Active Reaction Sites Research Articles

Reducing Intrinsic Carrier Recombination in Au/CuTCPP(Fe) Schottky Junction Through Spin Polarization Manipulation for Sensitive Photoelectrochemical Biosensing.

Schottky junctions have been widely applied to facilitate charge carrier separation through the formation of an internal electric field (IEF). However, the notably restricted spatial distribution of the IEF weakens the promotion of intrinsic carrier separation. In this study, we unveil that Au nanoparticles (NPs) in the Au/CuTCPP(Fe) Schottky junction can manipulate the spin polarization of CuTCPP(Fe) to inhibit inner carrier recombination. Experimental investigations and theoretical calculations reveal that the introduction of Au NPs leads to an increased population of spin-polarized electrons, effectively suppressing inner charge carrier recombination in CuTCPP(Fe) by employing the spin mismatch between spin-polarized photoexcited carriers. Moreover, as a typical active site for the oxygen reduction reaction, the oxygen adsorption configuration on spin-polarized Fe single-atom sites in Au/CuTCPP(Fe) is further optimized, resulting in boosted interfacial reactions. Leveraging the thiocholine-induced poisoning of the active sites and the magnetic-enhanced photoelectric response, Au/CuTCPP(Fe) is harnessed to develop a photoelectrochemical biosensing platform for organophosphorus pesticides. This work offers a promising method for manipulating the spin polarization of semiconductors in heterojunctions to mitigate intrinsic charge carrier recombination.

Molecular Engineering Spatially Separated Redox Centers Enable Efficient Piezo-Photocatalytic H2O2 Production.

Piezo-photocatalytic production of hydrogen peroxide (H2O2) from water and air is promising but still challenging as insufficient reaction active sites and low reaction efficiency. We have ingeniously applied molecular engineering methods to design an anthraquinone molecularly grafted metal-organic framework piezo-photocatalyst (denoted as UiO-66-AQ) for H2O2 generation from water and air. The catalyst achieves a peak H2O2 yield of 7872.4 μM g-1 h-1, primarily owing to the presence of spatially separated redox sites that enable simultaneously two-step single-electron water oxidation and two-electron oxygen reduction reactions. Notably, experimental and computational simulations confirm rapid carrier separation under the ligand-to-chain charge transfer mode. Electrons transfer to the AQ part and rapidly form internal peroxides for spontaneous oxygen reduction reaction while holes direct to the UiO-66 ligand for the water oxidation reaction. Additionally, a continuous flow tubular reactor with catalytic membranes made of UiO-66-AQ affords 96% removal of organic dyes through the self-Fenton process under visible light and vibrating water flow, confirming the significant potential of the catalyst for practical applications. This work deepens the understanding of directional carrier migration at piezo-photocatalytic spatial separation sites, opening new pathways for environmentally friendly and efficient H2O2 synthesis.

Molecular Engineering Spatially Separated Redox Centers Enable Efficient Piezo‐Photocatalytic H2O2 Production

Piezo‐photocatalytic production of hydrogen peroxide (H2O2) from water and air is promising but still challenging as insufficient reaction active sites and low reaction efficiency. We have ingeniously applied molecular engineering methods to design an anthraquinone molecularly grafted metal‐organic framework piezo‐photocatalyst (denoted as UiO‐66‐AQ) for H2O2 generation from water and air. The catalyst achieves a peak H2O2 yield of 7872.4 μM g‐1 h‐1, primarily owing to the presence of spatially separated redox sites that enable simultaneously two‐step single‐electron water oxidation and two‐electron oxygen reduction reactions. Notably, experimental and computational simulations confirm rapid carrier separation under the ligand‐to‐chain charge transfer mode. Electrons transfer to the AQ part and rapidly form internal peroxides for spontaneous oxygen reduction reaction while holes direct to the UiO‐66 ligand for the water oxidation reaction. Additionally, a continuous flow tubular reactor with catalytic membranes made of UiO‐66‐AQ affords 96% removal of organic dyes through the self‐Fenton process under visible light and vibrating water flow, confirming the significant potential of the catalyst for practical applications. This work deepens the understanding of directional carrier migration at piezo‐photocatalytic spatial separation sites, opening new pathways for environmentally friendly and efficient H2O2 synthesis.

