On Demand Electrochemical Peroxide Generation for Disinfection

Abstract

Novel technologies with limited earth support are required to enable habitation in microgravity spacecraft habitats such as International space station (ISS). One area of particular need for the interstellar travel community is cleaning/sanitizing supplies to meet personal hygiene requirements, which is currently accomplished through the use of pre-packaged, disposable, wetted wipes. These items represent an appreciable carry-along mass and disposal/replacement burden requiring earth-based support. Therefore, a system is desired that could utilize onboard utilities to create disinfecting solutions to eliminate storage/disposable problems of the wetted wipes and further reduce the astronaut’s dependence on earth-based supplies. We are addressing this challenge by demonstrating an electrochemical technology which utilizes on-board supplies of O2 and water for on demand generation of hydrogen peroxide. This concept is founded on the electrochemical reduction of oxygen to hydrogen peroxide by two electron transfer reactions which proceeds as [O2 + 2H+ + 2e- → H2O2 or O2 + 2H2O + 2e- → H2O2 + 2OH-][i]. Hydrogen peroxide is well-established disinfectant with non-toxic decomposition products (viz., O2 and H2O), that is safe enough for human contact to be sold commercially as a 3% w/w solution, which makes it an ideal disinfecting solution for closed space environments. We have designed and constructed an electrochemical reactor for generating peroxide that is compatible with the available low conductivity water stream based on a patented concept of one of our commercialization partners (De Nora Technology, Inc. U.S. patent number 6,254,762). The peroxide generation unit (PGU) system consists of oxygen chamber, catholyte chamber (with catalyzed GDE cathode[ii]), whose volume can be modified as desired by changing the catholyte plate (width/length) and size/density of the conductive bead packing material, and anolyte chamber with commercially-available mixed-metal oxide anode pressed against a cation exchange membrane, as shown in the conceptual schematic (Figure 1- left) and the modified PGU (Figure 1- right). Initial trials confirmed that the PGU can generate peroxide utilizing high conductivity sodium sulfate as catholyte. Further, the PGU was used to demonstrate the potential of generating >1 w/w% hydrogen peroxide in very low conductivity electrolytes such as reverse osmosis water (RO) by enabling transfer conductivity through the use of conductive “beads”. We are continuing the technology development efforts by demonstrating the potential of this device by evaluating it within a parabolic loop zero gravity flight test, which is scheduled for July 2019. In addition to being an integral component of long term life support on NASA manned space missions; this technology has the potential to be utilized for waste water disinfection, heat exchanger biofouling remediation, and laundry applications. Acknowledgements: The financial support of NASA Contract No. NNX16CA43P and NNX17CJ12C is acknowledged.