Four-electron Pathway Research Articles

Two-Dimensional Covalent Organic Frameworks with Carbazole-Embedded Frameworks Facilitate Photocatalytic and Electrocatalytic Processes

Catalytic technologies are pivotal in enhancing energy efficiency, promoting clean energy production, and reducing energy consumption in the chemical industry. The pursuit of novel catalysts for renewable energy is a long-term goal for researchers. In this work, we synthesized three two-dimensional covalent organic frameworks (COFs) featuring electron-rich carbazole-based architectures and evaluated their catalytic performance in photocatalytic organic reactions and electrocatalytic oxygen reduction reactions (ORRs). Pyrene-functionalized COF, termed as FCTD-TAPy, demonstrated excellent photocatalytic performance for amino oxidation coupling and showed a remarkable preference for substrates with electron-withdrawing groups (up to >99% Conv. and >99% Sel). Furthermore, FCTD-TAPy favored a four-electron transfer pathway during the ORR and exhibited favorable reaction kinetics (51.07 mV/dec) and a high turnover frequency (0.011 s−1). In contrast, the ORR of benzothiadiazole-based FCTD-TABT favored a two-electron transfer pathway, which exhibited a maximum double-layer capacitance of 14.26 mF cm−2, a Tafel slope of 53.01 mV/dec, and a hydrogen peroxide generation rate of 70.3 mmol g−1 h−1. This work underscores the potential of carbazole-based COFs as advanced catalytic materials and offers new insights into the design of metal-free COFs for enhanced catalytic performance.

The Construction of Face-to-Face Combination between NiFe-layered Double Hydroxide Nanosheets and Monolayer rGO for Efficient Water Splitting and Oxygen Reduction.

Developing cost-effective and efficient electrocatalysts is essential for advancing a green energy future. Herein, a NiFe-layered double hydroxide loaded on reduced graphene oxide (NiFe-LDHs@rGO) hybrid was synthesized using a straightforward three-step process involving exfoliation tearing, electrostatic self-assembly, and chemical reduction. The face-to-face packing and ultrathin exfoliation enable strong heterogeneous interactions, fully harnessing the potential of these complementary two-dimensional counterparts. Consequently, the resultant catalyst displays outstanding oxygen evolution reaction (OER) catalytic activity and stability, whose overpotential is as low as 241 mV at 30 mA cm-2 and 255 mV at 50 mA cm-2 with a low Tafel slope of 62.1 mV dec-1. Both the experimental results and density functional theory (DFT) calculations reveal that the face-to-face assembly strengthens the electronic interactions between NiFe-LDHs and rGO, which effectively modulates the d-band center of Ni and Fesites and improves the reaction kinetics for OER. Moreover, the resultant NiFe-LDHs@rGO hybrids exhibit excellent multifunctional catalytic performance. Its hydrogen evolution reaction (HER) activity is endowed by Fe-site of NiFe-LDHs and defect states rGO and achieves a low voltage of 1.68 V to drive a current density of 10 mA cm-2 for overall water splitting. The face-to-face heteroassembly also imparts NiFe-LDHs@rGO with superior oxygen reduction reaction (ORR) activity, with a half-wave potential of 0.70 V and a limiting current density of 4.2 mA cm-2. Its ORR primarily follows a four-electron transfer pathway with a minor contribution from a two-electron process. This study establishes the groundwork for optimizing two-dimensional heterogeneous interfaces in LDH@carbon-based materials for advanced energy conversion.

Cobalt Molybdenum Telluride as an Efficient Trifunctional Electrocatalyst for Seawater Splitting

