The method of fabricating nonprecious metal electrocatalysts with high activity and durability through a facile and eco-friendly procedure is of great significance to the development of low-cost fuel cells and metal-air batteries. Herein, we present that an ancient chemical reaction of "Pharaoh's snakes" can be a fast and convenient technique to prepare Fe-/N-doped carbon (Fe/N-C) nanosheet/nanotube electrocatalysts with sugar, soda, melamine, and iron nitrate as precursors. The resultant Fe/N-C catalyst has a hierarchically porous structure, a large surface area, and uniformly distributed active sites. The catalyst shows high electrocatalytic activities toward both the oxygen reduction reaction with a half-wave potential of 0.90 V (vs reversible hydrogen electrode) better than that of Pt/C and the oxygen evolution reaction with an overpotential of 0.46 V at the current density of 10 mA cm comparable to that of RuO. The activity and stability of the catalyst are also evaluated in primary and rechargeable Zn-air batteries. In both conditions, three-dimensional Fe/N-C exhibited performances superior to Pt/C. Our work demonstrates a success of utilizing an ancient science to make a state-of-the-art electrocatalyst.

High volumetric energy and power densities are crucial for Li-ion batteries, which are however hindered by the loose structure and/or insufficient conductivity of conventional electrode laminates. Herein, an efficiently conductive framework of graphene nanoribbons (GNRs) and graphene (G) is rationally constructed to wrap LiFePO4 (LFP) into a binder-free dense electrode by a coupling technique of spray deposition and vacuum filtration. The spray ensures a uniform mixing of LFP, G and GNRs, meanwhile the vacuum filtration leads to a dense packing of the mixture. With only 2 wt% of G and GNRs, the LFP/GNR/G electrode delivers a high rate capability and a stable (dis)charge cycling performance under high LFP loading conditions. Moreover, the dense LFP/GNR/G electrode exhibits superior volumetric properties among all the reported LFP electrodes on the basis of the entire electrode volume, including a Li storage capacity of 318 A h L-1, an energy density of 1020 W h L-1 and a power density of 5.1 kW L-1 at 5C rate. This unique assembly strategy and the electrode structure pave a new way for high-volumetric-performance batteries.

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Clay minerals are a major component of hydrocarbon reservoir rocks, and are known to play important roles in physical and elastic properties of rocks. However, it is difficult to directly measure these properties of single-crystal clays due to their small particle size. Therefore, we construct three sets of artificial clay samples with different compaction stresses to investigate the effect of the compaction stress and clay mineralogy on their elastic properties and anisotropy. All the dry samples are measured by the pulse-transmission method. The results indicate that the compaction stress and clay mineralogy have significant influence on the physical and elastic properties of the clay samples. The microstructures of clay samples indicate that the clay platelets are aligned almost perpendicularly to the direction of compaction stress, and the ultrasonic velocity analysis validates the assumption of transverse isotropy of our clay samples. The velocities increase with the compaction stress, especially at low stress, which corresponds to the rapid porosity reduction at low stress levels. Velocity anisotropy parameters increase with increasing of compaction stress due to the increase of texture sharpness for clay minerals during the compaction process. The elastic moduli of the clay samples display a significant stress sensitivity and a strong directional dependence, with the Young’s moduli increasing and the Poisson’s ratios decreasing with the compaction stress. A simple theoretical template is used to quantify the orientation distribution functions (ODF) of clay platelets, and the Generalised Legendre coefficients of ODF increase with the increase of compaction stress, especially at low stress. Further, both the P- and S- wave anisotropy increase with the ODF coefficients W200 and W400, especially P-wave anisotropy.

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