Several technologies are being explored to capture electrical energy from salinity gradients, which may exist naturally (e.g., seawater and river water) or be engineered (e.g., by using waste heat and thermolytic salts). One of the newest methods to produce energy from salinity gradients is capacitive and pseudo-capacitive mixing (CapMix). In this approach, capacitive electrodes are alternately exposed to solutions having high and low salt concentrations. CapMix has a critical advantage over other technologies being explored (e.g., pressure retarded osmosis, PRO; and reverse electrodialysis, RED) in that it does not require membrane materials, which are often prohibitively expensive. To date, however, CapMix has produced lower power densities than these membrane-based processes. The purpose of this project is to improve power production using CapMix through chemical modification of carbon electrode surfaces and testing novel metal-based electrodes. The use of salinity gradient energy is an opportunity to reach out to young scientists and engineers that are eager to find new ways to produce carbon-neutral electricity. The highly interdisciplinary nature of power production from salinity gradients presents a unique opportunity to showcase different technical fields that span solution and surface chemistry, water quality, renewable materials, engineering economics, and electrical power production. To convey information on salinity gradient energy, it is proposed to create a website and YouTube videos to inform students how to make and test these devices so that they could build these systems for home and school studies and science fairs. This will encourage creativity and learning at home through experimentation and through self-motivated learning via the internet, where the PI has had success in the past with high school student inquiries. The findings of this project could have important implications for global energy production using carbon-neutral technologies, and further advance achieving energy sustainability of the water infrastructure through such processes as energy recovery from waste heat.
To date, CapMix studies have used NaCl solutions to generate salinity gradients. This project will focus on a new approach that uses a thermolytic salts (i.e., ammonium bicarbonate, AmB) or chemicals (ammonia) that can be distilled at low temperatures (45 degrees C). The main objective is to demonstrate that CapMix power production can be substantially increased by using new, un-tested thermolytic solutions with metal and chemically-modified carbon electrodes. There are no data on this unique combination of materials and thermolytic chemicals, and these experiments will provide a proof of concept that altering the electrode type and chemistry can increase performance by widening the voltage window. For the metal electrodes, the team will measure the power densities generated by using novel manganese, silver, or copper based electrodes. For the carbon electrodes, we will examine the effects on performance of surface chemistry alterations using oxidative treatments, acidic treatments, and the bonding of specific chemicals. The work is guided in part by the success of modifying activated carbon to function as supercapacitors in sulfuric acid solutions, although here the AmB solution conditions will be sufficiently different such that the trends will likely differ from previous results. This approach is considered to be based on sustainable chemistry, as most of the materials (e.g., carbon electrodes, ammonia) are Earth-abundant and are used in closed-loop systems.
