Abstract Engineering the electrode–electrolyte interface has emerged as a critical strategy to overcome sluggish kinetics of alkaline hydrogen evolution reaction (HER). However, the dynamic and complex nature of the double electric layer makes mechanistic understanding at the molecular level and rational interfacial regulation highly challenging. Herein, we demonstrate that molecular modification of Ni-doped MoS2 catalyst with a zwitterionic molecule (z-Ni-MoS2) markedly enhances alkaline HER kinetics. In-situ Raman spectroscopy combined with ab initio molecular dynamics (AIMD) simulations reveals that the quaternary ammonium cation reconstructs interfacial water into linear hydrogen-bond chains via electrostatic repulsion of potassium ions from the z-Ni-MoS2 surface. This distinctive interfacial microenvironment enables water molecules within hydrogen-bond chains to directly relay protons to sulfur sites via a Grotthuss-associated mechanism. In contrast to the conventional diffusion-dominated, non-Grotthuss-associated mechanism, this mechanism lowers the water-dissociation barrier and promotes interfacial proton transport, thereby accelerating alkaline HER kinetics. To evaluate device-level applicability, z-Ni-MoS2 was incorporated into an anion exchange membrane water electrolyzer (AEM-WE). The system delivers outstanding performance of 5.21 A cm–2 at 1.8 V and 9.57 A cm–2 at 2 V, 80 °C, surpassing the United States Department of Energy (DOE) 2026 target (3 A cm–2 at 1.8 V). This work provides molecular-level insight for interfacial water restructuring as a design principle for high-performance alkaline HER catalysts.

Alkaline stability is a critical challenge for anion exchange membranes (AEMs) in energy conversion and storage devices. Although stable dimethylpiperidinium is an ideal moiety for the construction of AEMs, its stability diminished significantly when it was incorporated into the polyarylpiperidinium polymer. Herein, poly(arylmethyl m-piperidinium) (m-PAMP) was easily synthesized by using highly active purchasable monomers with only 50% superacid usage compared with conventional methods. This rational design strategy simultaneously reduces the beta-H content and diminishes the backbone effect on piperidinium, improving the upper limit of the alkaline stability of piperidinium-based AEMs. m-PAMP showed no E2 elimination or backbone degradation after 4000 h at 80 degrees C in 1 M KOH. A fully nonprecious-metal catalyst water electrolyzer assembled with m-PAMP not only achieved exceptional performance (8.31 A cm-2 at 2 V) but also maintained stability for over 1900 h under 2 A cm-2, highlighting the substantial potential of m-PAMP for advancing sustainable hydrogen production technologies.

Terawatt-scale hydrogen production using anion exchange membrane water electrolyzers (AEM-WEs) requires the development of facilely prepared, alkali-stable, and high-performance anion exchange membranes (AEMs). State-of-the-art polyarylpiperidinium AEMs fail to match the alkaline stability of piperidinium due to conformational deformation caused by the stiff cardo structure. Herein, polyarylmethylpiperidinium (PAMP) AEM with pendant structure is constructed by utilizing 4-formylpiperidine as a functional monomer. The inclusion of an aldehyde group in the synthesis enhances polymerization reactivity, reduces the amount of superacid required, and ensures that the piperidinium is suspended from the ether-free polymer backbone. The accelerated aging analysis demonstrates that the pendant structure of piperidinium effectively suppresses the Hofmann elimination, resulting in PAMP AEM with exceptional alkali stability, surpassing that of the commercial PiperION-A40. Most importantly, when assembled with non-noble metal OER/HER catalysts, the related AEM-WE achieves a remarkably high transient current density of 7.35 A cm −2 (@2 V, 80 °C, 1  m KOH). Moreover, the AEM-WE can operate stably at industrial current density over 1500 h (≈1.70 V at 1.0 A cm −2 ).

Due to the intrinsically flexible skeletons, loose aggregation and disorder packing of organic materials, organic photovoltaic nanoparticle (OPV-NP) encounters inferior exciton dissociation and charge recombination, especially poor operational stability when applied in photocatalytic hydrogen production. To alleviate these shortages, two new acceptors were constructed by boosting 2-cantilever XZ-1 to 4-cantilever XZ-2 and 6-cantilever XZ-3, thus greatly extending the conjugated plane towards two-dimensionality. Consequently, the decreased reorganization energies, weaker exciton binding, prolonged exciton lifetimes and more ordered molecular packings were observed for 6-cantilever XZ-3, further affording an excellent hydrogen yielding rate (184.68 mmol g -1 h-1). For the PM6:XZ-3 system, the hydrogen production rate was maintained at 106.1% at 40 h compared to the first 10 h of the photocatalytic hydrogenation rate. By unveiling a clear relationship of molecular spatial size-dependent photocatalytic performance, our work paves a new avenue for improving both photocatalytic activity and stability of OPV-NPs synergistically.

