N-doped carbon single-atom catalysts (M–N–C) have emerged as some of the most efficient electrocatalysts, offering both high activity and selectivity. To date, stabilization of single atoms on conductive carbon has been achieved almost exclusively through coordination with nitrogen atoms. Here, we introduce copper single-atom catalysts (Cu SACs) uniquely coordinated by oxygen within a stable oxocarbon network derived from tetrahydroxyquinone (THQ)-Cu metal-organic frameworks. By thermal condensation with MgCl 2 ·6H 2 O at 600 °C, we achieve an oxygen-rich carbonaceous material (30 wt% O) hosting highly dispersed Cu atoms. Advanced electron microscopic, spectroscopic, and scattering techniques, including high-resolution scanning transmission electron microscopy (HR-STEM), X-ray absorption spectroscopy (XAS), pair distribution functions (PDF), and electron energy loss spectroscopy (EELS), provide definitive experimental evidence of predominant Cu–O coordination, distinguishing these catalysts (M–O–C) from conventional nitrogen-coordinated SACs. The resulting Cu–O–C catalyst exhibits high selectivity (85% Faradaic efficiency) for electrochemical glycerol oxidation into formic acid under alkaline conditions, outperforming traditional Cu-based systems. In comparison with traditional Cu–N–C system, Cu–O–C shows faster reactions kinetic, arising from unique Lewis basicity of oxygen coordination, facilitating electron-proton transfer reactions. This study not only pioneers Cu–O–C SACs but also introduces oxocarbons as promising supports, offering novel pathways for designing highly efficient single-atom electrocatalysts.

Engineering interfaces between organic semiconductors is an effective way to tailor organic electronic device performance, as charge transport and light interaction efficiency are strongly influenced by electronic coupling at molecular interfaces. Scanning transmission electron microscopy is routinely used to analyze interfaces at the atomic scale; however, its use for organic materials is limited due to the electron beam sensitivity of organic molecules, buried interfaces, and the semicrystalline nature of organics. In this work, we developed a workflow to correlate charge behavior at organic interfaces with their chemistry and structure, even when interface components are chemically and structurally similar and mixed at the nanoscale. We used this workflow to reveal the nanoscale mechanism behind enhanced charge transfer at the heterojunction between two-dimensional carbon nitride catalysts (poly-heptazine imide (PHI) and poly-triazine imide (PTI)) during the oxygen reduction reaction. We found that PHI crystallites grow on PTI layers formed at the gas-liquid interface in the salt melt, following the [001]PTI/[001]K-PHI orientation. This crystallographic alignment promotes the charge transfer from PTI to PHI and creates an electron-rich interface. Electron energy loss spectroscopy showed quaternary N atoms in the heterojunction, which aid O2 adsorption and 2e- reduction to H2O2, as well as a higher proportion of terminal and bridging N atoms, promoting charge separation during the reaction.

Understanding sulfur confinement and chemical transformation in hybrid sulfur-carbon materials is critical for advancing metal-sulfur batteries. Here, we investigate the structural evolution of a sulfur-rich polymer into a hybrid sulfur-carbon via inverse vulcanization and thermal condensation. Multiscale analyses reveal a stepwise transformation, beginning with the emergence of sulfur radicals at ∼175°C, followed by the progressive development of a carbon matrix above 300°C that stabilizes the radical species. Around 450°C, a transitional phase forms, consisting of conjugated carbon clusters covalently bonded to sulfur chains. This hybrid structure confines sulfur within pseudo-graphitic nanodomains, effectively suppressing polysulfide dissolution and enhancing redox stability. DFT simulations show how sulfur confinement modulates Na-S reaction energetics, while electrochemical testing confirms high sulfur utilization, delivering ∼1000 mAh g SC - 1 ${\mathrm{g}}_{{\mathrm{SC}}}^{ - 1}$ and 1200 Wh kg SC - 1 ${\mathrm{kg}}_{{\mathrm{SC}}}^{ - 1}$ , setting a new performance benchmark for room-temperature Na─S batteries. These findings provide critical insights into the correlation between structural evolution and electrochemical performance, offering design principles for next-generation sulfur-based electrodes.

