Oxygen Adsorption Energy Research Articles

Oxygen adsorption, absorption and diffusion in FeCrNi medium entropy alloy: an ab initio study.

Despite tremendous efforts to understand interstitial diffusion in bulk alloys, a clear understanding of the principal elemental effect on surface interstitial diffusion is still lacking. In this study, a first-principles approach is employed to study oxygen interstitial diffusion in FeCrNi medium entropy alloy (MEA) based on principal element content at various subsurface sites. Oxygen adsorption energy on surfaces, solution energy at interstitial sites, and activation energy for oxygen permeation are calculated. The adsorption energy for oxygen cohesion to all investigated surfaces was lowest for the sites containing Cr, suggesting a positive effect of Cr in producing a chromium oxide scale. In addition, we have calculated the contribution of the principal element to the stability of the interstitial sites and the activation energy to diffuse between them. This work provides insights into the formation of chromium scaling based on oxygen adsorption and permeation, with potential implications in the design of oxidation-resistant surfaces for high-temperature applications.

Compositional optimization for enhanced oxidation resistance of high-entropy carbide ceramics

Excellent oxidation resistance is essential for the viability of high-entropy carbides (HECs) in high-temperature environments. However, the vast HEC compositional space presents a significant challenge in developing desirable formulations with improved oxidation tolerance. In this work, we establish a computational framework to guide the optimization of oxidation-tolerant HEC compositions and further validate the theoretical predictions through systematic oxidation experiments. Leveraging first-principles calculations, we initially determine the heterogeneous oxygen adsorption ability of different constituent elements in HECs, which is subsequently harnessed to regulate preferential oxidation and suppress the formation of detrimental oxides during the oxidation process. Incorporating this fundamental-level understanding, multi-objective optimization (MOO) was performed to identify a compositional region with potentially intrinsic oxidation immunity, achieving a balance between the compactness of the oxidation product and the thermodynamic stability of the HEC matrix. Based on our analysis, we propose a compositional design strategy involving the strategic reduction of elements with higher oxygen adsorption energies, such as Nb, Ta, and Ti in (NbTaZrHfTi)C, to effectively improve the oxidation performance of HECs. The theoretical findings are robustly corroborated by our comparative oxidation experiments, which demonstrate that the selected NbTa-depletion HEC exhibits superior antioxidant performance compared to the equiatomic counterpart. The integrated computational-experimental approach presented in this work serves as a powerful framework to accelerate the discovery and development of oxidation-resistant HECs, paving the way for their expanded applications in demanding high-temperature, oxygen-rich environments.

Fluorine-doped carbon dots decorated on iron-cobalt selenide nanosheets as superior electrocatalysts for oxygen evolution in seawater

Developing oxygen evolution reaction (OER) catalysts that can efficiently and stably operate at high current densities in seawater electrolysis is urgently demanded but challenging. In this study, selenium-vacancies-rich iron-cobalt selenide nanosheets (FeCoSe-VSe) decorated with fluorine-doped carbon dots (FCDs) are rationally designed and prepared on nickel foams (NF) through the successive processes of hydrothermal treatment and selenization. Benefiting from the large accessible surface area and abundant active sites provided by FCDs and selenium vacancy defects, as well as the coupled interface between FCDs and FeCoSe-VSe that optimizes the oxygen adsorption energy and accelerates the kinetic process, the FCDs/FeCoSe-VSe/NF composite exhibits excellent OER catalytic activities with a low overpotential of 258 mV at a current density of 200 mA cm−2 in 1 M KOH and a small Tafel slope of 34.7 mV dec–1. In the electrolytes of simulated and natural seawater, the overpotentials of the FCDs/FeCoSe-VSe/NF electrode are slightly higher, measured to be 264 and 297 mV, respectively. More profoundly, the introduction of FCDs enhances the corrosion resistance of the catalyst in alkaline electrolytes, ensuring the long-term stability. This work offers a guidance to improve the electrochemical performances of catalysts for high-efficiency seawater oxidation.

