Proton Generation Using Chitin–Chitinase and Collagen–Collagenase Composites

Hydrogen energy is focused on as next-generation energy without environmental load. Therefore, hydrogen production without using fossil fuels is a key factor in the progress of hydrogen energy. In the present work, it was found that chitin–chitinase and collagen–collagenase composites can generate protons by the hydrolysis of the enzyme. The concentration of the generated proton in the chitin–chitinase and collagen–collagenase composites are 1.68 × 1017 cm−3 and 1.02 × 1017 cm−3, respectively. Accompanying these results, proton diffusion constants in the chitin and collagen membranes are also estimated to be 8.59 × 10−8 cm2/s and 8.69 × 10−8 cm2/s, respectively. Furthermore, we have fabricated the bio-fuel cell using these composites as hydrogen fuel and demonstrated that these composites become a fuel of the fuel cell.

Mechanisms of the antiferro-electric ordering in superprotonic conductors Cs3H(SeO4)2 and Cs3D(SeO4)2

Wide ranges of absorbance spectra were measured to elucidate a difference in the antiferro-electric (AF) ordering mechanisms below 50 and 168 K in Cs3H(SeO4)2 and Cs3D(SeO4)2, respectively. Collective excitations due to deuterons successfully observed at 610 cm−1 exhibit a remarkable isotope effect. This indicates that the transfer state in the dimer of Cs3D(SeO4)2 is dominated by a deuteron hopping in contrast to Cs3H(SeO4)2, where a proton hopping makes a tiny contribution compared to a phonon-assisted proton tunneling (PAPT) associated with 440-cm−1 defbend . The fluctuation relevant to the AF ordering in Cs3D(SeO4)2 is not driven by the conventional deuteron hopping but by the phonon-assisted deuteron hopping associated with 310-cm−1 defbend . Consequently, Cs3D(SeO4)2 has a distinct ordering mechanism from Cs3H(SeO4)2, in which quantum fluctuations toward the AF ordering are enhanced through the PAPT associated with the in-phase libration.

Solid-State Hydrogen Fuel by PSII–Chitin Composite and Application to Biofuel Cell

Biomaterials attract a lot of attention as next-generation materials. Especially in the energy field, fuel cells based on biomaterials can further develop clean next-generation energy and are focused on with great interest. In this study, solid-state hydrogen fuel (PSII–chitin composite) composed of the photosystem II (PSII) and hydrated chitin composite was successfully created. Moreover, a biofuel cell consisting of the electrolyte of chitin and the hydrogen fuel using the PSII–chitin composite was fabricated, and its characteristic feature was investigated. We found that proton conductivity in the PSII–chitin composite increases by light irradiation. This result indicates that protons generate in the PSII–chitin composite by light irradiation. It was also found that the biofuel cell using the PSII–chitin composite hydrogen fuel and the chitin electrolyte exhibits the maximum power density of 0.19 mW/cm2. In addition, this biofuel cell can drive an LED lamp. These results indicate that the solid-state biofuel cell based on the bioelectrolyte “chitin” and biofuel “the PSII–chitin composite” can be realized. This novel solid-state fuel cell will be helpful to the fabrication of next-generation energy.

Fuel Cell Using Squid Axon Electrolyte and Its Proton Conductivity

Fuel cells using biomaterials have the potential for environmentally friendly clean energy and have attracted a lot of interest. Moreover, biomaterials are expected to develop into in vivo electrical devices such as pacemakers with no side effects. Ion channels, which are membrane proteins, are known to have a fast ion transport capacity. Therefore, by using ion channels, the realization of fuel cell electrolytes with high-proton conductivity can be expected. In this study, we have fabricated a fuel cell using an ion channel electrolyte for the first time and investigated the electrical properties of the ion channel electrolyte. It was found that the fuel cell using the ion channel membrane shows a power density of 0.78 W/cm² in the humidified condition. On the other hand, the power density of the fuel cell blocking the ion channel with the channel blocker drastically decreased. These results indicate that the fuel cell using the ion channel electrolyte operates through the existence of the ion channel and that the ion channel membrane can be used as the electrolyte of the fuel cell in humidified conditions. Furthermore, the proton conductivity of the ion channel electrolyte drastically increases above 85% relative humidity (RH) and becomes 2 × 10^-2 S/m at 96% RH. This result indicates that the ion channel becomes active above 96%RH. In addition, it was deduced from the impedance analysis that the high proton conductivity of the ion channel electrolyte above 96% RH is caused by the activation of ion channels, which are closely related to the fractionalization of water molecule clusters. From these results, it was found that a fuel cell using the squid axon becomes a new fuel cell using the function of the ion channel above 96% RH.

