Microdroplet-Mediated Multiphase Cycling in a Cloud of Water Drives Chemoselective Electrolysis

Abstract

Electrification of water in clouds leads to fascinating redox reactions on Earth. However, little is known about cloud electrochemistry, except for lightning, a natural hazard that is nearly impossible to harness. We report a controllable electrochemistry that can be enabled in microclouds by fast phase switching of water between the microdroplet, vapor, and bulk phase. Due to the size-dependent charge transfer between droplets during atomization, this process generates an alternating voltage arising from the self-electrification and discharging of microdroplets, vapor, and bulk phase by electron and ion transfer. We show that the microclouds with alternating voltage cause 1,2-dichloroethane (ClH₂C-CH₂Cl) to be converted to vinyl chloride (H₂C═CHCl) at ∼80% selectivity. These findings highlight the importance of controlled cloud electrochemistry in accelerating the removal of volatile organic compounds and treating contaminated water. We suggest that this work opens an avenue for harnessing cloud electrochemistry to solve challenging chemoselectivity problems in aqueous reactions of environmental and industrial importance.

Figure 1

Schematics of paired electrolysis by (a) direct current, (b) alternating current (AC), (c) spray–coalescence cycles of charged water microdroplets and vapor, and (d) chemoselective electro-dechlorination of DCE driven by phase switched microcloud water.

Figure 2

Measurements of the potential difference between the bulk phase and the above atmosphere of the phase switched water (a,b) in the open system and (c,d) in the closed system. “on” and “off” refer to activating and deactivating the spray, respectively. The slopes of voltage decay during the “off” phase are (a) k₁ = 0.0124 V/s, k₂ = 0.0166 V/s and k₃ = 0.0253 V/s.

Figure 3

Observation of radicals formed in the electro-dechlorination of DCE in bulk phase as detected by (a) EPR spectroscopy and (b) liquid chromatography high-resolution mass spectrometry and in (c) offline-captured and (d) online-captured microdroplets, as detected by EPR spectroscopy.

Figure 4

Evolution of VC in the DCE–water system under ultrasonic spraying. (a) Effect of water–DCE ratio on the generation of VC. (b) Time course of VC product generated by ultrasonic spraying and cavitation. (c,d) Effect of phase switching frequency on evolution of VC. (e) Time course of C₂ gas products generated in the reactor with a height-diameter ratio of 5. (f) Evolution of VC concentration in the presence of various organic chlorides. ^aConstant diameter for reactors of varied height-diameter ratios. ^bConstant height-diameter ratio of 5 while simultaneously increasing the height and diameter by 1.2-fold.