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Understanding what controls the reaction rate on iridium-based catalysts is central to designing more active and stable electrocatalysts for the water oxidation reaction in proton exchange membrane (PEM) electrolysers. Here, we quantify the densities of redox active centres and probe their binding strengths on amorphous IrOx and rutile IrO2 using a combination of operando time-resolved optical spectroscopy, X-ray absorption spectroscopy (XAS) and time of flight secondary ion mass spectrometry (TOF-SIMs). Firstly, our results show that although IrOx exhibits an order of magnitude higher geometry current density compared to IrO2, the intrinsic rates of reaction per active state, on IrOx and IrO2 are comparable at a given potential. Secondly, we establish a quantitative experimental correlation between the intrinsic rate of water oxidation and the energetics of the active states. We use density functional theory (DFT) based models to provide a molecular scale interpretation of our data. We find that the *O species formed at water oxidation potentials have repulsive adsorbate-adsorbate interactions, and thus increasing their coverage weakens their binding and promotes the rate-determining O-O bond formation. Finally, we provide insights into how the intrinsic water oxidation kinetics can be increased by optimising both the binding energy and the interaction strength of the catalytically active states.

Understanding charge carrier extraction from the perovskite photoactive layer is critical to optimizing the design of perovskite solar cells. Herein, we demonstrate a simple time-resolved photoluminescence method to characterize the kinetics of charge transport across the bulk perovskite and charge transfer from the perovskite layer to the interlayers, elucidating the dependence of these dynamics on film thickness, grain boundaries (GBs), and interlayers. Using asymmetric laser excitation, we selectively probe charge transport by generating charges both close to and far from the heterojunction interface and correlate these results with device performance. We observe that both film thickness and GBs affect the asymmetry between electron and hole charge transport across the bulk perovskite and charge transfer from the bulk perovskite to the respective interlayers.

Objective An estimated 3.8% of the global population experiences depression, according to the [2019] WHO report. Evidence supports the efficacy of exercise training (EX) for depression; however, its comparative efficacy to conventional, evidence-supported psychotherapies remains understudied. Therefore, we conducted a network meta-analysis to compare the efficacy of exercise training (EX), behavioral activation therapy (BA), cognitive-behavioral therapy (CBT), and non-directive supportive therapy (NDST). Methods Our search was performed in seven relevant databases (inception to March 10, 2020) and targeted randomized trialsomparing psychological interventions head-to-head and/or to a treatment as usual (TAU) or waitlist (WL) control for the treatment of adults (18 years or older) with depression. Included trials assessed depression using a validated psychometric tool. Results From 28,716 studies, 133 trials with 14,493 patients (mean age of 45.8 years; 71.9% female) were included. All treatment arms significantly outperformed TAU (standard mean difference [SMD] range, -0.49 to -0.95) and WL (SMD range, -0.80 to -1.26) controls. According to surface under the cumulative ranking (SUCRA) probabilities, BA was mostly likely to have the highest efficacy (1.6), followed by CBT (1.9), EX (2.8), and NDST (3.8). Effect size estimates between BA and CBT (SMD = -0.09, 95% CI = -0.50 to 0.31), BA and EX (-0.22, -0.68 to 0.24), and CBT and EX (-0.12, -0.42 to 0.17) were very small, suggesting comparable treatment effects of BA, CBT, and EX. With individual comparisons of EX, BA, and CBT to NDST, we found small to moderate effect sizes (0.09 to 0.46), suggesting EX, BA, and CBT may equally outperform NDST. Conclusions Findings provide preliminary yet cautionary support for the clinical use of exercise training for adult depression. High study heterogeneity and lack of sound investigations of exercise must be considered. Continued research is needed to position exercise training as an evidence-based therapy.