Engineering medium-entropy alloy nanoparticle nanotubes for efficient oxygen reduction

Fuel cells, as promising energy conversion devices, realize the direct conversion of hydrogen fuel chemical energy into electrical energy. The kinetics of cathodic oxygen reduction reaction (ORR) is slow and plays a decisive role in the output efficiency of fuel cells. Platinum catalysts have been commercialized, but their high cost, relatively low catalytic activity and poor cycling durability limit the development of fuel cells. The introduction of non-platinum components is an effective strategy to minimize the cost and maximize the activity. In this study, PtPdCu medium entropy alloy nanoparticle nanotubes (PtPdCu MEANPTs) that demonstrate high catalytic activity and long durability are presented. Combined with density functional theory calculations, the introduction of Pd and Cu modulates surface electronic structure and optimizes the oxygen adsorption energy, thus enhancing the catalytic activity. The 0D/1D hybrid structure exposes more surface sites and inhibits particle maturation. The atomic migration and rearrangement are emerged during the initial stage of potential cycling process, induing a palladium-rich outer layer and preventing the oxidation of platinum atoms. The best-performing Pt24Pd28Cu48 MEANPTs deliver the impressive ORR activity (1.42 A/mgPt at 0.9 V vs. RHE, which is 6.17 times that of commercial Pt/C) and durability (retaining 2.87 times the initial activity of benchmark catalyst after 30,000 potential cycles). Theoretical calculations have confirmed the regulation of alloying on the surface oxygen affinity and revealed the true active sites on the catalyst surface. This work explores the research direction of platinum-based multi-element catalysts with low platinum content and high catalytic activity.

Investigation on the reaction of sulphur with Ag–Cu–Zn-Ge alloy: Experimental and computational study

Silver and its alloys undergo tarnishing with time, which is a black stain on the surface due to the formation of Ag2S. Developing a tarnish resistant Ag alloy was attempted by alloying Ag with elements that form a passive oxide layer on the surface. Germanium is proven to provide better tarnish resistance to sterling Silver alloy (92.5 wt% pure) which is available under the trade name of Argentium©. The present work investigates the tarnish resistance behavior of sterling silver alloy (92.5 wt% pure) containing various additions of Copper, Zinc, and Germanium. The alloys were prepared by melting and casting route, followed by Passivation Heat Treatment (PHT) to create a stable and continuous oxide layer. The temperature for PHT was optimized using thermogravimetry analysis (TGA) of the alloys prepared. Accelerated tarnish test was carried out to investigate the tarnishing behavior of alloy samples obtained before and after PHT. The samples were characterized using XRD, SEM-EDX, and micro-Raman Spectroscopy. The change in reflectance of the samples after tarnish test is determined using UV–Visible reflectance spectroscopy. The mechanism behind the tarnish resistance was derived using Density Functional Theory (DFT) by comparing sulphur (S2) and Oxygen (O2) adsorption energies (BE) of the alloying elements. The lower value of S2 (BE)/O2 (BE) indicates better oxidation and tarnish resistance. The ratio ranges between 222 % (Pure Ag) and 132 % (for Ag-4.2Cu-2.8Zn-1.4Ge) and the p-p between Ge and O has contributed to the reduction in the ratio.

Performance and catalytic mechanism of CNTs/Ti3C2Tx MXene composite cathode for air-breathing hybrid lithium-air batteries

Hybrid lithium-air batteries (HLABs) have not been widely used due to high overpotential, low cycling, slow kinetic rate, and poor cathode catalytic performance. CNTs/Ti3C2Tx MXene composite material was first used as a cathode for HLABs. The cycling performance of batteries equipped with composite cathodes with different mass ratios is tested in an air environment. It is found that when the mass ratio is mCNTs:mTi3C2TxMXene=1:1, the cycling performance of the battery is the best, reaching 405 cycles, i.e., 1620 h of cyclic charging and discharging under fixed capacity. In deep discharge testing, when the mass ratio of the composite cathode is mCNTs:mTi3C2TxMXene=1:1, the battery exhibits extremely high specific capacity, with a maximum value of 22,092.91 mAh/g. The first principles calculate the catalytic mechanism of Ti3C2Tx MXene as the catalyst for HLABs, and the adsorption energy of oxygen on the surface of Ti3C2Tx MXene and ORR processes is calculated. The experiments and calculations confirm that Ti3C2Tx MXene is suitable as a cathode catalyst for HLABs.

