Mass Transfer Evolution Research Articles

A 1.9 solar-mass neutron star candidate in a 2-year orbit

We report discovery and characterization of a main-sequence G star orbiting a dark object with mass 1.90±0.04M⊙. The system was discovered via Gaia astrometry and has an orbital period of 731 days. We obtained multi-epoch RV follow-up over a period of 639 days, allowing us to refine the Gaia orbital solution and precisely constrain the masses of both components. The luminous star is a ≳12,Gyr-old, low-metallicity halo star near the main-sequence turnoff (,K; ; ; M≈0.79M⊙) with a highly enhanced lithium abundance. The RV mass function sets a minimum companion mass for an edge-on orbit of M2>1.67M⊙, well above the Chandrasekhar limit. The Gaia inclination constraint, i=68.7±1.4,deg, then implies a companion mass of M2=1.90±0.04M⊙. The companion is most likely a massive neutron star: the only viable alternative is two massive white dwarfs in a close binary, but this scenario is disfavored on evolutionary grounds. The system’s low eccentricity ( e=0.122±0.002) disfavors dynamical formation channels and implies that the neutron star likely formed with little mass loss ( ≲1M⊙) and with a weak natal kick (). Stronger kicks with more mass loss are not fully ruled out but would imply that a larger population of similar systems with higher eccentricities should exist. The current orbit is too small to have accommodated the neutron star progenitor as a red supergiant or super-AGB star. The simplest formation scenario – isolated binary evolution – requires the system to have survived unstable mass transfer and common envelope evolution with a donor-to-accretor mass ratio >10. The system, which we call Gaia NS1, is likely a progenitor of symbiotic X-ray binaries and long-period millisecond pulsars. Its discovery challenges binary evolution models and bodes well for Gaia’s census of compact objects in wide binaries.

The white dwarf binary pathways survey – X. Gaia orbits for known UV excess binaries

ABSTRACT White dwarfs with an F, G, or K type companion represent the last common ancestor for a plethora of exotic systems throughout the galaxy, though to this point very few of them have been fully characterized in terms of orbital period and component masses, despite the fact several thousand have been identified. Gaia data release 3 has examined many hundreds of thousands of systems, and as such we can use this, in conjunction with our previous UV excess catalogues, to perform spectral energy distribution fitting in order to obtain a sample of 206 binaries likely to contain a white dwarf, complete with orbital periods, and either a direct measurement of the component masses for astrometric systems, or a lower limit on the component masses for spectroscopic systems. Of this sample of 206, four have previously been observed with Hubble Space Telescope spectroscopically in the ultraviolet, which has confirmed the presence of a white dwarf, and we find excellent agreement between the dynamical and spectroscopic masses of the white dwarfs in these systems. We find that white dwarf plus F, G, or K binaries can have a wide range of orbital periods, from less than a day to many hundreds of days. A large number of our systems are likely post-stable mass transfer systems based on their mass/period relationships, while others are difficult to explain either via stable mass transfer or standard common envelope evolution.

Influence of desorption hysteresis effects on coalbed methane migration and production based on dual-porosity medium model incorporating hysteresis pressure

Desorption hysteresis affects gas mass transfer and migration in coal seams, which is not considered in current dual-porosity medium models, leading to inaccurate assessment and prediction of gas extraction. This study proposed a desorption hysteresis pressure to address this issue of the gas mass transfer in the model. On this basis, two coupled gas migration models, considering (DGMH) and without considering (DGM) desorption hysteresis effects, were developed incorporating mass transfer, gas desorption, gas seepage, and permeability evolution. The models were solved and compared using the finite element method. The results demonstrate that the DGM model yields higher production assessment compared to the DGMH model. This discrepancy can be attributed to the hysteresis effects, which prevent the matrix gas from supplementing the fractures timely after fracture gas flows into the borehole. The DGMH model shows less mass transfer, coal seam permeability, and gas extraction compared to the DGM model. The desorption hysteresis effects are more pronounced in coal seams with higher permeability. In addition, neglecting hysteresis effects when calculating permeability from field gas production data may result in inaccurate values. The hysteresis effects is recommended to be considered in the prediction of coalbed methane extraction, permeability calculation, and risk control of delayed coal and gas outbursts.

