Experimental Study of Ice Electrolysis under UV Irradiation

Abstract

The type of photocharge carriers in ice was determined by means of an electrolysis technique. It was suggested earlier that irradiation of ice by UV light above 6.5 eV generates positive H3O+ ions, neutral OH• radicals, solvated electrons es -, D defects, and vacancies of water molecules according to the “autoionization” reaction. Is the photoconductivity (PC) observed purely “protonic”, due to motion of H3O+ ions and D defects, or does it have an additional electron component related to the motion of solvated electrons es - or their analogies? The presence of the electron component should not produce any additional gas release near the electrodes during an electrolysis process and for that reason can be easily detected as a deviation from Faraday's law of electrolysis. We found that the amount of gas released per coulomb of charge flow is the same with or without the UV light. Therefore, the UV light does not change the composition (the proportion) of mobile charge carriers in ice, and in 25% of our tests the PC directly demonstrates a purely protonic nature. We also concluded that solvated electrons do not participate in the dc conductivity of ice. Probable reasons are discussed for the absence of a 100% gas release rate when the density of electric currents was below 100 μA/cm.

Metastable hydronium ions in UV-irradiated ice

“…The proton migration distance is about two water molecules in ice at ∼54 K and increases to about six molecules at 100 K. A sizable portion of hydroniums survive for an extraordinarily long time even at 140 K, probably due to the deficiency of OH − in comparison to H 3 O + in the ice sample. We consider the UV-induced formation of hydroniums to be consistent with observations from previous photoionization studies, including the enhanced electrical conductivity of UV-irradiated ice 5,6,8 and the occurrence of the H/D exchange reaction in ice. 23 Further, we suggest the possibility that metastable hydroniums play an important role in the acid-base chemistry of ice in UV-irradiated environments.…”

“…There are several reports on the occurrence of the indirect photoionization of ice at lower photon energies. Petrenko et al 5,6,8 observed enhanced electrical conductivity of ice during UV irradiation at an energy as low as 6.5 eV. They proposed that the UV irradiation generates H 3 O + in the ice as positive charge carriers responsible for the observed photoconductivity, along with photoelectrons, OH radicals, and various defects (Reaction (R5)):…”

“…Devlin 23 reported that the dissociative ionization of ice can be induced by visible (2.5 eV) photons, based on the observation that the hydrogen-deuterium (H/D) exchange of ice is induced by incident light. Petrenko and co-workers 5,6,8 measured the photoconductivity of ice during its UV irradiation at an energy above 6.5 eV and concluded that UV light creates positive photo-charge carriers in ice, which are responsible for the observed long-term photoconductivity of the ice. Apart from these works investigating the effects of photon radiation on ice, the properties of H 3 O + in ice have been extensively studied using ice samples doped with strong acids or acid precursors.…”

Photodissociation of water in crystalline ice: A molecular dynamics study

“…Note that the rigidity of the molecules excludes the possibility of vibrational energy transfer to intramolecular vibrational modes and reactions involving bond breaking in H 2 O molecules not initially photodissociated. Nor can the 'solvated electron' observed after UV irradiation of liquid water and ice [17][18][19][20] be treated explicitly. The initial ice configuration obeys the ice rules [21] and has a zero dipole moment.…”

Water and ice-repellent properties of nanocomposite coatings based on silicone rubber /

“…Generally, atmospheric icing is the deposition of frozen water on surfaces at or below freezing which may result of rain, freezing rain, wet snow, fog, supercooled clouds or vapour, or from spray or splashing water. Ice adhesion produces numerous troubles in many areas of human activity such as transportation, power transmission and distribution, aircraft, wind turbine blades, ships, and bridges [27]. Icing of power transmission lines during winter storms is a persistent problem that causes outages and costs millions of dollars in repair expenses [28].…”