Low Intrinsic Activity Research Articles

Toward Finding the Role of Surface Iron Ions in Enhancing Oxygen-Evolution Reaction.

The oxygen evolution reaction (OER) in alkaline media is crucial for energy conversion technologies, and Fe-based catalysts have garnered significant attention for their efficacy. In this study, we provide an investigation of Fe-based catalysts under OER conditions using some techniques. Our findings reveal minimal structural alterations in the bulk FeHxOy framework during OER, indicating that the bulk structure remains largely intact. Instead, the catalytic activity is primarily localized on the material's surface. This conclusion is corroborated by the measured low electrochemical surface area (ECSA) of FeHxOy, suggesting that its limited OER performance stems from a paucity of active sites rather than low intrinsic activity. The superior efficiency of Fe ions in conductive oxides or on conductive metal substrates (e.g., copper and gold) in OER is attributed to the increased availability of surface-active sites in these systems. To further elucidate this phenomenon, we investigated two additional systems: NiFe and VFe (hydr)oxides. For NiFe (hydr)oxides, we demonstrate that only surface Fe ions contribute actively to OER. In contrast, in VFe (hydr)oxides, the removal of vanadium resulted in a marked increase in ECSA and the generation of defect sites, significantly enhancing OER activity. These findings provide critical insights into the surface-specific role of Fe ions in catalytic activity and could inform future design strategies for more efficient OER catalysts by optimizing the availability and reactivity of surface-active Fe sites.

Nitrogen-doped carbon nanosheet confined PtNi alloy for efficient acidic electrocatalytic hydrogen evolution reaction

Low intrinsic electrocatalytic activity and inferior conductivity limit the application of Ni/NC in acidic electrocatalytic hydrogen evolution reaction (HER). Herein, we prepared nitrogen-doped carbon nanosheet confined PtNi alloy electrocatalysts (PtNi/NC-10) using PtCl62− electrostatic adsorption coupling melamine pyrolysis nitriding strategy. PtNi alloying was confirmed by the crystallinity decrease and lattice expansion of Ni/NC. The alloying and confinement effect of Metal-Organic Frameworks (MOFs) suppresses the oxidation and agglomeration of metal nanoparticles during pyrolysis, thus significantly reducing particle size, increasing specific surface area, and promoting the exposure of active sites. The strong electronic interaction between Pt and Ni optimizeds the surface charge distribution, enhancing the adsorption of H species on electron-rich Pt sites, thereby improving reaction kinetics. In addition, PtNi alloying improves the conductivity of the material, accelerating charge transfer and proton transport. Consequently, the prepared PtNi/NC-10 exhibits superior HER performance than Ni/NC in 0.5 M H2SO4 solution, even comparable to commercial 20 wt% Pt/C, with the overpotentials of 35 mV at 0.01 A cm−2. Furthermore, the electrocatalysts assembled PtNi/NC-10-CP‖RuO2-TFF proton exchange membrane (PEM) electrolyzer only requires 2.32 V cell voltage to achieve 1 A cm−2, presenting practical application prospects. Our work provides a novel idea for designing efficient and stable MOFs confined to alloy-based HER electrocatalysts.

Al-etching-induced defect engineering in NiAl LDHs for promoting multifunctional electrocatalytic oxidations: Water oxidation and urea oxidation

Electrocatalytic water splitting is a promising avenue to produce green hydrogen for future sustainable development. Developing multifunctional catalysts with high-performance toward urea oxidation reaction (UOR) and oxygen evolution reaction (OER) offers a unique approach for simultaneously achieving the degradation of urea-containing wastewater and energy-saving hydrogen production. Ni-based materials are a kind of promising materials for electrocatalysis, since its abundant reserve and tolerance. However, low intrinsic activity and catalytic efficiency hinder its wide application. Here, a defect engineering strategy is developed to create vacancies on NiAl layer double hydroxides (LDHs) catalysts by selectively etching Al ions in strong alkaline solution. The obtained NiAl LDHs with rich defects (D-NiAl LDHs) exhibit good OER performance with overpotential of 264 mV to achieve a current density of 10 mA cm−2 and a Tafel slope of 39.8 mV dec−1. In addition, the D-NiAl LDHs catalysts also show excellent UOR activity using a potential of 1.328 V vs. RHE @ 10 mA cm−2 in alkaline solution. In comparation to NiAl LDHs, the enhanced performance of D-NiAl LDHs toward oxidation of small-molecule OH− and urea could be attributed to electronic regulation of defects and a larger electrochemical surface area. Partially replacing the OER with the UOR, the driving voltage of overall water splitting reduces effectively from 1.856 V to 1.688 V at a current of 100 mA cm−2.

