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Metal free carbon nitrogen carbon type hybrid electrocatalysts for peroxide producing oxygen reduction reaction
Get PDFHydrogen peroxide H2O2 is a widely utilized chemical in environmental cleaning, medical disinfection, and chemical engineering. Compared to the traditional anthraquinone oxidation method, the electrocatalytic oxygen reduction reaction ORR has become a promising alternative following the trends towards decentralized production schemes for base chemicals as well as the implementation of renewable energy sources to drive chemical reactions. ORR is attractive for the production of H2O2 due to its environmental friendliness, safety, and reliability. However, its wider application is still restricted by the sluggish reaction kinetics and low selectivity due to the competitive reaction of the oxygen reduction to H2O. In this context, nitrogen rich carbon electrocatalysts with tunable adsorption properties and high electrical conductivity are promising materials for improved selectivity. A precise tailoring of their chemical structure is however required to embed peroxide producing catalytic sites within a conductive environment. Herein, a metal free carbon nitrogen CN type nanoporous carbon loaded onto a carbon matrix CN C was designed as an ORR catalyst for highly selective peroxide synthesis in alkaline media. An average electron transfer number of 2.2 has been determined by the Kouteck Levich analysis, indicating that CN C materials exhibit a high selectivity for electrochemical H2O2 synthesi
Surface accumulation and acid base equilibrium of phenol at the liquid vapor interface
Get PDFWe have investigated the surfactant properties of phenol in aqueous solution as a function of pH and bulk concentration using liquid jet photoelectron spectroscopy LJ PES and surface tension measurements. The emphasis of this work is on the determination of the Gibbs free energy of adsorption and surface excess of phenol and its conjugate base phenolate at the bulk pKa 9.99 , which can be determined for each species using photoelectron spectroscopy. These values are compared to those obtained in measurements well below and well above the pKa, where pure phenol or phenolate, respectively, are the dominant species, and where the Gibbs free energy of adsorption determined from surface tension and LJ PES data are in excellent agreement. At the bulk pKa the surface sensitive LJ PES measurements show a deviation of the expected phenol phenolate ratio in favor of phenol, i.e., an apparent upward shift of the Image ID d4cp02212b t1.gif at the surface. In addition, the Gibbs free energies of adsorption determined by LJ PES at the bulk pKa for phenol and phenolate deviate from those observed for the pure solutions. We discuss these observations in view of the different surface propensity of phenol and phenolate as well as potential cooperative interactions between them in the near surface regio
Chemical Interface Structures in CdS RbInSe2 Cu In,Ga Se2 Thin Film Solar Cell Stacks
Get PDFPerformance enhancing heavy alkali based post deposition treatments PDT of Cu In,Ga Se2 CIGSe thin film solar cells absorbers often induce the formation of a Rb In Se phase on the CIGSe absorber. Co evaporation of an interfacial RbInSe2 RISe layer between buffer and absorber can also benefit cell performance. A detailed analysis of the chemical interface structures in CdS RISe CIGSe layer stacks is performed using hard X ray photoelectron spectroscopy HAXPES . For comparison, stacks without RISe and based on RbF PDT CIGSe absorbers are also studied. When aiming for the direct co evaporation of a RISe layer on the CIGSe absorber, the formation of an additional In Se phase is found. For the RbF PDT CIGSe absorbers, the study only finds small amounts of Rb and no indication for a RISe layer formation. Examining layer stacks prepared via additional chemical bath deposition CBD of CdS reveals a clear impact of the presence of Rb or of Rb containing species on the CIGSe surface. In these cases, an increase of the induction coalescence period is found at the beginning of the CBD buffer layer growth process and the formation of Cd amp; 9472;Se bonds; thereafter, a more compact CdS layer growth is observe
Vapor phase deposition of perovskite photovoltaics short track to commercialization
Get PDFWhile perovskite based photovoltaics PV is progressing toward commercialization, it remains an open question which fabrication technology solution based, vapor based, or combinations will pave the way to faster economic breakthrough. The vast majority of research studies make use of solution processed perovskite thin films, which benefit from a rapid optimization feedback and inexpensive to procure tools in modern research laboratories, but vapor phase deposition processes dominate today s established thin film manufacturing. As research and development of vapor phase processed perovskite thin films are still strongly underrepresented in literature, their full potential is yet to be identified. In this collaborative perspective of academic influenced by industrial views, we convey a balanced viewpoint on the prospects of vapor based processing of perovskite PV at an industrial scale. Our perspective highlights the conceptual advantages of vapor phase deposition, discusses the most crucial process parameters in a technology assessment, contains an overview about relevant global industry clusters, and provides an outlook on the commercialization perspectives of the perovskite technology in genera
The big bang of halide perovskites The starting point of crystallization
Get PDFHybrid halide perovskites HHPs are very promising absorber materials for solar cells due to their high power conversion efficiency and the low cost solution based processing methods. We applied small angle X ray scattering to MAPbI3, FAPbI3 and MAPbBr3 precursor solutions in different solvents GBL, DMF, and mixtures to gain a deeper understanding of the building blocks during the early stage of HHP formation. We present a core shell model where the core is formed by [PbX6] octahedra surrounded by a shell of solvent molecules, which explains the arrangement of the precursors in solution and how the solvent and the halide influence such arrangemen
Structural, Electronic, and Magnetic Curiosities of an Unprecedented Chromate II
