## 3 Results and Discussion
### Influence of Moisture Level on Proton Transport in the Composite Membranes  
The above study on water uptake, condensed state of water, and IEC comes to the conclusion: both s-HPS and c-HPS participated in restructuring hydrophilic channel in Nafion matrix, entrapped additional amount of water in the tiny cavities, and functioned as supplement pendant acid sites. Similar phenomena were also observed previously [43,44]. The enhancement of water reservation and reachability of acid sites on proton transport and electrochemical polarization was examined in this section. Figure 7 investigated variation of proton conductivity of the three membranes with temperature at 100% RH. A clear sequence of N/s-HPS \(>\) N/c-HPS \(>\) Nafion was presented over the temperature range (25-95 \({}^{\circ}\)C). This sequence is consistent with the water uptake, which favored the Grotthuss or hopping mechanism, and with the density of acid groups, which enhanced proton flux and possibly the vehicle mechanism [45]. Regarding the superior conductivity of N/s-HPS over N/c-HPS, the stronger -SO\({}_{3}\)H (based on ionization constant \(K_{a}\)) than -CO\({}_{2}\)H is an additional factor besides the above two. Following the examination on the water uptake under various RH% (Figure 5), the three membranes revealed different rising trends of proton conductivity with the increase in temperature from 20 to 90 \({}^{\circ}\)C under constant 10% RH (Figure 8a). In such a chamber, the membranes captured just  
Figure 7: The proton conductivity–temperature relation of the various membranes under 100% RH. 6-9 wt % water at 20 \({}^{\circ}\)C and the bulk moisture levels would be lower than this range at higher temperatures. This test demonstrated the impact of the bound acid groups as well as the structure of hydrophilic channel on transport of protons because the Grothuss mechanism became subsidiary at such moisture level. The conductivity values though show the order of magnitude of \(-3\) under 10% RH, the discrepancies of them tell the capability of shipping protons by pendant acid groups, \(-\)SO\({}_{3}\)H and \(-\)CO\({}_{2}\)H. The N/s-HPS membrane presented the strongest capability of shipping protons through contact of spherical surface (Scheme 2) because this two-dimensional mould is far more efficient than transport along tangled polymer chains. A similar test was conducted to collate the proton-conductivity decreasing profile with the measurement time under 10% RH and at 20 \({}^{\circ}\)C (Figure 8b). Figure 8: Examination of water retention capability of the membranes under 10% RH: (**a**) the effect of temperature and (**b**) the effect of exposing time at 20 \({}^{\circ}\)C.  
In this test, a fully hydrated membrane sample was employed at the beginning of test. The capability of deferring moisture evaporation as well as maintaining proton transport with decreasing of bulk humidity was assessed. Taking the conductivity values at 110 min as example, N/s-HPS held a conductivity of at least 5 times greater than N/c-HPS, while the Nafion membrane became almost non-proton conductive. This sequence is consistent with that displayed in Figure 5, in which water-retention power originates from the content of freezable water (Table 1) since it reflects the impact of micro-environment, including size of cavity and the type of acid group the hydrophilic shell bears, on water-retention capability of the membrane. Unlike the proton conductivity measurement that reveals the structural effect on small proton flux, the electrochemical polarization curve of a single H\({}_{2}\)-PEMFC manifests the capability of the loaded membrane to sustain a larger stream of protons. Figure 9a displays the polarization curves of the four membranes including the commercial Nafion N-112 membrane at 20 \({}^{\circ}\)C without external humidification. The two composite membranes held higher cell voltages with the increase in current density than the two pristine Nafion membranes.