Physics

High Resolution Image Download MS PowerPoint Slide Contrasting the characteristic properties of PFSAs such as Nafion and hydrocarbon membranes suggests that PEM water electrolysis could become a first showcase for the competitive use of hydrocarbon membranes. The main reasons are high proton conductivity and low hydrogen permeability of many sulfonated polyarylenes and phenylenes under water electrolysis conditions. Within this class of ionomers, we have, therefore, downselected according to thermohydrolytic stability, a conditio sine qua non for the use of membranes in PEM electrolyzers. We identified the family of sulfonated poly(phenylene sulfones) (sPPS) as virtually inert hydrocarbon ionomers. The remaining critical issues of sPPS membranes, especially exaggerated swelling at high ion exchange capacity, softening in hot water ( T = 80 °C) and fatigue under wet/dry cycling conditions, were significantly mitigated by (i) introducing into the homogeneously (ordered) sulfonated polymer structure uniform unsulfonated segments aggregating into well-connected networks counterbalancing osmotic pressure and (ii) introducing ductile polyethylene nanoporous reinforcements serving as fracture toughener. The present rational design approach provided the basis for successful in situ electrolyzer tests of 24 μm thick sPPS-based membranes published in a separate paper. This features lower ohmic losses along with a more than 2-fold reduced hydrogen crossover compared to Nafion 211 and stable operation over 2000 h at a current density of 1 A cm –2 without failure to the end of the test.

Silicon/carbon (Si/C) composites are now the demonstrated successor to graphite as high-energy density lithium-ion battery (LIB) anodes due to the increased capacity of silicon and only slight change to the overall charge/discharge potential and reversibility in optimized cases. However, selection of the scaffold and overall guiding principles for the composite structure remain under active investigation. Herein, three carbon scaffold families spanning a broad phase space of crystallinity and surface area were employed as substrates for silane and acetylene deposition experiments to yield Si/C composites with varying structural characteristics and compositions. Differential thermogravimetric analysis (DTGA) was employed to determine the content of silicon, carbon, and silicon oxide present in each Si/C composite. The silicon environments formed in the composites could be distinctly classified as Type I (intraparticle, nanoscale) or Type II (interparticle, bulk scale) by comparison to a series of pure silicon samples. These classifications were correlated with electrochemical performance, demonstrating that Type I and Type II silicon contents could be relevant predictors for the LIB performance of present and future Si/C composite anodes.

Hydrogels and microscale hydrogels containing micron-scale pores are extensively utilized in diverse fields because of their superior mass transport properties, large surface area, and strong resemblance to biological tissues, making them especially valuable in biomedical applications and devices. For this reason, accurately characterizing their porosity and pore interconnectivity under realistic ambient conditions─rather than the vacuum environments often used in conventional studies─is essential. In this work, the nano- and microstructural features of hydrogels are investigated using ptychographic X-ray computed tomography (PXCT), achieving a spatial resolution of 127 nm and covering a field of view of approximately 100 × 30 μm 2 under ambient conditions. The hydrogel microscopic samples exhibited a modification of the bulk pore size (from ∼0.9 μm) and porosity (from ∼20%) with decreasing thickness (toward ∼0.7 μm and 5%, respectively) and with increasing departure from the bulk region (toward ∼1.2 μm and 30%, respectively). Furthermore, pore throat sizes are estimated to fall mainly below ∼200 nm for narrower connections and 400–500 nm for wider ones. Notably, pore connectivity─and thus transport efficiency─is greater in the out-of-plane direction than in-plane. These findings are critical for understanding transport behavior and performance in real biological environments.

High Resolution Image Download MS PowerPoint Slide This article provides an overview of the studies performed in our laboratories for developing nitrogen-doped carbon nanostructures (CN x ) as precious-metal-free bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts for unitized regenerative fuel cells (URFCs). Additionally, our recent studies exploring the applications of these catalysts in halogen production via oxygen-depolarized cathode (ODC) technology have also been discussed. Future perspectives, challenges, and potential research avenues for exploring these materials as ‘multifunctional’ electrocatalysts have also been highlighted.