A mixed-metal ternary chalcogenide, cobalt molybdenum telluride (CMT), has been identified as an efficient tri-functional electrocatalyst for seawater splitting, leading to enhanced oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR). The CMT was synthesized by a single step hydrothermal technique. Detailed electrochemical studies of the CMT-modified electrodes showed that CMT has a promising performance for OER in the simulated seawater solutions, exhibiting a small overpotential of 385 mV at 20 mA cm−2, and superior catalyst durability for prolonged period of continuous oxygen evolution. Interestingly, while gas chromatography analysis confirmed the evolution of oxygen in an anodic chamber, it showed that there was no chlorine evolution from these electrodes in alkaline seawater, highlighting the novelty of this catalyst. CMT also displayed remarkable ORR activity in simulated seawater as indicated by its four-electron reduction pathway forming water as the dominant product. One of the primary challenges of seawater splitting is chlorine evolution from the oxidation of dissolved chloride salts. The CMT catalyst successfully and significantly lowers the water oxidation potential, thereby separating the chloride and water oxidation potentials by a larger margin. These results suggest that CMT can function as a highly active tri-functional electrocatalyst with significant stability, making it suitable for clean energy generation and environmental applications using seawater.

Indium oxide layer dual functional modified bismuth vanadate photoanode promotes photoelectrochemical oxidation of water to hydrogen peroxide.

The photoelectrochemical (PEC) dual-electron pathway for water oxidation to produce hydrogen peroxide (H2O2) shows promising prospects. However, the dominance of the four-electron pathway leading to O2 evolution competes with this reaction, severely limiting the efficiency of H2O2 production. Here, we report a In2O3 passivator-coated BiVO4 (BVO) photoanode, which effectively enhances the selectivity and yield of H2O2 production via PEC water oxidation. Based on XPS spectra and DFT calculations, a heterojunction is formed between In2O3 and BVO, promoting the effective separation of interface and surface charges. More importantly, Mott-Schottky analysis and open-circuit potential measurements demonstrate that the In2O3 passivation layer on the BVO photoanode shifts the hole quasi-Fermi level towards the anodic direction, enhancing the oxidation level of holes. Additionally, the widening of the depletion layer and the flattening of the band bending on the In2O3-coated BVO photoanode favor the generation of H2O2 while suppressing the competitive O2 evolution reaction. In addition, the coating of In2O3 can also inhibit the decomposition of H2O2 and improve the stability of the photoanode. This work provides new perspectives on regulating PEC two/four-electron transfer for selective H2O2 production via water oxidation.

Enhanced electron transfer kinetics via constructing co-catalytic system of cerium oxide and carbon dots enabling efficient electrosynthesis of hydrogen peroxide in neutral media

The sluggish kinetics coupled with the competition of four-electron pathway in neutral media diminishes the production efficiency of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e− ORR). To address this dilemma, this contribution proposes one electron modulation strategy to expedite the charge transfer capability by integrating carbon dots with CeO2 (CDs/CeO2) for the efficient neutral electrosynthesis of H2O2. It was found that the integration could effectively bolster both the activity and selectivity of 2e− ORR on CDs and CeO2. Remarkably, the highest 2e− selectivity could reach up to 92 % for the optimized CDs/CeO2, substantially surpassing that (77 %) of pristine CeO2, together with about 1.5 times enhancement of activity. Meanwhile, it also delivered a superior long durability at 20 mA cm−2 for 24 h and a high Faraday efficiency of 97 %. Further in-situ transient potential scanning (TPS) technique revealed that the pseudo-capacitance and charge storage capacity of CeO2 were significantly tuned by CDs during dynamic ORR process, being conducive to the reaction kinetics and the 2e− selectivity. The findings in this work not only extends the co-catalytic system based on CDs and rare earth materials for 2e− ORR, but also offers novel insights into correlation between their electron distribution dynamics and 2e− ORR performance.

Spartina alterniflora-Derived Carbons for High-Performance Oxygen Reduction Reaction (ORR) Catalysts

Being an alien species, Spartina alterniflora has occupied the living space of native animals and plants, causing irreversible damage to the environment. Converting Spartina alterniflora into carbon or its derivatives offers a valuable solution to manage both invasive biomass and an energy shortage. Herein, through a simple activation process, we successfully prepared Spartina alterniflora-derived carbon (SAC) and its N-doped derivative SANC, and used them as metal-free catalysts for an oxygen reduction reaction (ORR). SAC exhibits good electrochemical performance and holds significant potential in catalysis. After N-doping by melamine as a nitrogen source, electronegativity is redistributed in SANC, leading to enhanced performance (a half-wave potential of 0.716 V vs. RHE, and a four-electron transfer pathway with a H2O2 yield of only 2.05%). This work presents a straightforward and cost-effective approach to the usage of obsolete invasive biomass and shows great potential in energy generation.

