5 The Possible Prevention Measures
of Membrane Aging and Degradation
In response to the aging and degradation of ion-exchange
membranes summarized in this view, the following possible
measures could be insightful.
On the one hand, desirable membranes with better
property like anti-fouling or anti-degradation (chemically
inert) are urgently needed in practice. (1) Anti-fouling
materials—For example, membrane surface modification
method probably attach a protective layer to the surface of
the membrane, which can reduce the adsorption-induced
fouling of the membrane (Xu 2003). Grebenyuk et al.
(Grebenyuk et al. 1998) demonstrated that the modification
of AEM by high molecular mass surfactants enhanced the
fouling resistance. The non-polar radicals of high molecular
mass surfactants attached horizontally to the surface of the
membranes form a protective layer on the membranes,
making them less prone to a decrease of selectivity with
respect to counterion transfer, or an acceleration of the
voltage drop during electrodialysis. (2) Anti-degradation
materials—Regarding the degradation possibly occurs in
electrode compartment, a strong anti-oxidation membrane is
recommended as the first membrane close to the electrode
rinse solution. Rubinstein et al. (1984) found that replacing
the AEM contains a quaternary ammonium group with an
AEM contains a crown ether group can reduce water splitting, which to some degree ensure long lifetime of membrane by reducing the exposure of the membrane to the
overlimiting current region.
On the other hand, the IEM-base processes should be
operated with enough care in various aspects like membrane
cleaning, pretreatment of the inflow or improving the process operation and setup/module design. (1) Membrane
cleaning—For localized concentration polarization, measures such as online washing, periodic pickling, addition of
anti-fouling agent, and reverse polarity operation are often
used regarding to the process operation parameters (Jun et al.
2001). (2) Pretreatment—Improving the quality of the inflow
water through pretreatment is widely used and proven successful in protecting the membrane in many other processes
and definitely cannot be ignored in the IEM-based processes.
(3) Operation improvement—Means to strengthen the mass
transfer (or reduce the thickness of the boundary layer or
mass transfer resistance) are meaningful to avoid the harsh
conditions, like replacing the mesh with good agitation and
ion conductive materials (Jun et al. 2001). During the
operation of the fuel cell, a free radical scavenger is once
suggested as it can reduce the concentration of free radicals,
thereby reducing the rate of membrane degradation caused
by free radical attack (Collier et al. 2006). (4) System
improvement—A delicate setup/module modification could
further protect the membrane used; for example, protective
chamber consisting of an anti-oxidation inert membranes is
once proposed.
6 Conclusion and Perspectives
Ion-exchange membranes (IEMs) are experiencing large
popularity in various fields ranging from water treatment to
energy production. Due to the aging and degradation of IEMs,
many adverse consequences, such as decreased permselectivity, increased membrane resistance, more energy consumption yet lower efficiency as well as membrane damage,
greatly reduce the membranes lifetime and deteriorate the
membrane lifetime. But, there are as yet few studies on the
aging and degradation of IEM materials during long-term use.
In this view, we summarized the various aging and/or
degradation observations reported in different IEM-based
processes, such as (reverse) electrodialysis, bipolar electrodialysis, electrodeionization, fuel cell.
Since many membrane characteristics are highly interdependent for the IEM, the aging and degradation often
occur with several characteristics’ clear change, normally
toward decreasing the permselectivity and efficiency of the
IEM. Three major mechanisms are accordingly proposed,
namely membrane fouling, membrane burning under overlimiting current region, and membrane degradation under
extreme conditions like solution pH and temperature at the
membrane interface. We also proposed prevention measures
to deal with different kinds of aging and degradation of IEM.
The measures proposed in this review to prevent aging
and degradation of IEM are of great significance to further
improve its applications. Future work could be categorized
as the two following domains: (1) To comprehensively
optimize the systems from aspects of membrane materials
(polymeric or inorganic or even mixed type), stack/cell
design (channel dimension, flow geometry), water quality
characteristics and process operation conditions. (2) To
better understand the membrane degradation and aging
phenomena occurring at the interface or the inside part of the
membrane, including its reasons, dynamics, and influential
factors, as well as the mechanism involved.
References
Choi, J.-H., & Moon, S.-H. (2003). Structural change of ion-exchange
membrane surfaces under high electric fields and its effects on
membrane properties. Journal of Colloid and Interface Science,
265, 93–100.
Collier, A., Wang, H., Ziyuan, X., Zhang, J., & Wilkinson, D. (2006).
Degradation of polymer electrolyte membranes. International
Journal of Hydrogen Energy, 31, 1838–1854.
