LaNi0.6Co0.4−xFexO3−δ as Air-Side Contact Material for La0.3Ca0.7Fe0.7Cr0.3O3−δ Reversible Solid Oxide Fuel Cell Electrodes

The goal of the current work was to identify an air-side-optimized contact material for La0.3Ca0.7Fe0.7Cr0.3O3−δ (LCFCr) electrodes and a Crofer22APU interconnect for use in reversible solid oxide fuel cells (RSOFCs). LaNi0.6Co0.4−xFexO3 (x = 0–0.3) perovskite-type oxides were investigated in this work. The partial substitution of Co by Fe decreased the thermal expansion coefficient values (TEC) closer to the values of the LCFCr and Crofer 22 APU interconnects. The oxides were synthesized using the glycine–nitrate method and were characterized using X-ray thermodiffraction and 4-probe DC electrical conductivity measurements. Based on the materials characterization results from the Fe-doped oxides investigated here, the LaNi0.6Co0.2Fe0.2O3−δ composition was selected as a good candidate for the contact material, as it exhibited an acceptable electrical conductivity value of 395 S·cm−1 at 800 °C in air and a TEC value of 14.98 × 10−6 K−1 (RT-900 °C).

Scalable Sacrificial Templating to Increase Porosity and Platinum Utilisation in Graphene-Based Polymer Electrolyte Fuel Cell Electrodes

Polymer electrolyte fuel cells hold great promise for a range of applications but require advances in durability for widespread commercial uptake. Corrosion of the carbon support is one of the main degradation pathways; hence, corrosion-resilient graphene has been widely suggested as an alternative to traditional carbon black. However, the performance of bulk graphene-based electrodes is typically lower than that of commercial carbon black due to their stacking effects. This article reports a simple, scalable and non-destructive method through which the pore structure and platinum utilisation of graphene-based membrane electrode assemblies can be significantly improved. Urea is incorporated into the catalyst ink before deposition, and is then simply removed from the catalyst layer after spraying by submerging the electrode in water. This additive hinders graphene restacking and increases porosity, resulting in a significant increase in Pt utilisation and current density. This technique does not require harsh template etching and it represents a pathway to significantly improve graphene-based electrodes by introducing hierarchical porosity using scalable liquid processes.

Functionalized and Platinum-Decorated Multi-Layer Oxidized Graphene as a Proton, and Electron Conducting Separator in Solid Acid Fuel Cells

In the present article, electrodes containing a composite of platinum on top of a plasma-oxidized multi-layer graphene film are investigated as model electrodes that combine an exceptional high platinum utilization with high electrode stability. Graphene is thereby acting as a separator between the phosphate-based electrolyte and the platinum catalyst. Electrochemical impedance measurements in humidified hydrogen at 240 °C show area-normalized electrode resistance of 0.06 Ω·cm−2 for a platinum loading of ∼60 µgPt·cm−2, resulting in an outstanding mass normalized activity of almost 280 S·mgPt−1, exceeding even state-of-the-art electrodes. The presented platinum decorated graphene electrodes enable stable operation over 60 h with a non-optimized degradation rate of 0.15% h−1, whereas electrodes with a similar design but without the graphene as separator are prone to a very fast degradation. The presented results propose an efficient way to stabilize solid acid fuel cell electrodes and provide valuable insights about the degradation processes which are essential for further electrode optimization.

Biomass-Derived Carbons as Versatile Materials for Energy-Related Applications: Capacitive Properties vs. Oxygen Reduction Reaction Catalysis

Biomass-derived carbons are very attractive materials due to the possibility of tuning their properties for different energy-related applications. Various pore sizes, conductivities and the inherent presence of heteroatoms make them attractive for different electrochemical reactions, including the implementation of electrochemical capacitors or fuel cell electrodes. This contribution demonstrates how different biomass-derived carbons prepared from the same precursor of viscose fibers can reach appreciable capacitances (up to 200 F g−1) or a high selectivity for the oxygen reduction reaction (ORR). We find that a highly specific surface area and a large mesopore volume dominate the capacitive response in both aqueous and non-aqueous electrolytic solutions. While the oxygen reduction reaction activity is not dominated by the same factors at low ORR overpotentials, these take the dominant role over surface chemistry at high ORR overpotentials. Due to the high selectivity of the O2 reduction to peroxide and the appreciable specific capacitances, it is suggested that activated carbon fibers derived from viscose fibers are an attractive and versatile material for electrochemical energy conversion applications.

Protonated Phosphonic Acid Electrodes for High Power Heavy-Duty Vehicle Fuel Cells

Fuel cells operating at above 100 °C under anhydrous conditions provide an ideal solution for the heat rejection problem of heavy-duty vehicle applications. Here, we report protonated phosphonic acid electrodes that remarkably improve fuel cell performance. The protonated phosphonic acids are comprised of tetrafluorostyrene phosphonic acid and perfluorosulfonic acid polymers in which a proton of the perfluorosulfonic acid is transferred to the phosphonic acid to enhance the anhydrous proton conduction of fuel cell electrodes. By implementing this material into fuel cell electrodes, we obtained a fuel cell exhibiting a rated power density of 780 milliwatts per square centimeter at 160 °C, with minimal degradation during 2,500 hours of operation, and 700 thermal cycles from 40 to 160 °C under load.

An approach to emerging optical and optoelectronic applications based on NiO micro- and nanostructures

Nickel oxide (NiO) is one of the very few p-type semiconducting oxides, the study of which is gaining increasing attention in recent years due to its potential applicability in many emerging fields of technological research. Actually, a growing number of scientific works focus on NiO-based electrochromic devices, high-frequency spintronics, fuel cell electrodes, supercapacitors, photocatalyst, chemical/gas sensors, or magnetic devices, among others. However, less has been done so far in the development of NiO-based optical devices, a field in which this versatile transition metal oxide still lags in performance despite its potential applicability. This review could contribute with novelty and new forefront insights on NiO micro and nanostructures with promising applicability in optical and optoelectronic devices. As some examples, NiO lighting devices, optical microresonators, waveguides, optical limiters, and neuromorphic applications are reviewed and analyzed in this work. These emerging functionalities, together with some other recent developments based on NiO micro and nanostructures, can open a new field of research based on this p-type material which still remains scarcely explored from an optical perspective, and would pave the way to future research and scientific advances.