Novel Biofuel Cell Using Hydrogen Generation of Photosynthesis

Energies based on biomaterials attract a lot of interest as next-generation energy because biomaterials are environmentally friendly materials and abundant in nature. Fuel cells are also known as the clean and important next-generation source of energy. In the present study, to develop the fuel cell based on biomaterials, a novel biofuel cell, which consists of collagen electrolyte and the hydrogen fuel generated from photochemical system II (PSII) in photosynthesis, has been fabricated, and its property has been investigated. It was found that the PSII solution, in which PSII was extracted from the thylakoid membrane using a surfactant, generates hydrogen by the irradiation of light. The typical hydrogen-generating rate is approximately 7.41 × 10¹⁴ molecules/s for the light intensity of 0.5 mW/cm² for the PSII solution of 5 mL. The biofuel cell using the PSII solution as the fuel exhibited approximately 0.12 mW/cm². This result indicates that the fuel cell using the collagen electrolyte and the hydrogen fuel generated from PSII solution becomes the new type of biofuel cell and will lead to the development of the next-generation energy.

Proton Conduction via Water Bridges Hydrated in the Collagen Film

Collagen films with proton conduction are a candidate of next generation of fuel-cell electrolyte. To clarify a relation between proton conductivity and formation of water networks in the collagen film originating from a tilapia’s scale, we systematically measured the ac conductivity, infrared absorption spectrum, and weight change as a function of relative humidity (RH) at room temperature. The integrated absorbance concerning an O–H stretching mode of water molecules increases above 60% RH in accordance with the weight change. The dc conductivity varies in the vicinity of 60 and 83% RH. From those results, we have determined the dc conductivity vs. hydration number (N) per unit (Gly-X-Y). The proton conduction is negligible in the collagen molecule itself, but dominated by the hydration shell, the development of which is characterized with three regions. For 0 < N < 2, the conductivity is extremely small, because the water molecule in the primary hydration shell has a little hydrogen bonded with each other. For 2 < N < 4, a quasi-one-dimensional proton conduction occurs through intra-water bridges in the helix. For 4 < N, the water molecule fills the helix, and inter-water bridges are formed in between the adjacent helices, so that a proton-conducting network is extended three dimensional.

Phonon-assisted proton tunneling in the hydrogen-bonded dimeric selenates of Cs3H(SeO4)2

In phases III and IV of Cs₃H(SeO₄)₂, the vibrational state and intrabond transfer of the proton in the dimeric selenates are systematically studied with a wide range of absorbance spectra, a spin-lattice relaxation rate of ¹H-NMR (T₁ ^-1), and DFT calculations. The OH stretching vibrations have extremely broad absorption at around 2350 (B band) and 3050 cm^-1 (A band), which originate from the 0-1 and 0-2 transitions in the asymmetric double minimum potential, respectively. The anharmonic-coupling calculation makes clear that the A band couples not only to the libration but also to the OH bending band. The vibrational state (nano-second order) is observed as the response of the proton basically localized in either of the two equivalent sites. The intrabond transfer between those sites (pico-second order) yields the protonic fluctuation reflected in T₁ ^-1. Together with the anomalous absorption [ν_p2 phonon, libration, tetrahedral deformation (δ₄₄₀), and 610-cm^-1 band], we have demonstrated that the intrabond transfer above 70 K is dominated by the thermal hopping that is collectively excited at 610 cm^-1 and the phonon-assisted proton tunneling (PAPT) relevant to the tetrahedral deformation [PAPT(def)]. Below 70 K, T₁ ^-1 is largely enhanced toward the antiferroelectric ordering and the distinct splitting emerges in the libration, which dynamically modulates the O(2)-O'(2) distance of the dimer. The PAPT(lib) associated with the libration is confirmed to be a driving force of the AF ordering.