A deep understanding of defects is essential for the optimisation of materials for solar energy conversion. This is particularly true for metal oxide photo(electro)catalysts, which typically feature high concentrations of charged point defects that are electronically active. In photovoltaic materials, except for selected dopants, defects are considered detrimental and should be eliminated to minimise charge recombination. However, photocatalysis is a more complex process where defects can play an active role, for example, by stabilising charge separation and mediating rate-limiting catalytic steps. Here, we review the behaviour of electronic defects in metal oxides, paying special attention to the principles underpinning the formation and function of trapped charges in the form of polarons. We focus on how defects alter the electronic structure, statically or transiently upon illumination, and discuss the implications of such changes in light-driven catalytic reactions. Finally, we consider the applicability of lessons learned from oxide defect chemistry to new photocatalysts based on carbon nitrides, polymers and metal halide perovskites., Review paper. Nat Rev Mater (2022)

Die Beschlagnahme von Unterlagen über wissenschaftliche Interviews schränkt die Forschungsfreiheit tatsächlich ein, weil sie die Gesprächsbereitschaft von Gesprächspartnern in Frage stellt. Dafür fehlt derzeit im Regelfall, dass der betroffene Forscher die Ergebnisse seiner Forschung publizieren will, angesichts der Ausnahmetatbestände eine gesetzliche Grundlage. Soweit das Gesetz die Beschlagnahme solcher Unterlagen zulässt, ist es Sache der rechtsanwendenden Richter, bei der Anwendung der Rechtsgrundlage Sorge zu tragen, dass keine Grundrechte unverhältnismäßig verkürzt werden.

The covalent attachment of molecules to 2D materials is an emerging area as strong covalent chemistry offers new hybrid properties and greater mechanical stability compared with nanoparticles. A nickel bis-aminothiophenol catalyst was grafted onto a range of 2D carbon nitrides (C3NxHy) to form noble metal-free photocatalysts for H2 production. The hybrids produce H2 beyond 8 days with turnover numbers reaching 1360 based on nickel, a more than 3 fold higher durability than reported molecular catalyst-carbon nitride mixtures, and under longer wavelengths (>475 nm). Time-resolved spectroscopy reveals sub-microsecond electron transfer to the grafted catalyst, six orders of magnitude faster compared with similar reports of non-grafted catalysts. The photoelectrons on the catalyst have a ca. 1000 times longer half-time (7 ms) compared with bare carbon nitride (10 μs). The grafting strategy operates across a range of molecular catalyst-carbon nitride combinations, thus paving the way for robust efficient photocatalysts based on low-cost tunable components., A nickel bis-aminothiophenol catalyst grafted onto a 2D carbon-nitride photocatalytically produces H2 beyond 8 days with turnover numbers reaching 1360.

Transition metal complexes (TMCs) are widely used as light absorbers and catalysts for photochemical energy conversion processes such as photocatalytic reactions in liquid environments. Of particular interest are TMCs which incorporate multiple bridged metal centres because they represent a step towards more complex supramolecular assemblies that can ultimately enable control of the charge flow in solution-based photo-redox processes. However, the development of design guidelines for such molecular assemblies is impeded by an incomplete understanding of the coupling between their electronic and nuclear dynamics, including the interplay of TMCs with their liquid environment upon photoexcitation. Probing the involved processes requires high spatial sensitivity towards electronic motion and the ability to capture atomic motion on ultrafast timescales – a combination which is not readily available for optical transient spectroscopic techniques. X-ray free electron lasers (XFELs) have revolutionized the field of ultrafast science in recent years. XFELs generate tuneable and extremely bright X-ray pulses with a typical pulse duration of 1,2 Applied to TMCs, XFEL probes are sensitive to the local electronic structure in such molecular systems as well as to intra- and inter-molecular structural reorganization at an atomic level.3 In this talk, I will present work on the interaction of a linear trimetallic cyanide-bridged iron-ruthenium complex (FeRuFe) with its solvent environment, carried out using the LCLS XFEL facility at SLAC National Accelerator Laboratory. The focus of this study lies on elucidating how photoinduced intramolecular electron transfer processes in FeRuFe are affected by hydrogen bonding interactions between its cyanide ligands and the surrounding solvent molecules. In water, such solvent-solute hydrogen bonding interactions are stronger for Fe(II) than Fe(III), leading to substantial changes in solute-solvent interactions upon photoinduced electron transfer between metal centres. The experiment is performed in a pump-probe geometry on a liquid jet, where a visible/near-infrared pump induces a metal-to-metal charge transfer (MMCT) between Ru and Fe which is followed by an ultrafast back-electron transfer (BET). The excited state dynamics are monitored using hard X-ray pulses as a function of time delay between the laser pump and the X-ray probe pulses. To resolve and correlate electronic and structural dynamics upon MMCT excitation, we simultaneously perform ultrafast Fe Kβ X-ray emission spectroscopy (XES) and X-ray solution scattering (XSS) measurements, where XES is sensitive to the oxidation and spin state of the Fe centres and XSS provides information on atomic motion in solute and solvent, as demonstrated in previous work on a similar system.4 To evaluate the effect of solute-solvent hydrogen bonding interactions on the electron transfer dynamics, we perform measurements in a series of solvents with different hydrogen bonding properties, including water, methanol, and acetonitrile. We find that the BET increases as a function of decreasing hydrogen bonding ability of the solvent, and that distinct signatures of solvation dynamics are present in the scattering data. The resulting molecular level understanding of solvent reorganization coupled to electron transfer demonstrates that the strength and type of solute-solvent interactions are a central factor in determining the outcome of photoinduced charge transfer processes in TMCs. References Bergmann, U. et al. Using X-ray free-electron lasers for spectroscopy of molecular catalysts and metalloenzymes. Nat. Rev. Phys. 3, 264–282 (2021). Schoenlein, R. et al. Recent advances in ultrafast X-ray sources. Philos. Trans. R. Soc. Math. Phys. Eng. Sci. 377, 20180384 (2019). Gaffney, K. J. Capturing photochemical and photophysical transformations in iron complexes with ultrafast X-ray spectroscopy and scattering. Chem. Sci. 12, 8010–8025 (2021). Biasin, E. et al. Direct observation of coherent femtosecond solvent reorganization coupled to intramolecular electron transfer. Nat. Chem. 13, 343–349 (2021).