Low oxygen adsorption energy barrier architectures to facilitate microenvironmental photocatalytic disinfection in Wei River

Photocatalytic disinfection is an eco-friendly strategy that uses solar energy to purify bacteria-contaminated water. However, improvements in photocatalysts tend to focus on thermodynamics while neglecting kinetic interactions that involve oxygen. Here, we propose the MOF-on-MOF heterojunction NR-HKUST-1@Cu/ZIF-8 (NH@CZ) for kinetic photocatalytic disinfection; the heterojunction reduced bacterial load by nearly 8-log within 20 min. The NH@CZ structure exhibits a high specific surface area with Cu2O8 and CuN4 sites that provide substantial oxygen storage capacity and binding sites. In vitro experiments demonstrated the effective delivery of oxygen to photocatalytic reactions via NH@CZ, leading to enhanced superoxide radical (·O2-) generation. Experimental analysis and theoretical calculations confirm that the formation of heterojunctions in NH@CZ provides an efficient pathway for oxygen reduction by reducing the energy barrier associated with oxygen adsorption. Mechanistic studies show that reactive oxygen species (ROS) disrupt bacterial cell membranes, resulting in the release of cellular contents (e.g., potassium ions and macromolecular proteins) and subsequent cell death. Furthermore, the oxygen-carrying NH@CZ killed all microorganisms in Wei River water samples within 45 min. The MOF-on-MOF heterojunction offers a promising pathway to enhance ROS generation and provides valuable insights into advances in water disinfection technology.

Improved electrochemical performance of Ag-modified Bi0.7Sr0.3FeO3 cathodes by electroless plating for intermediate-temperature solid oxide fuel cells

The Bi0.7Sr0.3FeO3-δ (BSFO)-Ag composite cathode is prepared by modifying BSFO with in-situ chemical plating of Ag. The plated Ag effectively reduces the polarization resistance (Rp) of BSFO. At the Ag loading of 20 wt.%, the optimized Rp of BSFO at 650oC in air condition is 0.35 Ω cm2, which is only 18.6% of that of BSFO cathode (1.88 Ω cm2). The electrochemical performance improvement is primarily attributed to the low oxygen adsorption energy (Eads) domain at the interfaces of BSFO-Ag, as indicated by the first-principles calculations (Eads, -0.81eV). Thus, the addition of Ag changes the cathodic reaction rate control step from the molecular oxygen on the cathode surface adsorption and diffusion to charge transfer on the cathode. The maximum power density (Pmax) of the prepared single cell at 650oC is 450.98 mW cm-2 using H2 (∼3 vol.% H2O) as fuels. The open-circuit voltage (OCV) does not decay significantly (around 0.66 V) after 50 h at the current density of 400 mA cm-2, showing good long-term stability.

Curvature-Induced Electron Spin Catalysis with Carbon Spheres.

Here, we report curvature-induced electron spin catalysis by using solid carbon spheres as catalysts, which were synthesized using positive curvature molecular hexabromocyclopentadiene as a precursor molecule, following a radical coupling mechanism. The curvature spin of carbon is regarded as an overlapping state of σ- and π-radical, which is identified by the inverse Laplace transform of pulse-electron paramagnetic resonance. The growth mechanism of carbon spheres abiding by Kroto's model, is supported by the density functional theory study of thermodynamics and kinetics calculations. The solid carbon spheres present excellent catalytic behaviour of oxidation coupling of amines to form corresponding imines with the conversion of >99%, selectivity of 98.7%, and yield of 97.7%, which is attributed to the predominantly curvature-induced electron spin catalysis of carbon, supported by the calculation of oxygen adsorption energy. This work proposes a view of curvature-induced spin catalysis of carbon, which opens up a research direction for curvature-induced electron spin catalysis.

