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The implementation of electrochemical water splitting demands the development and application of electrocatalysts to overcome sluggish reaction kinetics of hydrogen/oxygen evolution reaction (HER/OER). Hollow nanostructures, particularly for hollow heterostructured nanomaterials can provide multiple solutions to accelerate the HER/OER kinetics owing to their advantageous merit. Herein, the recent advances of hollow heterostructured nanocatalysts and their excellent performance for water splitting are systematically summarized. Starting by illustrating the intrinsically advantageous features of hollow heterostructures, achievements in engineering hollow heterostructured electrocatalysts are also highlighted with the focus on structural design, interfacial engineering, composition regulation, and catalytic evaluation. Finally, some perspective insights and future challenges of hollow heterostructured nanocatalysts for electrocatalytic water splitting are also discussed.

The hard and stiff strata (key strata) bear the overburden load in the form of a voussoir beam structure (VBS) after break. The VBS affects both the surface subsidence and the stope underground pressure. Therefore, the reasonable method to predict the surface subsidence is based on the whole subsidence formulae of the VBS. This study first establishes the subsidence formulae of the VBS analytically. The influence of the block length on the subsidence curve and the VBS level on the zero-subsidence range are then analyzed based on the subsidence formulae of the VBS. The results show the half-subsidence curve of the VBS is an S-shaped curve. The block length hardly affects the S-shaped subsidence curve determined by the width of the undercompacted zone. Furthermore, a greater undercompacted zone width corresponds to a greater offset distance of the inflection point. The higher the VBS level, the farther the zero-subsidence range, and the flatter the subsidence curve. The subsidence of the highest VBS can approximately represent the surface subsidence when the topsoil is thin enough.

Oxygen evolution reaction (OER) is regarded as the rate determining step of electrocatalytic overall water splitting, enabling the OER electrocatalysts should meet the standards of high activity, low cost, good...

Strata movement boundary is not only a parameter for the prediction of overburden strata movement and deformation but also a key index of setting shafts, roadways and protective coal pillars. Based on physical and mechanical properties of rock mass, the overburden strata are divided into bedrock and unconsolidated stratum. By means of theoretical analysis, physical simulation and numerical simulation, this paper studies the movement boundary shapes of bedrock and unconsolidated stratum, builds fitting equations of movement boundary of the two, analyzes the influence of key strata (KS) on the shape of strata movement boundary, and determines the principle of setting protective coal pillars. The results show that the movement boundaries of bedrock and unconsolidated strata are located at the outside of coal mining boundary. They are concave-upward power function curves that cannot be merged into a smooth one due to their different mechanisms of movement and deformation. The movement boundary of bedrock can approximate a straight line when lithology of the overburden is relatively uniform with thin strata in different positions; the surface movement boundary extends when the overburden has thick and stiff KS that are common in deeply buried coal seam. Therefore, the width of protective coal pillar is small if the movement boundary is regarded as a straight line. According to the curve movement boundary, the protective coal pillar for the passenger roadway of Panel 31010 of Pingdingshan No.1 mine is at least 99.4 m in width, larger than the designed one, which is the actual reason for its deformation and breakage.

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