Defect physics investigations in bulk NaBiO3 photocatalysts via Heyd-Scuseria-Ernzerhof hybrid density functional theory calculations.

This study employs Heyd-Scuseria-Ernzerhof hybrid density functional theory calculations to thoroughly investigate the n-type and p-type conductivity mechanisms of NaBiO3 photocatalysts. The results reveal that the intrinsic interstitial defect Na1+i is dominant under most growth conditions because of its lower formation energy. It is an excellent donor because of its shallower charge transition level. This makes it easily reach and even exceed the significant concentration of 1021 cm-3 with Na chemical potential regulation. Thus, in most circumstances, the intrinsic n-type conductivity of NaBiO3 found in experiments should primarily originate from the contribution of the interstitial defect Na1+i. The anti-site defect Bi2+Na also contributes to the unintentional n-type conductivity behavior. Especially under Na-poor and Bi-rich growth conditions, Bi2+Na becomes the dominant defect and is most responsible for the intrinsic n-type conductivity. The two major intrinsic defects, including Na1+i and Bi2+Na defects, can act as the photocatalytic reaction active sites or as a hole capture center (Bi2+Na) rather than as the recombination centers of the photo-generated electrons and holes in NaBiO3. On the other hand, based on thermodynamic simulation, the study examines the impacts of n-type and p-type doping at a fixed donor D+ or acceptor A- concentration on the conductive properties of NaBiO3 under different chemical potential conditions. It is indicated that p-type doping can convert the intrinsic n-type NaBiO3 into a p-type semiconductor only under non-thermal equilibrium growth conditions (quenching method). In contrast, n-type doping can easily enhance its n-type carrier concentration. Our results can guide optimizing the growth conditions to achieve high donor doping and high photocatalytic performance in NaBiO3 or NaBiO3-based materials.

Z-scheme heterojunction BiOBr/MIL-100(Fe) visible photocatalytic-permonosulfate degradation of AO7

ABSTRACT Metal–organic frameworks (MOFs) have garnered significant interest in the field of photocatalysis. In this study, Z-scheme heterojunction BM-x composites consisting of bismuth bromide oxide (BiOBr) and iron-based metal–organic backbone (MIL-100(Fe)) were successfully synthesized using ethylene glycol as a solvent. The composites were characterized using various techniques. BM-x exhibit abundant functional groups, large specific surface areas, and narrow band gap energy, thus provide numerous active sites for catalytic reactions and respond well to visible light. Notably, BM-7 displays remarkable catalytic activity in a visible light-activated permonosulfate (PMS) system and achieves a degradation rate of 99.02% over 100 mg/L gold orange II (AO7) within 60 min. The effects of BM-7 and PMS addition, initial AO7 concentration, initial pH, inorganic anions, and humic acid on the degradation system were investigated. The proposed mechanism of the Z-scheme heterojunction in the BM-7 photocatalyst demonstrates effective photoelectron transfer from the BiOBr conduction band to the MIL-100(Fe) valence band, resulting in excellent catalytic activity. Radical burst experiments identified 1O2, h+, and ·O2− as the main active substances. BM-7 has high stability and reusability, with a degradation rate reduction of only 14.48% after three recycles. These findings provide valuable insights into using persulfate combined with visible light.

Construction of Ni–P/TiO2 Schottky heterojunction via photo-deposition to enhance photocatalytic hydrogen evolution activity