Curvature‐Induced Electron Spin Catalysis with Carbon Spheres

Here, we report curvature‐induced electron spin catalysis by using solid carbon spheres as catalysts, which were synthesized using positive curvature molecular hexabromocyclopentadiene as a precursor molecule, following a radical coupling mechanism. The curvature spin of carbon is regarded as an overlapping state of σ‐ and π‐radical, which is identified by the inverse Laplace transform of pulse‐electron paramagnetic resonance. The growth mechanism of carbon spheres abiding by Kroto’s model, is supported by the density functional theory study of thermodynamics and kinetics calculations. The solid carbon spheres present excellent catalytic behaviour of oxidation coupling of amines to form corresponding imines with the conversion of >99%, selectivity of 98.7%, and yield of 97.7%, which is attributed to the predominantly curvature‐induced electron spin catalysis of carbon, supported by the calculation of oxygen adsorption energy. This work proposes a view of curvature‐induced spin catalysis of carbon, which opens up a research direction for curvature‐induced electron spin catalysis.

A chitosan-based hydrogel with ultrasound-driven immuno-sonodynamic therapeutic effect for accelerated bacterial infected wound healing

Sonodynamic therapy has attracted much attention as a noninvasive treatment for deep infections. However, it is challenging to achieve high antibacterial activity for hydrogels under ultrasonic irradiation due to the relatively weak sono-catalysis capability of sonosensitizers. Herein, an ultrasound-responsive antibacterial hydrogel (Fe3O4/HA/Ber-LA) composed of Fe3O4-grafted-Berberine, chitosan molecules modified with L-arginine and poly (vinyl alcohol) is prepared for enhanced sonodynamic therapy and immunoregulation. The formation of heterojunction between berberine and Fe3O4 with different work function promotes the charge separation and electron flow and disrupts the conjugated structure of berberine, causing a significant decrease in the band gap, eventually enhancing the sonocatalytic activity. The combination of berberine with Fe3O4 also significantly improves the oxygen adsorption energy, enabling more O2 molecules to react with the electron-rich regions on the surface of Fe3O4 to generate more reactive oxygen species (ROS). L-arginine grafted in the hydrogel is catalyzed by the ROS to release nitric oxide, which not only possesses antibacterial activity, but also positively affects macrophage M1 polarization to display potent phagocytosis to Staphylococcus aureus, thus achieving immuno-sonodynamic therapy. Hence, Fe3O4/HA/Ber-LA hydrogel under ultrasound irradiation shows excellent antibacterial activity. Furthermore, the antioxidative activity and anti-inflammatory effect of berberine released from the hybrid hydrogel induces macrophages to polarize towards the anti-inflammatory M2 status as infection comes under control, thus accelerating the wound healing. The hybrid hydrogel based on the immuno-sonodynamic therapy may be an extraordinary candidate for the treatment of deep infections.

Constructing heterointerfaces to enhance electron transfer of CoFe/CoFe2O4 mediated electro-Fenton process for bisphenol A degradation: Mechanistic insights and performance evaluation

The inefficient electron transfer and Fe(III)/Fe(II) cycle remain significant obstacles in the electro-fenton process. Herein, a nitrogen-doped graphite felt (NGF)-supported CoFe/CoFe2O4 heterostructure is synthesized that achieves highly efficient interfacial electron transfer and stable Co/Fe redox cycle. Theoretical calculations demonstrate that the CoFe/CoFe2O4 heterointerfaces induce local charge redistribution benefiting from the electronic communication between electron acceptor (CoFe2O4) and electron donor (CoFe). Analysis of the Fermi level indicates that the introduction of CoFe alloy enhances the electron density of the catalyst. The CoFe/CoFe2O4@NGF cathode can remove bisphenol A (BPA) completely in 90 min, and the pseudo-first-order kinetic constant (0.0625 min−1) is 23 times higher than the GF system. Notably, the CoFe/CoFe2O4@NGF electrode maintains excellent catalytic capability and stability within a broad pH range (3–11). The construction of the CoFe/CoFe2O4 heterostructure reduces the adsorption energy of oxygen, which ultimately increases the yield of reactive oxygen species (ROS). Quenching experiments revealed that hydroxyl radical (·OH) played a dominant role in the degradation of BPA, and significantly reduced the biotoxicity of intermediate products. This work offers a dependable approach for developing bimetallic catalysts with high catalytic activity.

