There are 49 elements in this category but only a few have significant binding energy
“Atoms which can bind positrons” C. Harabati, V. A. Dzuba, and V. V. Flambaum School of Physics, University of New South Wales, Sydney 2052, Australia https://arxiv.org/pdf/1308.0649 Calculations of the positron binding energies to all atoms in the periodic table are presented and atoms where the positron-atom binding actually exists are identified. Executive summary: barium has the strongest binding energy for positrons. Speculation alert: Why this may be of interest. The soluble salt of barium with iodine, when used as an electrolyte could be a candidate for energetic interaction with an “aether” composed of positronium (having a binding energy equal to that of iodine). Such an aether would include the quantum foam of Wheeler, for which there is some proof. There could be an interface to the aether (aka “quantum foam) which is accessible from 3-space. This assumes that actual annihilation of electrons and positrons is quite rare under ambient conditions, which appears to be the case.