Proton Conduction Mechanism in Water anotube of ew Molecular Porous Crystal Tohoku Univ.. Matsui Tokyo Univ. of Science M. Tadokoro Structure and dynamics of confined water in nanospace the present water network (water nanotube) in the nanochannel Quasi one-dimensional high proton conductor Infrared spectra + microwave conductivity the motif of hydrated proton (estimation of the mobility) SSPC16
~1.5 nm c axis Water network is formed inside the hydrophilic nanochannel. TMA 3- trimesic acid 2,2 -biinidazole cobalt(iii) complex M. Tadokoro et al. Chem. Commun. (2006) 1274; J. Phys. Chem. B 114 (2010) 2091.
DSC experiment IT WT melting of bulk water Water nanotube (WT) X-ray crystal structural analysis Ice nanotube (IT) melting! Primary hydration layer (eutron exp.)
Infrared Spectroscopy + Microwave conductivity on-contact cavity perturbation technique c axis. Matsui et al. J. Phys. Soc. Jpn. 79 (2010) 103601 ; J. Chem. Phys. to be published.
TE 011 mode resonating at 16.3 Gz Transmitted wave Incident wave Coupling hole Resonance curve : Lorentzian Transmission intensity Resonance width : Γ s, Γ 0 Resonance frequency : f s, f 0 S : sample installed in the cavity 0 : empty cavity f Maximum electric field E ac Scheme of a depolarization regime
Microwave conductivity (real part) along c axis under R ~ 100 % σ 1 (Ωcm) -1 0.03 0.02 0.01 0.00 (E g ~ 0.3 ev) 2 -WT D 2 -WT 246K 240K Vacuum R ~ 100% E-115 234K 242K 150 200 250 T (K)
Microwave conductivity (real part) along c axis under R ~ 100 % Anisotropic conduction is remarkable in WT state. σ 1 (Ωcm) -1 0.03 0.02 0.01 0.00 (E g ~ 0.3 ev) 2 -WT D 2 -WT 246K 240K Vacuum R ~ 100% E-115 234K 242K 150 200 250 T (K) σ 1 T ( (Ωcm) -1 K ) 10 1 0.1 c // c R ~ 80% E g ~ 0.3eV Long-range proton transfer is available along c. Rotational motions of water molecule? 4.0 4.5 5.0 1000/T (K -1 )
~1700cm -1 bending ~2160cm -1 Additional Band 3000~4000cm -1 stretching Spectra of WT above 240K A (arb. unit) 1700 2160 294K 234K 100K 6K 4080 3400 3600 3800 5160 Spectra of IT below 240K dynamically fluctuating - distance in WT is identical to one in IT 2000 3000 4000 5000 Wavenumber (cm -1 ) WT possesses regulated structure as well as IT!
at 293 K under R ~100 % A (arb. unit) Parallel to c axis Long range proton transfer occurs along c direction (microwave exp.) A = A para -A perp hydrated protons! Parpendicular to c axis 2000 2500 3000 3500 Wavenumber (cm -1 ) emergence of hydrated protons transferable along c direction Resonant wavenumber relating to - distance c axis
ovak s correlation Additional band ~2200 cm -1 - distance ~ 2.56 Å much shorter than dominant - distance 2.7~ 2.9 Å Fig. 8 in Chem. Mat. 8 (1996) 610, K.D. Kreuer. - distance ~ 1.03 Å distance ~ 1.53 Å
R Asymmetric coordinate : δ = R 0.25 0. 1 2 > Experimentally categorized as an Eigen-like motif! The transfer of protons accompanies a local distortion! 2.7~ 2.9 Å ~ 2.56 Å hopping distorted Eigen complex in Cl solution J. Xu, Y. Zhang and G. A. Voth, J. Phys. Chem. Lett. 2, 81 (2011).
WT = Quasi one-dimensional high proton conductor dynamically fluctuating in the vicinity of the regulated positions in IT with maintaining the - distance The additional band (~2200 cm -1 ) indicating polarization effect the - distance around protonated site shrinks to ~ 2.56 Å Mobile hydrated proton = Eigen-like motif Proton-lattice coupling plays significant role! reminiscent of Polaron
dissociation occurs in the water molecule just contacting to carboxylate oxygen atoms of TMA 3- carrier density : = 2.3 x 10 21 (cm -3 ) Mobile protons are released in WT Co Co + σ 1 ~ 0.03 (Ωcm) -1 mobility = 2.6 x 10-2 (cm 2 /Vs) ice: 8 x 10-2 (cm 2 /Vs) > water: 3.6 x 10-3 (cm 2 /Vs) < The carrier density is not large, but high mobility yields the high conductivity! eutron Crystal structural analysis