Amorphous and defective Co-P-O@NC ball-in-ball hollow structure for highly efficient electrocatalytic overall water splitting

Electrochemical water splitting using hollow and defect-rich catalysts has emerged as a promising strategy for efficient hydrogen production. However, the rational design and controllable synthesis of such catalysts with intricate morphology and composition present significant challenges. Herein, we propose a template-engaged approach to fabricate a novel ball-in-ball hollow structure of Co-P-O@N-doped carbon with abundant oxygen vacancies. The synthesis process involves the preparation of uniform cobalt-glycerate (Co-gly) polymer microspheres as precursors, followed by surface coating with ZIF-67 layer, adjustable chemical etching by phytic acid, and controllable pyrolysis at high temperature. The resulting ball-in-ball structure offers a large number of accessible active sites and high redox reaction centers, facilitating efficient charge transport, mass transfer, and gas evolution, which are beneficial for the acceleration of electrocatalytic reaction. Additionally, density functional theory (DFT) calculations indicate that the incorporation of oxygen and the presence of Co-P dangling bonds in CoP significantly enhance the adsorption of oxygenated species, leading to improved intrinsic electroactivity at the single-site level. As a sequence, the titled catalyst exhibits remarkable electrocatalytic activity and stability for water splitting in alkaline media. Notably, it only requires a low overpotential of 283 mV to achieve a current density of 10 mA cm−2 for the oxygen evolution reaction. This work may provide some new insights into the design of complex hollow structures of phosphides with abundant defects for energy conversion.

A Semi-Empirical Approach for Predicting the Effects of Shrinkage on the Convective Mass Transfer Evolution During the Solar Drying of Foodstuffs

A Semi-Empirical Approach for Predicting the Effects of Shrinkage on the Convective Mass Transfer Evolution During the Solar Drying of Foodstuffs

Criteria for Dynamical Timescale Mass Transfer of Metal-poor Intermediate-mass Stars

The stability criteria of rapid mass transfer and common-envelope evolution are fundamental in binary star evolution. They determine the mass, mass ratio, and orbital distribution of many important systems, such as X-ray binaries, type Ia supernovae, and merging gravitational-wave sources. We use our adiabatic mass-loss model to systematically survey intermediate-mass (IM) stars’ thresholds for dynamical timescale mass transfer. The impact of metallicity on the stellar responses and critical mass ratios is explored. Both tables (Z = 0.001) and fitting formulae (Z = 0.001 and Z = 0.02) of the critical mass ratios of IM stars are provided. An application of our results to intermediate-mass X-ray binaries (IMXBs) is discussed. We find that the predicted upper limit to mass ratios, as a function of orbital period, is consistent with the observed IMXBs that undergo thermal or nuclear timescale mass transfer. According to the observed peak X-ray luminosity, L X, we predict the range of L X for IMXBs as a function of the donor mass and the mass-transfer timescale.

Study of microwave cooking of legumes with excess water: The case of chickpeas

In the context of the agro-ecological transition towards sustainable systems, legumes are a real opportunity in terms of agronomy and nutrition. The development of vegetable seed consumption is currently hampered by the problem of the long hydration and cooking stages of current processes. Low CO2 emission processes, such as microwave treatment, are preferred. The efficiency of these processes relies on the transformation of the energy contained in an electromagnetic wave into heat within materials with dielectric losses. The objective of the presented work is to study the evolution of the characteristics of leguminous seeds during the operation of cooking in excess of water by microwave treatment. Kinetics of texture modification and mass gain of the seeds were performed for three different levels of microwave power (between 400 and 1200 W) and compared to hot plate cooking. Empirical models by multi-parameter equations were proposed and validated by a 1000 W treatment. The results show that the evolution of hardness and mass gain is strongly related to the evolution of mass transfer coupled with volume heat transfer phenomena, specific to electromagnetic wave heating. Two different profiles of hardness and mass gain were observed depending on the type and intensity of the treatment. This work is a preliminary experimental study allowing to express hypotheses, which will be validated later by a more thorough study.

Model-Based Evaluation of Drying Kinetics and Solvent Diffusion in Pharmaceutical Thin Film Coatings

Fluid-bed coating processes make it possible to manufacture pharmaceutical products with tuneable properties. The choice of polymer type and coating thickness provides control over the drug release characteristics, and multi-layer pellet coatings can combine several active ingredients or achieve tailored drug release profiles. However, the fluid-bed coating is a parametrically sensitive process due to the simultaneous occurrence of polymer solution spraying and solvent evaporation. Designing a robust fluid-bed coating process requires the knowledge of thin film drying kinetics, which in turn critically depends on an accurate description of concentration-dependent solvent diffusion in the polymer. This work presents a mathematical model of thin film drying as an enabling tool for fluid-bed process design. A custom-built benchtop drying cell able to record and evaluate the drying kinetics of a chosen polymeric excipient has been constructed, validated, and used for data collection. A semi-empirical mathematical model combining heat transfer, mass transfer, and film thickness evolution was formulated and used for estimating the solvent diffusion coefficient and solvent distribution in the polymer layer. The combined experimental and computational methodology was then used for analysing the drying kinetics of common polymeric excipients: poly(vinylpyrrolidone) and two grades of hydroxypropyl methylcellulose. The experimental setup together with the mathematical model represents a valuable tool for predictive modeling of pharmaceutical coating processes.

