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Role of Fe decoration on the oxygen evolving state of Co3O4 nanocatalysts
No full textThe production of green hydrogen through alkaline water electrolysis is the key technology for the future carbon neutral industry. Nanocrystalline Co3O4 catalysts are highly promising electrocatalysts for the oxygen evolution reaction and their activity strongly benefits from Fe surface decoration. However, limited knowledge of decisive catalyst motifs at the atomic level during oxygen evolution prevents their knowledge driven optimization. Here, we employ a variety of operando spectroscopic methods to unveil how Fe decoration increases the catalytic activity of Co3O4 nanocatalysts as well as steer the near surface active state formation. Our study shows a link of the termination dependent Fe decoration to the activity enhancement and a significantly stronger Co3O4 near surface structural adaptation under the reaction conditions. The near surface Fe and Co O species accumulate an oxidative charge and undergo a reversible bond contraction during the catalytic process. Moreover, our work demonstrates the importance of low coordination surface sites on the Co3O4 host to ensure an efficient Fe induced activity enhancement, providing another puzzle piece to facilitate optimized catalyst desig
Correction to Interfacial Chemistry in the Electrocatalytic Hydrogenation of CO2 over C Supported Cu Based Systems
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Nitrogen Terminated Milled Nanodiamond Surfaces by Plasma Exposure
No full textThis study investigates surface modifications of hydrogen terminated milled nanodiamond H MND drop cast films by microwave MW and radio frequency RF nitrogen plasma exposures. The RF N2 damaging plasma treatment results in the highest nitrogen adsorption amp; 8764;7.5 at. followed by MW N2 amp; 8764;4.2 at. and RF N2 nondamaging amp; 8764;3.8 at. plasma treatments. Upon MW N2 plasma exposure, nitrogen predominantly adsorbs in C N C amp; 9552;N and NH states, whereas RF N2 treatments result in mixed C N C amp; 9552;N, C amp; 8801;N, and NH states, as revealed by electron spectroscopy. Crystalline edges strongly influence N, H, and O adsorption onto MND and act as active adsorption sites. The NH ads concentration is notably higher on MND surfaces compared to that on poly single crystalline surfaces, likely favored by the additional bonding configuration of hydrogen on the MND. NH ads species desorbed upon vacuum annealing in the 500 700 C range, leaving CN adsorbed species onto the MND surfaces. The nitrogen and oxygen concentration monotonically decreases with annealing temperatures from 300 to 1000 C. Upon high temperature annealing, partial recovery of the MND surfaces occurs, depending on plasma exposure conditions. This study may be critical in all ex situ applications influenced by the near surface physicochemical and electronic properties of nitrogen terminated MND surfaces, such as NV centers in nanocrystal
Machine learning assisted equivalent circuit identification for dielectric spectroscopy of polymers
Get PDFPolymers have become indispensable across fields of application, and understanding their structure property relationships and dynamic behaviour is essential for performance optimization. Polymer membranes, particularly ion exchange membranes, play a crucial role in renewable energy conversion technologies, fuel cells, solar energy conversion, and energy storage. In this context, broadband dielectric spectroscopy BDS offers a powerful, non destructive approach to investigate the electrical response and relaxation dynamics of polymers. These properties are investigated by parametrizing the system s impedance response in terms of a network of circuit elements, i.e. the electrical equivalent circuit EEC , whose impedance resembles the one of the system under investigation. However, the determination of the EEC from BDS data is challenging due to system complexity, interdependencies of circuit elements, and researcher biases. In this work, we propose a novel approach that incorporates a convolutional neural network CNN model to predict the EEC topology. By reducing user bias and enhancing data analysis, this approach aims to make BDS accessible to both experienced users and those with limited expertise. We show that the combination of machine learning and BDS provides valuable insights into the dynamic behaviour of polymer membranes, thus facilitating the design and characterization of tailored polymers for various applications. We also show that our model outperforms state of the art machine learning methods with a top 5 accuracy of around 80 for predicting the circuit topology and a parameter fitting error as low as 0.0