Exploring the catalytic characteristics of binuclear bimetallic FeM sites (M = Co, Ni, Pt) on nitrogen-doped graphene through density functional theory and ab initio molecular dynamics

Certain supported bimetallic catalysts exhibit high efficiency in both oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). However, the catalytic mechanism of double-atom catalysts and how different-atom active sites affect charge transfer efficiency have not been fully revealed. In this work, we provide density functional theory (DFT) simulations of ORR/OER on FeM-NC (M = Co, Ni, Pt) supported on nitrogen-doped graphene. The stability of structures, electrical properties, adsorption energies of intermediates, and catalytic activity of ORR/OER on FeM-NC have been investigated. The results indicate that the Fe-atom in stable FeM-NC structures is a catalytically active site and that the FeM-NC-1 structures may be more appropriate as catalysts. The overpotentials for ORR/OER on FeM-NC-1 (M = Co, Ni, Pt) are 0.42/0.29 V on FeCo-NC-1, 0.57/0.33 V on FeNi-NC-1, and 0.64/0.33 V on FePt-NC-1, which is significantly lower than those on Pt(111) surfaces. Ab initio molecular dynamics (AIMD) simulations suggest that ORR/OER may occur vis a typical four-electron mechanism on FeNi-NC-1 and FePt-NC-1 configurations, while on FeCo-NC-1 structures, it may involve two different four-electron pathways. This study increases our knowledge of the structural stability of FeM-NC-1 structures as bifunctional catalysts and the ORR/OER pathway in acidic solution, and it also shows that three FeM-NC-1 structures are suitable candidate catalysts for ORR/OER.

Exploring the Kinetics of Oxygen Reduction Reaction in Relation to Pitting Corrosion Resistance in Fe-Cr Alloys

Pitting corrosion, a major concern in materials science and engineering, threatens critical metallic structures and components. Its implications reach across daily life and industries such as energy, transportation, and infrastructure, potentially causing environmental harm, economic losses, and even loss of life. This complex process is influenced by factors including material composition, local environment, and mechanical stresses.1 Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film.2 In Fe-Cr alloys, the ORR occurs on this film, undergoing a mixed diffusion and kinetic-controlled process. The number of electrons involved and the corrosion rate are determined by the thermodynamically stable state of the passive film.This research studies the ORR kinetics on FeCr alloys fabricated by arc-melting, using both computational and experimental methods. The rotating disc electrode technique was employed across various Fe:Cr alloys in alkaline and neutral electrolytes. The Koutecky-Levich analysis showed a dominant four-electron ORR pathway in all tested Fe-Cr alloys, with the ORR significantly inhibited by higher proportions of Cr2O3 in the film, suggesting a correlation with high chromium content. Experimental ORR overpotentials, when combined with theoretical potential-pH (Pourbaix) diagrams, helped discern the likely characteristics of the passive films on the alloys. It was deduced that the catalytic properties of potential passive films increased in the order Cr2O3 < Fe3O4 < Fe2O3 < FeCr2O4. These findings, excellently aligned with density functional theory (DFT) modelling, underscore the role of increased chromium levels in slowing pitting progression by suppressing the ORR.In summary, this research offers distinctive insights into the correlation between the kinetics of the ORR and the resistance to localized corrosion in Fe-Cr alloys, which enhances our understanding of the underlying mechanisms of pitting corrosion. Keywords FeCr alloy, pitting corrosion, ORR, rotating disc electrode, DFT Reference [1] B. Zhang, J. Wang, B. Wu, X. W. Guo, Y. J. Wang, D. Chen, Y. C. Zhang, K. Du, E. E. Oguzie, and X. L. Ma, Nat. Commun. (2018) 9, 2559.[2] G. T. Burstein, P. C. Pistorius, and S. P. Mattin, Corros. Sci. (1993) 35, 57.

