In situ UV Vis absorption spectroscopy study of the water electrooxidation on cobalt oxide catalysts

Despite the current prominence of cobalt oxides as electrocatalysts for the alkaline oxygen evolution reaction OER , there is a lack of unambiguous demonstration for the presence and the role of Co4 prior to during the OER. Here, we combine electrochemistry with in situ UV Vis absorption spectroscopy to investigate and discuss the previously unaddressed effect of different OH amp; 8722; concentrations in the range from 1 M to 0.016 M on the population of Co4 in thin films of CoOx and its concomitant impact on their OER performance. Evidence for Co4 is provided by in situ X ray absorption spectroscopy. Our UV Vis absorption spectroscopic findings indicate that, not only can the overall redox conversion of Co be qualitatively monitored as a function of potential and OH amp; 8722; concentration, but also the formation of oxidized Co i.e.,Co3 and Co4 assigned to a peak at 800 nm can be more quantitatively tracked in situ via stepped potential spectroelectrochemistry; with their optical signals becoming stronger at higher OH amp; 8722; concentrations above 1.2 V vs. RHE, which is consistent with voltammetric redox couples, indicating an enhancement in Co oxidation state and the consequent predominance of Co4 under conditions of elevated OH amp; 8722; concentrations. Furthermore, the evolved oxygen due to OER does not depend on Co4 or OH amp; 8722; activity at 1.54 V vs. RHE, while a correlation with both Co4 and OH amp; 8722; is identified at 1.59 V vs. RHE. This study not only provides spectral insight into the redox chemistry of Co at OER relevant potentials but also highlights the importance of Co4 in facilitating the alkaline OER at high OH amp; 8722; concentrations and current densitie

Printing of tin perovskite solar cells via controlled crystallization

The urgent need for sustainable electricity has driven progress in solar technologies, with perovskite photovoltaics standing out as a top contender. However, the presence of toxic lead in current perovskite devices necessitates the exploration of alternative materials. This study addresses the challenges associated with tin perovskite fabrication and the industrial scale up of this lead free technology. It introduces a new approach to regulate the key process of crystallization, involving a combination of new additives and a gas pulse to trigger and subsequently control nucleation and crystal growth. In situ optical spectroscopy probed the crystallization and enabled the optimization of the printing conditions. Solar cells were fabricated with a power conversion efficiency of 5.38 for 0.1 cm2, 4.02 for 1 cm2 and 2.31 for 5 cm2 devices. They were tested under indoor lighting conditions and functioned at similar efficiency levels, thereby demonstrating the potential of this technology for commercial applications. Our new crystallization control method for printing Sn perovskites enabled the fabrication of the first Sn based solar cell via slot die coating, which is ideally suited for roll to roll manufacturing. This innovation opens new avenues for the development of fully printed lead free perovskite photovoltaics, contributing significantly to the advancement of sustainable energy technologie

Controlled Formation of Skyrmion Bags

Topologically non trivial magnetic solitons are complex spin textures with a distinct single particle nature. Although magnetic skyrmions, especially those with unity topological charge, have attracted substantial interest due to their potential applications, more complex topological textures remain largely theoretical. In this work, the stabilization of isolated higher order skyrmion bags beyond the prototypical amp; 960; skyrmion in ferromagnetic thin films is experimentally demonstrate, which has posed considerable challenges to date. Specifically, controlled generation of skyrmionium 2 amp; 960; skyrmion , target skyrmion 3 amp; 960; skyrmion , and skyrmion bags with variable topological charge are achieved through the introduction of artificially engineered anisotropy defects via local ion irradiation. They act as preferential sites for the field or laser induced nucleation of skyrmion bags. Remarkably, ultrafast laser pulses achieve a substantially higher conversion rate transforming skyrmions into higher order skyrmion bags compared to their formation driven by magnetic fields. High resolution x ray imaging enables direct observation of the resulting skyrmion bags. Complementary micromagnetic simulations reveal the pivotal role of defect geometry particularly diameter in stabilizing closed loop domain textures. The findings not only broaden the experimental horizon for skyrmion research, but also suggest strategies for exploiting complex topological spin textures within a unified material platform for practical application

