TY - JOUR
T1 - Quantum chemical analysis of the deprotonation of sulfonic acid in a hydrocarbon membrane model at low hydration levels
AU - Sakai, Hironori
AU - Tokumasu, Takashi
N1 - Funding Information:
We thank the New Energy and Industrial Technology Development Organization (NEDO) of Japan for financial support. We also thank the Advanced Fluid Information Research Center, Tohoku University .
Publisher Copyright:
© 2015 Elsevier B.V. All rights reserved.
PY - 2015/6
Y1 - 2015/6
N2 - Abstract We conducted a quantum chemical analysis of the deprotonation reaction of the sulfonic group (SO3H) in a model of a hydrocarbon (HC) membrane, which has been proposed as a new proton conductor for polymer electrolyte membranes (PEMs) of polymer electrolyte fuel cells (PEFCs). By comparison with perfluorosulfonic acid (PFSA) species, activation energies are higher at all hydration levels. When deprotonation occurs in the PFSA at hydration level three, the activation energy in the model HC is still higher than the thermal energy of the PEFC operation temperature and therefore it is difficult or impossible to overcome it. Moreover, at hydration level three, the deprotonated state is not stable, in contrast to PFSA, and deprotonation of SO3H and protonation of the sulfonate (SO3-) should occur with the same probability. Because the activation energy is high and the deprotonation state is unstable, it is difficult to deprotonate the SO3H of the model HC to SO3- at hydration level three. Moreover, a bond-order analysis shows that SO3- is more strongly connected to H3O+ than it is for PFSA. These appear to be the main causes of the remarkably reduced proton conductivity in HC membranes at low hydration levels.
AB - Abstract We conducted a quantum chemical analysis of the deprotonation reaction of the sulfonic group (SO3H) in a model of a hydrocarbon (HC) membrane, which has been proposed as a new proton conductor for polymer electrolyte membranes (PEMs) of polymer electrolyte fuel cells (PEFCs). By comparison with perfluorosulfonic acid (PFSA) species, activation energies are higher at all hydration levels. When deprotonation occurs in the PFSA at hydration level three, the activation energy in the model HC is still higher than the thermal energy of the PEFC operation temperature and therefore it is difficult or impossible to overcome it. Moreover, at hydration level three, the deprotonated state is not stable, in contrast to PFSA, and deprotonation of SO3H and protonation of the sulfonate (SO3-) should occur with the same probability. Because the activation energy is high and the deprotonation state is unstable, it is difficult to deprotonate the SO3H of the model HC to SO3- at hydration level three. Moreover, a bond-order analysis shows that SO3- is more strongly connected to H3O+ than it is for PFSA. These appear to be the main causes of the remarkably reduced proton conductivity in HC membranes at low hydration levels.
KW - Activation energy
KW - First principle calculation
KW - Hydrogen bond
KW - Polymer electrolyte fuel cells
KW - Transition state
UR - http://www.scopus.com/inward/record.url?scp=84925432572&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84925432572&partnerID=8YFLogxK
U2 - 10.1016/j.ssi.2015.03.005
DO - 10.1016/j.ssi.2015.03.005
M3 - Article
AN - SCOPUS:84925432572
VL - 274
SP - 94
EP - 99
JO - Solid State Ionics
JF - Solid State Ionics
SN - 0167-2738
M1 - 13606
ER -