Pyridine Functionalized Carbon Nanotubes: Unveiling the Role of External Pyridinic Nitrogen Sites for Oxygen Reduction Reaction

Engineering Localized Alkalinity and Oxygen Enrichment for Efficient Acidic O2-to-H2O2 Electroreduction via Carbon-Based Triphase Interfaces

The sustainable production of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e⁻ ORR) on carbon-based catalysts offers a compelling alternative to the energy-intensive anthraquinone process. However, the slow kinetics of the 2e⁻ ORR in acidic media limits its efficiency. Herein, a novel strategy is introduced to overcome this limitation by engineering a needle-shaped hydrophobic carbon felt embedded with hard carbon as a natural air diffusion electrode (ADE). In situ and ex situ characterization show this design creates an oxygen-enriched, locally alkaline microenvironment at the triphase interface, which accelerates 2e⁻ ORR kinetics by confining oxygen enrichment within the hard carbon layer. Quantitatively, this oxygen-enriched hydrothermal carbon electrocatalyst achieves a remarkable H2O2 selectivity of 95.47% at near-zero overpotential and a high production rate of 487.82 mg L-1 h-1 at 200 mA cm-2. Furthermore, density functional theory calculations reveal that the carboxyl and ether functional groups in hydrothermal hard carbon optimize O2 * and OOH* adsorption, promoting the desired 2e⁻ pathway. Importantly, this ADE design not only exhibits exceptional performance and long-term stability but also demonstrates a significantly reduced global warming potential compared to conventional methods, highlighting its potential to revolutionize industrial-scale H2O2 electrosynthesis by replacing commercial carbon black-based cathodes.

Enhancing Oxygen Reduction Reaction of Single-Atom Catalysts by Structure Tuning

Deciphering the fine structure has always been a crucial approach to unlocking the distinct advantages of high activity, selectivity, and stability in single-atom catalysts (SACs). However, the complex system and unclear catalytic mechanism have obscured the significance of exploring the fine structure. Therefore, we endeavored to develop a three-component strategy to enhance oxygen reduction reaction (ORR), delving deep into the profound implications of the fine structure, focusing on central atoms, coordinating atoms, and environmental atoms. Firstly, the mechanism by which the chemical state and element type of central atoms influence catalytic performance is discussed. Secondly, the significance of coordinating atoms in SACs is analyzed, considering both the number and type. Lastly, the impact of environmental atoms in SACs is reviewed, encompassing existence state and atomic structure. Thorough analysis and summarization of how the fine structure of SACs influences the ORR have the potential to offer valuable insights for the accurate design and construction of SACs.

Ar/NH3 Plasma Etching of Cobalt-Nickel Selenide Microspheres Rich in Selenium Vacancies Wrapped with Nitrogen Doped Carbon Nanotubes as Highly Efficient Air Cathode Catalysts for Zinc-Air Batteries

This work utilizes defect engineering, heterostructure, pyridine N-doping, and carbon supporting to enhance cobalt-nickel selenide microspheres' performance in the oxygen electrode reaction. Specifically, microspheres mainly composed of CoNiSe2 and Co9Se8 heterojunction rich in selenium vacancies (VSe·) wrapped with nitrogen-doped carbon nanotubes (p-CoNiSe/NCNT@CC) are prepared by Ar/NH3 radio frequency plasma etching technique. The synthesized p-CoNiSe/NCNT@CC shows high oxygen reduction reaction (ORR) performance (half-wave potential (E1/2) = 0.878 V and limiting current density (JL) = 21.88 mA cm-2). The JL exceeds the 20 wt% Pt/C (19.34 mA cm-2) and the E1/2 is close to the 20 wt% Pt/C (0.881 V). It also possesses excellent oxygen evolution reaction (OER) performance (overpotential of 324 mV@10 mA cm-2), which even exceeds that of the commercial RuO2 (427 mV@10 mA cm-2). The density functional theory calculation indicates that the enhancement of ORR performance is attributed to the synergistic effect of plasma-induced VSe· and the CoNiSe2-Co9Se8 heterojunction. The p-CoNiSe/NCNT@CC electrode assembled Zinc-air batteries (ZABs) show a peak power density of 138.29 mW cm-2, outperforming the 20 wt% Pt/C+RuO2 (73.9 mW cm-2) and other recently reported catalysts. Furthermore, all-solid-state ZAB delivers a high peak power density of 64.83 mW cm-2 and ultra-robust cycling stability even under bending.

Structure-Activity Relationships in Oxygen Electrocatalysis

Oxygen electrocatalysis, as the pivotal circle of many green energy technologies, sets off a worldwide research boom in full swing, while its large kinetic obstacles require remarkable catalysts to break through. Here, based on summarizing reaction mechanisms and in situ characterizations, the structure-activity relationships of oxygen electrocatalysts are emphatically overviewed, including the influence of geometric morphology and chemical structures on the electrocatalytic performances. Subsequently, experimental/theoretical research is combined with device applications to comprehensively summarize the cutting-edge oxygen electrocatalysts according to various material categories. Finally, future challenges are forecasted from the perspective of catalyst development and device applications, favoring researchers to promote the industrialization of oxygen electrocatalysis at an early date.