Impact of acid etching on surfaces and near surface region in nitrogen plasma terminated polycrystalline diamond

In this study, the influence of tri acid HClO4 H2SO4 HNO3 1 3 4 etching on the surface and near surface chemical properties of radio frequency RF nitrogen plasma terminated polycrystalline diamond PCD surfaces is reported. From the C 1s and N 1s high resolution X ray photoelectron spectroscopy HR XPS measured as a function of photon energy, it is clearly shown that acid etching reduced the thickness of the disordered C sp2 layer created by the nitrogen plasma treatment exposing an upper surface of a larger C sp3 character alongside the formation of C Ox bonds. This is accompanied by a reduction in the nitrogen surface concentration and the N 1s XP peak full width at half maximum FWHM , suggesting a more homogeneous nitrogen bonding to the diamond surface. High resolution electron energy loss spectroscopy HREELS shows that NH ads species produced by the plasma processes are preferentially etched alongside the formation of C O ads , C O ads , and COOC ads species, whereas hydrogen is bonded in various CHy ads configurations. The C K edge NEXAFS spectra show characteristic peaks in the pre edge structure clearly associated with nitrogen bonding. Following acid etching, the intensities of peaks related to defect states are reduced, whereas the diamond second band gap at 302.4 eV increases in intensity. N K edge NEXAFS of the nitrogen plasma terminated surfaces show peaks associated to C N ads and C N ads bonding, which acid etching results in the preferred depopulation of C N ads bond

Observation of distorted tilted conical phase at the surface of a bulk chiral magnet with resonant elastic x ray scattering

We report on various magnetic configurations including spirals and skyrmions at the surface of the magnetic insulator Cu2OSeO3 at low temperatures with a magnetic field applied along 100 using resonant elastic X ray scattering REXS . We observe a well ordered surface state referred to as a distorted tilted conical spiral dTC phase over a wide range of magnetic fields. The dTC phase shows characteristic higher harmonic magnetic satellites in the REXS reciprocal space maps. Skyrmions emerge following static magnetic field cycling and appear to coexist with the dTC phase. Our results indicate that this phase represents a distinct and stable surface state that does not disappear with field cycling and persists until the field strength is increased sufficiently to create the field polarized stat

Boon and Bane of Local Solid State Chemistry on the Performance of LSM Based Solid Oxide Electrolysis Cells

High temperature solid oxide cells are highly efficient energy converters. However, their lifetime is limited by rapid deactivation. Little is known about the local, atomic scale transformation that drive this degradation. Here, reaction induced changes are unraveled at the atomic scale of a solid oxide electrolysis cell SOEC operated for 550 h by combining high resolution scanning transmission electron microscopy with first principles and force field based atomistic simulations. We focus on the structural evolution of lanthanum strontium manganite LSM yttria stabilized zirconia YSZ regions and the corresponding solid solid interface. It is found that the strong inter diffusion of cations leads to the additional formation and growth of a multitude of localized structures such as a solid solution of La Mn, nano domains of secondary structures or antisite defects in the YSZ, as well as a mixed ion and electron conduction region in the LSM and complexion. These local structures can be likewise beneficial or detrimental to the performance, by either increasing the catalytically active area or by limiting the supply of reactants. The work provides unprecedented atomistic insights into the influence of local solid state chemistry on the functioning of SOECs and deepens the understanding of the degradation mechanism in SOECs, paving the way towards nanoscopic rational interface design for more efficient and durable cell

Impact of nitrogen functionalization and porosity on the electrosorption of ionic liquids on templated porous carbons