Impact of Exposed Crystal Facets on Oxygen Reduction Reaction Activity in Zeolitic Imidazole Frameworks

Oxygen reduction reactions (ORR) are critical reactions for efficient sustainable and renewable energy storage. However, the limitation of ORR is a slow kinetic reaction due to the multi-step transfer mechanism of electrons. Therefore, electrocatalysts with high ORR activity and stability are needed to overcome the reaction limitations. Zeolitic imidazole framework-67 (ZIF-67) has attracted attention in electrochemical applications due to its multiple redox-active sites and high stability in alkali conditions. The Co-doped porous carbon catalysts derived from ZIF-67 have the potential to be used as ORR catalysts with high performance, while pure phase ZIF-67 electrocatalyst for ORR is rarely studied. The work studies the importance of crystal facets on ORR reactivity. The results show that ZIF-67 nanocube exhibits excellent ORR activity with lower half wave-potential and faster kinetics process compared to its bulk structure. It is proposed that ZIF-67 nanocube provides improvement of selectivity for the four-electron pathway, which is a favorable process with higher reaction efficiency. The density functional theory (DFT) calculations suggest unsaturated Co2+ active sites with enriched (100) facets in the cubic crystal. Therefore, the fast diffusion of oxygen molecules to active sites and strong interaction with intermediate are observed in a cubic structure. The correspondence between experiment and calculation offers enhancement of ORR activity and selectivity from control-specific growth of (100) facet with cubic shape. The work introduces a new strategy for designing highly efficient ORR electrocatalysts with facet-controlled, allowing further study in other electrochemical reactions.

Single Atom Catalysts Based on Earth-Abundant Metals for Energy-Related Applications.

Anthropogenic activities related to population growth, economic development, technological advances, and changes in lifestyle and climate patterns result in a continuous increase in energy consumption. At the same time, the rare metal elements frequently deployed as catalysts in energy related processes are not only costly in view of their low natural abundance, but their availability is often further limited due to geopolitical reasons. Thus, electrochemical energy storage and conversion with earth-abundant metals, mainly in the form of single-atom catalysts (SACs), are highly relevant and timely technologies. In this review the application of earth-abundant SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or products with high energy content is discussed. The oxygen reduction reaction is also appraised, which is primarily harnessed in fuel cell technologies and metal-air batteries. The coordination, active sites, and mechanistic aspects of transition metal SACs are analyzed for two-electron and four-electron reaction pathways. Further, the electrochemical water splitting with SACs toward green hydrogen fuel is discussed in terms of not only hydrogen evolution reaction but also oxygen evolution reaction. Similarly, the production of ammonia as a clean fuel via electrocatalytic nitrogen reduction reaction is portrayed, highlighting the potential of earth-abundant single metal species.

Eco-friendly synthesis of bimetallic FeCo nanocatalysts within heteroatom-doped carbon for oxygen reduction and zinc-air battery enhancement

Structural engineering emerges as a pivotal approach in crafting cost-effective and highly efficient catalysts for oxygen reduction reaction (ORR), emphasizing large surface areas, abundant reactive sites, and enhanced porosity. The incorporation of trace non-precious metals can significantly boost ORR performance through structural refinement. Here, we report on the synthesis of bimetallic FeCo nanoparticles embedded within a heteroatoms-doped carbon framework utilizing eco-friendly chitosan. This configuration yields a catalyst with marked activity for ORR in alkaline conditions, attributable to synergistic effects among Fe, Co, N, and O dopants. Comparative analysis reveals the superior performance of the FeCo-NC variant, characterized by a higher degree of defects and disorders. The standout FeCo-NC800W sample, with its 347.616 m2/g surface area and pyrolysis-induced graphene coating exhibits optimal ORR activity, closely adhering to a four-electron transfer pathway. Moreover, this catalyst demonstrates remarkable longevity and methanol resistance in ORR applications. FeCo-NC800W surpasses the conventional 20% Pt/C + RuO2 cathode in peak power density in a zinc-air battery setup, highlighting its potential as a high-performance, sustainable electrocatalyst.