Performance Optimization Study of an Adsorption Solar Refrigerator System with Special Reference to the Effect of the Collector-Adsorber Tilt Angle

This paper presents an optimization study of an adsorption solar refrigerator through dynamic modeling and simulation of the system behavior using the zeolite/water couple. Thus, a mathematical model representing the evolution of heat and mass transfer at each component of the adsorption solar refrigerator has been developed. The results of this study showed that increasing the angle of inclination of the collector from 0° to 13° with respect to the horizontal causes an increase in the temperature of the zeolite. The result is an increase in the mass of water vapor cycled, but also an improvement in the performance of the solar refrigerator. When the value of the angle of inclination exceeds 13°, the mass of water vapor cycled decreases and subsequently leads to a decrease in the performance of the refrigeration system.

Partial-envelope stripping and nuclear-timescale mass transfer from evolved supergiants at low metallicity

Stable mass transfer from a massive post-main sequence (post-MS) donor is thought to be a short-lived event of thermal-timescale mass transfer (∼10−3 M⊙ yr−1) which within ≲104 yr strips the donor star of nearly its entire H-rich envelope, producing a hot, compact helium star. This long-standing picture is based on stellar models with rapidly expanding Hertzprung gap (HG) donor stars. Motivated by a finding that in low-metallicity binaries, post-MS mass transfer may instead be initiated by donors already at the core-helium burning (CHeB) stage, we used the MESA stellar-evolution code to compute grids of detailed massive binary models at three metallicities: those of the Sun, the Large Magellanic Cloud (LMC, ZFe; LMC/ZFe; ⊙ ≈ 0.36), and the Small Magellanic Cloud (SMC, ZFe; SMC/ZFe; ⊙ ≈ 0.2). Our grids span a wide range in orbital periods (∼3 to 5000 days) and initial primary masses (10 M⊙ to 36 − 53 M⊙, depending on metallicity). We find that metallicity strongly influences the course and outcome of mass-transfer evolution. We identify two novel types of post-MS mass transfer: (a) mass exchange on the long nuclear timescale (ΔTMT ≳ 105 yr, Ṁ ∼ 10−5 M⊙ yr−1) that continues until the end of the CHeB phase, and (b) rapid mass transfer leading to detached binaries with mass losers that are only partially stripped of their envelopes. At LMC and SMC compositions, the majority of binary models with donor masses ≥17 M⊙ follow one of these two types of evolution. In neither (a) nor (b) does the donor become a fully stripped helium star by the end of CHeB. Boundaries between the different types of post-MS mass transfer evolution are associated with the degree of rapid post-MS expansion of massive stars and, for a given metallicity, are sensitive to the assumptions about internal mixing. At low metallicity, due to partial envelope stripping, we predict fewer hot fully stripped stars formed through binary interactions as well as higher compactness of the presupernova core structures of mass losers. Nuclear-timescale post-MS mass transfer suggests a strong preference for metal-poor host galaxies of ultra-luminous X-ray sources with black-hole (BH) accretors and massive donors, some of which might be the immediate progenitors of binary BH mergers. It also implies a population of interacting binaries with blue and yellow supergiant donors. Partially stripped stars could potentially explain the puzzling nitrogen-enriched slowly rotating (super)giants in the LMC.