Photocatalytic hydrogen evolution (PHE) is sustainable and environmentally friendly. Titanium dioxide (TiO2) is commonly chosen as a photocatalyst of PHE due to its non-toxicity, robust stability, and superior photocatalytic activity. However, the efficacy of TiO2 is restricted by rapid electron–hole pair recombination, limited electron mobility, and sluggish surface reactions. To address these issues, we have synthesized a Ni–P alloy onto the surface of TiO2 (Ni–P/TiO2) using a safe and efficient photo-deposition method, thereby constructing a Schottky heterojunction photocatalyst. The construction of the heterojunction significantly reduces the recombination rates of photoinduced electron–hole pairs and enhances the charge transfer rates within the photocatalyst. Additionally, the incorporation of the Ni–P alloy increases the density of oxygen vacancies, providing abundant active sites for the reduction reaction. The metallic properties of the Ni–P alloy improve the overall light absorption capacity. As a result, Ni–P/TiO2 exhibits exceptional photocatalytic hydrogen production capability. When the mass ratio of the Ni–P alloy to TiO2 is 12 wt. %, the hydrogen evolution rate reaches its maximum value at 1654.2 μmol g−1 h−1. Furthermore, density functional theory calculations substantiate that the formation of an internal electric field between the Ni–P alloy and TiO2 facilitates electron migration and carrier separation. This investigation provides a promising strategy for constructing TiO2-based Schottky heterojunctions to improve the photocatalytic hydrogen evolution performance.

MXene‐Enhanced Metal–Organic Framework‐Derived CoP Nanocomposites as Highly Efficient Trifunctional Electrocatalysts for OER, HER, and ORR

Developing robust active electrocatalysts from readily available earth‐abundant elements for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR) remains an unresolved challenge. Herein, Ti3C2Tx MXene‐containing metal–organic framework‐derived CoP nanocomposite electrocatalysts are successfully prepared by phosphidation of in situ‐produced ZIF‐67/MXene composite precursor at various heat treatment temperatures. The obtained nanocomposite catalysts are characterized by X‐ray diffraction, Brunauer–Emmett–Teller, X‐ray photoelectron spectroscopy, field emission‐scanning electron microscope/energy dispersive X‐ray spectroscopy (EDS), and high‐resolution transmission electron microscopy/EDS. In the produced composites, Ti3C2Tx MXene functions as a supportive substrate to facilitate mass transfer, as well as ion transport, and to improve electrical conductivity. Moreover, the introduction of MXene into the heterostructured CoP@C/Ti3C2Tx enables it to expose and provide extra active sites for electrochemical reactions. The as‐prepared CoP@C/MXene‐360 (abbreviated as CPMX‐360) nanocomposite is a promising trifunctional electrocatalyst toward OER, HER, and ORR. CPMX‐360 exhibits excellent electrocatalytic activity with an overpotential of 235 mV at 10 mA cm−2 in OER, an overpotential of 220 mV at −10 mA cm−2 in HER, and an Eonset and E1/2 of 0.82 and 0.74 V in ORR, respectively. This research provides a viable method to develop nonprecious trifunctional electrocatalyst via phosphidation of metal–organic framework and MXene with excellent performance for OER, HER, and ORR.

Cr-doped NiFe sulfides nanoplate array: Highly efficient and robust bifunctional electrocatalyst for the overall water splitting and seawater electrolysis

To replace precious metals and reduce production costs for large-scale hydrogen production, developing stable, high-performance transition metal electrocatalysts that can be used in a wide range of environments is desirable yet challenging. Herein, a self-supported hybrid catalyst (NiFeCrSx/NF) with high electrocatalytic activity was designed and constructed using conductive nickel foam as a substrate via manipulation of the cation doping ratio of transition metal compounds. Due to the strong coupling synergy between the metal sulfides NiS2, Fe9S11, and Cr2S3, as well as their interaction with the conductive nickel foam (NF), the energy barrier for catalytic reactions is reduced, and the charge transfer rate is enhanced. This significantly improves the hydrogen evolution reaction (HER) performance of NiFeCrSx/NF, achieving a current density of 10 mA cm−2 with an overpotential of just 66 mV. Furthermore, doping with chromium generates different valence states of Cr during the catalytic process, which can synergize with the high-valent Fe and Ni, promoting the formation of oxygen vacancies and enriching the active sites for the oxygen evolution reaction (OER). Consequently, at a current density of 10 mA cm−2 in 1.0 M KOH, the overpotential for OER is only 223 mV for NiFeCrSx/NF. Additionally, the in situ grown of self-supporting nanoflower structure on NiFe-LDH not only provides a large catalytic surface area but also facilitates electrolyte penetration during the catalytic process, endowing NiFeCrSx/NF with high long-term stability. When used as a bifunctional catalyst for overall water splitting, the NiFeCrSx/NF||NiFeCrSx/NF electrolyzer requires only 1.29 V to deliver a current density of 10 mA cm−2. Simultaneously, Cr doping protects the Fe sites by maintaining stable valence states, ensuring high performance and stability of NiFeCrSx/NF, even when it is utilized for seawater splitting. This strategy offers novel concepts for creating catalysts based on non-precious metals that can be utilized in various application scenarios.