This study systematically investigates the influence of nitrogen functionalities and their content in nitrogen rich carbon materials, specifically carbon carbon nitride nanohybrids, on their performance as electrode materials in electric double layer capacitors EDLCs operated with ionic liquid electrolyte 1 Ethyl 3 methylimidazolium bis trifluoromethylsulfonyl imide . The loading amounts of cyanamide as carbon nitride precursor as well as the condensation temperature are varied over a wide range to obtain materials with significantly different porosity, nitrogen contents, and chemical properties of the nitrogen species. Thermogravimetric analysis, combustion elemental analysis, gas physisorption, and X ray photoelectron spectroscopy measurements show that the nitrogen loss from carbon nitride starts to become significant between 500 and 600 degrees C and that different nitrogen species are created shifting from more pyridinic forms to graphitic and oxidized nitrogen. For the EDLC application, it is found that the mass specific capacitance is dictated by the specific surface area whereas the capacitance normalized to the specific surface area determined by gas physisorption can be slightly enhanced by the presence of pyridinic nitrogen species. In addition, lowering of the total pore volume leads to higher areal active material loadings and lower dead volume which needs to be filled with electrolyt

Femtosecond charge and spin dynamics in a Co50Pt50 alloy

The use of advanced x ray sources plays a key role in the study of dynamic processes in magnetically ordered materials. The progress in x ray free electron lasers enables the direct and simultaneous observation of the femtosecond evolution of electron and spin systems through transient x ray absorption spectroscopy and x ray magnetic circular dichroism, respectively. Such experiments allow us to resolve the response seen in the population of the spin split valence states upon optical excitation. Here, we utilize circularly polarized ultrashort soft x ray pulses from the new helical afterburner undulator at the free electron laser FLASH in Hamburg to study the femtosecond dynamics of a laser excited CoPt alloy at the Co L3 edge absorption. Despite employing a weaker electronic excitation level, we find a comparable demagnetization for the Co 3d states in CoPt compared to previous measurements on CoPd. This is attributed to the distinctly different spin orbit coupling between 3d and 4d vs 3d and 5d elements in the corresponding alloys and multilayer

Offset Finding of Beamline Parameters on the METRIXS Beamline at BESSY II Using Machine Learning

Beamline alignment is challenging as the beamline components must be set up ideally so that the rays follow the desired optical path. Automated methods using a digital twin allow for faster diagnostics and improved beam properties compared to manual tuning. We introduce an automated method of finding the offsets to improve this digital twin model. These offsets represent the unknown but constant differences between the beamline parameter positions as set up at the physical beamline and the corresponding parameter positions of its digital twin. Our method assumes the capability to execute precise relative movements with a known step size for these parameters, although the absolute position information is unknown. By combining the surrogate model with a global optimizer, we successfully determine offsets for 34 beamline parameters on a simulated METRIXS beamline at the BESSY II synchrotron radiation source in Berli

Size and Surface Effects in the Ultrafast Dynamics of Strongly Cooperative Spin Crossover Nanoparticles

Cooperative photoinduced switching of molecular materials at the nanoscale is still in its infancy. Strongly cooperative spin crossover nanomaterials are arguably the best prototypes of photomagnetic and volume changing materials that can be manipulated by short pulses of light. Open questions remain regarding their non equilibrium dynamics upon light excitation and the role of cooperative elastic interactions in nanoscale systems that are characterized by large surface volume ratios. Femtosecond resolved broadband spectroscopy is performed on nanorods of the strongly cooperative Fe triazole, which undergoes a reversible low spin to high spin HS phase transition amp; 8776;360 K. Supported by density functional theory and mechano elastic Monte Carlo simulations, a marked difference is observed in the photoswitching dynamics at the surface of the nanoparticles compared with the core. Surprisingly, under low excitation lt;2 conditions, there occurs a transient increase in the HS population at the surface on the picosecond time scale, while the HS population in the core decays concomitantly. These results shed light onto the importance of surface properties and dynamical size limits of nanoscale photoresponsive nanomaterials that can be used in a broad range of application