Evaluation of hydrogen sorption and permeation parameters in liquid metal membranes via Sieverts' apparatus

We have recently proposed sandwiched liquid metal membranes (SLiMM) for hydrogen separation. To evaluate SLiMM, thermodynamic and kinetic parameters such as the solubility, diffusion coefficient, and absorption kinetics of hydrogen in the liquid metal are needed. While there are some theoretical approaches to estimate these parameters, including our own published recently, it is important to obtain experimental corroboration. This study utilizes the classical Sieverts' apparatus in an effort to estimate these parameters by monitoring the change in pressure with time of hydrogen introduced over a pool of liquid metal within a container. The solubility was calculated from the change in pressure over the entire duration of the experiment as it attained equilibrium, while typically the diffusion coefficient could be determined from the short-time response. The theory behind the Sieverts' apparatus is extended here to provide full-time solution by linearizing Sieverts' law, along with early (very short) time solutions to determine the sorption kinetics in addition to the diffusion coefficient. In this manner, new theoretical and experimental results are obtained for hydrogen sorption and diffusion in liquid gallium and indium at different temperatures. The results corroborate the hydrogen permeability in a gallium SLiMM.