Porous Carbon-Based Phase Change Material Host Matrix from Semicoking Wastewater

The capture and storage of solar energy using phase change materials (PCMs) are very important for cost-effective energy management. However, their low thermal conductivity and liquid phase leakage pose persistent challenges for effectively harvesting thermal energy with PCMs. Herein, using semicoking wastewater-derived phenolic resin (SWPR) as the carbon source and potassium hydroxide as activator, hierarchical porous carbon (HPC) materials with abundant porous structures were synthesized to confine the PCM. The HPCs generated microporous and mesoporous layered cavities that provided more space as well as capillary adsorption and physical interaction for PCM storage. Shape-stable phase change composites (PCCs) were then fabricated by vacuum impregnation of the HPCs with paraffin wax to address the problems of low thermal conductivity and liquid melt leakage. The PCCs exhibited high energy storage densities of up to 84.07 J g–1, dimensional stability, excellent thermal cycle stability, and the phase transition enthalpy of around 80.25 J g–1 after 500 heating–cooling cycles. The carbon support increased the thermal conductivity of the optimum PCC by 166% compared to that of pure paraffin wax. This study provides a cost-effective and environmentally friendly method for shape-stable PCMs based on waste-derived porous carbon materials with potential applications in solar–thermal energy storage

Two-Dimensional Mn₃O₄ Nanosheets with Dominant (101) Crystal Planes on Graphene as Efficient Oxygen Catalysts for Ultrahigh Capacity and Long-Life Li–O₂ Batteries

Designing oxygen catalysts with well-defined shapes and high-activity crystal facets is of great importance to boost catalytic performance of Li–O2 batteries but challenging. Herein, we report the facet engineering of an ultrathin Mn3O4 nanosheet (NS) with dominant (101) crystal planes on graphene (Mn3O4 NS/G) as efficient and durable oxygen catalysts for high-performance Li–O2 batteries with ultrahigh capacity and long-term stability. Notably, the Mn3O4 NS/G with the (101) facets and enriched oxygen vacancies offers a lower charge overpotential of 0.86 V than that of Mn3O4 nanoparticles on graphene (1.15 V). Further, the Mn3O4 NS/G cathode exhibits a long-term stability over 1300 h and an ultrahigh specific capacity up to 35,583 mAh g–1 at 200 mA g–1, outperforming most Mn-based oxides for Li–O2 batteries reported. Both the experimental and theoretical results prove the lower adsorption energy of Mn3O4 (101) for Li2O2 in comparison with Mn3O4 (211), manifesting the easier decomposition of Li2O2 during the charging process. This work will open many opportunities to engineer Mn-based materials with a defined crystal facet for high-performance Li–O2 batteries

Precision Engineering of Nano-assemblies in Superfluid Helium by Use of Weak van der Waals Forces

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Assessing the alignment accuracy of state-of-the-art deterministic fabrication methods for single quantum dot devices

The realization of efficient quantum light sources relies on the integration of self-assembled quantum dots (QDs) into photonic nanostructures with high spatial positioning accuracy. In this work, we present a comprehensive investigation of the QD position accuracy, obtained using two marker-based QD positioning techniques, photoluminescence (PL) and cathodoluminescence (CL) imaging, as well as using a marker-free in-situ electron beam lithography (in-situ EBL) technique. We employ four PL imaging configurations with three different image processing approaches and compare them with CL imaging. We fabricate circular mesa structures based on the obtained QD coordinates from both PL and CL image processing to evaluate the final positioning accuracy. This yields final position offset of the QD relative to the mesa center of $\mu_x$ = (-40$\pm$58) nm and $\mu_y$ = (-39$\pm$85) nm with PL imaging and $\mu_x$ = (-39$\pm$30) nm and $\mu_y$ = (25$\pm$77) nm with CL imaging, which are comparable to the offset $\mu_x$ = (20$\pm$40) nm and $\mu_y$ = (-14$\pm$39) nm obtained using the in-situ EBL method. We discuss the possible causes of the observed offsets, which are significantly larger than the QD localization uncertainty obtained from simply imaging the QD light emission from an unstructured wafer. Our study highlights the influences of the image processing technique and the subsequent fabrication process on the final positioning accuracy for a QD placed inside a photonic nanostructure