Highly active manganese nitride-europium nitride catalyst for ammonia synthesis

The development of efficient catalysts for ammonia synthesis under mild conditions is critical for establishing a carbon-neutral society powered by renewable ammonia. While significant effort has been focused on Fe and Ru-based catalysts, there have been very limited studies on manganese-based catalysts for ammonia synthesis because of their low intrinsic catalytic activity. Herein, we report that the synergy between manganese nitride (Mn4N) and europium nitride (EuN) yields an ammonia synthesis rate that is 41 and 25 times higher than that of neat Mn4N and EuN, respectively. Detailed studies suggest that a [Eu-N-Mn] species at the interface of Mn4N and EuN plays a pivotal role in ammonia synthesis. Compositing of Mn4N with other rare earth metal nitrides such as LaN, PrN, and CeN also leads to a significant enhancement in catalytic activity. This work broadens the scope of advanced nitride catalysts for ammonia synthesis.

Asymmetric defective sites-mediated high-valent cobalt-oxo species in self-suspension aerogel platform for efficient peroxymonosulfate activation

The main pressing problems should be solved for heterogeneous catalysts in activation of peroxymonosulfate (PMS) are sluggish mass transfer kinetics and low intrinsic activity. Here, oxygen vacancies (Vo)-rich of Co3O4 nanosheets were anchored on the superficies of spirulina-based reduced graphene oxide-konjac glucomannan (KGM) aerogel (R-Co3O4-x/SRGA). The porous structure and superhydrophilicity conferred by KGM maximized the diffusion and transport of reactant. More interestingly, R-Co3O4-x/SRGA came true self-suspension rather than conventional self-floating without the aid of external force, maximizing space utilization and facilitating catalysts recovery. Anchored R-Co3O4-x nanosheets acted as “engines” to drive the reaction. Density functional theory (DFT) manifested Vo was capable of breaking the symmetry of the electronic structure of Co3O4. The formation of asymmetric active sites (Vo) was revealed to modulate the d-band center, enhanced affinity for PMS, and promoted evolution of high-valent cobalt-oxo (Co(IV)=O) species. R-Co3O4-x/SRGA achieved complete removal of sulfamethoxazole (SMX) within 12 min. Furthermore, R-Co3O4-x/SRGA demonstrated exceptional stability in the presence of various environmental interference factors and continuous flow device. This insightful work cleverly integrates the macroscopic design of structure, and the microscopic regulation of active sites is expected to open up new opportunities for the development of water treatment.

Understanding Performance Limitation of Liquid Alkaline Water Electrolyzers

Green hydrogen production via water electrolysis powered by renewable energy is a critical technology in the pursuit of a net-zero emission economy1. Liquid alkaline water electrolyzers (LAWEs), being the most commercially mature electrolyzer technology, play a pivotal role in large-scale green hydrogen production2. The utilization of earth-abundant and cost-effective nickel and iron-based materials as cell components of LAWEs reduces capital cost of large-scale electrolyzer cells3. However, LAWEs suffer from low operational efficiency, primarily due to low intrinsic activity of unoptimized electrode materials, as well as high ohmic resistance introduced by separators and gas bubbles within thick electrodes. Herein, we used a lab-scale LAWE cell in combination with various electrode configurations to gain a deeper understanding of the limiting factors affecting conventional LAWE performance. Our results show that the electrochemical active surface area (ECSA), chemical compositions, and pore structure of the electrodes are key design parameters to achieve high efficiencies for advanced LAWEs. Besides, particular attention should be paid to the micro-gaps in between electrode and separator, which can be minimized through using electrodes with lower surface porosity and smaller pore size. Consequently, these enabled us to build LAWEs that are capable of sustaining 2 A cm-2 at 2.2 V and operating steadily at 1 A cm-2 for nearly 600 h with negligible performance decay. These findings establish essential criteria for selecting electrodes to achieve high-performance in LAWE and, in turn, expedite the adoption of LAWE technology in green hydrogen production and the transition towards a low-carbon economy. Acknowledgement The authors acknowledge the Department of Energy-Office of Energy Efficiency and Renewable Energy-Hydrogen and Fuel Cell Technologies Office (DOE-EERE-HFTO) and the H2 from Next-generation Electrolyzers of Water (H2NEW) consortium for funding under Contact Number DE-AC02-05CH11231.

