SusChem: Manganese oxide supercapacitor charging/discharging mechanisms to capture energy using capacitive mixing (CapMix)

1603635

Gorski, Christopher A.

Treating wastewater currently consumes 2-5% of the total national energy demand and there are tremendous opportunities for providing this energy from renewable on-site sources at wastewater treatment plants and industrial sites in the form of salinity gradients and waste heat. The goal of the proposed work is to explore a new concept using charging and discharging of manganese oxide to generate electricity, on site, at wastewater treatment plants. This approach uses low-cost and non-toxic materials and will be able to store energy in the form of a concentrated salt solution which can be used when there is an energy demand.

Treated wastewater discharged into seawater releases as much as 19 gigawatts globally due to entropic energy released through mixing of the low-salinity wastewater with high-salinity seawater. Over 1000 gigawatts GW of waste heat is available in the U.S. at industrial sites and power plants, which can be used to produce heat-generated salinity gradients through evaporative or distillation processes. A new approach for generating electrical energy from both these sources is using electrodes that undergo capacitive and/or pseudo-capacitive redox reactions when exposed to solutions with different salinities. This approach, referred to as Capacitive Mixing or CapMix, can use low-cost and non-toxic materials. When CapMix is used in conjunction with waste heat sources, it can store energy in the form of a concentrated solution that can be used when there is an energy demand. CapMix processes are advantageous over previously explored methods to capture salinity gradient energy, such as pressure retarded osmosis and reverse electrodialysis, because they do not require membranes that are often prohibitively expensive. CapMix processes have only recently been invented and investigated, and consequently the relevant reactions that occur remain poorly characterized and have not been optimized for energy production. The goal of the proposed work is to determine Manganese (Mn) oxide charging and discharging mechanisms as a function of aqueous solution conditions and Mn oxide structure and particle size, and to use this information to optimize the power densities of Mn oxide electrodes in CapMix cells. To reach this goal, the PIs will pursue three fundamental research questions: 1) What is the mechanism of Mn oxide charging in sodium chloride solutions, and how does it change as a function of Mn oxide structure and particle size? 2) Does changing the salt from sodium chloride to those relevant to heat-generated salinity gradients alter the Mn oxide charging and discharging mechanisms? If so, how? 3) What are the maximum achievable power densities for natural and heat-generated salinity gradients when the Mn oxide and cell deign are optimized? To communicate this research and help to educate young scientists, the researchers will develop and conduct a 1-day workshop for approximately 100 young women each year through the Penn State Outreach and Scientific Engagement Office. These efforts, and others, will benefit society by addressing the national need to capture energy from renewable, carbon-neutral sources through research and outreach activities.