Novel fluorinated MIL-88B assisted hydrogen-bonded organic framework derived high efficiency oxygen reduction catalyst in microbial fuel cell

The crux to promote the utilization of air-cathode microbial fuel cell (AC-MFC) is to find high-efficiency and low-budget oxygen reduction reaction (ORR) catalysts, which can replace Pt-based catalysts, reduce electrode cost and thus improve the cost-effectiveness of AC-MFC. In this work, a three-dimensional network carbon structure F-MIL-HOF loaded with Fe2O3 material composites have been successfully synthesized by carbonizing by NH4F-fluorinated MIL-88B combined with a high nitrogen content hydrogen-bonded organic framework (HOF) to evince excellent catalytic property for ORR in both alkaline and neutral electrolytes. The Fe2O3 obtained after carbonization of MIL-88B portrays efficient ORR catalytic activity, and the combination with the natural pore-rich HOF precisely solves the problems of uncontrolled growth and agglomeration during Fe2O3 synthesis, achieving the high dispersion and full exposure of Fe2O3 nanoparticles as active sites. As-synthesized F-MIL-HOF as cathodic catalyst reaches a limiting current density of 6.40 mA cm−2 in alkaline condition, which exhibits an advantage performance over commercial Pt/C (6.26 mA cm−2). Furthermore, F-MIL-HOF shows approximately four-electron pathway with better methanol resistance and stability than Pt/C, and the performance only decreases by 10.2 % in the stability test, which still had efficient ORR catalytic performance. F-MIL-HOF is an emerging alternative electro-catalyst for AC-MFC.

Nitrogen-bridged Cu-Zn dual-atom cooperative interface sites for efficient oxygen reduction reaction in Zn-air battery

Developing nonprecious catalysts with excellent behaviors for oxygen reduction reaction (ORR) has assumed considerable importance, but remains an arduous issue. Herein, we demonstrate a Kirkendall effect-pyrolysis (KEP) strategy to construct N-bridged Cu-Zn dual-atom supported on hollow N-doped carbon (Cu-Zn DA/HNC) for ORR. The hollow structure of N-doped carbon facilitates mass transfer and exposes more actives. What’s more, the shared N atom between Cu and Zn atoms is beneficial to enhance their synergetic effect, creating an appropriately enhanced O* binding. The resulting Cu-Zn DA/HNC displays excellent ORR activity in an alkaline electrolyte, following a nearly four-electron pathway of ORR. Even employing Cu-Zn DA/HNC as the cathode in ZABs, Cu-Zn DA/HNC presents a long cycling life up to 910 h and robust low-temperature adaptability. The facile and straightforward fabrication plus the outstanding ORR performance of Cu-Zn DA/HNC endows its great potential as a significant candidate in practical applications of ZAB.

Transition Metal-Based Polyoxometalates for Oxygen Electrode Bifunctional Electrocatalysis

Polyoxometalates (POMs) with transition metals (Co, Cu, Fe, Mn, Ni) of Keggin structure and lamellar-stacked multi-layer morphology were synthesized. They were subsequently explored as bifunctional electrocatalysts for oxygen electrodes, i.e., oxygen reduction (ORR) and evolution (OER) reaction, for aqueous rechargeable metal-air batteries in alkaline media. The lowest Tafel slope (85 mV dec−1) value and the highest OER current density of 93.8 mA cm−2 were obtained for the Fe-POM electrocatalyst. Similar OER electrochemical catalytic activity was noticed for the Co-POM electrocatalyst. This behavior was confirmed by electrochemical impedance spectroscopy, where Fe-POM gave the lowest charge transfer resistance of 3.35 Ω, followed by Co-POM with Rct of 15.04 Ω, during the OER. Additionally, Tafel slope values of 85 and 109 mV dec−1 were calculated for Fe-POM and Co-POM, respectively, during the ORR. The ORR at Fe-POM proceeded by mixed two- and four-electron pathways, while ORR at Co-POM proceeded exclusively by the four-electron pathway. Finally, capacitance studies were conducted on the synthesized POMs.

