A pH-Gradient Flow Cell for Converting Waste CO₂ into Electricity

The CO₂ concentration difference between ambient air and exhaust gases created by combusting fossil fuels is an untapped energy source for producing electricity. One method of capturing this energy is dissolving CO₂ gas into water and then converting the produced chemical potential energy into electrical power using an electrochemical system. Previous efforts using this method found that electricity can be generated; however, electrical power densities were low, and expensive ion-exchange membranes were needed. Here, we overcame these challenges by developing a new approach to capture electrical power from CO₂ dissolved in water, the pH-gradient flow cell. In this approach, two identical supercapacitive manganese oxide electrodes were separated by a nonselective membrane and exposed to an aqueous buffer solution sparged with either CO₂ gas or air. This pH-gradient flow cell produced an average power density of 0.82 W/m², which was nearly 200 times higher than values reported using previous approaches.