Recent progress in use and observation of surface hydrogen migration over metal oxides.

Hydrogen migration over a metal oxide surface is an extremely important factor governing the activity and selectivity of various heterogeneous catalytic reactions. Passive migration of hydrogen governed by a concentration gradient is called hydrogen spillover, which has been investigated broadly for a long time. Recently, well-fabricated samples and state-of-the-art measurement techniques such as operando spectroscopy and electrochemical analysis have been developed, yielding findings that have elucidated the migration mechanism and novel utilisation of hydrogen spillover. Furthermore, great attention has been devoted to surface protonics, which is hydrogen migration activated by an electric field, as applicable for novel low-temperature catalysis. This article presents an overview of catalysis related to hydrogen hopping, sophisticated analysis techniques for hydrogen migration, and low-temperature catalysis using surface protonics.