ABSTRACT Transition metal nitrides (TMNs) are attractive for cutting‐edge energy storage technology, especially emerging lithium–sulfur (Li–S) batteries, owing to their electronic structures resembling those of noble metals. Herein, we unveil the underlying mechanism by which TMNs accelerate reaction kinetics, showcasing two nanostructured TMNs (Mo2N and VN) embedded within tailored carbon architectures. A novel, unexplored self‐nitriding approach was developed to synthesize TMNs with precisely controlled solid (sC) or hollow (hC) carbon architectures, achieved through a colloidal route using imidazolium‐based poly(ionic liquid) (PIL) nanoparticles as both a nitrogen‐rich template and morphology‐directing agent. Compact TMN architectures as sulfur hosts enhance ion diffusion and reaction kinetics, enabling efficient active site access and delivering high performance, such as VN@sC with high initial capacity of 792 mAh g−1 at 2 C and cyclability up to 650 cycles. Meanwhile, hollow architectures (VN@hC and Mo2N@hC) featuring hierarchical porous structures serve as cathode electrocatalytic additives, enabling high sulfur loading and delivering an initial capacity of 1143 mAh g−1 at 0.1 C. Remarkably, this performance is achieved with only 5 wt% additive content in scalable 7.9 × 11 cm2 and 12‐layer pouch cells designed for drone power systems.

ABSTRACT Direct electrochemical conversion of nitrate to ammonia (NH 3 ) represents a sustainable route for NH 3 production while simultaneously mitigating nitrate pollution. Carbon nitrides (CNs) have emerged as promising supports for transition‐metal single‐atom catalysts due to their high nitrogen content and abundant coordination sites. However, conventional CNs generally suffer from poor electrical conductivity and difficulty in stabilizing high densities of atomically dispersed metal centers, which limits catalytic efficiency and selectivity in the nitrate reduction reaction. Herein, we overcome these limitations by constructing cobalt poly(heptazine imides) ( Co PHI), an ionic carbon nitride in which Co 2+ species are coordinated to negatively charged imide‐bridging nitrogen atoms. This coordination environment enables a high density of isolated Co active sites (1.092 wt.%) while enhancing charge transport through the PHI framework. As a result, Co PHI achieves a Faradaic efficiency of 93.5% and an NH 3 yield rate of 46.1 mg·h −1 ·mg cat. −1 at −0.8 V versus RHE, outperforming conventional Co─N─C and Co ─C 3 N 4 systems. Combined experimental and theoretical studies show that Co PHI promotes strong nitrate adsorption, facilitates water dissociation to supply protons, and stabilizes key intermediates, collectively enabling efficient and selective nitrate‐to‐ammonia conversion.

Two polymorphs of lithium-scandium sulfate hydrate LiSc(SO4)22H2O are isolated by chimie douce crystallization. Neutron- and X-ray powder diffraction data unveil their monoclinic shape (sp.gr. C2/c, m109-LSS) and orthorhombic lattices (sp.gr. P212121, o-LSS). An elevated temperature during prolonged crystallization yields solely o-LSS. Thermal dehydration of both polymorphs to an anhydrous state proceeds as a lineage of intermediates LiSc(SO4)2(2 - x)H2O identified for the first time by a combination of high-temperature neutron- and X-ray powder diffractions, thermal analysis, and vibrational and NMR spectroscopies. DFT calculations establish the phase priority during dehydration and the inevitable coexistence of different intermediates. Remarkably, heating up to 50 degrees C or X-ray radiation stimulates a reversible phase transition from m109-LSS to another monoclinic phase m107-LSS (sp.gr. C2/c). NMR data confirm that the lattices of both monoclinic as well as orthorhombic polymorphs possess a different coordination environment of water molecules and lithium ions in the space between the scandium sulfate layers. A greater strength of hydrogen bonds of "rigidly bound" water molecules is obtained within orthorhombic structure than that within a monoclinic one.

Visible-light responsive, stable, and abundant absorbers are required for the rapid integration of green, clean, and renewable technologies in a circular economy. Photoactive solid-solid heterojunctions enable multiple charge pathways, inhibiting recombination through efficient charge transfer across the interface. This study spotlights the physico-chemical synergy between titanium dioxide (TiO2) anatase and carbon nitride (CN) to form a hybrid material. The CN(10%)-TiO2(90%) hybrid outperforms TiO2 and CN references and literature homologs in four photo and photoelectrocatalytic reactions. CN-TiO2 achieved a four-fold increase in benzylamine conversion, with photooxidation conversion rates of 51, 97, and 100 % at 625, 535, and 465 nm, respectively. The associated energy transfer mechanism was elucidated. In photoelectrochemistry, CN-TiO2 exhibited 23 % photoactivity of the full-spectrum measurement when using a 410 nm filter. Our findings demonstrate that CN-TiO2 displayed a band gap of 2.9 eV, evidencing TiO2 photosensitization attributed to enhanced charge transfer at the heterointerface boundaries via staggered heterojunction type II.

