Ion transport-triggered rapid flexible hydrovoltaic sensing.

The hydrovoltaic effect, based on interactions at the solid-liquid interface, offers a promising route for ion sensing. However, it is hampered by long response times, typically several minutes, due to slow ion diffusion equilibrium in nanochannels. Here, we demonstrate a rapid, flexible hydrovoltaic ion sensing strategy enabled by fast ion transport. Apart from the drag resistance reduction resulting from the ordered nanochannels and gravity elimination along the nanochannel direction, the liquid-driven effect concurrent with low-resistance shear flow at the liquid-liquid transport zone in semi-dry nanochannels are proposed to achieve an open-circuit voltage exceeding 4.0 V within 0.17 s, being two orders of magnitude faster than previous works with infiltration channels. Moreover, the obtained flexible hydrovoltaic device exhibits a wide ion sensing range of 10 to 10M, a maximum sensitivity up to -1.69 V dec for NaCl, and distinctive multi-dimensional signals, enabling its application in selective ion sensing and sweat electrolyte monitoring.