized by hydrothermal methods can function as an extremely effective photo-coupled electrochemical oxygen evolution reaction (POER) catalyst. In this study, NiTe was synthesized by hydrothermal method at 145°C within just an hour of reaction time. In dark conditions, the NiTe deposited on carbon cloth substrate shows a small oxygen evolution reaction overpotential (261mV) at a current density of 10mA cm-2, a reduced Tafel slope (65.4mV dec-1), and negligible activity decay after 12h of chronoamperometry. By virtue of its enhanced photo response, excellent light harvesting ability, and increased interfacial kinetics of charge separation, the NiTe electrode under simulated solar illumination displays exceptional photoelectrochemical performance exhibiting overpotential of 165mV at current density of 10mA cm-2, which is about 96mV less than on dark conditions. In addition, Density Functional Theory investigations have been carried out on the NiTe surface, the results of which demonstrated a greater adsorption energy for intermediate -OH on the catalyst site. Since the -OH adsorption on the catalyst site correlates to catalyst activation, it indicates the facile electrocatalytic activity of NiTe owing to favorable catalyst activation. DFT calculations also revealed the facile charge density redistribution following intermediate -OH adsorption on the NiTe surface. This work demonstrates that arrays of NiTe elongated nanostructure are a promising option for both electrochemical and photoelectrocatalytic water oxidation and offers broad suggestions for developing effective PEC devices.

Surface exsolved NiFeOx nanocatalyst for enhanced alkaline oxygen evolution catalysis

A synergistically improved alkaline oxygen evolution catalyst of the NiFeOx nanoalloy oxide structure is introduced using an in-situ exsolution method. The separately doped Ni and Fe ions are exsolved on the surface of the perovskite as homogeneously distributed NiFeOx oxide alloy catalysts via following reduction and oxidation processes. The incorporation of additional Fe into the surface embedded NiFeOx catalyst improved the inherent oxygen evolution reaction (OER) property with fast reaction kinetics. Density functional theory (DFT) result indicates the lowest OER overpotential of NiFeOx catalyst is originated from the reduced energy barrier of surface *O formation from *OH group. The NiFeOx exsolved catalyst shows the smallest overpotential of 0.49 V (j = 10 mA∙cm−2) and Tafel slope (93 mV∙dec-1), compared with that of single NiO (0.54 V, 132 mV∙dec-1) and Fe3O4 catalyst. This study provides an effective method for developing nanosized OER catalysts for various energy conversion and storage electrode materials.

High-throughput screening of dual atom catalysts for oxygen reduction and evolution reactions and rechargeable zinc-air battery

We provide the rational design of dual atom catalysts (DACs) supported on nitrogen-doped graphene for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through high-throughput computational screening of M1M2N6-DAC systems, where M1 and M2 represent Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt metals. We predict that FeRuN6-DAC at the summit of the volcano plot exhibits a low theoretical ORR overpotential (ηORR) of 0.24 V and a low theoretical OER overpotential (ηOER) of 0.19 V. The low ηORR and ηOER result from the catalytic performance of the Fe site being tuned to electronic properties that facilitate adsorption and desorption of the OH* intermediate. Inspired by these hybrid density functional theory (DFT) computational and machine learning (ML) results, we synthesized FeRuN6-DAC, FeN4-SAC, and RuN4-SAC and characterized them using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and in-situ electron spin resonance (ESR). Our in-situ ESR spectroscopy signifies that the spin of the Fe active site increases with increasing applied potential due to the increase in the concentration of OH* intermediate on Fe. We verified experimentally the predicted catalytic performances, finding that FeRuN6-DAC leads to an experimental ORR overpotential of 0.29 V with a Tafel slope of 104 mVdec−1 and an OER overpotential of 0.27 V with a Tafel slope of 124 mVdec−1. The rechargeable Zinc-air battery setup was fabricated with FeRuN6-DAC in place of the cathode, showing a maximum power density of 0.45 W/cm2 at the current density of 0.44 A/cm2 and good stability after 120 cycles. According to our findings, we demonstrate that DFT-guided strategies are useful for designing advanced DACs applicable to ORR, OER, and Zinc-air battery applications.

In-Situ Nanoarchitectonics of Fe/Co LDH over Cobalt-Enriched N-Doped Carbon Cookies as Facile Oxygen Redox Electrocatalysts for High-Rate Rechargeable Zinc-Air Batteries.