Progenitor, environment, and modelling of the interacting transient AT 2016jbu (Gaia16cfr)

ABSTRACT We present the bolometric light curve, identification and analysis of the progenitor candidate, and preliminary modelling of AT 2016jbu (Gaia16cfr). We find a progenitor consistent with a ∼ 22–25 M⊙ yellow hypergiant surrounded by a dusty circumstellar shell, in agreement with what has been previously reported. We see evidence for significant photometric variability in the progenitor, as well as strong Hα emission consistent with pre-existing circumstellar material. The age of the environment, as well as the resolved stellar population surrounding AT 2016jbu, supports a progenitor age of >10 Myr, consistent with a progenitor mass of ∼22 M⊙. A joint analysis of the velocity evolution of AT 2016jbu and the photospheric radius inferred from the bolometric light curve shows the transient is consistent with two successive outbursts/explosions. The first outburst ejected material with velocity ∼650 km s−1, while the second, more energetic event ejected material at ∼4500 km s−1. Whether the latter is the core collapse of the progenitor remains uncertain. We place a limit on the ejected 56Ni mass of <0.016 M⊙. Using the Binary Population And Spectral Synthesis (BPASS) code, we explore a wide range of possible progenitor systems and find that the majority of these are in binaries, some of which are undergoing mass transfer or common-envelope evolution immediately prior to explosion. Finally, we use the SuperNova Explosion Code (SNEC) to demonstrate that the low-energy explosions within some of these binary systems, together with sufficient circumstellar material, can reproduce the overall morphology of the light curve of AT 2016jbu.

A Statistical View of the Stable and Unstable Roche Lobe Overflow of a Tertiary Star onto the Inner Binary in Triple Systems

Abstract In compact stellar triple systems, an evolved tertiary star can overflow its Roche lobe around the inner binary. Subsequently, the tertiary star can transfer mass to the inner binary in a stable manner, or Roche lobe overflow (RLOF) can be unstable and lead to common-envelope (CE) evolution. In the latter case, the inner binary enters the extended envelope of the tertiary star and spirals in toward the donor’s core, potentially leading to mergers or ejections. Although studied in detail for individual systems, a comprehensive statistical view on the various outcomes of triple RLOF is lacking. Here, we carry out 105 population synthesis simulations of tight triples, self-consistently taking into account stellar evolution, binary interactions, and gravitational dynamics. Also included are prescriptions for the long-term evolution of stable triple mass transfer, and triple CE evolution. Although simple and ignoring hydrodynamic effects, these prescriptions allow for a qualitative statistical study. We find that triple RLOF occurs in ∼0.06% of all triple systems. Of these 0.06%, ∼64% of cases lead to stable mass transfer, and ∼36% to triple CE evolution. Triple CE is most often (∼76%) followed by one or multiple mergers in short succession, most likely an inner binary merger of two main-sequence stars. Other outcomes of triple CE are a binary+single system (∼23%, most of which do not involve exchange interactions), and a stable triple (∼1%). We also estimate the rate of type Ia supernovae involving white dwarf mergers following triple RLOF, but find only a negligible contribution.

Effect of Adsorbent/Adsorbate Couple on the Performance of Adsorption Solar Refrigerator

This work presents a contribution to the study of the process of cold production by adsorption from solar energy. In this paper, we discuss a comparative study of the operation of a solar adsorption refrigerator using the silica gel-water couple and the zeolite-water couple through dynamic modeling and simulation. The mathematical model representing the evolution of heat and mass transfer at each component of the adsorption solar refrigerator has been developed. It appears from this study that the evolution of the temperature of the two adsorbents (zeolite and silica gel) is quasi-similar throughout the operating cycle. However, the maximum mass of water vapor adsorbed by the silicagel (0.24 kg/kg) is higher than that adsorbed by the zeolite (0.201 kg/kg). In the same way, the mass of water vapor cycled, obtained with the silicagel-water couple which is 0.14 kg/kg, is higher than that obtained with the zeolite-water couple which is 0.081 kg/kg. Therefore, the amount of cold produced 9.178 MJ and the solar coefficient of performance 0.378 obtained with the solar refrigerator using the silica gel-water couple, are better.

Mass Transfer and Stellar Evolution of the White Dwarfs in AM CVn Binaries

Abstract We calculate the stellar evolution of both white dwarfs (WDs) in AM CVn binaries with orbital periods of P orb ≈ 5–70 minutes. We focus on the cases where the donor starts as a M He < 0.2M ⊙ helium WD and the accretor is a M WD > 0.6 M ⊙ WD. Using Modules for Experiments in Stellar Astrophysics, we simultaneously evolve both WDs assuming conservative mass transfer and angular momentum loss from gravitational radiation. This self-consistent evolution yields important feedback of the properties of the donor on the mass-transfer rate, M ̇ , as well as the thermal evolution of the accreting WD. Consistent with earlier work, we find that the high M ̇ 's at early times forces an adiabatic evolution of the donor for P orb < 30 minutes so that its mass–radius relation depends primarily on its initial entropy. As the donor reaches M He ≈ 0.02–0.03 M ⊙ at P orb ≃ 30 minutes, it becomes fully convective and could lose entropy and expand much less than expected under further mass loss. However, we show that the lack of reliable opacities for the donor’s surface inhibit a secure prediction for this possible cooling. Our calculations capture the core heating that occurs during the first ≈107 yr of accretion and continue the evolution into the phase of WD cooling that follows. When compared to existing data for accreting WDs, as seen by Cheng and collaborators for isolated WDs, we also find that the accreting WDs are not as cool as we would expect given the amount of time they have had to cool.