Remarkable improvement in photocatalytic activity of g-C3N4 for NO oxidation through surface hydroxylation

The nitrogen oxide emissions originating from combustion pose significant risks to the environment. Photocatalysis is considered an efficient and environmentally friendly strategy to alleviate this problem. Graphitic carbon nitride (g-C3N4) is regarded as one of the most promising organic photocatalytic materials for environmental purification. However, its small specific surface area, weak adsorption and high recombination rate of charge carriers result in low intrinsic photocatalytic activity. To overcome these obstacles, a hydrothermal treatment of dicyandiamide-derived g-C3N4 (DCN) at different temperatures (140–200 °C) was employed to enhance the photocatalytic activity for NO oxidation. The experimental results demonstrated a significant improvement in the photocatalytic oxidation removal rate of NO after a hydrothermal treatment. The optimal photocatalyst, DCN-180, treated at 180 °C, demonstrated the highest NO removal efficiency (65.0 %), which is twice the value of pristine DCN (32.5 %). Additionally, the formation of the toxic intermediate NO2 was effectively suppressed during the reaction. Photoelectrochemical tests revealed that DCN-180 exhibited higher photocurrent density and smaller impedance radius compared to the untreated g-C3N4 sample. Moreover, density functional theory (DFT) calculations confirmed that the DCN-180 sample showed a stronger ability to adsorb O2 and NO. The enhanced photocatalytic NO oxidation performance of DCN-180 has been primarily attributed to its enlarged specific surface area (from 10.7 to 35.5 m2 g−1), local polarization effect, reduced interfacial charge transfer resistance, and improved adsorption abilities for NO and O2 molecules. This study provides valuable insights for designing and preparing highly efficient g-C3N4 based photocatalysts through surface modification for photocatalytic NO purification.

Local spin-state tuning enables high-efficiency nickel sulfide cathode for stable alkaline Zn batteries

Nickel sulfide (Ni3S2) has shown great promise as advanced cathode in alkaline nickel-zinc batteries (ANZBs) for its good electrochemical reversibility and electronic conductivity. However, due to the unfavorable OH− adsorption capability and low intrinsic activity of Ni sites originated from the unsuitable d-electron spin state, the overall performances of Ni3S2 are yet unsatisfactory for practical ANZBs. Herein, we demonstrate the engineering of local spit state of Ni sites via a facile electrochemical activation in Ni3S2 to significantly boost its comprehensive energy storage capability. After electrochemical treatment, the spit state of fractional Ni2+ (eg4t2g4) sites of Ni3S2 is successfully transformed into high-valence Ni3+ (eg4t2g3), which considerably enhances the OH− adsorption capability and redox reactivity. The optimal Ni3S2 electrode exhibits a high capacity of 1.11 mAh cm−2 at 1 mA cm−2 and no capacity decay after 3000 cycles, which are far greater than the pristine Ni3S2 (0.39 mAh cm−2) electrode and also comparable to the best ever-reported alkaline cathodes. Furthermore, the assembled full ANZB can afford a peak energy density of 1.59 mWh cm−2 and power density of 33.92 mW cm−2. This work affords valuable insights into local electronic structure modulation of electrode materials for aqueous energy storage devices.

Recent Progress on Computation‐Guided Catalyst Design for Highly Efficient Nitrogen Reduction Reaction

AbstractElectrochemical nitrogen reduction reaction (NRR) for ammonia synthesis has attracted great interest in recent years, which presents a carbon‐free alternative to the energy‐intensive Haber–Bosch process. Besides, NRR also provides a promising coverage route of renewable energy since NH3 is considered the second generation of hydrogen energy while possessing established technologies of liquefaction, storage, and transport. However, there are long‐term challenges in catalyst design for NRR due to its low intrinsic activity and unsatisfied selectivity. Fortunately, by conducting extensive explorations in this field, much progress is achieved in boosting the NRR performance. Herein, from a view of the atomic/electronic level, three promotion effects are summarized for NRR (i.e., electron effect, geometry effect, and ligand effect), which tackle the challenges of activity and selectivity. Representative studies with taking fully advantages of the promotion effects are reviewed, which realized remarkable NRR performance. Finally, the future research directions and prospects are discussed. It is highly expected that this review will enable the advancement of NRR catalysts and promote the further development of electrochemical NRR.