Ultrafast Electron Dynamics at the P rich Indium Phosphide TiO2 Interface
Get PDFThe current efficiency records for generating green hydrogen via solar water splitting are held by indium phosphide InP based photo absorbers, protected by TiO2 layers grown through atomic layer deposition ALD . InP is also a leading material for photonic integrated circuits and computing, where ultrafast near surface behavior is key. A previous study described electronic pathways at the phosphorus rich P rich surface of p doped InP 100 using time resolved two photon photoemission tr 2PPE spectroscopy. Here, the intricate electron pathways of the P rich InP surface modified with ALD deposited TiO2 are explored. Photoexcited bulk InP electrons migrate through a bulk to surface transition cluster of states and surface states and inject into the TiO2 conduction band CB . Energy levels and occupation dynamics of CB states in P rich InP and TiO2 adlayers are observed, with discrete states preserved up to 10 nm TiO2 deposition. Thermalization lifetimes of excited electrons gt; 0.8 eV above the InP conduction band minimum CBM are preserved for layer thicknesses up to 2.5 nm. Annealing at 300 C to achieve crystalline TiO2 reconstructions destroys interfacial states, affecting charge transfer. These observations enable innovative engineering of the P rich InP TiO2 heterointerface, opening new possibilities for studying hot carrier extraction, adsorbate effects, surface plasmons, and improving photovoltaic and PEC water splitting devices
Electronic Structure and Stability of the Active Surface Phase of NixCo3 xO4 Spinel Alkaline O2 Evolution Electrocatalysts From an Epitaxial Model Catalyst Perspective
No full textIn this work, we investigate the relationship between the surface stability, electronic structure of Ni3 hole states, and oxygen evolution reaction OER activity in epitaxially grown NixCo3 xO4 x 0, 0.3, 1.0 model electrocatalysts through analysis of their electronic structure before and after electrochemical treatments. The use of flat, structurally well defined models allows us to apply advanced characterization methods, not applicable to powder catalysts. The OER activity of all NixCo3 xO4 samples increases consistently upon cyclic voltammetry CV between 1.22 V and 1.92 V vs RHE with proceeding cycles. Quasi in situ synchrotron X ray photoemission spectroscopy SXPS results show a gradual upshift of the Fermi level EF for all NixCo3 xO4 after proceeding with the OER electrochemical treatment, while near edge X ray absorption fine structure spectroscopy NEXAFS of the O K edge as well as the Co and Ni L edges show no significant changes in the hole state structure near the conduction band minimum as well as the oxidation state of Ni and Co upon the OER treatment. A combination of atomic force microscopy, spectroscopic ellipsometry, X ray diffraction, and X ray reflectivity measurements reveals that the surface of NixCo3 xO4 reconstructs and builds up oxygen deficiency upon OER treatment. While the upshift of the Fermi level is disadvantageous for the OER, the emerging oxygen deficiency together with morphology changes lead to an overall increase of OER activit
Growth of Ba2CoWO6 single crystals and their magnetic, thermodynamic and electronic properties
Get PDFThis study explores the bulk crystal growth, structural characterization, and physical property measurements of the cubic double perovskite Ba2CoWO6 BCWO . In BCWO, Co2 ions form a face centred cubic lattice with non distorted cobalt octahedra. The compound exhibits long range antiferromagnetic order below TN 14 K. Magnetization data indicated a slight anisotropy along with a spin flop transition at 10 kOe, a saturation field of 310 kOe and an ordered moment of 2.17 amp; 956;B at T 1.6 K. Heat capacity measurements indicate an effective j 1 2 ground state configuration, resulting from the combined effects of the crystal electric field and spin orbit interaction. Surface photovoltage analysis reveals two optical gaps in the UV Visible region, suggesting potential applications in photocatalysis and photovoltaics. The magnetic and optical properties highlight the significant role of orbital contributions within BCWO, indicating various other potential application