Trends in the oxygen adsorption energy derived from the thermodynamic potential model for the oxygen evolution reaction

Across the last years, substantial efforts were done to understand the limitations of the oxygen evolution reaction (OER) catalysts and to develop robust ones such as to solve the efficiency problem in water splitting. Fundamental understanding represents a pathway towards designing superior catalysts. In this direction, several descriptors (ηTD, ESSI, Gmax(η)) have been derived based on the adsorption energies of the OER intermediate moieties (∆EHO*/∆EO*/∆EHOO*) for faster screening of the materials. A universal scaling between the adsorption energies of HO* and HOO* was established for a wide range of materials and in many cases was shown to govern the minimum theoretical overpotential. On the other hand, the scaling between the adsorption energies of HO* and O* fragments have a large scattering along the trendline. In this work we derive five trends for the O* adsorption energies based on theoretical overpotential intervals, using data collected from the published studies employing DFT calculations for OER. It is shown that the best materials have an adsorption energy for HO* placed within a limited interval, yet sufficiently large for a pool of promising catalysts (-0.5,1.5 eV), and that the adsorption energies of O* scales with that of HO* at a slope of one and an intercept of 1.81 eV. Furthermore, a decrease of the intercept for the scaling between HOO* and HO* from 3.14 (valid for all data analyzed) to 3.03 eV is found. For three of the other four trends, the slope of the adsorption energies of O*/HO*scaling is one with intercepts closer either to HOO* (2.2/2.78) or to HO*(1.43/0.78) adsorption energies. For each set of data, the scaling between HOO* and HO* adsorption energies varies from 3 to 3.37 eV. Separately, the trends for O* adsorption energies were analyzed for the TiO2(110) semiconducting rutile surface when doped with transition metals and modified (i) with HO* or H* co-adsorbed fragments that act as charge donor/acceptor moieties or (ii) when the surface was provided with an excess or a lack of electrons. The analysis was performed using the data collected from the published literature, supplemented by additional calculations. Clear trends based on the amount of charge were obtained when standard GGA functionals were used. An understanding for the origin of the large variation of the oxygen adsorption energies for the systems that have similar adsorption energies for the HO*/HOO* is provided. However, when the Hubbard corrected GGA functional is used, some trends change. Clearly, it is still a challenge describing accurately and in a cost-effective manner the adsorption of OER moieties on the undoped or doped transition metal oxides, especially for O*. A strategy to get further insight into the origin of large variations of oxygen adsorption energies for the materials that have similar adsorption energies of HO* and HOO* is discussed.

Oxygen reduction reaction activity of Co3O4-modified Pt-graphene electrocatalysts

Abstract In this paper, the ORR activity of Pt/Co3O4-modified N-doped graphene electrocatalysts was investigated based on DFT theory. The Dmol3 module in Materials Studio software was used to optimize the construction of NG models under different doping conditions and to calculate the adsorption and desorption properties of oxygen molecules by optimizing the conformation of Pt13 clusters and substrates. A comparative analysis revealed that the Co3O4 modification reduced the oxygen adsorption energy of the Pt/G catalyst. However, after N doping, the oxygen adsorption energy of Pt/Co3O4/NG was superior to that of Pt/NG. After theoretical analysis, it was determined that it was because the doping of N atoms in graphene could promote the release of oxygen vacancies in Co3O4 and strengthen the adsorption interaction between Pt and graphene carriers to improve the oxygen adsorption energy.

Exploring the bifunctional electrocatalytic activity of tin sulfide decorated manganese iron oxide in alkaline and urea contaminated water

Efficient, affordable, and stable electrocatalysts are pivotal for large-scale water splitting. Herein, we report an optimized decoration of tin sulfide (SnS) bundles on porous manganese ferrite (MnFe2O4) on nickel foam for enhancing the overall water splitting. This decoration yielded an interfacial Sn-O bond between MnFe2O4 and SnS, stabilized the structure, and provided optimistic adsorption energies for oxygen and hydrogen. The decorated electrode exhibited overpotentials of 383 mV for the oxygen evolution reaction (OER) and 127 mV for the hydrogen evolution reaction (HER) at 20 mA.cm−2. Moreover, the decorated sample demonstrated reduced overpotentials of 272 mV and 75 mV (at 20 mA cm−2) for OER and HER in urea-contaminated water. The augmented double layer capacitance (Cdl) electrochemical surface area (ECSA) and X-ray photoelectron spectroscopy (XPS) studies of the decorated sample corroborated the enhanced performances and effectiveness of the SnS decoration. Furthermore, SnS-decorated MnFe2O4 showed outstanding performance in a two-cell configuration with a cell voltage of 1.69 V and 1.52 V (@10 mA cm−2) under alkaline KOH and urea (0.33 M) electrolyte, respectively. Further, the chronoamperometry and post-X-ray photoelectron spectroscopy studies demonstrated the stability and promising potential of this electrode for future non-noble metal-based bifunctional catalytic applications.

