<div><p>In the context of ion sources for Neutral Beam Injection (NBI) in magnetically confined nuclear fusion plasmas, negative ion production on two different surface materials exposed to low-temperature, low-pressure deuterium plasma is investigated. A novel electride material, promising for its potential to enable highly efficient negative ion production, is compared to gadolinium, a low work function metal, with the aim of highlighting both similarities and differences in surface-driven negative ion formation. For both materials, negative ion yields and surface work functions are measured. The lowest work function obtained for the electride material is 2.7 eV, higher than the previously reported value of 2.4 eV. No clear correlation is observed between the negative ion yield and the work function for the electride highlighting a behavior with respect to negative-ion production which is not the one of a metal . In contrast, gadolinium exhibits the expected behavior with a clear correlation between yield and work function. The lowest work function measured for gadolinium is 2.2 eV, a value comparable to that of caesium, the material currently used in NBI sources, and significantly lower than the tabulated value for pure gadolinium (2.9 eV), likely reflecting the influence of surface impurities.</p></div>
