Insights into ionic association boosting water oxidation activity and dynamic stability

Abstract

There have been reports about Fe ions boosting oxygen evolution reaction (OER) activity of Ni-based catalysts in alkaline conditions, while the origin and reason for the enhancement remains elusive. Herein, we attempt to identify the activity improvement and discover that Ni sites act as a host to attract Fe(III) to form Fe(Ni)(III) binary centres, which serve as the dynamic sites to promote OER activity and stability by cyclical formation of intermediates (Fe(III) → Fe(Ni)(III) → Fe(Ni)–OH → Fe(Ni)–O → Fe(Ni)OOH → Fe(III)) at the electrode/electrolyte interface to emit O2. Additionally, some ions (Co(II), Ni(II), and Cr(III)) can also be the active sites to catalyze the OER process on a variety of electrodes. The Fe(III)-catalyzed overall water-splitting electrolyzer comprising bare Ni foam as the anode and Pt/Ni-Mo as the cathode demonstrates robust stability for 1600 h at 1000 mA cm−2@∼1.75 V. The results provide insights into the ion-catalyzed effects boosting OER performance.