Switchable Anode and Cathode Materials for Water Splitting Under Alkaline Conditions

Abstract

The ability to store energy from intermittent renewable energy sources is a significant challenge that can be addressed by generating hydrogen as a storage medium via electrochemical water splitting. To ensure the production of hydrogen at scale, there is an urgent need to develop new cost-effective catalyst materials that are active yet stable. There has been a significant research effort in this area for both the hydrogen evolution reaction (HER) at the cathode and the more sluggish oxygen evolution reaction (OER) at the anode where the latter limits the overall efficiency of an electrolysis cell. In particular, transition metal based electrocatalysts containing chalcogenides (S and Se) or phosphorous have been extensively reported as bifunctional electrocatalysts for overall water splitting. However there remains the question as to whether the pristine material is truly bifunctional with regards to inherent activity for both the HER and the OER which has implications for their use in commercial electrolysers.In this talk I will summarise our recent work on the concept of bifunctional electrodes for overall water splitting. The importance of catalyst characterization post reaction is demonstrated to elucidate the true nature of the active material that is responsible for electrocatalytic activity and how the surface chemistry and crystallinity of the catalyst changes. The implications of this in developing bifunctional catalysts for electrolysers integrated with intermittent energy sources that may be subject to rapid start up and shut down conditions is also discussed. Finally demonstration of electrocatalysts that can be switched between the OER and HER under an accelerated stress test without loss of activity is presented.