No abstract

Geo-materials may present varying mechanical properties under different stress paths, especially for tunnel excavation, which is typically characterized by the decreased radial stress and increased axial stress during the complex loading and unloading process. This study carried out a comparative analysis between the loading and unloading model testing, which was then combined with PFC2D simulation, aiming to reveal the fracture propagation pattern, microscopic stress and force chain distribution of the rock mass surrounding the tunnel. Comparisons of extents and development of tensile strain between loading and unloading testing results were made. The overall stability, the integrity of rock mass, and the failure pattern transition under loading and unloading processes were systematically examined. In addition, for the two unloading cases with different vertical stresses imposed, the failure patterns were both identified as the collapse of the V − shaped extruded sidewall, due to the coupling of the shear failure and the vertical tensile failure in the sidewall wedge.

One of the key challenges of integrated energy storage devices is to develop a simple, low‐cost, and environmental‐friendly planar patterning technology. Herein, an ingenious and feasible laser‐engraved flash foam–assisted stamp technique of preparing flexible paper‐based planar‐integrated micro‐supercapacitors based on interdigital electrodes of self‐depositing electrochemically exfoliated graphene is proposed. The as‐synthesized flexible paper‐based planar‐integrated graphene micro‐supercapacitors exhibit excellent electrochemical performances with a remarkable area‐specific capacitance of 3.1 mF cm−2, and an excellent cycling stability in that capacitance retention reaches 95.8% even after 10 000 cycles. Furthermore, the paper‐based graphene micro‐supercapacitors are bent at different angles without significant electrochemical performance loss, and thus have outstanding mechanical flexibility. Therefore, such flexible paper‐based planar‐integrated graphene micro‐supercapacitors are expected to be applied in flexible wearable and portable electronics.

Oxygen reduction reaction (ORR) is an important half reaction in many renewable energy conversion and storage sources. The development of efficient, cost‐effective and durable non‐precious ORR catalysts with their catalytic efficiencies close to expensive Pt‐based catalysts is promising towards large‐scale practical applications of fuel cells and metal‐air batteries. Herein, we report a facile and scalable in‐situ synthesis of Fe3O4 nanoparticles supported on carbon nanotubes hybrid material using arc‐discharge method in low‐pressure air and use Fe3O4/CNTs hybrid as a highly efficient ORR electrocatalyst. The as‐synthesized Fe3O4/CNTs catalyst shows excellent ORR catalytic activity with its performance close to or even better than the commercial 20wt% Pt/C in alkaline media due to the synergistic effect between Fe3O4 and CNTs. This study provides a new insight into non‐precious metal ORR catalysts that are feasible in alkaline membrane fuel cells and metal‐air batteries.