Boosting the oxygen reduction activity of non-metallic catalysts via geometric and electronic engineering through nitrogen and chlorine dual-doping

The development of heteroatom dual-doped porous carbon frameworks with uniform doping is highly desirable for achieving highly efficient oxygen reduction reaction (ORR) activity, due to their tunable chemical and electronic structures. Herein, porous covalent triazine-based frameworks (CTFs) incorporating nitrogen/chorine dual-doped porous carbon networks were fabricated by selecting 1,3-bis(4-cyanophenyl) imidazolium chloride as a building block, in a facile and controllable way via a bottom-up strategy. The resulting nitrogen/chorine dual-doped catalyst CCTF-700 exhibits excellent ORR performance with a more positive onset and half-wave potential (0.85 V vs. RHE), higher diffusion-limited current density and significantly improved stability in comparison with the benchmark commercial 20 wt% Pt/C catalyst. It is worth mentioning that CCTF-700 shows one of the best ORR performances among all the reported metal-free electrocatalysts under alkaline conditions. This work paves the way for a controllable and reliable strategy to craft highly efficient heteroatom dual-doped carbon catalysts for energy conversion.

Catalytic effects of graphene structures on Pt/graphene catalysts

Pt/C catalysts have been considered the ideal cathodic catalyst for proton exchange membrane fuel cells (PEMFCs) due to their superior oxygen reduction reaction (ORR) catalytic activity at low temperatures. However, oxidation and corrosion of the carbon black support at the cathode result in the agglomeration of Pt particles, which reduces the active sites in the Pt/C catalyst. Graphene supports have shown great promise to address this issue, and therefore, finding out the main structural features of the graphene support is of great significance for guiding the rational construction of graphene-based Pt (Pt/graphene) catalysts for optimized ORR catalysts. In order to systematically study the influence of the structural features of the graphene support on the electro-catalytic properties of Pt/graphene catalysts, we prepared porous nitrogen-doped reduced graphene oxide (P-NRGO), nitrogen-doped reduced graphene oxide (NRGO), treated P-NRGO (TP-NRGO) and reduced graphene oxide (RGO) with different nitrogen species contents (7.76, 7.54, 3.24, and 0.14 at%), oxygen species contents (18.68, 18.12, 6.34 and 21.12 at%), specific surface areas (370.4, 70.6, 347.7 and 276.2 m2 g-1) and pore volumes (1.366, 0.1424, 1.3299 and 1.0414 cm3 g-1). The ORR activity of the four Pt/graphene catalysts when listed in the order of their half-wave potentials (E 1/2) and peak power densities was found to be as Pt/P-NRGO > Pt/NRGO > Pt/TP-NRGO > Pt/RGO. The long-term durability of Pt/P-NRGO for the operation of H2-air PEMFCs is better than that of commercial Pt/C catalysts. The excellent ORR catalytic performance of Pt/P-NRGO compared to that of the other three Pt/graphene catalysts is ascribed to the high nitrogen species content of P-NRGO that can facilitate the uniform dispersion of Pt particles and provide accessible active sites for ORR. The results indicate that the specific surface area (SSA) and heteroatom dopants have strong influence on the Pt particle size, and that the nitrogen species of graphene supports play a more important role than the oxygen species, specific surface area and pore volume for the Pt/graphene catalysts in providing accessible active sites.

Construction of Bimetallic-Anchored Two-Dimensional Nanosheets on COF for Rechargeable Zinc-Air Batteries

The preparation of carbon materials by doping bimetallic oxides into triazine frameworks (COFs) is a promising electrocatalyst with the potential to replace precious metals in energy storage systems. In this experiment, a covalent triazine framework (COF) was synthesized by 1,4-dicyanobenzene (DCB) and zinc chloride, in which the COF and transition metals were used as carbon, nitrogen, cobalt, and iron sources. According to the properties of this COF, the destruction of the catalyst during pyrolysis can be prevented. The enhanced catalytic performance of the catalysts can be seen by testing all of the samples of catalysts in an alkaline medium. The high half-wave potential (E1/2) of 0.86 V is comparable to Pt/C and also shows excellent durability by testing. Zinc-air batteries were assembled using the prepared catalysts, and the batteries were tested for specific capacity (548 mAh g-1) and power density (189 mW cm-2). This work provides a new direction for COF-derived catalysts for carbon materials.

Selective access to dihydrophenanthridines and phenanthridinones via cyclisation of aryl amines onto N-tethered arynes

5,6-Dihydrophenanthridines are prepared from aryl amines via intramolecular addition to N-tethered arynes under mild conditions. A new o-silylaryl triflate precursor was developed to increase reactivity and enable electron-rich and electron-poor aryl amines to undergo cyclisation. A complete switch in product selectivity occurs when the reaction is conducted in air, affording the corresponding phenanthridin-6(5H)-one as the sole product under otherwise identical reaction conditions.