Abstract
A direct borohydride fuel cell (DBFC) is a type of low temperature fuel cell which requires efficient and low cost proton exchange membranes in order to commercialize it. Herein, a binary polymer blend was formulated from inexpensive and ecofriendly polymers, namely polyethylene oxide (PEO) and poly vinyl alcohol (PVA). Phosphated titanium oxide nanotube (PO4TiO2) was synthesized from a simple impregnation–calcination method and later embedded for the first time as a doping agent into this polymeric matrix with a percentage of 1–3 wt%. The membranes’ physicochemical properties such as oxidative stability and tensile strength were enhanced with increasing doping addition, while the borohydride permeability, water uptake, and swelling ratio of the membranes decreased with increasing PO4TiO2 weight percentage. However, the ionic conductivity and power density increased to 28 mS cm−1 and 72 mWcm−2 respectively for the membrane with 3 wt% of PO4TiO2 which achieved approximately 99% oxidative stability and 40.3 MPa tensile strength, better than Nafion117 (92% RW and 25 MPa). The fabricated membrane with the optimum properties (PVA/PEO/PO4TiO2-3) achieved higher selectivity than Nafion117 and could be efficient as a proton exchange membrane in the development of green and low cost DBFCs.
Highlights
A direct borohydride fuel cell DBFC is an electrochemical device for energy conversion, that uses nonexplosive and nontoxic reactants, provides high energy density, and can operate at low temperatures while empowering its application in portable sectors and transportation [1,2,3,4]
A membrane is used as a separator in the fuel cell between the cathodic and anodic compartments which allows ions transport in order to keep the charges balanced in the fuel cell
The cation exchange membrane (CEM) can reduce the borohydride crossover as a result of electrostatic repulsion occurring between the BH4− negative charges and the negative charges of the CEM backbone [5]; CEM allows the transportation of Na+ ions from the anode to the cathode
Summary
A direct borohydride fuel cell DBFC is an electrochemical device for energy conversion, that uses nonexplosive and nontoxic reactants, provides high energy density, and can operate at low temperatures while empowering its application in portable sectors and transportation [1,2,3,4]. A membrane is used as a separator in the fuel cell between the cathodic and anodic compartments which allows ions transport in order to keep the charges balanced in the fuel cell. An anion-exchange membrane (AEM) can transfer OH− from the cathode to anode, but due to borohydride crossover, the fuel cell efficiency decreases. The cation exchange membrane (CEM) can reduce the borohydride crossover as a result of electrostatic repulsion occurring between the BH4− negative charges and the negative charges of the CEM backbone [5]; CEM allows the transportation of Na+ ions from the anode to the cathode. Membrane fuel cell development includes polymer sulfonation or polymer blending, and/or doping agent incorporation in the polymeric matrix, such as functionalized carbon materials and porous and functionalized inorganic materials to replace Nafion membranes [11,13]
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