In Situ X-ray Absorption Spectroscopy of Metal/Nitrogen-doped Carbons in Oxygen Electrocatalysis

Metal/nitrogen-doped carbons (M−N−C) are promising candidates as oxygen electrocatalysts due to their low cost, tunable catalytic activity and selectivity, and well-dispersed morphologies. To improve the electrocatalytic performance of such systems, it is critical to gain a detailed understanding of their structure and properties through advanced characterization. In situ X-ray absorption spectroscopy (XAS) serves as a powerful tool to probe both the active sites and structural evolution of catalytic materials under reaction conditions. In this review, we firstly provide an overview of the fundamental concepts of XAS and then comprehensively review the setup and application of in situ XAS, introducing electrochemical XAS cells, experimental methods, as well as primary functions on catalytic applications. The active sites and the structural evolution of M−N−C catalysts caused by the interplay with electric fields, electrolytes and reactants/intermediates during the oxygen evolution reaction and the oxygen reduction reaction are subsequently discussed in detail. Finally, major challenges and future opportunities in this exciting field are highlighted.</p

Photoelectrocatalytic conversion of CO2 : application of transition metal functionalised diamond particles

The electronic properties of diamond can not only be influenced by its termination, but also by different surface functionalisations. We present the immobilisation of transition metal complexes on linker-functionalised nanodiamond particles using the concept of click-chemistry. The resulting conjugates have been characterised using various spectroscopic methods investigating the influence on the electronic structure of the particles

Pyrophosphonate Covalent Organic Frameworks

Herein, we report a new family of covalent organic frameworks (COFs), namely pyrophosphonate-COFs, constructed via pyrophosphonate linkages. Pyrophosphonate-COFs can be synthesized via a single-step condensation reaction of the charge-assisted hydrogen-bonded organic framework (HOF) GTUB5, which is constructed from phenylphosphonic acid and 5,10,15,20‐tetrakis[p‐phenylphosphonic acid] porphyrin. The reported pyrophosphonate-COF, which we call GTUB5-COF was synthesized by simply heating its two-linker HOF precursor GTUB5 without using chemical reagents. GTUB5-COF exhibits good water and water vapor stability during the gas sorption measurements. Furthermore, GTUB5-COF exhibits exceptional electrochemical stability in 0.5 M Na2SO4 electrolyte in water. The formation of pyrophosphonate bonds upon heating was confirmed by magic angle spinning nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, and mass spectrometry coupled with thermal analysis. The condensed product pyrophosphonate-COF can efficiently adsorb CO2. It has a more favorable heat of adsorption value for CO2 capture at lower pressures than water vapor, making it a suitable candidate for selective CO2 capture in the presence of water vapor. The absorption and emission of GTUB5-COF are governed by localized transitions (Soret and Q bands) within the porphyrin unit, which results in broad-banded fluorescence in the near-infrared range at around 800 nm

Photoelectrocatalytic conversion of CO2 by transition metal functionalized diamond nanoparticles under solar illumination

Overcoming the energy barrier in CO2 reduction is a key avenue in the development of sustainable carbon capture and recycling systems spearheading against the climate emergency. Diamond, a wide-bandgap material, has shown promise in this aspect due its ability to produce highly reductive solvated electrons when irradiated with deep UV light. This requirement for high-energy optical illumination, however, hampers its sustainable application and limits its useful lifetime. Here we show the photosensitization of nanoscale detonation diamond in reductive photoelectrocatalysis through surface functionalisation with a ruthenium-based dye, demonstrating solar-light driven turnover of CO2 using the unique properties of diamond. The hybrid photosensitizer-nanodiamond materials demonstrated good colloidal and photochemical stability. The nature of electronic conjugation between diamond and photosensitizer was elucidated through X-ray absorption, transient optical absorption, and ultraviolet photoemission spectroscopies, with CO2 turnover significantly improved under solar conditions for photosensitized systems. The potential for photoexcited electron transfer (PET) mediated photosensitization in reductive diamond catalysis opens the way for further sustainable applications using diamond as a sustainable photoelectrocatalyst