Abstract The Mn4CaO5(6) cluster in photosystem II catalyzes water splitting through the S i state cycle (i = 0–4). Molecular O2 is formed and the natural catalyst is reset during the final S3 → (S4) → S0 transition. Only recently experimental breakthroughs have emerged for this transition but without explicit information on the S0-state reconstitution, thus the progression after O2 release remains elusive. In this report, our molecular dynamics simulations combined with density functional calculations suggest a likely missing link for closing the cycle, i.e., restoring the first catalytic state. Specifically, the formation of closed-cubane intermediates with all hexa-coordinate Mn is observed, which would undergo proton release, water dissociation, and ligand transfer to produce the open-cubane structure of the S0 state. Thereby, we theoretically identify the previously unknown structural isomerism in the S0 state that acts as the origin of the proposed structural flexibility prevailing in the cycle, which may be functionally important for nature’s water oxidation catalysis.

A precise molecular regulation approach was proposed to design high-performance and high-stability spatially crosslinking AEMs that boosted the industrial-scale AEM-WE.

The transport of ions through the anion exchange membrane (AEM) depends on the overall energy barriers imposed by the collective interplay of ion channel architecture. The efficient transport of water and ions can be observed ubiquitously in plants. Inspired by the pectin in nature, we developed a spatially topological strategy for designing high-performance AEMs. To achieve precision control at the molecular level, several spatially topological molecules such as triptycene and 9,9’-spirobifluorene were utilized as single or dual framework centers for the anion exchange membrane. By manipulating the ratio of triptycene and 9,9’-spirobifluorene in the polymer, a high ionic conductivity (197.4 mS cm-1 at 80 °C) and an exceedingly low swelling ratio (8.6% at 80 °C) can be attained. The present AEM-WEs achieved a new record high current density of 8.4 A cm−2 at 2.0 V with a 1 M KOH at 80 °C using platinum group metal (PGM)-free catalysts, which surpassed that of state-of-the-art proton exchange membrane water electrolyzers (PEM-WEs) (~ 6 A cm−2 at 2.0 V) and operated stably at a current density of 2 A cm−2 with a cell voltage of 1.8 V for more than 600 h at 60 °C. Notably, when we used the cell with five stacked PGM-free based membrane (T4-1.0-0.5, 80 μm) electrodes, a hydrogen production rate of 0.54 Nm3 h−1 was achieved. The industrial system demonstrates a high level of efficiency and stability while operating under working conditions with a current density of 1 A cm-2 at 2 V.

We utilize herein ultrafast mid-infrared probe laser pulses to explore the mechanism for the charge recombination/trapping process of photogenerated charges within the band gap of TiO2 and across interfaces. Low-energy photons solely probe the free electrons present in the conduction band of TiO2 and those captured in shallow-trap states. We found that >70% of the photogenerated charges disappear from the conduction band in the first few nanoseconds due to electron trapping followed by charge recombination at longer time scales. Moreover, the behavior of the dynamics of the free electrons within the band gap of TiO2 and electrons generated at the interface of adsorbed organic dyes was investigated and compared. This comparison shows that the main driving force for the efficient charge trapping of photogenerated charges within the picosecond time scale is the presence of photogenerated holes, within the band gap of TiO2, or close to the interface of TiO2. If the hole is far from the TiO2 surface, the electron trapping process is hindered, and almost 100% of photogenerated charges can survive up to nanoseconds. This work offers a deeper understanding of the charge trapping and charge recombination processes, by knowing the spatial hole effect, in TiO2 and similar semiconductors upon utilization in photonic devices and photocatalysis.

Anion exchange membranes (AEMs) are core components in anion exchange membrane water electrolyzers (AEM-WEs). However, the stability of functional quaternary ammonium cations, especially under high temperatures and harsh alkaline conditions, seriously affects their performance and durability. Herein, we synthesized a 1-methyl-3,3-diphenylquinuclidinium molecular building unit. Density functional theory (DFT) calculations and accelerated aging analysis indicated that the quinine ring structure was exceedingly stable, and the S N 2 degradation mechanism dominated. Through acid-catalyzed Friedel–Crafts polymerization, a series of branched poly(aryl-quinuclidinium) (PAQ-x) AEMs with controllable molecular weight and adjustable ion exchange capacity (IEC) were prepared. The stable quinine structure in PAQ-x was verified and retained in the ex situ alkaline stability. Furthermore, the branched polymer structure reduces the swelling rate and water uptake to achieve a tradeoff between dimensional stability and ionic conductivity, significantly improving the membrane's overall performance. Importantly, PAQ-5 was used in non-noble metal-based AEM-WE, achieving a high current density of 8 A cm −2 at 2 V and excellent stability over 2446 h in a gradient constant current test. Based on the excellent alkaline stability of this diaryl-quinuclidinium group, it can be further considered as a multifunctional building unit to create multi-topological polymers for energy conversion devices used in alkaline environments.

