Experimental study on the effect of high-voltage electrical pulses on the nanoscale pore structure of coal

Research on electric pulse fracturing technology has led to significant advances in the field of coal mine fracturing and permeability enhancement. However, few studies have focused on nanoscale pores. In this study, we investigate the effect of high-voltage electric pulses on the nanoscale pore structure of coal using a custom-built experimental device. The results revealed that the high-voltage electric pulse breakdown process decreased the specific surface area, pore volume, and number of micropores (pore size < 2 nm) and increased the specific surface area, pore volume, and number of macropores (pore size > 50 nm). In particular, the number of pores that were>100 nm increased significantly. Field emission scanning electron microscopy revealed that macropores were widely distributed on the surface of the post-breakdown coal samples and were connected to each other. The number of mesopores (pore size = 2–50 nm) were not significantly altered as they were supplemented by the formation of new pores while simultaneously expanding into larger pores. The electric pulse breakdown process increased the total pore volume, average pore size and pore connectivity, decreased structural complexity, and significantly improved the nanoscale pore structure of the coal samples. Raman spectroscopy further confirmed this observation. From a molecular point of view, post breakdown, the aromatic system in the coal sample dehydrogenated, the directly connected methyl groups broke, the carbon atoms were arranged in a more orderly manner, and the microcrystalline structure gradually improved, thereby providing suitable conditions for convenient gas desorption and diffusion.