36
L. Han
of Membrane Aging and Degradation
In response to the aging and degradation of ion-exchange
membranes summarized in this view, the following possible
measures could be insightful.
On the one hand, desirable membranes with better
property like anti-fouling or anti-degradation (chemically
inert) are urgently needed in practice. (1) Anti-fouling
materials—For example, membrane surface modification
method probably attach a protective layer to the surface of
the membrane, which can reduce the adsorption-induced
fouling of the membrane (Xu 2003). Grebenyuk et al.
(Grebenyuk et al. 1998) demonstrated that the modification
of AEM by high molecular mass surfactants enhanced the
fouling resistance. The non-polar radicals of high molecular
mass surfactants attached horizontally to the surface of the
membranes form a protective layer on the membranes,
making them less prone to a decrease of selectivity with
respect to counterion transfer, or an acceleration of the
voltage drop during electrodialysis. (2) Anti-degradation
materials—Regarding the degradation possibly occurs in
electrode compartment, a strong anti-oxidation membrane is
recommended as the first membrane close to the electrode
rinse solution. Rubinstein et al. (1984) found that replacing
the AEM contains a quaternary ammonium group with an
AEM contains a crown ether group can reduce water splitting, which to some degree ensure long lifetime of membrane by reducing the exposure of the membrane to the
overlimiting current region.
On the other hand, the IEM-base processes should be
operated with enough care in various aspects like membrane
cleaning, pretreatment of the inflow or improving the process operation and setup/module design. (1) Membrane
cleaning—For localized concentration polarization, measures such as online washing, periodic pickling, addition of
anti-fouling agent, and reverse polarity operation are often
used regarding to the process operation parameters (Jun et al.
2001). (2) Pretreatment—Improving the quality of the inflow
water through pretreatment is widely used and proven successful in protecting the membrane in many other processes
and definitely cannot be ignored in the IEM-based processes.
(3) Operation improvement—Means to strengthen the mass
transfer (or reduce the thickness of the boundary layer or
mass transfer resistance) are meaningful to avoid the harsh
conditions, like replacing the mesh with good agitation and
ion conductive materials (Jun et al. 2001). During the
operation of the fuel cell, a free radical scavenger is once
suggested as it can reduce the concentration of free radicals,
thereby reducing the rate of membrane degradation caused
by free radical attack (Collier et al. 2006). (4) System
improvement—A delicate setup/module modification could
further protect the membrane used; for example, protective
chamber consisting of an anti-oxidation inert membranes is
once proposed.
6 Conclusion and Perspectives
Ion-exchange membranes (IEMs) are experiencing large
popularity in various fields ranging from water treatment to
energy production. Due to the aging and degradation of IEMs,
many adverse consequences, such as decreased permselectivity, increased membrane resistance, more energy consumption yet lower efficiency as well as membrane damage,
greatly reduce the membranes lifetime and deteriorate the
membrane lifetime. But, there are as yet few studies on the
aging and degradation of IEM materials during long-term use.
In this view, we summarized the various aging and/or
degradation observations reported in different IEM-based
processes, such as (reverse) electrodialysis, bipolar electrodialysis, electrodeionization, fuel cell.
Since many membrane characteristics are highly interdependent for the IEM, the aging and degradation often
occur with several characteristics’ clear change, normally
toward decreasing the permselectivity and efficiency of the
IEM. Three major mechanisms are accordingly proposed,
namely membrane fouling, membrane burning under overlimiting current region, and membrane degradation under
extreme conditions like solution pH and temperature at the
membrane interface. We also proposed prevention measures
to deal with different kinds of aging and degradation of IEM.
The measures proposed in this review to prevent aging
and degradation of IEM are of great significance to further
improve its applications. Future work could be categorized
as the two following domains: (1) To comprehensively
optimize the systems from aspects of membrane materials
(polymeric or inorganic or even mixed type), stack/cell
design (channel dimension, flow geometry), water quality
characteristics and process operation conditions. (2) To
better understand the membrane degradation and aging
phenomena occurring at the interface or the inside part of the
membrane, including its reasons, dynamics, and influential
factors, as well as the mechanism involved.
References
Choi, J.-H., & Moon, S.-H. (2003). Structural change of ion-exchange
membrane surfaces under high electric fields and its effects on
membrane properties. Journal of Colloid and Interface Science,
265, 93–100.
Collier, A., Wang, H., Ziyuan, X., Zhang, J., & Wilkinson, D. (2006).
Degradation of polymer electrolyte membranes. International
Journal of Hydrogen Energy, 31, 1838–1854.
36
L. Han