Monolayer Ta2Se: A low-cost catalyst with enhanced stability and high basal plane activity for oxygen reduction reaction

The search for cost-effective two-dimensional (2D) electrocatalysts is accelerating as these materials emerge as pivotal alternatives to traditional energy technologies for fuel cells. In this work, we report a low-cost, high-performance Ta2Se monolayer as an electrocatalyst for the oxygen reduction reaction (ORR) through first-principles calculations. The Ta2Se monolayer exhibits notable stability and low cleavage energy, underscoring its practical potential for experimental synthesis. Our computations show that the Ta2Se monolayer has a metallic band structure with substantial electronic states at the Fermi level, which suggests the favorable electron transport properties. Remarkably, the outer Ta atoms in the basal plane of Ta2Se monolayer are identified as ORR active sites, exhibiting a competitive selection for dissociative and associative four-electron pathways alongside outstanding catalytic activity. Through examining the surface coverage impacts on ORR, we disclose that at a moderate oxygen coverage, the Ta2Se monolayer's limiting potential reaches approximately 0.9 eV, outstripping the conventional Pt electrodes, thus confirming its superior ORR catalytic capability. The low cost, active basal plane sites, and high ORR activity make the Ta2Se monolayer a competitive candidate for advanced fuel cell components.

Synergistic selenium doping and colloidal quantum dots decoration over ZnIn2S4 enabling high-efficiency photoelectrochemical hydrogen peroxide production

Photoelectrochemical (PEC) water splitting to value-added hydrogen peroxide (H2O2) production is more promising than the traditional O2 evolution. However, enabling efficient PEC H2O2 generation is still challenging due to competitive two-/four-electron water oxidation pathways. In this work, ZnIn2S4 (ZIS) photoanodes were engineered by Se doping and colloidal quantum dots (QDs) modification to boost the PEC H2O2 evolution efficiency. Morphology and elemental studies testify the successful Se doping in ZIS and the anchoring of QDs on ZIS-Se photoelectrodes. Photoinduced carrier kinetics investigation verifies the optimized band bending, suppressed charge recombination, and promoted charge transfer in as-prepared ZIS-Se and ZIS-Se/QDs photoanodes, exhibiting inhibited four-electron O2 evolution and facilitated two-electron H2O2 production during PEC water oxidation, as evidenced by the density functional theory (DFT) calculations. Accordingly, the Se-doped and QDs-decorated ZIS photoelectrodes demonstrate a gradually less upward band bending and improved photo-excited hole transfer to the surface, delivering a maximum H2O2 production rate of 1.32 μmol min−1 cm−2 with a Faraday efficiency of 86 % at 1.23 V versus reversible hydrogen electrode (RHE) under one sun illumination.

Graphsene as a novel porous two-dimensional carbon material for enhanced oxygen reduction electrocatalysis

Graphene allotropes with varied carbon configurations have attracted significant attention for their unique properties and chemical activities. This study introduces a novel two-dimensional carbon-based material, termed Graphsene (GrS), through theoretical study. Comprising tetra-, penta-, and dodeca-carbon rings, GrS’s cohesive energy calculations demonstrate its superior structural stability over existing graphene allotropes, including graphyne and graphdiyne families. Phonon dispersion analysis confirms GrS’s dynamic stability and its relatively low thermal conductivity. All calculated GrS elastic constants meet the Born criteria, ensuring mechanical stability. Ab-initio molecular dynamic simulations show GrS maintains its structure at 300 K. HSE06 calculations reveal a narrow electronic bandgap of 20 meV, with the electronic band structure featuring a highly anisotropic Dirac-like cone due to its intrinsic structural anisotropy along armchair and zigzag directions. Notably, GrS is predicted to offer exceptional catalytic performance for the oxygen reduction reaction, favoring the four-electron reduction pathway with high selectivity under both acidic and alkaline conditions. This discovery opens promising avenues for developing metal-free catalyst materials in clean energy production.

