Low-Pressure Deuterium Storage on Palladium-Coated Titanium Nanofilms: A Versatile Model System for Tritium-Based Betavoltaic Battery Applications

Deuterium (D-2(g)) storage of Pd-coated Tiultra-thinfilms at relatively low pressures is fine-tuned by systematicallycontrolling the thicknesses of the catalytic Pd overlayer, underlyingTi ultra-thin film domain, D-2(g) pressure (P (D2)), duration of D-2(g) exposure, and the thinfilm temperature. Structural properties of the Ti/Pd nanofilms areinvestigated via XRD, XPS, AFM, SEM, and TPD to explore new structure-functionalityrelationships. Ti/Pd thin film systems are deuterated to obtain aD/Ti ratio of up to 1.53 forming crystallographically ordered titaniumdeuteride (TiD x ) phases with strong Ti x+-D y- electronic interactions and high thermal stability, where >90%ofthe stored D resides in the Ti component, thermally desorbing at >460 & DEG;C in the form of D-2(g). Electronic interaction betweenPd and D is weak, yielding metallic (Pd-0) states whereD storage occurs mostly on the Pd film surface (i.e., without formingordered bulk PdD x phases) leading to thethermal desorption of primarily DOH(g) and D2O(g) at <265 & DEG;C. D-storage typically increases with increasing Ti film thickness, P (D2), T, and t, whereas D-storage is found to be sensitive to the thickness andthe surface roughness of the catalytic Pd overlayer. Optimum Pd filmthickness is determined to be 10 nm providing sufficient surface coveragefor adequate wetting of the underlying Ti film while offering an appropriatenumber of surface defects (roughness) for D immobilization and a relativelyshort transport pathlength for efficient D diffusion from Pd to Ti.The currently used D-storage optimization strategy is also extendedto a realistic tritium-based betavoltaic battery (BVB) device producingpromising & beta;-particle emission yields of 164mCi/cm(2), an open circuit potential (V (OC)) of 2.04 V, and a short circuit current (I (SC)) of 7.2 nA.

Automated summary

The storage of deuterium (D-2(g)) in Pd-coated Ti ultra-thin films at low pressures is fine-tuned by controlling the thicknesses of the Pd overlayer, Ti ultra-thin film domain, D-2(g) pressure, exposure duration, and film temperature. The structural properties of the Ti/Pd nanofilms are studied through various techniques to explore structure-functionality relationships. The optimized D-storage parameters and strategies are also applied to a betavoltaic battery device, showing promising performance.