Cathode bubbles induced by moisture electrolysis in TiO_2−x-based resistive switching cells

H₂ production has been predicted in some metal–insulator–metal resistive switching devices and similar structures, but experimentally has not yet been reported. Here we discovered cathode bubbles in Pt/TiO_2−x /Pt unipolar resistive switching cells when electroforming is implemented in a humid environment. But then these bubbles are absent when cells are operated in an anhydrous environment. The focused ion beam technique was used to observe the deformation of the cell induced by bubbles. These bubbles are deduced to be filled with H₂ generated at the cathode by the reduction of protons from adsorbed water. Reduced oxides containing abundant oxygen vacancies facilitate the dissociation of adsorbed water and supply sufficient protons diffusing towards the cathode. (letter)