Noble Metal-Based Catalysts for Selective Oxidation of HMF to FDCA: Progress in Reaction Mechanism and Active Sites

5-hydroxymethylfurfural (HMF) is oxidized to 2,5-furandicarboxylic acid (FDCA), which serves as a sustainable alternative to the petrochemical derivative terephthalic acid as a polyester monomer. Currently, noble metal catalysts that combine high HMF conversion rates with FDCA selectivity have become one of the mainstream catalytic systems for HMF oxidation. This paper summarizes and discusses the research progress on HMF oxidation to FDCA over different noble metal-based catalysts by combining DFT theoretical calculations, introducing various reaction pathways and mechanisms of HMF oxidation. It also analyzes the characteristics and electronic properties of metal active sites, geometric effects, metal–support interactions, and confinement effects, discussing and revealing the roles and activation mechanisms of different metal active sites, the structure of catalysts, active substances, metal valence states, activity, and the relationship between metal and the oxidation of C=O and OH groups. Finally, it presents views on the challenges and future development in the design of noble metal-based catalysts.

Constructing artificial photosynthetic system based on graphdiyne double heterojunction to enhance REDOX capacity and hydrogen evolution efficiency

Although traditional type II heterojunction designs for artificial photosynthesis show promise for photocatalytic hydrogen production, their redox capacity is somewhat limited due to the spatial separation of hydrogen evolution and oxidation reactions at less favorable sites. To overcome this limitation, ohmic junctions based on type II heterojunctions have been designed to enhance hydrogen evolution by transferring electrons to the metal component. In this study, a copper powder graphdiyne (Cu-GDY) composite catalyst with ohmic angle contact was synthesized by coupling copper foil with hexa-hexylbenzene. Incorporating Cu-GDY into CoGdO3 results in an interleaved band structure forming a type II heterojunction at the contact interface. This configuration overcomes the issue of the unfavorable conduction band position of CoGdO3, thereby promoting charge transfer. The internal electric field created by the Fermi level difference between Cu-GDY and CoGdO3, increase in REDOX capacity is the main reason for the increase of carrier separation rate. In addition, the plasmonic properties of copper expand the active reaction sites and promote the hydrogen evolution reaction. The composite catalyst exhibits b a hydrogen production rate that is 10.5 times higher than that of the individual catalysts. This work demonstrates that the formation of two distinct contact interfaces between Cu-GDY and CoGdO3 significantly improves the electron transfer and hydrogen evolution performance.

Calcination Temperature Effects on Ni/ZrO2 Catalysts for Dry Reforming of Methane

In this study, calcination temperatures (550, 650, and 750 °C) are utilized to analyze theefficiency of Ni-based catalyst for dry reforming of methane (DRM), a potential technique forreduction in greenhouse gases and synthesis of syngas. Ni catalysts were obtained from theimpregnation of 10 wt.% Ni onto ZrO2 prepared in the laboratory. A study of the synthesizedcatalysts was carried out using characterization techniques such as N2 physisorption, XRD,FTIR, and SEM. This analysis showed that calcination temperature affects the catalytic activityof the material investigated in the study. For those catalysts showing initially fairly highconversion of methane (more than 50 %), an increase in calcination temperature resulted in alower conversion of methane. It is believed that Ni nanoparticles sinter at higher temperatures resulting in decreased active surface area of the catalyst which in turn minimizes the number of active sites for the DRM reaction. On the other hand, for the catalysts with lower initial activity below 40 %, the effect of calcination temperature to the catalyst activity was not highly significant. This could be because the Ni particles in these catalysts are larger, or else the metalsupport bonds are not so strong that the catalysts cannot resist sintering at high temperatures. From the tested catalysts, NZS-10 has shown the highest performance with the average conversion of CH4 and CO2 at 60.5% and 62% respectively, and the lowest deactivation rate of 5%. This superior performance can be attributed to a combination of factors, including high surface area, optimal Ni particle size, strong metal-support interactions, resistance to sintering, and a well-developed porous structure. Fine-tuning certain characteristics of the NZS-10 catalyst can make the catalyst more efficient and have longer stability.

