The humidity-voltaic effect, i.e. generation of open-circuit voltage (V,,c), in Au-porous silicon (PS) interface in humid atmosphere (up to 450 mV at 95% relative humidity) in dark and daylight illumination is discovered. The humidity-stimulated voltage generation is attributed to the splitting of water and hydrogen molecules on the surfaces of the Au catalyst, where further diffusion penetration of hydrogen ions into the Au-PS interface results in the formation of dipoles, thus inducing V-oc across dipoles. The generation of Voc (up to 550 mV) has also been observed on dipping of Au-PS structures in different hydrogen-containing solutions (ethanol, benzine, sodium tetraborate pentahydrate, etc). Data of response time-dependent changes of the open-circuit voltage generated in Au-PS structures under humid conditions were used for the estimation of diffusion coefficients of hydrogen. The temperature dependence of the diffusion coefficient of hydrogen at 323-353 K via the pore surfaces of PS is attributed to be D = 1.3 x 10(-2) exp(-0.25/kT).