Light-driven modulation of supramolecular interactions underpins many biological functions and has inspired the development of artificial molecular machines and adaptive materials. Rather than using light to toggle between two ground-state species, we instead generate an excited state whose binding affinity differs markedly from that of the ground state, enabling transient and reversible manipulation of host–guest interactions. To accomplish this, we employed one of several euco dyes that undergoes twisted intramolecular charge separation upon photoexcitation. Our findings show that this excited-state process induces significant electronic and structural reorganization, reducing the dye’s affinity for 2D materials and ultimately promoting light-triggered desorption from their surfaces in water. Excited-state control offers distinct advantages over ground-state strategies by allowing reversible and short-lived tuning of molecular binding with 2D materials. This mechanism outlines a new design principle for dynamic, adaptive systems operating under physiological conditions, with potential applications in sensing, drug delivery, and materials science.

In recent years, carbon nitride (C₃N₄) has increasingly achieved a remarkable role in the world of semiconductors owing to its chemical and thermal stability alongside its bandgap (≈2.8 eV), which makes the material a well-established photocatalyst^[1]. In particular, doping with non-metals such as B, S, and P has proven to be an efficient and environmentally friendly way to overcome charge recombination and extend the absorption interval of the semiconductor, while also avoiding the use of common -and often critical- metallic elements^[2]. This contribution reports a straightforward and sustainable synthesis of P-doped carbon nitride starting from two cheap and abundant precursors: thiourea and (NH₄)₂HPO₃, which are two of the most widely available fertilizers. Elucidation on the structure, the composition, and the optical properties is performed with a broad range of analytical methodologies, including microscopies (HR-SEM, TEM), spectroscopies (DRS UV-vis, FT-IR, EPR, PL, TCSPC, EDS, XPS), XRD, and N₂ physisorption. Under blue LED light, the material is to effectively catalyzes the photodegradation of four different polluting dyes (Rhodamine B, Malachite Green, Indigo Carmine, and Congo Red) in water, as well as the oxidation of benzyl alcohol and benzyl amine in acetonitrile. Mechanistic studies revealed that the P-doped carbon nitride behaves like a dual-function photocatalyst, being able to rapidly degrade the pollutants and simultaneously produce H₂O₂, thus making this material of great promise for further research.

Poly(heptazine imide) (PHI) is a semi-crystalline carbon nitride, consisting of layered, graphene-like sheets built from heptazine units interconnected through negatively charged imide linkers. This arrangement yields a periodic 2D framework with well-defined ionic pores and long-range structural order. Owing to their crystallinity and ionic character, PHI materials display enhanced charge mobility, chemical robustness, non-toxicity, low cost, and visible-light absorption, while also serving as ideal hosts for stabilizing isolated metal atoms. As such, they have emerged as highly promising semiconductors for energy conversion, artificial photosynthesis1, photodiodes2, microswimmers3, and neuromorphic devices such as photomemristors4.

Given the global demand for sustainable energy solutions, extensive research has been devoted to PHI-based photocatalysts for H2 evolution5. Achieving high H2 production efficiencies, however, requires not only structural refinement but also rational engineering of photogenerated charge carriers. Among the most effective approaches is the introduction of electron-rich heteroelements, such as sulfur or phosphorus, into the PHI lattice, aiming at to narrow the band gap and improve charge-carrier dynamics6-8. Although such strategies have been explored in amorphous carbon nitrides, with only partial success due to their intrinsic structural disorder, no study to date has demonstrated the effective incorporation of heteroelements into the crystalline PHI framework.

We propose a controlled sulfur-doping strategy for PHI aimed at preserving the original crystalline framework and chemical structure while narrowing the band gap and extending the absorption edge toward lower-energy. The approach relies on introducing thioacetamide as the sulfur source during polymerization, together with urea as the primary precursor for the heptazine-based backbone, and a eutectic NaCl/KCl mixture functioning as a structural directing medium to induce PHI crystallization. A series of four materials was prepared: one pristine PHI (S-free) and three sulfur-containing analogues with progressively increasing thioacetamide content. This systematic series allows direct evaluation of how incremental sulfur introduction affects polymerization, dopant incorporation, and optoelectronic properties.