Lewis and Brønsted Acids Synergy in Photocatalytic Aerobic Alcohol Oxidations.

Photocatalytic chemical transformations for green organic synthesis has attracted much interest. However, their development is greatly hampered by the lack of sufficient reactive sites on the photocatalyst surface for the adsorption and activation of substrate molecules. Herein, we demonstrate that the introduction of well-defined Lewis and Brønsted acid sites coexisting on the surface of TiO2 (SO42-/N-TiO2) creates abundant active adsorption sites for photoredox reactions. The electron-deficient Lewis acid sites supply coordinatively unsaturated surface sites to adsorb molecular oxygen, and the Brønsted acid sites are liable to donate protons to form hydrogen bonds with the OH groups of alcohols like benzyl alcohol (BA). These coexistent acid sites result in a strong synergistic effect in photocatalytic aerobic oxidation of BA. For example, the conversion of BA to benzaldehyde was found to be 88.6%, being much higher than those of pristine TiO2 (14.7%), N-doped TiO2 (N-TiO2, 24.6%), sulfated TiO2 (SO42-/ TiO2, 35.4%), and even their sum. The apparent quantum efficiency (AQE) was determined to be 58.1% at 365 nm and 12.9% at 420 nm over SO42-/N-TiO2. This strategy to create effective synergistic Lewis and Brønsted acids on the catalyst surfaces enables us to apply it to other semiconducting photocatalytic organic transformations.

Catalytic Performance of B-Site Doped LST Modified NiO/YSZ Cathodes for CO2 Reduction in a Solid Oxide Electrolyzer

Abstract The NiO/YSZ modified with B-site doped lanthanum strontium titanate (LST) was investigated as cathode materials for the reduction of CO2 in a solid oxide electrolysis cell (SOEC). The electrocatalytic activity evaluated in CO2/H2 under solid oxide fuel cell and SOEC conditions both demonstrated that the cobalt-doped LST (LSTC) performs better than pristine NiO/YSZ and is the best among the doped LSTs. The high performance of the LSTC-modified cathode was ascribed to its good CO2 reduction ability, as evidenced by infrared and temperature-programmed surface reaction studies. Furthermore, LSTC was believed to play a role not only in serving active sites for the CO2 reaction, but also in relieving stress induced by Ni oxidation, thus stabilizing the cathode structure. Direct electrolysis in the absence of H2 further confirmed that the LSTC modified cell exhibits better performance. On the contrary, the other LST-modified cells and a CaO-modified one suffered from severe electrode polarization. These results present the potential to construct a cell combining B-site doped LST oxides with Ni cermet in a SOEC for energy conversion.

Concentrated Solar-Driven Catalytic CO2 Reduction: From Fundamental Research to Practical Applications.

Concentrated solar-driven CO2 reduction is a breakthrough approach to combat climate crisis. Harnessing the in-situ coupling of high photon flux density and high thermal energy flow initiates multiple energy conversion pathways, such as photothermal, photoelectric, and thermoelectric processes, thereby enhancing the efficient activation of CO2. This review systematically presents the fundamental principles of concentrated solar systems, the design and classification of solar-concentrating devices, and industrial application case studies. Meanwhile, key technological advances-from theoretical foundations to practical applications-are also discussed. At the microscopic level, a comprehensive analysis of multiscale reaction kinetics within the domain of photothermal synergistic catalysis has been conducted. This analysis elucidates the significance of catalyst design, further detailing the intricate regulatory mechanisms governing reaction pathways and active sites through nanostructured catalysts, single-atom catalysts, and metal-support interactions. However, the transition from laboratory research to industrial-scale application still faces challenges, including the complexity of system integration, energy density optimization, and economic feasibility. This review provides a theoretical framework and practical guidance through a complete investigation of current technological bottlenecks and future development directions, with the aim of driving key advances in concentrated solar-driven CO2 reduction catalysis.