Get PDFThe ternary sulfido chromate II , K2[Cr3S4], was synthesized through a straightforward solid state method as the first alkali metal chalcogenido chromate with the formal oxidation state 2, which was verified by X ray absorption spectroscopy. Single crystal diffraction analysis reveals the chromium ions to be coordinated by sulfur in two geometric arrangements square planar and square pyramidal. Both environments are unusual for transition metal complexes with a d4 electron configuration. Structural distortions from the ideal arrangement are present in both coordination environments. Measurement of the magnetic moment indicates a value of 3.60 amp; 956;B per chromium ion, which appears at first glance to contradict the standard ligand field theory. Quantum chemical calculations suggest high spin states for both coordination geometries with a spin delocalization due to Cr Cr interactions, leading to an intermediate spin state with magnetic moment values very close to the experimental results, and attributing the structural distortions as the first example of the Jahn Teller active d4 system with nonoctahedral coordination geometries. The optical, dielectric, and impedance measurement results indicate the potential as a synergic insulator, capacitor, and high dielectric constant materia
Reducing p Doping of Tin Halide Perovskites by Trivalent Cation Doping
No full textWe investigate trivalent doping of tin halide perovskites as a means to decrease p doping and control defect activity. Through density functional theory calculations and experimental characterization, we demonstrate that doping with scandium, lanthanum, and cerium successfully accomplishes Fermi level upshift, reducing background carrier concentration and defect densities, thereby improving material performance. Solar cell fabrication and testing highlight the doping efficacy, with lanthanum delivering increased photocurrent and open circuit voltage compared to control devices, despite being nonoptimized. This research underscores the potential of cation doping in enhancing the functionality of p doped tin perovskites for advanced optoelectronic application
Impact of Ion Migration on the Performance and Stability of Perovskite Based Tandem Solar Cells
Get PDFThe stability of perovskite based tandem solar cells TSCs is the last major scientific technical challenge to be overcome before commercialization. Understanding the impact of mobile ions on the TSC performance is key to minimizing degradation. Here, a comprehensive study that combines an experimental analysis of ionic losses in Si perovskite and all perovskite TSCs using scan rate dependent current voltage J V measurements with drift diffusion simulations is presented. The findings demonstrate that mobile ions have a significant influence on the tandem cell performance lowering the ion freeze power conversion efficiency from gt;31 for Si perovskite and gt;30 for all perovskite tandems to amp; 8776;28 in steady state. Moreover, the ions cause a substantial hysteresis in Si perovskite TSCs at high scan speeds 400 s amp; 8722;1 , and significantly influence the performance degradation of both devices through internal field screening. Additionally, for all perovskite tandems, subcell dominated J V characterization reveals more pronounced ionic losses in the wide bandgap subcell during aging, which is attributed to its tendency for halide segregation. This work provides valuable insights into ionic losses in perovskite based TSCs which helps to separate ion migration related degradation modes from other degradation mechanisms and guides targeted interventions for enhanced subcell efficiency and stabilit
Enhancing Chiroptical Responses in Helical Nanographenes via Geometric Engineering of Double [7]Helicenes
No full textHelical nanographenes with high quantum yields and strong chiroptical responses are pivotal for developing circularly polarized luminescence CPL materials. Here, we present the successful synthesis of novel amp; 960; extended double [7]helicenes ED7Hs where two helicene units are fused at the meta or para position of the middle benzene ring, respectively, as the structural isomers of the reported ortho fused ED7H. The structural geometry of these ED7Hs is clearly characterized by single crystal X ray analysis. Notably, this class of ED7Hs exhibits bright luminescence with high quantum yields exceeding 40 amp; 8201; . Through geometric regulation of two embedded [7]helicene units from ortho , meta to para position, these ED7Hs display exceptional amplification in chiroptical responses. This enhancement is evident in a remarkable approximate fivefold increase in the absorbance and luminescence dissymmetry factors gabs and glum , respectively, along with a boosted CPL brightness up to 176 amp; 8197;M amp; 8722;1 amp; 8201;cm amp; 8722;1, surpassing the performance of most helicene based chiral NGs. Furthermore, DFT calculations elucidate that the geometric adjustment of two [7]helicene units allows the precise alignment of electric and magnetic transition dipole moments, leading to the observed enhancement of their chiroptical responses. This study offers an effective strategy for magnifying the CPL performance in chiral NGs, promoting their expanded application as CPL emitter
Model Catalytic Studies on the Thermal Dehydrogenation of the Benzaldehyde Cyclohexylmethanol LOHC System on Pt 111
No full textWe investigated the dehydrogenation reaction and the thermal robustness of the liquid organic hydrogen carrier LOHC couple benzaldehyde cyclohexylmethanol on a Pt 111 model catalyst in amp; 8197;situ in synchrotron radiation photoelectron spectroscopy and complementary temperature programmed desorption experiments. The system stores hydrogen in a cyclohexyl group and a primary alcohol functionality and achieves an attractive hydrogen storage capacity of 7.0 amp; 8197;mass amp; 8201; . We observed a stepwise dehydrogenation mechanism, characterized by a low temperature dehydrogenation of the alcohol group at 235 amp; 8197;K. However, stability limitations challenge the system s application as reversible hydrogen storage solution, as the resultant aldehyde was found to decompose during the dehydrogenation of its cyclohexyl group between 250 and 350 amp; 8197;K . A comparison of cyclohexylmethanol with the structurally related secondary alcohol 1 cyclohexylethanol; 6.3 amp; 8197;mass amp; 8201; hydrogen revealed a parallel stepwise dehydrogenation pattern for both compounds, but a technically relevant superior thermal robustness of the latter, demonstrating the influence of the alcohol group s substitution degree on the dehydrogenation characteristics of alcohol functionalized LOHCs. Density functional theory calculations are in agreement with the experimentally observed stability tren