Sulfur incorporation was confirmed by elemental analysis and EDX, which collectively indicate substitution of nitrogen atoms within the PHI lattice by sulfur. This is evidenced by a progressive decrease in nitrogen content concomitant with an increase in sulfur as the thioacetamide amount is raised, suggesting that the heteroatom replace the N in the lattice. The results also reveal an intrinsic upper limit for sulfur incorporation of approximately 0.4 wt%. From a structural standpoint, PXRD, FT-IR, and ss-NMR data show that S-doping levels up to ~0.2 wt% preserve the characteristic semi-crystalline PHI framework. Beyond this threshold, higher sulfur loadings induce increasing amorphous character, with the materials gradually approaching the structural features of melon-like carbon nitride. These observations demonstrate that sulfur incorporation into crystalline PHI is feasible but constrained to a narrow compositional window before long-range order is compromised.

Optoelectronically, S-incorporation exhibit a progressive emergence of Urbach tails, indicative of localized electronic states introduced by structural disorder, likely associated with regions of incomplete condensation containing –NH2 or –SH terminations. Consistently, the optical band gap decreases following the same trend, from 2.74 eV in pristine PHI to 2.02 eV in the most heavily doped sample, enabling absorption close to the red-light region.

All materials were subsequently evaluated for photocatalytic H2 evolution under different irradiance conditions and wavelengths. The highest performance was achieved by the NaK-PHI 1%S sample, reaching approximately 10000 µmol g-1 h-1 under 410 nm irradiation. Moreover, this material sustained activity under green light, producing ~1700 µmol g-1 h-1, an ability not observed for the pristine PHI. Samples with higher sulfur loadings exhibited a progressive decrease in activity, correlating with their reduced crystallinity and increasing similarity to amorphous carbon nitride. Nevertheless, even these more disordered materials maintained appreciable H2 evolution under green-light irradiation.

Heterogeneous photocatalysis is an attractive enabler of the efficient execution of various im-portant environmental (e.g., hydrogen production and C-based fuel production) and organic reac-tions utilizing solar energy. In a typical batch reactor, a heterogeneous photocatalyst is dispersed in a given solution together with reactants, and upon illumination, a chemical reaction occurs. Despite its simplicity, the overall process faces some challenges related to the intrinsic nature of the reaction conditions: light penetration significantly decreases with distance, the photocatalyst should be continuously stirred to avoid sedimentation, separating the products from the photocata-lyst is not trivial, the catalyst is hard to recycle, the reaction is dependent on the concentration of starting reactants, and scalability is questionable.
An alternative approach is to use a panel based on a photocatalytic material. This configuration enhances light management and facilitates easy recycling and scalability, similar to that of solar cells. Furthermore, the photocatalyst panel can be easily incorporated into a continuous-flow re-actor, facilitating constant reactant feed and product separation. In recent years, polymeric carbon nitride (CN) materials have emerged as a class of photocatalysts for many reactions, from solar fuel production to biomass conversion and complex organic transformations. Nevertheless, most studies have focused on using CN powders as heterogeneous photocatalysts. Some pioneering works have shown the utilization of CN panels, primarily for H2 production. However, all these panels were prepared by drop-casting or screen-printing a synthesized catalyst with a polymer containing perfluoro groups (i.e., Nafion) or a SiO2 binder onto frosted glass or steel plates. The use of a binder can lead to photocatalyst detaching from the substrate due to the formation of radicals during the reaction, such as reactive organic species (ROS). This phenomenon primarily occurs in organic chemical reactions, where ROS intermediates can react with the binder to pro-duce unwanted byproducts.
This talk will introduce facile and scalable approaches for growing polymeric carbon nitride (CN) layers on conductive substrates with tunable structural and photophysical properties for photocata-lytic applications. We demonstrate CN-based photocatalytic panels as highly stable, efficient plat-forms for converting organic molecules into value-added chemicals while simultaneously produc-ing hydrogen and hydrogen peroxide. Additionally, I will demonstrate the use of CN-films as highly stable photocatalytic panels for various catalytic and cascade reactions.