Photogenerated charge carrier dynamics on Pt-loaded SrTiO3 nanoparticles studied via transient-absorption spectroscopy.

Loading cocatalysts on semiconductor-based photocatalysts to create active reaction sites is a preferable method to enhance photocatalytic activity and a widely adopted strategy to achieve effective photocatalytic applications. Although theoretical calculations suggest that the broad density of states of noble metal cocatalysts, such as Pt, act as a recombination center, this has never been experimentally demonstrated. Herein, we employed pico-nano and nano-micro second transient absorption spectroscopy to investigate the often overlooked photogenerated holes, instead of the widely studied electrons on Pt- and Ni-loaded SrTiO3 to evaluate the effects of cocatalysts as a recombination center. It is demonstrated that Pt serves as the recombination center with no sacrificial agent; recombination can be suppressed by a hole scavenger, while recombination is not significant on Ni with localized density of states. It is also found that photo-generated holes in SrTiO3 tend to migrate to Pt within 400 ps, and photo-generated holes generated in the bulk gradually migrate to Pt cocatalysts in a micro-second regime.

Electron Push-Pull Effect of Benzotrithiophene-Based Covalent Organic Frameworks on the Photocatalytic Degradation of Pharmaceuticals and Personal Care Products.

A covalent organic framework (COF) has emerged as a promising photocatalyst for the removal of pharmaceutical and personal care product (PPCP) contaminants; however, high-performance COF photocatalysts are still scarce. In this study, three COF photocatalysts were successfully synthesized by the condensation of benzo[1,2-b:3,4-b':5,6-b'']trithiophene-2,5,8-tricarbaldehyde (BTT) with 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (TAPT), 1,3,5-Tris(4-aminophenyl)benzene (TAPB), and 4,4',4''-nitrilotris(benzenamine) (TAPA), namely, BTT-TAPA, BTT-TAPB, and BTT-TAPT, respectively. The surface areas of BTT-TAPA, BTT-TAPB, and BTT-TAPT were found to be 800.46, 1203.60, and 1413.58 cm2∙g-1, respectively, providing abundant active sites for photocatalytic reactions. Under visible-light irradiation, BTT-TAPT exhibited the highest removal rate of tetracycline (TC), reaching 82.7% after 240 min. The superior photocatalytic performance of BTT-TAPT was attributed to its large specific surface area and the strong electron-acceptor properties of the triazine group. Electron paramagnetic resonance capture experiments and liquid chromatograph mass spectrometer analysis confirmed that superoxide radicals played a pivotal role in the degradation of TC and ciprofloxacin. Moreover, BTT-TAPT exhibited high stability and reproducibility during the photocatalytic degradation process. This study confirms that BTT-based COFs are a class of promising photocatalysts for the degradation of PPCPs in water, and their performance can be further optimized by tuning the structure and composition of the frameworks.

V‐/O‐Doping to Endow Ag2S‐based Bimetal Oxysulfide with Sulfur Vacancies and Heterovalent States for Rapid Reduction of Organic and Cr(VI) Pollutants in the Dark

AbstractA novel AgVOS oxysulfide catalyst for rapid catalytic reduction of toxic organic substances and Cr(VI) under dark is synthesized by a facile method. With the V/O co‐doping, the doped Ag2S catalyst has the effectively regulated electron transfer performance, the hydrazine‐driven V5+‐to‐V4+ reduction to disturb charge equilibrium, and the formed sulfur vacancy balanced by oxygen doping to maintain charge equilibrium. The formed sulfur vacancy acts as the active site for electrophilic nucleophilic reaction, while the orbital hybridization of O2p and S3p stabilizes the valence state of S2−. A suitable ratio of n(V4+/V5+) is regulated during the hydrazine‐driven synthesis to facilitate the electron transfer and enhance the V5+‐to‐V4+ reduction reaction. V/O co‐doped AgVOS‐3 prepared by a suitable hydrazine content exhibits super catalytic reduction performance of organic 4‐NP (4‐nitrophenol), MB (methyl blue), MO (methyl orange), and RhB (Rhodamine B, 20 ppm, 100 mL) dyes, which are completely reduced within 8, 8, 10, and 8 min, respectively. In comparison, Cr6+ (50 ppm, 100 mL) is also completely reduced within 6 min by AgVOS‐3, indicating its good catalytic reduction activity for organic and inorganic mixture pollutants. Furthermore, AgVOS‐3 has good stability after cyclic tests to maintain a reduction efficiency of 96.5%. Therefore, the AgVOS catalyst shows a promising application for industrial wastewater treatment.