Polyoxometallate Cluster Induced High-Entropy Oxide Sub-1 nm Nanosheets as Photoelectrocatalysts for Zn-Air Batteries.

The lack of highly efficient and inexpensive catalysts severely hinders the large-scale application of Zn-air batteries (ZABs). High-entropy oxides (HEOs) exhibit unique structures and attractive properties; thus, they are promising to be used in ZABs. However, conventional high-temperature synthesis methods tend to obtain microscale HEOs with a lower exposure rate of active sites. Here, we report a facile solvothermal strategy for preparing two-dimensional (2D) HEO sub-1 nm nanosheets (SNSs) induced by polyoxometalate (POM) clusters. Taking advantage of the special 2D sub-1 nm structure and precise element regulation, these 2D HEOs-POM SNSs exhibit enhanced bifunctional oxygen evolution and oxygen reduction reaction activity under light irradiation. Further applying these 2D HEOs-POM SNSs to ZABs as cathode catalysts, the CoFeNiMnCuZnOx-phosphomolybdic acid SNSs-based ZABs deliver a low charge/discharge voltage gap of 0.25 V at 2 mA cm-2 under light irradiation. Meanwhile, it could maintain an ultralong-term stability for 1600 h at 2 mA cm-2 and 930 h at 10 mA cm-2. The 2D sub-1 nm structure and fine element control in HEOs provide opportunities to solve the problems of low intrinsic activity, limited active sites, and instability of air cathodes in ZABs.

Electron Redistribution in Iridium-Iron Dual-Metal-Atom Active Sites Enables Synergistic Enhancement for H2O2 Decomposition.

Developing efficient heterogeneous H2O2 decomposition catalysts under neutral conditions is of great importance in many fields such as clinical therapy, sewage treatment, and semiconductor manufacturing but still suffers from low intrinsic activity and ambiguous mechanism understanding. Herein, we constructed activated carbon supported with an Ir-Fe dual-metal-atom active sites catalyst (IrFe-AC) by using a facile method based on a pulsed laser. The electron redistribution in Ir-Fe dual-metal-atom active sites leads to the formation of double reductive metal active sites, which can strengthen the metal-H2O2 interaction and boost the H2O2 decomposition performance of Ir-Fe dual-metal-atom active sites. Ir-Fe dual-metal-atom active sites show a high second-order reaction rate constant of 3.53 × 106 M-1·min-1, which is ∼106 times higher than that of Fe3O4. IrFe-AC is effective in removing excess intracellular reactive oxygen species, protecting DNA, and reducing inflammation under oxidative stress, indicating its therapeutic potential against oxidative stress-related diseases. This study could advance the mechanism understanding of H2O2 decomposition by heterogeneous catalysts and provide guidance for the rational design of high-performance catalysts for H2O2 decomposition.

Oxygen vacancies enhanced electrocatalytic water splitting of P-FeMoO4 initiated via phosphorus doping

Transition metal oxides (TMOs) are abundant and cost-effective materials. However, poor conductivity and low intrinsic activity limit their application in electrolyzed water catalysts. Herein, we prepared P-FeMoO4 in situ on nickel foam (P-FMO@NF) by phosphorylation-modified FeMoO4 to optimize its electrocatalytic properties. Interestingly, phosphorus doping is accompanied by the generation of oxygen vacancies and surface phosphates. Oxygen vacancies accelerated Mo dissolution during the oxygen evolution reaction (OER), leading to the rapid reconfiguration of P-FMO@NF to FeOOH and regulating the electronic structure of P-FMO@NF. The formation of phosphates is caused by the substitution of some molybdates with phosphates, which further increases the amount of oxygen vacancies. Hence, the OER overpotential of P-FMO@NF at a current density of 10 mA cm−2 is only 206 mV, and the hydrogen evolution reaction (HER) overpotential is 154 mV. It was assembled into a water splitting cell with a voltage of just 1.59 V at 10 mA cm−2 and shows excellent stability over 50 h. These excellent electrocatalytic properties are mainly attributed to the oxygen vacancies, which improve the interfacial charge transfer properties of the catalysts. This study provides new insights into phosphorus doping and offers a new perspective on the design of electrocatalysts.