The reality of long-term rechargeable and high-performance zinc-air batteries relies majorly on cost-effective and eminent bifunctional electrocatalysts, which can perform both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Herein, we demonstrate a new approach for the synthesis of in-situ-grown layered double hydroxide of iron and cobalt over a cobalt nanoparticle-enriched nitrogen-doped carbon frame (CoL 2:1) by a simple coprecipitation reaction with facile scale-up and explore its electrocatalytic ORR and OER activity for an electrically rechargeable zinc-air battery. Consequently, the developed composite displays excellent ORR and OER activity with an ORR half-wave potential of 0.84 V, a limiting current density of 5.85 mA/cm2, and an OER overpotential of 320 mV with exceptional stability. The outstanding bifunctionality index of the catalyst (ΔE = 0.72 V) inspired us to utilize it as a cathode catalyst in an in-house developed prototype zinc-air battery. The battery could easily supply a specific capacity of 804 mAh/g with a maximum peak power density of 161 mW/cm2. The battery exhibits an attractive charge-discharge profile with a lesser voltage gap of 0.76 V at 10 mA/cm2 with durability for a period of 200 h and a voltage efficiency of 97%, which surpassed the corresponding Pt/C + RuO2-based zinc-air battery. Further, a maximum load of 50 mA/cm2 could easily be sustained during cycling, revealing its outstanding stability. A series-connected two CoL 2:1-based zinc-air batteries effortlessly enlighten a pinwheel fan and LED panel simultaneously, revealing its practicality. The high electrical conductivity and greater specific surface area of Co/N-C and its robust attachment with Fe/Co LDH preserves both active sites, thereby resulting in exceptional performance. Our method is capable of being flexible enough to create various bifunctional Co/N-C-based composite electrodes, opening up a feasible pathway to rechargeable zinc-air batteries with maximum energy density.

Microwave assisted synthesis of cobalt-doped copper selenite nanorice as bifunctional electrocatalyst for overall water splitting

In the research and development of noble-metal free catalysts, copper-based materials such as copper selenite have shown interest as electrocatalysts to drive the oxygen evolution reaction (OER) in basic medium, however their Hydrogen evolution reaction (HER) activity is still unexplored. Therefore, we have performed the synthesis of cobalt doped copper selenite nanoparticles which can robustly and effectively do electrocatalysis for both the OER and HER in basic medium electrolyte. The novelty lies in the fact that microwave synthesis procedure utilizing oxidizing agent as a key precursor is entirely new, this particular material was never employed in water splitting and catalyst need very low amount of binder. The results revealed that cobalt doped copper selenite have a relatively lower starting potential and a higher current density due to the synergistic effects of a large active area, quick charge, mass transport, and a three-dimensional conducting path, having OER and HER overpotentials of 359 mV and 226 mV at 10 mA/cm2 current densities, respectively. We found a novel doped structure featuring porous surfaces and distinctive rice like morphology which facilitate an efficient electron transportation during the water splitting thereby illustrating an exceptional performance of this system along with rapid synthesis and lower costs.

Prediction of Feasibility of Polaronic OER on (110) Surface of Rutile TiO2.

The polaronic effects at the atomic level hold paramount significance for advancing the efficacy of transition metal oxides in applications pertinent to renewable energy. The lattice-distortion mediated localization of photoexcited carriers in the form of polarons plays a pivotal role in the photocatalysis. This investigation focuses on rutile TiO2, an important material extensively explored for solar energy conversion in artificial photosynthesis, specifically targeting the generation of green H2 through photoelectrochemical (PEC) H2O splitting. By employing Hubbard-U corrected and hybrid density functional theory (DFT) methods, we systematically probe the polaronic effects in the catalysis of oxygen evolution reaction (OER) on the (110) surface of rutile TiO2. Theoretical understanding of polarons within the surface, coupled with simulations of OER at distinct titanium (Ti) and oxygen (O) active sites, reveals diverse polaron formation energies within the lattice sites with strong preference for bulk and surface bridge (Ob) oxygen sites. Moreover, we provide the evidence for the facilitative role of polarons in OER. We find that hole polarons situated at the equatorial oxygen sites near the Ti-active site, along with bridge site hole polarons distal from the Ob active site yield a small reduction in OER overpotential by ~0.06 eV and ~0.12 eV, respectively. However, subsurface, equatorial, and bridge site hole polarons significantly reduce the Ti-active site OER overpotential by ~0.4 eV through the peroxo-type oxygen pathway. We also observe that the presence of hole polarons stabilizes the *OH, *O, and *OOH intermediate species compared to the scenario without hole polarons. Overall, this study provides a detailed mechanistic insight into polaron-mediated OER, offering a promising avenue for improving the catalytic activity of transition metal oxide-based photocatalysts catering to renewable energy requisites.

Enhancing the Performance of 2D Ni-Fe Layered Double Hydroxides by Cabbage-Inspired Carbon Conjunction for Oxygen Evolution Reactions.

Layered double hydroxide (LDH) nanosheets as one type of two-dimensional materials have garnered increasing attention in the field of oxygen evolution reaction (OER) in recent decades. To address the challenges associated with poor conductivity and limited electron and charge transfer capability in LDH materials, we have developed a straightforward one-pot synthesis method to successfully fabricate a composite material with a microstructure resembling cabbage, which encompasses NiFe-LDH and nanocarbon (referred as NiFe-LDH@C). Atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM) revealed that the monolayer NiFe-LDH with a height of ~ 0.5-0.8 nm is uniformly distributed and closely bonded to the carbon support, leading to a significant enhancement in conductivity and facilitating faster electron and charge transfer. Moreover, the NiFe-LDH@C exhibits a substantial number of surface defect sites, which enhances the interaction with oxygen species. This dual enhancement in charge transfer and oxygen species-mediated transfer greatly improves the catalytic OER performance, which is further corroborated by theoretical calculations. Notably, the Ni10Fe6-LDH@C with the highest concentration of surface oxygen vacancies demonstrated superior water oxidation performance, surpassing commercially available RuO2 catalysts; an OER overpotential of 231 mV@10 mA cm-2 with a Tafel slope of 71 mV dec-1 was achieved.