An all-nanofibrous Janus textile with directional perspiration for triboelectric nanogenerator and self-powered e-skin sensor

Due to the increased demand for health monitoring and disease alarm, the self-powered epidermal electric sensors have attracted extensive attention, such as triboelectric nanogenerator (TENG)-based electric skin (e-skin). However, the humidity accumulation at the interface between e-skin and skin will threaten the stability and reliability of the monitoring signals. Moisture absorptivity and perspiration are still great challenges that need to be addressed. Here, inspired by the internal structure of plants used to transport water, we fabricated an all-nanofiber Janus textile via a continuous electrospinning/electrospray technology, presenting a double gradient variations in the pore size and wettability along the thickness direction. Janus textile was constructed from the hydrolyzed polyacrylonitrile (HPAN)/hexagonal boron nitride nanosheets (BNNS) fibrous membrane with small pores and hydrophilicity, conducting Ag nanowire (NW)layer, and polyurethane (TPU) nanofibrous membrane with large pores and hydrophobicity. By utilizing the wicking effect of external HPAN/BNNS layer, the sweat droplet could be transported from the interface between the skin and Janus textile to the external environment, meanwhile, the returned sweat will be blocked by interior TPU layer to keep the dry state of the skin. Therefore, the directional moisture transportation was realized. As the near-skin side, TPU was used as the other triboelectric layer, the optimal triboelectrification output reached 78.10 V, 0.16 μA, and 3.31 W m−2. Moreover, the damped Janus textile also exhibited an open-circuit voltage of 30 V, a short-circuit current of 0.051 μA, and a power density of 0.14 W m−2. With the assistance of an adhesive layer, Janus textile e-skin could easily adhere to the skin surface, generating stable movement and physiological sensing signals. In short, this work presents a noval way to construct Janus e-skin patch with directional sweating and breathability for monitoring long-term real-physiological signals.