Tensile machine

Burst pressure, ultimate tensile strength (UTS) and Young’s modulus of grafts (N = 4 in each group) were measured with an electronic manometer (Extech instruments HD750) or an Instron tensile machine (Norwood, MA, USA) as described previously^{10 (link)}.

Hydrogen charging was carried out by an electrochemical method at 50 mA cm⁻² current density in a 0.5 M H₂SO₄ solution with 5 g L⁻¹ thiourea (CH₄N₂S) at the temperature of 298 K. The counter electrode was a piece of platinum plate. The samples were first pre-charged for 24 h at 50 mA cm⁻². After that they were continuously in situ charged during the entire duration of the tensile tests. The uniaxial tensile tests were conducted in an Instron tensile machine with an initial strain rate of 1 × 10⁻⁴ s⁻¹ at a temperature of 300 K. The tensile specimens with gage dimensions of 3 mm × 1 mm × 10 mm were prepared along the rolling direction by spark cut. The gage part of the tensile specimens was charged with hydrogen. The hydrogen desorption was investigated via a custom-designed UHV-based Thermal Desorption Analysis instrument in conjunction with a Mass Spectrometer detector. The heating temperature range was selected from 25 °C up to 800 °C with a constant heating rate of 26 °C min⁻¹. The total hydrogen concentration stored in the MEA samples was determined by conducting cumulative desorbed hydrogen probing during a heating experiment using a gradual heating rate up to 800 °C.

Hydrogen was introduced into the specimens by electrochemical charging with various current densities at ambient temperature (25 °C) in 0.1 M NaOH solution plus 0.05 g·L⁻¹ CH₄N₂S at pH = 13. A platinum wire was used as the counter electrode. The samples were pre-charged for 12 h at 15 mA·cm⁻², 72 h at 25 mA·cm⁻², and 240 h at 100 mA·cm⁻², respectively. Then the samples were continuously in-situ charged during the entire tensile testing to avoid the release of hydrogen. The tensile tests were conducted in an Instron tensile machine at the tensile rate of 1 × 10⁻⁴ S⁻¹. Uniaxial tensile tests were conducted using specimens with thickness of 1.5 mm and gauge length of 10 mm. Three samples for each condition were tested to confirm reproducibility. The hydrogen desorption rates were measured by using a custom-designed UHV-based Thermal Desorption Analysis instrument in conjunction with a Mass Spectrometer detector set up (TDA-MS) from 25 °C to 800 °C, and the corresponding heating rate was 26 °C min⁻¹. The diffusible hydrogen concentration was determined by measuring cumulative desorbed hydrogen from 25 °C to 600 °C.