Heptazine‐based polymeric carbon nitrides (PCN) are promising photocatalysts for light‐driven redox transformations. However, their activity is hampered by low surface area resulting in low concentration of accessible active sites. Herein, we report a bottom‐up preparation of PCN nanoparticles with a narrow size distribution (ca. 10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months. They allow photocatalysis to be carried out under quasi‐homogeneous conditions. The superior performance of water‐soluble PCN, compared to conventional solid PCN, is shown in photocatalytic H2O2 production via reduction of oxygen accompanied by highly selective photooxidation of 4‐methoxybenzyl alcohol and benzyl alcohol or lignocellulose‐derived feedstock (ethanol, glycerol, glucose). The dissolved photocatalyst can be easily recovered and re‐dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity.

We report results of a combined experimental and computational model study on the interaction of the battery-relevant ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis­(trifluoromethylsulfonyl)­imide ([BMP]+[TFSI]−) with Li on pristine highly oriented pyrolytic graphite (HOPG), which aims at a molecular-/atomic-level understanding of the processes at the electrode|electrolyte interface of Li-ion batteries. Employing mainly X-ray and ultraviolet photoelectron spectroscopy as well as dispersion-corrected density functional calculations (DFT-D), we find intact anion–cation pairs for adsorbed [BMP]+[TFSI]− (sub)­monolayers on HOPG at 300 K and also on lithiated HOPG at 80 K, that is, under conditions where the mobility of Li+ in the bulk is low. Vapor deposition of [BMP]+[TFSI]− on lithiated HOPG at 300 K results in rapid accumulation of Liδ+ at the surface or in the surface region, indicating that deintercalation is activated under these conditions. This is explained by a dynamic equilibrium between bulk Li+ and surface Liδ+, which is established independent of whether Li is deposited as metallic Li0 from the vacuum side or segregates as Li+ from the bulk of lithiated HOPG to the surface and which is shifted to the side of surface Liδ+ by stabilization of these species. Stabilization occurs either by formation of stable Li-containing surface compounds by reactive decomposition mainly of the [TFSI]− anions (Li3N, Li2S, LiF, etc.) or by interaction of partially charged Liδ+ species with [TFSI]− anions in the adlayer. DFT-D calculations reveal that a possible initial step in the reactive decomposition is the transfer of electrons from the HOPG surface covered with Liδ+ into the lowest unoccupied molecular orbital of [TFSI]−, resulting in elongation and cleavage of the S–N bond and finally insertion of Li into it. Alternatively, stabilization of Liδ+ is possible by formation of a polar bond with the oxygen atoms of [TFSI]− within the IL adlayer. The resulting calculated work function decrease ΔΦ with respect to that of the bare graphite (0001) surface is in excellent agreement with experimental observations. The interaction of [BMP]+[TFSI]− and Li at the HOPG interface is considered as the initial stage of the solid|electrolyte interphase formation at the electrode|electrolyte interface in Li-ion batteries.

In spite of the enormous promise that polymeric carbon nitride (PCN) materials hold for various applications, the fabrication of high-quality, binder-free PCN films and electrodes has been a largely elusive goal to date. Here, we tackle this challenge by devising, for the first time, a water-based solÀ gel approach that enables facile preparation of thin films based on poly(heptazine imide) (PHI), a polymer belonging to the PCN family. The solÀ gel process capitalizes on the use of a water-soluble PHI precursor that allows formation of a non-covalent hydrogel. The hydrogel can be deposited on conductive substrates, resulting in formation of mechanically stable polymeric thin layers. The resulting photoanodes exhibit unprecedented photoelectro-chemical (PEC) performance in alcohol reforming and highly selective (~100 %) conversions with very high photocurrents (> 0.25 mA cm À 2 under 2 sun) down to < 0 V vs. RHE. This enables even effective PEC operation under zero-bias conditions and represents the very first example of a 'soft matter'-based PEC system capable of bias-free photoreforming. The robust binder-free films derived from solÀ gel processing of watersoluble PCN thus constitute a new paradigm for high-performance 'soft matter' photoelectrocatalytic systems and pave the way for further applications in which high-quality PCN films are required.