Heterointerface MnO2/RuO2 with rich oxygen vacancies for enhanced oxygen evolution in acidic media.

The design and synthesis of oxygen evolution reaction (OER) electrocatalysts that operate efficiently and stably under acidic conditions are important for the preparation of green hydrogen energy. The low intrinsic catalytic activity and poor acid resistance of commercial RuO2 limit its further development, and the construction of heterointerface structures is the most promising strategy to break through the intrinsic activity limitation of electrocatalysts. Herein, we synthesized spherical and oxygen vacancy-rich heterointerface MnO2/RuO2 using morphology control, which promoted the kinetics of the oxygen evolution reaction with the interaction between oxygen vacancies and the oxide heterointerface. MnO2/RuO2 was reported to be an acidic OER catalyst with excellent performance and stability, requiring only an ultra-low overpotential of 181 mV in 0.5 M H2SO4 to achieve a current density of 10 mA cm-2. The catalyst activity remained essentially unchanged in a 140 h stability test with an ultra-high mass activity (858.9 A g-1@ 1.5 V), which was far superior to commercial RuO2 and most previously reported noble metal-based acidic OER catalysts. The experimental results showed that the effect of more oxygen vacancies and the heterointerfaces of manganese ruthenium oxides broke the intrinsic activity limitation, provided more active sites for the OER, accelerated reaction kinetics, and improved the stability of the catalyst. The excellent performance of the catalyst suggests that MnO2/RuO2 provides a new idea for the design and study of heterointerfaces in metal oxide nanomaterials.

Ti3C2Tx@Co(OH)2/Co3O4 nanocomposites with heterojunction enhancement effect for toluene detection at room temperature

Ti3C2Tx MXene possesses excellent conductivity, tunable electronic structure, and large surface area, thereby ideal for use in gas sensors. However, Ti3C2Tx MXene is limited by low sensitivity linked to its low intrinsic activity and susceptibility to oxidation. Herein, Ti3C2Tx@Co(OH)2/Co3O4 nanocomposites were prepared by self-assembly strategy. High sensitivity to toluene at room temperature can be obtained by adjusting the input ratio of Ti3C2Tx MXene (MXCo-40). MXCo-40 obtained with 40 mg of Ti3C2Tx MXene input exhibited a remarkable response of 514 % to 100 ppm toluene, 737 times higher than Ti3C2Tx MXene, with response and recovery times of 9 s and 5 s. Ultraviolet photoelectron spectrometer, ultraviolet–visible absorbance spectroscopy, and diffuse reflection infrared fourier transform spectroscopy analyses revealed the heterojunction structure and monitored the gas-sensing reaction. The results suggested that the improved performance can be attributed to the formation of enhanced heterojunction structure, the electron-supplying ability of Co low-lying 3d orbitals, and high local charge concentration facilitating toluene polarization and bond breaking. In summary, the proposed composite structure looks promising for the preparation of Ti3C2Tx MXene-based gas sensors for enhanced gas-sensing applications.

(Invited) Novel Strategies in the Design of the Oxygen Evolving Catalysts for Water Electrolysis

Hydrogen producing electrolytic water splitting is one of the most important electrochemical technologies supporting the de-fossilization of the society and enabling integration of renewable energy sources into electric grid. The water electrolysis in fact combines two electrocatalytic reactions – a two electron hydrogen evolution and four electron oxygen evolution, which in most cases represents the kinetically limiting process determining the efficiency of the green hydrogen production. Given the harsh conditions at which the oxygen evolution is driven in water electrolysers a design of practical oxygen evolving catalysts needs to reflect not only the intrinsic activity, but also stability and feasibility. To reflect these additional factors a specific challenges connected with the pH at which the intended water electrolysis ought to operate need to be included into catalyst design. The development of the anode materials for alkaline water electrolyzers faces less restrictions given reasonable stability of the non-noble transition metal oxides/oxihydroxides at operando conditions. The development of novel anode materials for polymer electrolyte water electrolyzers is far more challenging due the low stability of transition metals at OER potentials in acid media which restricts the available catalysts to those based on scarce Ru, or Mn.The presented paper will describe two approaches attempting development of novel OER catalysts for acid media. The first approach aims at following the high entropy concept pioneered theoretically by Svane and Rossmeisl [1]. The synergetic effects encountered in high entropy oxides will be demonstrated on mixed Ru-Ir pyrochlores stabilized by lanthanides prepared by spray freeze freeze drying technique. While the high entropy oxides are highly active in OER the need to explore noble metal oxides may still represent a stumbling block in large scale deployment. This restriction may be removed by targeted activation of wide band semiconducting oxides by simultaneous n- and p- co-doping [2]. The co-doping strategy alters the electronic structure of the host oxide generating a pseudo-band in the materials band gap facilitating an electrocatalytic activity (in dark). The concept predicts that a wide band semiconductors based on , e.g. Ti, may be activated into a active OER catalysts potentially compensating a lower intrinsic activity with low price. The potential of the approach will be demonstrated on two systems – co-doped anatase polymorph of TiO2 and on co-doped cubic titanate based perovskites.

