Poly(vinyl alcohol)-based crosslinked ternary polymer blend doped with sulfonated graphene oxide as a sustainable composite membrane for direct borohydride fuel cells

Abstract

Large-scale production of low-temperature fuel cells, such as the direct borohydride fuel cell (DBFC), demands the development of less expensive membranes. Herein, composite membranes are produced based on an ecological and simple approach via polymer crosslinking and casting techniques. First, a ternary crosslinked polymer is prepared from low-cost and readily available polymers, containing poly (vinyl alcohol), poly (ethylene oxide) and poly (vinyl pyrrolidone). Sulfonated graphene oxide (SGO) is then synthesized from expanded graphite and incorporated as doping agent into the polymer matrix, as confirmed by SEM, TEM, XRD, FTIR, XPS and Raman spectroscopy. The prepared membranes' physicochemical properties (tensile strength, chemical stability, ionic conductivity) are improved as a result of good compatibility between the oxygen-containing functional groups of SGO and the polymers’ functional groups. The introduction of SGO in the membrane decreases the swelling ratio to 17% and lowers the permeability to borohydride anion by two orders of magnitude (to 0.18× 10−6 cm2 s−1). Peak power density of DBFC using SGO-doped membrane separator (65 mW cm−2) is close to that of Nafion®117 (81 mW cm−2) under the same testing conditions. The simple processing and general features of these composite membranes enable the development of cost-effective and, therefore, more sustainable DBFCs.