Constraining Progenitors of Observed Low-mass X-ray Binaries Using Convection and Rotation-Boosted Magnetic Braking

Abstract We present a new method for constraining the mass transfer evolution of low-mass X-ray binaries (LMXBs)—a reverse population synthesis technique. This is done using the detailed 1D stellar evolution code MESA (Modules for Experiments in Stellar Astrophysics) to evolve a high-resolution grid of binary systems spanning a comprehensive range of initial donor masses and orbital periods. We use the recently developed convection and rotation-boosted (CARB) magnetic braking scheme. The CARB magnetic braking scheme is the only magnetic braking prescription capable of reproducing an entire sample of well-studied persistent LMXBs—those with mass ratios, periods, and mass transfer rates that have been observationally determined. Using the reverse population synthesis technique, where we follow any simulated system that successfully reproduces an observed LMXB backward, we have constrained possible progenitors for each observed well-studied persistent LMXB. We also determined that the minimum number of LMXB formations in the Milky Way is 1500 per Gyr if we exclude Cyg X-2. For Cyg X-2, the most likely formation rate is 9000 LMXB Gyr−1. The technique we describe can be applied to any observed LMXB with well-constrained mass ratio, period, and mass transfer rate. With the upcoming GAIA DR3 containing information on binary systems, this technique can be applied to the data release to search for progenitors of observed persistent LMXBs.

Processing of Cf/SiC Composites through Two-Channel Temperature-Control CVI: I, Modeling

A two-channel temperature-control CVI scheme was proposed to fabricate thicker and denser composites. The two-channel structure helps to densify a thick preform, and a precise temperature control will guarantee a low and uniform porosity distribution. Validation simulations containing hydrodynamics, mass transfer, heat transfer and pore structure evolution were first carried out. Modeling results confirm that a two-step densification based on the new scheme can work well: At step I, all gases pass through the preform and the high-temperature bottom-preform is densified; At step II, by altering the outlet, temperature and infiltration time, part of gases are sucked into the preform and the remaining coarse preform is densified. The scheme can fabricate tick, uniform and dense composite, it can also avoid huge pump pressure thus protecting fibers from cracking. It is hoped to enlighten the CVI processing of ceramic matrix composites.

A review on metal additive manufacturing: modeling and application of numerical simulation for heat and mass transfer and microstructure evolution

Metal additive manufacturing technology has been widely used in prototyping, parts manufacturing and repairing. Metal additive manufacturing is a multi-scale and multi-physical coupling process with complex physical phenomena of heat and mass transfer and microstructure evolution. It is hard to directly observe the dynamic behavior and microstructure evolution of molten pool during additive manufacturing. Therefore, numerical simulation of additive manufacturing process is significant since it can efficiently and pertinently predict and analyze the physical phenomena in the process of metal additive manufacturing, and provide a reference for technological parameters selection. In this review, the research progress of numerical simulation of metal additive manufacturing is discussed. Various aspects of numerical simulation models are reviewed, including: (1) Introduction of basic control method and physical description of numerical simulation models; (2) Comparison of various heat and mass transfer models based on different physical assumptions (heat conduction model; heat flux coupling model; discrete powder particle heat flux coupling model); (3) Applications of various microstructure evolution models [phase field (PF), cellular automata (CA), and Monte Carlo (MC)]. Finally, the development trend of numerical simulation of metal additive manufacturing, including the thermal-flow-solid coupling model and deep learning for numerical model, is analyzed.