The development of materials with high activity for photocatalytic water splitting is a central challenge for the production of renewable hydrogen using sunlight. Owing to advantages such as low cost, elemental abundance, and chemical stability, transition metal oxides (TMOs) are some of the most widely used materials for this purpose. The most efficient systems developed to date reach solar-to-hydrogen conversion efficiencies (STH) of around 1%1 and are based on wide bandgap TMOs such as SrTiO3.2 Because such wide bandgap materials often absorb UV light only, TMOs with extended visible light absorption are key to bridge the activity gap towards the target for commercial applications,3 often considered to be 10% STH. While large research efforts have been devoted to TMOs with smaller bandgaps, efficiencies for such materials have typically remained relatively far from their theoretical limit. For example, Fe2O3 is one of the most studied TMOs in the field of solar fuel production, but it has so far reached only 1/3 of its theoretical maximum activity for water oxidation,4 raising the question of limitations of more fundamental nature. In this talk, I will discuss the links between ultrafast charge recombination and polaron formation in TMOs – two of the main processes considered to impose efficiency limitations. Firstly, Fe2O3, Cr2O3, and Co3O4, which have absorption onsets of around 2.1 eV, 1.9 eV, and 1.6 eV, respectively, are studied using time-resolved optical spectroscopic techniques to probe their excited state dynamics on a timescale of femtoseconds to seconds following light absorption. I will demonstrate how common photophysical features and dynamics suggest a shared pathway for the recombination and localisation of photogenerated charges in these materials, but with different branching ratios. Secondly, a comparison to wide bandgap metal oxides reveals a different relative importance of these recombination and localisation pathways compared to TMOs with smaller bandgaps. Taken together, a more general photophysical model emerges, providing insights into the performance limiting factors in TMOs, including those with extended visible light absorption. References: Wang, Q. et al. Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%. Nat. Mater. 1–3 (2016). Takata, T. et al. Photocatalytic water splitting with a quantum efficiency of almost unity. Nature 581, 411–414 (2020). Chen, S., Takata, T. & Domen, K. Particulate photocatalysts for overall water splitting. Nat. Rev. Mater. 2, 17050 (2017). Kim, J. Y. et al. Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting. Sci. Rep. 3, 2681 (2013).

