Ultrafast Real-Time Dynamics of CO Oxidation over an Oxide Photocatalyst

Additive Manufacturing: A Paradigm Shift in Revolutionizing Catalysis with 3D Printed Photocatalysts and Electrocatalysts Toward Environmental Sustainability

Semiconductor-based materials utilized in photocatalysts and electrocatalysts present a sophisticated solution for efficient solar energy utilization and bias control, a field extensively explored for its potential in sustainable energy and environmental management. Recently, 3D printing has emerged as a transformative technology, offering rapid, cost-efficient, and highly customizable approaches to designing photocatalysts and electrocatalysts with precise structural control and tailored substrates. The adaptability and precision of printing facilitate seamless integration, loading, and blending of diverse photo(electro)catalytic materials during the printing process, significantly reducing material loss compared to traditional methods. Despite the evident advantages of 3D printing, a comprehensive compendium delineating its application in the realm of photocatalysis and electrocatalysis is conspicuously absent. This paper initiates by delving into the fundamental principles and mechanisms underpinning photocatalysts electrocatalysts and 3D printing. Subsequently, an exhaustive overview of the latest 3D printing techniques, underscoring their pivotal role in shaping the landscape of photocatalysts and electrocatalysts for energy and environmental applications. Furthermore, the paper examines various methodologies for seamlessly incorporating catalysts into 3D printed substrates, elucidating the consequential effects of catalyst deposition on catalytic properties. Finally, the paper thoroughly discusses the challenges that necessitate focused attention and resolution for future advancements in this domain.

Photoinduced Dynamics at the Water/TiO_{2}(101) Interface

We present a femtosecond time-resolved optical pump-soft x-ray probe photoemission study in which we follow the dynamics of charge transfer at the interface of water and anatase TiO_{2}(101). By combining our observation of transient oxygen O 1s core level peak shifts at submonolayer water coverages with Ehrenfest molecular dynamics simulations we find that ultrafast interfacial hole transfer from TiO_{2} to molecularly adsorbed water is completed within the 285 fs time resolution of the experiment. This is facilitated by the formation of a new hydrogen bond between an O_{2c} site at the surface and a physisorbed water molecule. The calculations fully corroborate our experimental observations and further suggest that this process is preceded by the efficient trapping of the hole at the surface of TiO_{2} by hydroxyl species (-OH), that form following the dissociative adsorption of water. At a water coverage exceeding a monolayer, interfacial charge transfer is suppressed. Our findings are directly applicable to a wide range of photocatalytic systems in which water plays a critical role.

Atom-Specific Probing of Electron Dynamics in an Atomic Adsorbate by Time-Resolved X-Ray Spectroscopy

The electronic excitation occurring on adsorbates at ultrafast timescales from optical lasers that initiate surface chemical reactions is still an open question. Here, we report the ultrafast temporal evolution of x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) of a simple well-known adsorbate prototype system, namely carbon (C) atoms adsorbed on a nickel [Ni(100)] surface, following intense laser optical pumping at 400 nm. We observe ultrafast (∼100  fs) changes in both XAS and XES showing clear signatures of the formation of a hot electron-hole pair distribution on the adsorbate. This is followed by slower changes on a few picoseconds timescale, shown to be consistent with thermalization of the complete C/Ni system. Density functional theory spectrum simulations support this interpretation.

Terahertz-slicing - an all-optical synchronization for 4th generation light sources

A conceptually new approach to synchronizing accelerator-based light sources and external laser systems is presented. The concept is based on utilizing a sufficiently intense accelerator-based single-cycle terahertz pulse to slice a thereby intrinsically synchronized femtosecond-level part of a longer picosecond laser pulse in an electro-optic crystal. A precise synchronization of the order of 10 fs is demonstrated, allowing for real-time lock-in amplifier signal demodulation. We demonstrate successful operation of the concept with three benchmark experiments using a 4th generation accelerator-based terahertz light source, i.e. (i) far-field terahertz time-domain spectroscopy, (ii) terahertz high harmonic generation spectroscopy, and (iii) terahertz scattering-type scanning near-field optical microscopy.

Concluding remarks: Photoelectron spectroscopy and the future of surface analysis

The Faraday Discussion on Photoelectron Spectroscopy and the Future of Surface Analysis was held both in person and virtually in London, April 20-22, 2022. In my concluding lecture I have highlighted three different recent directions in the field; (i) in situ and operando, (ii) buried interfaces and (iii) time resolved measurements. I have based my lecture on most recent studies conducted in my research group in all these 3 directions. In particular, the new operando instrument POLARIS, located at the brightest hard X-ray beamline at DESY for photoelectron spectroscopy, has opened new avenues to address important problems in catalysis that are essential for society to become fossil free.

TiO2 Polarons in the Time Domain: Implications for Photocatalysis

Exploiting the availability of solar energy to produce valuable chemicals is imperative in our quest for a sustainable energy cycle. TiO₂ has emerged as an efficient photocatalyst, and as such its photochemistry has been studied extensively. It is well-known that polaronic defect states impact the activity of this chemistry. As such, understanding the fundamental excitation mechanisms deserves the attention of the scientific community. However, isolating the contribution of polarons to these processes has required increasingly creative experimental techniques and expensive theory. In this Perspective, we discuss recent advances in this field, with a particular focus on two-photon photoemission spectroscopy (2PPE) and density functional theory (DFT), and discuss the implications for photocatalysis.

Impact of vibronic coupling effects on light-driven charge transfer in pyrene-functionalized middle and large-sized metalloid gold nanoclusters from Ehrenfest dynamics

Theoretical calculations are an effective strategy to complement and understand the experimental results in atomistic detail. Ehrenfest molecular dynamics simulations based on the real-time time-dependent density functional tight-binding (RT-TDDFTB) approach are performed to reveal for the first time the electron dynamics for the charge separation of pyrene-functionalized middle-sized Au₇₀S₂₀(PH₃)₁₆ and large-sized Au₁₀₈S₂₄(PR₃)₁₆ (R = H, CH₃, C₂H₅, C₆H₅) clusters. The proposed mechanism uncovers an ultrafast and irreversible photoinduced charge transfer from the gold nanocluster (GNC) unit to the pyrene derivative in all cases. By a Fourier transform analysis of the dynamics, the effect of vibronic couplings is highlighted. The Au₁₀₈S₂₄(PPh₃)₁₅PPh₂Pyr system exhibits the best performance for charge separation.