18 research outputs found
Application of silver in microtubular solid oxide fuel cells
In this paper, the behaviour of silver as cathode conductive material, interconnect wire, and sealing for anode lead connection for microtubular solid oxide fuel cells (µSOFC) is reported. The changes in silver morphology are examined by scanning electron microscopy on cells that had been operated under reformed methane. It is found that using silver in an solid oxide fuel cell (SOFC) stack can improve the cell performance. However, it is also concluded that silver may be responsible for cell degradation. This report brings together and explains all the known problems with application of silver for SOFCs. The results show that silver is unstable in interconnect and in cathode environments. It is found that the process of cell passivation/activation promotes silver migration. The difference in thermal expansion of silver and sealant results in damage to the glass. It is concluded that when silver is exposed to a dual atmosphere condition, high levels of porosity formation is seen in the dense silver interconnect. The relevance of application of silver in SOFC stacks is discussed
Atomically-thin micas as proton conducting membranes
Monolayers of graphene and hexagonal boron nitride (hBN) are highly permeable
to thermal protons. For thicker two-dimensional (2D) materials, proton
conductivity diminishes exponentially so that, for example, monolayer MoS2 that
is just three atoms thick is completely impermeable to protons. This seemed to
suggest that only one-atom-thick crystals could be used as proton conducting
membranes. Here we show that few-layer micas that are rather thick on the
atomic scale become excellent proton conductors if native cations are
ion-exchanged for protons. Their areal conductivity exceeds that of graphene
and hBN by one-two orders of magnitude. Importantly, ion-exchanged 2D micas
exhibit this high conductivity inside the infamous gap for proton-conducting
materials, which extends from 100 C to 500 C. Areal conductivity of
proton-exchanged monolayer micas can reach above 100 S cm-2 at 500 C, well
above the current requirements for the industry roadmap. We attribute the fast
proton permeation to 5 A-wide tubular channels that perforate micas' crystal
structure which, after ion exchange, contain only hydroxyl groups inside. Our
work indicates that there could be other 2D crystals with similar nm-scale
channels, which could help close the materials gap in proton-conducting
applications
Performance variability of Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode on proton-conducting electrolyte SOFCs with Ag and Au current collectors
Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-d (BSCF) is one of the most active cathode materials and shows significant hydration effect suggesting possible proton conductivity. In this study, the performance of BSCF cathode on a proton-conducting BaZr 0.1 Ce 0.7 Y 0.2 O 3-d (BZCY) electrolyte with silver and gold current collectors was determined. The electrochemical characteristics of the symmetrical and anode-supported cell with diluted silver electrode, silver current collector or gold current collector on BSCF electrode were compared. The significant result is that, although the diluted silver electrode itself shows poor operation stability, the silver current collector has strong electrocatalytic contribution to the BSCF cathode performance on the proton-conducting electrolyte, leading to higher cell performance than that with the gold current collector