Improved performance and stability of direct borohydride fuel cells (DBFCs) with porous polypyrrole support

摘要

This work focused on the development of a method to fabricate a multilayer macro/mesoporous polypyrrole (PPPr) support to provide a high surface area for catalyst deposition in a direct borohydride fuel cell (DBFC) using sodium borohydride as a fuel and hydrogen peroxide as an oxidant. The multilayer macroporous structure was constructed through simultaneous electropolymerisation of two-monomer mixture (i.e. pyrrole and methylene blue) on an NH4Cl salt template; poly(methylene blue) and NH4Cl were later selectively removed from the composite film as verified by FTIR. The SEM and TEM results demonstrated that a uniform distribution of polypyrrole particles was obtained with an apparent macroporous structure in a varied range of 18–65 µm which consequently provided a well-dispersed and well–distributed Pt deposition. It was also apparent that the PPPr had a higher BET surface area by the introduction of macro/mesoporous structure as compared to the bulk polypyrrole sample (BPPr). In addition, the PPPr was highly electrically conducting with the surface conductivity of 9.6 ± 0.8 × 101 S cm−1 and electrochemically active surface area of 5.4 cm2, which were increased to 42.5 ± 0.9 × 101 S cm−1 and 30.0 cm2 respectively with the presence of Pt catalyst within the PPPr-Pt sample. The application of PPPr-Pt to DBFC was shown to have an excellent electrochemical stability and an improved power density of 2-fold and 3.6-fold higher than the BPPr and commercial Vulcan XC-72 carbon black respectively. By increasing fuel concentration to 0.3 M and using counter flow operation, the DBFC using PPPr-Pt catalyst exhibited a maximum power density of 139 mW cm−2.