Monolayer pentagonal PdTe 2 , recently synthesized experimentally, provides a realistic platform for atomically thin semiconductor devices. In this work, we design p–n junction diodes, p–i–n field‐effect transistors, and p–i–n phototransistors based on monolayer penta‐PdTe 2 . We systematically investigate their electronic and transport properties by using first principles combined with the nonequilibrium Green’s function (NEGF) method. The p–n junction diode exhibits pronounced unidirectional transport, with a reverse‐bias current density of −1084.46 mA/mm at 0.6 V and a high rectification ratio of about 10 17 . Transmission spectra and projected local density of states reveal that the rectification behavior originates from reverse‐bias band‐to‐band tunneling. By introducing an intrinsic channel and gate modulation, the p–i–n field‐effect transistor further enhances the reverse current while suppressing forward leakage, yielding an ultrahigh rectification ratio up to 10 22 . Moreover, the p–i–n phototransistor exhibits a maximum photocurrent density of 64.49 mA/mm 2 under AM1.5 illumination. These results demonstrate that monolayer penta‐PdTe 2 is a promising atomically thin channel material for high‐rectification diodes, gate‐controlled transistors, and optoelectronic detectors.

A comprehensive investigation on the structural, electronic, optical, mechanical, and thermodynamic properties of CsFeX 3 (X = F, Cl, Br, I) using ab initio total energy calculations is performed. These cesium ferrous trihalides exhibit 100% spin polarization, with semiconducting spin‐up electrons and metallic spin‐down electrons. DFT + U calculations using varying strengths of the Coulomb interaction parameter confirm half‐metallic behavior with no band gap opening in the spin‐down band structures. These halides exhibit a strong infra‐red region absorption owing to the intraband d – d spin down electron level transitions of Fe and a high (>4) refractive index. Only CsFeCl 3 and CsFeBr 3 satisfy the Born criteria of mechanical stability. CsFeBr 3 is more ductile, and CsFeCl 3 has a smaller anisotropy in the Poisson’s ratio, shear, and Young’s modulus. CsFeCl 3 is the most promising cesium ferrous trihalide for spintronic and IR‐region optoelectronic device applications, being half‐metallic with good optical, mechanical, and thermodynamic characteristics.

The tribological performance of additively manufactured Ti6Al4V alloy is strongly influenced by its metastable microstructure and surface condition. This work investigates the effect of shot peening with ceramic beads and CrNi steel shots on the friction and wear behavior of DMLS‐fabricated Ti6Al4V under technically dry sliding conditions using a ball‐on‐disc configuration with an Al 2 O 3 counterbody. Shot peening led to a significant increase in surface hardness (up to ∼42%) and a reduction in surface roughness, resulting in lower friction coefficient and wear rate compared to the as‐built condition. Despite similar hardness and roughness levels, distinct tribological responses were observed depending on the peening media. SEM and EDS analyses revealed phase‐dependent wear mechanisms, indicating that shot‐induced redistribution of the metastable α′ and β phases plays a key role in governing wear behavior.

Evaporating refractory metals such as tungsten (W) to grow their corresponding oxides remains challenging for molecular beam epitaxy (MBE) due to their high melting points and low vapor pressures at conventional effusion-cell temperatures. Conventional approaches using oxide precursors like WO3 often suffer from incongruent evaporation and flux instability caused by oxygen loss. Here, we utilize an in situ surface-oxidation method to generate a volatile oxide flux directly from a refractory W metal source for epitaxial tungsten-oxide thin film growth. In this approach, the W metal source is heated under a controlled oxygen partial pressure, dynamically forming and evaporating a surface oxide layer. This process produces a stable, high-purity, and tunable oxide flux at temperatures well below those required for metal evaporation. By controlling the oxygen partial pressure and electron-beam power, we can selectively generate tungsten-oxide species for epitaxial growth. In the low-flux regime (1–3 × 10−3 Å s−1), the deposition rate scales linearly with oxygen partial pressure and remains constant for over an hour, enabling the reproducible growth of ultrathin epitaxial WO3 films. Extending this approach to thermal-laser epitaxy achieves deposition rates up to ∼1.5 Å s−1 while maintaining excellent crystallinity. This surface-oxidation-assisted synthesis approach offers several advantages including the use of high-purity elemental sources, precise flux control, long-term stability, and selective generation of oxide species during growth, providing an alternative pathway for the MBE growth of high-quality oxides involving refractory metals with improved control and reliability.