NOVELTY - Glass-sealing composition comprises a preselected glass that includes a gas-releasing agent in it, where the gas-releasing agent releases a gas at or above the softening temperature of the glass that expands the glass retaining a structure upon crystallization attained during expansion that fills and seals a void space (30) when introduced to it.    USE - The glass-sealing composition is useful for filling and sealing a void space i.e. a by-pass channel in a high-temperature device i.e. an electrochemical device including a solid oxide fuel cell or its component (all claimed), where the void space includes flow paths and tolerance channel of the solid oxide fuel cell and the device includes solid oxide electrolyte electrochemical devices, electrolyzers, and electrochemical sensors.    ADVANTAGE - The glass-sealing composition is capable of filling void spaces during fabrication or coupling of components (e.g. metal and ceramic parts) in a solid oxide fuel cell without introducing new flow paths or channels, thus operating the solid oxide fuel cells with maximum fuel efficiency at high temperatures.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for sealing a void space in a high-temperature device comprising: dispensing a preselected quantity of a glass composition of a preselected particle size and a gas-releasing agent in it configured to release a gas at or above a preselected softening temperature of the glass composition; and heating the glass composition at a preselected rate to a temperature above the glass softening temperature to release gas from the gas-releasing agent i.e. retained within, and expands, the glass to form an expanded glass structure, thus filling and sealing the void space in the high-temperature device.    DESCRIPTION OF DRAWING(S) - The figure shows a single solid oxide fuel cell element i.e. filled and sealed with glass-sealing composition.    Anode (5)    Electrolyte layer (10)    Frame (20)    Void space (30)    Single solid oxide fuel cell device. (50)