The Extent of Platinum-Induced Hydrogen Spillover on Cerium Dioxide.

Hydrogen spillover from metal nanoparticles to oxides is an essential process in hydrogenation catalysis and other applications such as hydrogen storage. It is important to understand how far this process is reaching over the surface of the oxide. Here, we present a combination of advanced sample fabrication of a model system and in situ X-ray photoelectron spectroscopy to disentangle local and far-reaching effects of hydrogen spillover in a platinum-ceria catalyst. At low temperatures (25-100 °C and 1 mbar H2) surface O-H formed by hydrogen spillover on the whole ceria surface extending microns away from the platinum, leading to a reduction of Ce4+ to Ce3+. This process and structures were strongly temperature dependent. At temperatures above 150 °C (at 1 mbar H2), O-H partially disappeared from the surface due to its decreasing thermodynamic stability. This resulted in a ceria reoxidation. Higher hydrogen pressures are likely to shift these transition temperatures upward due to the increasing chemical potential. The findings reveal that on a catalyst containing a structure capable to promote spillover, hydrogen can affect the whole catalyst surface and be involved in catalysis and restructuring.

Elucidating the Humidity-Induced Degradation of Ni-Rich Layered Cathodes for Li-Ion Batteries.

Ni-rich layered oxides, in a general term of Li(NixCoyMn1-x-y)O2 (x > 0.5), are widely recognized as promising candidates for improving the specific energy and lowering the cost for next-generation Li-ion batteries. However, the high surface reactivity of these materials results in side reactions during improper storage and notable gas release when the cell is charged beyond 4.3 V vs Li+/Li0. Therefore, in this study, we embark on a comprehensive investigation on the moisture sensitivity of LiNi0.85Co0.1Mn0.05O2 by aging it in a controlled environment at a constant room-temperature relative humidity of 63% up to 1 year. We quantitatively analyze the gassing of the aged samples by online electrochemical mass spectrometry and further depict plausible reaction pathways, accounting for the origin of the gas release. Transmission electron microscopy reveals formation of an amorphous surface impurity layer of ca. 10 nm in thickness, as a result of continuous reactions with moisture and CO2 from the air. Underneath it, there is another reconstructed layer of ca. 20 nm in thickness, showing rock salt/spinel-like features. Our results provide insight into the complex interfacial degradation phenomena and future directions for the development of high-performance Ni-rich layered oxides.