Solar fuel production by photocatalysis is becoming more and more efficient and economic, especially when driven by earth abundant and organic materials. In this talk, we present ways to probe and tailor (ion-enhanced) light-mater interactions in organic photocatalysts in general, and 2D CNx in particular, in order to yield beneficial solar energy conversion properties.

While organics’ bottom-up design possibilities promise tailorable structure-function relationships for enhanced activity, the advancement is often hindered by limiting knowledge of interwoven photo-physical processes and properties that lead to recombination losses.[1] I will explain how different time-resolved (transient) spectroscopy techniques in combination with varying environmental conditions can be used to provide insights into the very beginning of the solar energy conversion process chain, focussing on exciton generation and separation, and charge stabilization being responsible for most efficiency losses. This enables to better understand light-matter interactions, and to tailor them to address bottlenecks associated with exciton recombination, especially occurring in organic materials.

We introduce Terahertz-Time Domain Spectroscopy (THz-TDS) measurements as convenient technique to probe the complex permittivity, and with that the dielectric properties of organic semiconductors on the very ps-time scales. The dielectric response defines exciton binding and is hence relevant for charge carrier photogeneration in all solar energy conversion technologies, but its values are highly frequency dependent, and commonly extracted at timescales orders magnitude off the ps-regime. Our study focussing on carbon nitrides now reveals dielectric screening and transport properties at the early time scales of solar energy conversion process chains. At the same time, it shows that also in this ultrafast regime, the environment and ions can matter, and strongly enhance photophysical parameters.[2]

Second, we present novel insight to ultrafast time resolved transient optical spectroscopies on 2D CNx, shedding light on their uncommon and environmentally dependent pathways to generate charges for photocatalytic energy conversion.

In recent years, a plethora of material systems have been designed and prepared to increase the performance of light harvesting and light-emitting technologies, and to develop new and attractive applications. Limitations of state-of-the-art devices based on organics (both conjugated polymers or small molecules/oligomers) derive largely from material stability issues after prolonged operation. This challenge could be tackled by leveraging the enhanced stability of carbon nanostructures (CNSs, including carbon nanotubes and the large family of graphene based materials) in carefully designed nano-hybrid or nano-composite architectures to be integrated within photo-active layers, paving the way to the exploitation of these materials in contexts in which their potential has not been yet fully revealed [1]. In this talk, I will discuss the theoretical background behind CNSs hybridization with other materials such as graphene with donor-acceptor molecules [2], for the establishment of novel optoelectronic properties and provide an overview of new optoelectronic and transfer properties of organic interfaces consisting of low-dimensional mateirals assembly [3-5] that allow to forecast interesting future perspectives for use in real devices.

In 2020, Demirci et al. [1] predicted a two-dimensional monolayer polymorph of boron nitride with an orthorhombic structure (o-B₂N₂) using first-principles calculations. Subsequently, Li et al. [2] showed that the band gap of monolayer o-B₂N₂, calculated at the GW level, is 2.446 eV. Recently, several groups have proposed applications for monolayer o-B₂N₂ in renewable energy. For instance, the potential of o-B₂N₂ for applications in batteries has been explored [3]. Nevertheless, the properties of few-layer and bulk-layered o-B₂N₂ remain largely unexplored.

Here we investigate the structural and optoelectronic properties of few-layer and bulk-layered o-B₂N₂ using first-principles calculations. We use density functional theory (DFT) calculations, including van der Waals corrections, to show that the energetically favorable stacking order is AB, with B atoms sitting above N atoms and vice versa. We also studied the electronic properties of these systems using many-body GW calculations and solved the Bethe-Salpeter equations to include excitonic effects. The band gaps calculated at the GW level decrease as the number of layers increases, reaching 1.28 eV for bulk o-B₂N₂. Exciton binding energies also decrease as a function of the number of layers. The band gap we predict for bulk o-B₂N₂, along with the fact that the calculated optical absorption closely matches solar irradiance, makes this material a promising candidate for photovoltaic applications. We propose a heterostructure, where o-B₂N₂ is the active layer, that can perform quite efficiently as a solar cell.

