Ammonia is traditionally an essential chemical for fertilizers and other nitrogencontaining products that have been supporting most of the world population for over a century. Recently, ammonia is receiving renascent attentions as a potential hydrogen storage medium and carbon-free fuel, due to its advantages of easy liquefication to achieve a higher volumetric energy density and more facile transportation as compared with other gas-based fuels. [1] Conventionally, the industry-scale production of ammonia, based on the Habor-Bosch method through a nitrogen reduction reaction (NRR), is high-cost, energy-intensive, and environmentally unfriendly, as it not only consumes a large amount of fossil energy but also is associated with the release of Electrochemical nitrogen reduction reaction (NRR) over nonprecious-metal and single-atom catalysts has received increasing attention as a sustainable strategy to synthesize ammonia. However, the atomic-scale regulation of such active sites for NRR catalysis remains challenging because of the large distance between them, which significantly weakens their cooperation. Herein, the utilization of regular surface cavities with unique microenvironment on graphitic carbon nitride as "subnano reactors" to precisely confine multiple Fe and Cu atoms for NRR electrocatalysis is reported. The synergy of Fe and Cu atoms in such confined subnano space provides significantly enhanced NRR performance, with nearly doubles ammonia yield and 54%-increased Faradic efficiency up to 34%, comparing with the single-metal counterparts. First principle simulation reveals this synergistic effect originates from the unique Fe-Cu coordination, which effectively modifies the N 2 absorption, improves electron transfer, and offers extra redox couples for NRR. This work thus provides new strategies of manipulating catalysts active centers at the sub-nanometer scale.

The exploration of sodium ion batteries (SIBs) is a profound challenge due to the rich sodium abundance and limited supply of lithium on earth. Here, amorphous SnO2/graphene aerogel (a‐SnO2/GA) nanocomposites have been successfully synthesized via a hydrothermal method for use as anode materials in SIBs. The designed annealing process produces crystalline SnO2/graphene aerogel (c‐SnO2/GA) nanocomposites. For the first time, the significant effects of SnO2 crystallinity on sodium storage performance are studied in detail. Notably, a‐SnO2/GA is more effective than c‐SnO2/GA in overcoming electrode degradation from large volume changes associated with charge–discharge processes. Surprisingly, the amorphous SnO2 delivers a high specific capacity of 380.2 mAh g−1 after 100 cycles at a current density of 50 mA g−1, which is almost three times as much as for crystalline SnO2 (138.6 mAh g−1). The impressive electrochemical performance of amorphous SnO2 can be attributed to the intrinsic isotropic nature, the enhanced Na+ diffusion coefficient, and the strong interaction between amorphous SnO2 and GA. In addition, amorphous SnO2 particles with the smaller size better function to relieve the volume expansion/shrinkage. This study provides a significant research direction aiming to increase the electrochemical performance of the anode materials used in SIBs.

Transient heat transfer problems with phase-changes, also known as the ''Stefan problems'' or ''movingboundary problems,'' are practically significant in many engineering and technological fields. Injection molding, one of the most widely used plastics processing techniques, mainly consists of filling, packing, and cooling, and the cooling stage is crucial since it considerably affects the productivity and quality of the molded parts. Thus, solutions for transient phase-change heat conduction problems during injection molding will be instructive. In this article, the enthalpy transforming scheme proposed by Cao and Faghri, which could handle the Stefan problems for generalized multidimensional phase-change structures, is applied coupled with the control-volume/finite-difference techniques. Considering the polydispersity and hierarchical structures, the polymer extended phase change temperature range or mushy zone was included in the two-dimensional enthalpy formulation to forecast the transient phase-change heat conduction during the cooling stage for injection-molded high density polyethylene (HDPE) parts. Experiments were performed and good agreement has been achieved, which reveals that the enthalpy transforming model gives good prediction, especially for the cooling analysis for the injection molding of thick-walled parts of crystalline polymers. The understanding of the phase-change heat conduction characteristics may facilitate the optimal designs of polymer injection molding process for industrial applications.

A nanocomposite anode material for lithium batteries is designed and fabricated by the insertion of graphite nanosheets (GNS) into the ceramic network of silicon oxycarbide (SiOC) ceramics for the development of structurally and electrochemically stable lithium batteries. The GNS forms a layered phase in the SiOC ceramic network from the self-assembly of graphite oxides (GO) introduced in a polysiloxane precursor through thermal transformations after pyrolysis. The composite anode (GNS/ SiOC) exhibits an initial discharge capacity attaining 1141 mAh g À1 . The discharging capacity decreases in the first eight cycles and stays at 364 mAh g À1 in the following cycles. This reversible discharging capacity is higher than that of a graphite reference (328 mAh g À1 ) and a SiOC monolithic. Correlating the discharge capacities to the material compositions and structures suggest that the interface between SiOC and GNS contributes to the enhanced capacity of the composite anode, in addition to those from GNS and SiOC. Further increasing the electrochemical performance is possible by the increase of the amount of GNS in the composite.

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