Metal-free N, B, F ternary-doped carbon electrocatalyst for boosting the oxygen reduction reaction and high-performance zinc–air battery

Developing efficient metal-free carbon-based electrocatalysts for the oxygen reduction reaction (ORR) is significant and challenging to reduce the cost of fuel cells and metal–air batteries for large-scale applications. Herein, a novel metal-free N, B, F ternary-doped carbon electrocatalyst (FBNCΔ(1:6)-950) exhibited an excellent ORR performance with half-wave potential of 0.858 V vs. reversible hydrogen electrode (RHE) via an almost exclusively four-electron transfer pathway in 0.1 M KOH, even better than the commercial Pt/C (20 %). Moreover, the FBNCΔ(1:6)-950-based zinc–air battery (ZAB) shown an excellent power density of 147 mW·cm−2 and long-term stability of 100 h. The FBNCΔ(1:6)-950 was constructed via pyrolyzing zeolite imidazole framework (ZIF-8) precursor containing BF4– at 950 °C under N2 to volatilize the Zn. According to the structural characterization and theoretical calculations, B and F from BF4– not only increased the number of active sites of pyridine-N by etching intact carbon matrix, but also co-modified part of pyridine-N to further optimize the electronic structure and reduce the adsorption energy of *OH, both of which together result in the excellent performance of FBNCΔ(1:6)-950. This work provides a fresh perspective on the advancement of highly active metal-free carbon-based electrocatalysts for the ORR and ZAB.

Encapsulated cementite enhances catalytic performance of carbon nanotubes for oxygen reduction reaction

Nonprecious-metal-based materials show great potential to be highly efficient catalysts for oxygen reduction reaction (ORR). There is still room for improvement in the performances of nonprecious-metal-based catalysts for ORR. In this paper, we investigated the catalytic performances of N-doped carbon nanotubes (CNTs) with encapsulated cementite (Fe3C@CNT) for ORR. The encapsulation structure was confirmed by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses. The catalytic performances of Fe3C@CNT for ORR were investigated by cyclic voltammetry, linear sweep voltammetry, Tafel analysis, rotating disk electrode, and rotating ring-disk electrode tests. The results showed that both the onset potential and half-wave potential of Fe3C@CNT-catalyzed ORR were 60 mV higher than those of 20 wt% Pt/C catalyst. Fe3C@CNT catalyzed ORR mainly happened through a four-electron pathway. The long-time running stability of the Fe3C@CNT was also superior to that of the 20 wt% Pt/C catalyst. The eutectic layers between the CNTs and cementite enhanced the electron transfer from the inner-layer CNT to the surface-layer N-doped CNT. Calculations revealed that the iron and carbon in the cementite were in positive and negative electronic states, respectively. The encapsulated cementite promoted the formation of equipotential circles on the surface-layer CNT, which greatly enhanced the catalytic performance of the Fe3C@CNT for ORR. N-doped CNTs with encapsulated cementite show great potential to be high-performance catalysts for ORR.

First-principles study on the electronic properties and feasibility of photocatalytic water splitting on Z-scheme GaN/MoS2 heterostructure

In recent years, van der Waals heterostructures have played a significant role in fields such as photocatalysis, quantum devices, sensors, etc., due to their excellent performance exhibited through synergistic interactions between multiple components and the highly customizable design. Two-dimensional transition metal dichalcogenides, with their highly tunable band structures and excellent electrochemical activity, are well-suited for constructing heterostructures. To investigate the specific electronic and photocatalysis properties of relative heterostructure, GaN/MoS2 heterostructure is constructed. Through the first-principles calculation, the Z-scheme GaN/MoS2 heterostructure shows a direct band gap of 0.869 eV. The excellent capability for separating the photogenerated carriers can be inferred from the conduction band offset as high as 1.915 eV and electrostatic potentials Ep of 6.361 eV. At pH = 14, oxygen evolution reaction can spontaneously occur under the photocatalytic action of the GaN/MoS2 heterostructure according to the negative Gibbs differences of −0.514 eV, −3.809 eV, −2.576 eV and −5.718 eV in the four-electron pathways. Therefore, the Z-scheme GaN/MoS2 heterostructure has great prospects in the application of optoelectronic devices and photocatalysis.