The transition to a sustainable energy matrix faces significant challenges, such as grid instability due to the intermittency of renewable sources. While green hydrogen is pivotal for decarbonizing the chemical industry, direct solar-to-chemical conversion offers a compelling, albeit underestimated, alternative pathway to valorize abundant solar energy. This presentation posits that Poly(heptazine imide) (PHI), a class of ionic, crystalline carbon nitride semiconductors, can bridge the gap between solar harvesting and chemical synthesis. By leveraging a cation exchange strategy, we demonstrate how metal Single-Atom Catalysts (SACs)—such as Fe, Ni, and Mn—can be stabilized within the PHI framework to create precise active sites and tune band structures.

Here, a series of recent examples are presented, demonstrating that these tailored photocatalysts can be successfully employed to drive the synthesis of commodity chemicals. First, we address the production of Green Hydrogen, showing that Nickel-based PHI catalysts (Ni-PHI) can effectively replace costly platinum, challenging the economic feasibility barriers of conventional photocatalysis. Second, we illustrate the versatility of these materials in organic synthesis through the selective photoreduction of phenylacetylene to styrene under mild conditions. Finally, we report on the sustainable production of hydrogen peroxide (H₂O₂) using H-PHI and Na-PHI, utilizing glycerol as a sacrificial reagent. These examples collectively demonstrate that single-atom functionalized carbon nitrides can drive a "solar-to-chemical" industry, offering a disruptive solution to safeguard the transition toward a low-carbon economy.

Catalysis has a fundamental role to solve arduous tasks in synthetic chemistry and is thus involved in the global economy in many industrial fields. In fact, in the last 50 years, catalysis has seen enormous progress in the development of optimized large-scale productions within the area of pharmaceutical, agrochemical and petrochemical industry. Moreover, a catalytic approach presents multiple benefits for business and sustainability compared to stoichiometric processes. These include cost reduction, time and energy saving, waste reduction, carbon-footprint minimization, among others. In this context, our research activity aims at designing and developing novel catalytic organic transformations which address unsolved problems in synthetic chemistry. The final goal is therefore the production of effective, inexpensive and safe catalytic systems that will find widespread use in modern organic synthesis. To this end, we effectively employed aromatic molecules as photocatalytic systems to drive the synthesis of relevant organic compounds. As a matter of fact, the great structural variety of these molecules combined with the easy fine-tuning of their electronic properties has unlocked new possibilities for the generation of reactive intermediates under mild operative conditions.[1-2] In addition, we worked on the development of novel nano-catalytic organic transformations. In particular, we design new carbon-based nano-organocatalytic systems, namely carbon nitrides and carbon dots.[3-7] These materials have been efficiently used to drive relevant organic reactions, including enantioselective transformations, under mild operative conditions.

References:

[1] C. Rosso, J. D. Williams, G. Filippini, M. Prato, C. O. Kappe, Org. Lett., 2019, 21, 5341-5345.

[2] C. Rosso, S. Cuadros, G. Barison, P. Costa, M. Kurbasic, M. Bonchio, M. Prato, L. Dell’Amico, G. Filippini, ACS Catalysis, 2022, 12, 4290-4295.

[3] C. Rosso, G. Filippini, M. Prato, ACS Catalysis, 2020, 10, 8090-8105.

[4] C. Rosso, G. Filippini, A. Criado, M. Melchionna, P. Fornasiero, M. Prato, ACS  Nano, 2021, 15, 3621-3630.

[5] G. Filippini, F. Amato, C. Rosso, G. Ragazzon, A. Vega-Peñaloza, X. Companyó, L. Dell’Amico, M. Bonchio, M. Prato, Chem, 2020, 6, 3022-3037.

[6] G. Filippini, F. Longobardo, L. Forster, A. Criado, G. Di Carmine, L. Nasi, C. D’Agostino, M. Melchionna, P. Fornasiero, M. Prato, Sci. Adv., 2020, 6, eabc9923.