The anion exchange membrane water electrolysis is widely regarded as the next-generation technology for producing green hydrogen. The OH − conductivity of the anion exchange membrane plays a key role in the practical implementation of this device. Here, we present a series of Z−S-x membranes with dibenzothiophene groups. These membranes contain sulfur-enhanced hydrogen bond networks that link surrounding surface site hopping regions, forming continuous OH − conducting highways. Z−S-20 has a high through-plane OH − conductivity of 182±28 mS cm −1 and ultralong stability of 2650 h in KOH solution at 80 °C. Based on rational design, we achieved a high PGM-free alkaline water electrolysis performance of 7.12 A cm −2 at 2.0 V in a flow cell and demonstrated durability of 650 h at 2 A cm −2 at 40 °C with a cell voltage increase of 0.65 mV/h.

A new class of polymeric hole-transport materials (HTMs) are explored by inserting a two-dimensionally conjugated fluoro-substituted pyrene into thiophene and selenophene polymeric chains. The broad conjugated plane of pyrene and “Lewis soft” selenium atoms not only enhance the π–π stacking of HTM molecules greatly but also render a strong interaction with the perovskite surface, leading to an efficient charge transport/transfer in both the HTM layer and the perovskite/HTM interface. Note that fluorine substitution adjacent to pyrene boosts the stacking of HTMs towards a more favorable face-on orientation, further facilitating the efficient charge transport. As a result, perovskite solar cells (PSCs) employing PE10 as dopant-free HTM afford an excellent efficiency of 22.3 % and the dramatically enhanced device longevity, qualifying it among the best PSCs based on dopant-free HTMs.

To gain a deeper understanding of the underlying charge processes in dye sensitized photocathodes, lateral electron hopping across dye-sensitized NiO photocathodes was investigated. For dye-sensitized systems, hole hopping across photoanodes has been studied extensively in the literature but no expansive studies on electron hopping in sensitized photocathodes exist today. Therefore, an organic p-type dye (TIP) with donor-linker-acceptor design, showing high stability and electrochemical reversibility, was used to study the electron transfer dynamics (electron-hopping) between dyes with temperature dependent spectroelectrochemistry and computational simulations. Besides intermolecular electron-hopping across the surface with a rate constant in the order of 10(5) s(-1), our results show a second electron hopping pathway between NiO surface states with a rate constant in the order of 10(7) s(-1), which precedes the electron hopping between the dyes. Upon application of a potential step negative enough to reduce both the dye and NiO surface states, the majority of NiO surface states need to be reduced before intermolecular electron transfer can take place. The results indicate that, in contrast to sensitized photoanodes where intermolecular charge transfer is known to influence recombination kinetics, intermolecular charge transport processes in TIP dye sensitized NiO photocathodes is less relevant because the fast electron transport between NiO surface states likely dominates recombination kinetics.

Ab initio molecular dynamics simulations were employed to investigate the regeneration of the oxidized organic dye LEG4+ by the reducing agents Fc0 and Co[(bpy)3]2+. Dynamical Mulliken spin population analyses suggest that the oxidized LEG4+ may be regenerated by Fc0 and Co[(bpy)3]2+ directly in specific configurations providing that the Fe2+ and Co2+ are in a low-spin state. An exponential coupling relation was found between the distance between the dye and the redox mediators. The rate of the LEG4+ regeneration by Fc0 and Co[(bpy)3]2+ ranges between 5.41 mu s-1 similar to 3.80 ps-1 and 0.58 mu s-1 similar to 0.04 ps-1, respectively, which spans the window of all experimentally reported rates.

