Germanium Electrode in an Electrochemically Active Heterostructure with Hydroxide Proton Conductor at Room Temperature
Ioffe Physical Technical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia email: baikov.solid@mail.ioffe.ru Received February 6, 2014
Abstract—A macroscopic heterostructure synthesized in the form of a germanium–hydroxide proton con ductor–graphite assembly generates electric voltage comparable with that in polymer microfuel cells (0.7 V). Germaniumcontaining heterostructures, operating at room temperature and involving no precious metals, can be used as electric current sources for lowpower devices. From the fundamental standpoint, a new com bination of solid hydroxide proton conductors with groupIV electrodes is also of interest.
At present, the interest in various electrochemi cally active structures is determined primarily by the efficiency of their operation in sources of electric cur rent and/or voltage for various technical applications. The search for and development of electrochemical cells with new electrolytes or new electrode–electro lyte assemblies is based on fundamental investigations of the electrochemical activity of materials. Moreover, the main requirement to new cells consists in the com patibility of new electrolytes with wellknown elec trodes and new electrodes with wellknown electro lytes. This Letter considers a new search direction, the novelty of which is determined by the previously unknown combination of wellknown materials in a membrane–electrode assembly. These are a solid elec trolyte based on potassium hydroxide monohydrate and a semiconductor electrode material (germanium). We have experimentally studied electrochemically active cells of the (–)Ge|KOH ⋅ nH2O|C(+) type.
We have originally studied this electrolyte (KOH monohydrate) since 2007. It is a member of the family of water–potassium hydroxide system that is well and long known in the physical chemistry. Our interest was devoted to KOH ⋅ nH2O hydrates with n = 0.5, 1.0, and 2.0 [1, 2]. Graphite (C), which is well known as a poly functional electrode material, was been initially used in our investigations as a counterelectrode for Ni, Ti, TiFe intermetallide, and metallic tin (Sn). Recently, it has been shown [3] that silicon (Si) in heterostructures with solid potassium hydroxide mono and dihydrate exhibits electrochemical activity, the character of which depends on the doping level. It was naturally of interest to expand the group of previously studied elec trode materials (C, Si, and Sn) in contact with solid hydroxide proton conductors by including another groupIV element—germanium (Ge). Below, we present the main results of current–volt age (I–U) and impedance measurements for a (⎯)Ge|KOH ⋅ xH2O|C(+) type cell with x = 1.05. The choice of this electrolyte composition with a crystalli zation temperature between 130 and 147°C simplifies the technology of cell formation and eliminates undesired premelting effects during roomtempera ture measurements. The function of electrodes was performed by pGe plates (ρ = 28 Ω cm) and analyti calgrade graphite rods with a diameter of 6 mm. The interelectrode distance was about 1 cm. The room temperature resistivity of the electrolyte was within 1.3–2 kΩ. The internal volume of a cell was ~7 cm3 for a tube and 10 cm3 for a specially designed Teflon cup. In the latter cell, an additional (third) Pt electrode was introduced into the electrolyte in order to measure the electrode potentials relative to this reference elec trode.
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