Novel Chitosan–Mg(OH)₂-Based Nanocomposite Membranes for Direct Alkaline Ethanol Fuel Cells

Abstract

The present work describes novel polymer-based nanocomposite anion-exchange membranes (AEMs) with improved features for direct alkaline fuel cell applications. AEMs based on chitosan (CS), magnesium hydroxide (Mg(OH) 2), and graphene oxide (GO) with benzyltrimethylammonium chloride (BTMAC) as the hydroxide conductor were fabricated by a solvent casting method. To impart better mechanical properties and suppressed swelling, the enzymatic cross-linking with dodecyl 3,4,5-trihydroxybenzoate having C-10 alkyl chain was employed. The structure and surface morphology, KOH uptake and swelling ratio, ethanol permeability, mechanical property, ionic conductivity, cell performance, and stability of AEMs were investigated. The as-obtained AEMs showed improved hydroxide conductivity compared with previously reported CS AEMs. The highest value for hydroxide conductivity, 142.5 ± 4.0 mS cm −1 at 40°C, was achieved for the CS + Mg(OH) 2 + GO + BTMAC AEMs with an ethanol permeability value of 6.17 × 10 −7 ± 1.17 × 10 −7 cm 2 s −1 in spite of its relative high KOH uptake (1.43 g KOH/g membrane). The highest peak power density value of 72.7 mW cm −2 was obtained at 209 mA cm −2 when the pristine CS + Mg(OH) 2 AEM was used as the polymer electrolyte membrane in the direct alkaline ethanol fuel cell at 80°C. This is the highest reported power density value for CSbased membranes.

Efficient Chitosan/Nitrogen-Doped Reduced Graphene Oxide Composite Membranes for Direct Alkaline Ethanol Fuel Cells

“…Surface morphology further contributes to the operation of the fuel cell, since it can, to a certain degree, even offset the effect of advantageous high conductivity. Our previous study [ 12 ] reported that smooth CS membranes pushed the fuel cell performance past samples, which exhibited a more structured and nanoporous surface yet possessed higher conductivity values. The smoothness of the surface was speculated to contribute to a reduction of the interfacial resistance in the membrane electrode assembly, and, thus, resulted in a higher power output.…”

“…We assume that the in-plane direction of performing the tensile strength affects the results in the way that a sheet-like orientation of the filler (as typical for flake-like rGO) is most beneficial. Reduction of tensile modulus and tensile strength in the case of N-rGONRs’ addition can be attributed to the disturbance of the interaction between CS polymers upon the addition of this component [ 12 ], already at low concentration, where even the largest surface area of 200.3 m 2 /g (BET data) compared to other fillers cannot compensate. Addition of higher concentrations of each type of filler reduce the tensile modulus and tensile strength values, which are expected and reported phenomena when graphene-derivatives are dispersed within the CS films, instead of reduction after membranes’ formation; in the latter, the short-range interactions are more intensive, due to the proximity of both components [ 28 ].…”

“…This shift in power output might be explained by the surface morphology, mechanical properties, and conductivity of the membranes. A smooth surface reduces the interfacial resistance in the membrane electrode assembly [ 12 ]. Therefore, pristine CS might show better cell performance at room temperature than CS/N pEAO.…”

“…In recent years, a variety of AEMs have been prepared by the introduction of quaternary ammonium (QA), imidazolium, guanidinium, phosphonium groups, or permethyl cobaltocenium into various polymer backbones, such as poly(styrene), poly(vinyl alcohol), poly(phenylene oxide), poly(arylene ether ketone), and poly(arylene ether sulfone) [ 11 ]. In a previous article [ 12 ], our group used GO with oxygen functional groups (epoxy, carboxy, keto, hydroxy, etc. ), which are similar to poly(styrene), poly(vinyl alcohol), poly(phenylene oxide), and poly(arylene ether ketone).…”

Engineering Electronic Structure and Band Alignment of 2D Mg(OH)2 via Anion Doping for Photocatalytic Applications

“…Widely available and non-toxic Mg(OH) 2 represents a fine example of multifunctional compounds with extensive technological and industrial applications [ 1 ], such as removing pollutants using its adsorptive and coagulative properties [ 2 , 3 , 4 , 5 , 6 ], acting as an effective antibacterial agent [ 7 ], protecting paper by reducing the paper ageing [ 8 ], adding as a component in organic-inorganic composite membrane [ 9 , 10 ], utilizing as a new-generation flame retardant and smoke suppression [ 11 , 12 ]. In addition, Mg(OH) 2 has been considered as a photocatalyst for degradation of organic dyes in wastewaters, such as Rhodamine B [ 13 ], and methyl orange [ 14 ], and for CO 2 conversion to solar fuels such as CO, CH 4 , CH 3 OH, HCOOH, and HCOH [ 15 , 16 ].…”