Improved Response Time of a Thin Film Hydrogen Storage Alloy Unimorph Structure after Platinum Surface Treatment

Abstract

In this study, the effect of a platinum surface treatment on the mechanical response of a LaNi 5 thin film actuator deposited on polyimide substrates was investigated. Since this actuator could be reversibly driven by hydrogen pressure control, it could function as a sensor and/or controller of the hydrogen gas flux in various hydrogen related devices. In the experiments, the incubation period of the actuation after hydrogen gas exposure was reduced from 100 to 10 s by the platinum surface treatment. This significantly modified mechanical response is attributed to a switching of the reaction rate determining steps. The platinum treatment enhanced the decomposition rate of hydrogen gas molecules at the surface. The platinum treatment should bring about a change of rate determining step to a permeation/diffusion of the hydrogen atoms into the film.

Hydrogenation Induced Bending Motion of Composite Device of La-Ni Alloy Film Deposited on Copper Foil

“…In addition, if the high stiffness of copper prevents the elongation of the length and suppresses the extensive motion, the enlargement of the bending motion by Cu thin foil can be explained, because the elasticity of Cu is about 10 times higher than that of polyimide. 10,11) Figure 2 also shows the motion strain of the sample with and without catalytic layer exposed for 10 3 s. While a large motion is not found for the untreated sample within 10 2 s, the bending motion can be noticed after 10 2 to 10 3 s. Bending motion of the sample with palladium and platinum over-layer deposition exhibits the higher response just after the hydrogen exposure, where a large bending motion occurs from 10 2 to 10 3 s. Although both Pd and Pt coatings shorten the start points of bending motions related to incubation periods of hydrogenation for La-Ni films on polyimide sheet, 8,9) the substrate conversion from thin Cu foil to a thick polyimide sheet 1000s 0s 10s 100s 50s 5 mm Fig. 3 Optical photograph of bending motion of 16 MPa-loaded composite device, which is driven by La-Ni hydrogen storage alloy film on Cu foil after hydrogenation within 1000 s. indicates no difference in the strain within the initial 5 s (see Fig.…”

“…Both Pd and Pt coating enhance the bending motions of La-Ni alloy film on polyimide, 8,9) as shown in Fig. 2.…”

“…8,9) Since the substrate thickness is strongly related to mechanical properties to the bending motion, the thinning substrate from 125 to 10 mm also enlarges the bending motion. Additionally, substrate material is also an important factor.…”

“…The elasticity of copper (Cu) is 10 times larger than that of polyimide, 10,11) therefore, a Cu thin foil substrate (10 mm thick) is expected to yield a larger bending motion than that of thick polyimide sheet (125 mm thick). 8,9,12) The higher stiffness of Cu prevents the elongation of the composite device length, which results in a larger displacement. In this study, therefore, in order to confirm the enlarged bending motion and responsiveness, the La-Ni film with Pd over-layer deposited on Cu thin foil substrate (10 mm thick) has been prepared and examined.…”

Reversible Bending Motion of Unimorph Composites Driven by Combining LaNi<SUB>5</SUB> Alloy Powders Dispersed Polyurethane and Thin Supporting Copper Sheet under Partial Hydrogen Gas Pressure

“…1) Thus, two types of soft mover composites, which are constructed with the driving part coated on the supporting part, are LaNi 5 film deposited on supporting sheets [2][3][4][5] and LaNi 5 powders dispersed soft composites supported by pure silicone rubber rod, [6][7][8][9] have been recently proposed in our previous works. Both of them exhibit the bending motion operated by hydrogen gas pressure change, as if a bimetal operated by temperature change.…”