The intercalation and deintercalation of lithium (Li) into / out of graphite(0001), which is a highly important process in Li-ion batteries, was investigated under ultrahigh vacuum conditions as a function of temperature, employing X-ray and ultraviolet photoelectron spectroscopy. Both the up-shifts of the core-level binding energy and the lowering of the work function ΔΦ reveal that heating of a monolayer of the battery-relevant ionic liquid (IL) 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSI]) adsorbed on lithiated graphite at 80 K to >230 K facilitates an accumulation of partially charged Li atoms at the IL-graphite(0001) interface. This is accompanied by a partial IL decomposition, which is associated with the initial stages of the chemical formation of the solid-electrolyte interphase.

Solar hydrogen evolution from water is a necessary step to overcome the challenges of rising energy demand and associated environmental concerns. Low-cost photocatalytic architectures based on polymeric light absorbers coupled...

Heptazine‐based polymeric carbon nitrides (PCN) are promising photocatalysts for light‐driven redox transformations. However, their activity is hampered by low surface area resulting in low concentration of accessible active sites. Herein, we report a bottom‐up preparation of PCN nanoparticles with a narrow size distribution (ca. 10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months. They allow photocatalysis to be carried out under quasi‐homogeneous conditions. The superior performance of water‐soluble PCN, compared to conventional solid PCN, is shown in photocatalytic H2O2 production via reduction of oxygen accompanied by highly selective photooxidation of 4‐methoxybenzyl alcohol and benzyl alcohol or lignocellulose‐derived feedstock (ethanol, glycerol, glucose). The dissolved photocatalyst can be easily recovered and re‐dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity.

Ionic carbon nitrides based on poly(heptazine imides) (PHI) represent a vigorously studied class of materials with possible applications in photocatalysis and energy storage. Herein, for the first time, the photogenerated charge dynamics in highly stable and binder-free PHI photoanodes using in operando transient photocurrents and spectroelectrochemical photoinduced absorption measurements is studied. It is discovered that light-induced accumulation of long-lived trapped electrons within the PHI film leads to effective photodoping of the PHI film, resulting in a significant improvement of photocurrent response due to more efficient electron transport. While photodoping is previously reported for various semiconductors, it has not been shown before for carbon nitride materials. Furthermore, it is found that the extraction kinetics of untrapped electrons are remarkably fast in these PHI photoanodes, with electron extraction times (ms) comparable to those measured for commonly employed metal oxide semiconductors. These results shed light on the excellent performance of PHI photoanodes in alcohol photoreforming, including very negative photocurrent onset, outstanding fill factor, and the possibility to operate under zero-bias conditions. More generally, the here reported photodoping effect and fast electron extraction in PHI photoanodes establish a strong rationale for the use of PHI films in various applications, such as bias-free photoelectrochemistry or photobatteries.

Charge accumulation in photoactive molecules and materials holds great promise in solar energy conversion as it allows for decoupling solar‐driven charging from (dark) redox reactions. In this contribution, light‐driven charge accumulation was investigated for a recently reported novel water‐soluble carbon nitride [K,Na‐poly(heptazine imide); K,Na‐PHI] photocatalyst, which exhibits excellent activity and stability in highly selective photocatalytic oxidation of alcohols and concurrent reduction of dioxygen to H2O2 under quasi‐homogeneous conditions. An excellent charge storage ability of the K,Na‐PHI material was demonstrated, showing an optimal density of accumulated electrons (32.2 μmol of electrons per gram) in the presence of 10 vol % MeOH as a sacrificial electron donor. The long‐lived electrons accumulated under anaerobic conditions as K,Na‐PHI.− radical ions were utilized in interfacial electron transfer to O2 or methyl viologen in a subsequent dark reaction. Ultrafast time‐resolved spectroscopy was employed to reveal the kinetics of charge‐carrier recombination and methanol oxidation. Geminate recombination of electrons and holes within approximately 100 ps was followed by trap‐assisted recombination. The presence of methanol as a sacrificial electron donor accelerated the decay of the transient absorption signal when a static sample was used. This behavior was ascribed to the faster charge recombination in the presence of the radical anions generated after hole extraction. The work suggests that photodriven electron storage in the water‐soluble carbon nitride is enabled by localized trap states, and highlights the importance of the effective electron donor for creating long‐lived photo‐generated carbon nitride radicals.