[7] M. Marchi, E. Raciti, S. M. Gali, F. Piccirilli, H. Vondracek, A. Actis, E. Salvadori, C. Rosso, A. Criado, C. D’Agostino, L. Forster, D. Lee, A. C. Foucher, R. K. Rai, D. Beljonne, E. A. Stach, M. Chiesa, R. Lazzaroni, G. Filippini, M. Prato, M. Melchionna, P. Fornasiero, Adv. Sci. 2023, 10, 2303781.

Surface terminations are a defining feature of MXenes, crucially governing their structural stability, electronic configuration, and interfacial chemistry. [1-2] By capping the exposed metal atoms, these terminations modulate the band structure, conductivity, superconducting behavior, and electrochemical activity of MXenes, providing a powerful handle for property tailoring. However, most reported MXenes remain limited to a narrow range of simple, monoatomic terminations (e.g., O, F, or Cl), leaving vast opportunities for innovation in surface chemistry.

In this presentation, I will highlight our recent advances in termination engineering to expand the chemical diversity and functional landscape of MXenes. We developed a flux-assisted eutectic molten etching strategy to introduce ordered triatomic-layer borate (OBO) terminations, achieving significant enhancements in charge carrier mobility and conductivity. [3] Furthermore, a gas–liquid–solid triphasic etching route was established to synthesize MXenes with highly pure and compositionally tunable halogen terminations (Cl, Br, I, and mixed types). [4] We also realized redox-active phosphorus–oxygen (PO₂) terminations through a targeted conversion of hybrid MXene–black phosphorus membranes, [5] and achieved covalent grafting of multifunctional organic molecules onto MXene surfaces via diazonium chemistry. [6] Together, these approaches open new avenues for rationally designing MXenes with tailored surface chemistries. I will further discuss how such termination control dictates charge transport mechanisms and electrochemical storage behavior, offering insights into structure–property relationships and guiding principles for next-generation functional MXenes.

Nanoporous carbon materials play an ever increasing role in various fields like gas purification, electrochemical energy storage/conversion, and catalysis [1]. In all of them, adsorption phenomena on the carbon surface are crucial for the working principles of the respective devices. It is well known that the adsorption properties of such materials are a function of their pore architecture. Pore size, pore geometry, pore connectivity, and pore hierarchy determine important factors like mass transport and the strength of interaction with different guest species. Another (and possibly even more powerful) “regulation screw” to control the adsorption properties of nanoporous carbon materials is their atomic construction. The controlled integration of heteroatoms (most often nonmetallic group III or group V and VI elements with nitrogen being the most widely studied heteroatom) into porous sp²-based carbon networks can significantly change their physicochemical properties [2]. This includes but is not limited to their acidity/basicity, oxidation resistance, electric conductivity, and surface polarity. In order to make use of these effects it is important that the heteroatoms are significant in number, that they are uniformly distributed over the bulk of the material, and that the local atomic construction motives are as defined as possible. The synthesis of nitrogen-rich carbon materials by controlled condensation of well-defined nitrogen-rich molecular precursors is a particularly elegant way to synthesize porous carbon materials with large concentrations and precisely incorporated heteroatoms [2].

My presentation will give an overview of the attempts in my research group at the FSU Jena to develop synthetic methods for the precise tailoring of the chemical architecture and pore structure of functional nanoporous carbon materials [3]. Special focus will be on the fabrication of all-carbon hybrid materials which combine a rather heteroatom-rich carbon phase and a pristine porous carbon on the nanoscale to combine, for instance, a demanded chemical property with high electrical conductivity. The structure-property-relationships of these materials in some selected energy applications like the adsorption and electrochemical conversion of small molecules (CO₂ or N₂) as well as in sodium ion battery electrodes will also be presented.