Transparent ferroelectrics with high linear electro-optic (EO) coefficients are critical for advanced electro-optical devices. However, achieving optical transparency in ferroelectric ceramics remains challenging due to visible light scattering caused by defects such as domain walls, grain boundaries, and pores. Here, we report the successful fabrication of transparent ferroelectric ceramics through innovative chemical composition design and an advanced two-step sintering process in the La-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 system. The optical transparency, which is near the theoretical upper limit, can be attributed to the wide band gap and the minimization of light scattering of defects. By minimizing porosity and engineering grain/domain sizes to differ significantly from the wavelengths of visible light, we suppress scattering, achieving optical transparency near the theoretical upper limit. Strikingly, these ceramics exhibit an ultrahigh linear EO coefficient of ∼1417 pm/V, over 65 times greater than that of LiNbO3 single crystals, the current industry standard. We attribute this exceptional performance to dynamic atomistic polar structures within switchable, thermally stable domains, which enhance electronic polarization sensitivity. This mechanism is corroborated by dielectric spectroscopy, high-resolution transmission electron microscopy and simulation. Our findings offer insights into the design of cost-effective transparent materials with exceptional EO properties, paving the way for next-generation electro-optical devices.

Two polymorphs of lithium-scandium sulfate hydrate LiSc(SO4)2·2H2O are isolated by chimie douce crystallization. Neutron- and X-ray powder diffraction data unveil their monoclinic shape (sp.gr. C2/c, m109-LSS) and orthorhombic lattices (sp.gr. P212121, o-LSS). An elevated temperature during prolonged crystallization yields solely o-LSS. Thermal dehydration of both polymorphs to an anhydrous state proceeds as a lineage of intermediates LiSc(SO4)2·(2 - x)H2O identified for the first time by a combination of high-temperature neutron- and X-ray powder diffractions, thermal analysis, and vibrational and NMR spectroscopies. DFT calculations establish the phase priority during dehydration and the inevitable coexistence of different intermediates. Remarkably, heating up to 50 °C or X-ray radiation stimulates a reversible phase transition from m109-LSS to another monoclinic phase m107-LSS (sp.gr. C2/c). NMR data confirm that the lattices of both monoclinic as well as orthorhombic polymorphs possess a different coordination environment of water molecules and lithium ions in the space between the scandium sulfate layers. A greater strength of hydrogen bonds of "rigidly bound" water molecules is obtained within orthorhombic structure than that within a monoclinic one.

Carbon nitrides are among the most efficient and extensively studied transition‐metal‐free photocatalysts, yet their industrial application is limited by high charge recombination, poor charge transport, and insufficient absorption above 460 nm. This study investigates how fine‐tuning the crystal structure of carbon nitrides helps to overcome these challenges and to enhance their photocatalytic performance. We used poly(heptazine imides) (PHIs) with various cations (M = H⁺, Na⁺, K⁺, Mg 2 ⁺) as a model system. Na‐PHI exhibits the highest activity among PHIs with monovalent cations, as the combination of solvated Na⁺ cations and rotational defects, experimentally observed in this study for the first time, optimizes interlayer charge transfer. Greater photocatalytic efficiency observed for Mg‐PHI is attributed to the preservation of rotational defects and the higher oxidation state of Mg 2 ⁺, which enhances charge density and facilitates charge transfer. Density functional theory (DFT) and spectroscopic analyses reveal that Na‐PHI and Mg‐PHI share a valence band dominated by nitrogens and a conduction band primarily influenced by carbons, with both cations contributing to n‐type doping. Mg‐PHI features sub‐gap impurity states, reducing the band gap and extending light absorption. Excited‐state molecular dynamic simulations further demonstrate that water molecules contribute more significantly to charge transfer. highlighting an additional key factor in optimizing photocatalytic performance.

Covalent and metal-organic frameworks (COFs and MOFs) have shown great promise in light-driven processes mainly due to their ligand-to-metal charge-separation properties, as well as having access to a diverse range of photoactive metalloligands and organic linkers. However, both frameworks present individual drawbacks that can potentially be avoided by combining both systems (metal and covalent) to produce metal-covalent organic frameworks (MCOFs), exhibiting the advantages of both material types. Yet, due to their poor crystallinity, the understanding of the structure-properties relation of MCOFs remains unclear. Herein, we report photoactive linkers in the form of a [Ru(tpy)2]2+ (tpy: 2,2',6,2″-terpyridine) complex which covalently binds to a luminescent pyrene core to yield a new, photoactive Schiff-base MCOF. The structure, thermal, electronic, and optical properties of this novel material have been exhaustively characterized by a wide range of microscopy, spectroscopic, and computational methods. This combined experimental and computational work represents a significant step toward the fundamental understanding of the photoactive units within the framework, their hierarchical arrangement and interactions with substrates, which is essential for the future design of efficient photocatalytic materials.