Superhydrophobic Co/Fe sulfide nanoparticles and single-atoms doped carbon nanosheets composite air cathode for high-performance zinc-air batteries

Development of a high-performance bifunctional catalyst is essential for the actual implementation of zinc-air batteries in practical applications. Herein, a bifunctional cathode of Co3S4/FeS heterogeneous nanoparticles embedded in Co/Fe single-atom-loaded nitrogen-doped carbon nanosheets is designed. Cobalt-iron sulfides and single atomic sites with Co-N4/Fe-N4 configurations are confirmed to coexist on the carbon matrix by EXAFS spectroscopy. 3D self-supported super-hydrophobic multiphase composite cathode provides abundant active sites and facilitates gas–liquid-solid three-phase interface reactions, resulting in excellent electrocatalytic activity and batteries performance, i.e., an OER overpotential (η10) of 260 mV, a half-wave potential (E1/2) of 0.872 V for ORR, a ΔE of 0.618 V, and a discharge power density of 170 mW cm−2, a specific capacity of 816.3 mAh g−1. DFT analysis shows multiphase coupling of sulfide heterojunction through single-atomic metal doped carbon nanosheets reduces offset on center of electronic density of states before and after oxygen adsorption, and spin density of adsorbed oxygen with same spin orientation, leading to weakened charge/spin interactions between adsorbed oxygen and substrate, and a lowered oxygen adsorption energy to accelerate OER/ORR.

Highly Dispersed Mn-Doped Ceria Supported on N-Doped Carbon Nanotubes for Enhanced Oxygen Reduction Reaction.

The weak adsorption of oxygen on transition metal oxide catalysts limits the improvement of their electrocatalytic oxygen reduction reaction (ORR) performance. Herein, a dopamine-assisted method is developed to prepare Mn-doped ceria supported on nitrogen-doped carbon nanotubes (Mn-Ce-NCNTs). The morphology, dispersion of Mn-doped ceria, composition, and oxygen vacancies of the as-prepared catalysts were analyzed using various technologies. The results show that Mn-doped ceria was formed and highly dispersed on NCNTs, on which oxygen vacancies are abundant. The as-prepared Mn-Ce-NCNTs exhibit a high ORR performance, on which the average electron transfer number is 3.86 and the current density is 24.4% higher than that of commercial 20 wt % Pt/C. The peak power density of Mn-Ce-NCNTs is 68.1 mW cm-2 at the current density of 138.9 mA cm-2 for a Zn-air battery, which is close to that of 20 wt % Pt/C (69.4 mW cm-2 at 106.1 mA cm-2). Density functional theory (DFT) calculations show that the oxygen vacancy formation energies of Mn-doped CeO2(111) and pure CeO2(111) are -0.55 and 2.14 eV, respectively. Meanwhile, compared with undoped CeO2(111) (-0.02 eV), Mn-doped CeO2(111) easily adsorbs oxygen with the oxygen adsorption energy of only -0.68 eV. This work provides insights into the synergetic effect of Mn-doped ceria for facilitating oxygen adsorption and enhancing ORR performance.

Regulation of d-band center of TiO2 through fluoride doping for enhancing photocatalytic H2O2 production activity

