We report the fabrication of sandwich-type metal/TiO2 nanotube (TNT) array/metal structures as well as their betavoltaic effects under build-in voltage through contact potential difference. The sandwiched structure is integrated by immobilized TNT arrays on Ti foil with radioisotope Ni-63 planar source on Ni substrate (Ni-Ni-63/TNT array/Ti). Under irradiation of the Ni-63 source with activity of 8 mCi, the structure (TNT diameter similar to 130 nm, length similar to 11 mu m) presents optimum energy conversion efficiency of 7.30% with open-circuit voltage of 1.54 V and short-circuit current of 12.43 nA. The TNT arrays exhibit a highly potential for developing betavoltaic batteries due to its wide band gap and nanotube array configuration. The TNT-betavoltaic concept offers a facile solution for micro/nano electronics with high efficiency and long life-time instead of conventional planar junction-type batteries. (C) 2015 Elsevier B.V. All rights reserved.