Fabrication of Hydrogen-Permeable Ni–Zr Thin Films for Efficient Hydrogen Separation and Their Application in Graphene Oxide-Hydrogen Membrane Fuel Cells

Abstract

Graphene oxide membrane (GOM) shows promise as an alternative for proton exchange membrane fuel cells (PEMFCs) due to its hydrophilic nature, which promotes attractive proton conductivity under wet conditions. However, GOM-based fuel cells (GOMFCs) exhibit lower maximum power density than Nafion(R) due to issues such as fuel crossover, membrane degradation, and loss of oxygen surface functional groups. In this study, amorphous double-layer Ni64Zr36/Ni36Zr64 thin films demonstrate superior hydrogen permeability compared to double-layer Ni64Zr36/Ni36Zr64 (crystalline), single-layer Ni64Zr36 (amorphous/crystalline), and Pd77Ag23 thin films at low temperatures, particularly near room temperature. Two types of amorphous and crystalline Ni–Zr metal films, with double or single layers, were characterized, and their hydrogen purification performance was reported. For hydrogen membrane fuel cell (HMFC) applications, a silanization process was employed by reacting a 50 wt % (5 mg/mL) solution of graphene oxide (GO) with an equimolar ratio of (3-mercaptopropyl)trimethoxysilane [MPTS, HS(CH2)3Si(OCH3)3] (0.790 g/mL) to form a MPTS-modified GO composite electrolyte (MGC-50). In the HMFCs, double-layer membranes composed of GOM or MGC-50 and the hydrogen-permeable Ni–Zr thin film developed in this study were investigated as an electrolyte membrane. A hydrogen-permeable metal thin film, around 40 nm in thickness, was deposited onto GOM or MGC-50 using a Pd or Ni–Zr target via DC magnetron sputtering, resulting in a double-layer graphene oxide-hydrogen membrane (GOHM) electrolyte. The fuel cell performance of the fabricated Pd- and Ni–Zr-based GOHMFCs was compared with conventional PEMFCs.