Comparison between endocrine activity assessed using ToxCast/Tox21 database and human plasma concentration of sunscreen active ingredients/UV filters.

Sunscreen products are composed of ultraviolet (UV) filters and formulated to reduce exposure to sunlight thereby lessening skin damage. Concerns have been raised regarding the toxicity and potential endocrine disrupting (ED) effects of UV filters. The ToxCast/Tox21 program, that is, CompTox, is a high-throughput in vitro screening database of chemicals that identify adverse outcome pathways, key events, and ED potential of chemicals. Using the ToxCast/Tox21 database, octisalate, homosalate, octocrylene, oxybenzone, octinoxate, and avobenzone, 6 commonly used organic UV filters, were found to have been evaluated. These UV filters showed low potency in these bioassays with most activity detected above the range of the cytotoxic burst. The pathways that were most affected were the cell cycle and the nuclear receptor pathways. Most activity was observed in liver and kidney-based bioassays. These organic filters and their metabolites showed relatively weak ED activity when tested in bioassays measuring estrogen receptor (ER), androgen receptor (AR), thyroid receptor, and steroidogenesis activity. Except for oxybenzone, all activity in the endocrine assays occurred at concentrations greater than the cytotoxic burst. Moreover, except for oxybenzone, plasma concentrations (Cmax) measured in humans were at least 100× lower than bioactive (AC50/ACC) concentrations that produced a response in ToxCast/Tox21 assays. These data are consistent with in vivo animal/human studies showing weak or negligible endocrine activity. In sum, when considered as part of a weight-of-evidence assessment and compared with measured plasma concentrations, the results show these organic UV filters have low intrinsic biological activity and risk of toxicity including endocrine disruption in humans.

Engineering oxygen vacancies in perovskite oxides by in-situ electrochemical activation for highly efficient nitrate reduction

Perovskite oxides have emerged as a new category of catalysts for NO3RR, yet their low intrinsic catalytic activity results in unsatisfactory performance. Oxygen vacancy engineering has recently been found to be effective for improving the NO3RR performance of perovskite oxides. Herein, a novel and efficient strategy of electrochemical activation for in-situ oxygen vacancies (OVs) creation in perovskite oxide La0.9FeO3-δ was reported. The results showed that the NO3−-N removal rate increased 2.6-fold on activated La0.9FeO3-δ in comparison to pristine La0.9FeO3-δ. The enhanced NO3RR performance was attributed to the presence of more OVs, which served to increase the adsorption energy of NO3− while also promoting atomic H* formation for NO3−-N hydrogenation. Furthermore, a continuous experiment lasting 240 h found the activated La0.9FeO3-δ exhibited extremely high stability. Additionally, we demonstrated that the electrochemical activation method was applicable to other typical perovskite oxides, such as LaCoO3, indicating its generalizability. This study provides a simple and scalable approach for the preparation of a high-performance perovskite oxide-type electrocatalysts for NO3RR.

Correlating the Valence State with the Adsorption Behavior of a Cu-Based Electrocatalyst for Furfural Oxidation with Anodic Hydrogen Production Reaction.