Decoding Dual-Functionality in N-doped Defective Carbon: Unveiling Active Sites for Bifunctional Oxygen Electrocatalysis.

Oxygen electrocatalysis plays a pivotal role in energy conversion and storage technologies. The precise identification of active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for developing an efficient bifunctional electrocatalyst. However, this remains a challenging endeavor. Here, it is demonstrated that metal-free N-doped defective carbon material derived from triazene derivative exhibits excellent bifunctional activity, achieving a notable ΔE value of 0.72V. Through comprehensive X-ray photoelectron spectroscopy and Raman spectroscopic analyses, the active sites responsible for oxygen electrocatalysis are elucidated, resolving a long-standing issue. Specifically, pyridinic-N sites are crucial for ORR, while graphitic-N are good for OER. A predictive model utilizing π-electron descriptors further aids in identifying these sites, with theoretical insights aligning with experimental results. Additionally, insitu ATR-FTIR spectroscopy provides clarity on reaction intermediates for both reactions. This research paves the way for developing metal-free, site-specific electrocatalysts for practical applications in energy technologies.

Nitrogen doping turns carbonaceous materials into fast-reacting catalysts for reductive dechlorination.

Nitrogen (N) doping of biomass prior pyrolysis has been identified as an effective approach for enhancing biochar catalytic reactivity. However, high-temperature pyrolysis of N-rich biomass may produce N-devoid biochars with high reactivity, calling for attention to the true causes of the reactivity increases and the role of nitrogen. In this study, N-doped wheat straw biochar (N-BC) materials were produced using urea as N dopant and different pyrolysis conditions, and their catalytic reactivity assessed for the reduction of trichloroethylene (TCE) by green rust (GR), a layered Fe(II)Fe(III) hydroxide. Overall, the extent and rate of TCE reduction increased from ∼8 to ∼90 % and 0.064 to 0.299 h-1, respectively, with increasing urea dosage from 0 to 25 wt%. A similar increase in catalytic activity was also seen with an increase in pyrolysis temperature during N-doping, from 600 to 800 or 1000 oC, while increasing pyrolysis duration had a lower impact. Principal component analysis and Pearson correlation analysis demonstrated some correlation between TCE catalytic reactivity and structural properties of N-BC materials. However, little correlation was seen between catalytic reactivity, and N content and N surface functional groups of N-BC materials; even though N surface functional groups are often described as the key redox active sites in these dechlorination reactions, and also the reason why N-doping is applied. For comparison, N-doping and TCE catalytic reactivity with GR was also performed with a highly conductive graphene (GP) substrate. N-doping of GP led to a similar increase in the rate and extent of TCE as was observed for N-BC, demonstrating the importance of N-doping to create catalytically active sites in these carbonaceous materials. Surprisingly, highly reactive N-GP materials produced at 800 and 1000 °C exhibited no N surface functional groups but instead, N-doping created structural defect sites. Overall, this study demonstrates that N-doping of the bio-substrate may increase catalysis of reductive dechlorination by a factor of ∼5 times but this is not due to the formation of catalytically active N-functional groups, rather we attribute it to changes of the carbonaceous material structure. With this understanding we can then embark on the production of catalytic active biochar materials also from other substrates than wheat straw, forming the basis for optimizing other reductive contaminant degradation systems.

Bimetallic nanoparticles: advances in fundamental investigations and catalytic applications

Bimetallic nanoparticles provide promising active sites for many reactions, and such materials can be synthesized with different spatial distributions, such as disordered alloys, core–shell structures, and Janus-type heterogeneous structures.