Nafion Hybrid Membranes for Use in Redox Flow Batteries

Abstract

The membrane is the key component of a redox flow system, as it has to avoid cross-contamination of the ions of the active material as well as to permit high proton conductivity. A membrane with drastically reduced cross-contamination ability would overcome the main problem of several redox couples and, in consequence, a wider variety of redox couples would potentially allow redox flow systems with higher energy densities or lower material costs. This work deals with modifications of Nafion membranes to decrease the cross-contamination ability without affecting the proton conductivity. Several in situ gel reactions were used for modification of the membranes. Cross-contamination has been reduced in this work by a factor of 2 compared to previous works by Xi et al. [ J. Power Sources , 166 , 531 (2007)] and Teng et al. [ J. Power Sources , 189 , 1240 (2009)] .

Membrane Development for Vanadium Redox Flow Batteries

“…[16] Recently Schulte et al used this approach to decrease vanadium ion transport through Nafion. [49] They modified the synthesis of both Nafion/SiO 2 and Nafion/ORMOSIL membranes by adding ammonia solution during the sol-gel reaction. Presumably this treatment increases the particle size of SiO 2 inside the Nafion channels [49] and the observed V 4+ ion diffusion through their membranes is about half that reported by Xi et al [41] and Teng et al [42] However, modification of Nafion using diethoxydimethylsilane as the precursor for the sol-gel synthesis of SiO 2 with no addition of ammonia yielded the best result.…”

“…[49] They modified the synthesis of both Nafion/SiO 2 and Nafion/ORMOSIL membranes by adding ammonia solution during the sol-gel reaction. Presumably this treatment increases the particle size of SiO 2 inside the Nafion channels [49] and the observed V 4+ ion diffusion through their membranes is about half that reported by Xi et al [41] and Teng et al [42] However, modification of Nafion using diethoxydimethylsilane as the precursor for the sol-gel synthesis of SiO 2 with no addition of ammonia yielded the best result. This pub-lication does not contain any data related to VRFB performance with the new membranes, but the authors reported that the electrical resistance of the modified membranes was similar to that observed for pure Nafion.…”

“…This pub-lication does not contain any data related to VRFB performance with the new membranes, but the authors reported that the electrical resistance of the modified membranes was similar to that observed for pure Nafion. [49] A different Nafion/inorganic hybrid membrane was investigated by Sang et al [43,44] By using a synthesis approach similar to that reported for the preparation of the Nafion/SiO 2 membranes described above, a-Zr(HPO 4 ) 2 ·2 H 2 O was deposited inside the channel network of N1135 and on the membrane surfaces. The advantage of using a-Zr(HPO 4 ) 2 ·2 H 2 O lies in the inherent proton conductivity ( % 10 À2 S cm À1 ) of this inorganic solid.…”

“…[25] Unlike the N117/SiO 2 membranes, which were prepared by sol-gel impregnation of N117 with in situ synthesized SiO 2 (see Section 3.1.1. ), [41,42,49] these researchers synthesized sulfonic acid groups containing SiO 2 (SiO 2 -SO 3 H) using a sol-gel process and subsequent annealing, and then added the SiO 2 -SO 3 H particles to the solution in N,N'-dimethylacetamide from which the SPEEK membranes were cast. [25] For comparison purposes, they also modified SPEEK membranes with commercially available SiO 2 (Evonik Degussa, Germany).…”

Prospects of practical application of hybrid membranes

“…The commonly used dopants are nanoparticles of silica [112,113], including those with a modified surface [114,115], and titania [116]. Modification provides an increase in the coulombic efficiency of RFBs compared with the results for Nafion membranes.…”