The Property Of "Solid/Water" Interface And The Applicability Of Some Construction Materials In PEM-water Electrochemical Reactors

Hydrogen is generally considered as the ideal secondary energy material, apparently due to its rich resources, high specific energy density, easy storage and zero-pollution of combustion processes.For the production and utilization of hydrogen fuel a special class of electrochemical reactions has been developed, is which sheets of polymer electrolyte membrane (PEM) are used as electrolyte, such as the PEM fuel cells, the PEM water electrolizer and the PEM hydrogen purifier(concentration). This category of PEM electrochemical reactors may also include the PEM ozone generation and the PEM oxygen purifier(concentration). All those PEM electrochemical reactors also contain large amount of pure water, either as reactant or product of electrochemical reactions, or used as humidifier to moisturize the membrane and the catalyst layer.Therefore, in these PEM/water electrochemical reactors there much be large areas of "solid/water" interfaces, including the "catalyst/water" interfaces. In the literature there are very few works related to the functions and properties of these "solid/water" interfaces. In the present thesis we tried to study these problems from fundamental points of view, and the following main results have been achieved:(1) The basic electrochemical environments of the various types of "solid/water" interfaces in PEM/water electrochemical reactors have been analyze, and pH-potential diagrams were modified to show the stability of various "catalyst/water" and "construction material/water" interfaces in PEM reactors. The stabilities of Pt, Au, Ag, Rs, Os, Ru and Ir at the "catalyst/membrane" and "catalyst/water" interfaces and the stabilities of Ti, Ta, Nb and Al at the "construction material/water" interfaces have been analysed.(2) Strip of Nafion membrane were employed as ion-conducting "bridge" to connect the reference hydrogen electrode to the pure water media in which the electrochemical properties of various materials were studied. The principle and accuracy of PEM "bridge" were been analyzed by theory of membrane potential and tested by experiments, and successfully applied though-out in experiments in this thesis.(3) A novel six-probe technique was innovated to measure the contact resistance between wires of various construction materials, and the technique has been successfully applied though-out in experimental works in this thesis.(4) The electrochemical properties of XC-72 carbon, graphite powder(GP),304 stainless steel(SS), Ti, Ta, Nb, Ti6A14V and Al in 0.5MH2SO4 and pure water studied and compared by CV and LSV experiments. Among these materials Ti seems to the most promising construction materials for PEM/water electrochemical reactors.