Protonic conduction on oxide surfaces—role and applications in electrochemical energy conversion

Protonic conduction on surfaces of oxides has over the last two decades drawn attention for its possible utilisation in electrolytes for energy conversion at low temperatures and for its roles in enhancement of catalytic activity. This has led to deeper investigation and increased understanding of the phenomenon and development of quantifiable models. Along with this has emerged apparent demonstrations of use of such conduction in low-drain fuel cells as well as acknowledgement of the role of surface protonic conduction in electrodes for solid-state electrochemical and photoelectrochemical cells. Here is provided a brief review and elaboration of the fundamentals of the interaction of water and hydrogen with oxide surfaces, and models for the resulting protonic conduction in chemisorbed and physisorbed layers. We finally discuss aspects of surface protonic conduction in a range of applications, including sensors, catalysis, and electrochemical and photoelectrochemical energy conversion.