Simultaneous water and electricity harvesting from low-grade heat by coupling a membrane distiller and an electrokinetic power generator

Abstract

Producing clean water and electricity from low-grade thermal energy has attracted escalating interest to alleviate fresh water and energy stress. Here, we present a novel hybrid system by coupling the membrane distillation process with a microfluidic power generator for simultaneous clean water production and power generation. A temperature difference between low-grade heat sources and the environment is used to drive water evaporation across a hydrophobic PTFE membrane from the hot reservoir at ambient pressure to the cold reservoir at a higher hydrostatic pressure. The pressurized water flux in the cold permeate channel is then depressurized through a hydrophilic micro-porous Al₂O₃ membrane to generate electricity via electrokinetic phenomena before it is collected. As a result, 13.4 kg m⁻² h⁻¹ of permeate flux and 147 μW m⁻² of power density are achieved under a temperature difference of 40 °C on both sides of the hydrophobic PTFE membrane. This tandem system provides a new perspective to simultaneously produce clean water and generate electricity by utilizing low-grade thermal energy in the environment.