Triazine-based graphitic carbon nitride is a semiconductor material constituted of cross-linked triazine units, which differs from widely reported heptazine-based carbon nitrides. Its triazine-based structure gives rise to significantly different physical chemical properties from the latter. However, it is still a great challenge to experimentally synthesize this material. Here, we propose a synthesis strategy via vapor-metal interfacial condensation on a planar copper substrate to realize homogeneous growth of triazine-based graphitic carbon nitride films over large surfaces. The triazine-based motifs are clearly shown in transmission electron microscopy with high in-plane crystallinity. An AB-stacking arrangement of the layers is orientationlly parallel to the substrate surface. Eventually, the as-prepared films show dense electrochemical lithium deposition attributed to homogeneous charge transport within this thin film interphase, making it a promising solution for energy storage.

Heptazine-based carbon nitrides are a class of transition metal free semiconductors, which are extensively studied in various photocatalytic processes. The localized nature of the excitons, incomplete exciton conversion into the charge-separated state and the recombination of the charge carriers are the factors that limit performance of the pristine heptazine-based carbon nitrides. Herein, we design heterojunctions composed of poly(triazine imide) intercalated by LiCl and poly(heptazine imide) phases. The donor-acceptor character of the heterojunctions improves the charge separation yield. The heterojunction with the optimal composition of the phases shows an apparent quantum yield of H2O2 formation of 14% at 365 nm and 7% at 465 nm, while the H2O2 production rate reaches 7.8 mol L-1 gphotocatalyst-1 h-1 (39 mmol L-1 h-1 produced by 5 mg of photocatalyst) in batch and 15.9 mol kgphotocatalyst-1 h-1 in flow using a packed-bed photoreactor. The heterojunction undergoes photocharging under anaerobic conditions. The charges stored in the material after irradiation enable O2 reduction to H2O2 in the dark with the rate 367 µmol gphotocatalyst-1 h-1 (1.8 µmol h-1 stored in 5 mg of photocatalyst).

Developing high-performance carbonaceous anode materials for sodium-ion batteries (SIBs) is still a grand quest for a more sustainable future of energy storage. Introducing sulfur within a carbon framework is one of the most promising attempts toward the development of highly efficient anode materials. Herein, a microporous sulfur-rich carbon anode obtained from a liquid sulfur-containing oligomer is introduced. The sodium storage mechanism shifts from surface-controlled to diffusion-controlled at higher synthesis temperatures. The different storage mechanisms and electrode performances are found to be independent of the bare electrode material's interplanar spacing. Therefore, these differences are attributed to an increased microporosity and a thiophene-rich chemical environment. The combination of these properties enables extending the plateau region to higher potential and achieving reversible overpotential sodium storage. Moreover, in-operando small-angle X-ray scattering (SAXS) reveals reversible electron density variations within the pore structure, in good agreement with the pore-filling sodium storage mechanism occurring in hard carbons (HCs). Eventually, the depicted framework will enable the design of high-performance anode materials for sodium-ion batteries with competitive energy density.

Oxyapatites A10(GeO4)6O2 (A – alkaline, rare‐earth elements) are considered promising materials for applications in solid‐state lighting and non‐contact thermometry. The temperature dynamics of the oxygen sublattice have a crucial influence on the luminescent properties of these optical hosts. Here, the structural evolution with temperature of germanates with the general formula ALa9(GeO4)6O2 (A – Li, Na, K, Rb) is investigated, using X‐ray and neutron powder diffraction methods. These compounds crystallize in space‐group P63/m. NPD experiments helped to determine the oxygen and alkaline metal positions. Thermally‐induced reentrant structural transitions relating to the oxygen in the apatite channel are discovered for the first time. In the example of Eu‐doped RbLa9(GeO4)6O2 and KLa9(GeO4)6O2, it is demonstrated that the luminescence of the Eu3+ ion is influenced by small changes in the crystal structure.

