Vacancy engineering in tungsten oxide nanofluidic membranes for high-efficiency light-driven ion transport.

Bioinspired light-driven ion transport has shown great potential in solar energy harvesting. To achieve efficiencies comparable to biological counterparts, effective coregulation of permselectivity and photoresponsivity is crucial. Herein, vacancy engineering has been proven to be a powerful strategy for considerably increasing the efficiency of light-driven ion transport in tungsten oxide (WO_3-x) nanofluidic membranes by enhancing the negative surface charges and narrowing bandgaps. The enhancement in light-driven ion transport can be attributed to the efficient redistribution of surface charges due to the effective separation of photogenerated carriers. At an optimized vacancy concentration, WO_2.66 membrane (WO_2.66M) delivers an ionic photocurrent of 0.8 μA cm^-2 in a 10^-4 M KCl electrolyte, which is four times higher than that generated by the original WO_2.85 membrane (WO_2.85M). Following this strategy, uphill ion transport and photoenhanced osmotic energy conversion are successfully achieved in the WO_3-x nanofluidic membrane system. This study shows that atomic vacancy engineering is an efficient approach to increase the light-driven ion transport dynamics of nanofluidics, providing an efficient strategy to enhance light-driven ion transport for potential applications in power harvesting and ion separation.