When the electric current is zero, the frequency
of the NMR signal is almost the same as the frequency of the oscillator adjusted at the static magnetic field of the magnet H0. The waveforms after the NMR signal was detected at a frequency of ω0 only vary slightly, as shown in Fig. 6a. We refer to this as being “on resonance”. On the other hand, when the PEFC generates electric power and electric current flows through the MEA, the frequency of the NMR signal shifts. In this case, the waveforms detected at a frequency of ω0 oscillate violently, as shown in Fig. 6b. The frequency shift of the NMR signal, Δω, can be calculated from the speed which the phase angle of the waveform, θ, rotates. The phase angle θ is calculable from the arctangent of the waveform (SI, SQ) . The phase angle was calculated in the time period “A” illustrated in Fig. 6a, and is shown in Fig. 7a. The frequency shift PD0332991 nmr Metformin chemical structure ΔωNo-curr in the case when the current was zero was calculated by approximating the change of the phase angle as a straight line. Fig. 7b shows the phase angle calculated similarly when the PEFS was generating electricity. Because the phase angle rotates between −π to +π, the phase angle θ shown in Fig.
7b was corrected by additions of multiples of π so that the phase angle was continuous. The frequency shift ΔωCurr when the PEFC was generating electricity was calculated from the slope of the phase angle. A substantial frequency shift Δω was obtained from the difference (ΔωCurr − ΔωNo-curr). The spatial distribution of the frequency shift, Δωexp(y) measured in an experiment when the PEFC had just started electrical power generation at t = 0 s, is shown in Fig. 8. The shape of the spatial distribution is almost a straight line with a constant slope. The frequency shift, Δωexp(y), at the position y = 0 is not zero as shown in the figure. The gap from zero was caused by another additional magnetic field formed by current flowing into the electric wire which connected the PEFC to
the electric load. On the other hand, if a spatial distribution of the local electric current density, Thalidomide i(y), generated within the PEFC is assumed, the additional magnetic field formed by the current, Hi,th(y), can be analyzed theoretically using the Biot-Savart law . In this analysis, it was assumed that the electric current had a spatial distribution only in the y direction, which is the direction of the gas inlet and outlet, and that it was uniformly distributed in the x direction. The justification for this assumption is that the differences of gas concentration and water content in the PEM are large in the gas flow direction and are very small in the x direction. The additional magnetic field, Hi,th(y), can be replaced by the frequency shift, Δωth(y) using Eq. (2).