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 ground 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.Faraday Technology Inc. is addressing this challenge by demonstrating an electrochemical technology which utilizes on-board supplies of air and water for on demand generation of hydrogen peroxide. This concept is based 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 1-5 w/w% solution, which makes it an ideal disinfecting solution for closed space environments.Previously, Faraday has demonstrated electrochemical generation of 3 w/w% hydrogen peroxide in a ‘H-cell’ electrochemical laboratory set-up utilizing a sodium sulfate electrolyte[ii]. Following on, Faraday designed and constructed an electrochemical sub-scale reactor for generating >1 w/w% hydrogen peroxide in RO water enabled by ion conductive resin[iii]. The next step was to understand the effects of zero-gravity on the hydrogen peroxide reactor. The electrochemical reactor and components were assembled in a zero-gravity test setup. Optimized conditions from ground-based performance data were implemented during the zero-gravity flight test. The flight tests indicated there were no adverse effects of zero-gravity on the performance of the hydrogen peroxide generation system vis-à-vis ground operation[iv]. In order to facilitate use of low conductive DI water stream available aboard the International Space Station (ISS), Faraday modified the reactor design by utilizing anion exchange membrane (AEM) within the sub-scale reactor, which reduced flooding and improved reactor stability (Figure 1)[v]. The modified sub-scale reactor was used to demonstrate the potential of generating >2 w/w% hydrogen peroxide in very low conductivity electrolytes such as DI and pure oxygen. On-going activities at Faraday are defining the effects of capsule air and contaminants in the DI water on performance of the sub-scale reactor. The system is also being scaled to deliver 1L of ~2% w/w% hydrogen peroxide for disinfectant applications from DI water feed-stream with air as a feed source[v]. This system eliminates the need to ferry disinfectant wipes to manned space capsules and is a critical enabling technology for future moon-based missions and beyond. Acknowledgements: Financial support of NASA Contracts NNX16CA43P, NNX17CJ12C, and 80NSSC20C0070 is acknowledged.