The low-potential furfural oxidation reaction (FFOR) on a Cu-based electrocatalyst can produce H2 at the anode, thereby providing a bipolar H2 production system with an ultra-low cell voltage. However, the intrinsic activity and stability of the Cu-based electrocatalyst for the FFOR remain unsatisfactory for practical applications. This study investigates the correlation between the valence state and the adsorption behavior of the Cu-based electrocatalyst in furfural oxidation. Cu0 is the adsorption site with low intrinsic activity. Cu+ , which exist in the form of Cu(OH)ads in alkaline electrolyte, has no adsorption ability but can improve the performance of Cu0 by promoting adsorption of FF. Moreover, a mixed-valence Cu-based electrocatalyst (MV Cu) with high intrinsic activity and stability is prepared electrochemically. With the MV Cu catalyst, the assembled dual-side H2 production electrolyzer has a low electricity requirement of only 0.24 kWh·mH2 -3 at an ultra-low cell voltage of 0.3V, and it exhibits sufficient stability. This study not only correlates the valence state with the adsorption behavior of the Cu-based electrocatalyst for the low-potential FFOR with anodic H2 production but also reveals the mechanism of deactivation to provide design principles for Cu-based electrocatalysts with satisfactory stability. This article is protected by copyright. All rights reserved.

Co3O4[sbnd]CeO2 heterogenous interfaces as a high-efficient catalyst for soot oxidation

Developing advanced catalysts for efficiently eliminating soot particles could be significant for achieving the goal of Euro 6 and China VIB. Co3O4/CeO2 nanocomposites containing Co3O4CeO2 interfaces are considered as efficient catalysts for removing soot particles, while the role of Co3O4CeO2 interfaces is still unclear. In this study, Co3O4/CeO2 nanocomposites with different contents of Co3O4CeO2 interfaces were prepared to investigate the role of Co3O4CeO2 interfaces in promoting soot oxidation. Experimental results show that Co3O4CeO2 interfaces can efficiently eliminate soot nanoparticles, while the content of which weakly influences the elimination temperatures and products selectivity. It was found that the reaction dynamic and intrinsic activity are found to change with the content of Co3O4CeO2 interfaces. Further investigations demonstrate that a few amounts of Co3O4CeO2 interfaces can significantly increase the O2-preferred active sites, but not significantly enhance the movability of active oxygen species and the activation of NO. Increasing Co3O4CeO2 interfaces can enrich the NO-preferred active sites and enhance the movability of active oxidative species. As a result, rich Co3O4CeO2 interfaces lead to low soot-eliminating temperatures (T50: 407 °C) and high intrinsic activity (TOF: 0.99 h−1), while a few amounts of Co3O4CeO2 interfaces perform low soot-eliminating temperatures (T50: 403 °C) with low intrinsic activity (TOF: 0.68 h−1). Results of this work might be meaningful in designing robust nanomaterials with heterogenous interfaces.

Heterogeneous Fe-Co dual-atom catalyst outdistances the homogeneous counterpart for peroxymonosulfate-assisted water decontamination: New surface collision oxidation path and diatomic synergy.

Heterogeneous catalysts lag far behind their homogeneous counterparts in activating peroxymonosulfate (PMS) for water decontamination due to the low site intrinsic activity and sluggish mass transfer. The single-atom catalyst can bridge the gap between heterogeneous and homogeneous catalysts, but the difficulty to break scaling relations originating from the site monotony restricts further efficiency upgradation. Herein through modulating the crystallinity of NH2-UIO-66, a porous carbon support with ultrahigh surface area (1721.71 m2 g-1) is obtained to anchor the dual-atom FeCoN6 site, which exhibits superior turnover frequency over single-atom FeN4 and CoN4 sites (13.07 versus 9.97, 9.07 min-1). The as-synthesized composite thus outperforms the homogeneous catalytic system (Fe3++Co2+) for sulfamethoxazole (SMZ) degradation, and the catalyst-dose-normalized kinetic rate constant (99.26L min-1 g-1) exceeds reported values by 1∼2 orders of magnitude. Moreover, only 20mg of the catalyst can run a fluidized-bed reactor to realize continuous zero discharge of SMZ in multiple actual waters for up to 8.33h. Unlike all reported reaction routes, the catalysis on the diatomic site follows a new surface collision oxidation path, i.e. the dispersed catalyst adsorbs PMS to generate surface-activated PMS with high potential, which collides with surrounding SMZ and directly seizes electron from it to induce pollutant oxidation. Theoretical calculation indicates that the enhanced activity of FeCoN6 site stems from the diatomic synergy, leading to stronger PMS adsorption, larger near-Fermi-level density of states and optimal global Gibbs free energy evolution. Overall, this work provides an effective strategy of constructing heterogeneous dual-atom catalyst/PMS process to achieve faster pollution control than homogeneous system, and sheds light on the interatomic synergetic mechanism for PMS activation.