In the ambition to improve the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs), it will be essential to understand the mechanisms and rates of dye regeneration. Although the mechanism of dye regeneration has been studied by static density functional theory (DFT) and classical molecular dynamics (CMD) simulations, ab initio molecular dynamics simulation (aiMD) has the potential to combine the insights from both methods for a deeper understanding. In this work, a series of aiMD simulations has been performed to study the interaction between an oxidized organic model dye, LEG4, and an electrolyte containing iodide ions as reducing agents. Dynamic Mulliken and natural spin population analyses show that two iodide ions, I-center dot center dot center dot I-, are required for dye regeneration. It was found that a distance between I-center dot center dot center dot I(-)of less than 6.5 angstrom at site 1 benefits from the electrostatic environment of the triphenylamine group of the LEG4 dye, and a corresponding distance of 4.8 angstrom at site 2 is essential for the dye regeneration process to take place. The rate constants of the LEG4 regeneration by two iodine ions range from 10(5) to 10(12) s(-1), spanning a window in which results from both experimental and static theoretical calculations fall. It is also verified that the probability of electron transfer from a radical I-2(-) to the oxidized LEG4 dye is extremely low due to the rapid electron back transfer. However, it has been found that the addition of an additional iodide ion at a distance of 5 angstrom with respect to the radical I-2(-) opens the pathway for the reduction of the oxidized LEG4 dye with an associated formation of I-3(-). The current results highlight the necessity for a dynamical approach for a full understanding of the regeneration process.

Adequate hole mobility is the prerequisite for dopant-free polymeric hole-transport materials (HTMs). Constraining the configurational variation of polymer chains to afford a rigid and planar backbone can reduce unfavorable reorganization energy and improve hole mobility. Herein, a noncovalent conformational locking via S–O secondary interaction is exploited in a phenanthrocarbazole ( PC ) based polymeric HTM, PC6 , to fix the molecular geometry and significantly reduce reorganization energy. Systematic studies on structurally explicit repeats to targeted polymers reveals that the broad and planar backbone of PC remarkably enhances π–π stacking of adjacent polymers, facilitating intermolecular charge transfer greatly. The inserted “Lewis soft” oxygen atoms passivate the trap sites efficiently at the perovskite/HTM interface and further suppress interfacial recombination. Consequently, a PSC employing PC6 as a dopant-free HTM offers an excellent power conversion efficiency of 22.2 % and significantly improved longevity, rendering it as one of the best PSCs based on dopant-free HTMs.

The charge-transport dynamics at the dye-TiO2 interface plays a vital role for the resulting power conversion efficiency (PCE) of dye sensitized solar cells (DSSCs). In this work, we have investigated the charge-exchange dynamics for a series of organic dyes, of different complexity, and a small model of the semiconductor substrate TiO2. The dyes studied involve L1, D35 and LEG4, all well-known organic dyes commonly used in DSSCs. The computational studies have been based on ab initio molecular dynamics (aiMD) simulations, from which structural snapshots have been collected. Estimates of the charge-transfer rate constants of the central exchange processes in the systems have been computed. All dyes show similar properties, and differences are mainly of quantitative character. The processes studied were the electron injection from the photoexcited dye, the hole transfer from TiO2 to the dye and the recombination loss from TiO2 to the dye. It is notable that the electronic coupling/transfer rates differ significantly between the snapshot configurations harvested from the aiMD simulations. The differences are significant and indicate that a single geometrically optimized conformation normally obtained from static quantum-chemistry calculations may provide arbitrary results. Both protonated and deprotonated dye systems were studied. The differences mainly appear in the rate constant of recombination loss between the protonated and the deprotonated dyes, where recombination losses take place at significantly higher rates. The inclusion of lithium ions close to the deprotonated dye carboxylate anchoring group mitigates recombination in a similar way as when protons are retained at the carboxylate group. This may give insight into the performance-enchancing effects of added salts of polarizing cations to the DSSC electrolyte. In addition, solvent effects can retard charge recombination by about two orders of magnitude, which demonstrates that the presence of a solvent will increase the lifetime of injected electrons and thus contribute to a higher PCE of DSSCs. It is also notable that no simple correlation can be identified between high/low transfer rate constants and specific structural arrangements in terms of atom-atom distances, angles or dihedral arrangements of dye sub-units.

A new crosslinked polymer, called P65, with appropriate photo-electrochemical, opto-electronic, and thermal properties, has been designed and synthesized as an efficient, dopant-free, hole-transport material (HTM) for n-i-p type planar perovskite solar cells (PSCs). P65 is obtained from a low-cost and easily synthesized spiro[fluorene-9,9′-xanthene]-3′,6′-diol (SFX-OH)-based monomer X65 through a free-radical polymerization reaction. The combination of a three-dimensional (3D) SFX core unit, hole-transport methoxydiphenylamine group, and crosslinked polyvinyl network provides P65 with good solubility and excellent film-forming properties. By employing P65 as a dopant-free hole-transport layer in conventional n-i-p type PSCs, a power conversion efficiency (PCE) of up to 17.7% is achieved. To the best of our knowledge, this is the first time a 3D, crosslinked, polymeric dopant-free HTM has been reported for use in conventional n-i-p type PSCs. This study provides a new strategy for the future development of a 3D crosslinked polymeric dopant-free HTM with a simple synthetic route and low-cost for commercial, large-scale applications in future PSCs.