Transition metal dichalcogenides (TMDs) are a class of two-dimensional materials consisting of individual 2D sheets held together by van der Waals forces. Molybdenum disulfide (MoS2) is an intriguing member of this materials family since it can act as intercalation host for a variety of cations. MoS2 morphology and crystallite size have been known to tremendously impact the electrochemical properties, for example, it was reported that reducing crystallite size and/or introducing lattice disorder can lead to a pseudocapacitive intercalation signature for lithium ions from organic electrolytes.

Besides controlling particle and/or crystallite size, direct manipulation of the lattice parameters such as the interlayer spacing between individual layers can have an impact on the electrochemical response. Utilizing organic molecules that act as pillars between the layers, the d-spacing of MoS2 can be effectively tuned.

In this contribution, our group’s efforts in controlling MoS2 structure over several length scales is introduced. By using a bottom-up hydrothermal synthesis approach, MoS2 crystallite size and interlayer spacing can be simultaneously controlled by pH adjustment and the use of organic pillars, respectively, and the interlayer composition can be adjusted by varying pillar concentration.[1] Moreover, we will demonstrate that the interaction between pillar and MoS2 host dictates the resulting electrochemical properties: While non-covalently interacting 1,6-hexanediammonium pillars lead to a capacitor-like electrochemical signature, covalently attached 1,6-hexanedithiol pillars yield more battery-like properties.[2]

Finally, we will give an outlook on the viability of such pillaring approaches via top-down synthetic approaches of commercial, bulk-sized MoS2, paving the way for obtaining larger batch sizes of interlayer-functionalized transition metal dichalcogenides.

Achieving high capacity and stability in sodium-ion batteries (SIBs) remains a major challenge due to sluggish ion kinetics and unstable interphases at carbon–electrolyte interfaces. Here, we present a conformal carbon film (CF) coating strategy that fundamentally transforms sodium storage behavior in porous carbon electrodes. Using chemical vapor deposition (CVD), uniform carbon films are grown on activated carbon fiber (ACF) scaffolds, forming CF/ACF hybrid electrodes that combine nanoconfinement, interfacial stability, and structural integrity in a single architecture.

This conformal coating enables a controlled transition from surface-driven adsorption to diffusion-dominated sodium storage. The CF layer homogenizes the interfacial reaction environment and stabilizes SEI formation, effectively suppressing parasitic side reactions typically observed in pristine ACF. As a result, CF/ACF electrodes deliver record reversible capacities of up to 515 mAh g^-1, including a distinct plateau capacity of 420 mAh g^-1 (<0.15V vs. Na⁺/Na), representing the highest reported value for carbon-based sodium-ion anodes.

Electrochemical analysis reveals that sodium storage proceeds through a two-stage mechanism: (i) rapid adsorption at accessible surface sites, followed by (ii) gradual filling of confined sub-nanometer pores beneath the carbon film. This confinement-driven process promotes uniform ion transport, enhanced reversibility, and excellent rate capability, maintaining high capacity even under extended cycling.

This work establishes a scalable, composition-flexible CVD strategy to convert low-cost carbon powders and fibers into high-performance sodium-ion battery anodes. The process achieves a synthetic SEI-like film that controls the electrode-electrolyte interface, promotes uniform SEI formation atop, and enables nanoconfinement of sodium. The generality of the approach is validated across multiple commercial carbons, including activated carbon fibers, powders, and carbide-derived carbons.

Overall, this study bridges fundamental gas-phase deposition chemistry with advanced battery interface engineering, opening new pathways for tailoring ion-host interactions in porous materials for next-generation energy storage systems.

Investigation of Ionic Radius Effects on Aqueous Electrolyte Performance in Mo₂C-based MXene Supercapacitors

Samaneh Vaez,^a,b Ahmad Bagheri,^a,b Hossein Beydaghi,^a Sebastiano Bellani,^a,c Teresa Gatti, and Francesco Bonaccorso ^a

^a BeDimensional S.p.A., Lungotorrente Secca 30R, 16163 Genoa, Italy

^b Department of Applied Science and Technology (DISAT), Politecnico di Torino, 10129 Torino, Italy