The design of robust, high‐performance photocatalysts is key for the success of solar fuel production by CO2 conversion. In this study, hypercrosslinked polymer (HCP) photocatalysts have been developed for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly outperforming the benchmark material, TiO2 P25, using only sacrificial H2O. It is hypothesized that superior H2O adsorption capacities facilitate access to photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2. These polymers are an intriguing set of organic photocatalysts, displaying no long‐range order or extended π‐conjugation. The as‐synthesized networks are the sole photocatalytic component, requiring no added cocatalyst doping or photosensitizer, representing a highly versatile and exciting platform for solar‐energy conversion., This is how it fuels: Hypercrosslinked polymers are an intriguing set of organic photocatalysts. They seemingly display no extended π‐conjugation and are able to photoreduce gaseous CO2 to CO using H2O under visible light.

The design of robust, high-performance photocatalysts is key for the success of solar fuel production via CO2conversion. Herein, we present hypercrosslinked polymer (HCP) photocatalysts for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly out-performing the benchmark material, TiO2 P25, using only sacrificial H2O. We hypothesise that superior H2O adsorption capacities led to concentration at photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2. These polymers are an intriguing set of organic photocatalysts, displaying no long-range order or extended pi-conjugation. The as-synthesised networks are the sole photocatalytic component, requiring no co-catalyst doping or photosensitiser, representing a highly versatile and exciting platform for solar-energy conversion.

Most organic semiconductor photocatalysts for solar fuels production are linear polymers or polymeric networks with a broad distribution of molecular weights. Here, we study a series of molecular dibenzo[b,d]thiophene sulfone and fluorene oligomers as well-defined model systems to probe the relationship between photocatalytic activity and structural features such as chain length and planarity. The hydrogen evolution rate was found to vary significantly with bridge head atom, chain length, and backbone twisting. A trimer (S3) of only three repeat units has excellent activity for proton reduction with an EQE of 8.8% at 420 nm, approaching the activity of its polymer analogue and demonstrating that high molar masses are not a prerequisite for good activity. The dynamics of long-lived electrons generated under illumination in the S3 oligomer are very similar to the corresponding polymer, both under transient and quasi-continuous irradiation conditions.

Semiconducting polymers are versatile materials for solar energy conversion and have gained popularity as photocatalysts for sunlight-driven hydrogen production. Organic polymers often contain residual metal impurities such as palladium (Pd) clusters that are formed during the polymerization reaction, and there is increasing evidence for a catalytic role of such metal clusters in polymer photocatalysts. Using transient optical spectroscopies on nanoparticles of F8BT, P3HT, and the dibenzo[b,d]thiophene sulfone homopolymer, P10, we demonstrate how differences in the timescale of electron transfer to Pd clusters translate into hydrogen evolution activity optima at extremely different residual Pd concentrations. For F8BT nanoparticles with common Pd concentrations of >1000 ppm (>0.1 wt. %), we find that residual Pd clusters quench photogenerated excitons via energy and electron transfer on the fs – ns timescale, thus outcompeting reductive quenching via the electron donor diethylamine in the solution phase. We spectroscopically identify reduced Pd clusters in our F8BT nanoparticles from the µs timescale onwards and show that the predominant location of long-lived electrons gradually shifts to the F8BT polymer when the Pd content is lowered. However, a low yield of long-lived electrons limits the hydrogen evolution activity of F8BT. P10, on the other hand, exhibits a substantially higher hydrogen evolution activity, which we demonstrate results from higher yields of long-lived electrons compared to F8BT due to more efficient reductive quenching. Surprisingly, and despite the higher performance of P10, long-lived electrons reside on the P10 polymer rather than on the Pd clusters in P10 particles, even at very high Pd concentrations of 27,000 ppm (2.7 wt. %). We show that these long-lived electrons in P10 react orders of magnitude slower at lower Pd levels, which suggests that their transfer to Pd sites constitutes a kinetic bottleneck and thus reveals a direction towards further improvements for this already very performant material. In contrast, long-lived electrons in F8BT already reside on Pd clusters before the typical timescale of hydrogen evolution. This comparison illustrates that P10 exhibits efficient reductive quenching but slow electron transfer to residual Pd clusters, whereas the opposite is the case for F8BT. We discuss possible reasons for this pronounced difference in the predominant location of long-lived electrons in F8BT and P10. Our results suggest that the development of even more efficient polymer photocatalysts should target materials that combine both rapid reductive quenching and rapid charge transfer to a metal-based co-catalyst.