Influence of etching of polycrystalline Au-, Pt- and glassy carbon surfaces with OH radicals on electrodeposition of metals

Rational Design of Ultrathin Gas Barrier Layer via Reconstruction of Hexagonal Boron Nitride Nanoflakes to Enhance the Chemical Stability of Proton Exchange Membrane Fuel Cells

Hexagonal boron nitride (hBN) has great potential as a promising gas barrier layer in proton exchange membrane fuel cells (PEMFCs) as it shows high proton conductivity as well as excellent gas-blocking capability. However, structural defects and mechanical damage during the transfer of the hBN layer and membrane swelling have limited the application of hBN sheets to PEMFCs. Here, an ultrathin gas barrier layer is successfully fabricated on a proton exchange membrane via reconstruction of mechanically exfoliated hBN nanoflakes using a direct spin-coating process. The hBN-coated layer effectively suppresses the gas crossover and inhibits the formation of reactive oxygen radicals in the electrodes without reducing the proton conductivity of the membrane. It is also demonstrated that the structural advantages of hBN-coated gas barrier layers promise high performance of a unit cell even after a open-circuit voltage (OCV) hold test for 100 h. Furthermore, through in-depth postmortem analyses, a time-dependent degradation mechanism of membrane electrode assembly under the OCV condition is rationally proposed.

Dissolution of Pt at moderately negative potentials during oxygen reduction in water and organic media

The electrocatalytic oxygen reduction reaction (ORR) is central to alternative energy systems and sensors. An important practical issue in these systems is the loss of active surface area of the catalyst. The unexpected dissolution of Pt at moderately negative potentials during ORR in water and organic media was detected by combining nanoelectrochemistry with AFM imaging. The possibility to connect this phenomenon with the previously observed formation of hydroxyl radicals has been explored. The loss of Pt occurred only under the experimental conditions at which the formation of hydroxyl radicals was reported in the literature. This process can contribute to cathode degradation in fuel cells and other electrochemical systems. In electrochemical experiments employing a Pt electrode at negative potentials, the reduction of oxygen may be accompanied by the dissolution of the electrode surface.