^c Antares Electrolysis S.r.l., Piazza della Vittoria 14/19, 16121 Genova, Italy

This study proposes an effective strategy for designing advanced electrode materials, featuring a molybdenum carbide chloride/few-layer graphene hybrid (Mo₂CCl₂/FLG) as a high-performance negative electrode, paired with curved graphene/few-layer graphene (CG/FLG) as the positive electrode for aqueous asymmetric supercapacitors (ASCs). The Mo₂CCl₂/FLG hybrid exhibits outstanding electrochemical performance due to the synergistic interaction between pseudocapacitive Mo₂CCl₂ and the highly conductive FLG, which enhances charge-transfer kinetics, accelerates ion diffusion, and improves electrochemical reversibility. ^{[1, 2]} To investigate the impact of electrolyte composition, ASCs were assembled in three aqueous electrolytes: 3 M H₂SO₄, 2 M NaCl, and 8 m NaNO₃. Among these, the 3 M H₂SO₄-based device achieved the highest specific capacitance of 29.57 F/g at 1 A/g, attributed to rapid proton transport and favorable redox reactions at the Mo₂CCl₂ interface. ^[3] However, despite its high ionic conductivity, the acidic electrolyte is limited by a narrow electrochemical stability window, restricting safe operating voltage and energy density due to water decomposition. ^[4] In contrast, sodium-based electrolytes provided wider potential windows and improved voltage stability. The ASC with 8 m NaNO₃ delivered an energy density of ~8 Wh kg⁻¹ and excellent cycling stability, retaining 94% of its initial capacitance after 12000 cycles. The 2 M NaCl electrolyte showed stable long-term performance, indicating suitability for durable aqueous energy-storage systems. ^[5] Electrochemical impedance spectroscopy revealed distinct electrolyte-dependent behaviors. The 3 M H₂SO₄ system exhibited the lowest series resistance (Rₛ ≈ 0.04 Ω), consistent with rapid ionic transport, whereas 8 m NaNO₃ displayed higher resistance due to slower diffusion of larger hydrated ions. Overall, the Mo₂CCl₂/FLG // CG/FLG ASC configuration demonstrates strong potential for high-performance, scalable aqueous supercapacitors when coupled with optimized electrolytes. These results provide key design principles for tuning electrode–electrolyte interactions and offer valuable guidance for developing next-generation aqueous energy-storage devices with balanced energy and power characteristics.

The increasing demand for hydrogen energy calls for more economical and green hydrogen production pathways.[1] Compared to conventional water electrolysis, which relies on scarce high-purity freshwater, seawater electrolysis has attracted increasing attention due to its use of natural seawater.[2] However, the complex composition of seawater introduces significant challenges. Because catalysts are highly sensitive to electrolyte compositions,[3] directly using seawater can obscure fundamental mechanisms and hinder rational catalyst design. Therefore, focusing on the effect of individual ion is essential for establishing more solid scientific basis for future seawater electrolysis development.

Chloride ion (Cl^-), which is difficult to remove even through water purification,[4] is widely regarded as the primary cause of corrosion and competitive side reactions.[5] To address it, catalyst design generally falls into two categories: enhancing intrinsic OER activity or introducing a protective outer layer. The former is limited by the scaling relationship between OER and CER,[6] while the latter has been reported to reduce catalytic activity by blocking exposed active sites.[7,8] Among the protective layer materials, δ-MnO₂ is widely used due to its high oxygen evolution reaction (OER) selectivity and corrosion resistance. However, because of its low intrinsic OER activity when intercalated with proton or alkali metal cations, δ-MnO₂ has been primarily regarded as a protective layer rather than an active phase, limiting its potential to achieve both high selectivity and OER activity.

