Wednesday, 4 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
Currently, two enormous potential energy sources remain largely untapped: waste heat from energy production and industrial processes and carbon dioxide emissions from power plants. Industrial sites and nuclear plants produce enough potential energy in the form of waste heat to meet approximately half the U.S. energy demand (29000 TWh in 2013), and CO2 emissions can theoretically provide over one-third of the electricity demand (4078 TWh in 2015). Current technologies used to capture this potential energy are inefficient and/or use expensive materials. Here we propose a novel pH flow battery, which uses pH-dependent redox couples to extract energy from a pH gradient created from either low-grade waste heat or CO2 flue gases. For waste heat, ammonia (NH3) is dissolved in water to create a pH gradient that can be reversed by distillation using low-grade waste heat. Similarly, CO2 dissolved in water forms carbonic acid (H2CO3), which dissociates into bicarbonate (HCO3-) and protons (H+) to create an acidic solution that can be subsequently removed by sparging with air. The goal of the study is to test the viability of the pH flow battery compared to other technologies. Cyclic voltammetry was used to test a suite of compounds to determine the pH dependency of reduction potentials, electrode kinetics, and compound stability. For sparingly soluble compounds, we evaluated the use of a hydrotropic agent, nicotinamide (vitamin B3), to increase solubility. Ideal compounds were then tested in a pH flow battery to evaluate power production, the ability to recharge the battery with waste heat or CO2, and cycling stability. From the compound survey, several Flavin-based compounds were identified as candidates due to fast electrode kinetics, pH-dependent reduction potentials over a wide pH range, and stability in oxygen. Nicotinamide added in high concentrations was shown to increase solubility of Flavin compounds at low pH and promising results were obtained from preliminary tests of the pH flow battery.