The role of mass transfer and common envelope evolution in the formation of merging binary black holes

As the number of merging binary black holes observed with ground-based gravitational-wave detectors grows, increasingly accurate theoretical models are required to compare them to the observed sample and disentangle contributions from multiple channels. In formation models involving isolated binary stars, important uncertainties remain regarding the stability of mass transfer and common-envelope evolution. To study some of these uncertainties, we have computed binary simulations using the MESA code consisting of a 30 M⊙ star in a low metallicity (Z⊙/10) environment with a black-hole companion. We have developed an updated prescription to compute mass transfer rates including the possibility of outflows from outer Lagrangian points, as well as a method to self-consistently determine the core-envelope boundary in cases where there is common-envelope evolution. We find that binaries survive common-envelope evolution only if unstable mass transfer happens after the formation of a deep convective envelope, resulting in a narrow range (0.2 dex) in period for successful envelope ejection. All cases where binary interaction is initiated with a radiative envelope have large binding energies (∼1050 erg), and they result in mergers during the common-envelope phase even under the assumption that all the internal and recombination energy of the envelope, as well as the energy from an inspiral, is used to eject the envelope. This is independent of whether or not helium is ignited in the core of the donor, conditions under which various rapid-population synthesis calculations assume a successful envelope ejection is possible. Moreover, we find that the critical mass ratio for instability is such that across a large range in initial orbital periods (∼1−1000 days), merging binary black holes can be formed via stable mass transfer. A large fraction of these systems undergo overflow of their L2 equipotential, in which case we find that stable mass transfer produces merging binary black holes even under extreme assumptions of mass and angular momentum outflows. Our conclusions are limited to the study of one donor mass at a single metallicity, but they suggest that population synthesis calculations overestimate the formation rate of merging binary black holes produced by common-envelope evolution and that stable mass transfer could dominate the formation rate from isolated binaries. This is in agreement with a few other recent studies. Further work is required to extend these results to different masses and metallicities as well as to understand how they can be incorporated into rapid population synthesis calculations.

Pore-scale study of multicomponent multiphase heat and mass transfer mechanism during methane hydrate dissociation process

The understanding of the multiple physicochemical and thermal processes in methane hydrate dissociation is fundamental to accurately predict the methane recovery with the hydrate depressurization-induced technique. Pore-scale investigation can enlighten the accurate REV (Representative Elementary Volume) scale simulation models to take heat transfer and mass transfer limitation into account for better recovery forecast. In this work, a pore-scale numerical model based on the lattice Boltzmann method was developed to couple the multicomponent multiphase flow, heat and mass transfer, heterogeneous reaction, and solid structure evolution during the dissociation of gas hydrates. Numerical simulation of the methane hydrate dissociation in an idealized square cavity and a realistic porous structure was studied to understand the influence of mass transport, water saturation, and heat transfer. This study distinguished the hydrate dissociation characteristics in the kinetics-limited and diffusion-limited regimes. The mass-transfer-limitation in the diffusion-limited regime indicated that the enriched methane on the hydrate-water interface decreased the hydrate dissociation rate with the increasing water saturation. The methane concentration gradient across the water layer varied with the water layer thickness and contributed to the decomposition nonuniformity. The decreasing temperature gradually reduced methane recovery efficiency and yield during the endothermic decomposition due to decreasing the equilibrium pressure and intrinsic kinetic rate. Some implications were addressed from the pore-scale understanding of the transfer and kinetics characteristics. The local thermal equilibrium at the solid–fluid interface implied that the one-temperature equation is sufficient to model the heat transfer at the REV scale. The present study proposed a corrected reaction model based on the equivalent water layer thickness and introduced the implementation procedure in the REV-solution to account for the mass-transfer-limitation on the hydrate dissociation rate.

Selective Se doping of NiFe2O4 on an active NiOOH scaffold for efficient and robust water oxidation

There remains a challenge in designing electrocatalysts for water oxidation to create highly efficient catalytic sites for the oxygen evolution reaction (OER) while maintaining their robustness at large outputs. Herein, an etching-assisted synthesis approach was developed to integrate highly active NiFe2O4 nanoparticles with a robust and active NiOOH scaffold directly on commercial stainless steel. A precise selenization strategy was then introduced to achieve selective Se doping of NiFe2O4 to further enhance its intrinsic OER activity while maintaining a three-dimensional NiOOH nanosheet array as a robust scaffold for prompt mass transfer and gas evolution. The resulting NiFe2O4−xSex/NiOOH electrode exhibited superior electrocatalytic activity with low overpotentials of 153 and 259 mV to deliver benchmark current densities of 10 and 500 mA cm−2, respectively. More importantly, the catalyst exhibited remarkable durability at a stable current output of 100 mA cm−2 for hundreds of hours. These findings may open up opportunities for exploring efficient and robust electrocatalysts for scalable hydrogen production with practical materials.