In our previous study, we demonstrated that transition metal (TM) cations (Fe³⁺, Ni²⁺) intercalated into interlayers of δ-MnO₂ act as active sites and significantly enhance OER activity. Based on this, this work further focuses on the influence of Cl^- on δ-MnO₂ intercalated with Fe³⁺ and Ni²⁺. Linear sweep voltammetry (LSV) curves and chronoamperometry (CA) reveal an enhanced activity of Fe³⁺/MnO₂ in the presence of Cl^-, while Ni²⁺/MnO₂ shows decreased activity. X-ray photoelectron spectroscopy (XPS) spectra of TM sites, Mn, and residual Cl indicate that this contrasting behavior follows the Hard and Soft Acid and Base (HSAB) theory that Cl^- coordinates with weaker Lewis acids (Ni²⁺), suppressing active sites, but binds to lattice defects when stronger Lewis acids (Fe³⁺) are present. Ex/in situ Raman, XRD, and operando FTIR further reveal that Cl^- facilitates the phase transformation of MnO₂ and the formation of a water-rich interlayer environment. Overall, this work uncovers the critical role of interaction between electrolyte ions and catalysts, highlights the potential role of Cl^- in enhancing OER activity for future seawater electrolysis.

Photo-active bismuth oxyhalides (BiOX, X = Cl, Br, I) have attracted considerable interest as semiconductor materials for photoelectrocatalytic (PEC) water splitting due to their layered crystal structures, tunable band gaps, and intrinsic internal electric fields that promote efficient charge separation. Among this family, BiOI stands out as the most promising candidate owing to its suitable band gap and stability under photoelectrochemical conditions. Nevertheless, its catalytic performance remains insufficient for practical applications, necessitating further improvement. Recent progress in BiOI material engineering—particularly in nano-structuring and surface modification—has led to notable enhancements in charge transport and interfacial reaction kinetics. In this work, we introduce a straightforward approach to boost photocurrent by exfoliating BiOI microspheres synthesized via a microwave-assisted method. The resulting exfoliated BiOI exhibits a broader distribution of species compared to the pristine material. While these additional species do not directly improve PEC oxygen evolution reaction (OER) activity, they are gradually consumed or transformed during OER, generating more active sites and reducing system resistance, which collectively enhances OER performance. Furthermore, we present automated electrode-fabrication strategies derived from the traditional successive ionic layer adsorption and reaction (SILAR) process, highlighting their potential for scalable production of BiOI-based photoelectrodes.

Two-dimensional (2D) molybdenum sulfide (MoS₂) is an attractive noble-metal-free electrocatalyst for the hydrogen evolution (HER) in acids. Tremendous effort has been made to engineer MoS₂ catalysts with either more active sites or higher conductivities to enhance their HER activity. However, little attention has been paid to structural and electronic modulations of MoS₂ synergistically. Moreover, the H_ads energies for most of MoS₂ based catalysts have not been well-clarified so far.

Herein, 2D hydrogenated graphene (HG) was introduced as the support of MoS₂ nanosheets for the construction of MoS₂/HG hybrid catalysts. The optimized MoS₂/HG hybrid catalysts characterized using scanning microscopy and transmission electron microscopy showed that vertical MoS₂ ultrathin nansheets arrays are highly ordered and uniformly distributed on the surface of HG. Wrinkled MoS₂ nanosheets are interconnected with each other, leading to the formation of a porous structure. The characteristic bonds of C-Mo were observed in Raman spectrum. These unique structure characteristics make vertically aligned MoS₂ nanosheets feature more accessible catalytic active sites and ultrafast electron transfer from the HG substrate to the MoS₂ edges within one S-Mo-S layer.

To gain further the idea about the electronic structures of MoS₂ on HG and the H_ads energy of the optimized hybrid catalysts, Density Functional Theory (DFT) calculations were conducted. The simulation results confirmed the improvement of the content of H_ads on MoS₂ by the adequate ferromagnetism of HG support as well as the optimized electronic structure (the enhanced active sites) from C-Mo bonds at the interface of MoS₂ and HG.

These structure characteristics, electronic properties and moderate hydrogen adsorption energy contribute to the excellent HER performance achieved on the optimized MoS₂/HG hybrid catalyst. A low overpotential of 124 mV at the current density of 10 mA cm⁻² and a small Tafel slope of 41 mV dec⁻¹ have been achieved together with long-term durability for 24 h continuous operation at 30 mA cm⁻² and without observable fading. This strategy paves a way to design and develop other highly efficient, stable, and noble metal-free HER electrocatalysts.