No abstract

Photoelectrochemical (PEC) water splitting offers an elegant approach for solar energy conversion into hydrogen fuel. Large-scale hydrogen production requires stable and efficient photoelectrodes and scalable PEC cells that are fitted for safe and cost-effective operation. One of the greatest challenges is the collection of hydrogen gas from millions of PEC cells distributed in the solar field. In this work, a separate-cell PEC system with decoupled hydrogen and oxygen cells was designed for centralized hydrogen production, using 100 cm 2 hematite (-Fe 2 O 3) photoanodes and nickel hydroxide (Ni(OH) 2) / oxyhydroxide (NiOOH) electrodes as redox mediators. The operating conditions of the system components and their configuration were optimized for daily cycles, and ten 8.3 h cycles were carried out under solar simulated illumination without additional bias at an average short-circuit current of 55.2 mA. These results demonstrate successful operation of a decoupled PEC water splitting system with separate hydrogen and oxygen cells.

Anion conductive nanofiber mats from FAA-3 ionomers are obtained by electrospinning. Depending on the solvent used in the precursor solution, nanofibers with either nonhollow cylindrical or flat ribbon-like cross-sections are prepared. The anion conductivity and water uptake of the ionomeric nanofiber mats are measured as a function of the relative humidity in the 10-90% range and compared to that of a solid membrane cast from the same ionomer. In addition, the anion conductivity of an isolated single fiber of the ionomer is measured for the first time. The anion conductivity of the electrospun single fiber is found to be higher than that of the mats, which is, in turn, one order of magnitude higher than that of the solid ionomer membrane. The higher conductivity of the mats relative to the solid membrane (in both inplane and through-plane directions) is found to be related to the variation in water uptake, which stems from the morphological distinctions. These results increase the understanding of the electrospinning process of ionomers, toward the development and design of new anion conductive ionomer fibers, useful for high performance electrochemical devices.

Anion-conducting ionomer-based nanofibers mats are prepared by electrospinning (ES) technique. Depending on the relative humidity (RH) during the ES process (RHES), ionomer nanofibers with different morphologies are obtained. The effect of relative humidity on the ionomer nanofibers morphology, ionic conductivity, and water uptake (WU) is studied. A branching effect in the ES fibers found to occur mostly at RHES < 30% is discussed. The anion conductivity and WU of the ionomer electrospun mats prepared at the lowest RHES are found to be higher than in those prepared at higher RHES. This effect can be ascribed to the large diameter of the ionomer fibers, which have a higher WU. Understanding the effect of RH during the ES process on ionomer-based fibers’ properties is critical for the preparation of electrospun fiber mats for specific applications, such as electrochemical devices.