Titanium dioxide (TiO2) has received extensive attention for photocatalytic hydrogen peroxide (H2O2) production, with the d-band center related to the adsorption performance, which affects the photocatalytic reaction process. Herein, an ingenious strategy to lower the antibonding-orbital occupancy in the Ti 3d orbital by fluoride ion (F−) doping is proposed, with density functional theory calculations predicting that F-doping into TiO2 induces a non-uniform charge distribution and enables an upshift of the d-band center in F/TiO2. This manipulation provides accessible active centers with favorable d-band energy levels, which can improve the charge-transfer behavior, strengthen the interaction between the adsorbed oxygen and the photocatalyst, and reduce the adsorption energy of oxygen, eventually promoting the photocatalytic H2O2 production rate. The experimental results further confirm that a lower antibonding-orbital occupancy can intensify the adsorption of atomic oxygen at the Ti sites. Electron paramagnetic resonance experiment reveals that the presence of F− ions in the lattice induces the formation of Ti3+ centers that localize the extra electron needed for charge compensation. Femtosecond transient absorption (fs-TA) spectroscopy suggests that photogenerated electrons are transferred from the conduction band of F/TiO2 to the Ti3+ surface states and surface F− ions, expediting the separation of electrons and holes. Consequently, with F− doping in TiO2, the photocatalytic H2O2 production yields improved from 277 to 467 μmol·g−1·h−1, with ethanol as a sacrificial reagent. This study provides a new strategy for regulating the d-band center to optimize the adsorption strength between the photocatalyst and oxygen atoms and achieve enhanced photocatalytic H2O2 production performance.

NiMn layered double hydroxides with promoted surface defects as bifunctional electrocatalysts for rechargeable zinc–air batteries

Layered double hydroxides (LDHs) are attractive bidimensional materials for electrochemical applications because of their high activity in the oxygen evolution reaction (OER). However, their limited bifunctionality due to the slow kinetics of the oxygen reduction reaction (ORR) is a bottleneck for their use in secondary Zn-air batteries (ZABs). In this work, cobalt-free NiMn LDHs were rationally designed by optimizing the Ni composition and incorporating surface defects onto the LDH (oxygen vacancies, Ov) while performing interface engineering using a carbonaceous support enriched with nitrogen heteroatoms. The LDHs without induced defects presented the optimal activity for the OER at a 3:1 Ni/Mn atomic ratio (onset potential 1.47 V vs. 1.45 V for IrO2/C), while the ORR was unfavorable. However, the further optimization by introducing Ov and N–heteroatoms (labeled as Ov-NiMn LDH/NCNTG) allowed bifunctionality by improving the onset potential to 0.90 V while decreasing the half-wave potential difference from 180 mV for the material without induced defects to 100 mV, and by improving the limiting current density by a factor of two. In this regard, density of states (DOS) calculations suggested that surface defects improved the electronic transfer while decreasing the oxygen adsorption energy. ZAB tests indicated that the interface-engineered material allowed a battery voltage of 1.47 V, and a power density of 64 mW cm−2. The battery also maintained stability over 180 charge/discharge cycles at 10 mA cm−2 (50 h), with ΔV below 150 mV between the initial and final cycles.

Electron redistribution and proton transfer induced by atomically fully exposed Cu-O-Fe clusters coupled with single-atom sites for efficient oxygen electrocatalysis

Single-atom catalysts have garnered significant attention by showing sparkling performance in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the air cathode side of energy devices such as metal-air batteries and fuel cells. This work presents a novel catalyst, AC-CuFe-NC, that incorporates Fe-doped CuO atomic clusters (CuOFe) synergistically with single-atom sites. The AC-CuFe-NC demonstrates outstanding ORR performance (half-wave potential of 0.92 V) and an oxygen overpotential gap between ORR and OER as low as 0.61 V, which is among the top reported performances. Combined with in situ ATR-SEIRAS and DFT calculations, it is shown that the synergistic CuOFe atomic clusters are effective in inducing the electronic structure redistribution of the Fe single-atom site, modulating oxygen adsorption energy, and lowering ORR barriers. More importantly, it is revealed that the synergistic adsorption of clusters and single-atom sites establishes hydrogen bonds between the oxygenated intermediates and the electrolyte H2O molecules. The constructed hydrogen bond can provide a pathway for efficient proton transport as supported by kinetic isotope experiments, leading to a substantial enhancement in reaction kinetics. Additionally, the oxygenated intermediates are stabilized, and the Fe-O bond is elongated during the final step of ORR, thereby facilitating the desorption of OH*. The excellent bifunctional electrocatalytic performance of AC-CuFe-NC enable it to show promising application in rechargeable Zn-air batteries. The innovative catalyst structure and synergistic mechanism demonstrated in this study shed light on the development of high-performance catalysts in energy devices.