Finite temperature tensor network algorithm for frustrated two dimensional quantum materials
Get PDFAimed at a more realistic classical description of natural quantum systems, we present a two dimensional tensor network algorithm to study finite temperature properties of frustrated model quantum systems and real quantum materials. For this purpose, we introduce the infinite projected entangled simplex operator ansatz to study thermodynamic properties. To obtain state of the art benchmarking results, we explore the highly challenging spin 1 2 Heisenberg antiferromagnet on the Kagome lattice, a system for which we investigate the melting of the magnetization plateaus at finite magnetic field and temperature. Making a close connection to actual experimental data of real quantum materials, we go on to studying the finite temperature properties of Ca10Cr7O28. We compare the magnetization curve of this material in the presence of an external magnetic field at finite temperature with classically simulated data. As the first theoretical tool that incorporates both thermal fluctuations as well as quantum correlations in the study of this material, our work contributes to settling the existing controversy between the experimental data and previous theoretical works on the magnetization proces
ZP2 cleavage blocks polyspermy by modulating the architecture of the egg coat
No full textFollowing the fertilization of an egg by a single sperm, the egg coat or zona pellucida ZP hardens and polyspermy is irreversibly blocked. These events are associated with the cleavage of the N terminal region NTR of glycoprotein ZP2, a major subunit of ZP filaments. ZP2 processing is thought to inactivate sperm binding to the ZP, but its molecular consequences and connection with ZP hardening are unknown. Biochemical and structural studies show that cleavage of ZP2 triggers its oligomerization. Moreover, the structure of a native vertebrate egg coat filament, combined with AlphaFold predictions of human ZP polymers, reveals that two protofilaments consisting of type I ZP3 and type II ZP1 ZP2 ZP4 components interlock into a left handed double helix from which the NTRs of type II subunits protrude. Together, these data suggest that oligomerization of cleaved ZP2 NTRs extensively cross links ZP filaments, rigidifying the egg coat and making it physically impenetrable to sper
Reactivity and Stability of Reduced Ir Weight TiO2 Supported Oxygen Evolution Catalysts for Proton Exchange Membrane PEM Water Electrolyzer Anodes
No full textReducing the iridium demand in Proton Exchange Membrane Water Electrolyzers PEM WE is a critical priority for the green hydrogen industry. This study reports the discovery of a TiO2 supported Ir IrO OH x core shell nanoparticle catalyst with reduced Ir content, which exhibits superior catalytic performance for the electrochemical oxygen evolution reaction OER compared to a commercial reference. The TiO2 supported Ir IrO OH x core shell nanoparticle configuration significantly enhances the OER Ir mass activity from 8 to approximately 150 A gIr 1 at 1.53 VRHE while reducing the iridium packing density from 1.6 to below 0.77 gIr cm 3. These advancements allow for viable anode layer thicknesses with lower Ir loading, reducing iridium utilization at 70 LHV from 0.42 to 0.075 gIr kW 1 compared to commercial IrO2 TiO2. The identification of the Ir IrO OH x TiO2 OER catalyst resulted from extensive HAADF EDX microscopic analysis, operando XAS, and online ICP MS analysis of 30 80 wt Ir TiO2 materials. These analyses established correlations among Ir weight loading, electrode electrical conductivity, electrochemical stability, and Ir mass based OER activity. The activated Ir IrO OH x TiO2 catalyst support system demonstrated an exceptionally stable morphology of supported core shell particles, suggesting strong catalyst support interactions CSIs between nanoparticles and crystalline oxide facets. Operando XAS analysis revealed the reversible evolution of significantly contracted Ir O bond motifs with enhanced covalent character, conducive to the formation of catalytically active electrophilic OI ligand species. These findings indicate that atomic Ir surface dissolution generates Ir lattice vacancies, facilitating the emergence of electrophilic OI species under OER conditions, while CSIs promote the reversible contraction of Ir O distances, reforming electrophilic OI and enhancing both catalytic activity and stabilit