Enhancing durability of automotive fuel cells via selective electrical conductivity induced by tungsten oxide layer coated directly on membrane electrode assembly.

The poor durability, attributed to catalyst corrosion during start-up/shutdown (SU/SD), is a major obstacle to the commercialization of fuel cell electric vehicles (FCEVs). We recently achieved durability enhancement under SU/SD conditions by implementing a metal-insulator transition (MIT) using proton intercalation/deintercalation in WO3. However, such oxide-supported catalysts were unsuitable for direct application to the mass production stage of membrane electrode assembly (MEA) process due to their physical and chemical properties. Here, we report a unique approach that achieves the same durability enhancement in SU/SD situations while being directly applicable to the conventional MEA fabrication process. We coated WO3 on the bipolar plate, gas diffusion layer, and MEA to investigate whether the MIT phenomenon was realized. The WO3-coated MEA demonstrated 94% performance retention during SU/SD, the highest level to our knowledge. It can directly contribute to enhancing the durability of commercial FCEVs and be immediately applied to the MEA mass production process.

Efficient Alkaline Hydrogen Evolution Reaction Using Superaerophobic Ni Nanoarrays with Accelerated H2 Bubble Release.

Despite the adverse effects of H2 bubbles adhering to catalyst's surface on the performance of water electrolysis, the mechanisms by which H2 bubbles are effectively released during the alkaline hydrogen evolution reaction (HER) remain elusive. In this study, a systematic investigation on the effect of nanoscale surface morphologies on H2 bubble release behaviors and HER performance by employing earth-abundant Ni catalysts consisting of an array of Ni nanorods (NRs) with controlled surface porosities is performed. Both aerophobicity and hydrophilicity of the catalyst's surface vary according to the surface porosity of catalysts. The Ni catalyst with the highest porosity of ≈52% exhibits superaerophobic nature as well as the best HER performance among the Ni catalysts. It is found that the Ni catalyst's superaerophobicity combined with the effective open pore channels enables the accelerated release of H2 bubbles from the surface, leading to a significant improvement in geometric activities, particularly at high current densities, as well as intrinsic activities including both specific and mass activities. It is also demonstrated that the superaerophobicity enabled by highly porous Ni NRs can be combined with Pt and Cr having optimal binding abilities to further optimize electrocatalytic performance.

Electroconductive, Adhesive, Non-Swelling, and Viscoelastic Hydrogels for Bioelectronics.

As a new class of materials, implantable flexible electrical conductors have recently been developed and applied to bioelectronics. An ideal electrical conductor requires high conductivity, tissue-like mechanical properties, low toxicity, reliable adhesion to biological tissues, and the ability to maintain its shape in wet physiological environments. Despite significant advances, electrical conductors that satisfy all these requirements are insufficient. Herein, a facile method for manufacturing a new conductive hydrogels through the simultaneous exfoliation of graphite and polymerization of zwitterionic monomers triggered by microwave irradiation is introduced. The mechanical properties of the obtained conductive hydrogel are similar to those of living tissue, which is ideal as a bionic adhesive for minimizing contact damage due to mechanical mismatches between hard electronics and soft tissues. Furthermore, it exhibits excellent adhesion performance, electrical conductivity, non-swelling, and high conformability in water. Excellent biocompatibility of the hydrogel is confirmed through a cytotoxicity test using C2C12 cells, a biocompatibility test on rat tissues, and their histological analysis. The hydrogel is then implanted into the sciatic nerve of a rat and neuromodulation is demonstrated through low-current electrical stimulation. This hydrogel demonstrates a tissue-like extraneuronal electrode, which possesses high conformability to improve the tissue-electronics interfaces, promising next-generation bioelectronics applications.

Cathodic Protection System against a Reverse-Current after Shut-Down in Zero-Gap Alkaline Water Electrolysis.

Growing the hydrogen economy requires improving the stability, efficiency, and economic value of water-splitting technology, which uses an intermittent power supply from renewable energy sources. Alkaline water electrolysis systems face a daunting challenge in terms of stabilizing hydrogen production under the condition of transient start-up/shut-down operation. Herein, we present a simple but effective solution for the electrode degradation problem induced by the reverse-current under transient power condition based on a fundamental understanding of the degradation mechanism of nickel (Ni). It was clearly demonstrated that the Ni cathode was irreversibly oxidized to either the ß-Ni(OH)2 or NiO phases by the reverse-current flow after shut-down, resulting in severe electrode degradation. It was also determined that the potential of the Ni electrode should be maintained below 0.6 VRHE under the transient condition to keep a reversible nickel phase and an activity for the hydrogen evolution reaction. We suggest a cathodic protection approach in which the potential of the Ni electrode is maintained below 0.6 VRHE by the dissolution of a sacrificial metal to satisfy the above requirement; irreversible oxidization of the cathode is prevented by connecting a sacrificial anode to the Ni cathode. In the accelerated durability test under a simulated reverse-current condition, lead was found to be the most promising candidate for the sacrificial metal, as it is cost effective and demonstrates chemical stability in the alkaline media. A newly defined metric, a reverse-current stability factor, highlights that our system for protecting the cathode against the reverse-current is an efficient strategy for stable and cost effective alkaline hydrogen production.

Tailoring Binding Abilities by Incorporating Oxophilic Transition Metals on 3D Nanostructured Ni Arrays for Accelerated Alkaline Hydrogen Evolution Reaction.

Developing efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER) in alkaline water electrolysis plays a key role for renewable hydrogen energy technology. The slow reaction kinetics of HER in alkaline solutions, however, has hampered advances in high-performance hydrogen production. Herein, we investigated the trends in HER activity with respect to the binding energies of Ni-based thin film catalysts by incorporating a series of oxophilic transition metal atoms. It was found that the doping of oxophilic atoms enables the modulation of binding abilities of hydrogen and hydroxyl ions on the Ni surfaces, leading to the first establishment of a volcano relation between OH-binding energies and alkaline HER activities. In particular, Cr-incorporated Ni catalyst shows optimized OH-binding as well as H-binding energies for facilitating water dissociation and improving HER activity in alkaline media. Further enhancement of catalytic performance was achieved by introducing an array of three-dimensional (3D) Ni nanohelixes (NHs) that provide abundant surface active sites and effective channels for charge transfer and mass transport. The Cr dopants incorporated into the Ni NHs accelerate the dissociative adsorption process of water, resulting in remarkably enhanced catalytic activities in alkaline medium. Our approach can provide a rational design strategy and experimental methodology toward efficient bimetallic electrocatalysts for alkaline HER using earth-abundant elements.