Commercial Nafion Membranes for Harvesting Osmotic Energy from Proton Gradients that Exceed the Commercial Goal of 5.0 W/m 2 .

Osmotic energy from proton gradients in industrial acidic wastewater can be harvested and converted to electricity through membranes, making it a renewable and sustainable power source. However, the currently designed membranes for harvesting proton gradient energy in acidic wastewater cannot simultaneously achieve excellent chemical/mechanical stability and high power density under a large-scale area and require high cost and complex operations. Here, we demonstrate that commercial Nafion membranes with high chemical/mechanical stability and proton transport selectivity can generate a power density of 5.1 W/m 2 for harvesting osmotic energy from proton gradients under a test area of 0.2 mm 2 , which exceeds the commercial goal of 5.0 W/m 2 . Even under a test area of 12.5 mm 2 , a power density of 2.1 W/m 2 can be achieved under a strong acid condition. In addition, the heat can greatly promote proton transport, and the power density is increased, i.e., 8.1 W/m 2 at 333 K (5.1 W/m 2 at 293 K) under a test area of 0.2 mm 2 . By matching membranes with ion selectivity, our work demonstrates the potential of Nafion membranes for harvesting proton gradient energy in acidic wastewater and provides an approach for large-scale conversion of osmotic energy.