The ways to overcome surface charge recombination and poor interface contact are still the central challenges for the development of inorganic-organic hybrid halide perovskite solar cells (PSCs). [6,6]-Phenyl C-61 butyric acid methyl ester (PCBM) is commonly employed in PSCs, but it has some disadvantages including high charge recombination and poor surface coverage. Therefore, the addition of an interfacial engineering layer showing efficient surface passivation, electron extraction, and excellent interface contact can solve the above problems. Furthermore, by employing interface engineering with a spike structure of the energy levels, the reduced energy losses are beneficial to elevating the open-circuit voltage (V-oc) in PSCs. Herein, the linear naphthalene imide dimer containing an indacenodithiophene unit (IDTT2NPI) has been developed as an excellent interface engineering material to strengthen the perovskite performance. The introduction of a spike interface on the top of a methylammonium lead triiodide (MAPbI(3)) film resulted in a high V-oc of 1.12 V with the optimal efficiency reaching 20.2%. The efficiency enhancement can be traced to the efficient surface passivation and enhanced interface contact. The mechanism of IDTT2NPI as the interface engineering layer was investigated by both experiments and theoretical calculations. This work provides a promising naphthalene imide-based interfacial material for high-efficiency and stable PSCs.

Conjugated polymers are regarded as promising candidates for dopant-free hole-transport materials (HTMs) in efficient and stable perovskite solar cells (PSCs). Thus far, the vast majority of polymeric HTMs feature structurally complicated benzo[1,2-b:4,5-b']dithiophene (BDT) analogs and electron-withdrawing heterocycles, forming a strong donor-acceptor (D-A) structure. Herein, a new class of phenanthrocarbazole (PC)-based polymeric HTMs (PC1, PC2, and PC3) has been synthesized by inserting a PC unit into a polymeric thiophene or selenophene chain with the aim of enhancing the π-π stacking of adjacent polymer chains and also to efficiently interact with the perovskite surface through the broad and planar conjugated backbone of the PC. Suitable energy levels, excellent thermostability, and humidity resistivity together with remarkable photoelectric properties are obtained via meticulously tuning the conformation and elemental composition of the polymers. As a result, PSCs containing PC3 as dopant-free HTM show a stabilized power conversion efficiency (PCE) of 20.8% and significantly enhanced longevity, rendering one of the best types of PSCs based on dopant-free HTMs. Subsequent experimental and theoretical studies reveal that the planar conformation of the polymers contributes to an ordered and face-on stacking of the polymer chains. Furthermore, introduction of the "Lewis soft" selenium atom can passivate surface trap sites of perovskite films by Pb-Se interaction and facilitate the interfacial charge separation significantly. This work reveals the guiding principles for rational design of dopant-free polymeric HTMs and also inspires rational exploration of small molecular HTMs.

As the two-dimensional square ice in graphene nanocapillaries 10 was observed by transmission electron microscopy (TEM), a variety of theoretical methods have been applied to explore this phenomenon. However, a satisfactory model has not yet been described. Here, we investigate the structural properties and phase behavior of the confined water in graphene nanocapillaries by using the ABEEM sigma pi polarizable force field (PFF) with the ABEEM-7P water model and ABEEM sigma pi graphene model. The ordered AB-stacked bilayer and ABA-stacked trilayer square ice samples are acquired in 8.0 and 10.2 angstrom graphene nanocapillaries, respectively, at 298 K at a constant volume. Furthermore, the bilayer and trilayer ices demonstrate rhombus-square-triangular ice as the graphene nanocapillary changes from 7.8 to 8.6 and 10.0 to 11.0 angstrom, respectively. The results yielded by using a fixed charge force field with the SPC/E water model are different from those obtained by ABEEM sigma pi PFF. By changing the constant pressure from 0.5 to 1.5 GPa, the monolayer (bilayer) triangular ice is transformed to bilayer (trilayer) square ice in a 6.5 (9.0) angstrom graphene nanocapillary system. Additionally, the van der Waals interactions, density of the confined water, confinement width, polarization effects, and pressure all play decisive roles in the distribution of the confined water. Our study provides some clues for clarifying the experimental consequences of TEM.