Nanoconfinement is a promising strategy in chemistry enabling increased reaction rates, enhanced selectivity, and stabilized reactive species. Sulfur's abundance and highly reversible two-electron transfer mechanism have fueled research on sulfur-based electrochemical energy storage. However, the formation of soluble polysulfides, poor reaction kinetics, and low sulfur utilization are current bottlenecks for broader practical application. Herein, a novel strategy is proposed to confine sulfur species in a nanostructured hybrid sulfur-carbon material. A microporous sulfur-rich carbon is produced from sustainable natural precursors via inverse vulcanization and condensation. The material exhibits a unique structure with sulfur anchored to the conductive carbon matrix and physically confined in ultra-micropores. The structure promotes Na+ ion transport through micropores and electron transport through the carbon matrix, while effectively immobilizing sulfur species in the nanoconfined environment, fostering a quasi-solid-state redox reaction with sodium. This translates to ≈99% utilization of the 2e- reduction of sulfur and the highest reported capacity for a room temperature Na-S electrochemical system, with high rate capability, coulombic efficiency, and long-term stability. This study offers an innovative approach toward understanding the key physicochemical properties of sulfurcarbon nanohybrid materials, enabling the development of high-performance cathode materials for room-temperature Na-S batteries with efficient sulfur utilization.

Renewable-electricity-powered carbon dioxide (CO2) reduction (eCO2R) to high-value fuels like methane (CH4) holds the potential to close the carbon cycle at meaningful scales. However, this kinetically staggered 8-electron multistep reduction suffers from inadequate catalytic efficiency and current density. Atomic Cu-structures can boost eCO2R-to-CH4 selectivity due to enhanced intermediate binding energies (BEs) resulting from favorably shifted d-band centers. In this work, 2D carbon nitride (CN) matrices, viz. Na-polyheptazine (PHI) and Li-polytriazine imides (PTI), are exploited to host Cu-N2 type single-atom sites with high density (≈1.5 at%), via a facile metal-ion exchange process. Optimized Cu loading in nanocrystalline Cu-PTI maximizes eCO2R-to-CH4 performance with Faradaic efficiency (FECH4) of ≈68% and a high partial current density of 348 mA cm-2 at -0.84 V vs reversible hydrogen electrode (RHE), surpassing the state-of-the-art catalysts. Multi-Cu substituted N-appended nanopores in the CN frameworks yield thermodynamically stable quasi-dual/triple sites with large interatomic distances dictated by the pore dimensions. First-principles calculations elucidate the relative Cu-CN cooperative effects between the matrices and how the Cu local environment dictates the adsorbate BEs, density of states, and CO2-to-CH4 energy profile landscape. The 9N pores in Cu-PTI yield cooperative Cu-Cu sites that synergistically enhance the kinetics of the rate-limiting steps in the eCO2R-to-CH4 pathway.

Heptazine-based carbon nitrides are a class of transition metal free semiconductors, which are extensively studied in various photocatalytic processes. The localized nature of the excitons, incomplete exciton conversion into the charge-separated state and the recombination of the charge carriers are the factors that limit performance of the pristine heptazine-based carbon nitrides. Herein, we design heterojunctions composed of poly (triazine imide) intercalated by LiCl and poly(heptazine imide) phases. The donor-acceptor character of the heterojunctions improves the charge separation yield. The heterojunction with the optimal composition of the phases shows an apparent quantum yield of H2O2 formation of 14 % at 365 nm and 7 % at 465 nm, while the H2O2 production rate reaches 7.8 mol L(-1)g(photocatalyst)(-1) h(-1) in flow using a packed-bed photoreactor. The heterojunction undergoes photocharging under anaerobic conditions. The charges stored in the material after irradiation enable O-2 reduction to H2O2 in the dark with the rate 367 mu mol kg(photocatalyst)(-1) h(-1) (1.8 mu mol h(-1) stored in 5 mg of photocatalyst).

In this work, melem-based supramolecular assemblies were obtained in one step by thermal treatment of melamine in an autoclave in the presence of sodium chloride. The detailed analysis showed that the obtained powder consists of two phases: poorly crystalline Na-PHI flakes and rod-shaped melem hydrate single crystals (several micrometers long and similar to 300-500 nm wide). Melem hydrate crystals absorb light in the visible range (Eg=2.7 eV) and demonstrate photocatalytic activity in the reaction of partial oxidation of benzyl alcohol to benzaldehyde by air under visible light with high selectivity for the target product. At 60 % conversion of benzyl alcohol, the selectivity of benzaldehyde formation is above 95 %.