Engineering a local acid-like environment in alkaline medium for efficient hydrogen evolution reaction.

Tuning the local reaction environment is an important and challenging issue for determining electrochemical performances. Herein, we propose a strategy of intentionally engineering the local reaction environment to yield highly active catalysts. Taking Pt δ- nanoparticles supported on oxygen vacancy enriched MgO nanosheets as a prototypical example, we have successfully created a local acid-like environment in the alkaline medium and achieve excellent hydrogen evolution reaction performances. The local acid-like environment is evidenced by operando Raman, synchrotron radiation infrared and X-ray absorption spectroscopy that observes a key H 3 O + intermediate emergence on the surface of MgO and accumulation around Pt δ- sites during electrocatalysis. Further analysis confirms that the critical factors of the forming the local acid-like environment include: the oxygen vacancy enriched MgO facilitates H 2 O dissociation to generate H 3 O + species; the F centers of MgO transfers its unpaired electrons to Pt, leading to the formation of electron-enriched Pt δ- species; positively charged H 3 O + migrates to negatively charged Pt δ- and accumulates around Pt δ- nanoparticles due to the electrostatic attraction, thus creating a local acidic environment in the alkaline medium.